<prompt> Mechanism of action of vincristine in the treatment of ALL is:Inhibition of topoisomerase II to cause breaks in DNA strandsAlkylation and cross linking DNA strandsInhibition of DNA mediated RNA synthesisInhibition of polymerization of tubulin to form microtubules  <response>: Vinca alkaloids like vincristine and vinblastine act by inhibiting the formation of mitotic by spindle inhibiting polymerization of tubulin. These drugs are selective for M phase of cell cycle. 