EFFECTS OF THE NOVEL ANTIINFLAMMATORY COMPOUNDS, N-[2-(CYCLOHEXYLOXY)-4-NITROPHENYL] METHANESULFONAMIDE (NS-398) AND SULPHONAMIDO-6-(2,4-DIFLUOROTHIOPHENYL)-1-INDANONE (L-745,337), ON THE CYCLOOXYGENASE ACTIVITY OF HUMAN BLOOD PROSTAGLANDIN ENDOPEROXIDE SYNTHASES

1 We have evaluated the selectivity of ketoprofen and two novel nonste roidal anti-inflammatory drugs, -(cyclohexyloxy)-4-nitrophenyl]methane sulphonamide (NS-398) and sulphonamido-6-(2,4-difluorothiophenyl)-1-in danone (L-745,337), in inhibiting the cyclo-oxygenase activity of pros taglandin endoperoxide synthase-2 (PGHS-2) vs PGHS-1 in human blood mo nocytes and platelets, respectively. 2 Heparinized whole blood samples were drawn from healthy volunteers pretreated with aspirin, 300 mg 48 h before sampling, to suppress the activity of platelet PGHS-1 and in cubated at 37 degrees C for 24 h with increasing concentrations of the test compounds in the presence of lipopolysaccharide (LPS, 10 mu g ml (-1)). Immunoreactive PGE(2) levels were measured in plasma by a speci fic radioimmunoassay as an index of the cyclo-oxygenase activity of LP S-induced monocyte PGHS-2. 3 The effects of the same inhibitors on pla telet PGHS-1 activity were assessed by allowing whole blood samples, d rawn from the same subjects in aspirin-free periods, to clot at 37 deg rees C for 1 h in the presence of the compounds and measuring immunore active thromboxane B-2 (TXB(2)) levels in serum by a specific radioimm unoassay. 4 Under these experimental conditions, ketoprofen enantiosel ectively inhibited the cyclo-oxygenase activity of both PGHS-1 and PGH S-2 with equal potency (IC50 ratio: approx. 0.5 for both enantiomers), while L-745,337 and NS-398 achieved selective inhibition of monocyte PGHS-2 (IC50 ratio: > 150). L-745,337 and NS-398 did not affect LPS-in duced monocyte PGHS-2 biosynthesis to any detectable extent. 5 We conc lude that L-745,337 and NS-398 are selective inhibitors of the cyclo-o xygenase activity of human monocyte PGHS-2. These compounds may provid e adequate tools to test the contribution of this novel pathway of ara chidonate metabolism to human inflammatory disease.