Epothilones: tubulin polymerization as a novel target for prostate cancer therapy

Microtubules are vital and dynamic cellular organelles and many agents have been developed that target them. The cytotoxic effects of taxanes and epothilones are mediated by stabilization of microtubule dynamics. Taxanes are one of the most effective cytotoxic agents, and have a broad spectrum of antitumor activity. However, their efficacy is limited by the development of resistance to these effects. Epothilones have a similar mechanism of action to taxanes, but a decreased propensity for drug resistance. Epothilones are macrolides, and have in vitro and in vivo activity in taxane-resistant or taxane-insensitive human cancer cell lines. Several epothilones are in clinical development: ixabepilone, patupilone, BMS-310705, KOS-862, KOS-1584, and ZK-EPO. Multiple dosing schedules of ixabepilone and patupilone have been studied. The toxicity profiles of epothilones are quite diverse and depend on the compound and the administration schedule. The epothilones have demonstrated a wide range of clinical activity, including important antitumor effects, in advanced prostate cancer. Epothilones are particularly useful in patients with prostate cancer who have previously been treated with taxanes or who have taxane-refractory tumors. In the setting of castrate metastatic prostate cancer, ixabepilone and patupilone showed encouraging clinical activity in the phase II setting and further studies are needed to determine if they provide additional clinical benefit to patients with advanced disease.