News Release

Vion's TAPET® administered to first patients in Phase I human intratumoral safety trial at the Cleveland Clinic Foundation

Peer-Reviewed Publication

Vion Pharmaceuticals, Inc.

NEW HAVEN, CONN., DECEMBER 8, 1999 -- VION PHARMACEUTICALS, INC. (NASDAQ NM: VION) today announced that VNP20009, the company's first generation TAPET® bacterial vector, has been administered to the first patients enrolled into Vion's Phase I intratumoral trial, which is being conducted at The Cleveland Clinic Foundation. The patients were initially monitored in the hospital and subsequently discharged. Potential safety and efficacy will continue to be monitored according to the protocol. The Phase I study is designed to evaluate the safety, potential efficacy and optimum biological dose of an intratumoral administration for patients with either cutaneous or subcutaneous solid tumors. Patients will be evaluated for the accumulation of VNP20009 in the tumor and non-injected lesions. Patient accrual continues for this trial, which may involve up to 20-30 patients.

TAPET (Tumor Amplified Protein Expression Therapy), Vion's core platform technology, are highly attenuated bacteria that, in preclinical studies, have demonstrated preferential replication in tumors compared to normal tissues. The bioengineered bacteria have demonstrated an excellent safety profile in preclinical toxicology studies. Preferential replication allows the bacteria to produce and deliver a variety of anti-cancer therapeutic products at high concentrations to tumors while minimizing toxicity to normal tissues. By bringing the "drug factory" preferentially to the tumor, Vion believes that TAPET may result in a cancer therapy that is more concentrated, more effective and less toxic to normal tissue. Furthermore, the unarmed bacteria by themselves have shown good anti-tumor activity in animal models. Vion plans to develop the unarmed TAPET alone as an anti-tumor agent and to develop second-generation products that produce and deliver potent therapeutic anti-cancer agents.

Vion Pharmaceuticals, Inc. is a biopharmaceutical company engaged in the research, development and commercialization of cancer treatment technologies. Vion's product portfolio consists of TAPET, a drug delivery platform, and three cancer therapeutics (Promycin®, Triapine® and Sulfonyl Hydrazine Prodrugs). TAPET has been shown in preclinical models to effectively deliver anticancer agents while having a minimal toxic effect on healthy normal tissues. TAPET uses genetically altered strains of Salmonella as a bacterial vector, or vehicle, for delivering cancer fighting drugs preferentially to solid tumors. Promycin, which attacks oxygen depleted cancer cells, is currently being evaluated with radiation in a multicenter Phase III clinical trial for the treatment of head and neck cancer. Triapine, which is designed to prevent the replication of tumor cells by blocking a critical step in the synthesis of DNA, is currently being evaluated for its safety in a Phase I clinical trial. Sulfonyl Hydrazine Prodrugs, compounds that are designed to be converted to unique potent, alkylating agents, are currently being evaluated in preclinical studies.

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Statements included in this press release which are not historical in nature are forward-looking statements made pursuant to the safe-harbor provisions of the Private Securities Litigation Reform Act of 1995. Forward-looking statements regarding the company's future business prospects, plans, objectives, expectations and intentions are subject to certain risks, uncertainties and other factors that could cause actual results to differ materially from those projected or suggested in the forward-looking statements, including, but not limited to those contained in the company's Registration Statement filed on Form S-3/A (file no. 333-79939). This press release shall not constitute an offer to sell or the solicitation of an offer to buy the common stock nor shall there be any sale of these securities in any state in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state.


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