Distinction of microsomal prostaglandin E synthase-1 (mPGES-1) inhibition from cyclooxygenase-2 inhibition in cells using a novel, selective mPGES-1 inhibitor

Inflammation-induced microsomal prostaglandin E synthase-1 (mPGES-1) is the terminal Enzyme that synthesizes prostaglandin E(2) (PGE(2)) downstream of cyclooxygenase-2 (COX-2). The efficacy of nonsteroidal anti-inflammatory drugs and COX-2 inhibitors in the treatment of the signs and symptoms of osteoarthritis, rheumatoid arthritis and inflammatory pain, largely attributed to the inhibition of PGE(2) synthesis, provides a rationale for exploring mPGES-1 inhibition as a potential novel therapy for these diseases. Toward this aim, we identified PF-9184 as a novel mPGES-1 inhibitor. PF-9184 potently inhibited recombinant human (rh) mPGES-1 (IC(50)=16.5+/-3.8nM), and had no effect against rhCOX-1 and rhCOX-2 (>6500-fold selectivity). In inflammation and clinically relevant biological systems, mPGES-1 expression, like COX-2 expression was induced in cell context- and time-dependent manner, consistent with the kinetics of PGE(2) synthesis. In rationally designed cell systems ideal for determining direct effects of the inhibitors on mPGES-1 function, but not its expression, PF-9184 inhibited PGE(2) synthesis (IC(50) in the range of 0.5-5 microM in serum-free cell and human whole blood cultures, respectively) while sparing the synthesis of 6-keto-PGF(1alpha) (PGF(1alpha)) and PGF(2alpha). In contrast, as expected, the selective COX-2 Inhibitor, SC-236, inhibited PGE(2), PGF(1alpha) and PGF(2alpha) synthesis. This profile of mPGES-1 inhibition, distinct from COX-2 inhibition in cells, validates mPGES-1 as an attractive target for therapeutic intervention.