Synthesis and Evaluation of a Novel Bivalent Selective Antagonist for the Mu-Delta Opioid Receptor Heterodimer that Reduces Morphine Withdrawal in Mice

A major limitation in the study of the mu-delta opioid receptor heterodimer (MDOR) is that few selective pharmacological tools exist and no heteromer-selective antagonists. We thus designed a series of variable-length (15–41 atoms) bivalent linked peptides with selective but moderate/low-affinity pharmacophores for the mu and delta opioid receptors. We observed a U-shaped MDOR potency/affinity profile in vitro, with the 24-atom spacer length (<b>D24M</b>) producing the highest MDOR potency/affinity (<1 nM) and selectivity (≥89-fold). We further evaluated <b>D24M</b> in mice and observed that <b>D24M</b> dose-dependently antagonized tail flick antinociception produced by the MDOR agonists CYM51010 and Deltorphin-II, without antagonizing the monomer agonists DAMGO and DSLET. We also observed that <b>D24M</b> sharply reduced withdrawal behavior in models of acute and chronic morphine dependence. These findings suggest that <b>D24M</b> is a first-in-class high-potency MDOR-selective antagonist both in vitro and in vivo

6'-Guanidinonaltrindole (6'-GNTI) is a potent and functionally unique kappa opioid agonist that displays bias against beta-arrestin recruitment and receptor internalization

<p>Endogenous ligands, and drugs which mimic their effects, can activate multiple second messenger pathways through one receptor. Structurally distinct ligands can bias G protein coupled receptor (GPCR) signaling towards selected cellular signaling pathways both in cell culture and in vivo. The implications of such signaling divergence is particularly intriguing considering that engaging differential pathways may be useful for imparting different and distinct pharmacological effects in vivo. The kappa opioid receptor (KOR) can be activated in just such a manner to induce differential signaling. In this study, we find that 6'-guanidinonaltrindole (6’-GNTI) is a partial agonist at KOR in regards to G protein coupling while it is a full agonist at the receptor for activating ERK and for its ability to induce changes in cellular impedance. In all three signaling assays, 6’-GNTI is more potent than the standard selective kappa opioid agonist, U69,593. Interestingly, 6’-GNTI does not promote βarrestin-2 recruitment and receptor internalization and therefore displays bias against this signaling pathway. Moreover, 6’-GNTI partially antagonizes U69,593-stimulated G protein coupling and fully blocks U69,593-stimulated βarrestin2 coupling and KOR internalization. 6’-GNTI also displays functional selectivity in vivo by acting as an inverse agonist for G protein coupling in spinal cord but not striatum, and by differentially activating ERK MAPK and Akt in primary neonatal striatal neurons. Thus, 6’-GNTI is a unique ligand of the KOR that may prove useful in delineating functionally selective signaling complexes and behaviors both in vitro and in vivo.</p> <p>Presented on 10th April 2011 at Experimental Biology (Washington DC).</p> <p>Abstract published as:</p> <p>Streicher JM, Groer CE, Munro T, Béguin C, Cohen BM, Bohn LM (2011): 6'-Guanidinonaltrindole (6'-GNTI) is a potent and functionally unique kappa opioid agonist that displays bias against beta-arrestin recruitment and receptor internalization.<br>The FASEB Journal, 25(Meeting Abstracts):626.2.</p> <p>Full report subsequently published as:</p> <p>Schmid CL, Streicher JM, Groer CE, Munro TA, Zhou L, Bohn LM (2013): Functional Selectivity of 6′-Guanidinonaltrindole (6′-GNTI) at κ-Opioid Receptors in Striatal Neurons.<br>Journal of Biological Chemistry, 288(31):22387-22398. doi:10.1074/jbc.M113.476234<br>© the American Society for Biochemistry and Molecular Biology.</p

17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-(4′-pyridylcarboxamido)morphinan (NAP) Modulating the Mu Opioid Receptor in a Biased Fashion

Mounting evidence has suggested that G protein-coupled receptors can be stabilized in multiple conformations in response to distinct ligands, which exert discrete functions through selective activation of various downstream signaling events. In accordance with this concept, we report biased signaling of one C6-heterocyclic substituted naltrexamine derivative, namely, 17-cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-(4′-pyridylcarboxamido)­morphinan (NAP) at the mu opioid receptor (MOR). NAP acted as a low efficacy MOR partial agonist in the G protein-mediated [³⁵S]­GTPγS binding assay, whereas it did not significantly induce calcium flux or β-arrestin2 recruitment. In contrast, it potently blocked MOR full agonist-induced β-arrestin2 recruitment and translocation. Additionally, NAP dose-dependently antagonized MOR full agonist-induced intracellular calcium flux and β-arrestin2 recruitment. Further results in an isolated organ bath preparation confirmed that NAP reversed the morphine-induced reduction in colon motility. Ligand docking and dynamics simulation studies of NAP at the MOR provided more supporting evidence for biased signaling of NAP at an atomic level. Due to the fact that NAP is MOR selective and preferentially distributed peripherally upon systemic administration while β-arrestin2 is reportedly required for impairment of intestinal motility by morphine, biased antagonism of β-arrestin2 recruitment by NAP further supports its utility as a treatment for opioid-induced constipation

Discovery of Small Molecule Kappa Opioid Receptor Agonist and Antagonist Chemotypes through a HTS and Hit Refinement Strategy

Herein we present the outcome of a high throughput screening (HTS) campaign-based strategy for the rapid identification and optimization of selective and general chemotypes for both kappa (κ) opioid receptor (KOR) activation and inhibition. In this program, we have developed potent antagonists (IC₅₀ < 120 nM) or agonists of high binding affinity (<i>K</i>_i < 3 nM). In contrast to many important KOR ligands, the compounds presented here are highly modular, readily synthesized, and, in most cases, achiral. The four new chemotypes hold promise for further development into chemical tools for studying the KOR or as potential therapeutic lead candidates