Mode of action of the new selective leukotriene synthesis inhibitor BAY X 1005 ((R)-2-[4-(quinolin-2-yl-methoxy)phenyl]-2-cyclopentyl acetic acid) and structurally related compounds.

BAY X 1005 ((R)-2-[4-(quinolin-2-yl-methoxy)phenyl]-2-cyclopentyl acetic acid) has been demonstrated to be a potent inhibitor of leukotriene B4 (LTB4) and 5-hydroxyeicosatetraenoic acid (5-HETE) synthesis in various in vitro systems. Using mainly human polymorphonuclear leukocytes (PMNL) this study elucidates the mechanism of inhibition of 5-lipoxygenase (5-LOX, EC 1.13.11.34)-derived arachidonic acid metabolites by BAY X 1005. At concentrations of BAY X 1005 which almost totally inhibited the formation of 5-LOX-derived metabolites, both arachidonic acid release and platelet-activating factor synthesis were only modestly affected. This suggests that the inhibitory effect of BAY X 1005 is not due to a limitation of substrate availability for 5-LOX. Compared to the inhibition of leukotriene synthesis in intact human PMNL about 800-fold higher concentrations of BAY X 1005 were required to inhibit leukotriene formation in a cell-free system suggesting that the inhibitory effect of BAY X 1005 cannot be explained by a direct effect on 5-LOX. In an attempt to identify possible target proteins of BAY X 1005, [14C]BAY X 1005 was used in binding studies under equilibrium conditions. The quantitative analysis of specific binding in intact human PMNL revealed two binding sites for BAY X 1005. Upon subcellular fractionation of these cells the BAY X 1005 high affinity binding site was localized in the microsomal fraction whereas the low affinity binding site was localized in the granule fraction. The Kd for BAY X 1005 binding to the high affinity binding site (0.165 mumol/L) was almost identical to the IC50 value for inhibition of LTB4 synthesis (0.22 mumol/L). Furthermore, the IC50 values for competition of BAY X 1005 binding at the high affinity binding site were almost identical to the IC50 values for inhibition of LTB4 synthesis in the case of BAY X 1005, 12 other structurally related quinoline derivatives and the reference compounds REV-5901, WY-50,295 and MK-886, but not in the case of the direct 5-LOX inhibitors A-64077 and AA-861. The analysis of BAY X 1005 binding in rat PMNL also revealed two binding sites. Whereas the low affinity binding site in rat PMNL exhibited a Kd similar to the human, the rat high affinity binding site showed a 5.5-fold higher affinity for BAY X 1005 compared to the human. This correlates well with the 8.5-fold higher sensitivity of rat versus human PMNL concerning inhibition of LTB4 synthesis.(ABSTRACT TRUNCATED AT 400 WORDS)