Structural and functional insights into the G protein-coupled receptors: CB1 and CB2.

The cannabinoid receptors CB1 and CB2 mediate a variety of physiological processes and continue to be explored as desirable drug targets. Both receptors are activated by the endogenous endocannabinoids and the psychoactive components of marijuana. Over the years, many efforts have been made to make selective ligands; however, the high degree of homology between cannabinoid receptor subtypes introduces challenges in studying either receptor in isolation. Recent advancements in structure biology have resulted in a surge of high-resolution structures, enriching our knowledge and understanding of receptor structure and function. In this review, of recent cannabinoid receptor structures, key features of the inactive and active state CB1 and CB2 are presented. These structures will provide additional insight into the modulation and signaling mechanism of cannabinoid receptors CB1 and CB2 and aid in the development of future therapeutics.

Improved cyclobutyl nabilone analogs as potent CB1 receptor agonists.

In earlier work, we explored the SAR for the C3 side chain pharmacophore in the hexahydrocannabinol template represented by the drug nabilone, which resulted in the development of AM2389. In an effort for further optimization, we have merged features of nabilone and AM2389 and explored the C3 side chain with varying chain lengths and terminal substitutions. Of the compounds described here, a nabilone analog, AM8936, with the C6'-cyano-substituted side chain, was identified as the most successful analog capable of serving as a potential candidate for further development and a valuable tool for further in vivo studies. AM8936 behaved as a balanced and potent CB1 agonist in functional assays and was a potent and efficacious CB1 agonist in vivo. Our SAR studies are highlighted with the docking of AM8936 on the crystal structure of the hCB1 receptor.

Novel Functionalized Cannabinoid Receptor Probes: Development of Exceptionally Potent Agonists.

We report the development of novel cannabinergic probes that can stabilize the cannabinoid receptors (CBRs) through tight binding interactions. Ligand design involves the introduction of select groups at a judiciously chosen position within the classical hexahydrocannabinol template (monofunctionalized probes). Such groups include the electrophilic isothiocyanato, the photoactivatable azido, and the polar cyano moieties. These groups can also be combined to produce bifunctionalized probes potentially capable of interacting at two distinct sites within the CBR-binding domains. These novel compounds display remarkably high binding affinities for CBRs and are exceptionally potent agonists. A key ligand (27a, AM11245) exhibits exceptionally high potency in both in vitro and in vivo assays and was designated as "megagonist," a property attributed to its tight binding profile. By acting both centrally and peripherally, 27a distinguishes itself from our previously reported "megagonist" AM841, whose functions are restricted to the periphery.

Activation and Signaling Mechanism Revealed by Cannabinoid Receptor-Gi Complex Structures.

Human endocannabinoid systems modulate multiple physiological processes mainly through the activation of cannabinoid receptors CB1 and CB2. Their high sequence similarity, low agonist selectivity, and lack of activation and G protein-coupling knowledge have hindered the development of therapeutic applications. Importantly, missing structural information has significantly held back the development of promising CB2-selective agonist drugs for treating inflammatory and neuropathic pain without the psychoactivity of CB1. Here, we report the cryoelectron microscopy structures of synthetic cannabinoid-bound CB2 and CB1 in complex with Gi, as well as agonist-bound CB2 crystal structure. Of important scientific and therapeutic benefit, our results reveal a diverse activation and signaling mechanism, the structural basis of CB2-selective agonists design, and the unexpected interaction of cholesterol with CB1, suggestive of its endogenous allosteric modulating role.