WY-50,295 tromethamine, a novel, orally active 5-lipoxygenase inhibitor: biochemical characterization and...

WY-50,295 tromethamine demonstrates significant 5-lipoxygenase inhibitory activity with IC50 values ranging from 0.055 microM in rat peritoneal exudate cells, to 0.16 microM in mouse macrophages, 1.2 microM in human peripheral neutrophils and 8.1 microM in rat blood leukocytes. This activity appeared selective for 5-lipoxygenase as concentrations up to 10 microM in rat peritoneal exudate cells, and 1 microM in mouse macrophages did not effect prostaglandin generation. In non-cellular enzyme assays, WY-50,295 tromethamine displayed inhibitory activity against a soluble 5-lipoxygenase from guinea pig peritoneal exudate cells (IC50 = 5.7 microM), while it was essentially inactive against 12-lipoxygenase, 15-lipoxygenase, or prostaglandin H synthetase at concentrations up to 500 microM, or against human phospholipase A2 at concentrations up to 50 microM. In purified human blood neutrophils the inhibitory activity was reversible but did not appear dependent upon substrate concentration. IN contrast, in the guinea pig cell-free 5-lipoxygenase assay changing the arachidonic acid substrate concentration from 5 to 500 microM produced a concentration-dependent reduction in inhibitory activity. WY-50,295 tromethamine inhibited the release of peptidoleukotrienes from fragmented guinea pig lung with an IC50 of 0.63 microM. When administered p.o. with a 4 h pretreatment time, WY-50,295 tromethamine inhibited ex vivo leukotriene B4 production in rat blood leukocytes with an ED50 of 19.6 mg/kg. Against an ovalbumin-induced leukotriene dependent bronchoconstriction in anesthetized sensitized guinea pigs, WY-50,295 tromethamine inhibited the ovalbumin-induced bronchoconstriction with an i.v. ED50 of 2.5 mg/kg (5 min pretreatment) and a p.o. ED50 of 7.3 mg/kg (4 h pretreatment). Significant activity was also evident with an 18 h pretreatment. Thus WY-50,295 tromethamine is an potent and selective 5-lipoxygenase inhibitor in a number of in vitro systems. Additionally the compound is orally efficacious and has a long duration of action in an allergic bronchoconstriction model. This data suggests that WY-50,295 tromethamine may have utility in the treatment of asthma and other leukotriene-dependent pathologies.