Methylation Products of 6β- N-Heterocyclic Substituted Naltrexamine Derivatives as Potential Peripheral Opioid Receptor Modulators

Design, Synthesis, and Biological Evaluation of NAP Isosteres: A Switch from Peripheral to Central Nervous System Acting Mu-Opioid Receptor Antagonists

The μ opioid receptor (MOR) has been an intrinsic target to develop treatment of opioid use disorders (OUD). Herein, we report our efforts on developing centrally acting MOR antagonists by structural modifications of 17-cyclopropylmethyl-3,14-dihydroxy-4,5α-epoxy-6β-[(4'-pyridyl) carboxamido] morphinan (NAP), a peripherally acting MOR-selective antagonist. An isosteric replacement concept was applied and incorporated with physiochemical property predictions in the molecular design. Three analogs, namely, 25, 26, and 31, were identified as potent MOR antagonists in vivo with significantly fewer withdrawal symptoms than naloxone observed at similar doses. Furthermore, brain and plasma drug distribution studies supported the outcomes of our design strategy on these compounds. Taken together, our isosteric replacement of pyridine with pyrrole, furan, and thiophene provided insights into the structure-activity relationships of NAP and aided the understanding of physicochemical requirements of potential CNS acting opioids. These efforts resulted in potent, centrally efficacious MOR antagonists that may be pursued as leads to treat OUD.

Verifying the role of 3-hydroxy of 17-cyclopropylmethyl-4,5α-epoxy-3,14β-dihydroxy-6β-[(4'-pyridyl) carboxamido]morphinan derivatives via their binding affinity and selectivity profiles on opioid receptors

In the present study, the role of 3-hydroxy group of a series of epoxymorphinan derivatives in their binding affinity and selectivity profiles toward the opioid receptors (ORs) has been investigated. It was found that the 3-hydroxy group was crucial for the binding affinity of these derivatives for all three ORs due to the fact that all the analogues 1a-e exhibited significantly higher binding affinities compared to their counterpart 3-dehydroxy ones 6a-e. Meanwhile most compounds carrying the 3-hydroxy group possessed similar selectivity profiles for the kappa opioid receptor over the mu opioid receptor as their corresponding 3-dehydroxy derivatives. [³⁵S]-GTPγS functional assay results indicated that the 3-hydroxy group of these epoxymorphinan derivatives was important for maintaining their potency on the ORs with various effects. Further molecular modeling studies helped comprehend the remarkably different binding affinity and functional profiles between compound 1c (NCP) and its 3-dehydroxy analogue 6c.

Comparison of Pharmacological Properties between the Kappa Opioid Receptor Agonist Nalfurafine and 42B, Its 3-Dehydroxy Analogue: Disconnect between in Vitro Agonist Bias and in Vivo Pharmacological Effects

Nalfurafine, a moderately selective kappa opioid receptor (KOR) agonist, is used in Japan for treatment of itch without causing dysphoria or psychotomimesis. Here we characterized the pharmacology of compound 42B, a 3-dehydroxy analogue of nalfurafine and compared with that of nalfurafine. Nalfurafine and 42B acted as full KOR agonists and partial μ opioid receptor (MOR) agonists, but 42B showed much lower potency for both receptors and lower KOR/MOR selectivity, different from previous reports. Molecular modeling revealed that water-mediated hydrogen-bond formation between 3-OH of nalfurafine and KOR accounted for its higher KOR potency than 42B. The higher potency of both at KOR over MOR may be due to hydrogen-bond formation between nonconserved Y^7.35 of KOR and their carbonyl groups. Both showed modest G protein signaling biases. In mice, like nalfurafine, 42B produced antinociceptive and antiscratch effects and did not cause conditioned place aversion (CPA) in the effective dose ranges. Unlike nalfurafine, 42B caused motor incoordination and hypolocomotion. As both agonists showed G protein biases, yet produced different effects on locomotor activity and motor incoordination, the findings and those in the literature suggest caution in correlating in vitro biochemical data with in vivo behavior effects. The factors contributing to the disconnect, including pharmacodynamic and pharmacokinetic issues, are discussed. In addition, our results suggest that among the KOR-induced adverse behaviors, CPA can be separated from motor incoordination and hypolocomotion.

Endogenous Opiates and Behavior: 2018

This paper is the forty-first consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2018 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (2), the roles of these opioid peptides and receptors in pain and analgesia in animals (3) and humans (4), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (5), opioid peptide and receptor involvement in tolerance and dependence (6), stress and social status (7), learning and memory (8), eating and drinking (9), drug abuse and alcohol (10), sexual activity and hormones, pregnancy, development and endocrinology (11), mental illness and mood (12), seizures and neurologic disorders (13), electrical-related activity and neurophysiology (14), general activity and locomotion (15), gastrointestinal, renal and hepatic functions (16), cardiovascular responses (17), respiration and thermoregulation (18), and immunological responses (19).

Pharmacological characterization of 17-cyclopropylmethyl-3,14-dihydroxy-4,5-epoxy-6-[(3'-fluoro-4'-pyridyl)acetamido]morphinan (NFP) as a dual selective MOR/KOR ligand with potential applications in treating opioid use disorder

For thousands of years opioids have been the first-line treatment option for pain management. However, the tolerance and addiction potential of opioids limit their applications in clinic. NFP, a MOR/KOR dual-selective opioid antagonist, was identified as a ligand that significantly antagonized the antinociceptive effects of morphine with lesser withdrawal effects than naloxone at similar doses. To validate the potential application of NFP in opioid addiction treatment, a series of in vitro and in vivo assays were conducted to further characterize its pharmacological profile. In calcium mobilization assays and MOR internalization studies, NFP showed the apparent capacity to antagonize DAMGO-induced calcium flux and etorphine-induced MOR internalization. In contrast to the opioid agonists DAMGO and morphine, cells pretreated with NFP did not show apparent desensitization and down regulation of the MOR. Though in vitro bidirectional transport studies showed that NFP might be a P-gp substrate, in warm-water tail-withdrawal assays it was able to antagonize the antinociceptive effects of morphine indicating its potential central nervous system activity. Overall these results suggest that NFP is a promising dual selective opioid antagonist that may have the potential to be used therapeutically in opioid use disorder treatment.

Characterization of 17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6α-(indole-7-carboxamido)morphinan (NAN) as a Novel Opioid Receptor Modulator for Opioid Use Disorder Treatment

The opioid crisis is a significant public health issue with more than 115 people dying from opioid overdose per day in the United States. The aim of the present study was to characterize the in vitro and in vivo pharmacological effects of 17-cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6α-(indole-7-carboxamido)morphinan (NAN), a μ opioid receptor (MOR) ligand that may be a potential candidate for opioid use disorder treatment that produces less withdrawal signs than naltrexone. The efficacy of NAN was compared to varying efficacy ligands at the MOR, and determined at the δ opioid receptor (DOR) and κ opioid receptor (KOR). NAN was identified as a low efficacy partial agonist for G-protein activation at the MOR and DOR, but had relatively high efficacy at the KOR. In contrast to high efficacy MOR agonists, NAN did not induce MOR internalization, downregulation, or desensitization, but it antagonized agonist-induced MOR internalization and stimulation of intracellular Ca2+ release. Opioid withdrawal studies conducted using morphine-pelleted mice demonstrated that NAN precipitated significantly less withdrawal signs than naltrexone at similar doses. Furthermore, NAN failed to produce fentanyl-like discriminative stimulus effects in rats up to doses that produced dose- and time-dependent antagonism of fentanyl. Overall, these results provide converging lines of evidence that NAN functions mainly as a MOR antagonist and support further consideration of NAN as a candidate medication for opioid use disorder treatment.