Microtubule stabilization agent that promotes tubulin polymerization and induces G2-M cell cycle arrest (EC50 = 3 - 92 nM). Potently inhibits a variety of human cancer cell lines (IC50 values are 0.13 - 0.64 nM), including MDR cells overexpressing the P-glycoprotein efflux pump. Exhibits potent anticancer activity in numerous human tumor xenografts in vivo.