KOSAN Biosciences, Inc. Announces Clinical Data To Be Presented At The 2006 Annual Meeting Of The American Society Of Clinical Oncology

HAYWARD, Calif., May 8 /PRNewswire-FirstCall/ -- Kosan Biosciences Incorporated announced today that clinical trial data from the company’s two lead oncology programs will be presented at the 2006 Annual Meeting of the American Society of Clinical Oncology (ASCO) in Atlanta, Georgia, June 2-6, 2006.

ASCO Overview

Kosan will present data from two Phase Ib clinical trials of its lead heat shock protein 90 (Hsp90) inhibitor product candidate, KOS-953, administered in combination with trastuzumab (Herceptin(R)) in patients with metastatic breast cancer, and with bortezomib (Velcade(R)) in patients with relapsed refractory multiple myeloma. The company will also present Phase I single-agent clinical trial results of intravenous KOS-1022, a second-generation Hsp90 inhibitor, in patients with advanced hematological malignancies. In its epothilone program, Kosan and its partner Roche will also present clinical data on KOS-862, the companies’ most advanced epothilone drug candidate, administered in combination with Herceptin in HER-2 positive metastatic breast cancer. In addition, data will be reported from two Phase I clinical trials of KOS-1584, a novel “fast-follower” epothilone product candidate with different pharmacokinetic properties than KOS-862 that may result in an improved safety and efficacy profile.

Hsp90 Inhibitor Program

Oral Presentation:

Abstract # 501: Phase I trial of KOS-953, a heat shock protein 90 inhibitor, and trastuzumab. (Oral presentation by Shanu Modi, M.D, Memorial Sloan-Kettering Cancer Center, New York, NY, on Saturday, June 3, 8:00-9:30 a.m.; Hall C1).

Poster Presentations:

Abstract # 2081: Phase I pharmacokinetic (PK) and pharmacodynamic (PD) study of the Hsp90 inhibitor, KOS-1022 (17-DMAG) in patients with refractory hematological malignancies. (Poster Session by Jeffrey Lancet, M.D., H. Lee Moffitt Cancer Center, Tampa, FL, on Sunday, June 4, 2:00-6:00 p.m., Hall B5).

Abstract # 3066: Phase I clinical trial of KOS-953 + bortezomib (BZ) in relapsed refractory multiple myeloma. (Poster Session by Asher Chanan-Khan, M.D., Roswell Park Cancer Center, Buffalo, NY, on Sunday, June 4, 2:00-6:00 p.m.; Hall B5).

In addition, Kosan’s collaborator, the National Cancer Institute, through its Cancer Therapy Evaluation Program (CTEP), will present clinical data on certain of its Hsp90 trials at ASCO. Included will be an oral presentation of data from a Phase I pharmacokinetic and pharmacodynamic study of 17-DMAG, or KOS-1022, in patients with advanced solid tumors (Abstract # 3021), and poster presentations of data from two Phase I studies of 17-AAG in pediatric patients with solid tumors (Abstracts # 9022 and # 9018).

Epothilone Program

Oral Presentation:

Abstract # 2003: First-in-human Phase I trial of a novel epothilone, KOS- 1584. (Oral presentation by Miguel Villalona-Celero, M.D., Ohio State University, Columbus, OH, on Tuesday, June 6, 8:00-11:00 a.m.; Room A302).

Poster Presentations:

Abstract # 2041: Phase I trial of a novel epothilone, KOS-1584, using a weekly dosing schedule. (Poster Session, by Alison Stopeck, M.D., University of Arizona, Tucson, AZ, on Sunday, June 4, 2:00-6:00 p.m.; Hall B5).

Abstract # 2028: A Phase I trial of weekly combination of KOS-862 (Epothilone D) and trastuzumab in HER-2 overexpressing malignancies. (Poster and Discussion Session, by Javier Cortes, M.D. Hospital Universitaro Vall D’Hebron, Barcelona, Spain, on Sunday, June 4, 2:00-6:00 p.m.; Room A311 and Discussion Session on Monday, June 4, 5:00-6:00 p.m., Room A411).

About Kosan

Kosan Biosciences is a biotechnology company advancing two new classes of anticancer agents through clinical development. Its Hsp90 inhibitor, KOS-953, is in Phase I and II clinical trials, primarily for multiple myeloma and HER2 positive breast cancer. KOS-953 is Kosan’s proprietary formulation of 17-AAG, a geldanamycin analog. In addition, intravenous and oral formulations of its second-generation Hsp90 inhibitor, KOS-1022, are currently in Phase I clinical trials. These compounds have a novel mechanism of action targeting multiple pathways involved in cancer cell growth and survival.

Kosan is also developing KOS-862 in Phase II clinical trials in breast cancer. KOS-862 is an epothilone with a mechanism of action similar to taxanes, one of the most successful classes of anti-tumor agents. Its follow- on epothilone, KOS-1584, is in Phase I clinical trials. Its epothilone program is partnered with Hoffmann-La Roche Inc. and F. Hoffmann-La Roche Ltd., collectively Roche, through a global development and commercialization agreement. For additional information on Kosan Biosciences, please visit the company’s website at www.kosan.com.

This press release contains forward-looking statements within the meaning of the “safe harbor” provisions of the Private Securities Litigation Reform Act of 1995 (the “Act”). Such forward-looking statements include statements relating to presentations of data from clinical studies of Kosan’s product candidates. Any statements contained in this press release that are not statements of historical fact may be deemed to be forward-looking statements. There are a number of important factors that could cause the results of Kosan to differ materially from those indicated by these forward-looking statements, including, among others, risks detailed from time to time in the Company’s SEC reports, including its Annual Report on Form 10-K for the year ended December 31, 2005 and other periodic filings with the SEC. Kosan does not undertake any obligation to update forward-looking statements.

NOTE: Herceptin(R) (trastuzumab) is a registered trademark of Genentech, Inc., and Velcade(R) (bortezomib) is a registered trademark of Millennium Pharmaceuticals, Inc.

Kosan Biosciences Incorporated

CONTACT: Robert G. Johnson, Jr., M.D., Ph.D., Chief Executive Officer ofKosan Biosciences, +1-510-732-8400, ext. 5243, or johnson@kosan.com

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