New Dosing Schedule Suggests Potential Amplified Clinical Activity of This Novel KSP Inhibitor

SOUTH SAN FRANCISCO, CA -- (Marketwire) -- 06/02/09 -- Cytokinetics, Incorporated (NASDAQ: CYTK) announced today that a poster presentation summarizing interim data from the Phase I portion of a Phase I/II clinical trial evaluating ispinesib, a novel inhibitor of kinesin spindle protein (KSP), in patients with locally advanced or metastatic breast cancer was presented at the 2009 Annual Meeting of the American Society of Clinical Oncology (ASCO) held from May 29 - June 2, 2009 in Orlando, FL. This poster highlights the safety and tolerability of ispinesib and tumor-reductions of 30 percent in 3 patients in this ongoing Phase I/II clinical trial of ispinesib dosed on days 1 and 15 of a 28-day cycle. In this trial, ispinesib appears to demonstrate anti-cancer activity with a similar toxicity profile when compared with prior clinical trials conducted with a once every 21 days dosing schedule.

"In the ongoing Phase I portion of this Phase I/II clinical trial, we have observed signs of clinical activity for ispinesib in patients with locally advanced or metastatic breast cancer without our having yet reached the maximum-tolerated dose," stated Henry Gomez, M.D., Instituto Nacional de Enfermedades Neoplasicas, Lima, Peru. "Amplification of the anti-cancer signal on this newer dosing schedule, combined with a favorable tolerability profile, suggests the potential for this drug candidate in the treatment of metastatic breast cancer patients."

"The dosing schedule, an intravenous 1-hour infusion on days 1 and 15 of a 28-day cycle, studied in this Phase I/II clinical trial appears to be both well-tolerated and generating encouraging signs of clinical activity," stated Andrew A. Wolff, MD, FACC, Cytokinetics' Senior Vice President of Clinical Research and Development and Chief Medical Officer. "We look forward to continuing the dose-escalation of ispinesib in this trial as we explore the possible role of this novel drug candidate in patients with metastatic breast cancer."

Poster Presentation at ASCO

A poster titled, "A Phase I/II Trial of Ispinesib, a Kinesin Spindle Protein (KSP) Inhibitor, Dosed q14d in Patients with Advanced Breast Cancer Previously Untreated with Chemotherapy for Metastatic Disease or Recurrence" was presented on Monday, June 1, 2009. This poster summarized interim data from the Phase I portion of an ongoing Phase I/II clinical trial evaluating ispinesib in patients with advanced breast cancer. The primary objectives of the Phase I portion of this clinical trial are to determine the dose-limiting toxicities (DLTs) and maximum-tolerated dose and to assess the safety and tolerability of ispinesib administered as a 1-hour intravenous infusion on days 1 and 15 of a 28-day cycle. The secondary objectives are to characterize the pharmacokinetics of ispinesib on this schedule and to evaluate the potential effect of ispinesib on biomarkers of cell proliferation in patients with accessible tumors. The authors concluded that one Response Evaluation Criteria in Solid Tumors (RECIST)-confirmed partial response (PR) with a duration of 6 months has been reported.