Biochem/physiol Actions

(-)-Epothilone A is a microtubule (MT) stabilizing drug and natural macrolide antitumor from myxobacteria Sorangium cellulosum. EpoA exhibits kinetics similar to paclitaxel by inducing tubulin polymerization in vitro and producing enhanced microtubule stability and bundling in cultured cells. In contrast to paclitaxel, Epothilone A exhibits a greater cytotoxicity against P-glycoprotein-expressing multidrug resistant (MDR) cells (IC₅₀ = 20 nM for MDR CCRF-CEM/VBL₁₀₀ cells). Epothilone A is a competitve inhibitor of ³H-paclitaxel binding with comparable IC₅₀ to paclitaxel in displacement competition assays. EpoA causes cell cycle arrest at the G₂/M transition leading to cytotoxicity.