Potent inhibition of human 5-lipoxygenase and microsomal prostaglandin E2 synthase-1 by the anti-carcinogenic and anti-inflammatory agent embelin.

Embelin (2,5-dihydroxy-3-undecyl-1,4-benzoquinone) possesses anti-inflammatory and anti-carcinogenic properties in vivo, and these features have been related to interference with multiple targets including XIAPs, NFκB, STAT-3, Akt and mTOR. However, interference with these proteins requires relatively high concentrations of embelin (IC50>4 µM) and cannot fully explain its bioactivity observed in several functional studies. Here we reveal human 5-lipoxygenase (5-LO) and microsomal prostaglandin E2 synthase (mPGES)-1 as direct molecular targets of embelin. Thus, embelin potently suppressed the biosynthesis of eicosanoids by selective inhibition of 5-LO and mPGES-1 with IC50=0.06 and 0.2 µM, respectively. In intact human polymorphonuclear leukocytes and monocytes, embelin consistently blocked the biosynthesis of various 5-LO products regardless of the stimulus (fMLP or A23187) with IC50=0.8-2 µM. Neither the related human 12- and 15-LO nor the cyclooxygenases-1 and -2 or cytosolic phospholipase A2 were significantly affected by 10 µM embelin. Inhibition of 5-LO and mPGES-1 by embelin was (I) essentially reversible after wash-out, (II) not impaired at higher substrate concentrations, (III) unaffected by inclusion of Triton X-100, and (IV) did not correlate to its proposed antioxidant properties. Docking simulations suggest concrete binding poses in the active sites of both 5-LO and mPGES-1. Because 5-LO- and mPGES-1-derived eicosanoids play roles in inflammation and cancer, the interference of embelin with these enzymes may contribute to its biological effects and suggests embelin as novel chemotype for development of dual 5-LO/mPGES-1 inhibitors.

Dopamine/serotonin receptor ligands. 16.(1) Expanding dibenz[d,g]azecines to 11- and 12-membered homologues. Interaction with dopamine D(1)-D(5) receptors.

Oxygenated 7-methyl-5,6,7,8,9,14-hexahydrodibenz[d,g]azecines are potent dopamine receptor antagonists, preferentially at D1/D5. We synthesized the hydroxylated, methoxylated, and chlorinated 11-membered and 12-membered homologues of these 10-membered heterocycles. Their affinities for the human cloned D1-D5 receptors (radioligand binding) and functionalities (calcium assay) were measured. Enlarging the dibenzazecines to the corresponding dibenzazacycloundecenes and dibenzazacyclododecenes generally maintains the high antagonistic affinity for D1/D5 but also leads to a compound with a clozapine-like binding profile due to additional affinity for D4.