The δ-opioid receptor positive allosteric modulator BMS 986187 is a G-protein-biased allosteric agonist

Abstract

Background and Purpose: The δ-opioid receptor is an emerging target for the management of chronic pain and depression. Biased signalling, the preferential activation of one signalling pathway over another downstream of δ-receptors, may generate better therapeutic profiles. BMS 986187 is a positive allosteric modulator of δ-receptors. Here, we ask if BMS 986187 can directly activate the receptor from an allosteric site, without an orthosteric ligand, and if a signalling bias is generated. Experimental Approach: We used several clonal cell lines expressing δ-receptors, to assess effects of BMS 986187 on events downstream of δ-receptors by measuring G-protein activation, β-arrestin 2 recruitment, receptor phosphorylation, loss of surface receptor expression, ERK1/ERK2 phosphorylation, and receptor desensitization. Key Results: BMS 986187 is a G protein biased allosteric agonist, relative to β-arrestin 2 recruitment. Despite showing direct and potent G protein activation, BMS 986187 has a low potency to recruit β-arrestin 2. This appears to reflect the inability of BMS 986187 to elicit any significant receptor phosphorylation, consistent with low receptor internalization and a slower onset of desensitization, compared with the full agonist SNC80. Conclusions and Implications: This is the first evidence of biased agonism mediated through direct binding to an allosteric site on an opioid receptor, without a ligand at the orthosteric site. Our data suggest that agonists targeting δ-receptors, or indeed any GPCR, through allosteric sites may be a novel way to promote signalling bias and thereby potentially produce a more specific pharmacology than can be observed by activation via the orthosteric site.