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

We document in vitro and in vivo effects of a novel, selective cannabinoid CB1 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 CB1 receptor is 4 and 10 nM, respectively. Imidazole 24b binds to human cannabinoid CB2 receptor with an affinity of 297 nM; in vitro, it is a receptor inverse agonist at both cannabinoid CB1 and CB2 receptors as it causes a further increase of forskolin-induced cAMP increase. Oral administration of Imidazole 24b blocked CP-55940-induced hypothermia, demonstrating cannabinoid CB1 receptor antagonist efficacy in vivo. Using ex vivo autoradiography, Imidazole 24b resulted in dose-dependent increases in brain cannabinoid CB1 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 CB1 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 CB1 receptor inverse agonists such as Imidazole 24b have potential for the treatment of obesity.