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

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

Physiological function of gastrin-releasing peptide and neuromedin B receptors in regulating itch scratching behavior in the spinal cord of mice.

Pruritus (itch) is a severe side effect associated with the use of drugs as well as hepatic and hematological disorders. Previous studies in rodents suggest that bombesin receptor subtypes i.e. receptors for gastrin-releasing peptide (GRPr) and neuromedin B (NMBr) differentially regulate itch scratching. However, to what degree spinal GRPr and NMBr regulate scratching evoked by intrathecally administered bombesin-related peptides is not known. The first aim of this study was to pharmacologically compare the dose-response curves for scratching induced by intrathecally administered bombesin-related peptides versus morphine, which is known to elicit itch in humans. The second aim was to determine if spinal GRPr and NMBr selectively or generally mediate scratching behavior. Mice received intrathecal injection of bombesin (0.01-0.3 nmol), GRP (0.01-0.3 nmol), NMB (0.1-1 nmol) or morphine (0.3-3 nmol) and were observed for one hour for scratching activity. Bombesin elicited most profound scratching over one hour followed by GRP and NMB, whereas morphine failed to evoke scratching response indicating the insensitivity of mouse models to intrathecal opioid-induced itch. Intrathecal pretreatment with GRPr antagonist RC-3095 (0.03-0.1 nmol) produced a parallel rightward shift in the dose response curve of GRP-induced scratching but not NMB-induced scratching. Similarly, PD168368 (1-3 nmol) only attenuated NMB but not GRP-induced scratching. Individual or co-administration of RC-3095 and PD168368 failed to alter bombesin-evoked scratching. A higher dose of RC-3095 (0.3 nmol) generally suppressed scratching induced by all three peptides but also compromised motor function in the rotarod test. Together, these data indicate that spinal GRPr and NMBr independently drive itch neurotransmission in mice and may not mediate bombesin-induced scratching. GRPr antagonists at functionally receptor-selective doses only block spinal GRP-elicited scratching but the suppression of scratching at higher doses is confounded by motor impairment

Effects of individual or co-administration of GRPr antagonist RC-3095 and NMBr antagonist PD168368 on the dose response curve of bombesin-induced scratching.

<p>Antagonists were administered intrathecally 10 min prior to bombesin. Mice were observed immediately after the administration of bombesin up to 1 h. Each value represents Mean ± SEM (n = 6) for number of scratching bouts. Different symbols represent different dosing conditions.</p

Effects of GRPr antagonist RC-3095 and NMBr antagonist PD168368 on intrathecal GRP- and NMB-induced scratching, respectively.

<p>Antagonists were administered intrathecally 10 min prior to GRP or NMB. Mice were observed immediately after the administration of GRP or NMB up to 1 h. Top panel shows changes in the dose response curve of GRP-induced scratching following RC-3095 pretreatment (A). Bottom panel shows changes in the dose response curve of NMB-induced scratching following PD168368 pretreatment (B). Each value represents mean ± SEM (n = 6) for number of scratching bouts observed across 1 h. Different symbols represent different dosing conditions.</p

Effects of high dose of intrathecal RC-3095 on scratching induced by bombesin-related peptides and motor function.

<p>Top panel shows effects of RC-3095 on GRP, NMB and bombesin-induced scratching (n = 6) (A). Bottom panel shows effects of RC-3095 on the time spent by a mouse balancing on the rotarod (B). Mice (n = 10) were placed on the rotarod 10 min after the injection of RC-3095 and allowed to balance for 180 sec at different speeds. Different symbols represent different dosing conditions. Each value represents Mean ± SEM. An asterisk (*) represents significant difference from the vehicle controls (open bars or open circles; 0 µg) (P<0.05).</p

Cross examination of the effects of GRPr antagonist RC-3095 and NMBr antagonist PD168368 on intrathecal GRP- and NMB-induced scratching.

<p>Antagonists were administered intrathecally 10 min prior to GRP or NMB. Mice were observed immediately after the administration of GRP or NMB up to 1 h. Top panel shows changes in the dose response curve of GRP-induced scratching following pretreatment with active doses of PD168368 and RC-3095 (A). Bottom panel shows changes in the dose response curve of NMB-induced scratching following pretreatment with active doses of RC-3095 and PD168368 (B). Each value represents mean ± SEM (n = 6) for number of scratching bouts observed across 1 h. Different symbols represent different dosing conditions.</p

Comparison of dose response curves of intrathecal bombesin, GRP, NMB and morphine-induced scratching in mice.

<p>Each value represents mean ± SEM (n = 6) for number of scratching bouts observed for 1 h.</p

Effects of intrathecal administration of bombesin-related peptides and morphine on scratching behavior.

<p>Left panels show duration of scratching response and right panels show total number of scratching bouts for bombesin (A,B), GRP (C,D), NMB (E,F) and morphine (G,H). Mice were observed immediately after the intrathecal injections up to 1 h. Each value represents mean ± SEM (n = 6). Symbols represent different dosing conditions. An asterisk (*) represents significant difference from the vehicle controls (open bars; 0 µg) (P<0.05).</p