TY - JOUR T1 - Investigating mGlu5 Allosteric Modulator Cooperativity, Affinity and Agonism: Enriching Structure-function Studies and Structure-activity Relationships JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.112.080531 SP - mol.112.080531 AU - Karen J Gregory AU - Meredith J Noetzel AU - Jerri M Rook AU - Paige N Vinson AU - Shaun R Stauffer AU - Alice L Rodriguez AU - Kyle A Emmitte AU - Ya Zhou AU - Aspen C Chun AU - Andrew S Felts AU - Brian A Chauder AU - Craig W Lindsley AU - Colleen M Niswender AU - P. Jeffrey Conn Y1 - 2012/08/03 UR - http://molpharm.aspetjournals.org/content/early/2012/08/03/mol.112.080531.abstract N2 - Increasingly, drug discovery programs are focusing on allosteric modulators as a means to modify activity of G protein-coupled receptor (GPCR) targets. Allosteric binding sites are topographically distinct from the endogenous ligand-(orthosteric) binding site, allowing for co-occupation of a single receptor with the endogenous ligand and an allosteric modulator that can alter receptor pharmacology. Negative allosteric modulators (NAMs) inhibit, while positive allosteric modulators (PAMs) enhance, the affinity and/or efficacy of the orthosteric agonist. Established approaches for estimating affinities and efficacy of orthosteric ligands are not appropriate for allosteric modulators and this raises challenges in fully understanding the actions of novel modulators of GPCRs. Metabotropic glutamate receptor 5 (mGlu5) is a family C GPCR for which a large array of allosteric modulators has been identified. We have taken advantage of the wealth of tools for probing allosteric sites on mGlu5 to validate an operational model of allosterism that allows quantitative estimates of modulator affinity and cooperativity. Affinity estimates derived from functional assays fit well with measured affinities from radioligand binding experiments for both PAMs and NAMs from diverse chemical scaffolds with varying degrees of cooperativity. Interestingly, we observed modulation bias for PAMs when comparing mGlu5-mediated Ca++ mobilization and phosphorylation of ERK1/2. Furthermore, we utilize this model to quantify the impact of mutations that reduce binding or potentiation by PAMs. This model can be applied to PAM and NAM potency curves in combination with maximal fold shift data to derive reliable estimates of modulator affinity. ER -