Folate antagonist

"Folate antagonist" is **not a specific molecule or receptor**, but rather refers to a **class of drugs**—also called antifolates or folic acid antagonists—that inhibit the action of folic acid (vitamin B9) in cells. These agents are primarily used as antimetabolite medications in cancer chemotherapy, antimicrobial therapy, and for certain inflammatory and autoimmune diseases. The most common mechanism is inhibition of the enzyme dihydrofolate reductase (DHFR), which is essential for converting dietary folates into their active forms required for DNA synthesis and cell division. By blocking this pathway, antifolates prevent cell proliferation—especially affecting rapidly dividing cells such as cancer cells or microbes. Common drugs in this class include methotrexate, pemetrexed, pralatrexate, raltitrexed (used mainly in oncology), trimethoprim and pyrimethamine (antibacterial/antiparasitic), and proguanil (antimalarial). Because "folate antagonist" does not refer to a unique protein target but rather to any agent that blocks the biological effects of folic acid through various mechanisms—most often DHFR inhibition—it should not be considered a canonical therapeutic target like an enzyme or receptor. Instead, it describes a pharmacological strategy targeting one or more enzymes within the folic acid metabolic pathway. Notable safety concerns include bone marrow suppression due to effects on rapidly dividing hematopoietic cells and significant teratogenic risk if used during pregnancy. Resistance can develop via upregulation of DHFR expression by tumor cells. In summary: "Folate antagonist" is **not itself a molecular target** but denotes any drug that inhibits cellular utilization of folic acid; thus it should not be treated as an individual therapeutic target entry.

Other names

AntifolateFolic acid antagonistFolate analogAntifol

Inhibition of dihydrofolate reductase (DHFR); Inhibition of thymidylate synthase or other folate-dependent enzymes