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Biochem/physiol Actions

Aminopterin is a synthetic derivative of pterin. It is used as a folic acid antagonist. It competitively inhibits dihydrofolate reductase (DHFR) and blocks tetrahydrofolate synthesis. This inhibition blocks DNA, RNA and protein synthesis.Aminopterin is actively transported into cells by the folate transporter. In the cell, it is converted to a high molecular weight polyglutamate metabolite by folylpolyglutamate synthase that, in turn, binds to dihydrofolate reductase and inhibits its activity. Aminopterin-polyglutamate is degraded intracellularly by γ-glutamyl hydrolase.Aminopterin was first administered for cancer therapy, as a drug targeting metabolism, specifically in pediatric leukemia. Later on it was demonstrated to be more potent yet more toxic than methotrexate.