Synthesis and Pharmacological Characterization of a Novel Cannabinoid Receptor 1 Antagonist

The endocannabinoid (eCB) system regulates several brain functions and is implicated in numerous conditions affecting the brain. Thus, the pharmacological blockade of cannabinoid receptors has a therapeutic potential but produces severe psychiatric side effects. Hence, new cannabinoid compounds with different pharmacological profiles are needed to potentially minimize this toxicity. The objective of this study, featuring original chemical insights, pharmacological analysis, and robust computational methods, was to synthesize and characterize a series of novel antagonists/inverse agonists of cannabinoid receptors. To do so, we first synthesized and then screened 11 novel compounds for affinity for cannabinoid receptors. After that, we characterized in depth the pharmacological profile of the most promising one, UVI3502, which showed affinity for two [³H]-CP55,940 binding sites (IC_50Hi 0.026 ± 0.43 nM and IC_50Lo 772 ± 49.40 nM, R ² = 0.59) in the rat cortex. Binding assays performed in membranes overexpressing cannabinoid receptors 1 and 2 (CB₁ and CB₂) confirmed moderate affinity for both receptor subtypes, about 10-fold higher for the first one, indicating limited receptor subtype specificity. In key brain areas from the rodent brain, which have a much higher CB₁ receptor density than CB₂, the affinity of UVI3502 was further studied with neuroanatomical specificity by autoradiography. Functional [³⁵S]-GTPγS assays demonstrated that UVI3502 behaved as an antagonist of CB₁ receptors, blocking the stimulation evoked by the potent cannabinoid receptor agonist CP55,940. The in silico characterization of the binding to the CB₁ receptor through molecular docking and molecular dynamics suggests that this activity is explained by the planar and rigid structure of UVI3502, which is optimal for interactions with the inactive state of the receptor. Hence, we synthesized and characterized UVI3502 as a novel antagonist of CB₁, making it a new pharmacological tool for the study of the eCB system and for blocking cannabinoid receptors in the central nervous system.