Theriva Biologics Reports Third Quarter 2023 Operational Highlights and Financial Results - VIRAGE, the Phase 2b clinical trial of VCN-01 in combination with chemotherapy for metastatic Pancreatic Ductal Adenocarcinoma r

Theriva Biologics Reports Third Quarter

2023 Operational Highlights and Financial Results

- VIRAGE, the Phase 2b clinical trial of VCN-01

in combination with chemotherapy for metastatic Pancreatic Ductal Adenocarcinoma remains on track to complete enrollment in the first

half of 2024; multiple patients have received second doses of VCN-01, which continues to be well tolerated with a safety profile consistent

with prior clinical trials -

- Presented survival outcomes data from the

Phase 1 investigator-sponsored study evaluating VCN-01 in combination with durvalumab in patients with recurrent/metastatic squamous cell

carcinoma of the head and neck at the European Society for Medical Oncology (ESMO) Congress 2023-

- Data from the Phase 1 investigator-sponsored

study evaluating VCN-01 in combination with CAR-T cell immunotherapy in patients with pancreatic and serous epithelial ovarian cancer

was presented at the Society for Immunotherapy of Cancer's (SITC) 2023 Annual Meeting -

- As of September 30, 2023, Theriva Biologics

reports $31.2 million in cash, which is expected to provide runway into the first quarter of 2025 -

- Conference call and webcast to be held on

Monday, November 13th at 8:30 a.m. ET -

Rockville, MD, November 13, 2023 -

Theriva Biologics (NYSE American: TOVX), a diversified clinical-stage company developing therapeutics designed to treat cancer

and related diseases in areas of high unmet need, today reported financial results for the third quarter ended September 30, 2023, and

provided a corporate update.

"We are encouraged by the growing clinical data that underscores

the promise of our systemically administered oncolytic adenovirus and lead program, VCN-01, in key indications and combinations,"

said Steven A. Shallcross, Chief Executive Officer of Theriva Biologics. "Data from the ongoing study of VCN-01 in combination with

durvalumab in patients with recurrent/metastatic squamous cell carcinoma of the head and neck (R/M HNSCC) were recently presented at the

annual ESMO Congress. Results showed enhanced patient survival, which correlated with VCN-01 mediated increases in the CPS (combined positive

score for PD-L1 staining), a key determinant of outcomes with anti-PD-(L)1 checkpoint inhibitor therapies. Together with data presented

at this year's SITC meeting, these data further validate the feasibility of combining VCN-01 with immunotherapies."

Mr. Shallcross continued, "We continue to advance VIRAGE, our

Phase 2b trial of VCN-01 in newly-diagnosed metastatic pancreatic ductal adenocarcinoma (PDAC), with patients dosed across sites in the

U.S. and Spain. We have observed a consistent safety and tolerability profile and remain on track to complete enrollment for VIRAGE in

the first half of 2024. As part of our commitment to transforming therapeutic approaches for devastating cancers, we will meet with the

FDA before year-end to discuss the development pathway for VCN-01 as an adjunct to chemotherapy in pediatric patients with advanced retinoblastoma.

While our key area of focus is on advancing and maximizing the therapeutic potential of VCN-01, we continue to explore opportunities to

bolster our pipeline with new oncolytic virus candidates from utilizing our Albumin Shield technology."

Recent Program Highlights and Anticipated

SYN-004 (ribaxamase):

Third Quarter Ended September 30, 2023 Financial Results

General and administrative expenses decreased

to $212,000 for the three months ended September 30, 2023, from $2.4 million for the three months ended September 30, 2022. This decrease

of 91% is primarily comprised of the decrease in the fair value of the contingent consideration of $1.6 million, along with lower salary

and bonus costs, investor relations fees, audit fees, travel, and VCN administrative expenses not included in the prior year, offset by

an increase in consulting fees. The charge related to stock-based compensation expense was $95,000 for the three months ended September

30, 2023, compared to $93,000 for the three months ended September 30, 2022.

Research and development expenses increased to

$4.0 million for the three months ended September 30, 2023, from approximately $2.6 million for the three months ended September 30, 2022.

This increase of 56% is primarily the result of higher clinical trial expenses related to our VIRAGE Phase 2 clinical trial of VCN-01

in PDAC, offset by decreased expenses related to our Phase 1b/2a clinical trial of SYN-004 (ribaxamase) in allogeneic HCT recipients,

Phase 1a clinical trial of SYN-020, and decreased manufacturing expenses related to our Phase 1a clinical trial of SYN-020. We anticipate

research and development expense to increase as we continue enrollment in our VIRAGE Phase 2 clinical trial of VCN-01 in PDAC and our

ongoing Phase 1 clinical trial in retinoblastoma, expand GMP manufacturing activities for VCN-01, and continue supporting our VCN-11 and

other preclinical and discovery initiatives. The charge related to stock-based compensation expense was $40,000 for the three months ended

September 30, 2023, compared to $28,000 related to stock-based compensation expense for the three months ended September 30, 2022.

Other income was $388,000 for the three months

ended September 30, 2023 compared to other income of $161,000 for the three months ended September 30, 2022. Other income for the three

months ended September 30, 2023 is primarily comprised of interest income of $382,000 and an exchange gain of $6,000. Other income for

the three months ended September 30, 2022 is primarily comprised of interest income of $170,000 offset by an exchange loss of $9,000.

Cash and cash equivalents totaled $31.2 million

as of September 30, 2023, compared to $41.8 million as of December 31, 2022.

Theriva Biologics will host a conference call on Monday, November

13, 2023, at 8:30 a.m. ET to discuss its financial results for the quarter ended September 30, 2023 and provide a corporate update. Individuals

may participate in the live call via telephone by dialing 1-877-451-6152 (domestic) or 1-201-389-0879 (international) and using the conference

ID: 13741546. Participants are asked to dial in 15 minutes before the start of the call to register. Investors and the public can access

the live and archived webcast of this call via the "News & Media" section of the company's website, https://www.therivabio.com,

under "Events" or by clicking here, up to 90 days after the call.

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 is advancing 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 VIRAGE remaining on track to complete enrollment in the first half of 2024, VCN-01 continuing to be well

tolerated with a safety profile consistent with prior clinical trials, cash providing a runway into the first quarter of 2025, continuing

to advance VIRAGE in newly-diagnosed metastatic PDAC with patients dosed across sites in the U.S. and Spain, the therapeutic potential

of VCN-01 to elicit an extended anti-tumor immune response, plans to meet with regulatory agencies before year-end to discuss the development

pathway for VCN-01 as an adjunct to chemotherapy in pediatric patients with advanced retinoblastoma, continuing to explore opportunities

to bolster the Company's pipeline with new oncolytic virus candidates from utilizing its Albumin Shield technology, the VIRAGE trial

enrolling 92 patients, the SYN-004 trial being on track to complete the second cohort in H1 2024 and research and development expense

increasing as the Company continues enrollment in the VIRAGE Phase 2 clinical trial of VCN-01 in PDAC and its ongoing Phase 1 clinical

trial in retinoblastoma, expanding GMP manufacturing activities for VCN-01, and continuing supporting our VCN-11 and other preclinical

and discovery initiatives. 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 Company's

and VCN's ability to reach clinical milestones when anticipated, including completion of enrollment in Virage in the first half

of 2024 and completing the SYN-004 second cohort in the first quarter of 2024, generating clinical data that establishes VCN-01 being

an adjunct to chemotherapy in pediatric patients with advanced retinoblastoma and combining with immunotherapy products to treat solid

tumors, the Company's ability to successfully combine and operate the business of the Theriva Biologics and VCN, the Company's

and VCN's product candidates demonstrating safety and effectiveness, as well as results that are consistent with prior results;