BMS-229724 is a tight-binding inhibitor of cytosolic phospholipase A(2) that acts at the lipid/water interface and possesses anti-inflammatory activity in skin inflammation models

Cytosolic phospholipase A(2) (cPLA(2)) catalyzes the selective release of a rachidonic acid from the sn-2 position of phospholipids and is believed to play a key cellular role in the generation of arachidonic acid. EMS-229724 (4-[4-[2-[2-[bis(4-chlorophenyl)methoxy]ethyl-sulfonyl]ethoxy]phenyl]-1,1,- trifluoro-2-butanone) was found to be a selective inhibitor of cPLA(2) (IC5 0 = 2.8 muM) in that it did not inhibit secreted phospholipase A(2) in vitr o, nor phospholipase C and phospholipase D in cells. The compound was activ e in inhibiting arachidonate and eicosanoid production in U937 cells, neutr ophils, platelets, monocytes, and mast cells. With a synthetic covesicle su bstrate system, the dose-dependent inhibition could be defined by kinetic e quations describing competitive inhibition at the lipid/water interface. Th e apparent equilibrium dissociation constant for the inhibitor bound to the enzyme at the interface (K-l(*app)) was determined to be 1.10(-5) mol% ver sus an apparent dissociation constant for the arachidonate-containing phosp holipid of 0.35 mol%. The unit of concentration in the interface is mole fr action (or mol%), which is related to the surface concentration of substrat e, rather than bulk concentration that has units of molarity. Thus, BMS-229 724 represents a novel inhibitor of cPLA(2), which partitions into the phos pholipid bilayer and competes with phospholipid substrate for the active si te. This potent inhibition of the enzyme translated into anti-inflammatory activity when applied topically (5%, w/v) to a phorbol ester-induced chroni c inflammation model in mouse ears, inhibiting edema and neutrophil infiltr ation, as well as prostaglandin and leukotriene levels in the skin. In hair less guinea pigs, BMS-229724 was active orally (10 mg/kg) in a UVB-induced skin erythema model in hairless guinea pigs.