ONYX Begins Testing of Adenovirus in Pancreatic Cancer.

RICHMOND, Calif.--(BW HealthWire)--March 3, 1997--ONYX Pharmaceuticals Inc. (NASDAQ:ONXX) announced today that it has expanded Phase I human clinical testing of its lead anticancer agent, ONYX-015, to include patients with pancreatic cancer.

This is the second Phase I clinical trial that ONYX has initiated with ONYX-015. The first Phase I study, directed at head and neck tumors, began in April 1996.

ONYX-015 is a genetically engineered adenovirus that efficiently replicates in and kills tumor cells deficient in the p53 tumor suppressor gene product. Mutations in p53 are the most common type of genetic abnormality in cancer, occurring in more than 50 percent of human cancer cases, including more than 50 percent of pancreatic cancers.

In this new study of ONYX-015, the product is administered either 1) by using computer-assisted tomography to guide the injection directly into the tumor mass; or 2) intra-operatively if, during surgery, it is discovered that a tumor cannot be completely removed. The patient would then receive an immediate intra-tumoral injection of ONYX-015.

The Phase I study is designed to determine safety and maximally tolerated dose, to assess the patient's immune response to the injected virus and to investigate any effects of the virus on tumor growth. The principal investigator for this pancreatic cancer trial is Sean Mulvihill, M.D. of the University of California San Francisco Medical Center. Alan Venook, M.D. and Robert Warren, M.D. are co-investigators.

When an unmodified adenovirus infects a normal cell, the cell is killed and thousands of virus particles are released to infect neighboring cells. To take control of the cell, the virus must first inactivate p53, which it does by making a protein called E1B 55k. E1B 55k then binds directly to p53 and blocks its function.

The ONYX-015 adenovirus is modified so that it cannot make E1B 55k and, as a result, it does not block the function of p53 in normal cells. Therefore, ONYX-015 cannot replicate efficiently in normal cells and should not destroy them. In the majority of cancer cells, however, the function of p53 is already disarmed through the mutation of the p53 gene or other mechanisms.

When ONYX-015 infects these cells, the virus growth cycle proceeds unchecked, the virus replicates and the cancer cells are killed. New virus particles are produced and neighboring cancer cells are infected and destroyed.

ONYX Pharmaceuticals was founded in 1992 for the purpose of discovering and developing novel therapeutics based upon the genetics of human disease, with an initial emphasis on cancer. The company focuses on defining the function of certain mutated genes which are known to cause cancer, and on developing innovative therapies to reverse the effects of the mutation or to kill the cancer cell.

ONYX pursues a strategy of establishing corporate partnerships that provide complementary skills in drug development, clinical trials, regulatory affairs, marketing and sales.

The statements made in this press release contain certain forward-looking statements that involve a number of risks and uncertainties. Actual events or results may differ from the company's expectations.

In addition to the matters described in this press release, timelines for clinical activity, results of pending or future clinical trials and changes in the status of the company's collaborative relationships, as well as the risk factors listed from time to time in the company's SEC reports, including but not limited to its Registration Statement on Form SB-2, may affect the actual results achieved by the company.

CONTACT: ONYX Pharmaceuticals

Jana R. Cuiper, 510/262-8775