Kosan to Reacquire Epothilone Program ...( Kosan to Commence Phase 2 C...)

Kosan to Commence Phase 2 Clinical Program for KOS-1584

HAYWARD, Calif., Oct. 25 /PRNewswire-FirstCall/ -- Kosan Biosciences Incorporated (Nasdaq: KOSN) today announced that Roche and Kosan are concluding their epothilone development and commercialization collaboration. The collaborative research, development and commercialization agreement entered into in September 2002 will terminate after a transition period, following which Kosan will reacquire worldwide rights to its epothilone program and have full control of clinical development of KOS-1584 and its other epothilone product candidates going forward.

"Based on our discussions with Roche, we believe that the ending of our epothilone collaboration has been driven by a re-prioritization within Roche's research and development group rather than the value of our epothilone program," said Robert G. Johnson, Jr., M.D., Ph.D., Kosan's President and Chief Executive Officer. "Our control of the program permits us to determine the optimal strategy for advancing KOS-1584 into larger-scale clinical trials, potentially with a new collaborative partner, which we plan to actively seek. In the meantime, we intend to commence a Phase 2 clinical program. We continue to believe that KOS-1584 has best-in-class potential in the emerging epothilone market."

Roche believes that KOS-1584 is worthy to proceed into Phase 2 clinical trials, and that the Roche-Kosan collaboration has been highly productive," said Dan Zabrowski, Global Head of Roche Pharma Partnering. "We believe that Kosan is in the best position to exploit the therapeutic and commercial potential of KOS-1584. Kosan has been an excellent development partner, and we have appreciated the opportunity to
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