Dimethylindanoylindole isomers revealed different pharmacological profiles at CB1 and CB2 cannabinoid receptors

Synthetic cannabinoid receptor agonists (SCRAs) represent one of the most rapidly growing classes of novel psychoactive substances (NPS) and exhibit higher efficacy and potency at CB1 and CB2 cannabinoid receptors (CB1 and CB2) compared to Δ ⁹ -tetrahydrocannabinol, contributing to distinct adverse effects absent in cannabis use. 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 using bioluminescence resonance energy transfer (BRET) assays to assess key CB1 and CB2 transducer pathways. Site-directed mutagenesis characterized contributions of non-conserved residues between CB1 and CB2 and aromatic residues on CB1 transmembrane helix 2 (TM2). This study provided insights into the molecular determinants of cannabinoid receptor selectivity and efficacy.