No abstract

BAY X1005, (R)-2-[4-(quinolin-2-yl-methoxy)phenyl]-2-cyclopentyl acetic acid, is an enantioselective inhibitor of leukotriene biosynthesis. It effectively inhibits the synthesis of LTB4 in A23187-stimulated leukocytes from rats, mice and humans (IC50 0.026, 0.039 and 0.22 mumol/l, respectively) as well as the formation of LTC4 (IC50 0.021 mumol/l) in mouse peritoneal macrophages stimulated with opsonized zymosan. The compound is, however, less active in inhibiting LTB4 synthesis in human whole blood (IC50 17.0 and 11.6 mumol/l, as measured by RIA or HPLC, respectively). BAY X1005 exhibits a high enantioselectivity in human whole blood (31 times over the (S)-enantiomer). BAY X1005 is shown to be a selective inhibitor of the formation of 5-lipoxygenase-derived metabolites in vitro, without effects on other routes of arachidonic acid metabolism such as 12-lipoxygenase in human whole blood and cyclooxygenase in both mouse macrophages and human whole blood. BAY X1005 is devoid of any antioxidant activity (methemoglobin induction and xanthine-xanthine oxidase assay), without effects on granule release and with only weak effects on reactive oxygen species generation in human PMNL.

Five-lipoxygenase (5-LOX) inhibition is gaining increasing importance as a novel approach to therapy of allergic asthma and other inflammatory diseases. Presently, two types of inhibitors are known, direct 5-LOX inhibitors (LOI) and the FLAP (five lipoxygenase activating protein) binding leukotriene synthesis inhibitors (LSI). The 5-LOX selective and orally active quinoline LSI, BAY X 1005, shares many mechanistic features with the indole LSI, MK-886. The binding of BAY X 1005 to FLAP correlates with LTB4 synthesis inhibition. BAY X 1005 has been shown to bind to the 18 kD protein FLAP. BAY X 1005 inhibits 5-LOX translocation from the cytosol to membranes and reverses 5-LOX translocation. The use of BAY X 1005 has helped to elucidate part of the complex FLAP/5-LOX interaction by showing that FLAP appears to represent a 5-LOX substrate transfer protein channelling endogenous and exogenous arachidonic acid to the leukotriene synthetizing 5-LOX. This notion presented by our group in 1992 has stimulated further mechanistic studies. These findings have additionally led to the hypothesis that substrate competition is not confined to the LSI/FLAP interaction but may also be true for the LOI/5-LOX interaction and that even mixed LSI/LOI 5-LOX inhibitors are feasible, yet have not been described. Further mechanistic work on LSI will be orientated not only to further elucidate the complex FLAP/5-LOX interaction, but also to identify FLAP-related eicosanoid binding proteins.

The synthesis of novel 1-thio-substituted butadienes, designed as mechanism-based 5-lipoxygenase inhibitors, is described. The structure of these compounds closely resembles a proposed high-energy intermediate during the lipoxygenation of arachidonic acid. They demonstrate 5-lipoxygenase inhibition in vitro and in vivo. The most potent compound is 15a with an IC50 of 1.8 microM in vitro. LTC4 release was inhibited by 80% after intraperitoneal administration of 15c at a dose of 2 mg/kg.

In psoriatic patients, anthralin is known to attenuate lesional inflammation, but often generates perilesional dermatitis. This phenomenon is well reflected by the contrasting action of anthralin on human leukocytes. The release of reactive oxygen species (ROS) is inhibited by anthralin in phorbol ester-activated leukocytes, whereas anthralin directly induces this cellular response in unstimulated cells. In order to elaborate further the underlying mechanisms, we compared the kinetics of anthralin and different well-characterized stimuli, including the phorbol ester, phorbol-12-myristate-13-acetate, in this test system. Compared with standard stimuli, anthralin only marginally induced the release of ROS from human leukocytes and displayed different kinetics. Protein kinase C (PKC), the major cellular phorbol ester receptor, is considered to be involved in the regulation of this cellular response. Furthermore, its involvement in the pathophysiology of psoriasis has been suggested. Therefore, we also investigated the effects of anthralin on purified PKC. Anthralin was found to inhibit the enzyme activity in a dose-dependent manner but not to display any stimulatory effects. The present results provide first evidence that the therapeutic activity of anthralin, at least in part, might be mediated by inhibition of PKC.