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Sunesis Pharmaceuticals Selects Development Candidate for Aurora Kinase Program

South San Francisco, CA, August 29, 2005 - Sunesis Pharmaceuticals, Inc. today announced that the company has selected an Aurora kinase development candidate, designated SNS-314, for IND-enabling preclinical development. SNS-314 is a small molecule kinase inhibitor that has shown promising selectivity and activity as a potential anti-cancer therapy in in vitro and in vivo testing. The company plans to file an Investigational New Drug (IND) application with the U.S. Food and Drug Administration and commence clinical trials for SNS-314 in 2006.

"I am pleased by the Sunesis team's rapid progress in the identification and selection of such a promising development candidate for our Aurora kinase anti-cancer program. Initiated less than two years ago, this program has advanced through discovery and into IND-enabling development in a timely manner," said Daniel Adelman, M.D., Senior Vice President, Drug Discovery and Development of Sunesis. "One of the goals of our Aurora program is to develop a mitotic inhibitor that has broad anti-tumor activity, but that will not result in significant peripheral neuropathy, a common and potentially debilitating side effect of certain chemotherapies. We believe SNS-314 has the potential to selectively target actively dividing tumor cells in a variety of cancer types and halt tumor cell proliferation."

Aurora kinases are overexpressed in a number of tumor types including colon cancer, breast cancer and leukemia. Aurora kinases are key enzymes involved in cell growth and division and play an essential role in the abnormal proliferation of tumor cells. SNS-314 is a targeted inhibitor of Aurora A and B intended to arrest cellular proliferation and limit tumor growth by initiating programmed cell death. SNS-314 has demonstrated the ability to inhibit tumor growth in vivo. In preliminary safety studies, SNS-314 does not cause any unanticipated toxicity when administered either orally or intravenously to mice or rats at therapeutic doses.

About Sunesis' Oncology Programs
Sunesis is advancing three proprietary oncology product candidates, SNS-595, SNS-032 and SNS-314, through in-house research and development efforts. All three are inhibitors of the cell division process, known as cell-cycle inhibitors, intended for the treatment of cancers. The company's lead product candidate, SNS-595, is a novel cytotoxic currently in Phase I clinical trials. SNS-032 is a CDK inhibitor and is expected to begin clinical studies in the second half of 2005. SNS-314, an Aurora kinase inhibitor, for the treatment of cancer, has the potential to limit the growth of multiple tumor types without causing significant peripheral neuropathy. We expect to commence clinical trials with SNS-314 in 2006. In addition to these proprietary programs, Sunesis is developing novel small molecule inhibitors of Raf and other oncology kinases in cooperation with Biogen Idec.

About Sunesis Pharmaceuticals
Sunesis is a clinical-stage biopharmaceutical company focused on the discovery, development and commercialization of novel small molecule therapeutics for oncology and other serious diseases. Sunesis has built a broad product candidate portfolio through internal discovery and in-licensing of novel cancer therapeutics. Sunesis is advancing its product candidates through in-house research and development efforts and strategic collaborations with leading pharmaceutical and biopharmaceutical companies. For further information, visit

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Forward-Looking Statements
This press release may contain forward-looking statements that involve substantial risks and uncertainties. Sunesis may not actually achieve the plans, intentions or expectations contained in such forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations contained in such forward-looking statements. Sunesis does not assume any obligation to update any such forward-looking statements.

Eric Bjerkholt, CFO
Sunesis Pharmaceuticals, Inc.,

BCC Partners
Karen L. Bergman or Michelle Coral
650.575.1509 or 415.794.8662