Public Release: 

VION and Yale University present preclinical data on novel sulfonyl hydrazine anticancer agent

Vion Pharmaceuticals, Inc.

-- Data Shows Broad Antitumor Activity with Unique Features for an Alkylating Agent --

NEW HAVEN, CT -- APRIL 6, 2000 -- VION PHARMACEUTICALS, INC. (NASDAQ NM: VION) and Yale University presented preclinical data on a new anticancer agent (VNP40101M) of the Sulfonyl Hydrazine Prodrug class. The agent demonstrated broad antitumor activity against leukemia, melanoma, lung and colon carcinomas in animal models. In addition, VNP40101M showed excellent penetration across the blood brain barrier with antitumor activity against leukemia in the brain, as well as activity against tumor cells resistant to the standard alkylating agents cyclophosphamide, BCNU and melphalan. The data were presented at the 2000 Annual Meeting of the American Association for Cancer Research (AACR). The studies were conducted in the laboratory of Alan C. Sartorelli, Ph.D., Chairman, Department of Pharmacology, Yale University School of Medicine, and Chairman of the Scientific Advisory Board and a Board Director at Vion.

VNP40101M was shown to be active over a wide dosage range, and produced long-term survivors in several preclinical tumor models even when administered at relatively low doses that were not associated with bone marrow suppression. Antitumor activity was observed in mice with both oral and systemic routes of administration in a leukemia model. Overall, the results support further preclinical development of VNP40101M, and suggest that it may add to or improve upon the spectrum of antitumor activity observed with the currently available cytotoxic anticancer agents.

Alan Kessman, president and CEO of Vion, commented, "The preclinical data generated on our Sulfonyl Hydrazine agent indicate that it has unique and favorable properties compared to the currently available alkylating agents and may therefore have an improved spectrum of activity compared to those agents in clinical use. The preliminary safety and efficacy data to date for VNP40101M are encouraging, and we are confident the upcoming toxicology studies will demonstrate an acceptable level of safety to proceed to clinical trials. This anticancer agent is another important candidate, combined with our TAPET®, Triapine® and Promycin® products currently under evaluation in human clinical trials, which not only strengthens our product pipeline, but could also make a substantial impact against this disease."

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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. For additional information on Vion and its research and product development programs, visit the company¹s Internet web site at http://www.vionpharm.com.

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-3/A (file no. 333-95671). The shares of Common Stock, described above, have not been registered under the Securities Act of 1933, as amended, and may not be offered and sold in the United States absent registration under such Act or an applicable exemption from registration. This press release shall not constitute an offer to sell or the solicitation of an offer to buy its securities 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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