CYTOKINETICS AND GLAXOSMITHKLINE AMEND COLLABORATION AND LICENSE AGREEMENT

Exhibit 99.1

CYTOKINETICS AND GLAXOSMITHKLINE AMEND COLLABORATION AND LICENSE AGREEMENT

Cytokinetics to Assume Clinical Development Responsibilities for Ispinesib and SB-743921

Company Provides Clinical Update for Phase II Trial Evaluating Ispinesib in Patients with Breast Cancer

South San Francisco, CA, November 27, 2006 — Cytokinetics, Incorporated (Nasdaq: CYTK) announced an amendment of the company’s collaboration and license agreement with GlaxoSmithKline (GSK), under which Cytokinetics will assume responsibility for the costs and activities of continued development of the kinesin spindle protein (KSP) inhibitors ispinesib (SB-715992) and SB-743921, subject to GSK’s option to resume responsibility for some or all development and commercialization activities associated with each of these novel drug candidates.

Under the revised structure, Cytokinetics plans to conduct a focused development program for ispinesib specifically designed to supplement the broad series of Phase I and Phase II clinical trials sponsored by GSK that have demonstrated clinical activity in the treatment of patients with metastatic breast and lung cancers and that have shown an acceptable tolerability profile for ispinesib in combination with standard chemotherapeutics. Cytokinetics is considering plans to conduct a focused clinical trials program in breast cancer patients in 2007. This program would be designed to further define the clinical activity profile of ispinesib in advanced breast cancer in preparation for potentially initiating a Phase III clinical trial of ispinesib for the second-line treatment of advanced breast cancer . Concurrent with this supplemental program for ispinesib , the National Cancer Institute (NCI) is continuing ongoing Phase II and Phase I clinical trials with ispinesib and Cytokinetics is continuing an ongoing Phase I/II clinical trial of SB-743921 in non-Hodgkin’s lymphoma (NHL) that was initiated earlier this year.

"We are pleased to have the opportunity to sponsor additional activities focused to advancing ispinesib as a potential next-generation approach for the treatment of breast cancer alongside our ongoing clinical trial now underway with SB-743921," stated James H. Sabry, M.D., Ph.D., Cytokinetics’ Chief Executive Officer. "We believe that the clinical trials data generated by GSK, alongside data arising from NCI sponsored trials, should serve as a foundation for a focused and cost effective development program going forward."

"We have been engaged with GSK in a collaboration for over five years. Our research and development collaboration activities have yielded two novel drug candidates and one potential drug candidate for the treatment of cancer," stated Andrew A. Wolff, M.D., F.A.C.C., Cytokinetics’ Senior Vice President of Clinical Research and Development and Chief Medical Officer. "We look forward to reviewing additional clinical trials data for ispinesib and SB-743921 and are pleased to take a more prominent role in ongoing development activities."

Update Regarding Phase II Trial Evaluating Ispinesib in Patients with Breast Cancer

GSK conducted a two-stage Phase II clinical trial designed to evaluate the safety and efficacy of ispinesib in the second- or third-line treatment of patients with locally advanced or metastatic breast cancer whose disease had recurred or progressed despite treatment with anthracyclines and taxanes. In this clinical trial, patients received ispinesib as monotherapy at 18 mg/m ² as a 1 hour infusion once every 21 days. As previously announced, in Stage 1 of this clinical trial, the best overall responses observed were 3 partial responses (as measured by the Response Evaluation Criteria in Solid Tumors, or RECIST) among 33 evaluable patients. These 3 patients had maximum decreases in tumor size ranging from 46% to 68% with the durations of response ranging from 7.1 weeks to 13.4 weeks. The most common adverse event was Grade 4 neutropenia. While fully analyzed data from Stage 2 of this clinical trial have not yet been provided to Cytokinetics, GSK has recently informed the company that the trial has been closed to enrollment at 50 patients and that an additional independently confirmed partial response was observed in the trial.

Moreover, as previously presented at the 18th Annual EORTC-NCI-AACR Symposium on Molecular Targets and Cancer Therapeutics in Prague, Czech Republic, a scientific poster entitled, "Phase I Study of Ispinesib (SB-715992), a Kinesin Spindle Protein Inhibitor, in Combination with Capecitabine in Patients with Advanced Solid Tumors," contained data from

- more -

Cytokinetics Collaboration Amendment Announcement
Page 2

an ongoing clinical trial demonstrating that the combination of ispinesib and capecitabine may have an acceptable tolerability profile on the clinical trial’s treatment schedule. The optimally tolerated regimen in this clinical trial has yet to be defined. However, the maximum tolerated dose of ispinesib of 18 mg/m ² , administered as an intravenous infusion every 21 days, was tolerated with therapeutic doses of capecitabine , specifically daily oral doses of 2000 mg/m ² and 2500 mg/m ² for 14 days of a 21 day cycle, and plasma concentrations of ispinesib were not affected by the presence of capecitabine . Dose limiting toxicities observed included Grade 2 rash that did not allow 75% of the capecitabine doses to be delivered and prolonged Grade 4 neutropenia. In this clinical trial, a total of 12 patients (including 4 with breast cancer, 3 with colorectal cancer, 3 with bladder cancer, 1 with thyroid cancer and 1 with tongue cancer) out of 24 total patients had a best response of stable disease as defined by the RECIST criteria (median 2.25 months, duration 2-12 months). A patient with breast cancer had the longest duration of stable disease at 12 months.

Terms of November 2006 Amendment to Collaboration Agreement

Under the terms of the November 2006 amendment to the collaboration agreement, Cytokinetics, at its expense, will assume responsibility for the continued research, development and commercialization of inhibitors of KSP, including ispinesib and SB-743921, and other mitotic kinesins, other than centromere-associated protein E (CENP-E) which is the focus of translational research activities being conducted by GSK and Cytokinetics and development activities being conducted by GSK. The ongoing activities for CENP-E are coordinated under an agreed joint research program during an extended research term under the June 2006 amendment to the collaboration agreement. Under the November 2006 amendment, Cytokinetics’ development of ispinesib and SB-743921 is subject to GSK’s option to resume responsibility for the development and commercialization of either or both drug candidates during a defined period and in accordance with agreed terms. If GSK exercises its option for a drug candidate, it will pay Cytokinetics an option fee equal to the costs Cytokinetics independently incurred for that drug candidate, plus a premium intended to compensate Cytokinetics for the cost of capital associated with such costs, subject to an agreed limit for such costs and premium. Upon GSK exercising its option for a drug candidate, Cytokinetics may receive additional pre-commercialization milestone payments with respect to such drug candidate and increased royalties on net sales of any resulting product, in each case, beyond those contemplated under the original agreement. If GSK does not exercise its option for a drug candidate, Cytokinetics will be obligated to pay royalties to GSK on the sales of any resulting products. The November 2006 amendment supersedes a previous amendment to the collaboration agreement dated September 2005, which specifically related to SB-743921.

Cytokinetics is considering a development plan for the further evaluation of ispinesib for the treatment of breast cancer and may further explore the combination treatment approach of ispinesib