Sunesis Issued Important U.S. Patent Covering Vosaroxin Clinical Formulation

Sunesis Pharmaceuticals, Inc. (NASDAQ: SNSS) today announced that the United States Patent and Trademark Office (USPTO) has granted U.S. Patent No. 7,829,577, claiming the Company's pharmaceutical compositions of lead drug candidate vosaroxin. This patent is scheduled to expire on March 14, 2025, and could be eligible for patent term extension beyond this date. Corresponding patent applications are pending in major markets throughout the world including Europe, Japan, Australia and Canada.

"This patent is an important new addition to our intellectual property estate, as it covers the formulation currently used in our clinical trials," stated Daniel Swisher, Chief Executive Officer of Sunesis. "Vosaroxin's extended patent life to 2025 increases not only the value of our AML franchise but also provides sufficient time for lifecycle evaluation of vosaroxin in other indications. We are pursuing a sophisticated and deliberate strategy to extend exclusive coverage in the vosaroxin patent estate beyond 2025. In addition to our granted patents, we have filed patent applications covering additional formulations, combination uses, dosing, manufacturing processes and composition of matter claims. We look forward to the successful prosecution of these patent applications in multiple territories around the world."

About Vosaroxin

Vosaroxin is a first-in-class anticancer quinolone derivative, or AQD, a class of compounds that has not been used previously for the treatment of cancer. Vosaroxin both intercalates DNA and inhibits topoisomerase II, resulting in replication-dependent, site-selective DNA damage, G2 arrest and apoptosis. Vosaroxin is currently being evaluated in a fully enrolled single agent Phase 2 clinical trial (known as the REVEAL-1 trial) in previously untreated elderly AML patients and in a fully enrolled Phase 2 clinical trial combining vosaroxin with cytarabine for the treatment of patients with relapsed/refractory AML. A Phase 2 single agent clinical trial in platinum-resistant ovarian cancer has also been completed. Sunesis plans to initiate the VALOR trial, a multinational, randomized, double-blind, placebo-controlled, pivotal Phase 3 clinical trial of vosaroxin in combination with cytarabine in a relapsed/refractory AML patient population, in the fourth quarter of this year.

About Sunesis Pharmaceuticals

Sunesis is a biopharmaceutical company focused on the development and commercialization of new oncology therapeutics for the treatment of solid and hematologic cancers. Sunesis has built a highly experienced cancer drug development organization committed to advancing its lead product candidate, vosaroxin, in multiple indications to improve the lives of people with cancer.

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

This press release contains forward-looking statements, including without limitation statements related to the prosecution of patent applications and Sunesis' plans to initiate a pivotal Phase 3 clinical trial of vosaroxin in the fourth quarter of this year. Words such as "evaluate," "planned," "will," "look forward" and similar expressions are intended to identify forward-looking statements. These forward-looking statements are based upon Sunesis' current expectations. Forward-looking statements involve risks and uncertainties. Sunesis' actual results and the timing of events could differ materially from those anticipated in such forward-looking statements as a result of these risks and uncertainties, which include without limitation, risks related to Sunesis' need for additional funding to fully finance the planned vosaroxin pivotal trial, the risk that Sunesis' development activities for vosaroxin could be halted or significantly delayed for various reasons, the risk that Sunesis' clinical studies for vosaroxin may not demonstrate safety or efficacy or lead to regulatory approval, the risk that data to date and trends may not be predictive of future data or results, the risk that Sunesis' nonclinical studies and clinical studies may not satisfy the requirements of the FDA or other regulatory agencies, risks related to the conduct of Sunesis' clinical trials, risks related to the manufacturing of vosaroxin, and the risk that Sunesis' proprietary rights may not adequately protect vosaroxin. These and other risk factors are discussed under "Risk Factors" and elsewhere in Sunesis' Quarterly Report on Form 10-Q for the quarter ended September 30, 2010 and other filings with the Securities and Exchange Commission. Sunesis expressly disclaims any obligation or undertaking to release publicly any updates or revisions to any forward-looking statements contained herein to reflect any change in the company's expectations with regard thereto or any change in events, conditions or circumstances on which any such statements are based.

SUNESIS and the logo are trademarks of Sunesis Pharmaceuticals, Inc.

Investor and Media Inquiries: David Pitts Argot Partners 212-600-1902 Eric Bjerkholt Sunesis Pharmaceuticals Inc. 650-266-3717