The inhibition of 5-lipoxygenase by RG 6866.

The generation of leukotrienes C4, D4 and E4 from arachidonic acid is dependent upon the activity of 5-lipoxygenase (5-LOX). The effects of RG 6866 (N-methyl-4-benzyloxyphenylacetohydroxamic acid) on the activity of guinea pig 5-LOXin vitro andin vivo were determined in the present study. The generation of 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) from arachidonic acid by isolated guinea pig peritoneal polymorphonuclear (PMN) cells was inhibited by incubation with RG 6866 (IC50=0.20 μM). A similar effect (IC50=0.23 μM) was observed when 5-HETE production was measured in a supernatant fraction from PMNs. Additionally, the compound did not inhibit3H-LTD4 binding to guinea pig membranes. In actively sensitized guinea pigs pretreated with indomethacin, propranolol and pyrilamine, RG 6866 inhibited antigen-induced systemic anaphylaxis and LTD4-dependent bronchoconstriction in a dose-dependent manner following oral administration. In the pulmonary anaphylaxis model, significant (p<0.05) inhibition of the mortality was observed within 30 min and maintained through four hours after treatment with RG 6866 (50 mg/kg i.g.). Finally, orally administered RG 6866 inhibited the formation of LTC4 in these animals with an ED50=24.0 mg/kg. These findings indicate that RG 6866 is an inhibitor of 5-LOX bothin vitro andin vivo.