GPR3 Ligands Discovered through Combined Virtual and Conformational Biosensor-Based Screening

GPR3 belongs to the protein superfamily of G protein-coupled receptors (GPCRs) and plays a central role in both benign and malignant physiological processes, such as energy expenditure in adipocytes and Alzheimer's disease pathology, respectively. Despite the therapeutic potential of both receptor agonists and inverse agonists, GPR3 so far has lacked drug-like ligands and innovative screening technologies, hindering effective drug discovery efforts targeting this receptor. To overcome the limitations of conventional ligand screening techniques based on cAMP accumulation or β-arrestin recruitment, we developed a conformational GPR3 biosensor to monitor receptor activity in living cells with high-throughput screening (HTS)-compatible sensitivity and robustness. Combined with virtual compound screening against homology models of GPR3 and classical medicinal chemistry, this biosensor enabled us to identify new ligands, one of which (compound 33) modulates GPR3-dependent G_s activity with an average potency in the nanomolar range. Our study not only presents novel GPR3 ligands for future optimization efforts and paves the way for even further expansion of the GPR3 ligand repertoire, but our sensor approach also provides a blueprint for targeting other therapeutically attractive yet challenging orphan GPCRs.