New drug SNS-032

Sunesis Pharmaceuticals, Inc. (Nasdaq: SNSS) announced today the dosing of the first patient in a Phase 1 clinical trial of SNS-032 in patients with advanced B-cell malignancies. SNS-032, a novel, selective and potent small-molecule inhibitor of cyclin-dependent kinases (CDK) 2, 7 and 9, has been shown in preclinical and clinical studies to deplete cells of myeloid cell leukemia sequence 1, or MCL-1, a protein associated with cell survival, particularly in lymphomas and other B-lymphoid malignancies.

"Based on non-clinical and Phase 1 pharmacodynamic data of SNS-032 from our ongoing trial in patients with advanced solid tumors, we are eager to learn more about this promising anticancer compound in patients with hematological cancers," said Daniel C. Adelman, M.D., Senior Vice President, Research & Development at Sunesis. "SNS-032 targets both cell-cycle and transcriptional-regulation pathways crucial to cancer cell growth and survival. SNS-032 is selective and potent, with IC50s for CDK2, 7 and 9 in the low nanomolar range. We are enthusiastic about initiating clinical trials in B-cell malignancies as we have seen evidence that SNS-032's mechanism of action may be particularly well-suited to indications including multiple myeloma, chronic lymphocytic leukemia, and mantle-cell lymphoma."

This Phase 1 trial is designed to examine the safety and tolerability, as well as the preliminary anti-tumor activity, of SNS-032 in patients with B- cell malignancies. The trial is a dose-escalation study to establish a maximum-tolerated dose in this setting. The clinical trial will enroll approximately 30-40 patients at three centers in the United States. Sunesis hopes to obtain initial safety results from this study by year end.

SNS-032 is a novel targeted inhibitor of CDKs 2, 7 and 9, which are critical in the communication and relay of signals to promote cellular growth and function. CDK2 is involved in cellular proliferation by regulating the initiation of and progression through the DNA-synthesis phase of the cell cycle. CDK7 and CDK9 are involved in transcriptional regulation of certain proteins involved in cell survival. Inappropriate activity by these CDKs can lead to unregulated proliferation, avoidance of apoptosis and increased cell survival, all of which are hallmarks of cancer. By selectively targeting these CDKs, SNS-032 may halt both aberrant cell proliferation and induce apoptosis.

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.

Sunesis Pharmaceuticals, Inc. http://www.sunesis.com/