Discovery of novel inhibitors of inducible nitric oxide synthase

We have discovered three compounds, 5-chloro-1,3-dihydro-2H-benzimidazol-2-one (FR038251), 1,3(2H,4H)-isoquinolinedione (FR038470) and 5-chloro-2,4(1H,3H)-quinazolonedione (FR191863), which show inhibition of inducible nitric oxide synthase (iNOS). The iNOS inhibitory activity of the compounds was examined in comparison with that of aminoguanidine, a representative iNOS inhibitor. FR038251, FR038470 and FR191863 inhibited mouse iNOS, with IC50 values of 1.7, 8.8 and 1.9 microM, respectively, in an in-vitro enzyme assay. These inhibitory activities are comparable with that of aminoguanidine (IC50 = 2.1 microM). The three compounds had iNOS selectivity 38- and 8-times, > 11- and 3-times, and 53- and 3-times compared with rat neuronal NOS and bovine endothelial NOS, respectively. These compounds concentration-dependently inhibited NO production in intact RAW264.7 mouse macrophages stimulated by lipopolysaccharide (LPS)/interferon-gamma. At 100 microM, FR038251, FR038470, FR191863 and aminoguanidine showed 81, 44, 54 and 78% inhibition of NO production, respectively. In an in-vivo experiment, FR038251, FR038470, FR191863 and aminoguanidine inhibited NO production in LPS-treated mice by 68, 40, 5 and 68% at an oral dose of 100 mg kg-1. The in-vivo inhibitory activity of FR038251 was almost identical to that of aminoguanidine. In conclusion, the three FR compounds are iNOS inhibitors with novel structures and may be candidate compounds leading to discovery of more iNOS inhibitors in the future.