Which mechanism best describes the action of vinca alkaloids?

• A. Interfering with topoisomerase I
• B. Inhibiting microtubule polymerization during cell division
• C. Alkylating DNA
• D. Inhibiting DNA synthesis

Answer: (B)

Vinca alkaloids block mitosis by binding to tubulin and preventing microtubule polymerization. Microtubules form the mitotic spindle, which is needed for chromosomes to align and separate during cell division. When polymerization is inhibited, the spindle cannot form properly, cells arrest in metaphase and undergo apoptosis. This cytoskeletal target is different from the DNA-focused actions described by the other options: topoisomerase I inhibitors affect DNA topology during replication, alkylating agents crosslink DNA, and antimetabolites disrupt DNA synthesis in S phase. So the action that best fits vinca alkaloids is inhibition of microtubule polymerization during cell division.