PT - JOURNAL ARTICLE AU - Kirstie A. Bennett AU - Benjamin Tehan AU - Guillaume Lebon AU - Christopher G. Tate AU - Malcolm Weir AU - Fiona H. Marshall AU - Christopher J. Langmead TI - Pharmacology and Structure of Isolated Conformations of the Adenosine A<sub>2A</sub> Receptor Define Ligand Efficacy AID - 10.1124/mol.112.084509 DP - 2013 May 01 TA - Molecular Pharmacology PG - 949--958 VI - 83 IP - 5 4099 - http://molpharm.aspetjournals.org/content/83/5/949.short 4100 - http://molpharm.aspetjournals.org/content/83/5/949.full SO - Mol Pharmacol2013 May 01; 83 AB - Using isolated receptor conformations crystal structures of the adenosine A2A receptor have been solved in active and inactive states. Studying the change in affinity of ligands at these conformations allowed qualitative prediction of compound efficacy in vitro in a system-independent manner. Agonist 5′-N-ethylcarboxamidoadenosine displayed a clear preference to bind to the active state receptor; inverse agonists (xanthine amine congener, ZM241385, SCH58261, and preladenant) bound preferentially to the inactive state, whereas neutral antagonists (theophylline, caffeine, and istradefylline) demonstrated equal affinity for active and inactive states. Ligand docking into the known crystal structures of the A2A receptor rationalized the pharmacology observed; inverse agonists, unlike neutral antagonists, cannot be accommodated within the agonist-binding site of the receptor. The availability of isolated receptor conformations opens the door to the concept of “reverse pharmacology” whereby the functional pharmacology of ligands can be characterized in a system-independent manner by their affinity for a pair (or set) of G protein–coupled receptor conformations.