Metabolism-blocked antifolates as potential anti-rheumatoid arthritis agents: 4-amino-4-deoxy-5,8,10-trideazapteroyl-d,l-4'-methyleneglutamic acid (CH-1504) and its analogs.

4-Amino-4-deoxy-5,8,10-trideazapteroyl-d,l-4'-methyleneglutamic acid (CH-1504) is the prototype of a potentially therapeutically more selective class of antifolates for rheumatoid arthritis treatment. This class is characterized by retention of dihydrofolate reductase (DHFR; EC 1.5.1.3) as their locus of action and transport by the reduced folate carrier (RFC; SLC19A1), but their lack of metabolism by known pathways of antifolate (e.g., methotrexate (MTX)) metabolism. Five new CH-1504 analogs (CHL-001-CHL-005) were synthesized and diastereomers of CH-1504 itself were obtained by preparative chiral HPLC; all were characterized biochemically. The analogs are not metabolized by aldehyde oxidase (EC 1.2.3.1), carboxypeptidase G2 (EC 3.4.17.11), or (excepting CHL-003) folylpolyglutamate synthetase (EC 6.3.2.17) and thus, unlike MTX, are "metabolism-blocked". All analogs are potent DHFR inhibitors; several are nearly as potent as MTX or CH-1504. Each analog uses the RFC for transport, although with varying apparent affinities. In contrast, each weakly inhibits other enzymes of folate metabolism relevant to rheumatoid arthritis therapy (thymidylate synthase (EC 2.1.1.45), two formyltransferases of purine biosynthesis (EC 2.1.2.2 and EC 2.1.2.3), and 5,10-methylenetetrahydrofolate reductase (EC 1.5.1.20)). Biochemical characterization showed one 4'-diastereomer of racemic CH-1504 was significantly more active than the other. Based on literature data concerning the effect of d- and l-glutamic acid substitution on antifolate activity, it is likely that the diastereomer containing l-4'-methylene-glutamic acid is the more active. Because of concern about potential pharmacokinetic and biochemical effects of d-4'-methylene-glutamic acid-containing species, these data suggest that future analogs should contain only l-4'-methylene-glutamic acid. Overall, these data provide several interesting new leads for preclinical development.