Roche And KOSAN Biosciences, Inc. (KOSN) Breast Cancer Phase II Trial To Proceed 
10/19/2005 5:13:12 PM

HAYWARD, Calif., April 5 /PRNewswire-FirstCall/ -- Kosan Biosciences Incorporated today announced that its Phase II clinical trial of KOS-862 (Epothilone D) as monotherapy for patients with metastatic breast cancer will proceed to full enrollment of the study following the successful completion of the interim analysis. The multi-center Phase II study is being conducted according to a two-stage Simon trial design, in which the primary objective must be met in the first stage of the trial before proceeding to the second stage.

"The decision to proceed to the next step of this Phase II study in breast cancer is encouraging. We look forward to presenting data in the first half of this year that will detail the response rates obtained in this trial to date. We are also evaluating KOS-862 in a Phase II monotherapy trial in prostate cancer, based on positive experience reported for the epothilone class of drugs in this indication," said Daniel V. Santi, M.D., Ph.D., Chairman and Chief Executive Officer of Kosan. "In addition, we have advanced a next-generation epothilone, KOS-1584, into Phase I clinical testing."

Peter Hug, The Global Head of the Roche Pharma Partnering Division, added, "Roche is confident in the potential of epothilones as important anticancer agents. We are pleased that the Roche-Kosan collaboration continues to move KOS-862 through the appropriate efficacy trials."

KOS-862 is a polyketide that inhibits cancer cells by the same mechanism as paclitaxel, and preclinical models have shown the compound to be effective against paclitaxel-resistant tumors. In addition to the Phase II monotherapy trials in breast and prostate cancer, Roche and Kosan are evaluating KOS-862 in three ongoing Phase Ib combination studies with Gemzar(R), Paraplatin(R) and Herceptin(R).

Roche and Kosan initiated their global development and commercialization agreement for KOS-862 and its back-up compounds in September 2002. According to the agreement, Roche has the worldwide exclusive right to market and sell KOS-862 and epothilone analogs owned by or licensed to Kosan for the treatment of cancer; Kosan will co-develop and has the right to co-promote Kosan/Roche epothilone products in the U.S. for the treatment of cancer.

About Kosan

Kosan Biosciences has two first-in-class anticancer agents in Phase II and Phase Ib clinical trials: KOS-862 (Epothilone D) and 17-AAG, an Hsp90 inhibitor and geldanamycin analog. KOS-862, the Company's lead drug candidate, has a mechanism of action similar to taxanes and is partnered with Roche in a global development and commercialization agreement, along with a follow-on compound, KOS-1584, currently in Phase I testing. 17-AAG targets multiple pathways required for tumor growth and is being developed in collaboration with the National Cancer Institute, in addition to a second-generation geldanamycin analog, KOS-1022 (DMAG), now in Phase I trials. Kosan also has a proprietary formulation of 17-AAG, called KOS-953, in Phase I and Phase Ib trials. Kosan has generated a pipeline of potentially significant products for cancer, infectious disease and other therapeutic areas based on its proprietary technologies for discovering, developing and manufacturing polyketide analogs. Polyketides are an important class of natural products that have yielded numerous pharmaceuticals for the treatment of cancer, infectious diseases, high cholesterol, transplant rejection and other diseases. For additional information on Kosan Biosciences, please visit the Company's website at

This press release contains "forward-looking" statements, including statements relating to ongoing and further development of KOS-862 and KOS-1584 in the treatment of cancer. 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 related to the clinical advancement of KOS-862 and other compounds and Kosan's dependence on the collaboration with Roche and other 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, 2004, and other periodic filings with the SEC. Kosan does not undertake any obligation to update forward-looking statements.

Kosan Biosciences Incorporated

CONTACT: Susan M. Kanaya, Chief Financial Officer, +1-510-732-8400,ext. 5227, or; or Shari Annes, +1-650-888-0902 (cell), or+1-510-731-5260, or, both of Kosan Biosciences