Cytokinetics Announces Phase I Results for SB-715992 presented at the 2004 Annual Meeting Of The American Society of Clinical Oncology

Safety and Tolerability Profile of SB-715992 Supports Initiation of Broad Phase II Program

South San Francisco, CA - June 7, 2004

Cytokinetics, Inc. (Nasdaq: CYTK) announced today that the results of two Phase I studies for SB-715992 conducted by GlaxoSmithKline were presented in oral and poster presentations at the 2004 Annual Meeting of the American Society of Clinical Oncology (ASCO) in New Orleans. The presentations focused on the safety and tolerability of SB-715992, a novel small molecule inhibitor of kinesin spindle protein (KSP), a mitotic kinesin protein essential for proper cell division. SB-715992 is the lead drug candidate in clinical development arising from a broad strategic collaboration between Cytokinetics and GlaxoSmithKline to discover, develop and commercialize novel small molecule therapeutics targeting human mitotic kinesins for applications in the treatment of cancer and other diseases. GlaxoSmithKline has initiated a broad Phase II clinical trial program for SB-715992.

The Phase I trials were open-label, non-randomized, dose-finding trials designed to study the safety, tolerability, pharmacokinetic and pharmacodynamic profile of SB-715992. In total, 75 patients with multiple advanced solid tumors were enrolled and treated with SB-715992 in these trials. The more common tumor types were colon, renal cell carcinoma, sarcoma, breast and lung cancer. All enrolled patients had relapsed or had been refractory to previous treatment with a variety of standard chemotherapeutic regimens that included, but were not limited to, drugs such as irinotecan, topotecan, gemcitabine, paclitaxel, vinblastine, and cyclophosphamide.

The presentation entitled “Phase I trial of novel kinesin spindle protein (KSP) inhibitor SB-715992 IV days 1, 8, 15, q 28 days” was presented on June 6, 2004 by Dr. Howard Burris, The Sarah Cannon Cancer Center, Nashville, TN. The principle objective of this trial was to determine the safety profile and tolerability of SB-715992. Within this dose-escalating trial, 30 patients received doses of SB-715992 intravenously on days 1, 8 and 15 over a 28-day period. By study design, dose escalation continued until dose-limiting toxicities were observed. The dose limiting toxicity was neutropenia preventing day 15 dosing in 2 of 3 patients. Neurotoxicities and alopecia were not observed; minimal GI toxicities, with a single event of greater than Grade 2 reported and were not considered dose-limiting. SB-715992 was well-tolerated in this advanced disease setting at all dose levels. Prolonged disease stabilization, ranging from 16 to more than 32 weeks, was observed in 8 of 30 patients representing a variety of tumor types.

A poster entitled “Phase I trial of novel kinesin spindle protein (KSP) inhibitor SB-715992 IV q 21 days” was presented on June 7, 2004 by Dr. Quincy Chu, Cancer Therapy and Research Center (CTRC), San Antonio, TX. The principle objective of this trial was also to determine the safety profile and tolerability of SB-715992 but under a different dosing schedule than that used in the Phase I trial mentioned above. Within this dose-escalating trial, 45 patients received doses of SB-715992 intravenously every 21 days. By study design, dose escalation continued until dose limiting toxicities were observed. The dose limiting toxicity was neutropenia for five or more days. In this study, SB-715992 was well-tolerated in this advanced disease setting at all dose levels. Prolonged disease stabilization, ranging from 7 to 43 weeks, was observed in 15 of 45 patients in a variety of tumor types. Neurotoxicities were not prevalent; alopecia was not reported. Based on the results of these trials, the 18 mg/m2 dose level was selected as a recommended Phase II dose for this dosing schedule.

“These studies suggest that SB-715992 may be well tolerated for patients suffering from advanced solid tumors,” stated Dr. James Sabry, Cytokinetics’ President and Chief Executive Officer. “Based on these data, GlaxoSmithKline has initiated a broad Phase II clinical trials program for SB-715992 and is also collaborating with the National Cancer Institute to evaluate the efficacy and clinical role of this novel, next generation cancer therapeutic in a variety of solid and hematological malignancies. The Phase II program will include non-small cell lung, breast, ovarian, colorectal, renal, head and neck, prostate, melanoma and hematological cancers.”

About Cytokinetics

Cytokinetics is a leading biopharmaceutical company focused on the discovery, development and commercialization of novel small molecule drugs that specifically target the cytoskeleton. The cytoskeleton is a complex biological infrastructure that plays a fundamental role within every human cell. Cytokinetics’ focus on the cytoskeleton enables it to develop novel and potentially safer and more effective classes of drugs directed at treatments for cancer, cardiovascular disease, fungal diseases and other diseases. Cytokinetics has developed a cell biology driven approach and proprietary technologies to evaluate the function of many interacting proteins in the complex environment of the intact human cell. Cytokinetics employs the PUMA™ system and Cytometrix™ technologies to enable early identification and automated prioritization of compounds that are highly selective for their intended protein targets without other cellular effects, and are thereby less likely to give rise to clinical side effects. Cytokinetics and GlaxoSmithKline have entered into a strategic alliance to discover, develop and commercialize small molecule therapeutics targeting human mitotic kinesins for applications in the treatment of cancer and other diseases. GlaxoSmithKline is conducting Phase II clinical trials for SB-715992 and a Phase I clinical trial with SB-743921, each a drug candidate that has emerged from the strategic alliance. Additional information about Cytokinetics can be obtained at www.cytokinetics.com.

This press release contains forward-looking statements for purposes of the Private Securities Litigation Reform Act of 1995 (the “Act”). Cytokinetics disclaims any intent or obligation to update these forward-looking statements, and claims the protection of the Safe Harbor for forward-looking statements contained in the Act. Examples of such statements include, but are not limited to, statements relating to advancing clinical development of SB-715992, SB-742921 and progressing Cytokinetics’ research programs and statements regarding the potential benefits of the Cytokinetics' drug candidates and the enabling capabilities of its proprietary technologies. Such statements are based on management’s current expectations, but actual results may differ materially due to various factors. Such statements involve risks and uncertainties, including, but not limited to, those risks and uncertainties relating to difficulties or delays in development, testing, regulatory approval, production and marketing of the Company’s drug candidates that could slow or prevent clinical development, product approval or market acceptance (including the risk that uncertainty of patent protection for the Company’s intellectual property or trade secrets, the Company’s ability to obtain additional financing if necessary and unanticipated research and development and other costs). For further information regarding these and other risks related to the Company’s business, investors should consult the Company’s filings with the Securities and Exchange Commission.