Background: Recent approved medicines whose active principles are Δ⁹Tetrahidrocannabinol (Δ⁹-THC) and/or cannabidiol (CBD) open novel perspectives for other phytocannabinoids also present in Cannabis sativa L. varieties. Furthermore, solid data on the potential benefits of acidic and varinic phytocannabinoids in a variety of diseases are already available. Mode of action of cannabigerol (CBG), cannabidiolic acid (CBDA), cannabigerolic acid (CBGA), cannabidivarin (CBDV) and cannabigerivarin (CBGV) is, to the very least, partial.

Hypothesis/purpose: Cannabinoid CB₁ or CB₂ receptors, which belong to the G-protein-coupled receptor (GPCR) family, are important mediators of the action of those cannabinoids. Pure CBG, CBDA, CBGA, CBDV and CBGV from Cannabis sativa L. are differentially acting on CB₁ or CB₂ cannabinoid receptors.

Study design: Determination of the affinity of phytocannabinoids for cannabinoid receptors and functional assessment of effects promoted by these compounds when interacting with cannabinoid receptors.

Methods: A heterologous system expressing the human versions of CB₁ and/or CB₂ receptors was used. Binding to membranes was measured using radioligands and binding to living cells using a homogenous time resolved fluorescence resonance energy transfer (HTRF) assay. Four different functional outputs were assayed: determination of cAMP levels and of extracellular-signal-related-kinase phosphorylation, label-free dynamic mass redistribution (DMR) and ß-arrestin recruitment.

Results: Affinity of cannabinoids depend on the ligand of reference and may be different in membranes and in living cells. All tested phytocannabinoids have agonist-like behavior but behaved as inverse-agonists in the presence of selective receptor agonists. CBGV displayed enhanced potency in many of the functional outputs. However, the most interesting result was a biased signaling that correlated with differential affinity, i.e. the overall results suggest that the binding mode of each ligand leads to specific receptor conformations underlying biased signaling outputs.

Conclusion: Results here reported and the recent elucidation of the three-dimensional structure of CB₁ and CB₂ receptors help understanding the mechanism of action that might be protective and the molecular drug-receptor interactions underlying biased signaling.