News Release

AstraZeneca executes option agreement for Vion-Epttco cancer therapy technology

Peer-Reviewed Publication

Vion Pharmaceuticals, Inc.

- AstraZeneca Provides Access to Technology for a Clinical Stage Prodrug -

NEW HAVEN, CT AND ABINGDON, UK, JANUARY 11, 2000 - Vion Pharmaceuticals, Inc. (NASDAQ NM: VION) and EPTTCO Limited today announced completion of an option agreement with AstraZeneca to collaborate on the evaluation of novel anticancer therapies jointly under current development by Vion and EPTTCO. Over the next nine months AstraZeneca will evaluate a version of Vion's TAPET® bacterial vector, armed with EPTTCO's prodrug activation technology, which uses enzymes to convert inactive prodrugs into cytotoxic anti-cancer agents.

Under the terms of the agreement, Vion and EPTTCO will co-develop these specific EPTTCO-armed TAPET vectors and test them in preclinical cancer models. AstraZeneca will provide access under its rights to certain prodrugs. AstraZeneca has been granted an exclusive option period to license the specific EPTTCO-armed TAPET vector. Financial details of the license, if exercised, will be determined at the time of exercise. Vion and EPTTCO will receive option fees to support the next stage of development, but details of financial and other terms were not disclosed.

"The Vion-EPTTCO therapeutic system is progressing towards key proof-of-principle studies in vivo. We are excited by the opportunity of being exclusively involved in these studies," said Dr. Mike Rose, Head of Oncology Bioscience at AstraZeneca. "Potentially, this project will also enable AstraZeneca to leverage its investment in prodrugs which it developed in collaboration with the Cancer Research Campaign for use in antibody-directed

Alan Kessman, president and CEO of Vion, said, "This option agreement with AstraZeneca represents a significant milestone event for the company, as strategic partnering is a key element in Vion's corporate strategy. In addition, this agreement enhances Vion's collaboration with EPTTCO, one of the first companies to embrace our unique TAPET technology, and also allows us both to advance the TAPET development program with AstraZeneca, one of the world‚s leading cancer therapy development companies. As part of a collaborative effort, we hope to create new cancer treatments that may be systemically delivered, potentially more effective against a wide range of solid tumors and less toxic to normal tissues than current chemotherapeutic therapies."

"The joint Vion-EPTTCO research team, working in the U.S., the U.K. and New Zealand, has made good progress in developing the armed TAPET system during the six months since signing our first agreement", said Trevor Twose, Chief Executive of EPTTCO. "One of our priorities now is to investigate AstraZeneca's prodrugs as part of the armed TAPET system, potentially accelerating later clinical development, so we are pleased to have secured AstraZeneca's involvement."

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 age!! nts.

EPTTCO has developed several proprietary prodrug-activating systems for 'arming' therapeutic delivery systems, such as TAPET and gene therapy vectors, to increase their ability to kill tumor cells. One of EPTTCO's enzyme genes is introduced into the delivery system in such a way that active enzymes are produced. A small molecule prodrug, which is inactive and safe prior to activation by the enzyme, is administered systemically and is converted to an active cytotoxic drug by the enzyme. The delivery system ensures that enzyme production and prodrug activation is selectively localized within tumors, resulting in local killing of tumor cells, whilst sparing other normal tissues from toxic effects. EPTTCO has demonstrated the efficacy and safety of its systems in preclinical models, including demonstrating long-term regressions of several human tumors in in vivo models. One of these prodrugs is currently in a Phase I clinical study in an ADEPT system. EPTTCO will provide sever! ! al other families of prodrugs for evaluation in the Vion-EPTTCO therapy system.

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 company‚s Internet web site at http://www.vionpharm.com.

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EPTTCO is a new U.K.-based company engaged in the design and development of therapeutics for cancer and other serious diseases, initially based on its prodrug activation systems. The company brings together research expertise and technology from the Cancer Research Centre and School of Medicine of the University of Auckland, New Zealand (ACSRC), the CRC Centre for Cancer Therapeutics, Institute for Cancer Research, Sutton, U.K. (ICR) and the Centre for Applied Microbiology, Porton Down, U.K. (CAMR). The company was formed in early 1999 by Cancer Research Campaign Technologies Limited, London, U.K. together with ACSRC, ICR and CAMR.

AstraZeneca is a major international healthcare business engaged in the research, development, manufacture and marketing of ethical (prescription) pharmaceuticals and the supply of healthcare services. It is one of the top five pharmaceutical companies in the world with healthcare sales of $13 billion and leading positions in sales of gastrointestinal, oncology, anaesthesia including pain management, cardiovascular, central nervous system (CNS) and respiratory products.

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 Vion Pharmaceutical‚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.

COMPANY CONTACT: Vion Pharmaceuticals, Inc.
Alan Kessman, President and CEO
Thomas E. Klein, VP Finance & CFO
203-498-4210 ph

AstraZeneca
Wendy Russell, R&D Communications and
PR Director
44-1625-515035 ph

EPPTCO
Trevor Twose, PhD, Chief Executive Officer
415-421-1899 ph ext. 1710

FINANCIAL COMMUNICATIONS CONTACT: CPR Financial Communications, LLC
Sue L. Yeoh (investors)
201-641-2408 ph

Lisa Bradlow (media)
212-579-7428 ph



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