Prostaglandin (PG)E-2 is a critical lipid mediator connecting chronic inflammation to cancer. The anti-carcinogenic epigallocatechin-3-gallate (EGCG) from green tea (Camellia sinensis) suppresses cellular PGE(2) biosynthesis, but the underlying molecular mechanisms are unclear. Here, we investigated the interference of EGCG with enzymes involved in PGE(2) biosynthesis, namely cytosolic phospholipase (cPL)A(2), cyclooxygenase (COX)-1 and -2, and microsomal prostaglandin E-2 synthase-1 (mPGES-1). EGCG failed to significantly inhibit isolated COX-2 and cPLA(2) up to 30 mu M and moderately blocked isolated COX-1 (IC50 > 30 mu M). However, EGCG efficiently inhibited the transformation of PGH(2) to PGE(2) catalyzed by mPGES-1 (IC50 = 1.8 mu M). In lipopolysaccharide-stimulated human whole blood, EGCG significantly inhibited PGE2 generation, whereas the concomitant synthesis of other prostanoids (i.e., 12(S)-hydroxy-5-cis-8,10-trans-heptadecatrienoic acid and 6-keto PGF(1 alpha)) was not suppressed. Conclusively, mPGES-1 is a molecular target of EGCG, and inhibition of mPGES-1 is seemingly the predominant mechanism underlying suppression of cellular PGE(2) biosynthesis by EGCG. (C) 2009 Elsevier Inc. All rights reserved.