News Release

VION applies bacteria to create unique TAPET® technology for novel and highly specific gene-based anti-cancer drug delivery

Peer-Reviewed Publication

Vion Pharmaceuticals, Inc.

- Armed TAPET Caused Complete Tumor Regression -

- Vion Pharmaceuticals Presents TAPET Anti-Cancer Data at The International Conference on Molecular Targets and Cancer Therapeutics in Washington, D.C.-

- Vion Enrolling Patients for Novel Cancer Therapy at The Cleveland Clinic -

NOVEMBER 17, 1999 -- VION PHARMACEUTICALS, INC. (VION) will present preclinical data on its drug delivery platform, TAPET® (Tumor Amplified Protein Expression Therapy), which uses Salmonella bacteria to colonize and multiply preferentially within the confines of a tumor, thereby inhibiting tumor growth, at The International Conference on Molecular Targets and Cancer Therapeutics in Washington, D.C., November 17-18, 1999.

The conference is being sponsored by The American Association for Cancer Research (AACR), The National Cancer Institute (NCI) and The European Organization for Research and Treatment of Cancer (EORTC). Stanley Lin, Ph.D., Senior Research Fellow, Michael F. Belcourt, Ph.D., and Caroline Clairmont, Ph.D., Senior Research Scientists at Vion, will present three separate TAPET studies at the conference and will be available for interviews prior to or following the presentations (B-roll video of the company is available to complement the story).

Presentation highlights include:
- Complete tumor regression in mice using a cytokine (TNF-alpha) producing TAPET vector

- TAPET bacteria may be bioengineered to express activators for certain types of anti-cancer prodrugs within solid tumors

- High safety profile in the unarmed TAPET vector, VNP20009

The company¹s Phase I human safety trial of an unarmed TAPET vector, VNP20009, is open for enrollment at the Cleveland Clinic Foundation and will be expanded to include additional sites in the near future. TAPET will be administered by injection directly into a surface tumor, a strategy that demonstrated significant anti-tumor effects against the injected lesion and distal metastases as observed in preclinical animal tumor models. To be eligible, patients must be ambulatory, have advanced cancer that is no longer responsive to standard treatment and must have one or more surface tumors that can be injected with TAPET. The company also intends to conduct intravenous studies. Patients seeking to participate in the trial may contact the Taussig Cancer Center Experimental Therapeutics Department at The Cleveland Clinic Foundation in Cleveland, Ohio, http://www.ccf.org, (216) 444-7925 ph.

What is TAPET?
Vion Pharmaceuticals is the first and only company investigating the motility and ³genetic packaging² potential of bioengineered bacteria to treat cancer. Vion believes that TAPET may prove to be an ideal delivery mechanism for the delivery of specific gene-based cancer-fighting drugs preferentially to solid tumors. In preclinical studies, after injection into the body, TAPET organisms migrated to and penetrated the deep, oxygen-starved interior of solid tumors where other anticancer drugs do not generally reach. The increase in quantity of TAPET organisms inhibited tumor growth and enabled the continuous delivery of anticancer drugs to tumors. By bringing the ³drug factory² preferentially to the tumor, it is reasoned that cancer therapy could be more concentrated, more effective and less toxic to normal tissue.

Is TAPET safe?
TAPET organisms have been genetically altered to significantly reduce the serious toxicities associated with infection from normal Salmonella bacteria. In three different animal species, the bacteria could be given in the therapeutic range without significant toxicity and were cleared from the body spontaneously without antibiotics. Moreover, for additional protection, TAPET organisms are designed to remain fully sensitive to antibiotic therapies. Therefore, if there is an adverse reaction, the patient can be treated with antibiotics at anytime during therapy. Preclinical studies have demonstrated these safety measures to be effective.

Vion Pharmaceuticals, Inc. is a biopharmaceutical company engaged in the research, development and commercialization of cancer treatment technologies. Vion¹s 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 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 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 company¹s 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 company¹s Registration Statement filed on Form S-1 (file no. 333-83837) and its amendments. This press release shall not constitute an offer to sell or the solicitation of an offer to buy any securities of Vion.

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