Cytokinetics Announces the Initiation of an Additional Phase II Clinical Trial for Lead Cancer Drug Candidate

Company Provides Update on Clinical Trials Program for SB-715992 and SB-743921

South San Francisco, CA - December 16, 2004

Cytokinetics, Inc. (Nasdaq: CYTK) today announced that GlaxoSmithKline (NYSE: GSK) has initiated an additional Phase II clinical trial of SB-715992, a small molecule inhibitor of kinesin spindle protein (KSP). This Phase II clinical trial is an international, 35-patient open-label monotherapy study designed to evaluate the safety and efficacy of SB-715992 at 18 mg/m² dosed every three weeks in the second-line treatment of patients with advanced ovarian cancer previously treated with a platinum and taxane-based regimen. The primary endpoint of this trial is response rate as determined by RECIST criteria and CA-125 levels. This study is the third Phase II clinical trial now underway to evaluate the potential anti-cancer effect of SB-715992 in solid tumor cancers.

"We are pleased that this next Phase II clinical study of SB-715992 is now enrolling patients. This additional trial expands the clinical program now underway with SB-715992 in taxane-sensitive tumor types," stated Andrew A. Wolff, MD, FACC, Cytokinetics' Senior Vice President, Clinical Research and Development and Chief Medical Officer. "The three Phase II studies conducted by GSK, as well as the additional six sponsored by the National Cancer Institute, should provide highly informative insights into the potential role that KSP inhibitors may play in a broad array of both solid and hematological cancers."

Other ongoing Phase II clinical trials of SB-715992 under GSK sponsorship are described below:

· NSCLC: GSK continues to enroll patients in an international, 70-patient Phase II monotherapy clinical trial evaluating the safety and efficacy of SB-715992 at 18 mg/m² every three weeks in the second-line treatment of patients with both platinum-sensitive and platinum-refractory non-small cell lung cancer. The trial's primary endpoint is response rate as determined using RECIST criteria.

· Breast: GSK continues to enroll patients in an international, 55-patient Phase II monotherapy clinical trial evaluating the safety and efficacy of SB-715992 at 18 mg/m² every three weeks in the second- or third-line treatment of patients with breast cancer whose disease has progressed despite treatment with anthracyclines and taxanes. The trial's primary endpoint is response rate as determined using RECIST criteria.

In addition to these Phase II clinical trials, GSK also recently began two additional dose-escalating Phase Ib clinical trials of SB-715992. These two studies are designed to evaluate the safety, tolerability, and pharmacokinetics of this novel drug candidate, in one study in combination with capecitabine and in the other, in combination with carboplatin. Concurrent with these studies, GSK continues to enroll patients in a third Phase Ib trial designed to evaluate SB-715992 in combination with docetaxel.

In parallel with the GSK-sponsored trials, the National Cancer Institute (NCI) will be conducting several additional Phase II and Phase I clinical trials that will further evaluate the safety and efficacy of SB-715992 across a variety of tumor types. The NCI-sponsored Phase II trials are described in more detail below:

· Colorectal: A Phase II trial of 75 patients to study SB-715992 in the second-line treatment of colorectal cancer. This open label, monotherapy study will contain two arms that evaluate different dosing schedules of SB-715992, either infused at 7 mg/m² on days 1, 8 and 15 of a 28-day schedule or at 18 mg/m² every three weeks. The primary endpoint is objective response as determined using RECIST criteria.

· Prostate: A Phase II trial of 40 patients to study SB-715992 in the second-line treatment of patients with hormone-refractory prostate cancer that has progressed after treatment with a single taxane-containing regimen. This open-label monotherapy study will evaluate SB-715992 infused at 18 mg/m² every three weeks. The primary endpoint is objective response as determined by PSA.

· Renal Cell: A Phase II trial of 29 patients to study SB-715992 in the second-line treatment of renal cell cancer. This open-label monotherapy study will evaluate SB-715992 infused at 18 mg/m² every three weeks. The primary endpoint is objective response as determined using RECIST criteria.

· Hepatocellular: A Phase II trial of 30 patients to study SB-715992 in the setting of hepatocellular cancer that has not been treated with any systemic chemotherapy. This open-label monotherapy study will evaluate SB-715992 infused at 18 mg/m² every three weeks. The primary endpoint will be objective response as determined using RECIST criteria.

· Head and Neck: A Phase II trial of 33 patients to study SB-715992 in the second-line treatment of head and neck cancer. This open-label monotherapy study will evaluate SB-715992 infused at 18 mg/m² infused every three weeks. The primary endpoint is objective response as determined using RECIST criteria.

· Melanoma: A Phase II trial of 25 patients to study SB-715992 in melanoma. Patients may have received adjuvant immunotherapy but no chemotherapy. This open-label monotherapy study will evaluate SB-715992 infused at 18 mg/m² every three weeks. The primary endpoint is objective response as determined using RECIST criteria.

In addition to these Phase II clinical trials, the NCI will be conducting two dose-escalating Phase I clinical trials to examine the safety, pharmacokinetics and pharmacodynamics of SB-715992 on a different dosing schedule with the study drug infused on days 1, 2 and 3 every three weeks. One of these studies is in the setting of acute leukemia refractory to standard induction therapy and the other is in the setting of histologically proven solid tumors that have failed all standard therapies.

Other Collaboration Activities
Cytokinetics and GSK established a major collaboration in June 2001 to discover, develop and commercialize small molecule therapeutics targeting human mitotic kinesins for applications in the treatment of cancer and other diseases. SB-715992 is the most advanced drug candidate to emerge from joint research and development activities. A second, structurally distinct KSP inhibitor, SB-743921, entered Phase I clinical trials in 2004. GSK continues to enroll patients in an open-label, dose-escalating Phase I clinical trial evaluating the safety, tolerability, and pharmacokinetics of this drug candidate in patients with advanced cancer. Collaborative research activities continue to be fruitful as the companies plan to advance compounds active against other mitotic kinesins towards development.

Background on KSP Inhibitors
Since their introduction over 40 years ago, anti-mitotic drugs (taxanes and vinca alkaloids) have advanced the treatment of cancer and are commonly used for the treatment of several tumor types. However, these drugs have demonstrated limited treatment benefit against certain cancers. In addition, these drugs target tubulin, a cytoskeletal protein involved not only in mitosis and cell proliferation, but also in other important cellular functions. Inhibition of these other cellular functions produces dose-limiting toxicities such as peripheral neuropathy, an impairment of the peripheral nervous system. Neuropathies result when these drugs interfere with the dynamics of microtubule filaments that are responsible for the long-distance transport of important cellular components within nerve cells.

Cytokinetics' cancer drug candidates, SB-715992 and SB-743921, are structurally distinct small molecule compounds that modulate cell proliferation and promote cancer cell death by specifically inhibiting KSP. KSP is a mitotic kinesin that is essential for cell proliferation, a process which when unregulated, results in tumor growth. Mitotic kinesins are essential to mitosis, and, unlike tubulin, appear to have no role in unrelated cellular functions. Drugs that inhibit KSP and other mitotic kinesins may represent the next generation of anti-mitotic cancer drugs by arresting mitosis and cell proliferation without impacting unrelated, normal cellular functions, avoiding many of the toxicities commonly experienced by patients treated with existing anti-mitotic drugs.

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 and Phase Ib clinical trials for SB-715992 and a Phase I clinical trial for SB-743921, each a drug candidate that has emerged from the strategic alliance. Additional information about Cytokinetics can be obtained at www.cytokinetics.com.

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