Design and synthesis of dihydrofolate reductase inhibitors encompassing a bridging ester group. Evaluation in a mouse colitis model.

Crohn's disease is a chronic inflammatory bowel disease characterized by inflammation of both the small and large intestines. Methotrexate (MTX), a classical dihydrofolate reductase (DHFR) inhibitor, has been used as a therapeutic agent in the treatment of patients with Crohn's disease in recent years. We sought to develop antifolates similar in structure to MTX that would be effective in reducing inflammation in a mouse disease model of colitis. Four classical DHFR inhibitors encompassing ester bridges in the central parts of the molecules were synthesized. These antifolates were efficient inhibitors of the DHFR enzyme derived from rat. They were also tested in vitro for their ability to inhibit induced proliferation of lymphocytes from mouse spleen. Inhibition of cell proliferation was achieved only in the micromolar range, whereas MTX was effective at low nanomolar concentrations. One of the DHFR inhibitors (1), with an IC(50) value for rlDHFR approximately 8 times higher than that of methotrexate, was selected for in vivo experiments in an experimental colitis model in mice. This compound demonstrated a clear antiinflammatory effect after topical administration, comparable to the effect achieved with the glucocorticoid budesonide. Three parameters were evaluated in this model: myeloperoxidase activity, colon weight, and inflammation scoring. A favorable in vivo effect of compound 1 (15 mg/(kg.day)) was observed in all three inflammatory parameters. However, the results cannot be explained fully by DHFR inhibition or by inhibition of lymphocyte cell proliferation, suggesting that other yet unidentified mechanisms enable reduction of inflammation in the colitis model. The mechanism of action of methotrexate analogues encompassing a bridging ester group is not well understood in vivo but seems to lend itself well to further development of similar compounds.