Structure-based design of bitopic ligands for the µ-opioid receptor.

Mu-opioid receptor (µOR) agonists such as fentanyl have long been used for pain management, but are considered a major public health concern owing to their adverse side effects, including lethal overdose ¹ . Here, in an effort to design safer therapeutic agents, we report an approach targeting a conserved sodium ion-binding site ² found in µOR ³ and many other class A G-protein-coupled receptors with bitopic fentanyl derivatives that are functionalized via a linker with a positively charged guanidino group. Cryo-electron microscopy structures of the most potent bitopic ligands in complex with µOR highlight the key interactions between the guanidine of the ligands and the key Asp ^2.50 residue in the Na ⁺ site. Two bitopics (C5 and C6 guano) maintain nanomolar potency and high efficacy at G _i subtypes and show strongly reduced arrestin recruitment-one (C6 guano) also shows the lowest G _z efficacy among the panel of µOR agonists, including partial and biased morphinan and fentanyl analogues. In mice, C6 guano displayed µOR-dependent antinociception with attenuated adverse effects, supporting the µOR sodium ion-binding site as a potential target for the design of safer analgesics. In general, our study suggests that bitopic ligands that engage the sodium ion-binding pocket in class A G-protein-coupled receptors can be designed to control their efficacy and functional selectivity profiles for G _i , G _o and G _z subtypes and arrestins, thus modulating their in vivo pharmacology.
(© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)