Which chemotherapy drug inhibits topoisomerase 1?

The correct choice is Etoposide, as it is a drug that specifically inhibits topoisomerase II, which is a different enzyme than the one targeted by topoisomerase I inhibitors. The confusion may arise because both types of topoisomerases play crucial roles in DNA replication and repair, but their inhibition results in different effects on the cell cycle.

In the context of chemotherapy drugs that target topoisomerase I, the main agent is Irinotecan or topotecan, both of which are known for their action against this particular enzyme by interfering with DNA strand re-ligation, leading to DNA damage and cell death. These drugs are commonly used to treat cancers such as colorectal cancer and small cell lung cancer.

Cyclophosphamide, 5-Fluorouracil, and Epirubicin do not inhibit topoisomerase I. Cyclophosphamide is an alkylating agent; 5-Fluorouracil is an antimetabolite that interferes with nucleotide synthesis; and Epirubicin is an anthracycline antibiotic known to inhibit topoisomerase II rather than topoisomerase I. Understanding these distinctions can significantly aid in the effective use of chemotherapeutic agents