Abstract

The microsomal prostaglandin E₂ synthase (mPGES)-1 is one of the terminal isoenzymes of prostaglandin (PG) E₂ biosynthesis. Pharmacological inhibitors of mPGES-1 are proposed as an alternative to nonsteroidal anti-inflammatory drugs. We recently presented the design and synthesis of a series of pirinixic acid derivatives that dually inhibit mPGES-1 and 5-lipoxygenase. Here, we investigated the mechanism of mPGES-1 inhibition, the selectivity profile, and the in vivo activity of α-(n-hexyl)-substituted pirinixic acid [YS121; 2-(4-chloro-6-(2,3-dimethylphenylamino)pyrimidin-2-ylthio)octanoic acid)] as a lead compound. In cell-free assays, YS121 inhibited human mPGES-1 in a reversible and noncompetitive manner (IC₅₀ = 3.4 μM), and surface plasmon resonance spectroscopy studies using purified in vitro-translated human mPGES-1 indicate direct, reversible, and specific binding to mPGES-1 (K_D = 10–14 μM). In lipopolysaccharide-stimulated human whole blood, PGE₂ formation was concentration dependently inhibited (IC₅₀ = 2 μM), whereas concomitant generation of the cyclooxygenase (COX)-2-derived thromboxane B₂ and 6-keto PGF_1α and the COX-1-derived 12(S)-hydroxy-5-cis-8,10-trans-heptadecatrienoic acid was not significantly reduced. In carrageenan-induced rat pleurisy, YS121 (1.5 mg/kg i.p.) blocked exudate formation and leukocyte infiltration accompanied by reduced pleural levels of PGE₂ and leukotriene B₄ but also of 6-keto PGF_1α. Taken together, these results indicate that YS121 is a promising inhibitor of mPGES-1 with anti-inflammatory efficiency in human whole blood as well as in vivo.