NYSE: TOVX

In February 2026, we entered into a license agreement (the “Rasayana License Agreement”) with Rasayana Therapeutics, Inc. (“Rasayana”), pursuant to which we granted Rasayana an exclusive worldwide license with the right to grant sublicenses to research, develop, manufacture and commercialize any Product (as such term is defined in the Rasayana License Agreement), which includes SYN-020, comprising, containing, or covered by the Licensed IP (as such term is defined in the Rasayana License Agreement) and/or devised, developed, or produced using the Licensed IP. Pursuant to the terms of the Rasayana License Agreement, Rasayana will assume all responsibility and costs for the development and commercialization of the Products. We believe that this arrangement will provide us with potential to derive value from our SYN-020 asset, without the need for us to continue to invest additional working capital into the further development of the product candidate, thereby allowing us to focus our efforts and expenditures on the development of our oncology assets.

Additionally, as part of our strategic transformation into an oncology focused company, we are exploring value creation options for our SYN-004 asset, including out-licensing or partnering.

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Our Current Product Pipeline

*Based on management’s current beliefs and expectations

allo-HCT allogeneic hematopoietic cell transplant. HNSCC head and neck squamous cell carcinoma. IV intravenous. IVit intravitreal. For other abbreviations see the text.

¹Final Phase 1b/2a study cohort contingent on grant funding or partnership.

²Pursuant to the Rasayana License Agreement, commencing February 7, 2026, Rasayana is responsible for all development and commercialization efforts, including all costs related thereto, of SYN-020, and is obligated to use commercially reasonable efforts to meet certain specified development milestones, as more particularly set forth in the Rasayana License Agreement.

Additional products with preclinical proof-of-concept include SYN-006 (carbapenemase) to prevent aGVHD, CDI, and microbiome damage in patients treated with carbapenem antibiotics and SYN-007 (ribaxamase) DR to prevent antibiotic associated diarrhea with oral β-lactam antibiotics.

Our Current Oncology-Focused Pipeline

Oncolytic Viruses

Our oncology platform is based on oncolytic virotherapy (“OV therapy”), which exploits the ability of certain viruses to kill tumor cells and trigger an anti-tumor immune response. This novel class of anticancer agents has unique mechanisms of action compared to other cancer drugs. Oncolytic viruses (“OVs”) exploit the fact that cancer cells contain mutations that cause them to lose growth control and form tumors. Once inside a tumor cell, OVs exploit the tumor cell machinery to generate thousands of additional copies of the virus, which then kill the tumor cell and spread to neighboring cells, causing a chain reaction of cell killing. This infection and tumor cell killing by OVs also alerts the immune system, which can then attack the virus infected tumor cells to help destroy the tumor in some instances.

Our OV product candidates are engineered to efficiently infect and selectively replicate to a high extent in tumor cells versus normal host cells, which enables intravenous delivery. By contrast, many other OVs in clinical development today are administered by direct injection into the tumor. Intravenous delivery has the potential to expand the therapeutic effect of OVs because the virus can infect both the primary tumor and tumor metastases throughout the body.

Our lead product candidate VCN-01 (zabilugene almadenorepvec), is a clinical stage oncolytic human adenovirus that is modified to express an enzyme, PH20 hyaluronidase, that is designed to degrade hyaluronan in the tumor stroma, which helps the virus and other

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molecules to penetrate and spread throughout the tumor. VCN-01 can be used alone or in combination with other cancer therapies, such as chemotherapy and immunotherapy, for difficult to treat cancers. An expanding intellectual property portfolio supports our oncology programs, and because our products are characterized as biologics with Orphan Drug designation in our target indications, if approved by the FDA they will be further protected by data and/or market exclusivity.

VCN-01 (zabilugene almadenorepvec) — An oncolytic human type-5 adenovirus engineered for intravenous administration and to express a tumor matrix degrading enzyme (PH20 hyaluronidase) the goal of which is to facilitate the entry of therapeutics and immune cells into tumors

VCN-01 is a genetically modified oncolytic adenovirus that has been engineered to contain four independent genetic modifications on the backbone of the wild-type human adenovirus serotype 5 (HAd5) genome. These modifications have been shown in preclinical and clinical studies to confer tumor selective replication and antitumor activity. VCN-01 was engineered to replicate in and kill virtually all types of solid tumor cells, to expose tumor neoantigens of lysed tumors, to reduce liver tropism, and to express PH20 hyaluronidase to enhance the penetration of virus, chemotherapy, immuno-oncology therapy, and immune cells into the tumor.

Malignant tumors are made up of tumor cells as well as significant supporting tissue known as tumor stroma. The tumor stroma supports the formation and growth of tumors and contains cells and other components that are required for robust tumor growth and metastasis. The stroma also forms an effective barrier to the entry of therapeutic agents such as chemotherapy and immuno-oncology products. A key structural component of the tumor stroma is hyaluronic acid, and tumor levels of hyaluronic acid have been clinically associated with reduced survival in metastatic pancreatic cancer patients. VCN-01 is designed to overcome the stroma barrier problem by expressing the hyaluronan degrading enzyme PH20 hyaluronidase after it infects tumor cells. Expression of PH20 by VCN-01 is designed to degrade the hyaluronic acid within the tumor stroma and to improve virus spread throughout the tumor. Based upon the foregoing, we believe our OV platform, exemplified by VCN-01, represents a new and potentially powerful form of therapy to be combined with tumor cell killing, anti-tumor immunity and stroma destruction after intravenous delivery.

The VCN-01 product candidate is provided as a sterile liquid concentrate that is diluted for infusion or injection. The proposed therapeutic indication for VCN-01 is the treatment of solid tumors, as its selectivity mechanism relies on cellular properties shared by virtually all human tumor cells. Our initial indication for clinical development is unresectable metastatic pancreatic cancer, a disease for which there is currently no cure and only limited therapeutic options.

At the time of the filing of this Annual Report, VCN-01 has been administered to 142 patients across multiple Phase 1 clinical trials and the Phase 2 VIRAGE trial, including patients with pancreatic cancer, head and neck squamous cell carcinoma, ovarian cancer, colorectal cancer, and retinoblastoma.

Pancreatic Ductal Adenocarcinoma

Cancer of the pancreas consists of two main histological types: cancer that arises from the ductal (exocrine) cells of the pancreas or, much less often, cancers that may arise from the endocrine compartment of the pancreas. Pancreatic ductal adenocarcinoma (“PDAC”) accounts for more than 90% of all pancreatic tumors. It can be located either in the head of the pancreas or in the body-tail. Pancreatic cancer usually metastasizes to the liver and peritoneum. Other less common metastatic sites are the lungs, brain, kidney and bone. In its early stages, pancreatic cancer does not typically result in any characteristic symptoms. In many instances, progressive abdominal pain is the first symptom. Therefore, in most cases, pancreatic cancer is diagnosed in its late stages (locally advanced non-metastatic or metastatic stage of the disease) when surgical resection and possibly curative treatment is not possible. It is generally assumed that only 10% of cases are resectable at presentation, whereas 30-40% of patients are diagnosed at the locally advanced/unresectable stage and 50-60% present with distant metastases.

PDAC Clinical Unmet Need and Market Opportunity

PDAC is currently the 3rd leading cause of cancer-related deaths in the United States and the 4th leading cause of cancer-related deaths in the European Union and it is projected to become the second leading cause of cancer-related deaths in the United States before 2030. Despite significant research efforts, minimal progress has been achieved to date. The five-year overall survival rate is < 10% and has not substantially improved over the last 30 years. Surgery is the only treatment that offers the prospect of long term-survival; however, the 5-year survival rate for the limited number of patients in whom resection is possible remains low (20 – 30 %). Patients with advanced disease are often managed with chemotherapy. In recent years, the combination of gemcitabine with albumin-bound paclitaxel (GA), and the combination of folic acid, 5-fluorouracil, irinotecan and oxaliplatin (FOLFIRINOX) have emerged as the standard of care. In 2024, liposomal irinotecan (ONIVYDE®), which was previously approved for second line PDAC in combination with fluorouracil and

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leucovorin, was approved in the United States and Europe as first line therapy for metastatic PDAC when administered along with oxaliplatin 5-FU and leucovorin (the NALIRIFOX regimen). However, the results are still very poor and new therapeutic interventions are needed. In recent years, the prevalence of PDAC has increased, which increase has been particularly evident in younger people. The rising incidence of pancreatic cancer and its current economic burden place increased pressure to improve outcomes for patients.

In May 2011, the Committee for Orphan Medicinal Products (“COMP”) from the European Medicines Agency (“EMA”) recommended granting Orphan Medicinal Product Designation to VCN-01 for the treatment of pancreatic cancer and in June 2011, the European Commission (“EC”) confirmed the designation under Regulation No 141/2000 of the European Parliament and of the Council.

In June 2023, the FDA granted Orphan Drug designation to VCN-01 for the treatment of pancreatic cancer.

In May 2024, the FDA granted Fast Track designation to VCN-01 for the treatment of pancreatic cancer.

Phase 1a/Proof of Concept Trial of VCN-01 (zabilugene almadenorepvec) by intratumoral administration in PDAC

In September 2019, VCN presented a poster at the European Society for Medical Oncology (“ESMO”) annual meeting describing initial mechanism of action data from a multicenter, Phase 1 dose escalation study of intratumoral (“IT”) VCN-01 administered to pancreatic cancer patients in combination with standard doses/schedules of either gemcitabine or nab-paclitaxel plus gemcitabine (NCT02045589). The study was conducted at three hospitals in Spain and 8 patients with confirmed histologic diagnosis of unresectable PDAC amenable to endoscopic ultrasound guided (“EUS”) injection were treated with 3 injections (coinciding with 1st day of the chemotherapy cycles) at two different dose levels of VCN-01 (6 patients had metastatic disease and 2 had locally advanced disease). The treatment regimen was generally well-tolerated. VCN-01-related adverse events were dose-dependent and mainly consisted of asthenia (6 patients), fever (4 patients), and transaminase increases (3 patients). One patient died from severe intra-abdominal fluid collection that was considered to be related to VCN-01 treatment. Evaluation of virus pharmacokinetics and PH20 levels in serum were consistent with strong virus replication in the tumors. This was supported by the presence of viral particles in tumor cells as assessed in paired tumor biopsies collected before and after treatment. Tumor stiffness was reduced in all VCN-01-injected lesions as measured by elastography. Disease stabilization of injected lesions was observed in 5 out of 6 patients although subsequent tumor progression was observed in most of the patients due to the appearance of new lesions or growth of distant, non-injected, metastatic lesions. This study provided encouraging mechanism of action data for VCN-01; however, intratumoral injection did not appear to deliver sufficiently high VCN-01 levels for effective delivery to non-injected tumors. We believe these results supported the evaluation of the safety/tolerability and potential efficacy of VCN-01 via intravenous administration in combination with chemotherapy and/or immunotherapies for the treatment of advanced PDAC. The results of this study were published in the Journal for Immunotherapy of Cancer. 2021 Nov;9(11):e003254. doi: 10.1136/jitc-2021-003254.

Phase 1 Trial of intravenous VCN-01 (zabilugene almadenorepvec) with or without nab-paclitaxel plus gemcitabine in patients with solid tumors and PDAC

In March 2022, we announced the peer-reviewed publication of data from a Phase 1, multicenter, open-label, dose-escalation study investigating the safety, tolerability and biodistribution of intravenous VCN-01 oncolytic adenovirus with or without standard-of-care (SoC) chemotherapy (gemcitabine/nab-paclitaxel) in patients with advanced solid tumors (NCT02045602). The data, published in the Journal for ImmunoTherapy of Cancer, suggests that intravenous treatment with VCN-01 is feasible and has been well tolerated, with encouraging biological and clinical activity. (Journal for Immunotherapy of Cancer 2022;10:e003255. doi:10.1136/jitc-2021-003255).

Data from the publication had previously been presented, in part, in a poster at the ESMO 2019 annual meeting. The published study was a multicenter, open-label, dose-escalation phase I clinical trial of a single dose of intravenous VCN-01 alone (Part I, 16 patients with advanced refractory solid tumors) or in combination with nab-paclitaxel plus gemcitabine (Part II and III; patients with pancreatic adenocarcinoma). In Part II, 12 patients received VCN-01 dose concurrent with chemotherapy on day 1, whereas in Part III 14 additional patients received the dose of VCN-01 seven days before chemotherapy. The recommended Phase 2 doses (RP2D) were determined to be 1x1013 viral particles (vp)/patient in Part I, 3.3x1012 vp/patient in Part II and 1x1013 vp/patient in Part III. Based on its apparent safety profile and the absence of dose-limiting toxicities, 1x1013 vp/patient using sequential dosing schedule was selected for further clinical development.

Pharmacokinetic data showed dose linearity, as well as relevant VCN-01 exposure. Analysis of VCN-01 clearance in patients enrolled in Part II did not show significant differences with respect to patients receiving VCN-01 as a single agent. VCN-01 viral genomes were detected in tumor tissue in 5 out of 6 biopsies. A second viral peak in plasma and increased hyaluronidase serum levels suggested replication after intravenous injection in all patients. Increased levels of immune biomarkers (IFNγ, sLAG3, IL-6, IL-10) were found

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after VCN-01 administration. In patients with pancreatic adenocarcinoma, the overall response rate (ORR) was 50% for Part II and 50% for Part III, as assessed by the investigators. Median progression free survival (PFS) for patients in Part III was 6.7 months, and median overall survival (OS) was 13.5 months. Eight patients (66.7%) survived more than 12 months. In addition, in April 2021, a subgroup analysis of patients at the RP2D (1.x1013 vp/patient followed by nab-paclitaxel plus gemcitabine one week later, n=6) was conducted and showed an ORR of 83%, with a median PFS of 6.3 months and median OS of 20.8 months. Some VCN-01 treated patients appeared to benefit from late-onset responses. This form of delayed anti-tumor activity is not common with chemotherapy but is frequently observed with immunotherapies. We believe an immune mechanism of action associated with the oncolytic activity of VCN-01 may be the underlying explanation. VCN-01 appeared to convert the typically immunosuppressive tumor microenvironment of pancreatic adenocarcinomas into an enhanced inflammatory microenvironment (IDO, CD28, PD-1, CTL signature up-regulation, and collagen formation) after treatment.

Phase 2 Trial of intravenous VCN-01 (zabilugene almadenorepvec) with nab-paclitaxel plus gemcitabine in patients with PDAC

In January 2023, we dosed the first patients in VIRAGE, the Phase 2b randomized, open-label, multicenter clinical trial of systemically administered VCN-01 in combination with SoC chemotherapy (gemcitabine/nab-paclitaxel) as a first line therapy for patients with newly-diagnosed metastatic pancreatic ductal adenocarcinoma. The study was conducted at approximately 17 sites in the US and EU. Two doses of VCN-01 were included in the treatment arm: the 1st dose was administered on day 1, then one week later 3 cycles of gemcitabine and nab-paclitaxel as standard of care was administered. The second VCN-01 dose was administered 7 days before the 4th cycle of chemotherapy (approximately 90 days after the first VCN-01 dose), followed by additional cycles of gemcitabine/nab-paclitaxel chemotherapy.

Patient dosing was initiated in the U.S. in July 2023 and, on September 23, 2024, we announced that we achieved our target patient enrollment of 92 evaluable patients in the VIRAGE Phase 2b clinical trial. Thirty - six patients received their second doses of intravenous VCN-01, which were well tolerated and demonstrated the expected VCN-01 adverse event profile. Positive topline data for the VIRAGE Phase 2b clinical trial from the first-line treatment of 96 newly-diagnosed metastatic PDAC patients was announced in the second quarter of 2025 and is described below.

On January 30, 2024, the accumulated clinical data from patients enrolled across 6 sites open in the U.S. and 9 sites open in Spain were reviewed by an Independent Data Monitoring Committee (IDMC). According to the IDMC’s assessment, the ongoing Phase 2b trial continued without any changes to the protocol. No safety concerns were raised based on the evaluation of data presented at the IDMC meeting. Intravenous VCN-01 has been well tolerated and demonstrated a safety profile consistent with prior clinical trials. Importantly, no additional toxicities were observed in patients receiving a second dose of VCN-01, providing the first clinical evidence of the feasibility of repeated systemic dosing.

On May 10, 2024, we presented data demonstrating enhanced anti-tumor effects in human pancreatic cancer xenograft-bearing mice treated with lead product candidate VCN-01 and liposomal irinotecan. These data support the potential synergy of VCN-01 and first-line pancreatic cancer chemotherapy regimens.

On May 23, 2024, we announced that the FDA granted Fast Track Designation (FTD) to lead clinical candidate VCN-01 in combination with gemcitabine and nab-paclitaxel to improve progression-free survival and overall survival in patients with metastatic pancreatic adenocarcinoma.

On December 5, 2024, we announced the outcomes of a Type D meeting with the FDA to obtain guidance on the design of a potential Phase 3 clinical study of VCN-01 in combination with SoC chemotherapy for the treatment of metastatic PDAC (“mPDAC”). The FDA advised that the optimal path forward for the VCN-01 PDAC program is to conduct a stand-alone Phase 3 study of VCN-01 with gemcitabine/nab-paclitaxel. The FDA provided general agreement with our proposed design for a Phase 3 clinical study and indicated that inclusion of additional SoC chemotherapy for mPDAC was not necessary as it would complicate the study design and analysis. The FDA meeting also highlighted the FDA’s preferences regarding certain statistical elements of confirmatory clinical studies, including methods for sample size estimation and the study population(s) used for data analysis.

On February 4, 2025, we received Scientific Advice from the Committee for Medicinal Products for Human Use (“CHMP”) of the European Medicines Agency (“EMA”) on the design of a potential Phase 3 clinical study of VCN-01 in combination with SoC chemotherapy for the treatment of mPDAC. Consistent with feedback from the FDA, CHMP advised that a marketing authorization application (“MAA”) for VCN-01 in mPDAC could be supported by positive results from a randomized, controlled, stand-alone Phase 3 study comparing VCN-01 combined with gemcitabine/nab-paclitaxel to gemcitabine/nab-paclitaxel SoC alone. The Scientific Advice also included CHMP suggestions regarding the study populations, inclusion/exclusion criteria, randomization and blinding, priority

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endpoints, and proposed statistical strategies for data analysis. An additional comment from the EMA Committee for Orphan Medicinal Products (“COMP”) noted that the potential benefit of VCN-01 with gemcitabine/nab-paclitaxel in a Phase 3 trial will be compared with the therapeutic effects of the other approved SoC chemotherapies (FOLFIRINOX, NALIRIFOX) when considering maintenance of the Orphan Medicinal Product status of VCN-01 at the time of an MAA.

On March 31, 2025, we announced that a second Independent Data Monitoring Committee (“IDMC”) review of data from the VIRAGE Phase 2b clinical trial in newly-diagnosed mPDAC found that VCN-01 was well tolerated in combination with SoC chemotherapy (gemcitabine/nab-paclitaxel) and the adverse event (“AE”) profile was as expected for the patient population and the medications being studied. The VCN-01 AE profile was consistent with that observed in prior clinical trials. The most common VCN-01 related AEs (pyrexia, flu-like illness, vomiting, nausea, and elevated transaminases) were transient and reversible. These AEs were observed to be less frequent and of reduced CTCAE grade after the second VCN-01 dose (administered on day 92) compared to the first VCN-01 dose (administered on day 1). The IDMC noted that the overall type and number of AEs in the VCN-01 treatment group was as expected for the pancreatic cancer population, the duration of treatment, and the administration of an oncolytic virus.

On May 7, 2025, we announced positive topline outcomes from the VIRAGE Phase 2b clinical trial evaluating our lead product candidate VCN-01 (zabilugene almadenorepvec) plus SoC chemotherapy gemcitabine/nab-paclitaxel as a first line therapy for patients with mPDAC for whom gemcitabine/nab-paclitaxel is the recommended first-line treatment option. Topline outcomes for the analysis of the VIRAGE trial includes the following data for first-line treatment of the 96 newly-diagnosed metastatic PDAC patients dosed in the clinical trial:

●In the primary endpoint analysis, the 48 patients treated with at least one dose of gemcitabine/nab-paclitaxel SoC had a median OS) of 8.6 months, while the 48 patients treated with VCN-01 followed by at least one dose of gemcitabine/nab-paclitaxel SoC had a median OS of 10.8 months [Hazard Ratio (HR) = 0.57, 95% CI 0.34-0.96, p=0.0546].

●The improvements in OS in the VCN-01+SoC treatment arm compared to the SoC control arm were reflected in increased progression free survival (PFS) [median PFS 7.0 vs 4.6 months; HR = 0.55, 95% CI 0.34-0.88, p= 0.0105].

●The median duration of response (“DoR”) was 5.4 months (n=15) in the SoC control arm, while the median DoR in the VCN-01+SoC treatment arm was doubled to 11.2 months (n=19, HR = 0.22, 95% CI 0.08-0.62, p=0.0035).

The increase in OS was greater for patients who received 2 doses of VCN-01 and 4 or more cycles of gemcitabine/nab-paclitaxel SoC (n=34) compared with patients who received 4 or more cycles of gemcitabine/nab-paclitaxel SoC (n=29) [median OS 14.8 and 11.6 months respectively; HR=0.44, 95% CI: 0.21-0.92, p=0.046], suggesting that the second dose of VCN-01 (administered 3 months after the first dose) provides a meaningful additional benefit in this treatment subgroup.

On October 20, 2025, expanded mPDAC data from the VIRAGE Phase 2b trial (NCT05673811) were presented in oral communication at the ESMO 2025 Annual Congress, which took place in Berlin, Germany. Results from the VIRAGE Phase 2b trial included in the abstract for the presentation titled “VIRAGE trial: randomized Phase IIb, open-label, study of Nab-Paclitaxel and Gemcitabine with/without intravenous VCN-01 in Patients with Metastatic Pancreatic Cancer (mPDAC )” are set forth below:

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112 patients were randomized. Patients in the modified intent to treat (“mITT”) population received at least 1 dose of gemcitabine/nab-paclitaxel (“GA”) standard of care chemotherapy (GA, Arm I) or VCN-01 (Arm II). Patients in the full analysis set (“FAS”) population received at least 1 dose of gemcitabine/nab-paclitaxel SoC chemotherapy (GA; Arm I) or VCN-01 followed by at least 1 dose of GA (Arm II).

​

Definitions -mo. (Months). OS (overall survival). PS or PFS (progression free survival). DoR (duration of response). ORR (objective response rate). HR (hazard ratio). CI (confidence interval).

Compared to patients who started GA cycle 4 alone (Arm I), patients who received 2 VCN-01 doses and started GA cycle 4 (Arm II) showed greater improvement in OS (14.8 vs 11.6 months; HR 0.44; 95% CI 0.21 - 0.92; P=0.046) and PFS (11.2 vs 7.4 months; HR 0.48; 95% CI 0.25 - 0.91; P=0.017). VCN-01 administration was well tolerated. All VCN- 01-related serious adverse events (n=13) were resolved, the most common being flu-like symptoms (13,2%), transaminase increase (5.7%) and drug-induced liver injury (3.8%). Viral genome analysis confirmed the bioactivity of the second VCN-01 dose.

This study met its primary endpoints. Patients receiving VCN-01 + GA had improved OS, PFS and DoR compared to GA standard of care.

Design of the Phase 3 Trial of intravenous VCN-01 with nab-paclitaxel plus gemcitabine in patients with mPDAC

On December 29, 2025, we announced the receipt of additional Scientific Advice (the “Additional Scientific Advice”) from the CHMP of the EMA on the design of a Phase 3 clinical trial of lead clinical candidate VCN-01 in combination with gemcitabine/nab-paclitaxel standard-of-care (SoC) chemotherapy for the first-line treatment of metastatic PDAC. CHMP advised that a potential future marketing authorization application (MAA) for VCN-01 in metastatic PDAC could be supported by Theriva’s proposed clinical development strategy comprising a single, high-quality, double-blinded, randomized, placebo-controlled Phase 3 trial if it demonstrates a compelling benefit-risk ratio with VCN-01 plus gemcitabine/nab-paclitaxel SoC compared to gemcitabine/nab-paclitaxel SoC alone. The Additional Scientific Advice included agreement on the proposed sample size, and the use of an adaptive design to potentially optimize trial timelines and outcomes. Inclusion/exclusion criteria, primary endpoint (overall survival), secondary endpoints (including progression free survival, duration of response, and patient reported outcomes) were also accepted. Importantly, CHMP recognized the increased improvement in overall survival rate of patients receiving 2 doses of VCN-01 in the VIRAGE study, and agreed with the proposed dosing of VCN-01 and gemcitabine/nab-paclitaxel in repeated “macrocycles”, enabling more than 2 doses of VCN-01 to be administered in the Phase 3 trial. They further suggested that more frequent dosing of VCN-01 could be considered. An End-of-Phase 2 meeting with the FDA is planned for first half of 2026, aiming to finalize the design of a pivotal multinational Phase 3 clinical trial in PDAC.

Retinoblastoma

Retinoblastoma is a tumor that originates in the retina and it is the most common type of eye cancer in children. It occurs in approximately 1/14,000 - 1/18,000 live newborns and accounts for 15% of the tumors in the pediatric population < 1 year old. The average age of pediatric patients at diagnosis is 2, and it rarely occurs in children older than 6. In the US, retinoblastoma shows an incidence rate of 3.3 per 1,000,000 with only about 200 to 300 children diagnosed per year according to the American Cancer Society. Bilateral

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retinoblastoma (Rb1 germinal mutation) represents 25-35% of the cases while unilateral retinoblastoma (sporadic mutation) accounts for 65-75%. While retinoblastoma is a highly curable disease in the US, with a current disease-free survival rate of >95%, the clinical challenge for those who treat retinoblastoma is to preserve life and to prevent the loss of an eye, blindness and other serious effects of treatment that reduce the patient’s life span or the quality of life. In addition, children with retinoblastoma have been more likely to lose their eye and die of metastatic disease in low-resource countries.

Current treatments are not without significant morbidity, which may include visual impairment and severe cosmetic deformity secondary to enucleation and/or irradiation of the orbital region. The use of intravenous chemotherapy and more recently intra-arterial and intravitreal chemotherapy have resulted in a significantly greater number of eyes preserved with fewer long-term effects compared to past treatments such as external radiation therapy. However, allowing patients with advanced intraocular disease to be treated conservatively, led to the appearance of a subgroup of patients with advanced intraocular disease who relapsed after an initial response. Most of these cases include those patients who present gross vitreous or subretinal seeding. Once the aforementioned treatments are exhausted, these patients rarely manage to preserve the eyes and vision and must be enucleated. The ocular preservation rate of these eyes with advanced disease is still less than 50%.

In February 2022, the FDA granted Orphan Drug designation to VCN-01 for the treatment of retinoblastoma.

Phase 1 Trial of intravitreal VCN-01 (zabilugene almadenorepvec) in patients with retinoblastoma

During the third quarter of 2017, VCN entered into a Clinical Trial Agreement with Hospital Sant Joan de Déu (Barcelona, Spain) to conduct an investigator sponsored Phase 1 clinical study evaluating the safety and tolerability of two intravitreal injections of VCN-01 in patients with intraocular retinoblastoma refractory to systemic, intra-arterial or intravitreal chemotherapy, or radiotherapy, in whom enucleation was the only recommended treatment (NCT03284268). Patients received two intravitreal injections of VCN-01, 14 days apart, at a dose of either 2 x 109 vp/eye (n=1) or 2 x 1010 vp/eye (n=8). The trial has concluded and the clinical study report has been completed.

On April 23, 2024, we announced positive topline data from this study, with agreement by the study Monitoring Committee that the study had a positive outcome. Per the terms of the clinical trial agreement, the determination by the study Monitoring Committee that the study had a positive outcome means we received an exclusive, worldwide technology license, and related patents from Hospital Sant Joan de Déu for the treatment of pediatric patients with advanced retinoblastoma and we are obligated to pay to Hospital Sant Joan de Déu the amount of three hundred twenty thousand, two hundred and sixty five Euros (€320,265) or approximately $334,000, half of which has been paid and the remaining half is expected to be paid upon invoice receipt.

A pre-Investigational New Drug (“IND”) meeting with the FDA was held on December 19, 2023 to discuss the path forward for VCN-01 as an adjunct to chemotherapy in pediatric patients with advanced retinoblastoma. The FDA provided some guidance on the potential endpoints and patient population for an advanced clinical trial and encouraged submission of a formal protocol under a US IND in order to provide more detailed commentary.

On July 30, 2024, we received notice from the FDA that we had been granted Rare Pediatric Drug Designation (“RPDD”) for VCN-01 for the treatment of retinoblastoma. The FDA grants RPDD for rare diseases (fewer than 200,000 affected persons in the United States) that are serious and life-threatening and primarily affect children ages 18 years or younger. If a Biologics License Application for VCN-01 for the treatment of retinoblastoma is approved by the FDA by September 30, 2029, we may be eligible to receive a Priority Review Voucher.

On October 11, 2024, the European Commission adopted the EMA recommendation to grant Orphan Medicinal Product Designation to VCN-01 for the treatment of retinoblastoma and the European Commission confirmed the designation under Regulation No 141/2000 of the European Parliament and of the Council.

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On May 27, 2025, we announced the presentation of the final data from an investigator-sponsored Phase 1 study of VCN-01 (zabilugene almadenorepvec) in refractory retinoblastoma patients in a poster presented by Dr. Jaume Català-Mora, Pediatric Ophthalmologist, Sant Joan de Déu-Barcelona Children’s Hospital at the 2025 ASCO annual meeting. Based on the study results, it was concluded that VCN-01 was well tolerated, after 2 intravitreal administrations at 2E10 vp/eye. The most frequently reported treatment-related adverse events were Grade 1 or 2-uveitis being the most common adverse event and one patient with Grade 3 uveitis who did not receive the second dose because of medical decision and also experienced glaucoma requiring treatment. No systemic toxicities occurred. There were no dose limiting toxicities and no ocular or systemic toxicities greater than Grade 3 during the evaluation period. Final findings include the following:

●Some degree of ocular inflammation and associated turbidity was observed after VCN-01 injection. Inflammation was managed, and vitreous haze improved in some cases, using pre-emptive oral and/or topical steroids.

●VCN-01 did not cause retinal toxicity, and selective VCN-01 replication in retinoblastoma cells was observed by immunohistochemical analysis. VCN-01 caused reversible changes in electroretinograms associated to turbidity.

●Replication of VCN-01 was detected over time within retinoblastoma tumors but was not observed in healthy tissue.

●Intravitreal VCN-01 demonstrated promising antitumor activity:

oFive patients presented a partial response, three presented stable disease and one, progressive disease

oThe eyes of 3 out of 5 patients with partial response were preserved with vision after receiving eye-conservative therapy (follow-up 12-49 months)

VCN-01 (zabilugene almadenorepvec) in combination with Immunomodulatory therapeutics

Based on the clinical and pre-clinical data described below, we believe that the administration of VCN-01, can elicit an anti-tumor immune response that could potentiate the effects of VCN-01 and co-administered therapeutics. Biopsies from the Phase 1 trial of PDAC patients administered intravenous VCN-01 demonstrated lymphocyte (CD8+) infiltration and modulated levels of immune markers in tumors, including an induction of the PD1/PD-L1 expression in tumor tissue from some of the patients. Preclinical experiments demonstrated that VCN-01 significantly increased extravasation of an anti-PD-L1 antibody into subcutaneous xenograft tumors compared to non-treated (PBS) tumors and also that PH20 hyaluronidase improves the ingress of T-cells in animal models. We believe that the administration of VCN-01 into the tumor may help to overcome the observed resistance to PD-L1 checkpoint inhibitors and to mesothelin-directed CAR-T cells.

Phase 1 Trial of intravenous VCN-01 (zabilugene almadenorepvec) in Combination with Durvalumab in Subjects with Recurrent/ Metastatic SCCHN

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In February 2019, VCN entered into a Clinical Trial Agreement with Catalan Institute of Oncology (ICO) (Spain) to conduct an investigator sponsored Phase 1 clinical study to evaluate the safety, tolerability and RP2D of a single intravenous injection of VCN-01 combined with durvalumab in two administration regimens: VCN-01 concomitantly with durvalumab, or sequentially with durvalumab starting two weeks after VCN-01 administration (NCT03799744). The study was also designed to evaluate whether VCN-01 treatment can re-sensitize PD-(l)-1 refractory tumors to subsequent anti-PD-L1 therapy. Durvalumab is a human monoclonal antibody (“mAb”) of the immunoglobulin G (IgG) 1 kappa subclass that inhibits binding of PD-L1. It is marketed as IMFINZI® by AstraZeneca/MedImmune, who supplied the product for its use in the clinical study. This Phase I trial was a multicenter, open label, dose escalation study in patients with histologically confirmed head and neck squamous cell carcinoma from specific sites: oral cavity, oropharynx, larynx or hypopharynx that is recurrent/metastatic (R/M) and not amenable to curative therapy by surgery or radiation. In addition, all patients should have undergone prior exposure to anti-PD-(L) 1 and progressed. Patients were entered at each dose level, according to a planned dose escalation schedule. The treatment was a single intravenous VCN-01 dose combined with concomitant intravenous durvalumab (MEDI4736) 1500 mg Q4W (Arm I) or durvalumab starting two weeks after VCN-01 administration (“sequential schedule”; Arm II). Patient recruitment into Arm I and Arm II was performed concurrently. Intravenous VCN-01 was administered to each patient only once during the trial at the VCN-01 dose level to which they were randomized. Durvalumab was administered Q4W until disease progression, unacceptable toxicity, withdrawal of consent, or another discontinuation criterion. Patient recruitment into the study was completed in February 2022 with a total of 18 patients enrolled. On September 5, 2022 we announced a presentation of initial data from this study in a poster at the ESMO Congress. The poster reported that treatment with VCN-01 was well tolerated when administered with durvalumab in the sequential schedule and the most common treatment-related adverse events were dose-dependent and reversible pyrexia, flu-like symptoms and increases in liver transaminases. Sustained blood levels of VCN-01 viral genomes and increased serum hyaluronidase levels were maintained for over six weeks and analysis of tumor samples showed an increase in CD8 T cells (a marker of tumor inflammation); upregulation of PD-L1; and downregulation of matrix-related pathways after VCN-01 administration. The trial has been completed and the clinical study report has been completed.

On October 16, 2023, we presented additional data from this study in a poster at the ESMO 2023 Congress held virtually and in Madrid, Spain from October 20-24, 2023. Key data and conclusions featured in the ESMO presentation include:

●20 patients were enrolled with a median of 4 prior lines of therapy, from which six in the concomitant (“CS”) (single dose of VCN-01 in combination with durvalumab on day 1) and 12 in the sequential (“SS”) (single dose of VCN-01 on day -14 and durvalumab on day 1) were evaluable for response.

●In the CS cohort at the 3.3×1012 viral particles (vp) dose, OS was 10.4 months.

●In the SS cohort at the 3.3×1012vp dose OS was 15.5 months, whereas in the SS cohort at the 1×1013 vp dose OS was 17.3 months.

●11 patients (61.1%) were alive >12 months (2 in CS; 5 in SS at 3.3×1012vp, 4 in SS at 1×1013 vp).

●In spite of the advanced stage of the disease, and a global objective response rate for the trial of 5.5%, most of the patients appeared to benefit from subsequent treatment, with 2 patients showing complete responses to palliative chemotherapy and at least one patient still alive 4 years after entering the study.

●Biological activity: Patients showed VCN-01 replication and increased serum hyaluronidase levels were maintained for over six weeks.

●Observed an increase in CD8 T cells, a marker of tumor inflammation and an upregulation of PD-L1 in tumors.

●Increase of PDL1-combined positive score (CPS; 16/21; p=0.013) and CD8 T-cells (12/21; p=0.007) from baseline were found in tumor biopsies.

●There was a statistically significant correlation between OS observed in patients and CPS on day 8 (p=0.005).

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Phase 1 Trial evaluating the safety and feasibility of huCART-meso cells when given in combination with VCN-01 (zabilugene almadenorepvec)

In July 2021, VCN entered into a Clinical Trial Agreement with the University of Pennsylvania (Philadelphia) to conduct an investigator sponsored Phase 1 clinical study to evaluate the safety, tolerability and feasibility of intravenous administration of VCN-01 in combination with lentiviral transduced huCART-meso cells (developed by the laboratory of Dr. Carl June) in patients with histologically confirmed unresectable or metastatic pancreatic adenocarcinoma and serous epithelial ovarian cancer (NCT05057715). This is a Phase 1 study evaluating the combination of VCN-01 when given in combination with huCART-meso cells in a dose-escalation design in two cohorts (N = 3-6), where patients receive VCN-01 as a single IV infusion (at 3.3x1012 or 1x1013 vp) on Day 0, followed by a single dose of 5x107 huCART-meso cells on Day 14 via IV infusion. huCART-meso cells are modified T-cells targeting the mesothelin antigen, which is frequently expressed in multiple tumor types, particularly in pancreatic and ovarian cancers. Dr. June’s previous clinical studies have shown that huCART-meso cells encounter significant challenges in the tumor microenvironment, including immunosuppressive cells and soluble factors as well as metabolic restrictions. Initial VCN-01 clinical data from the studies described above suggest that administration of VCN-01 may increase tumor immunogenicity and improve access of the huCART-meso cells to tumor cells. This Phase 1 study will evaluate the safety and tolerability of the VCN-01 huCART-meso cell combination and test the hypothesis that administration of VCN-01 may enhance the potential antitumor effects of the co-administered huCART-meso cells.

On July 8, 2022, we were notified that the first patient to be dosed with VCN-01 had passed the safety evaluation period in this study. On June 22, 2023, at their Cellicon Valley conference, and again at the Society for Immunotherapy of Cancer (SITC) meeting in San Diego, CA on November 3, 2023, and the International Oncolytic Virotherapy Conference (IOVC2023) in Calgary on November 13 2023, University of Pennsylvania investigators presented preliminary clinical safety and pharmacokinetic data from this study highlighting the feasibility of administering VCN-01 in sequence with huCART-meso cells in pancreatic and ovarian cancer patients. VCN-01 persistence was suggestive of tumor infection and active replication. The peak and duration of huCART-meso T cells in the peripheral blood as well as duration of stable disease in evaluable patients showed encouraging trends.

On October 16, 2024, at the 2024 Advancing Gene Therapy and Cell Therapies for Cancer conference by the American Society for Gene and Cell Therapy in Philadelphia, University of Pennsylvania investigators presented results from the Phase 1 trial of huCART-meso cells administered in combination with VCN-01 in patients with pancreatic and serous epithelial ovarian cancer. Safety was in line with expectations from monotherapy studies and 3.3x1012 was defined as the dose for further development. The Cmax of huCART-meso cells showed some signs of enhancement in patients previously infused with VCN-01. 66.6% (4 out of 6) patients with measurable disease receiving huCART-meso after VCN-01 showed tumor shrinkage, indicating a promising trend in disease stabilization in patients receiving huCART-meso and VCN-01 compared to either agent alone.

On November 19, 2024, we were notified by the investigators that they would not continue with the present clinical trial, instead preferring to focus on advancement of a next-generation mesothelin-specific CAR-T. This new CAR-T could potentially be evaluated in combination with VCN-01 in a future clinical trial. The trial is active, although not recruiting as treated patients are still on survival follow - up.

Phase 1 Trial evaluating the intravenous administration of VCN-01 (zabilugene almadenorepvec) in patients prior to surgical resection of high-grade brain tumors

In the second quarter of 2021, VCN entered into a Clinical Trial Agreement with the University of Leeds (UK) to sponsor a proof-of-concept Phase 1 clinical study to evaluate whether intravenously administered VCN-01 can cross the blood-brain barrier and infect the target brain tumor. This is an open-label, non-randomized, single center study of VCN-01 given intravenously at a dose of 1x1013 virus particles to patients prior to planned surgery for recurrent high-grade primary or metastatic brain tumors. We believe that the intravenous delivery of anti-cancer therapy to brain tumors, if effective, may enable the treatment of systemically disseminated brain metastases and may allow for reduction in the need to use neurosurgery to administer the drugs. This study aims to assess the presence of VCN-01 within the resected surgical specimen after systemic VCN-01 delivery and determine the safety of intravenous VCN-01 in patients with recurrent high-grade glioma or brain metastases. By confirming the presence of VCN-01 in high grade brain tumors following intravenous delivery, we believe this study may pave the way for larger trials to study VCN-01 efficacy, both as a monotherapy and in combination with PD-1/PD-L1 blockade. This trial has already received approval from Medicines & Healthcare Products Regulatory Agency (MHRA) from UK Government.

On January 9, 2023, we issued a press release announcing that the first patient was dosed in this study. Recruitment is on-going but challenging.

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On May 12, 2025, a protocol amendment was submitted for this trial to MHRA and on July 8, 2025 we were notified by the investigator that the protocol amendment had been approved.

VCN-01 (zabilugene almadenorepvec) + Topoisomerase Inhibitors

On May 10, 2024, we presented non-clinical data describing enhanced anti-tumor effects in human pancreatic cancer xenograft-bearing mice treated with lead product candidate VCN-01 and liposomal irinotecan in a poster at the 27th American Society of Gene and Cell Therapy (ASGCT) 2024 Congress held in Baltimore (Maryland) from May 7-11, 2024. These data support the potential synergy of VCN-01 and additional first-line pancreatic cancer chemotherapy regimens FOLFIRINOX and NALIRIFOX. Key findings reported in the poster include:

●The combination of VCN-01 + topoisomerase I (topo1) inhibitors, such as liposomal irinotecan, has a tolerable toxicity profile and may improve efficacy in the treatment of human pancreatic cancer.

●Viral protein expression was increased in human pancreatic cancer cell lines when they were exposed to topo1 inhibiting chemotherapeutics, irinotecan, its active metabolite, SN-38, and topotecan.

●Synergy of VCN-01 plus liposomal irinotecan was observed in animals bearing subcutaneous human pancreatic tumors.

oIn human pancreatic mouse xenograft models, treatment with VCN-01 at a dose of 4x1010 vp or liposomal irinotecan alone (at both the 10 mg/kg and 5 mg/kg doses) resulted in significant tumor growth inhibition compared to saline.

oCombination therapy with VCN-01 + liposomal irinotecan at either dose displayed significantly reduced tumor growth compared to each treatment alone.

oqPCR analyses performed on tumors collected at end of study confirmed the presence of viral genomes, indicating ongoing transcriptional activity of VCN-01, which is consistent with viral replication for several days after administration.

We believe that intravitreal coadministration of VCN - 01 with topotecan may provide a new treatment option for children with refractory retinoblastoma and vitreous seeds, which remains an unmet medical need in patients with this rare disease. Discussions are on - going with clinicians and key opinion leaders to define a clinical protocol for the VCN - 01 + topotecan combination in this patient population.

VCN-X Next Generation OVs and Albumin Shield™ Technology

We have also conducted research and development activities for next-generation oncolytic adenoviruses (termed VCN-X) with novel therapeutic payloads and structural modifications designed to increase tumor cell killing and improve systemic virus pharmacokinetics. Preclinical proof-of-concept has been established with VCN-11, which has been engineered to contain all the features of VCN-01 as well as an additional modification to include an albumin binding domain (ABD) in the virus capsid. The virus capsid is the target for neutralizing NAbs that are generated by the host immune system to destroy circulating viruses. The presence of an ABD, however, blocks the binding of most neutralizing antibodies, which allows the virus to reach the tumor following intravenous administration. This “Albumin Shield” works because human blood contains a large amount of albumin to coat the ABD-containing virus. Importantly, this coating of albumin appears to be displaced after the virus reaches tumor cells to infect them. In pre-clinical mouse studies to test the functionality of the “Albumin Shield”, mice pre-immunized with virus are able to completely neutralize an unmodified OV because they have a large concentration of Nabs in their blood. By contrast, viruses such as VCN-11 that contain the ABD are not neutralized and retain their ability to infect and destroy tumor cells. We believe the results with VCN-11 support the application of the Albumin Shield technology in our VCN-X program to advance treatments for tumors in which rapid multi-dosing may be beneficial. VCN-12 is currently the focus of our preclinical studies.

In March 2021, preclinical data obtained with VCN-11 was published (J Control Release. 2021 Apr 10;332:517-528), showing that the ABD-containing virus induced 450 times more cytotoxicity in tumor cells than in normal cells. Hyaluronidase production was confirmed by measuring the activity of the PH20 enzyme with a hyaluronic acid-degradation assay, and by measuring PH20 activity in VCN-11 infected tumors in vivo. The ABD-containing virus evaded NAbs from different sources and tumor levels of virus were demonstrated in the presence of high levels of NAbs in vivo, whereas the control virus without ABD was neutralized. VCN-11 showed a low toxicity profile in athymic nude mice and Syrian hamsters, allowing treatments with high doses and fractionated administrations without major toxicities (up to 1.2x1011vp/mouse and 7.5x1011vp/hamster). ALT levels were increased on day 3 within an acceptable range that returned to normal levels by day 9. Fractionated intravenous administration of the ABD-containing virus (splitting the dose into two portions

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administered 4 h apart) appeared to improve virus circulation kinetics and increase tumor levels. Antitumor efficacy was observed in the presence of NAbs against Ad5 and the ABD-containing virus.

In May 2022, we presented data at the 25th Annual Meeting of the ASGCT. The presentation included preclinical results showcasing the potential of the Albumin Shield Technology to effectively target tumors after intravenous re-administration, even in the presence of high level NAbs, with no major toxicities observed. Our internal VCN-X discovery programs are currently evaluating new oncolytic viruses armed with alternative payloads that may increase antitumor efficacy.

In October 2025, Dr. Ramón Alemany, co-founder of VCN (now Theriva Biologics S.L.) and Head of the Immunotherapy and Virotherapy Group at the ProCURE Program of the Catalan Institute of Oncology (ICO) and the Oncobell Program of the Biomedical Research Institute of Bellvitge (IDIBELL) in Barcelona, presented new mechanistic and preclinical data for VCN-12, a next generation oncolytic adenovirus selected from our VCN-X discovery program at the 32nd Annual Congress of the European Society of Gene & Cell Therapy (ESGCT) in Seville, Spain. VCN-12 is derived from lead clinical product VCN-01 (zabilugene almadenorepvec) and is armed with additional transgenes designed to improve tumor cell lysis, enhance stroma degradation, and augment the antitumor immune response. VCN-12 uses the same virus capsid as our lead clinical candidate VCN-01 (zabilugene almadenorepvec), but includes modifications intended to (i) increase stroma degradation by replacing human hyaluronidase PH20 with the more active bee hyaluronidase; and (ii) increase tumor cell lysis by expressing the pore forming protein parasporin-2 to enable both cytotoxic and immunogenic cell death. Parasporin-2 expression is expected to destroy both infected and surrounding uninfected tumor cells and stimulate a strong overall antitumor immune response and reduce viral immunodominance. Data presented by Dr. Alemany support the proposed VCN-12 mechanisms of action. VCN-12 showed increased cell killing compared to VCN-01 in a variety of cancer cell models in vitro. VCN-12 also displayed higher levels of hyaluronidase activity. In animal studies, intravenous VCN-12 had a similar toxicity profile to VCN-01 in immunodeficient mice bearing human tumor xenografts. Intratumoral VCN-12 significantly reduced tumor growth compared to VCN-01 in immunocompetent hamsters bearing HP-1 pancreatic tumors. The antitumor effect of VCN-12 was observed in both the injected tumors and second tumors-implanted 4-days later but not injected. Complete tumor regression of the first tumor was observed in two of nine hamsters and the second implanted tumor did not grow in these animals. VCN-12 appeared to stimulate a persistent immune response that prevented the establishment of tumors in these two complete responders when they were implanted with HP-1 cells 43 days after VCN-12 treatment. Further preclinical studies are planned to elaborate these initial findings.

THERICEL suspension cell lines for viral manufacturing

The THERICEL program is advancing a proprietary A549 suspension cell line for use in the manufacture of viral therapeutics. These cells are entering feasibility studies to support significant scale - up and potential Phase 3 GMP manufacture of VCN-01 (zabilugene almadenorepvec) for use in clinical trials. The use of the THERICEL suspension cells is expected to increase the efficiency and significantly reduce the cost of manufacture for VCN - 01 and other viral therapies.

We also have a Spanish government funded collaboration with the Universitat Autònoma de Barcelona to adapt the THERICEL suspension cell platform for the clinical manufacture of adeno - associated virus (“AAV”) therapies. If successful, adaptation of the THERICEL platform to AAV manufacture will provide an opportunity for potential commercial collaborations in the manufacture of a range of gene therapy products.

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Our Current Gastrointestinal (GI) and Microbiome-Focused Product Candidates

SYN-004 (ribaxamase) and SYN-020 are focused on the GI tract and the gut microbiome, which is home to billions of microbial species and composed of a natural balance of both “good” beneficial species and potentially “bad” pathogenic species. When the natural balance or normal function of these microbial species is disrupted, a person’s health can be compromised. All of our programs have been supported by a robust patent estate. As part of our strategic transformation into an oncology focused company, we (i) entered into the Rasayana License Agreement with Rasayana in February 2026, pursuant to which we granted Rasayana an exclusive worldwide license to research, develop, manufacture and commercialize any product related to or deriving from our SYN-020 asset, and (ii) we are exploring value creation options for our SYN - 004 asset, including out - licensing or partnering as we do not intend to further develop SYN-004 without receipt of grant funding or funding through a partnership or other collaboration.

SYN-004 (ribaxamase) — Prevention of antibiotic-mediated microbiome damage, thereby preventing overgrowth and infection by pathogenic organisms such as Clostridioides difficile infection (CDI) and vancomycin resistant Enterococci (VRE), and reducing the incidence and severity of acute graft-versus-host disease (aGVHD) in allogeneic HCT recipients

SYN-004 (ribaxamase) is a proprietary oral capsule prophylactic therapy designed to degrade certain IV beta-lactam antibiotics excreted into the GI tract and thereby maintain the natural balance of the gut microbiome. Preventing beta-lactam damage to the gut microbiome has a range of potential therapeutic outcomes, including prevention of CDI, suppression of the overgrowth of pathogenic species (particularly antimicrobial-resistant organisms) and potentially reducing the incidence and/or severity of aGVHD in allogeneic hematopoietic cell transplant (HCT) patients. SYN-004 (ribaxamase) 75 mg capsules are intended to be administered orally while patients are administered certain IV beta-lactam antibiotics. The capsule dosage form is designed to release the SYN-004 (ribaxamase) enzyme into proximal small intestine, where it has been shown to degrade beta-lactam antibiotics in the GI tract without altering systemic antibiotic levels. Beta-lactam antibiotics are a mainstay in hospital infection management and include the commonly used penicillin and cephalosporin classes of antibiotics.

Clostridioides difficile Infection

Clostridioides difficile (formerly known as Clostridium difficile and often called C. difficile or CDI) is a leading type of hospital acquired infection and is frequently associated with IV beta-lactam antibiotic treatment. The Centers for Disease Control and Prevention (CDC) identified C. difficile as an “urgent public health threat,” particularly given its resistance to many drugs used to treat other infections. CDI is a major unintended risk associated with the prophylactic or therapeutic use of IV antibiotics, which may adversely alter the natural balance of microflora that normally protect the GI tract, leading to C. difficile overgrowth and infection. Other risk factors for CDI include hospitalization, prolonged length of stay (estimated at 7 days), underlying illness, and immune-compromising conditions including the administration of chemotherapy and advanced age.

Limitations of Current Treatments and Market Opportunity

CDI is a widespread and often drug- resistant infectious disease. Approximately 20% of patients who have been diagnosed with CDI experience a recurrence of CDI within one to three months. Furthermore, controlling the spread of CDI has proven challenging, as the C. difficile spores are easily transferred to patients via normal contact with healthcare personnel and with inanimate objects. There is currently no vaccine or approved product for the prevention of primary (incident) CDI. The current standard of care for primary CDI, as outlined by the Infectious Disease Society of America (IDSA), is to treat with powerful antibiotics such as fidaxomicin or vancomycin. Prolonged use of fidaxomicin and vancomycin has been shown to further exacerbate damage to the gut microbiome, leading to increased risk of CDI recurrence as well as the emergence of pathogenic and antimicrobial-resistant (AMR) organisms, such as vancomycin-resistant enterococci (VRE). AMR is a serious global threat and one which world leaders have begun to take action against. According to the European Society of Clinical Microbiology and Infections Disease (ECCMID), failure to address AMR could lead to a potential “antibiotic Armageddon”, resulting in 10 million deaths worldwide by 2050 and may cost as much as $100 trillion in worldwide economic output.

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The latest CDC estimates found the crude overall incidence rate of CDI in the United States to be 117.2 cases per 100,000 persons (approximately 392,000 patients based on the estimated US population at the end of 2023) with a higher rate of community associated compared to healthcare associated infection (CDC Emerging Infections Program Healthcare-Associated Infections–Community Interface Report Clostridioides difficile Infection Surveillance, 2023. https://www.cdc.gov/healthcare-associated-infections/media/pdfs/2023-CDI-Report-508.pdf).

Phase 1a and 1b Clinical Trial Pharmacokinetic Data

In March 2015, we reported supportive pharmacokinetic data from a Phase 1a clinical trial (40 participants), which suggested that SYN-004 (ribaxamase) should have no effect on the IV antibiotic in the bloodstream, allowing the antibiotic to fight the primary infection. In February 2015, we reported supportive topline results from a subsequent Phase 1b clinical trial (24 participants) of escalating doses of oral SYN-004 (ribaxamase), with no safety or tolerability issues reported at dose levels and dosing regimens that were equivalent to or exceeded those expected to be studied in subsequent clinical trials.

Two Phase 2a Clinical Trials: Topline Results

In December 2015, we reported supportive topline results from our first Phase 2a clinical trial of SYN-004 (ribaxamase, NCT02419001). The study demonstrated that SYN-004 (ribaxamase) successfully degraded IV ceftriaxone in the chyme of ten participants with ileostomies without affecting the levels of ceftriaxone in the bloodstream. In May 2016, we reported supportive topline results from a second Phase 2a clinical trial of SYN-004 (ribaxamase) in 14 healthy participants with functioning ileostomies administered IV ceftriaxone with and without oral SYN-004 (ribaxamase) (NCT02473640). This second study demonstrated that the 150 mg dose of SYN-004 (ribaxamase), both alone and in the presence of the proton pump inhibitor (PPI), esomeprazole, degraded ceftriaxone excreted into the chyme resulting in ceftriaxone levels that were low or not-detectable. Ceftriaxone plasma concentrations in participants of the second study were not altered by SYN-004 (ribaxamase) in the presence or absence of an oral PPI, suggesting limited drug-drug interactions. The 150 mg dose of SYN-004 (ribaxamase) was well tolerated by all participants in this clinical trial.

Phase 2b Proof of Concept Clinical Trial Design & Results

On January 5, 2017, we announced positive topline data from our Phase 2b proof-of-concept clinical trial (412 participants-206 per group; NCT02563106) intended to evaluate the ability of SYN-004 (ribaxamase) to prevent CDI, CDAD (C. difficile-associated diarrhea) and AAD (antibiotic-associated diarrhea) in patients hospitalized for a lower respiratory tract infection and receiving IV ceftriaxone. Results from this study demonstrated that SYN-004 (ribaxamase) achieved its primary endpoint of significantly reducing CDI. Preliminary analysis of the data indicated seven confirmed cases of CDI in the placebo group compared to two cases in the SYN-004 (ribaxamase) treatment group. Patients receiving SYN-004 (ribaxamase) achieved a 71.4% relative risk reduction (p-value=0.045) in CDI rates compared to patients receiving placebo. SYN-004 (ribaxamase) treated patients also demonstrated a significant reduction in new colonization by vancomycin-resistant enterococci (VRE) compared to placebo (p-value=0.002). Results from this trial also demonstrated that patients administered ribaxamase in conjunction with IV-ceftriaxone demonstrated comparable cure rates (approximately 94%) for the treatment of primary infection compared to the placebo group. Results from this trial also demonstrated that the percentage of subjects reporting at least one treatment emergent adverse event (TEAE) was similar between SYN-004 (ribaxamase) and placebo treatment groups (40.8% vs 44.2%). Adverse events reported during this trial were comparable between treatment and placebo arms. Serious adverse events (SAEs) in the treatment arm, including fatal AEs, which exceeded those in the placebo arm, were not considered drug-related by investigators at the clinical sites, or by an independent third-party, each of whom determined SAEs were attributable to disparities in the underlying health and comorbidities between the groups.

On October 6, 2016 we were awarded a government contract in the amount of $521,014 by the CDC’s Broad Agency Announcement (BAA) 2016-N-17812 to examine changes in the gut resistome of patients in our Phase 2b clinical study. Data generated under this contract are consistent with SYN-004’s (ribaxamase) mode of action of preserving the normal gut flora by degrading ceftriaxone in the upper GI tract of study participants treated with SYN-004 (ribaxamase). The data further demonstrated that SYN-004 (ribaxamase) significantly reduced the loss of microbial diversity, reduced overgrowth of opportunistically pathogenic species (such as VRE), and reduced the emergence of AMR genes caused by ceftriaxone treatment in SYN-004 (ribaxamase) treated patients compared to placebo.

Future Potential Regulatory Strategy for Prevention of Primary CDI

On November 21, 2018, we announced results from our End-of-Phase 2 meeting with the FDA during which key elements of a Phase 3 clinical program were confirmed. Pursuant to the meeting, the FDA proposed criteria for Phase 3 clinical efficacy and safety which, if achieved, may support submission for marketing approval of SYN-004 (ribaxamase) on the basis of a single Phase 3 clinical trial. The

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proposed SYN-004 (ribaxamase) Phase 3 clinical program entails a single, global, event-driven clinical trial with a fixed maximum number of approximately 4,000 patients for total enrollment and evaluates the potential efficacy and safety of ribaxamase in a broad patient population by enrolling patients with a variety of underlying infections treated with a range of IV beta-lactam antibiotics.

The proposed Phase 3 clinical trial incorporates co-primary safety and efficacy endpoints (mortality and the reduction in the incidence of CDI at one month after the last drug dose in the SYN-004 (ribaxamase) treatment group versus placebo, respectively). We expect the clinical development costs to complete this trial to be in excess of $80 million and anticipate initiating the Phase 3 clinical program only after securing additional potential financing via a strategic partnership.

Acute Graft-Versus-Host-Disease in Allogeneic Hematopoietic Cell Transplant (allogeneic HCT) Recipients & SYN-004 (ribaxamase)

In parallel with our clinical and regulatory efforts, we completed a Health Economics Outcomes Research (“HEOR”) study, which was conducted to generate key insights on how we can expect Health Care Practitioners (“HCPs”), to evaluate patient access for SYN-004 (ribaxamase) while also providing a framework for potential reimbursement strategies. After evaluating findings from the study, we believe that there is significant potential value in exploring the development of SYN-004 (ribaxamase) in a narrower patient population where the incidence of the disease endpoint is high and the clinical development may be less costly.

We believe allogeneic hematopoietic cell transplant (“HCT”) recipients, who have a very high risk of CDI, VRE colonization and potentially fatal bacteremia, and acute-graft-vs-host disease (“aGVHD”), represent such a patient population. Published literature has demonstrated a strong association between these adverse outcomes and microbiome damage caused by IV beta-lactam antibiotics in these patients. Approximately 80-90% of HCT recipients receive IV beta-lactam antibiotics to treat febrile neutropenia. Penicillins and cephalosporins are first-line therapies in the USA and EU, whereas carbapenems are first-line in China. Antibiotic-mediated damage to the gut microbiome is strongly associated with GVHD, bloodstream infections, VRE bacteremia, transplant relapse, and increased mortality in HCT recipients, raising concern over the spectrum of antibiotics used during HCT.

CDI occurs in up to 31% of HCT patients and is associated with aGVHD and increased mortality. aGVHD occurs in 30-60% of allogeneic HCT recipients and is recognized as a primary contributor to morbidity and mortality in this patient population. The most recent available data indicate approximately 8,000 reported allogeneic HCT procedures each year in the USA, 19,800 procedures in Europe, 12,700 in China, and 3,500 in Japan. First-line treatments for aGVHD fail in more than 50% of patients and 2-year survival in patients with steroid refractory aGVHD is only 20%. At least one U.S. study found allogeneic HCT recipients who developed aGVHD had 3-times higher in-hospital mortality and almost 2-fold higher median hospital costs than patients who did not develop aGVHD. It has been reported that in-patient costs for allogeneic HCT in the USA range from $180,000-$300,000 depending on the disease severity. VRE infection is a persistent problem in HCT patients and VRE colonization after HCT has been associated with decreased patient survival.

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Phase 1b/2a Clinical Study in Allogeneic HCT Recipients

In August 2019, we entered into a Clinical Trial Agreement (CTA) with the Washington University School of Medicine (Washington University) to conduct a Phase 1b/2a clinical trial of SYN-004 (ribaxamase). Under the terms of this agreement, we serve as the sponsor of the study and supply SYN-004 (ribaxamase). Dr. Erik R. Dubberke, Professor of Medicine and Clinical Director, Transplant Infectious Diseases at Washington University and a member of the SYN-004 (ribaxamase) steering committee serves as the principal investigator of the clinical trial in collaboration with his Washington University colleague Dr. Mark A. Schroeder, Associate Professor of Medicine, Division of Oncology, Bone Marrow Transplantation and Leukemia.

The Phase 1b/2a clinical trial is a single center, randomized, double-blinded, placebo-controlled clinical trial of oral SYN-004 (ribaxamase) in up to 36 evaluable adult allogeneic HCT recipients. The goal of this study is to evaluate the safety, tolerability and potential absorption into the systemic circulation (if any) of oral SYN-004 (ribaxamase; 150 mg four times daily) administered to allogeneic HCT recipients who receive an IV carbapenem or beta-lactam antibiotic to treat fever. Study participants were enrolled into three sequential cohorts administered a different study-assigned IV antibiotic. Each cohort seeks to complete eight evaluable participants treated with SYN-004 (ribaxamase) and four evaluable participants treated with placebo. Safety and pharmacokinetic data for each cohort will be reviewed by an independent Data and Safety Monitoring Committee, which will make a recommendation on whether to proceed to the next IV antibiotic cohort. The study will also evaluate potential protective effects of SYN-004 on the gut microbiome as well as generate preliminary information on potential therapeutic benefits and patient outcomes of SYN-004 in allogeneic HCT recipients.

To date, we have completed 2 of 3 cohorts (Cohorts 1 and 2) in this study. On September 27, 2022, we issued a press release announcing positive outcomes from the Data and Safety Monitoring Committee (“DSMC”) review of results from the first Cohort and their recommendation that the study may proceed to enroll Cohort 2 in which study drug (SYN-004 or Placebo) is administered in combination with the IV beta-lactam antibiotic piperacillin/tazobactam. Initiation of the third cohort is dependent on potential grant funding.

On February 16, 2023 and April 13, 2023, we announced the presentation of safety and pharmacokinetic data from Cohort 1 and on October 3, 2024, we announced a positive outcome from the DSMC review of results from the second Cohort of our Phase 1b/2a randomized, double-blinded, placebo-controlled clinical trial of SYN-004 (ribaxamase) in allogeneic hematopoietic cell transplant (“HCT”) recipients for the prevention of acute graft-versus-host-disease. Based on a review of the safety and pharmacokinetic data, the DSMC recommended that the study may proceed to enroll Cohort 3 in which study drug (SYN-004 or Placebo) will be administered in combination with the IV beta-lactam antibiotic cefepime. Based upon our current available funding and our focus on our clinical development of VCN-01 we do not anticipate that enrollment for the third cohort will commence unless we obtain grant funding, or find a licensee or partner to fund the SYN-004 development program.

SYN-020 — Oral Intestinal Alkaline Phosphatase (IAP)

SYN-020 is a quality-controlled, recombinant version of bovine Intestinal Alkaline Phosphatase (IAP) produced under cGMP conditions and formulated for oral delivery. The published literature indicates that IAP functions to diminish GI and systemic inflammation, tighten the gut barrier to diminish “leaky gut,” diminish fat absorption, and promote a healthy microbiome. Despite its broad therapeutic potential, a key hurdle to commercialization has been the high cost of IAP manufacture which is commercially available for as much as $10,000 per gram. We believe we have developed technologies to traverse this hurdle and now have the ability to produce more than 3 grams per liter of SYN-020 and anticipate a cost of roughly a few hundred dollars per gram at commercial scale. Based on the known mechanisms as well as our own supporting animal model data, we initially intended to develop SYN-020 to mitigate the intestinal damage caused by radiation therapy that is routinely used to treat pelvic cancers. While we believe SYN-020 may play a pivotal role in addressing acute and long-term complications associated with radiation exposure to the GI tract, we have also explored the potential development of SYN-020 in large market indications with significant unmet medical needs. Such indications include celiac disease, non-alcoholic fatty liver disease (“NAFLD”), and indications to treat and prevent metabolic and inflammatory disorders associated with aging.

On June 29, 2021, we announced that enrollment, patient dosing and observation had been completed in the Phase 1, open-label, single ascending dose (“ SAD”) study of SYN-020. The SAD study enrolled 6 healthy adult volunteers into each of four cohorts with SYN-020 given orally as single doses ranging from 5 mg to 150 mg. The data demonstrated that SYN-020 maintained a favorable safety profile, was well tolerated at all dose levels, and no adverse events were attributed to the study drug. No SAEs were reported.

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Phase 1 Clinical Multiple-Ascending-Dose Study

During the third quarter of 2021 we initiated a Phase 1 clinical study evaluating multiple ascending doses (“MAD”) of SYN-020 (NCT05045833). The placebo-controlled, blinded study enrolled 32 healthy adult volunteers into four cohorts with SYN-020 administered orally in doses ranging from 5 mg to 75 mg twice daily for 14 days with a follow-up evaluation at day 35. Each cohort included six subjects who received SYN-020 and two who received placebo. On May 10, 2022, we announced positive safety data from the Phase 1 MAD study demonstrating that SYN-020 maintained a favorable safety profile and was well-tolerated across all dose levels. There were a few treatment-related adverse events, and all were mild (grade 1) and resolved without medical intervention. The most common adverse event, constipation, occurred in three out of 24 subjects in the treatment arm and in one out of eight subjects in the placebo arm. No adverse event led to discontinuation of the study drug and there were no serious adverse events. Additionally, fecal SYN-020 analyses verified intestinal bioavailability while plasma levels of SYN-020 were below the limit of quantitation in all samples at all timepoints verifying that SYN-020 was not absorbed into the systemic circulation.

The Phase 1 data from our SAD and MAD studies are intended to support the development of SYN-020 in multiple clinical indications including radiation enteritis, NAFLD, celiac disease, and diseases associated with aging.

Rasayana License Agreement

On February 17, 2026, we entered into the Rasayana License Agreement with Rasayana, pursuant to which we granted Rasayana an exclusive worldwide license with the right to grant sublicenses to research, develop, manufacture and commercialize any Product (as such term is defined in the Rasayana License Agreement), which includes SYN-020, comprising, containing, or covered by the Licensed IP (as such term is defined in the Rasayana License Agreement) and/or devised, developed, or produced using the Licensed IP. Under the terms and conditions of the Rasayana License Agreement, Rasayana has agreed to use commercially reasonable efforts to meet certain specified development milestones with respect to the Products. Additionally, pursuant to the terms of the Rasayana License Agreement, Rasayana will assume all responsibility and costs for the development and commercialization of the Products. Accordingly, going forward, we do not expect to continue to conduct research and development activities, including conducting further clinical studies, with respect to SYN-020, and do not expect to incur material expenditures in connection therewith.

As consideration for the license, on February 17, 2026, we received an upfront payment of $300,000 from Rasayana. In addition, we are entitled to receive from Rasayana development milestone payments of up to an aggregate of $16.0 million and sales milestone payments of up to an aggregate of $22.0 million upon achievement of certain development and net sales milestones with respect to Products. In addition, during the Royalty Term (as such term is defined in the Rasayana License Agreement), we are entitled to receive tiered royalties ranging from low to mid single digits on net sales of a Product. We will also be entitled to receive a certain percentage of any Sublicense Revenue (as such term is defined in the Rasayana License Agreement) received by Rasayana or its affiliates.

Intellectual Property

Our success depends in part on our ability to obtain and maintain proprietary protection for our product candidates and other discoveries, inventions, trade secrets and know-how that are critical to our business operations. Our success also depends in part on our ability to operate without infringing the proprietary rights of others, and in part, on our ability to prevent others from infringing our proprietary rights.

We rely primarily on a combination of patent, copyright, trademark, and trade secret laws, as well as contractual provisions with employees and third parties, to establish and protect our intellectual property (“IP”) rights. All of our programs are supported by a robust patent estate. In total, Theriva Biologics has over 135 U.S. and foreign patents and over 50 U.S. and foreign patents pending. VCN, through assignment or exclusive licenses, controls over 50 U.S. and foreign patents and over 15 U.S. and foreign patents pending.

The SYN-004 (ribaxamase) program is supported by IP that is assigned to Theriva Biologics, namely U.S. and foreign patents (in most major markets, e.g. Europe (including Germany, Great Britain and France), Japan, China and Canada, among others) and U.S. and foreign patents pending (in most major markets, e.g. Europe (including Germany, Great Britain and France), Japan, China and Canada, among others). For instance, U.S. Patent Nos. 8,894,994 and 9,587,234, which include claims to compositions of matter and pharmaceutical compositions of beta-lactamases, including SYN-004 (ribaxamase), have patent terms to at least 2031. Further, U.S. Patent 9,301,995 and 9,301,996, both of which will expire in at least 2031, cover various uses of beta-lactamases, including SYN-004 (ribaxamase), in protecting the microbiome, and U.S. Patent Nos. 9,290,754, 9,376,673, 9,404,103, 9,464,280, and 9,695,409 which will expire in at least 2035, covers further beta-lactamase compositions of matter related to SYN-004 (ribaxamase).

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The SYN-020 (oral intestinal alkaline phosphatase (IAP)) program is supported by IP that is assigned to Theriva Biologics, namely U.S. and foreign patents and patent applications (in many major markets, e.g. Europe, China, Japan, Korea, Canada, and Australia). These patents and patent applications, which cover various formulations, medical uses and manufacture of SYN-020, are expected to expire in 2038-2040, without taking potential patent term extensions or patent term adjustment into account. All such patents were licensed to Rasayana pursuant to the Rasayana Agreement entered into in February 2026.

The VCN-01 (zabilugene almadenorepvec) and Albumin Shield programs are supported by U.S. and foreign patents and patent applications that are either assigned to VCN or exclusively licensed from IDIBELL, ICO, and Hospital Sant Joan de Déu in Barcelona. The patents and patent applications include U.S. patents and foreign patents (in most major markets, e.g. Europe, China, Japan, Korea, Canada, Israel, Mexico, Russia, and Australia) and U.S. and foreign patents pending (in most major markets, e.g. Europe, China, Korea, Canada, Mexico, and India). The patents and patent applications cover compositions of matter and pharmaceutical compositions of oncolytic adenoviruses together with combination with other agents and various medical uses of the same. For instance, U.S. Patent No. 10,316,065, which expires in 2030 without taking potential patent term extensions or patent term adjustment into account, provides composition of matter and pharmaceutical composition coverage for a genus of engineered oncolytic adenovirus suitable for the treatment of solid tumors. Other patents and patent applications, if granted, will provide protection to 2037 without taking potential patent term extensions or patent term adjustment into account.

Our goal is to (i) obtain, maintain, and enforce patent protection for our products, formulations, processes, methods, and other proprietary technologies, (ii) preserve our trade secrets, and (iii) operate without infringing on the proprietary rights of other parties worldwide. We seek, where appropriate, the broadest intellectual property protection for product candidates, proprietary information, and proprietary technology through a combination of contractual arrangements and patents.

Acquisition of VCN Biosciences, S.L. (now known as Theriva Biologics, S.L.)

On March 10, 2022, we completed our acquisition (the “VCN Acquisition”) of all the outstanding shares of VCN (the “VCN Shares”) from the shareholders of VCN pursuant to the terms of the Share Purchase Agreement (“Purchase Agreement”) that we entered into with VCN and the shareholders of VCN Biosciences, S.L. (the “Sellers”) on December 14, 2021. Upon consummation of the Acquisition, VCN became our wholly owned subsidiary. As consideration for the purchase of the VCN Shares of capital stock, we paid $4,700,000 (the “Closing Cash Consideration”) to Grifols Innovation and New Technologies Limited (“Grifols”), the owner of approximately 86% of the equity of VCN, and issued to the remaining Sellers an aggregate of 2,639,530 shares of our Common Stock (the “Closing Shares”), representing 19.99% of the outstanding shares of our Common Stock on December 14, 2021, the date of the Purchase Agreement. As additional consideration for the purchase of the VCN Shares held by Grifols, we also agreed to make the following milestone payments to Grifols:

Milestone Payments

US$3MM upon VCN-01 US IND Safe to Proceed PDAC (or other first indication), which payment was made in Q4 2022 upon attaining the milestone

US$2.75MM upon VCN-01 US IND Safe to Proceed – retinoblastoma (“RB”, or other second indication)

US$3.25MM upon VCN-01 US first patient dosed– PDAC (or other first indication) after receipt of VCN-01 US IND Safe to Proceed for PDAC being informed, which payment was made in Q4 2023 upon attaining the milestone

US$3.25MM upon VCN-01 US first patient dosed – RB (or other second indication) after receipt of VCN-01 US IND Safe to Proceed for RB being informed

US$6MM upon VCN-01 US Phase 2 trial meets the primary endpoint or if a Phase 2 trial is not conducted and only a Phase 3 trial is conducted then upon a Phase 3 being initiated – PDAC (or other first indication), of which $1.0 million has been paid and the remaining $5.0 million payment has been deferred pending ongoing discussions with Grifols.

US$8MM upon VCN-01 Pivotal Trial meeting the primary endpoint or upon Submission of a Biologics License Application (‘BLA”)– RB (or other second indication)

US$12MM upon VCN-01 US Phase 3 trial meeting the primary endpoint or upon BLA Submission – PDAC (or other first indication)

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US$16MM upon VCN-01 BLA Approval – PDAC (or other first indication)

US$16MM upon VCN-01 BLA Approval – RB (or other second indication)

Pursuant to the Purchase Agreement, at the Closing we assumed $2,400,000 of liabilities of VCN, which includes certain loans from the Spanish Government and the Catalan Government Agency.

The Purchase Agreement contains customary representations, warranties and covenants of the Sellers and us. Subject to certain customary limitations, the Sellers have agreed to indemnify us and our officers and directors against certain losses related to, among other things, breaches of their representations and warranties, certain specified liabilities and the failure to perform covenants or obligations under the Purchase Agreement.

Our Current Collaborations

IDIBELL Technology Transfer Agreement

On August 31, 2010, VCN entered into a Technology Transfer Agreement (the “Technology Transfer Agreement”) with IDIBELL for the exclusive license of the right to use a Spanish patent number P200901201 titled “Oncolytic adenoviruses for treating cancer” which is co-owned by IDIBELL and ICO for the term of the patent. The Technology Transfer Agreement provides that IDIBELL is entitled to a low single digit percentage royalty on the income collected by VCN from the utilization of products derived from the licensed technology, prior to applying any value-added tax, if any, and low single digit percentage royalty on other income received by VCN arising from the use of the licensed technology, including income related to sublicenses of the licensed technology to third parties and advance payments or payments made for goals that were met and/or services associated with the licensed technology. The Technology Transfer Agreement terminates upon the expiration of the patent rights and is subject to early termination by either party in the event of a breach by the other party of its obligations thereunder. In addition, IDIBELL has the right to revoke the license if VCN ceases business activities for a continuous year or ceases to utilize the technology subject of the Technology Transfer Agreement, uses the technology in violation of the principals of IDIBELL or ICO or stops maintaining the patent licensed under the Technology Transfer Agreement

ICO Marketing License

On May 16, 2009, VCN entered into a Contract to Grant a Marketing License (the “ICO License Agreement”) with ICO for a manufacturing and marketing license of a patent P200700665 titled “Adenovirus with mutations in the area of endoplasmic retention of protein E3-19k and their use in the treatment of cancer” in connection with a sublicense identified therein. The validity period of the license granted is unlimited with the only applicable limit being the patent’s own validity. The ICO License Agreement provides that the ICO is entitled to a royalty of low double digit percentage of the net value of the income from the concession of the identified sublicense and low double digit percentage on other lump sums received thereunder. VCN and its sublicensees have an obligation to use all diligent and commercially reasonable efforts for the exploitation of the patent, otherwise, ICO may proceed to recover the license. The ICO License Agreement terminates upon the expiration of the patent rights and is subject to early termination by either party in the event of a breach by the other party of its obligations thereunder.

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IDIBELL/ICO License Agreement

On March 4, 2016, VCN entered into a License Agreement (the “IDIBELL/ICO License Agreement”) with IDIBELL and the ICO, for the exclusive license of the right to use a family of patents whose priority application is European patent application EP 14 38 2162.7 titled “Adenovirus comprising an albumin-binding moiety”. The License Agreement provides that IDIBELL and ICO, as licensors, are entitled to share a low single digit percentage royalty on the annual Net Sales (as defined in the IDIBELL/ICO License Agreement) collected by VCN from the utilization of products derived from the licensed technology and a royalty on sublicensing income received from the licensed technology at a rate of: low double digit percentage during the first 3 years following the effective date of the agreement, mid - single digit percentage during the term of 3 to 7 years following the effective date and low single digit percentage thereafter. The IDIBELL/ICO License Agreement also provides for certain fixed payments, including a payment 25 days following the date of concession of the licensed patent in a minimum of three European jurisdictions and a payment 25 days following the date of concession of an American patent derived from the licensed patent. The IDIBELL/ICO License has an indefinite term subject to early termination (i) by mutual agreement of the parties; (ii) by licensor in the event of at least two successive breaches or three alternate breaches calculated annually of the obligation to pay any consideration; (iii) by VCN at its discretion due to certain patent infringements of rights protected by the patents or due to the absence of protection of the patent in any countries in the territory which is worldwide or (iv) in the event of a breach by the other party of its obligations thereunder which are not remedied within thirty (30) days. In addition, the licensors have the right to revoke the IDIBELL/ICO License Agreement if VCN during a continuous period of two years abandons its research or development activities of the licensed patent or activities aimed at exploitation of the resulting products, VCN has undertaken no marketing whatsoever during the term of the IDIBELL/ICO License Agreement or uses the patent licensed for purposes other those as set forth in the IDIBELL/ICO License Agreement.

Sant Joan De Déu Collaboration and License Agreement

On February 15, 2016, VCN entered into a Collaboration Agreement to Conduct a Clinical Trial and Grant an Operating License (the “Collaboration and License Agreement”) with the Sant Joan De Déu Hospital (the “Hospital”) and the Sant Joan De Déu Foundation (the “Foundation”, and together with the Hospital, the “Institution”) regarding the conduct of a clinical trial to evaluate the safety and activity of VCN-01 in patients with refractory retinoblastoma. The Collaboration and License Agreement provides that if the trial results are positive and VCN is interested in continuing with the development of VCN-01 for the treatment of retinoblastoma; (a) the parties undertake to apply their best efforts to negotiate and, where appropriate, sign an agreement to collaborate in the development and execution of the following phases of the development of VCN-01 for the treatment of retinoblastoma; (b) the Institution shall grant to VCN an exclusive, worldwide and indefinite license to use and exploit the trial results and their possible patents exclusively for the treatment of retinoblastoma; (c) VCN shall pay the Foundation five hundred thousand Euros (€500,000), subject to reduction for any public and/or private economic aid that third parties may grant to the Institution for the conduct of the trial and/or any advance payments made by VCN before the end of the trial; (d) VCN shall pay the Foundation three hundred twenty thousand Euros (€320,000) once following the trial results of a pivotal study, to be carried out by VCN, has been completed which allows it to obtain the marketing authorization of the product following from the results, which payment must be made within a maximum period of four (4) years from the date on which Institution has delivered the final report of the trial to VCN; and (e) the parties will use their best efforts to negotiate and, where appropriate, sign a product supply agreement in order that the Hospital can use VCN-01 for compassionate use in the treatment of retinoblastoma. The Collaboration and License Agreement continues in force and effect until all obligations arising from the trial have been fulfilled, subject to early termination for a material breach by a party of any of their contractual and/or legal obligations, or, in the case of any other type of breach, when the breaching party has been asked in writing to remedy the breach and the breach is not cured within thirty (30) days from the date on which the written request was sent. Per the terms of the clinical trial agreement, the determination by the study Monitoring Committee that the study had a positive outcome means we will receive an exclusive, worldwide technology license, and related patents from Hospital Sant Joan de Déu for the treatment of pediatric patients with advanced retinoblastoma and we will pay to Hospital Sant Joan de Déu the amount of three hundred twenty thousand Euros (€320,265), or approximately $334,000, upon receipt by us of the final clinical study report.

On November 1, 2023, VCN and the Hospital entered into an agreement for an exclusive worldwide option to negotiate an exclusive license of certain Sant Joan de Deu intellectual property rights related to the use of VCN-01 in combination with topoisomerase I inhibitor chemotherapies for the treatment of cancer. This option was extended for an additional 12-months by an amendment signed in October, 2024 and again by an amendment signed January 2026. The collaboration builds on growing data that suggests coadministration of VCN-01 with topoisomerase I inhibitors such as topotecan can enhance VCN-01 replication and antitumor activity in preclinical cancer models. Combination of VCN-01 with a topoisomerase I inhibitor is expected to provide a synergistic antitumor effect wherein a chemotherapy-mediated increase in tumor VCN-01 levels may enable greater degradation of the tumor stroma, significantly increasing chemotherapy access and tumor destruction.

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Washington University School of Medicine in St. Louis Clinical Trial Agreement

On August 7, 2019, we entered into a clinical trial agreement (the “CTA”) with Washington University School of Medicine in St. Louis (“Washington University”) to conduct a Phase 1b/2a single-center, randomized, double-blinded, placebo-controlled clinical trial designed to evaluate the safety, tolerability and pharmacokinetics of oral SYN-004 (ribaxamase) in up to 36 adult allogeneic hematopoietic cell transplant (HCT) recipients (the “Study”). Under the terms of the CTA, we will serve as the sponsor of the Study and supply SYN-004 (ribaxamase), as well as compensate Washington University for all research services to be provided in connection with the Study which is estimated to cost approximately $3,200,000. Dr. Erik R. Dubberke, Professor of Medicine and Clinical Director, Transplant Infectious Diseases at Washington University will serve as the principal investigator of the trial in collaboration with his Washington University colleague Dr. Mark A. Schroeder, Associate Professor of Medicine, Division of Oncology, Bone Marrow Transplantation and Leukemia.

The CTA continues in effect until completion of all obligations under the CTA. Either party may terminate the CTA prior to completion of its obligations (i) if authorization of the study is withdrawn by the FDA; (ii) if the emergence of any adverse reaction or side effect with SYN-004 (ribaxamase) administered in the Study is of such magnitude or incidence in the opinion of either party to support termination; or (iii) upon a breach of the terms of the CTA if the breaching party fails to cure the breach within 30 days after receipt of notice. We have the right to terminate the CTA (i) effective immediately if Washington University fails to perform the study in accordance with the terms of the protocol, the CTA or applicable laws or regulations or if Washington University or the principal investigator become debarred or (ii) upon 14 days written notice and Washington University has the right to terminate the CTA upon 14 days notice if the principal investigator becomes unable to perform or complete the Study and the parties have not, prior to the expiration of such fourteen (14) day period, agreed to an alternative principal investigator. Based upon our current available funding and our focus on our clinical development of VCN-01 we do not anticipate that enrollment for the third cohort will commence unless we obtain grant funding, or find a licensee or partner for the SYN-004 development program.

Rasayana License Agreement

On February 17, 2026, we entered into the Rasayana License Agreement with Rasayana, whereby we granted Rasayana an exclusive worldwide license with the right to grant sublicenses to research, develop, manufacture and commercialize any Product (as such term is defined in the Rasayana License Agreement), which includes SYN-020, comprising, containing, or covered by the Licensed IP (as such term is defined in the Rasayana License Agreement) and/or devised, developed, or produced using the Licensed IP. Under the terms and conditions of the Rasayana License Agreement, Rasayana has agreed to use commercially reasonable efforts to meet certain specified development milestones with respect to the Products. Additionally, pursuant to the terms of the Rasayana License Agreement, Rasayana will assume all responsibility and costs for the development and commercialization of the Products. Accordingly, going forward, we do not expect to continue to conduct research and development activities, including conducting further clinical studies, with respect to SYN-020, and do not expect to incur material expenditures in connection therewith.

As consideration for the license, on February 17, 2026, we received an upfront payment of $300,000 from Rasayana. In addition, we are entitled to receive from Rasayana development milestone payments of up to an aggregate of $16.0 million and sales milestone payments of up to an aggregate of $22.0 million upon achievement of certain development and net sales milestones with respect to Products. In addition, during the Royalty Term (as such term is defined in the Rasayana License Agreement), we are entitled to receive tiered royalties ranging from low to mid single digits on net sales of a Product. We will also be entitled to receive a certain percentage of any Sublicense Revenue (as such term is defined in the Rasayana License Agreement) received by Rasayana or its affiliates.

The term of the Rasayana License Agreement commenced on February 17, 2026 and continues on a country-by-country basis until the expiration of the Royalty Term. If either we or Rasayana materially breaches any material obligation under the Rasayana License Agreement and does not cure such breach, the non-breaching party may terminate the Rasayana License Agreement in its entirety; provided that if such breach is capable of being cured but cannot be cured within such sixty (60) day period and the breaching party initiates actions to cure such breach within such period and thereafter diligently pursues such actions, the breaching party shall have one additional period of sixty (60) days to cure such breach. Either party may also terminate the Rasayana License Agreement, upon written notice, if the other party has an Insolvency Event (as such term is defined in the Agreement). Rasayana has the right to terminate the Rasayana License Agreement for any or no reason upon ninety (90) days’ written notice to us, including but not limited to instances in which the outcome of a clinical trial is adverse and/or unsatisfactory to Rasayana (in its reasonable discretion). If Rasayana suspends all material development efforts with respect to all Products for a period of one hundred and eighty (180) days, or fails to use commercially reasonable efforts to achieve any of the development milestones by the applicable deadline), then the Company may terminate the Rasayana License Agreement upon ninety (90) days prior written notice to Rasayana, unless Rasayana resumes material development

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efforts within such period. Upon a termination, the rights granted under the Rasayana License Agreement terminate and revert irrevocably to the Company.

Manufacturing

VCN-01 (zabilugene almadenorepvec), VCN-11 and VCN - 12

Our OV platform viruses (e.g. VCN-01, VCN-11, and VCN - 12) are biologics that can be readily synthesized by processes that we have developed in collaboration with Contract and Development Manufacturing Organizations (CDMOs) such as Thermo Fisher, BioReliance, Recipharm Advanced Bio, Fujifilm Diosynth and others. We do not own or operate manufacturing facilities for the production of our product candidates, but we do produce and test viruses and virus processes at our facilities in Spain. Our cell and virus seed stocks and master/working cell banks are used for current and future production. Our cells for manufacturing are approved by and licensed from US regulatory authorities. Clinical and commercial supplies will be manufactured in facilities and by processes that comply with the FDA and other regulatory agency requirements. We plan to rely on third parties to manufacture commercial quantities of products that we successfully develop through regulatory approval. We have contracted with CDMOs to provide what we believe are adequate clinical supplies for our planned clinical trials.

Our upstream and downstream processes for producing oncolytic viruses are well understood in the industry and use industry standard cell factories and single use bioreactors for manufacturing. All downstream purifications employ single-use columns and filters, and release testing is performed by third-party vendors using qualified or validated assays. Critical quality attributes and other product testing specifications for our clinical supplies are agreed to with regulatory authorities prior to release and use.

We previously encountered some delays in manufacturing due to the impact of COVID-19 on the supply chain. The potential impact of similar supply chain issues from a future pandemic or other disruption to global trade and supply chains, if any, on our on-going and future clinical trials is currently unknown.

SYN-004 (ribaxamase) and SYN-020

Our product candidates SYN-004 and SYN-020 are biologics that can be readily synthesized by processes that we have developed; however, the manufacturing for our product candidates, including SYN-004 and SYN-020 may require long lead times and was previously subject to COVID-19 related global supply chain interruptions. We do not own or operate manufacturing facilities for the production of these product candidates for preclinical and clinical activities. We rely on third-party contract manufacturers, and in most cases only one third-party, to manufacture critical raw materials, drug substance and final drug product for our research, preclinical development and clinical trial activities. Commercial quantities of any drugs we seek to develop will have to be manufactured in facilities and by processes that comply with the FDA and other regulations, and we plan to rely on third parties to manufacture commercial quantities of products we successfully develop through FDA approval.

Pursuant to the Rasayana License Agreement, commencing February 17, 2026, Rasayana is now responsible for the manufacture of SYN-020, including the sourcing, receipt, storage and processing of raw materials; the manufacture, processing, testing, packing, re-packing, holding and shipment of in-process or finished product; and all costs associated with the foregoing.

Research and Development

During the years ended December 31, 2025 and 2024, we incurred approximately $8.6 million and $12.0 million, respectively, in research and development expenses.

Government Regulation

In the U.S., the formulation, manufacturing, packaging, storing, labeling, promotion, advertising, distribution and sale of our products are subject to regulation by various governmental agencies, including primarily the FDA. Our proposed activities may also be regulated by various agencies of the states, localities and foreign countries in which our proposed products may be manufactured, distributed and sold. The FDA, in particular, regulates the formulation, manufacture and labeling of prescription drugs, such as those that we intend to distribute. FDA regulations require us and our suppliers to meet relevant cGMP regulations for the preparation, packing, labeling, and storage of all drugs.

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Any products manufactured or distributed by us pursuant to FDA approvals are subject to pervasive and continuing FDA regulation, including record-keeping requirements, reporting of adverse experiences, submitting periodic reports, drug sampling and distribution requirements, manufacturing or labeling changes, record-keeping requirements, and compliance with FDA promotion and advertising requirements. Drug manufacturers and their subcontractors are required to register their facilities with the FDA and state agencies, and are subject to periodic unannounced inspections for GMP compliance, imposing procedural and documentation requirements upon us and third-party manufacturers. Failure to comply with these regulations could result, among other things, in suspension of regulatory approval, recalls, suspension of production or injunctions, seizures, or civil or criminal sanctions. We cannot be certain that we or our present or future subcontractors will be able to comply with these regulations.

The FDA regulates prescription drug labeling and promotion activities in the United States. The FDA actively enforces regulations prohibiting the marketing of products for unapproved uses. The FDA permits the promotion of drugs for unapproved uses in certain circumstances, subject to stringent requirements. We and our product candidates are subject to a variety of state laws and regulations which may hinder our ability to market our products. Whether or not FDA approval has been obtained, approval by foreign regulatory authorities must be obtained prior to commencing clinical trials, and sales and marketing efforts in those countries. These approval procedures vary in complexity from country to country, and the processes may be longer or shorter than that required for FDA approval. We expect to incur significant costs to comply with these laws and regulations now or in the future.

The FDA, comparable foreign regulators and state and local pharmaceutical regulators impose substantial requirements upon clinical development, manufacture and marketing of pharmaceutical products. These and other entities regulate research and development and the testing, manufacture, quality control, safety, effectiveness, labeling, storage, record keeping, approval, advertising, and promotion of our products. The drug approval process required by the FDA under the Food, Drug, and Cosmetic Act (the “FDCA”) and Public Health Service Act (the “PHS Act”) (for biologics) generally involves:

●preclinical laboratory and animal tests;

●submission of an IND, prior to commencing human clinical trials;

●adequate and well-controlled human clinical trials to establish safety and efficacy for intended use;

●submission to the FDA of a new drug application (“NDA”) or BLA; and

●FDA review and approval of an NDA or BLA.

The testing and approval process requires substantial time, effort, and financial resources, and we cannot be certain that any approval will be granted on a timely basis, if at all. OVs such as VCN-01 are genetically modified organisms and their import and use are subject to additional review and approval by dedicated agencies in some countries where we propose to run clinical trials, including Spain and other European countries.

Preclinical tests include laboratory evaluation of the product candidate, its chemistry, formulation and stability, and animal studies to assess potential safety and efficacy. Certain preclinical tests must be conducted in compliance with good laboratory practice regulations. Violations of these regulations can, in some cases, lead to invalidation of the studies, requiring them to be replicated. In some cases, long-term preclinical studies are conducted concurrently with clinical studies.

We will submit the preclinical test results, together with manufacturing information and analytical data, to the FDA as part of an IND, which must become effective before we begin human clinical trials. The IND automatically becomes effective 30 days after filing, unless the FDA raises questions about conduct of the trials outlined in the IND and imposes a clinical hold, in which case, the IND sponsor and FDA must resolve the matters before clinical trials can begin. It is possible that our submissions may not result in FDA authorization to commence clinical trials. The timing and requirements of IND review may differ from the FDA in other countries, potentially delaying study initiation at sites in those countries.

Clinical trials must be supervised by qualified investigators in accordance with current good clinical practice (“cGCP”) regulations, which include informed consent requirements. Each study must be approved and monitored by the appropriate Institutional Review Boards (“IRBs”) or Institutional Ethics Committees (“IECs”) which are periodically informed of the study’s progress, adverse events and changes in research. OVs such as VCN-01 are genetically modified organisms and their use is also subject to review and approval by the Institutional Biosafety Committee (“IBC”) at each clinical trial site. Annual updates are submitted to the FDA and comparable foreign regulators (if required) with more frequent reporting if certain serious adverse events occur.

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Human clinical trials of drug candidates typically have three sequential phases that may overlap:

Phase 1: The drug is initially tested in healthy human subjects or patients for safety, dosage tolerance, absorption, metabolism, distribution, and excretion.

Phase 2: The drug is studied in a limited patient population to identify possible adverse effects and safety risks, determine efficacy for specific diseases and establish dosage tolerance and optimal dosage.

Phase 3: When Phase 2 evaluations demonstrate that a dosage range is effective with an acceptable safety profile, Phase 3 trials to further evaluate dosage, clinical efficacy and safety, are undertaken in an expanded patient population, often at geographically dispersed sites.

We cannot be certain that we will successfully complete Phase 1, Phase 2, or Phase 3 testing of our product candidates within any specific time period, if at all. Furthermore, the FDA or comparable foreign regulator, an IRB/IEC or the IND sponsor may suspend clinical trials at any time on various grounds, including a finding that subjects or patients are exposed to unacceptable health risk. Under the Pediatric Research Equity Act, we also must prepare, within 60 days of an End of Phase 2 meeting, a pediatric study plan or request for waiver or deferral of pediatric studies in the indication under development. Concurrent with these trials and studies, we also develop chemistry and physical characteristics data and finalize a manufacturing process in accordance with cGMP requirements. The manufacturing process must conform to consistency and quality standards, and we must develop methods for testing the quality, purity, and potency of the final products. Appropriate packaging is selected and tested, and chemistry stability studies are conducted to demonstrate that the product does not undergo unacceptable deterioration over its shelf-life. Results of the foregoing are submitted to the FDA as part of an NDA (or BLA in case of biologic products) for marketing and commercial shipment approval. The FDA reviews each NDA or BLA submitted and may request additional information. A 60-day period after the sponsor’s submission of an NDA or BLA is used by the FDA to determine whether the application is sufficiently complete to permit substantive review, in which case the application is accepted for filing. The timing and requirements of NDA or BLA review may differ from the FDA in other countries,

Once the FDA accepts the NDA or BLA for filing, it begins its in-depth review. The FDA has substantial discretion in the approval process and may disagree with our interpretation of the data submitted or identify new concerns. The process may be significantly extended by requests for new information or clarification of information already submitted. As part of this review, the FDA may refer the application to an advisory committee, typically a panel of clinicians. Manufacturing establishments are often inspected prior to NDA or BLA approval to assure compliance with GMPs and with manufacturing commitments made in the application.

Submission of an NDA or BLA with clinical data requires payment of a substantial fee. The FDA assigns a goal for review and decision on the application, in which the FDA may approve the NDA or BLA or issue a complete response letter outlining information needed to support approval, including a potential need for additional clinical data. Even if these data are submitted, the FDA may ultimately decide the NDA or BLA does not satisfy approval criteria. If the FDA approves the NDA or BLA, the product becomes available for marketing. Product approval may be withdrawn if regulatory compliance is not maintained or safety problems occur. The FDA may require post-marketing studies, also known as Phase 4 studies, as a condition of approval, and Risk Evaluation and Mitigation Strategies (REMS) requires surveillance programs to monitor approved products that have been commercialized. The agency has the power to require changes in labeling or prohibit further marketing based on the results of post-marketing surveillance.

Satisfaction of these and other regulatory requirements typically takes several years, and the actual time required may vary substantially based upon the type, complexity and novelty of the product. Government regulation may delay or prevent marketing of potential products for a considerable period of time and impose costly procedures on our activities. We cannot be certain that the FDA or other regulatory agencies will approve any of our product candidates on a timely basis, if at all. Success in preclinical or early-stage clinical trials does not assure success in later-stage clinical trials. Data obtained from preclinical and clinical activities are not always conclusive and may be susceptible to varying interpretations that could delay, limit or prevent regulatory approval. Even if a product receives regulatory approval, the approval may be significantly limited to specific indications or uses.

Even after regulatory approval is obtained, later discovery of previously unknown problems with a product may result in restrictions on the product or even complete withdrawal of the product from the market. Significant delays in obtaining, or failures to obtain regulatory approvals would have a material adverse effect on our business.

The FDA or comparable foreign regulatory agency may change their policies, and additional government regulations may be enacted which could prevent or delay regulatory approval of our potential products. In 2025, in connection with the U.S. presidential transition and change in administration, there were significant changes in leadership at the FDA as well as FDA priorities. Increased attention to

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the containment of health care costs worldwide could result in new government regulations materially adverse to our business. Public perception and sentiment regarding genetically modified organisms and/or viral therapies (including vaccines) can be highly variable and may impact legislation regarding the potential suitability of our products. We cannot predict the likelihood, nature or extent of adverse governmental regulation that might arise from future legislative or administrative action, either in the U.S. or abroad.

Orphan Drug Act

Under the Orphan Drug Act, as amended by the FDA Reauthorization Act of 2017, the FDA may grant orphan designation to a drug or biologic intended to treat a rare disease or condition, which is generally a disease or condition that affects fewer than 200,000 individuals in the United States, or more than 200,000 individuals in the United States and for which there is no reasonable expectation that the cost of developing and making available in the United States a drug for this type of disease or condition will be recovered from sales in the United States for that drug. Orphan Drug designation must be requested before submitting an NDA or BLA. After the FDA grants orphan drug designation, the name of the sponsor, identity of the drug or biologic and its potential orphan use are disclosed publicly by the FDA. The orphan drug designation does not shorten the duration of the regulatory review or approval process, but does provide certain advantages, such as a waiver of Prescription Drug User Fee Act (“PDUFA”) fees, enhanced access to FDA staff and potential waiver of pediatric research requirements.

If a product that has orphan drug designation subsequently receives the first FDA approval for the disease for which it has such designation, the product is entitled to orphan product exclusivity, which means that the FDA may not approve any other applications, including a full NDA, to market the same drug or biologic for the same indication for seven years, except in limited circumstances, such as a showing of clinical superiority to the product with orphan drug exclusivity. Orphan drug exclusivity does not prevent FDA from approving a different drug or biologic for the same disease or condition, or the same drug or biologic for a different disease or condition. Among the other benefits of orphan drug designation are tax credits for certain research and a waiver of the application user fee. A designated orphan drug may not receive orphan drug exclusivity if it is approved for a use that is broader than the indication for which it received orphan designation. In addition, exclusive marketing rights in the United States may be lost if the FDA later determines that the request for designation was materially defective or if the manufacturer is unable to assure sufficient quantities of the product to meet the needs of patients with the rare disease or condition.

In February 2022, the FDA granted orphan drug designation to VCN - 01 for the treatment of retinoblastoma, and in June 2023, the FDA granted Orphan Drug designation to VCN - 01 for the treatment of pancreatic cancer.

Accelerated Approval

There are a variety of pathways under which applicants may seek expedited approval from the FDA, including Fast Track, breakthrough therapy, priority review and accelerated approval. Fast Track is a process designed to facilitate the development and expedite the review of investigational drugs to treat serious conditions and that fill an unmet medical need. Drugs that receive Fast Track designation may be eligible for more frequent communications and meetings with the FDA to discuss the drug’s development plan, including the design of the proposed clinical trials, use of biomarkers and the extent of data needed to support approval. Drugs with Fast Track designation may also qualify for accelerated approval and priority review of new drug applications if relevant criteria are met. However, Fast Track designation may be withdrawn by the FDA if the FDA believes that the designation is no longer supported by data emerging in the clinical trial process.

The FDA may designate a product for priority review if it is a product that treats a serious condition and, if approved, would provide a significant improvement in safety or effectiveness. The FDA determines, on a case-by-case basis, whether the proposed product represents a significant improvement when compared with other available therapies. Significant improvement may be illustrated by evidence of increased effectiveness in the treatment of a condition, elimination or substantial reduction of a treatment-limiting product reaction, documented enhancement of patient compliance that may lead to improvement in serious outcomes, and evidence of safety and effectiveness in a new subpopulation. Under priority review, the FDA reviews an application in six months rather than ten months after it is accepted for filing.

The FDA accelerated approval program provides for early approval of drugs based on a drug on a clinical trial(s) showing that the drug meets a surrogate or an intermediate clinical endpoint rather than a clinical benefit endpoint. Accelerated approval is possible for drugs for serious conditions that fill an unmet medical need.

A surrogate endpoint used for accelerated approval is a marker, such as a laboratory measurement, that is thought to predict clinical benefit, but is not itself a measure of clinical benefit. Likewise, an intermediate clinical endpoint is a measure of a therapeutic effect that

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is considered reasonably likely to predict the clinical benefit of a drug, such as an effect on irreversible morbidity and mortality. Because it sometimes can take many years for a drug trial to show a clinical benefit, the use of a surrogate endpoint or an intermediate clinical endpoint can significantly shorten the time required to complete clinical trials and obtain FDA approval.

If a drug receives an accelerated approval, the company that sponsored the application must conduct a post-approval trial to confirm the anticipated clinical benefit. These trials are known as Phase 4 or post-approval confirmatory trials. If the confirmatory trial shows that the drug actually provides a clinical benefit, then the FDA grants traditional approval for the drug. Failure to conduct required post-approval studies, or confirm a clinical benefit during post-marketing studies, will allow the FDA to withdraw the drug from the market on an expedited basis. All promotional materials for drug candidates approved under accelerated regulations are subject to prior review by the FDA. If the confirmatory trial does not show that the drug provides clinical benefit, FDA has regulatory procedures in place that could lead to removing the drug from the market.

Rare Pediatric Disease Vouchers

The Rare Pediatric Disease Voucher Program is intended to encourage development of new drug and biological products for prevention and treatment of certain rare pediatric diseases. Although there are existing incentive programs to encourage the development and study of drugs and biologics for rare diseases, pediatric populations, and unmet medical needs, this program provides an additional incentive for the development of drugs and biologics for rare pediatric diseases, which may be used alone or in combination with other incentive programs. A rare pediatric disease is defined as a disease that is a serious or life-threatening disease in which the serious or life-threatening manifestations primarily affect individuals aged from birth to 18 years, including age groups often called neonates, infants, children, and adolescents; and is a rare disease or condition as defined in the FDCA, which includes diseases and conditions that affect fewer than 200,000 persons in the United States and diseases and conditions that affect a larger number of persons and for which there is no reasonable expectation that the costs of developing and making available the product in the United States can be recovered from sales of the product in the United States.

The sponsor of an application for a drug product that obtains rare pediatric disease designation may be eligible for a voucher that can be used or sold to obtain a priority review for a subsequent application submitted under section 505(b)(1) of the FDCA or section 351 of the PHS Act. A rare pediatric disease drug product must meet certain eligibility requirements for a priority voucher at the time the sponsor seeks approval. In February 2026, legislative authorization for the rare pediatric disease priority review voucher (PRV) program extended the program to enable award of PRVs for approved products until September 30, 2029.

If a BLA for VCN-01 (zabilugene almadenorepvec) for the treatment of retinoblastoma is approved by the FDA before the required deadline, we may be eligible to receive a priority review voucher.

Pediatric Information and Pediatric Exclusivity

Under the Pediatric Research Equity Act (“PREA”), certain NDAs and BLAs and certain supplements to an NDA or BLA must contain data to assess the safety and efficacy of the drug for the claimed indications in all relevant pediatric subpopulations and to support dosing and administration for each pediatric subpopulation for which the product is safe and effective. The FDA may grant deferrals for submission of pediatric data or full or partial waivers. The Food and Drug Administration Safety and Innovation Act (“FDASIA”), amended the FDCA to require that a sponsor who is planning to submit a marketing application for a drug that includes a new active ingredient, new indication, new dosage form, new dosing regimen or new route of administration submit an initial Pediatric Study Plan (“PSP”) within 60 days of an end-of-Phase 2 meeting or, if there is no such meeting, as early as practicable before the initiation of the Phase 3 or Phase 2/3 study. The initial PSP must include an outline of the pediatric study or studies that the sponsor plans to conduct, including study objectives and design, age groups, relevant endpoints and statistical approach, or a justification for not including such detailed information, and any request for a deferral of pediatric assessments or a full or partial waiver of the requirement to provide data from pediatric studies along with supporting information. The FDA and the sponsor must reach an agreement on the PSP. A sponsor can submit amendments to an agreed-upon initial PSP at any time if changes to the pediatric plan need to be considered based on data collected from preclinical studies, early phase clinical trials and/or other clinical development programs.

The Best Pharmaceuticals for Children Act, (“BPCA”), provides NDA holders a six-month extension of any exclusivity — patent or non-patent — for a drug if certain conditions are met. Pediatric exclusivity, if granted, adds six months to existing exclusivity periods and patent terms. Conditions for exclusivity include the FDA’s determination that information relating to the use of a new drug in the pediatric population may produce health benefits in that population, the FDA’s written request for pediatric studies, and the applicant’s agreeing to perform, and reporting on, the requested studies within the statutory timeframe. Applications under the BPCA are treated as priority applications, with all of the benefits that designation confers.

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Drug Development in the European Union

Orphan Drug Designation is also available in Europe from the European Medicines Agency (EMA) and provides for 10 years of market exclusivity if granted. The requirements, costs and timing for obtaining and maintaining EMA Orphan Drug Designation differ from the FDA.

In May 2011, the “COMP” from the EMA recommended granting Orphan Medicinal Product Designation to VCN-01 for the treatment of pancreatic cancer and in June 2011, the EC confirmed the designation under Regulation (“EC”) No 141/2000 of the European Parliament and of the Council.

In October 2024, the EC adopted EMA recommendation to grant Orphan Medicinal Product Designation to VCN-01 for the treatment of retinoblastoma. The European Commission confirmed the designation under Regulation No 141/2000 of the European Parliament and of the Council.

In the European Union, our future products may also be subject to extensive regulatory requirements. Similar to the United States, the marketing of medicinal products is subject to the granting of marketing authorizations by regulatory agencies. Also, as in the United States, the various phases of pre-clinical and clinical research in the European Union are subject to significant regulatory controls.

In the European Union, approval of new medicinal products can be obtained through one of three processes: the mutual recognition procedure, the centralized procedure and the decentralized procedure. We intend to determine which process we will follow, if any, in the future.

Mutual Recognition Procedure: An applicant submits an application in one European Union member state, known as the reference member state. Once the reference member state has granted the marketing authorization, the applicant may choose to submit applications in other concerned member states, requesting them to mutually recognize the marketing authorizations already granted. Under this mutual recognition process, authorities in other concerned member states have 55 days to raise objections, which must then be resolved by discussion among the concerned member states, the reference member state and the applicant within 90 days of the commencement of the mutual recognition procedure. If any disagreement remains, all considerations by authorities in the concerned member states are suspended and the disagreement is resolved through an arbitration process. The mutual recognition procedure results in separate national marketing authorizations in the reference member state.

Centralized Procedure: This procedure is currently mandatory for products developed by means of a biotechnological process and optional for new active substances and other “innovative medicinal products with novel characteristics.” Under this procedure, an application is submitted to the European Agency for the Evaluation of Medical Products. Two European Union member states are appointed to conduct an initial evaluation of each application. These countries each prepare an assessment report that is then used as the basis of a scientific opinion of the Committee on Proprietary Medical Products. If this opinion is favorable, it is sent to the European Commission, which drafts a decision. After consulting with the member states, the European Commission adopts a decision and grants a marketing authorization, which is valid throughout the European Union and confers the same rights and obligations in each of the member states as a marketing authorization granted by that member state.

Decentralized Procedure: The most recently introduced of the three processes for obtaining approval of new medicinal processes in the European Union, the decentralized procedure is similar to the mutual recognition procedure described above, but with differences in the timing that key documents are provided to concerned member states by the reference member state, the overall timing of the procedure and the possibility of, among other things, “clock stops” during the procedure.

Post-Marketing Requirements

Following approval of a new product, a pharmaceutical company and the approved product are subject to continuing regulation by the FDA and other regulatory authorities, including, among other things, monitoring and recordkeeping activities, reporting to applicable regulatory authorities of adverse experiences with the product, providing the regulatory authorities with updated safety and efficacy information, product sampling and distribution requirements, and complying with promotion and advertising requirements, which include, among others, standards for direct-to-consumer advertising, restrictions on promoting drugs for uses or in patient populations not described in the drug’s approved labeling (known as “off-label use”), and limitations on industry-sponsored scientific and educational activities. Although physicians may prescribe legally available drugs for off-label uses, drugs may be marketed only for the approved indications and in accordance with the provisions of the approved labeling. Modifications or enhancements to the products or labeling or changes of site of manufacture are often subject to the approval of the FDA and other regulators, which may or may not be

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received or may result in a lengthy review process. The FDA regulations require the products be manufactured in specific approved facilities and in accordance with current good manufacturing practices, and NDA holders must list their products and register their manufacturing establishments with the FDA. These regulations also impose certain organizational, procedural and documentation requirements with respect to manufacturing and quality assurance activities. Drug manufacturers and other entities involved in the manufacture and distribution of approved drugs are subject to periodic unannounced inspections by the FDA and certain state agencies for compliance with current good manufacturing practice and other laws. NDA holders using contract manufacturers, laboratories or packagers are responsible for the selection and monitoring of qualified firms. These firms are subject to inspections by the FDA at any time, and the discovery of violative conditions could result in enforcement actions that interrupt the operation of any such facilities or the ability to distribute products manufactured, processed or tested by them.

Pricing and Reimbursement

In both the U.S. and foreign markets, the ability to successfully commercialize product candidates that have obtained regulatory approval by the FDA or other governmental authorities depends in significant part on the availability of adequate financial coverage and reimbursement from third party payors, including, in the U.S., governmental payors such as Medicare and Medicaid, managed care organizations, and private commercial health insurers. There is significant uncertainty related to the insurance coverage and reimbursement of newly approved products. In the United States, the principal decisions about reimbursement for new products are typically made by the Centers for Medicare & Medicaid Services (“CMS”). Private payors tend to follow CMS to a substantial degree. However, no uniform or consistent policy of coverage and reimbursement for drug products exists among third-party payors. Therefore, coverage and reimbursement for drug products can differ significantly from payor to payor as well as from state to state. Consequently, the coverage determination process is often a time-consuming and costly process that must be played out across many jurisdictions and different entities. Further, a payor’s decision to provide coverage for a drug product does not imply that an adequate reimbursement rate will be approved.

In addition, direct or indirect governmental price regulation may affect the prices that we may charge for product candidates. For example, in the United States and some foreign jurisdictions, the prices of pharmaceutical products are subject to direct price controls (by law) and to drug reimbursement programs with varying price control mechanisms. There have been, and we expect there will continue to be, legislative and regulatory proposals to change the healthcare system in ways that could significantly affect the pharmaceutical industry, including the Patient Protection and Affordable Care Act of 2010 and the Inflation Reduction Act of 2022. We anticipate that in the U.S., Congress, state legislatures, and private sector entities will continue to consider and may adopt healthcare policies intended to curb rising healthcare costs.

Other Healthcare Laws and Compliance Requirements

In the United States, the research, manufacturing, distribution, sale and promotion of drug products and medical devices are potentially subject to regulation by various federal, state and local authorities in addition to the FDA, including the U.S. Department of Justice, state Attorneys General, and other state and local government agencies. The federal Anti-Kickback Statute prohibits any person, including a prescription drug manufacturer (or a party acting on its behalf), from knowingly and willfully soliciting, receiving, offering or providing remuneration, directly or indirectly, to induce or reward either the referral of an individual, or the furnishing, recommending or arranging for a good or service, for which payment may be made under a federal healthcare program such as the Medicare and Medicaid programs. The federal False Claims Act (“FCA”) imposes liability on any person or entity that, among other things, knowingly presents or causes to be presented, a false or fraudulent claim for payment by a federal healthcare program. The qui tam provisions of the FCA allow a private individual to bring civil actions on behalf of the federal government alleging that the defendant has submitted a false claim to the federal government, and to share in any monetary recovery. In addition, various states have enacted anti-kickback statues and false claims laws analogous to the FCA The Federal Physician Payments Sunshine Act within the Affordable Care Act, or the ACA, and its implementing regulations, require that certain manufacturers of drugs, devices, biological and medical supplies for which payment is available under Medicare, Medicaid or the Children’s Health Insurance Program (with certain exceptions) to report on an annual basis information related to certain payments or other transfers of value made or distributed to physicians and teaching hospitals, or to entities or individuals at the request of, or designated on behalf of, the physicians and teaching hospitals and certain ownership and investment interests held by physicians and their immediate family members, with the information made publicly available on a searchable website Also, the Health Insurance Portability and Accountability Act of 1996 (HIPAA) ), as amended by the Health Information Technology for Economic and Clinical Health Act (HITECH) and its implementing regulations, imposes certain requirements relating to the privacy, security and transmission of individually identifiable health information. Among other things, HITECH makes HIPAA’s privacy and security standards directly applicable to “business associates” — independent contractors or agents of covered entities that receive or obtain protected health information in connection with providing a service on behalf of a covered entity. HITECH also created four new tiers of civil monetary penalties, amended HIPAA to make civil and criminal penalties

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directly applicable to business associates and possibly other persons, and gave state attorneys general new authority to file civil actions for damages or injunctions in federal courts to enforce the federal HIPAA laws and seek attorneys’ fees and costs associated with pursuing federal civil actions.

Because of the breadth of these and other laws and the narrowness of available statutory and regulatory exemptions, it is possible that some of our business activities could be subject to challenge under one or more of such laws. If our operations are found to be in violation of any of the federal and state laws described above or any other governmental regulations that apply to us, we may be subject to penalties, including criminal and significant civil monetary penalties, damages, fines, imprisonment, exclusion from participation in government healthcare programs, injunctions, recall or seizure of products, total or partial suspension of production, denial or withdrawal of pre-marketing product approvals, private “qui tam” actions brought by individual whistleblowers in the name of the government or refusal to allow us to enter into supply contracts, including government contracts, and the curtailment or restructuring of our operations, any of which could adversely affect our ability to operate our business and our results of operations.

In order to market any product outside of the United States, a company also must comply with numerous and varying regulatory requirements of other countries and jurisdictions regarding quality, safety and efficacy and governing, among other things, clinical trials, use of genetically modified organisms, marketing authorization, commercial sales and distribution of products. Whether or not it obtains FDA approval for a product, an applicant will need to obtain the necessary approvals by the comparable foreign regulatory authorities before it can initiate clinical trials or market products in those countries or jurisdictions. Specifically, the process governing approval of medicinal products in the EU generally follows the same lines as in the United States. It entails satisfactory completion of pharmaceutical development, nonclinical studies and adequate and well-controlled clinical trials to establish the safety and efficacy of the medicinal product for each proposed indication. It also requires the submission to relevant competent authorities for clinical trials authorization and to the EMA or to competent authorities in EU Member States for a marketing authorization application, or MAA, and granting of a marketing authorization by competent authorities in EU Member States or the European Commission before the product can be marketed and sold in the EU.

Data Privacy

Strict data privacy laws regulating the collection, transmission, storage and use of employee data and consumers’ personally-identifying information are evolving in the European Union, U.S. and other jurisdictions in which we operate. Outside of the United States, the laws, regulations and standards in many jurisdictions apply broadly to the collection, use, and other processing of personal information. For example, in the European Union, the collection and use of personal data are governed by the provisions of the General Data Protection Regulation (the “GDPR”). The GDPR, together with national legislation, regulations and guidelines of the European Union. member states governing the processing of personal data, impose strict obligations on entities subject to the GDPR, including but not limited to: (i) accountability and transparency requirements, and enhanced requirements for obtaining valid consent from data subjects; (ii) obligations to consider data protection as any new products or services are developed and to limit the amount of personal data processed; (iii) obligations to comply with the data protection rights of data subjects; and (iv) obligations to report certain personal data breaches to governmental authorities and individuals. Data protection authorities from the different E.U. member states and other European countries may enforce the GDPR and national data protection laws differently, and introduce additional national regulations and guidelines, which adds to the complexity of processing European personal data. Failure to comply with the requirements of the GDPR and the related national data protection laws may result in significant monetary fines and other administrative penalties (the GDPR authorizes fines for certain violations of up to 4% of global annual revenue or €20 million, whichever is greater) as well as civil liability claims from individuals whose personal data was processed. Additionally, expenses associated with compliance could reduce our operating margins.

The GDPR also prohibits the transfer of personal data from the E.U. to countries outside of the E.U. unless made to a country deemed by the European Commission to provide adequate protection for personal data or accomplished by means of an approved data transfer mechanism (e.g., standard contractual clauses). Data protection authority guidance and enforcement actions that restrict companies’ ability to transfer data may increase risk relating to data transfers or make it more difficult or impossible to transfer E.U. personal data to the U.S.

Environmental, Health, and Safety Regulation

We are subject to numerous federal, state and local environmental, health and safety (“EHS”), laws and regulations relating to, among other matters, safe working conditions, product stewardship, environmental protection, and handling or disposition of products, including those governing the generation, storage, handling, use, transportation, release, and disposal of hazardous or potentially hazardous materials, medical waste, and infectious materials that may be handled by our research laboratories. Some of these laws and

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regulations also require us to obtain licenses or permits to conduct our operations. If we fail to comply with such laws or obtain and comply with the applicable permits, we could face substantial fines or possible revocation of our permits or limitations on our ability to conduct our operations. Certain of our development activities involve use of hazardous materials, and we believe we are in compliance with the applicable environmental laws, regulations, permits, and licenses. However, we cannot ensure EHS liabilities will not develop in the future. EHS laws and regulations are complex, change frequently and have tended to become more stringent over time. Although the costs to comply with applicable laws and regulations, have not been material, we cannot predict the impact on our business of new or amended laws or regulations or any changes in the way existing and future laws and regulations are interpreted or enforced, nor can we ensure we will be able to obtain or maintain any required licenses or permits.

Competitive Environment

The pharmaceutical and biotechnology industries are characterized by rapidly evolving technology and intense competition. Our competitors include major multi-national pharmaceutical companies and biotechnology companies developing both generic and proprietary therapies to treat serious diseases. Many of these companies are well-established and possess technical, human, research and development, financial, and sales and marketing resources significantly greater than ours. In addition, many of our potential competitors have formed strategic collaborations, partnerships and other types of joint ventures with larger, well established industry competitors that afford these companies potential research and development and commercialization advantages in the therapeutic areas we are currently pursuing.

Academic research centers, governmental agencies and other public and private research organizations are also conducting and financing research activities which may produce products directly competitive to those being developed by us. In addition, many of these competitors may be able to obtain patent protection, obtain FDA and other regulatory approvals and begin commercial sales of their products before us.

Our oncology product candidates compete with all other oncology products being developed by third parties for our target indications.

Only three OV products have been approved in different global markets. Amgen Inc.’s Imlygic® (T-VEC, OncoVEX) for melanoma (USA); Daiichi Sankyo Company, Limited‘s DELYTACT® for malignant glioma (Japan) and Shanghai Sunway Biotech Co., Ltd Oncorine® for patients with late-stage refractory nasopharyngeal cancer (China). A BLA resubmission by Replimune, Inc. for their OV RP1 (vusolimogene oderparepvec) in combination with nivolumab for patients with advanced melanoma has been accepted by the FDA with a Prescription Drug User Fee Act (PDUFA) action date of April 10, 2026. In June 2024, CG Oncology, Inc. announced that their Phase 3 OV cretostimogene grenadenorepvec was available in the U.S. for patients with BCG-unresponsive non-muscle invasive bladder cancer (“NMIBC”) who meet certain program eligibility criteria. On November 14, 2025, CG Oncology reported initiation of a rolling BLA submission to the FDA for cretostimogene monotherapy in high-risk (HR) BCG-unresponsive non-muscle invasive bladder cancer (NMIBC), with completion of the BLA submission in 2026.

More than 60 companies have publicly identified that they are pursuing clinical development of different forms of OV products. Adenoviruses are the most commonly used viruses in these programs, with modified adenoviruses under development by companies including AdCure Bio LLC, Calidi Biotherapeutics, Inc., Candel Therapeutics, Inc., CG Oncology, Inc., Elicera Therapeutics AB, EpicentRx, Inc., GeneMedicine, Co Ltd., Inc., Lokon Pharma AB, Memgen, Inc., NewGenPharm Incorporation, Oncolys BioPharma, Inc., Orca Therapeutics B.V., Akamis Bio Ltd (formerly PsiOxus Therapeutics Ltd), Shanghai Sunway Biotech Co., Ltd, Theolytics Ltd, TILT Biotherapeutics, Ltd., UroGen Pharma, and Valo Therapeutics Oy.

OV products have been or are being developed using other virus backbones, including: arenavirus (Hookipa Pharma, Inc.), Coxsackie virus (Viralytics Ltd., Oncorus Inc.); herpes simplex virus (Amgen, Inc., Candel Therapeutics, Inc., Daiichi Sankyo Company Ltd.,ImmVira Co. Ltd, Replimune, Inc., Takara Bio, Inc., Treovir LLC, Virogin Biotech, Inc. Wuhan Binhui Biotechnology Co., Ltd.); Maraba virus (Turnstone Biologics, Inc.); measles virus (Themis Biosciences GmbH, Vyriad, Inc.); myxoma virus (OncoMyx Therapeutics, Inc.); parvovirus (Oryx GmbH & Co. KG), reovirus (Oncolytics Biotech, Inc.); poliovirus (Istari Oncology, Inc.);Seneca Valley virus (Seneca Therapeutics Inc., Oncorus Inc.); vesicular stomatitis virus (Boehringer Ingelheim, Cytonus Therapeutics, Inc., Vyriad, Inc.); and vaccinia viruses (Genelux Corporation, Imugene Ltd, Joint Biosciences Ltd, KaliVir Immunotherapeutics LLC, SillaJen, Inc., Transgene SA, Turnstone Biologics, Corp.).

OV companies that have identified pancreatic cancer or PDAC as a proposed clinical indication include Akamis Bio Ltd, Boehringer Ingelheim GmbH, Candel Therapeutics, Inc., GeneMedicine, Co Ltd., Lokon Pharma AB, Memgen, Inc., NewGenPharm Incorporation, Oncolytics Biotech, Oryx GmbH & Co. KG, Takara Bio, Inc., TILT Biotherapeutics Ltd), V2ACT Therapeutics™ LLC (a Genelux

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Corporation joint venture), Virogin Biotech, Inc.,and Wuhan Binhui Biotechnology Co., Ltd. OV companies that have identified retinoblastoma as a potential target indication include Seneca Therapeutics Inc. and Shanghai Sunway Biotech Co., Ltd.

Theriva Biologics’ OV products are designed to be systemically, intratumorally or intravitreally injected; selectively replicate only in tumor cells versus normal host cells; have reduced liver tropism compared to wild type adenovirus type 5; and express an enzyme (PH20 hyaluronidase) that degrades the tumor stroma barrier. If confirmed in Phase 2 and later clinical trials, we believe these features significantly differentiate Theriva Biologics’ products from competing OVs and will enable our products to be co-administered with other therapeutic modalities such as chemotherapy and immuno - oncology products to improve cancer treatment outcomes.

Companies that currently sell or are developing proprietary products for the prevention and treatment of C. difficile infection include: Actelion Pharmaceutical Ltd., Artugen Therapeutics, Inc., Acurx Pharmaceuticals, Inc., Deinove, Pfizer Inc., Merck & Co. Inc., Merus B.V., Pfizer Inc., Rebiotix, Inc., Seres Therapeutics, Inc., Summit Therapeutics plc. and Vedanta Biosciences Inc. Companies that sell or are developing products for the treatment or prevention of acute graft - versus - host - disease (aGVHD) include: Amgen, Inc., Astellas Pharma, Janssen Biotech, Inc., Mallinckrodt plc, Mesoblast, Inc., Novartis International AG, Pfizer, Inc. Roche AG and Takeda Pharmaceutical Company Ltd.

Not only do our product candidates compete with other product candidates being developed for similar or the same indications, we also compete for employees, clinical trial sites, and clinical trial participants.

Corporate History

Our predecessor, Sheffield Pharmaceuticals, Inc., was incorporated in 1986, and in 2006 engaged in a reverse merger with Pipex Therapeutics, Inc., a publicly-traded Delaware corporation formed in 2001. After the reverse merger, we changed our name to Pipex Pharmaceuticals, Inc., and in October 2008 we changed our name to Adeona Pharmaceuticals, Inc. On October 15, 2009, we engaged in a merger with a wholly owned subsidiary for the purpose of reincorporating in the State of Nevada. On February 15, 2012, we changed our name to Synthetic Biologics, Inc. On August 10, 2018, we effected a one for thirty-five reverse stock split of our authorized, issued and outstanding Common Stock. On July 15, 2022, we effected a one for ten reverse stock split of our authorized, issued and outstanding Common Stock. On October 12, 2022, we changed our name to Theriva Biologics, Inc. Effective November 15, 2022, as part of our corporate rebranding, our subsidiary VCN changed its name to Theriva Biologics S.L. without other changes to its corporate structure. On August 26, 2024, we effected a one for twenty-five reverse stock split of our authorized, issued and outstanding Common Stock.

Human Capital

We believe that our success depends upon our ability to attract, develop and retain key personnel. As of March 12, 2026, we employed 16 individuals, all but one of whom are full-time employees. Ten (10) were part of VCN’s research and clinical development team located in Spain, Two (2) are part of VCN’s management team located in Spain and Four (4) (including the CEO) are part of our corporate development, financial reporting and accounting teams located in the United States.

A significant number of our management and professional employees have had prior experience with pharmaceutical, biotechnology or medical product companies. None of our employees in the United States are covered by collective bargaining agreements, and management considers relations with our employees to be in good standing. As is the usual situation in Spain, all the employees are currently covered by a collective bargaining system specific for the pharma sector. Management believes that it has sufficient human capital to operate its business successfully.

On September 28, 2025, our Board of Directors approved a plan to resize and restructure the company for purposes of focusing our attention on business development and licensing activities, clinical trial planning, exploratory VCN-01 manufacturing scale-up, limited preclinical activities related to VCN-01 and VCN-12 (the first candidate from our VCN-X discovery program), and interactions with the FDA and the EMA for proposed pivotal clinical trials of VCN-01 in patients with mPDAC and retinoblastoma (the “Plan”). Pursuant to the Plan, on September 30, 2025, we implemented a workforce reduction of seven employees or 32% of our then global workforce. The goal of this reduction was to direct our resources towards the activities detailed above in the Plan, which we believe will represent its best opportunity for success. We completed the employee reduction immediately and incurred a total of approximately $520,000 in charges in connection with the workforce reduction, which was accrued for as of September 30, 2025. These charges consist primarily of cash severance and benefits over a three-month period, in connection with the workforce reduction. The Plan is expected to save approximately $1.8 million in compensation and benefits annually, and together with additional anticipated operating cost reductions and capital raised pursuant to the ATM Sales Agreement, we expect that it will extend our cash runway into the first quarter of 2027;

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however, the current cash will only be sufficient to run certain clinical trials and no assurances can be provided and our cash could differ materially from our expectations based on various factors, many of which are out of our control.

Competitive Pay and Benefits

Our compensation programs are designed to align the compensation of our employees with our performance and to provide the proper incentives to attract, retain and motivate employees to achieve superior results. The structure of our compensation programs balances incentive earnings for both short-term and long-term performance. Specifically:

●we provide employee wages that are competitive and consistent with employee positions, skill levels, experience, knowledge and geographic location;

●we engage nationally recognized outside compensation and benefits consulting firms to independently evaluate the effectiveness of our executive compensation and benefit programs and to provide benchmarking against our peers within the industry;

●we align our executives’ long-term equity compensation with our shareholders’ interests by linking realizable pay with stock performance; and

●all employees are eligible for health insurance, paid and unpaid leaves, a retirement plan and life and disability/accident coverage. We also offer a variety of voluntary benefits that allow employees to select the options that meet their needs, including flexible time-off, telemedicine, and unpaid parental leave.

Available Information

Additional information about Theriva Biologics is contained on our website, www.therivabio.com. Information contained on our website is not incorporated by reference into, and does not form any part of, this Annual Report. We have included our website address as a factual reference and do not intend it to be an active link to our website. Our Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q and Current Reports on Form 8-K and amendments to those reports filed or furnished pursuant to Section 13(a) or 15(d) of the Exchange Act are available free of charge through the investor relations page of our internet website as soon as reasonably practicable after we electronically file such material with, or furnish it to, the Securities and Exchange Commission (the “SEC”). The following Corporate Governance documents are also posted on our website: Code of Conduct, Code of Ethics for Financial Management and the Charters for the Audit Committee, Compensation Committee and Nominations Committee of the Board of Directors. Our phone number is (301) 417-4364 and our facsimile number is (301) 417-4367. The SEC maintains an internet site that contains reports, proxy and information statements, and other information regarding issuers that file electronically with the Commission. The address of that website is www.sec.gov.

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