Which antineoplastic agent blocks mitosis in metaphase by binding to microtubular proteins?

Vincristine is an antineoplastic agent that specifically works by inhibiting mitosis during the metaphase of cell division. It achieves this by binding to tubulin, a protein that is essential for the formation of microtubules, which are necessary for proper cell division. By preventing the assembly of microtubules, vincristine effectively halts the progression of the cell cycle at the metaphase stage, leading to cell death.

This mode of action is particularly significant in the treatment of various cancers, as it targets rapidly dividing cells. The effectiveness of vincristine in disrupting the mitotic process makes it a valuable drug in chemotherapy regimens for specific malignancies, such as leukemias and lymphomas.

Other antineoplastic agents listed have different mechanisms of action. For instance, carboplatin is a platinum-based compound that forms DNA cross-links, leading to apoptosis. Etoposide inhibits topoisomerase II, affecting DNA unwinding and replication, while cyclophosphamide is a alkylating agent that damages DNA by adding alkyl groups. Each of these agents plays a vital role in cancer treatment but does not function by blocking mitosis at metaphase. Thus, vincristine's specific targeted action on micro