Characterization of a novel and selective cannabinoid CB1 receptor inverse agonist, Imidazole 24b, in rodents

Abstract We document in vitro and in vivo effects of a novel, selective cannabinoid CB 1 receptor inverse agonist, Imidazole 24b (5-(4-chlorophenyl)- N -cyclohexyl-4-(2,4-dichlorophenyl)-1-methyl-imidazole-2-carboxamide). The in vitro binding affinity of Imidazole 24b for recombinant human and rat CB 1 receptor is 4 and 10 nM, respectively. Imidazole 24b binds to human cannabinoid CB 2 receptor with an affinity of 297 nM; in vitro, it is a receptor inverse agonist at both cannabinoid CB 1 and CB 2 receptors as it causes a further increase of forskolin-induced cAMP increase. Oral administration of Imidazole 24b blocked CP-55940-induced hypothermia, demonstrating cannabinoid CB 1 receptor antagonist efficacy in vivo . Using ex vivo autoradiography, Imidazole 24b resulted in dose-dependent increases in brain cannabinoid CB 1 receptor occupancy (RO) at 2h post-dosing in rats, indicating that ∼ 50% receptor occupancy is sufficient for attenuation of receptor agonist-induced hypothermia. Imidazole 24b administered to C57Bl/6 mice and to dietary-induced obese (DIO) Sprague–Dawley rats attenuated overnight food intake with a minimal effective dose of 10 mg/kg, p.o. Administration had no effect in cannabinoid CB 1 receptor-deficient mice. DIO rats were dosed orally with vehicle, Imidazole 24b (1, 3 or 10 mg/kg), or dexfenfluramine (3 mg/kg) for 2 weeks. At 3 mg/kg, Imidazole 24b reduced cumulative food intake, leading to a non-significant decrease in weight gain. Imidazole 24b at 10 mg/kg and dexfenfluramine treatment inhibited food intake and attenuated weight gain. These findings suggest that selective cannabinoid CB 1 receptor inverse agonists such as Imidazole 24b have potential for the treatment of obesity.