Based on binding, functional, and pharmacological data, this study introduces
SR147778 [5-(4-bromophenyl)-1-(2,4-dichloro-phenyl)-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 (Ki = 0.56 and 3.5 nM) for both the rat brain and human CB1 recombinant receptors, respectively. It has low affinity (Ki = 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 microM). 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 (pA2 value = 8.1) and on
forskolin-stimulated
adenylyl cyclase activity in the U373 MG cell lines (pA2 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 [3H]-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.