Vincristine (brand name, Oncovin), also known as leurocristine,'s a vinca alkaloid from the Catharanthus roseus (Madagascar periwinkle), formerly Vinca rosea and hence its name. It's a mitotic inhibitor, and's used in cancer chemotherapy. Mode of action Tubulin's a structural protein which polymerises to form microtubules. The cell cytoskeleton and mitotic spindle, amongst other things, are made of microtubules. Vincristine binds to tubulin dimers, inhibiting assembly of microtubule structures.… (More on Vincristine)