APD791, 3-Methoxy-N-(3-(1-methyl-1H-pyrazol-5-yl)-4-(2-morpholinoethoxy)phenyl)benzamide, a Novel 5-Hydroxytryptamine 2A Receptor Antagonist: Pharmacological Profile, Pharmacokinetics, Platelet Activity and Vascular Biology

We have evaluated the receptor pharmacology, antiplatelet activity, and vascular pharmacology of APD791 [3-methoxy-N-(3-(1-methyl-1H-pyrazol-5-yl)-4-(2-morpholinoethoxy)phenyl)benzamide] a novel 5-hydroxytryptamine 2A (5-HT2A) receptor antagonist. APD791 displayed high-affinity binding to membranes (K-i = 4.9 nM) and functional inverse agonism of inositol phosphate accumulation (IC50 = 5.2 nM) in human embryonic kidney cells stably expressing the human 5-HT2A receptor. In competition binding assays, APD791 was greater than 2000-fold selective for the 5-HT2A receptor versus 5-HT2C and 5-HT2B receptors, and was inactive when tested against a wide panel of other G-protein-coupled receptors. APD791 inhibited 5-HT-mediated amplification of ADP-stimulated human and dog platelet aggregation (IC50 = 8.7 and 23.1 nM, respectively). Similar potency was observed for inhibition of 5-HT-stimulated DNA synthesis in rabbit aortic smooth muscle cells (IC50 = 13 nM) and 5-HT-mediated vasoconstriction in rabbit aortic rings. Oral administration of APD791 to dogs resulted in acute (1-h) and subchronic (10-day) inhibition of 5-HT-mediated amplification of collagen-stimulated platelet aggregation in whole blood. Two active metabolites, APD791-M1 and APD791-M2, were generated upon incubation of APD791 with human liver microsomes and were also indentified in dogs after oral administration of APD791. The affinity and selectivity profiles of both metabolites were similar to APD791. These results demonstrate that APD791 is an orally available, high-affinity 5-HT2A receptor antagonist with potent activity on platelets and vascular smooth muscle.