Pralatrexate, (S)- is a folate analog dihydrofolate reductase (DHFR) inhibitor exhibiting high affinity for reduced folate carrier-1 (RFC-1) with antineoplastic and immunosuppressive activities. Pralatrexate selectively enters cells expressing RFC-1; intracellularly, this agent is highly polyglutamylation and competes for the folate binding site of DHFR, blocking tetrahydrofolate synthesis.