PPA250 [3-(2,4-difluorophenyl)-6-[2-[4-(1H-imidazol-1-ylmethyl) phenoxy]ethoxy]-2-phenylpyridine], a novel orally effective inhibitor of the dimerization of inducible nitric-oxide synthase, exhibits an anti-inflammatory effect in animal models of chronic arthritis.

Nitric oxide (NO) plays an important role in various physiological processes. Excessive NO production is closely related to inflammatory and autoimmune diseases such as septic shock and rheumatoid arthritis. Suppression of excess NO formation in participating cells may be helpful in improving disease status. In this study, we examined the effects of a newly synthesized imidazole derivative, 3-(2,4-difluorophenyl)-6-[2-[4-(1H-imidazol-1-ylmethyl) phenoxy]ethoxy]-2-phenylpyridine (PPA250), on NO production in vitro and in vivo, as well as on the dimerization of inducible nitric-oxide synthase (iNOS). PPA250 at concentrations of 25 nM and higher inhibited NO production in activated mouse macrophage-like RAW264.7 cells. The IC(50) was approximately 82 nM. Western blot analysis revealed that PPA250 prevents dimerization of iNOS but has no effect on transcription and translation. In addition, oral administration of PPA250 (10 mg/kg and higher) reduced the NO concentration in serum from mice in which sepsis was induced by bacterial lipopolysaccharide. Since the inhibitory activity was observed not only in vitro but also in vivo, we examined the therapeutic potential of PPA250 in two animal models of arthritis, collagen-induced arthritis in mice and adjuvant arthritis in rats. PPA250 suppressed the development of a destructive polyarthritis in both models after the appearance of clinical signs. These results indicate that inhibitors of iNOS homodimerization, including PPA250, could be useful therapeutic agents for inflammatory and autoimmune diseases, such as rheumatoid arthritis, in which NO is involved.