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Sunesis Presents Data on Anti-Cancer Compound SNS-032 at American Association for Cancer Research Meeting

04/04/06

SNS-032 Demonstrated to Have Dual Activity, Targeting Both Proliferation and Apoptosis

WASHINGTON, April 4, 2006 /PRNewswire-FirstCall via COMTEX News Network/ -- Sunesis Pharmaceuticals, Inc. (Nasdaq: SNSS) presented data at the Annual Meeting of the American Association for Cancer Research (AACR) highlighting the mechanism of action for SNS-032 and providing new insights into its potential benefits for the treatment of various cancers. SNS-032 is currently in a Phase I/II clinical study to identify the maximum-tolerated dose, examine its safety and preliminary evidence of anti-tumor activity in patients with advanced solid tumor malignancies, including lung cancer, breast cancer or melanoma.

Data presented today from in vitro studies of SNS-032 conducted by Sunesis demonstrate that the compound is a potent, highly selective inhibitor of Cyclin Dependent Kinases (CDK) 2, 7 and 9. CDK2 and CDK7 are key regulators of cell-cycle progression. CDK9 and CDK7 additionally play a role in transcriptional regulation, particularly affecting short-half-life proteins including several survival proteins such as MCL-1. Cells treated with SNS-032 demonstrate cell-cycle arrest and apoptosis (programmed cell death). In addition, researchers observed that SNS-032 acts to deplete cells of MCL-1, a protein associated with cancer cell survival, particularly in B-cell malignancies such as CLL and multiple myeloma. These data indicate that SNS- 032 targets both proliferation and apoptosis pathways and, in addition to treatment of solid tumors, may be a useful treatment for hematologic tumors. Sunesis plans to begin a Phase I clinical trial of SNS-032 in patients with advanced B-cell malignancies later this year.

"SNS-032's ability to both target cell proliferation and to circumvent the mechanism by which certain cancers avoid apoptosis underline SNS-032's potential to be a useful treatment of a variety of cancer types," said Daniel C. Adelman, M.D., Senior Vice President, Research and Development at Sunesis. "The studies being presented today for SNS-032 underscore that our R&D group has an established strength in identifying and elucidating our oncology drug candidates' mechanisms of action and pharmacological properties. We believe this expertise enables Sunesis to make informed clinical strategy decisions to advance our portfolio of cell cycle inhibitors efficiently through clinical development."

The poster containing these data, "SNS-032 is a potent and selective inhibitor of CDK 2, 7 and 9 and induces cell death by inhibiting cell cycle progression and the expression of antiapoptotic proteins (abstract # 2079) was presented in the Cell Cycle Components as Therapeutics session of the AACR.

About Sunesis' Oncology Programs

In addition to SNS-032, Sunesis has built a portfolio of preclinical- and development-stage product candidates in oncology focused on novel pathways and targets, including inhibition of the cell cycle and survival signaling. Sunesis' most advanced product candidate is SNS-595, a promising first-in- class cancer therapeutic currently in a Phase I acute leukemia trial and Phase II non-small cell and small cell lung cancer trials. SNS-595, a napthyridine analog, has a novel mechanism of action that selectively targets and kills proliferating cells during the DNA replication phase of the cell cycle. SNS- 595 works through the DNA-protein kinase and p73 dependent pathways to induce apoptosis, or programmed cell death. In clinical trials conducted to date, SNS-595 has been well tolerated and has shown promising signs of clinical activity. In earlier preclinical evaluation, SNS-595 demonstrated broad and potent activity across xenograft, syngeneic and drug-resistant models. Sunesis is currently conducting preclinical studies of its Aurora kinase inhibitor drug candidate, SNS-314. In addition, in cooperation with Biogen Idec, Sunesis is developing novel small molecule inhibitors of Raf kinase and other oncology kinases.

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.

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. For further information on Sunesis Pharmaceuticals, please visit http://www.sunesis.com .

SOURCE Sunesis Pharmaceuticals, Inc.

investors, Eric Bjerkholt, CFO of Sunesis Pharmaceuticals, Inc., +1-650-266-3717; or
media, Karen L. Bergman, +1-650-575-1509, or Michelle Corral, +1-415-794-8662, both
of BCC Partners for Sunesis Pharmaceuticals, Inc.
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