Allostery at opioid receptors: modulation with small molecule ligands

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/144601/1/bph13823_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/144601/2/bph13823.pd

A promising chemical series of positive allosteric modulators of the μ-opioid receptor that enhance the antinociceptive efficacy of opioids but not their adverse effects

Positive allosteric modulators (PAMs) of the μ-opioid receptor (MOR) have been proposed to exhibit therapeutic potential by maximizing the analgesic properties of clinically used opioid drugs while limiting their adverse effects or risk of overdose as a result of using lower drug doses. We herein report in vitro and in vivo characterization of two small molecules from a chemical series of MOR PAMs that exhibit: (i) MOR PAM activity and receptor subtype selectivity in vitro, (ii) a differential potentiation of the antinociceptive effect of oxycodone, morphine, and methadone in mouse models of pain that roughly correlates with in vitro activity, and (iii) a lack of potentiation of adverse effects associated with opioid administration, such as somatic withdrawal, respiratory depression, and analgesic tolerance. This series of MOR PAMs holds promise for the development of adjuncts to opioid therapy to mitigate against overdose and opioid use disorders

Ligand-Based Discovery of a New Scaffold for Allosteric Modulation of the μ‑Opioid Receptor

With the hope of discovering effective analgesics with fewer side effects, attention has recently shifted to allosteric modulators of the opioid receptors. In the past two years, the first chemotypes of positive or silent allosteric modulators (PAMs or SAMs, respectively) of μ- and δ-opioid receptor types have been reported in the literature. During a structure-guided lead optimization campaign with μ-PAMs BMS-986121 and BMS-986122 as starting compounds, we discovered a new chemotype that was confirmed to display μ-PAM or μ-SAM activity depending on the specific substitutions as assessed by endomorphin-1-stimulated β-arrestin2 recruitment assays in Chinese Hamster Ovary (CHO)-μ PathHunter cells. The most active μ-PAM of this series was analyzed further in competition binding and G-protein activation assays to understand its effects on ligand binding and to investigate the nature of its probe dependence

Allosteric Modulation of the Mu Opioid Receptor.

The mu opioid receptor (MOPr), a G protein-coupled receptor (GPCR), is the pharmacological site of action of morphine and related opioid narcotic agonists that bind to the orthosteric site on MOPr, evolutionarily developed to accommodate the endogenous opioid peptides. MOPr activation results in analgesia but also causes a number of unwanted effects including constipation, respiratory depression, tolerance, and euphoria leading to a high addictive liability. In contrast, small molecule positive allosteric modulators of MOPr (MOPr-PAMs) bind to alternative sites on the protein to modulate receptor function. MOPr PAMs represent a potential avenue for pain relief with a better therapeutic profile. Studies described in this thesis seek to understand the mechanism of action of MOPr PAMs. The results show that MOPr-PAMs promote an active state of MOPr by disruption of the Na+ binding site on the receptor, a mechanism that may be applicable to other GPCRs. Furthermore,this active state can be captured and measured by the camelid antibody Nb39 providing a novel method for quantifying orthosteric and allosteric agonist efficacy. The work also demonstrates that the allosteric site on MOPr can accommodate structurally diverse ligands, and is somewhat conserved on the related delta opioid receptor. Lastly, this thesis explores the effects of chronic allosteric enhancement of MOPr signaling on the downstream processes of receptor desensitization and cellular tolerance in vitro.PhDPharmacologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/120895/1/kelsaliv_1.pd