Dimethylindanoylindole Isomers Revealed Different Pharmacological Profiles at CB1 and CB2 Cannabinoid Receptors

Abstract Synthetic cannabinoid receptor agonists (SCRAs) exhibit higher efficacy and potency at CB1 and CB2 cannabinoid receptors compared to Δ9-tetrahydrocannabinol, contributing to adverse effects associated with their growing prevalence as novel psychoactive substances. The indole-based SCRAs GBD-002 and GBD-003, incorporating 2,2-dimethylindane, differ by a single substituent position yet display markedly different receptor binding profiles. We evaluated both the GBD-002/GBD-003 pair and an analogous structural isomer pair JWH-018/JWH-018 2′-naphthyl using bioluminescence resonance energy transfer (BRET) assays to assess key CB1 and CB2 transducer pathways, including Gαi1 engagement, β-arrestin 2 recruitment, and cAMP inhibition. Site-directed mutagenesis characterized contributions of nonconserved residues between CB1 and CB2 as well as aromatic residues on CB1 transmembrane helix 2 (TM2). This study provided insights into the molecular determinants of cannabinoid receptor selectivity and efficacy.