The molecular mechanism of the inhibition by licofelone of the biosynthesis of 5-lipoxygenase products

Background and purpose: Licofelone is a dual inhibitor of the cyclooxygenase and 5- lipoxygenase ( 5- LO) pathway, and has been developed for the treatment of inflammatory diseases. Here, we investigated the molecular mechanisms underlying the inhibition by licofelone of the formation of 5- LO products. Experimental approach: The efficacy of licofelone to inhibit the formation of 5- LO products was analysed in human isolated polymorphonuclear leukocytes ( PMNL) or transfected HeLa cells, as well as in cell- free assays using respective cell homogenates or purified recombinant 5- LO. Moreover, the effects of licofelone on the subcellular redistribution of 5- LO were studied. Key results: Licofelone potently blocked synthesis of 5- LO products in Ca2+- ionophore- activated PMNL ( IC50=1.7 mu M) but was a weak inhibitor of 5- LO activity in cell-free assays (IC50>>10 mu M). The structures of licofelone and MK-886, an inhibitor of the 5-LO- activating protein ( FLAP), were superimposable. The potencies of both licofelone and MK- 886 in ionophore- activated PMNL were impaired upon increasing the concentration of arachidonic acid, or under conditions where 5- LO product formation was evoked by genotoxic, oxidative or hyperosmotic stress. Furthermore, licofelone prevented nuclear redistribution of 5- LO in ionophore- activated PMNL, as had been observed for FLAP inhibitors. Finally, licofelone as well as MK- 886 caused only moderate inhibition of the synthesis of 5- LO products in HeLa cells, unless FLAP was co- transfected. Conclusions and implications: Our data suggest that the potent inhibition of the biosynthesis of 5- LO products by licofelone requires an intact cellular environment and appears to be due to interference with FLAP.