Pralatrexate is an antimetabolite for the treatment of relapsed or refractory peripheral t-cell lymphoma. it is more efficiently retained in cancer cells than methotrexate.the selectivity of pralatrexate for cancer cells is based upon the observation that cancer cells generally have an overexpression of reduced folate carrier protein-1 (rtc-1) compared to normal somatic cells. this carrier protein allows the entrance of pralatrexate into the cell. upon entering the cell, folypolyglutamate synthase fpgs catalyzes the polyglutamination of pralatrexate so that it is retained inside the cell.