PGHS-2 inhibitors, NS-398 and DuP-697, attenuate the inhibition of PGHS-1 by aspirin and indomethacin without altering its activity

Since the discovery of the inducible form of prostaglandin (PG) H synthase (PGHS), PGHS-2, considerable effort has been made to design selective inhib itors of this isozyme. N-(2-cyclohexyloxy-4-nitrophenyl) methanesulfonamide (NS-398) and 5-bromo-2-(4-fluorophenyl)-3- (4-methylsulfonyl) thiophene (D uP-697) have been shown to interact reversibly with PGHS-1, while irreversi bly inhibiting PGHS-2 in a time-dependent manner. In the present study we h ave tested the effects of DuP-697 and NS-398 on the activity of PGHS-1 and further explored the interactions between these agents and the inhibition o f PGHS-1 by aspirin, indomethacin and ibuprofen. Three independent experime ntal systems, namely bovine aortic endothelial cells (BAEC), human fibrobla sts and ram seminal vesicle microsomes were used to investigate the effects of DuP-697 and NS-398 on PGHS-1. The results show that DuP-697 and NS-398, at concentrations ranges which do not inhibit PGHS-1 activity, significant ly attenuated the inhibition of PGHS-1 that was caused by aspirin and indom ethacin. The same concentrations of DuP-697 and NS-398 did not affect the i nhibition of PGHS-1 that was induced by the competitive reversible inhibito rs ibuprofen and naproxen. Similar effects of DuP-697 and NS-393 were obtai ned with ram seminal vesicle microsomes; These results suggest that PGHS-2 inhibitors DuP-697 and NS-398 possibly interact with PGHS-1 at a site diffe rent from the enzyme's catalytic site, thus causing attenuation of PGHS-1 i nhibition by aspirin and indomethacin without altering PGHS-1 basal activit y or the ibuprofen-induced inhibition. (C) 1999 Elsevier Science B.V. All r ights reserved.