SR147778 [5-(4-bromophenyl)-1-(2,4-dichlorophenyl)-4-ethyl-N-(1-piperidinyl)-1H-pyrazole-3-carboxamide], a new potent and selective antagonist of the CB1 cannabinoid receptor:: Biochemical and pharmacological characterization

Based on binding, functional, and pharmacological data, this study introduces SR147778 [5-(4-bromophenyl)-1-(2,4-dichlorophenyl)4- ethyl-N-(1-piperidinyl)-1H-pyrazole-3-carboxamide] as a highly potent, selective, and orally active antagonist for the CB1 receptor. This compound displays nanomolar affinity (K-i = 0.56 and 3.5 nM) for both the rat brain and human CB1 recombinant receptors, respectively. It has low affinity ( K-i = 400 nM) for both the rat spleen and human CB2 receptors. Furthermore, it shows no affinity for any of the over 100 targets investigated (IC50 > 1 muM). In vitro, SR147778 antagonizes the inhibitory effects of CP 55,940 [(1R, 3R, 4R)-3-[2-hydroxy-4-(1,1-dimethylheptyl) phenyl]-4-(3-hydroxypropyl) cyclohexan-1-ol] on both the mouse vas deferens contractions (pA(2) value = 8.1) and on forskolin-stimulated adenylyl cyclase activity in the U373 MG cell lines (pA(2) value = 8.2) but not in Chinese hamster ovary (CHO) cells permanently expressing the human peripheral cannabinoid receptor (hCB2). SR147778 is able to block the mitogen-activated protein kinase activity induced by CP 55,940 in the CHO cell line expressing human brain cannabinoid receptor ( IC50 = 9.6 nM) but was inactive in cells expressing hCB2. After oral administration, SR147778 displaced the ex vivo [H-3]-CP 55,940 binding to mouse brain membranes (ED50 = 3.8 mg/ kg) with a long duration of action, whereas it did not interact with the CB2 receptor expressed in the mouse spleen. Using different routes of administration, SR147778 (0.3 - 3 mg/ kg) is shown to antagonize pharmacological effects ( hypothermia, analgesia, and gastrointestinal transit) induced by R-(+)-(2,3-dihydro- 5-methyl-3-[{4-morpholinyl} methyl] pyrol [1,2,3-de]1,4- benzoxazin-6-yl)(1-naphthalenyl) methanone in mice. Finally, per se, SR147778 ( 0.3 - 10 mg/ kg) is able to reduce ethanol or sucrose consumption in mice and rats and food intake in fasted and nondeprived rats.