Effects of AF3442 [N-(9-ethyl-9H-carbazol-3-yl)-2-(trifluoromethyl)benzamide], a novel inhibitor of human microsomal prostaglandin E synthase-1, on prostanoid biosynthesis in human monocytes in vitro

Inhibitors of microsomal prostaglandin (PG) E synthase-1 (mPGES-1) are being developed for the relief of pain. Redirection of the PGH₂ substrate to other PG synthases, found both in vitro and in vivo, in mPGES-1 knockout mice, may influence their efficacy and safety. We characterized the contribution of mPGES-1 to PGH₂ metabolism in lipopolysaccharide (LPS)-stimulated isolated human monocytes and whole blood by studying the synthesis of prostanoids PGE₂, thromboxane (TX)B₂, PGF_2α and 6-keto-PGF_1α] and expression of cyclooxygenase (COX)-isozymes and down-stream synthases in the presence of pharmacological inhibition by the novel mPGES-1 inhibitor AF3442 N-(9-ethyl-9H-carbazol-3-yl)-2-(trifluoromethyl)benzamide]. AF3442 caused a concentration-dependent inhibition of PGE₂ in human recombinant mPGES-1 with an IC₅₀ of 0.06 μM. In LPS-stimulated monocytes, AF3442 caused a concentration-dependent reduction of PGE₂ biosynthesis with an IC₅₀ of 0.41 μM. At 1 μM, AF3442 caused maximal selective inhibitory effect of PGE₂ biosynthesis by 61 ± 3.3% (mean ± SEM, P < 0.01 versus DMSO vehicle) without significantly affecting other prostanoids (i.e. TXB₂, PGF_2α and 6-keto-PGF_1α). In LPS-stimulated whole blood, AF3442 inhibited in a concentration-dependent fashion inducible PGE₂ biosynthesis with an IC₅₀ of 29 μM. A statistically significant inhibition of mPGES-1 activity was detected at 10 and 100 μM (38 ± 14%, P < 0.05, and 69 ± 5%, P < 0.01, respectively). Up to 100 μM, the other prostanoids were not significantly affected. In conclusion, AF3442 is a selective mPGES-1 inhibitor which reduced monocyte PGE₂ generation also in the presence of plasma proteins. Pharmacological inhibition of mPGES-1 did not translate into redirection of PGH₂ metabolism towards other terminal PG synthases in monocytes. The functional relevance of this observation deserves to be investigated in vivo.