Which medication inhibits thymidylate synthase, affecting DNA synthesis?

The medication that inhibits thymidylate synthase and thereby affects DNA synthesis is 5-Fluorouracil (5-FU). This drug functions primarily as an antimetabolite, mimicking uracil and serving as a pyrimidine analogue.

5-FU is incorporated into RNA and ultimately interferes with RNA processing and function. Additionally, it inhibits thymidylate synthase, an enzyme critical for converting deoxyuridine monophosphate (dUMP) to deoxythymidine monophosphate (dTMP), which is necessary for DNA synthesis and, subsequently, DNA replication and cell division. By blocking this step, 5-FU effectively limits the availability of thymidine, impairing nucleic acid synthesis and leading to cytotoxic effects in rapidly dividing cells, such as those found in tumors.

This mechanism is a cornerstone of its use in oncological treatments, where suppressing the proliferation of cancer cells is desirable. Other medications mentioned do not directly impact thymidylate synthase or the processes of DNA synthesis in the same way. For instance, Methotrexate inhibits dihydrofolate reductase (not thymidylate synthase), cisplatin primarily causes DNA cross-linking