BU10038 as a safe opioid analgesic with fewer side-effects after systemic and intrathecal administration in primates

© 2019 British Journal of Anaesthesia. Published by Elsevier Ltd. All rights reserved.Background: The marked increase in mis-use of prescription opioids has greatly affected our society. One potential solution is to develop improved analgesics which have agonist action at both mu opioid peptide (MOP) and nociceptin/orphanin FQ peptide (NOP) receptors. BU10038 is a recently identified bifunctional MOP/NOP partial agonist. The aim of this study was to determine the functional profile of systemic or spinal delivery of BU10038 in primates after acute and chronic administration. Methods: A series of behavioural and physiological assays have been established specifically to reflect the therapeutic (analgesia) and side-effects (abuse potential, respiratory depression, itch, physical dependence, and tolerance) of opioid analgesics in rhesus monkeys. Results: After systemic administration, BU10038 (0.001–0.01 mg kg −1 ) dose-dependently produced long-lasting antinociceptive and antihypersensitive effects. Unlike the MOP agonist oxycodone, BU10038 lacked reinforcing effects (i.e. little or no abuse liability), and BU10038 did not compromise the physiological functions of primates including respiration, cardiovascular activities, and body temperature at antinociceptive doses and a 10–30-fold higher dose (0.01–0.1 mg kg −1 ). After intrathecal administration, BU10038 (3 μg) exerted morphine-comparable antinociception and antihypersensitivity without itch scratching responses. Unlike morphine, BU10038 did not cause the development of physical dependence and tolerance after repeated and chronic administration. Conclusions: These in vivo findings demonstrate the translational potential of bifunctional MOP/NOP receptor agonists such as BU10038 as a safe, non-addictive analgesic with fewer side-effects in primates. This study strongly supports that bifunctional MOP/NOP agonists may provide improved analgesics and an alternative solution for the ongoing prescription opioid crisis.Peer reviewedFinal Published versio

OREX-1038:A potential new treatment for pain with low abuse liability and limited adverse effects

Drugs targeting mu opioid receptors are the mainstay of clinical practice for treating moderate-to-severe pain. While they can offer excellent analgesia, their use can be limited by adverse effects, including constipation, respiratory depression, tolerance, and abuse liability. Multifunctional ligands acting at mu opioid and nociceptin/orphanin FQ peptide receptors might provide antinociception with substantially improved adverse-effect profiles. This study explored one of these ligands, OREX-1038 (BU10038), in several assays in rodents and nonhuman primates. Binding and functional studies confirmed OREX-1038 to be a low-efficacy agonist at mu opioid and nociceptin/orphanin FQ peptide receptors and an antagonist at delta and kappa opioid receptors with selectivity for opioid receptors over other proteins. OREX-1038 had long-acting antinociceptive effects in postsurgical and complete Freund's adjuvant (CFA)-induced thermal hyperalgesia assays in rats and a warm water tail-withdrawal assay in monkeys. OREX-1038 was active for at least 24 h in each antinociception assay, and its effects in monkeys did not diminish over 22 days of daily administration. This activity was coupled with limited effects on physiological signs (arterial pressure, heart rate, and body temperature) and no evidence of withdrawal after administration of naltrexone or discontinuation of treatment in monkeys receiving OREX-1038 daily. Over a range of doses, OREX-1038 was only transiently self-administered, which diminished rapidly to nonsignificant levels; overall, both OREX-1038 and buprenorphine maintained less responding than remifentanil. These results support the concept of dual mu and nociceptin/orphanin FQ peptide receptor partial agonists having improved pharmacological profiles compared with opioids currently used to treat pain.</p

A novel orvinol analog, BU08028, as a safe opioid analgesic without abuse liability in primates

Despite the critical need, no previous research has substantiated safe opioid analgesics without abuse liability in primates. Recent advances in medicinal chemistry have led to the development of ligands with mixed mu opioid peptide (MOP)/nociceptin-orphanin FQ peptide (NOP) receptor agonist activity to achieve this objective. BU08028 is a novel orvinol analog that displays a similar binding profile to buprenorphine with improved affinity and efficacy at NOP receptors. The aim of this preclinical study was to establish the functional profile of BU08028 in monkeys using clinically used MOP receptor agonists for side-by-side comparisons in various well-honed behavioral and physiological assays. Systemic BU08028 (0.001–0.01 mg/kg) produced potent long-lasting (i.e., >24 h) antinociceptive and antiallodynic effects, which were blocked by MOP or NOP receptor antagonists. More importantly, the reinforcing strength of BU08028 was significantly lower than that of cocaine, remifentanil, or buprenorphine in monkeys responding under a progressive-ratio schedule of drug self-administration. Unlike MOP receptor agonists, BU08028 at antinociceptive doses and ∼10- to 30-fold higher doses did not cause respiratory depression or cardiovascular adverse events as measured by telemetry devices. After repeated administration, the monkeys developed acute physical dependence on morphine, as manifested by precipitated withdrawal signs, such as increased respiratory rate, heart rate, and blood pressure. In contrast, monkeys did not show physical dependence on BU08028. These in vivo findings in primates not only document the efficacy and tolerability profile of bifunctional MOP/NOP receptor agonists, but also provide a means of translating such ligands into therapies as safe and potentially abuse-free opioid analgesics

Orvinols with mixed kappa/mu opioid receptor agonist activity

[Image: see text] Dual-acting kappa opioid receptor (KOR) agonist and mu opioid receptor (MOR) partial agonist ligands have been put forward as potential treatment agents for cocaine and other psychostimulant abuse. Members of the orvinol series of ligands are known for their high binding affinity to both KOR and MOR, but efficacy at the individual receptors has not been thoroughly evaluated. In this study, it is shown that a predictive model for efficacy at KOR can be derived, with efficacy being controlled by the length of the group attached to C20 and by the introduction of branching into the side chain. In vivo evaluation of two ligands with the desired in vitro profile confirms both display KOR, and to a lesser extent MOR, activity in an analgesic assay suggesting that, in this series, in vitro measures of efficacy using the [(35)S]GTPγS assay are predictive of the in vivo profile

Structural determinants of opioid and NOP receptor activity in derivatives of buprenorphine

The unique pharmacological profile of buprenorphine has led to its considerable success as an analgesic and as a treatment agent for drug abuse. Activation of nociceptin/orphanin FQ peptide (NOP) receptors has been postulated to account for certain aspects of buprenorphine’s behavioural profile. In order to investigate the role of NOP activation further, a series of buprenorphine analogues has been synthesised with the aim of increasing affinity for the NOP receptor. Binding and functional assay data on these new compounds indicate that the area around C20 in the orvinols is key to NOP receptor activity, with several compounds displaying higher affinity than buprenorphine. One compound, 1b, was found to be a mu opioid receptor partial agonist of comparable efficacy to buprenorphine, but with higher efficacy at NOP receptors

Borrowing hydrogen in the synthesis of biologically relevant molecules

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