Molecular mechanism of allosteric modulation of opioid receptors.

Opioid analgesics provide potent pain relief but are limited by severe adverse effects, tolerance, and interindividual genetic variability in response. Poly-pharmacology and allosteric modulation of opioid receptors offer promising strategies to enhance analgesic efficacy while mitigating these limitations. Pan-positive allosteric modulators (pan-PAMs), which simultaneously potentiate multiple opioid receptor subtypes, integrate the advantages of both approaches and represent an emerging therapeutic paradigm for pain management. However, the molecular mechanisms underlying pan-PAM activity at opioid receptors remain poorly understood. Here, we characterize BMS-986187 as a pan-PAM of opioid receptors and report the cryo-electron microscopy (cryo-EM) structures of multiple opioid receptor subtypes bound to this modulator, revealing a previously unidentified allosteric pocket. Structural and functional analyses revealed a conserved binding motif that mediates PAM recognition across the opioid receptor family and revealed the essential contributions of key opioid receptor residues to allosteric modulation by BMS-986187. Functionally, BMS-986187 enhances analgesic efficacy through an opioid-sparing effect, allowing lower opioid doses and reducing side effects, while restoring activity in loss-of-function (LOF) μ-opioid receptor variants. These findings define a previously unrecognized allosteric site in opioid receptors and establish a structural framework for the rational design of safer and more effective opioid therapeutics through allosteric modulation.