MX-68 is a newly synthesized anti-
folate, chemically designed not to undergo intracellular polyglutamation and to have increased affinity to
dihydrofolate reductase (DHFR). In the present study, we examined the in vitro and in vivo
biological activities of
MX-68 compared with
methotrexate (MTX) which forms several polyglutamates intracellularly.
MX-68 dose-dependently inhibited the proliferation of PHA-, anti-CD3-, or PMA plus
ionomycin-stimulated peripheral blood mononuclear cells (PBMC) and endothelial cells (EC) from normal subjects as well as
IL-1 beta- or
TNF alpha-stimulated synovial fibroblastic cells (SC) from
rheumatoid arthritis (RA) patients. Coaddition of
folinic acid completely reversed the anti-proliferative effects of both
MX-68 and MTX. Although the anti-proliferative activities of
MX-68 were almost comparable to those of MTX, the washout study clearly showed the characteristic nature of
MX-68. When drugs were removed during culture, the suppressive effect of
MX-68 completely disappeared, whereas suppression by MTX was merely weakened.
MX-68 dramatically suppressed the onset of
collagen-induced arthritis (CIA) in mice when the
drug was orally administered three times a week. starting from the day of first immunization. In this model, 2 mg/kg of
MX-68 was sufficient to completely suppress
arthritis, whereas suppression by the same dose of MTX was partial. These lines of evidence suggest that polyglutamation is not always a prerequisite in the anti-rheumatic effects of anti-
folate. In addition, since intracellular accumulation of polyglutamates is thought to have adverse effects,
MX-68 may become a more potent and less toxic
anti-rheumatic drug than MTX.