Kosan Biosciences (Nasdaq: KOSN - News) announced today at the 95th Annual Meeting of the American Association for Cancer Research in Orlando FL preclinical in vitro data on the cytotoxic and antiproliferative effects of Kosan's lead Hsp90 inhibitor 17-AAG when used in combination with 20 different standard and novel chemotherapeutics. Data from the study demonstrated broad synergistic activity consistent with the mechanism of action of Hsp90 inhibition. Clinical investigation of several of these combinations in humans is ongoing.

In the study the antiproliferative effects of combining 17-AAG and over 20 different anticancer agents in the human colon cancer cell line DLD-1 and breast cancer cell line SKBr3 were evaluated. The anticancer agents represented a broad range of mechanisms including alkylating agents antimetabolites anticancer antibiotics microtubule-interacting agents and protein kinase inhibitors. The results showed that in DLD-1 cells approximately 80% of the drugs demonstrated synergistic effects with 17-AAG whereas in SKBr3 cells approximately 50% of the drugs showed synergistic effects. More than 25% of the drugs including microtubule-interacting agents docetaxel vinblastine vincristine and KOS-862 were synergistic with 17-AAG in the colon and breast cancer cell lines regardless of treatment schedule.