CB(1) receptor allosteric modulators display both agonist and signaling pathway specificity

Area of Science:

• Pharmacology
• Neuroscience
• Molecular Biology

Background:

• Allosteric modulators of the cannabinoid CB(1) receptor (Org 27569, PSNCBAM-1) were previously identified.
• These compounds exhibit a paradoxical profile: increasing agonist binding while decreasing agonist efficacy.

Purpose of the Study:

• To investigate the effects of Org 27569 and PSNCBAM-1 on various CB(1) receptor-mediated signaling pathways.
• To elucidate the mechanism of action of these allosteric modulators on CB(1) receptor binding kinetics and signaling.

Main Methods:

• Assessed CB(1) receptor agonist-induced [(35)S]GTPγS binding, cAMP production (inhibition and stimulation), ERK phosphorylation, and β-arrestin recruitment.
• Investigated the impact of allosteric modulators on CB(1) agonist binding kinetics and saturation experiments.
• Evaluated ligand dependence and biased antagonism of the compounds.

Main Results:

• Org 27569 demonstrated biased antagonism, inhibiting Gα(s)-mediated signaling, Gα(i)-mediated cAMP production, and β-arrestin recruitment, while enhancing agonist-induced ERK phosphorylation.
• Both compounds acted as allosteric agonists alone, increasing cAMP production and ERK phosphorylation.
• Binding experiments indicated that Org 27569 and PSNCBAM-1 modulated maximum occupancy rather than affinity of orthosteric ligands.
• A common mechanism was identified where modulators increase high-affinity CB(1) agonist binding sites.

Conclusions:

• The allosteric modulators stabilize a receptor conformation that induces signaling and selectively directs orthosteric agonist signaling through the ERK phosphorylation pathway.
• These findings provide insight into the complex pharmacology of CB(1) receptor allosteric modulation and biased signaling.