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Sunesis Presents Results From Phase I Clinical and Preclinical Studies of SNS-595 at American Association for Cancer Research Meeting

04/04/06

SNS-595 Was Well Tolerated With Promising Signs of Clinical Activity

WASHINGTON, April 4, 2006 /PRNewswire-FirstCall via COMTEX News Network/ -- Sunesis Pharmaceuticals, Inc. (Nasdaq: SNSS) presented clinical and preclinical data on the company's lead compound, SNS-595 at the Annual Meeting of the American Association for Cancer Research (AACR).

In a poster titled "A Phase 1 trial of weekly SNS-595 in patients with refractory cancer," (abstract # 2074), Sunesis reported data from a dose-escalating clinical study of 21 patients with advanced solid tumors designed to examine the safety, tolerability and pharmacokinetics of a weekly dosing regimen. SNS-595 demonstrated promising signs of clinical activity, with 6 of 21 patients, or almost one-third, experiencing sustained disease control lasting at least 16 weeks, including a confirmed partial response at the maximum-tolerated dose in a patient with mesothelioma. SNS-595 was well tolerated; a dose-limiting toxicity of neutropenia was observed while other side effects were mild and consistent with the results from the company's prior Phase I study. Sunesis is currently conducting two Phase II clinical studies of SNS-595 among non-small cell lung cancer and small cell lung cancer patients, as well as a Phase I dose-escalation clinical study in patients with acute leukemias. The acute leukemia study is exploring two dose regimens, with weekly and twice-weekly dosing.

"SNS-595 appears to be a promising cancer therapeutic with a number of compelling characteristics. In two Phase I clinical studies in patients with a variety of advanced solid tumors, we have seen encouraging clinical activity, including two confirmed partial responses, and sustained disease control in almost one-third of the patients," said Daniel C. Adelman, M.D., Senior Vice President, Research and Development at Sunesis. "In addition, SNS-595 shows potential in both solid and hematologic tumors and we are encouraged by the compelling data from our clinical and preclinical studies that help inform our ongoing and future clinical trials."

Sunesis also presented SNS-595 preclinical data further elucidating the compound's mechanism of action and demonstrating that SNS-595 acts synergistically with a wide variety of chemotherapeutic agents in vitro and exhibits potent activity in vivo against hematologic malignancies. SNS-595 was found to be synergistic when combined with a number of chemotherapeutic drugs, including DNA-damaging agents, antimetabolites and an Hsp90 inhibitor, geldanamycin. In addition, preclinical studies of SNS-595 demonstrating potent anti-proliferative activity in human leukemic cell lines were used in the development of Sunesis' current Phase I clinical study among patients with acute leukemias.

About SNS-595

SNS-595 is a promising first-in-class cancer therapeutic currently in a Phase I acute leukemia clinical trial and Phase II non-small cell and small cell lung cancer clinical studies. 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.

About Sunesis' Oncology Programs

In addition to SNS-595, 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. SNS-032 is in a Phase I/II clinical study to examine the safety and preliminary anti-tumor activity among patients with a variety of solid tumors, including lung cancer, breast cancer or melanoma. SNS-032 is a potent and selective inhibitor of cyclin-dependent kinases 2, 7 and 9. 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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