An ansamycin antibiotic originally isolated from the Ethiopian shrub Maytenus serrata. Maytansine binds to tubulin at the rhizoxin binding site, thereby inhibiting microtubule assembly, inducing microtubule disassembly, and disrupting mitosis. Maytansine exhibits cytotoxicity against many tumor cell lines and may inhibit tumor growth in vivo. Check foractive clinical trials using this agent.