A compound isolated from the myxobacterium Sorangium cellulosum. Similar to paclitaxel, epothilone B induces microtubule polymerization and stabilizes microtubules against depolymerization conditions. In addition to promoting tubulin polymerization and stabilization of microtubules, this agent is cytotoxic for cells overexpressing P-glycoprotein, a characteristic that distinguishes it from the taxanes. Epothilone B may cause complete cell-cycle arrest