• Initiation of Cohort 2 Follows a Positive Review of Safety and Pharmacokinetic (PK) Data from Cohort 1 by an Independent Data and Safety Monitoring Committee 
  
• Cohort 2 Patient Dosing Highlights Momentum Across the Theriva Oncology-Focused Clinical Pipeline 

Theriva Biologics (NYSE American: TOVX), (“Theriva” or the “Company”), a diversified clinical-stage company developing therapeutics designed to treat cancer and related diseases in areas of high unmet need, today announced the first patient has been dosed in Cohort 2 of its 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 (aGVHD).

“We are encouraged by the growing evidence that demonstrates SYN-004 has the potential to reduce serious adverse events in patients undergoing allogeneic HCT to treat hematologic cancers, and are pleased with the program’s continued clinical advancement as part of our oncology-focused pipeline," said Steven A. Shallcross, Chief Executive Officer of Theriva Biologics. “We are very grateful for the tremendous support from Dr. Dubberke and his team at Washington University as we continue our progress towards improving treatment outcomes for these highly susceptible patients by overcoming existing limitations of broad-spectrum IV beta-lactam antibiotics.”

About the Phase 1b/2a Clinical Trial

The ongoing randomized, double-blinded, placebo-controlled Phase 1b/2a clinical trial is being conducted at Washington University School of Medicine in St. Louis. The trial is designed to evaluate the safety, tolerability, and potential absorption of oral SYN-004 (150 mg q.i.d. for a maximum of 28 days) into the systemic circulation of allogeneic HCT recipients who receive an IV antibiotic to treat fever. To mitigate risk, Cohort 1 of the study administered meropenem as the study-assigned antibiotic. Meropenem is a carbapenem antibiotic that is not metabolized by SYN-004. Patients in Cohorts 2 and 3 will be administered piperacillin/tazobactam and cefepime respectively, each of which can be metabolized by SYN-004. The trial is also designed to 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. The trial is expected to enroll up to 36 participants with three sequential cohorts, each evaluating a different study-assigned IV beta-lactam antibiotic. Safety and pharmacokinetic data for each cohort will be reviewed by an independent Data and Safety Monitoring Committee that will make a recommendation on whether to proceed to the next IV beta-lactam antibiotic. More information on the study is available here (NCT04692181).

About SYN-004 (ribaxamase)

SYN-004 (ribaxamase) is an oral prophylactic therapy designed to degrade certain IV beta-lactam antibiotics within the GI tract, thereby preventing antibiotic-mediated damage to the gut microbiome and reducing adverse outcomes associated with antibiotic-mediated gut dysbiosis. A previously completed placebo-controlled Phase 2b clinical trial of 412 patients treated with the IV β-latcam antibiotic ceftriaxone demonstrated that SYN-004 protected gut microbiome diversity, lowered the incidence of Clostridioides difficile infection (CDI) and reduced new colonization by opportunistic and potentially pathogenic microorganisms such as vancomycin resistant Enterococci (VRE). Patients undergoing allogeneic HCT are an ideal population for potential application of SYN-004 as these patients routinely receive long courses of IV beta-lactam antibiotics to treat infection following conditioning therapy. Antibiotic-mediated damage of the gut microbiome in these patients may lead to potentially fatal adverse outcomes including CDI, VRE colonization and bacteremia, and aGVHD.

About Theriva Biologics, Inc.

Theriva Biologics (NYSE American: TOVX), is a diversified clinical-stage company developing therapeutics designed to treat cancer and related diseases in areas of high unmet need. The Company’s subsidiary VCN Biosciences, S.L. (VCN), has been developing a new oncolytic adenovirus platform designed for intravenous (IV), intravitreal and antitumoral delivery to trigger tumor cell death, improve access of co-administered cancer therapies to the tumor, and promote a robust and sustained anti-tumor response by the patient’s immune system. The Company’s lead candidates are: (1) VCN-01, an oncolytic adenovirus designed to replicate selectively and aggressively within tumor cells, and to degrade the tumor stroma barrier that serves as a significant physical and immunosuppressive barrier to cancer treatment; (2) SYN-004 (ribaxamase) which is designed to degrade certain commonly used IV beta-lactam antibiotics within the gastrointestinal (GI) tract to prevent microbiome damage, thereby limiting overgrowth of pathogenic organisms such as VRE (vancomycin resistant Enterococci) and reducing the incidence and severity of acute graft-versus-host-disease (aGVHD) in allogeneic hematopoietic cell transplant (HCT) recipients); and (3) SYN-020, a recombinant oral formulation of the enzyme intestinal alkaline phosphatase (IAP) produced under cGMP conditions and intended to treat both local GI and systemic diseases. For more information, please visit Theriva Biologics' website at www.therivabio.com.

Forward-Looking Statement

This release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. In some cases forward-looking statements can be identified by terminology such as "may," "should," "potential," "continue," "expects," "anticipates," "intends," "plans," "believes," "estimates," and similar expressions, and include statements regarding the potential of SYN-004 to reduce serious adverse events in patients undergoing allogeneic HCT to treat hematologic cancers, the program’s continued clinical advancement as part of Theriva Biologics’ oncology-focused pipeline continuing progress towards improving treatment outcomes for these highly susceptible patients by overcoming existing limitations of broad-spectrum IV beta-lactam antibiotics, and the trial enrolling up to 36 participants with three sequential cohorts, each evaluating a different study-assigned IV beta-lactam antibiotic. These forward-looking statements are based on management's expectations and assumptions as of the date of this press release and are subject to a number of risks and uncertainties, many of which are difficult to predict that could cause actual results to differ materially from current expectations and assumptions from those set forth or implied by any forward-looking statements. Important factors that could cause actual results to differ materially from current expectations include, among others, the ability of SYN-004 to improve standard treatment for the highly susceptible patients by overcoming existing limitations of broad-spectrum IV beta-lactam antibiotics, the ability to enroll the anticipated number of patients in the Phase 1b/2a clinical trial, Theriva Biologics' ability to reach clinical milestones when anticipated, Theriva Biologics' ability to successfully combine and operate the business of Theriva Biologics and VCN, Theriva Biologics' and VCN's product candidates demonstrating safety and effectiveness, as well as results that are consistent with prior results; the ability to complete clinical trials on time and achieve the desired results and benefits, continuing clinical trial enrollment as expected; the ability to obtain regulatory approval for commercialization of product candidates or to comply with ongoing regulatory requirements, regulatory limitations relating to Theriva Biologics' and VCN's ability to promote or commercialize their product candidates for the specific indications, acceptance of product candidates in the marketplace and the successful development, marketing or sale of Theriva Biologics' and VCN's products, developments by competitors that render such products obsolete or non-competitive, Theriva Biologics' and VCN's ability to maintain license agreements, the continued maintenance and growth of Theriva Biologics' and VCN's patent estate, the ability to continue to remain well financed, and other factors described in Theriva Biologics' Annual Report on Form 10-K for the year ended December 31, 2021 and its other filings with the SEC, including subsequent periodic reports on Forms 10-Q and current reports on Form 8-K. The information in this release is provided only as of the date of this release, and Theriva Biologics undertakes no obligation to update any forward-looking statements contained in this release on account of new information, future events, or otherwise, except as required by law.

For further information, please contact:

Investor Relations:

Chris Calabrese

LifeSci Advisors, LLC

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