SELECTIVE-INHIBITION OF PROSTAGLANDIN ENDOPEROXIDE SYNTHASE-1 (CYCLOOXYGENASE-1) BY VALERYLSALICYLIC ACID

Aspirin causes a time-dependent inhibition of prostaglandin endoperoxi de H synthases (PGHS)-1 and -2 by acetylating active site serines pres ent in both isozymes. In the case of PGHS-1, aspirin acetylation block s cyclooxygenase activity, apparently by preventing arachidonate bindi ng to the cyclooxygenase active site. With PGHS-2, acetylation does no t block substrate binding but rather alters the enzyme in such a way t hat the acetylated form of PGHS-2 produces 15R-hydroxy-eicosatetraenoi c acid (15R-HETE) instead of the usual prostaglandin endoperoxide prod uct. Based on these differences between PGHS-1 and PGHS-2, we reasoned that a salicylate ester containing an acyl group somewhat larger than the acetyl group of aspirin might be a selective inhibitor of PGHS-2. Accordingly, we prepared and tested eight different acyl salicylates as inhibitors of human (h) PGHS-1 and -2 expressed transiently in cos- 1 cells. Valeryl (pentanoyl) salicylate (VSA) was the only compound in this series which showed isozyme selectivity, and, surprisingly, VSA inhibited hPGHS-1 much more effectively than hPGHS-2. Inhibition of hP GHS-1 by VSA was time-dependent. VSA also inhibited ovine PGHS-1 but d id not inhibit the S530A mutant of ovine PGHS-1. This latter mutant, w hich lacks the active site serine hydroxyl group, is also refractory t o inhibition by acetylsalicylate. Thus, we conclude that VSA acylates the active site serine of PGHS-1, VSA inhibited prostanoid synthesis b y serum-starved murine NIH 3T3 cells which express only PGHS-1; in con trast, VSA caused only partial inhibition of prostanoid synthesis by s erum-stimulated 3T3 cells which express both PGHS isozymes. Our result s establish that VSA can be used as a reasonably selective inhibitor o f PGHS-1. (C) 1995 Academic Press, Inc.