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Sunesis Presents Promising In Vivo Data on Aurora Kinase Program

02/28/05

Compound Discovered at Sunesis Shows Robust Activity in Xenograft Models

South San Francisco, CA, February 28, 2005 – Sunesis Pharmaceuticals, Inc. today presented positive results from in vivo studies of the company's Aurora kinase anti-cancer small molecule program at the Third International Protein Phosphorylation Drug Discovery World Summit being held February 28-March 1 in San Diego, CA.

In a talk entitled "Fragment-based Drug Discovery of Small Molecule Kinase Inhibitors," Sunesis presented promising results from preclinical testing of molecules from the company's Aurora kinase program. Sunesis' Aurora kinase inhibitors target cells in the mitotic phase of the cell cycle. In vivo results presented today demonstrate robust activity, including significant tumor growth retardation, exceeding 80 percent in multiple solid tumor mouse models. These results were consistent with compounds administered either orally or intraperitoneally (IP).

"We are very pleased by the broad and consistent pre-clinical anti-tumor activity demonstrated by our Aurora kinase inhibitors across multiple models," said Daniel Adelman, M.D., Senior Vice President of Drug Discovery and Development for Sunesis. "Kinases have long represented a significant opportunity for pharmaceutical development, and Sunesis' fragment-based drug discovery approach has enabled us to overcome key challenges involved with discovery of potent, selective kinase inhibitors and to rapidly advance our molecules forward."

Sunesis has built a portfolio of preclinical and development stage product candidates in oncology focused on novel pathways and targets, including inhibiting cell cycle and survival signaling. In addition to the company's Aurora kinase program now in preclinical evaluation, Sunesis is conducting Phase I clinical trials for its lead compound, SNS-595, a cell-cycle modulator that acts on proliferating cancer cells by inducing cell cycle arrest and apoptosis, or cell death. In cooperation with Biogen Idec, Sunesis is also developing novel small molecule inhibitors of Raf and other oncology kinases.

About Sunesis Pharmaceuticals
Sunesis is a clinical-stage biopharmaceutical company focused on the discovery, development and commercialization of small molecule therapeutics for oncology, inflammatory diseases and other unmet medical needs. Sunesis has built a product candidate portfolio through internal discovery and acquisition 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
www.sunesis.com.

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Forward-Looking Statement
This press release contains forward-looking statements concerning Sunesis Pharmaceuticals' and its product development plans, including plans to commence and conduct preclinical studies and clinical trials. Sunesis may not be successful in such plans.

Statements in this press release regarding Sunesis Pharmaceuticals' business which are not historical facts are "forward-looking statements" that involve risks and uncertainties. Forward-looking statements can be identified by, among other things, the use of forward-looking language, such as "anticipate," "believe," "could," "estimate," "expect," "future," "intends," "may," "plans," "should," "seeks," "potential," "will," or the negative of those terms, or other variations of those terms of comparable language, or by discussions of strategy or intentions. A number of important factors could cause actual results to differ materially from those projected or suggested in the forward-looking statements including, but not limited to, the ability of Sunesis to: (i) discover product candidates, (ii) successfully conduct preclinical studies and clinical trials of product candidates, (iii) obtain regulatory approval of any product candidates and (iv) obtain and enforce intellectual property rights. These statements speak only as of the date of this press release and the company assumes no obligation or responsibility to update or revise the statements.

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CONTACTS:
Investors:
Eric Bjerkholt
CFO of Sunesis Pharmaceuticals, Inc.
Tel: 650-266-3717

Media:
Karen Bergman or Michelle Corral
BCC Partners
Tel: 650-575-1509/415-794-8662