Mechanism of action of vincristine in the treatment of ALL is:: (A) Inhibition of topoisomerase II to cause breaks in DNA strands, (B) Alkylation and cross linking DNA strands, (C) Inhibition of DNA mediated RNA synthesis, (D) Inhibition of polymerization of tubulin to form microtubules
Answer is D. 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.