Folate analog nonsubstrates and inhibitors of folylpolyglutamate synthetase as potential cancer chemotherapy drugs.

Folate monoglutamates and classical antifols such as methotrexate (MTX) are converted intracellularly to poly-gamma-glutamyl forms by folylpolyglutamate synthetase (FPGS). Folylpolyglutamates are absolutely essential for cell survival and proliferation. MTX polyglutamates are strongly implicated in the cytotoxic mechanism of this drug. Two new types of antifol could be targeted toward polyglutamate synthesis. One type would be structurally analogous to a folate monoglutamate or MTX, except it would not form polyglutamates. In the case of a folate, this analog might induce cellular deficiency by displacing natural folates. In the case of MTX, the analog might have a therapeutic advantage if MTX polyglutamates are involved primarily in host toxicity. The second approach is through direct inhibitors of FPGS. Two relevant MTX analogs have been synthesized and tested: 4-amino-10-methylpteroyl-4-fluoroglutamate does not form polyglutamates or does so extremely poorly; the second, 4-amino-10-methylpteroyl-2,5-diaminopentanoate, is an inhibitor of mammalian FPGS, as predicted from the work of Shane and co-workers with reduced pteroyl-2,5-diaminopentanoate.