Which two enzymes are targeted by Methotrexate?

Methotrexate is an antimetabolite chemotherapy agent that primarily acts by inhibiting specific enzymes involved in folate metabolism, which are crucial for nucleotide synthesis and cellular replication. The correct choice highlights the targeting of dihydrofolate reductase and thymidylate synthase.

Dihydrofolate reductase is essential in the conversion of dihydrofolate to tetrahydrofolate, a reaction that is vital for the synthesis of purines and thymidylate. By inhibiting this enzyme, Methotrexate effectively reduces the availability of folate, leading to decreased nucleotide synthesis and ultimately impeding DNA replication and cell division, which is particularly beneficial in rapidly proliferating cancer cells.

Thymidylate synthase, on the other hand, is directly involved in the synthesis of thymidine, one of the building blocks of DNA. Inhibition of this enzyme further obstructs DNA synthesis, reinforcing the effects of Methotrexate on rapidly dividing cells.

The other choices refer to various agents or enzymes that do not interact directly with Methotrexate's mechanism of action. Cytarabine and Gemcitabine, for instance, are themselves chemotherapy drugs that target different processes in cancer cells, while ribon