Dual allosteric and orthosteric pharmacology of synthetic analog cannabidiol-dimethylheptyl, but not cannabidiol, on the cannabinoid CB receptor.

Cannabinoid CB receptor (CBR) is a class A G protein-coupled receptor (GPCR) involved in a broad spectrum of physiological processes and pathological conditions. For that reason, targeting CBR might provide therapeutic opportunities in neurodegenerative disorders, neuropathic pain, inflammatory diseases, and cancer. The main components from Cannabis sativa, such as Δ-tetrahydrocannabinol (Δ-THC) and cannabidiol (CBD), have been therapeutically exploited and synthetically-derived analogs have been generated. One example is cannabidiol-dimethylheptyl (CBD-DMH), which exhibits anti-inflammatory effects. Nevertheless, its pharmacological mechanism of action is not yet fully understood and is hypothesized for multiple targets, including CBR. The aim of this study was to further investigate the molecular pharmacology of CBD-DMH on CBR while CBD was taken along as control. These compounds were screened in equilibrium and kinetic radioligand binding studies and various functional assays, including G protein activation, inhibition of cAMP production and ß-arrestin-2 recruitment. In dissociation studies, CBD-DMH allosterically modulated the radioligand binding. Furthermore, CBD-DMH negatively modulated the G protein activation of reference agonists CP55,940, AEA and 2-AG, but not the agonist-induced ß-arrestin-2 recruitment. Nevertheless, CBD-DMH also displayed competitive binding to CBR and partial agonism on G protein activation, inhibition of cAMP production and ß-arrestin-2 recruitment. CBD did not exhibit such allosteric behavior and only very weakly bound CBR without activation. This study shows a dual binding mode of CBD-DMH, but not CBD, to CBR with the suggestion of two different binding sites. Altogether, it encourages further research into this dual mechanism which might provide a new class of molecules targeting CBR.