DM4, a structural analogue of maytansine, is a new thiol-containing and potent maytansinoid. DM4 is a cytotoxic maytansinoid drug. It is synthesized in order to link maytansinoids to antibodies via disulfide bonds. Maytansinoids inhibit tubulin polymerization and microtubule assembly and enhance microtubule destabilization, so there is potent suppression of microtubule dynamics resulting in a mitotic block and subsequent apoptotic cell death.