Cytokinetics Announces Interim Phase I Results for SB-743921 at the 2005 Annual Meeting of the American Society of Clinical Oncology.

SOUTH SAN FRANCISCO, Calif. -- Cytokinetics, Inc. (Nasdaq: CYTK) announced today that interim results from the Phase I clinical trial of SB-743921 being conducted by GlaxoSmithKline (GSK) were presented in a poster session at the 2005 Annual Meeting of the American Society of Clinical Oncology (ASCO) in Orlando, Florida. The presentation focused on the safety and tolerability of SB-743921, a novel small molecule inhibitor of kinesin spindle protein (KSP), a mitotic kinesin essential for proper cell division. SB-743921 is the second 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 the lead drug candidate from this program, ispinesib, formerly known as SB-715992.

The Phase I clinical trial is an ongoing, open-label, non-randomized, dose-finding trial for SB-743921. At the time of the interim analysis, 19 patients who collectively had a variety of advanced solid tumors had been enrolled and treated with SB-743921. The most frequent tumor types of patients in the clinical trial were colon, ovarian, hepatocellular and non-small cell lung cancer. All enrolled patients had relapsed or were refractory to previous treatment with a variety of standard chemotherapeutic regimens. These regimens included irinotecan, topotecan, gemcitabine, paclitaxel, vinblastine, cyclophosphamide and others.

The presentation entitled "Phase I study to determine tolerability and pharmacokinetics (PK) of SB-743921, a novel kinesin spindle protein (KSP) inhibitor" was presented on May 14, 2005 at 8:00 a.m. EDT by Dr. Kyle Holen, University of Wisconsin Comprehensive Cancer Center, Madison, Wisconsin. The principle objective of this clinical trial is to determine the safety profile and tolerability of SB-743921. Data were presented on patients who received doses of SB-743921 intravenously every 21 days. By study design, dose escalation continues until dose-limiting toxicities are observed. The dose-limiting toxicities to date are prolonged neutropenia, febrile neutropenia (with or without infection), elevated transaminases, hyperbilirubinemia and hyponatremia. In this clinical trial, SB-743921 appears to have an acceptable tolerability profile on the once every 21 day schedule. Neurotoxicities, mucositis, thrombocytopenia, alopecia and nausea/vomiting requiring pre-medication have not been observed. Determination of the maximally tolerated dose is still ongoing.

"This study suggests that SB-743921 has an acceptable tolerability profile for patients suffering from advanced solid tumors," stated Dr. James Sabry, Cytokinetics' President and Chief Executive Officer. "In addition, the safety and pharmacokinetic profiles of SB-743921 are adequately described to direct future studies."

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 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(TM) system and Cytometrix(TM) 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 and Phase Ib clinical trials for ispinesib (SB-715992) and a Phase I clinical trial for SB-743921, each a drug candidate that has emerged from the strategic alliance. Cytokinetics' heart failure program is the second program to leverage the company's expertise in cytoskeletal pharmacology. Cytokinetics expects to enter human clinical trials in 2005 with a novel small molecule cardiac myosin activator for the treatment of heart failure. 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 the expected timing, scope and results of our clinical development and research programs, including the initiation of clinical trials, and statements regarding the potential benefits of our drug candidates and potential drug candidates and the enabling capabilities of our 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 Cytokinetics' drug candidates that could slow or prevent clinical development, product approval or market acceptance (including the risks relating to uncertainty of patent protection for Cytokinetics' intellectual property or trade secrets, Cytokinetics' 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 Cytokinetics' business, investors should consult Cytokinetics' filings with the Securities and Exchange Commission.