The cannabinoid CB2 receptor (CB2R) represents a promising therapeutic target for various forms of tissue injury and inflammatory diseases. Although numerous compounds have been developed and widely used to target CB2R, their selectivity, molecular mode of action and pharmacokinetic properties have been poorly characterized. Here we report the most extensive characterization of the molecular pharmacology of the most widely used CB2R ligands to date. In a collaborative effort between multiple academic and industry laboratories, we identify marked differences in the ability of certain agonists to activate distinct signalling pathways and to cause off-target effects. We reach a consensus that HU910, HU308 and JWH133 are the recommended selective CB2R agonists to study the role of CB2R in biological and disease processes. We believe that our unique approach would be highly suitable for the characterization of other therapeutic targets in drug discovery research.

SUMMARY The function of G protein-coupled receptors (GPCRs) can be modulated by a number of endogenous allosteric molecules. In this study, we used molecular dynamics, radioligand binding and thermostability experiments to elucidate the role of the recently discovered sodium ion binding site in the allosteric modulation of the human A2A adenosine receptor, conserved among class A GPCRs. While the binding of antagonists and sodium ions to the receptor was non-competitive in nature, the binding of agonists and sodium ions appears to require mutually exclusive conformational states of the receptor. Amiloride analogs can also bind to the sodium binding pocket showing distinct patterns of agonist and antagonist modulation. These findings suggest that physiological concentrations of sodium ions affect functionally relevant conformational states of GPCRs, and can help to design novel synthetic allosteric modulators or bitopic ligands exploiting the sodium ion binding pocket.

Recently we identified a sodium ion binding pocket in a highresolution structure of the human adenosine A 2A receptor. In the present study we explored this binding site through site-directed mutagenesis and molecular dynamics simulations. Amino acids in the pocket were mutated to alanine, and their influence on agonist and antagonist affinity, allosterism by sodium ions and amilorides, and receptor functionality was explored. Mutation of the polar residues in the Na 1 pocket were shown to either abrogate (D52A 2.50 and N284A7.49