Translocation of arrestin induced by human A3 adenosine receptor ligands in an engineered cell line: Comparison with G protein-dependent pathways

Structurally diverse ligands were studied in A3 adenosine receptor (AR)-mediated β-arrestin translocation in engineered CHO cells. The agonist potency and efficacy were similar, although not identical, to their G protein signaling. However, differences have also been found. MRS542, MRS1760, and other adenosine derivatives, A3AR antagonists in cyclic AMP assays, were partial agonists in β-arrestin translocation, indicating possible biased agonism. The xanthine 7-riboside DBXRM, a full agonist, was only partially efficacious in β-arrestin translocation. DBXRM was shown to induce a lesser extent of desensitization compared with IB-MECA. In kinetic studies, MRS3558, a potent and selective A3AR agonist, induced β-arrestin translocation significantly faster than IB-MECA and Cl-IB-MECA. Non-nucleoside antagonists showed similar inhibitory potencies as previously reported. PTX pretreatment completely abolished ERK1/2 activation, but not arrestin translocation. Thus, lead candidates for biased agonists at the A3AR have been identified with this arrestin-translocation assay, which promises to be an effective tool for ligand screening.