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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549
FORM 8-K
CURRENT REPORT
Pursuant to Section 13 or 15(d)
of the Securities Exchange Act of 1934
Date of Report (Date of earliest event reported): October 8, 2025
THERIVA BIOLOGICS, INC.
(Exact name of registrant as specified in its charter)
| Nevada | 001-12584 | 13-3808303 | ||
| (State or other jurisdiction of incorporation) |
(Commission File No.) | (IRS Employer Identification No.) |
9605 Medical Center Drive, Suite 270
Rockville, Maryland 20850
(Address of principal executive offices and zip code)
(301) 417-4364
Registrant’s telephone number, including area code
N/A
(Former name or former address, if changed since last report)
Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):
| ¨ | Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) |
| ¨ | Soliciting material pursuant to Rule 14a-12(b) under the Exchange Act (17 CFR 240.14a-12) |
| ¨ | Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) |
| ¨ | Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c)) |
Securities registered pursuant to Section 12(b) of the Act:
| Title of each class | Trading Symbol(s) | Name of each exchange on which registered |
| Common stock, par value $0.001 per share | TOVX | NYSE American |
Indicate by check mark whether the registrant is an emerging growth company as defined in in Rule 405 of the Securities Act of 1933 (17 CFR §230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (17 CFR §240.12b-2 of this chapter).
Emerging growth company ¨
If an emerging growth company, indicate by checkmark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ¨
Item 8.01. Other Events.
On October 8, 2025, preclinical data for VCN-12, a next generation oncolytic adenovirus developed as part of the VCN-X discovery program of Theriva Biologics, Inc. (the “Company”), was presented by Dr. Ramon Alemany at the 32nd Annual Congress of the European Society of Gene & Cell Therapy. A copy of the presentation is filed as an exhibit to this Current Report on Form 8-K as Exhibit 99.1 and is incorporated herein by reference.
VCN-12 uses the same virus capsid as the Company’s 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.
Item 9.01. Financial Statements and Exhibits.
| (d) | Exhibits. |
| Exhibit Number |
Description | |
| 99.1 | Preclinical Data presented at the 32nd Annual Congress of the European Society of Gene & Cell Therapy | |
| 104 | Cover Page Interactive Data File (embedded within the XBRL document) |
SIGNATURES
Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.
| Dated: October 8, 2025 | THERIVA BIOLOGICS, INC. | ||
| By: | /s/ Steven A. Shallcross | ||
| Name: | Steven A. Shallcross | ||
| Title: | Chief Executive Officer and Chief Financial Officer | ||
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Virotherapy with armed OAd |
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Declaration of Interest: Honoraria, shares and funding from Theriva Biologics. |
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Nab-placlitaxel+gemcitabine weekly until progression RECIST VCN-01 (1E13vp iv) Transient and mild AEs: fever, nausea, transaminitis VCN01+CTx vs CTx VIRAGE randomized phase 2 trial for metastatic pancreatic cancer |
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VIRAGE phase 2B clinical trial Progression –free survival: 7.0 vs 4.6 mo (p=0.01; HR 0.55) Overall survival: 10.8 vs 8.6 mo (p=0.05; HR 0.57) |
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VIRAGE phase 2B clinical trial Duration of response: 11.2 vs 5.4 mo (p=0.003; HR 0.22) PFS if VCN-01 x 2: 11.2 vs 7.4 mo (p=0.01; HR 0.48) |
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Pore formation is the hallmark of PYROPTOSIS / immunogenic cell death From Bertheloot et al. Cell Mol Immunol 18, 1106–1121 (2021) |
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• Strong cytocidal activity against a broad range of human cancer cell lines • Minimal cytotoxicity toward normal hepatocytes and A549 cells • Inactive 37-kDa protoxin is processed to a 30-kDa active form by proteinase K • Exposure to the toxin causes striking morphological changes in susceptible cells, including swelling, blebbing, and lysis Rationale for pore-forming toxin parasporin-2 (PS2) From Akiba and Okumura, J Invertebr Pathol. (2017) |
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Parasporin 2 pore formation requires several unknown receptors Created with BioRender.com |
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PS2 may kill non-infected bystander cells and reduce viral immunodominance Created with BioRender.com |
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Parasporin2 (PS2) with furin-mediated activation Furin-sensitive linkers C-term Inhibitory domain N-term Inhibitory domain CT26 “Fritolysis” Furin cut Furin cut |
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Furin-cleavable linkers enhance cytotoxicity CT26 cells , MTS assay % Metabolic activity |
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A549 CT26 PS2 induces membrane calreticulin (marker of ICD) |
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CT26 (mouse colorectal adenocarcinoma) PS2 induces ATP release (marker of ICD) HepG2 (human hepatocellular carcinoma) A549 (human lung adenocarcinoma) RealTime-Glo extracellular ATP assay with SNs diluted ½ : |
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PS2 induces HMGB1 release (marker of ICD) CT26 (mouse colorectal adenocarcinoma) HepG2 (human hepatocellular carcinoma) A549 (human lung adenocarcinoma) Lumit HMGB1 immunoassay with SNs : |
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PS2 induces “fritolysis” in multiple mouse tumor cell lines CMT64-RG6 (mouse lung adenocarcinoma) CT26 (mouse colorectal adenocarcinoma) MC38 (mouse colorectal adenocarcinoma) TRAMPC2 (mouse prostate adenocarcinoma) B16-CAR (mouse melanoma) Sensitive Resistant KPC (mouse pancreatic ductal adenocarcinoma) |
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CT26 (mouse colorectal adenocarcinoma) MC38 (mouse colorectal adenocarcinoma) CMT64-RG6 (mouse lung adenocarcinoma) TRAMPC2 (mouse prostate adenocarcinoma) B16-CAR (mouse melanoma) Sensitive Resistant KPC (mouse pancreatic ductal adenocarcinoma) PS2 induces cytotoxicity in multiple mouse tumor cell lines |
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CT26 mixed with 293GL CT26 mixed with 293GL-PS2 A549 mixed with 293GL-PS2 PS2 induces bystander “fritolysis” |
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d0 1e+06 CMT64.6 d12 (~50-70 mm3) C57BL/6J 3 IT injections PS2FuT/Control SN d16 d19 Tumor volume (mm 3 ) SNs containig PS2 have antitumor activity |
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PS2 confers ICD-mediated antitumor immunity Antitumor immune responses were detected in a PS2FuT-treated mouse Created with BioRender.com |
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ICOVIR-15K-SA-PS2 SA pA Fiber RGDK E1a ∆24 MLP L1 L2 L3 L4 L5 E2F boxes PS2FuT N-term Inhibitory domain C-term Inhibitory domain Furin cut Furin cut |
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Created with BioRender.com PS2-armed OAd intratumoral replication and gene expression upon iv admin |
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*vs. PBS ICOVIR15K-PS2 vs ICOVIR15K body weight toxicity |
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****vs. PBS *vs. PBS #vs. ICO15K ICOVIR15K-PS2 vs ICOVIR15 antitumor efficacy |
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VCN-12: Next Generation OV Based on VCN-01 LITR E2F boxes E1A- ∆24 MLP RITR L1 L2 L3 L4 L5 Fiber RGDK VCN-01: PH20 IIIaSA LITR RITR E2F boxes E1A- ∆24 MLP L1 L2 L3 L4 L5 Fiber RGDK ∆E1B/19K ∆E3/19K VCN-12: Bee Hyal Parasporin2 IIIaSA T2A VCN-12 modifications vs VCN-01: • Replace PH20 with Bee hyaluronidase – greater specific activity • Insert the furin-modified pore-formin toxin Parasporin2 as a second transgene • Deletion of E1B-19K and E3-19K – create space in viral genome |
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PS2 activity in SN (CT26 cells): CT26 HepG2 Hyaluronidase and PS2 secreted from VCN-12-infected cells Hyaluronidase activity in SN (turbidometry) |
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2x Increased cytotoxicity of VCN-12 vs VCN01 in a panel of tumor cell lines SK-mel28 8x 3.4x 10x HT29 SW1116 3.5x SK-CO1 13.7x A549 HP1 6x CMT64-RG6-hCAR 6x HKT-1097 Human Hamster Mouse |
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VCN-12 shows a similar toxicity profile to VCN-01 No differences between VCN-12 and VCN-01 in: • Biochemical, hematological and coagulation parameters • Liver pathology analysis Liver transaminases VCN-12 VCN-12 Body weight loss |
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*p-value<0.05 (IIIa-BH-PS2 vs PBS) *p-value<0.05 (VCN-12 vs PBS) ºp-value<0.05 (VCN-01 vs PBS) #p-value<0.05 (VCN-12 vs VCN-01) # Syrian hamster Hamster sc. Tumors HP-1 (pancreatic) Day -11 Day 1 Day 4 Virus administration (IT) Right tumor 2.5E10vp/animal Inoculation Right flank Inoculation Left flank Treated tumors Non-treated tumors Monitor tumor volume VCN-12 shows more antitumor activity than VCN-01 in treated and contralateral tumors in an immunocompentent animal model |
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# * *p-value<0.05 (VCN-12 vs PBS) #p-value<0.05 (VCN-12 vs VCN-01) Survival Rejections Syrian hamster Hamster sc. Tumors HP-1 (pancreatic) Day -11 Day 1 Day 4 Virus administration (IT) Right tumor 2.5E10vp/animal Inoculation Right flank Inoculation Left flank Monitor tumor growth Same 2 animals eradicated initial treated tumor and would not establish new tumor VCN-12 improves survival and induces complete responses in hamsters with HP1 tumors |
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VCN-12 induces long-lasting antitumor immune responses in responders * * Historical control Tumor rechallenge 2 cured hamsters Day 1 Rechallenge with HP-1 tumor cells Monitor tumor growth Day -43 Tumor disappearance |
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Summary Parasporin 2 pore-forming toxin activated by furin linkers and secreted from plasmid-transfected or oncolytic adenovirus infected cells has cytotoxic and immunogenic cell death properties. Bee Hyaluronidase and PS2-armed VCN-12 is superior to VCN-01 in tumor cytotoxicity and immunogenicity |
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Laura Moya Mar Tarinas Stan Peters Rafael Moreno Marcel Costa Silvia Torres Pau Fiol Josep M. Piulats Luís Rojas Ana Mato Victoria Maliandi Paz Moreno Carlos López Sheila Connelly Manel Cascalló Collaborators: Cristina Fillat Javier García Castro Manuel Ramírez Orellana Judith Perisé Barrios Juan Fueyo PID2020-119692RB-C21 |
