CH-1504

CH-1504, being developed by Chelsea Therapeutics Inc under license from the University of South Alabama, is an orally available, metabolically inert antifolate, for the potential treatment of rheumatoid arthritis (RA). CH-1504 is an analog of methotrexate (MTX) but differs from the classical antifolates because of an improved safety and tolerability profile. A significant proportion of the toxicity profile of MTX can be attributed to its polyglutamylated and hydroxylated metabolites; therefore, metabolism-blocked antifolates, such as CH-1504, have been designed to prevent the accumulation of toxic metabolites. Preclinical studies and phase II clinical trials indicated that CH-1504 and MTX inhibit dihydrofolate reductase activity with equal potency. In a phase II, proof-of-concept trial in patients with RA, CH-1504 was associated with improved tolerability and reduced hepatotoxicity as compared with MTX; in addition, improvements in the American College of Rheumatology response rates were similar following treatment with either CH-1504 or MTX. Furthermore, Chelsea Therapeutics are developing the L-isomer of CH-1504, CH-4051, which displays improved in vitro potency over with racemate and appears to be Chelsea Therapeutics' preferred candidate for future development. Inert antifolates appear to be a promising drug class for the treatment of RA because the disease-modifying properties of MTX are retained, but the therapeutic window of the inert antifolates is improved. However, further trials are required to establish the efficacy and long-term safety in a wider population of patients with RA.

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.