Functional Profile of Systemic and Intrathecal Cebranopadol in Nonhuman Primates

Cebranopadol, a novel long-acting opioid agonist with low abuse liability, to treat opioid use disorder: Preclinical evidence of efficacy

Maintenance therapy with buprenorphine and methadone is the gold standard pharmacological treatment for opioid use disorder (OUD). Despite these compounds demonstrating substantial efficacy, a significant number of patients do not show optimal therapeutic responses. The abuse liability of these medications is also a concern. Here we used rats to explore the therapeutic potential of the new long-acting pan-opioid agonist Cebranopadol in OUD. We tested the effect of cebranopadol on heroin self-administration and yohimbine-induced reinstatement of heroin seeking. In addition, we evaluated the abuse liability potential of cebranopadol in comparison to that of heroin under fixed ratio 1 (FR1) and progressive ratio (PR) operant self-administration contingencies. Oral administration of cebranopadol (0, 25, 50 μg/kg) significantly attenuated drug self-administration independent of heroin dose (1, 7, 20, 60μg/inf). Cebranopadol also reduced the break point for heroin (20 μg/inf). Finally, pretreatment with cebranopadol significantly attenuated yohimbine-induced reinstatement of drug seeking. In abuse liability experiments under FR1 contingency, rats maintained responding for heroin (1, 7, 20, 60μg/inf) to a larger extent than cebranopadol (0.03, 0.1, 0.3, 1.0, 6.0μg/inf). Under PR contingency, heroin maintained responding at high levels at all except the lowest dose, while the break point (BP) for cebranopadol did not differ from that of saline. Together, these data indicate that cebranopadol is highly efficacious in attenuating opioid self-administration and stress-induced reinstatement, while having limited abuse liability properties. Overall, the data suggest clinical potential of this compound for OUD treatment.

Lumbar Intrathecal Injection in Adult and Neonatal Mice

This article describes a step-by-step process of lumbar intrathecal injection of Evans blue dye and AAV9-EGFP in adult (2-month-old) and neonatal (postnatal day 10) mice. Intrathecal injection is a clinically translatable technique that has already been extensively applied in humans. In mice, intrathecal injection is considered a challenging procedure that requires a trained and experienced researcher. For both adult and neonatal mice, lumbar intrathecal injection is directed into the L5-L6 intervertebral space. Intrathecally injected material enters the cerebrospinal fluid (CSF) within the intrathecal space from where it can directly access the central nervous system (CNS) parenchyma. Simultaneously, intrathecally injected material exits the CSF with pressure gradient and enters the endoneurial fluid and ultimately the peripheral nerves. While in the CSF, the injectable material also enters the bloodstream and systemic circulation through the arachnoid villi. A successful lumbar intrathecal injection results in adequate biodistribution of the injectable material in the CNS, PNS, and peripheral organs. When correctly applied, this technique is considered as minimally invasive and non-disruptive and can be used for the lumbar delivery of any solute. © 2024 Wiley Periodicals LLC. Basic Protocol 1: C57BL/6 adult and P10 mice lumbar intrathecal injection Basic Protocol 2: Tissue collection and preparation for evaluating Evans blue dye diffusion Basic Protocol 3: Tissue collection and preparation for immunohistochemistry staining Basic Protocol 4: Tissue collection and vector genome copy number analysis.

Impact of the COVID-19 Pandemic on Functions of Nursing Professionals in the Care of Opioid Use Disorder: Systematic Review

BACKGROUND

Nursing professionals are vitally involved in the cascade of care for opioid use disorders (OUDs). The global spread of COVID-19 has had complex effects on public health aspects of major diseases, including OUDs. There are limited data on the major ways in which the COVID-19 pandemic has affected the functions of nursing professionals in the care of OUDs.

METHOD

This systematic review followed Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines and examined published data for trends in OUD care during the first 2 years of the COVID-19 pandemic, focusing on nursing functions. The National Library of Medicine PubMed database and the EMBASE database were examined for peer-reviewed studies with primary data published between January 1, 2020, and December 31, 2021.

REVIEW FINDINGS AND CONCLUSIONS

Rapid changes were observed in numerous aspects of OUDs during the early pandemic stage, as well as its care by nursing and other health professionals. These changes include increased overdoses (primarily from synthetic opioids such as fentanyl) and emergency department visits. These trends varied considerably across U.S. jurisdictions, underscoring the importance of region-specific examinations for public health policy and intervention. Out of necessity, healthcare systems and nursing professionals adapted to the challenges of OUD care in the pandemic. These adaptations included increases in telehealth services, increases in take-home doses of methadone or buprenorphine/naloxone, and expansion of layperson training in the use of naloxone for overdose reversal. It is likely that some of these adaptations will result in long-term changes in standards of care practices for OUDs by nursing professionals.

Novel Opioids in the Setting of Acute Postoperative Pain: A Narrative Review

Although traditional opioids such as morphine and oxycodone are commonly used in the management of acute postoperative pain, novel opioids may play a role as alternatives that provide potent pain relief while minimizing adverse effects. In this review, we discuss the mechanisms of action, findings from preclinical studies and clinical trials, and potential advantages of several novel opioids. The more established include oliceridine (biased ligand activity to activate analgesia and downregulate opioid-related adverse events), tapentadol (mu-opioid agonist and norepinephrine reuptake inhibitor), and cebranopadol (mu-opioid agonist with nociceptin opioid peptide activity)-all of which have demonstrated success in the clinical setting when compared to traditional opioids. On the other hand, dinalbuphine sebacate (DNS; semi-synthetic mu partial antagonist and kappa agonist), dual enkephalinase inhibitors (STR-324, PL37, and PL265), and endomorphin-1 analog (CYT-1010) have shown good efficacy in preclinical studies with future plans for clinical trials. Rather than relying solely on mu-opioid receptor agonism to relieve pain and risk opioid-related adverse events (ORAEs), novel opioids make use of alternative mechanisms of action to treat pain while maintaining a safer side-effect profile, such as lower incidence of nausea, vomiting, sedation, and respiratory depression as well as reduced abuse potential.

Cebranopadol, a novel long-acting opioid agonist with low abuse liability, to treat opioid use disorder: Preclinical evidence of efficacy

The gold standard pharmacological treatment for opioid use disorder (OUD) consists of maintenance therapy with long-acting opioid agonists such as buprenorphine and methadone. Despite these compounds having demonstrated substantial efficacy, a significant number of patients do not show optimal therapeutic responses. Moreover, the abuse liability of these medications remains a major concern. Cebranopadol, is a new, long-acting pan-opioid agonist that also activates the nociception/orphanin FQ NOP receptor. Here we used rats to explore the therapeutic potential of this agent in OUD. First, in operant intravenous self-administration experiments we compared the potential abuse liability of cebranopadol with the prototypical opioid heroin. Under a fixed ratio 1 (FR1) contingency, rats maintained responding for heroin (1, 7, 20, 60 μg/inf) to a larger extent than cebranopadol (0.03, 0.1, 0.3, 1.0, 6.0 μg/inf). When the contingency was switched to a progressive ratio (PR) reinforcement schedule, heroin maintained responding at high levels at all except the lowest dose. Conversely, in the cebranopadol groups responding decreased drastically and the break point (BP) did not differ from saline controls. Next, we demonstrated that oral administration of cebranopadol (0, 25, 50 μg/kg) significantly attenuated drug self-administration independent of heroin dose (1, 7, 20, 60 μg/inf). Cebranopadol also reduced the break point for heroin (20 μg/inf). Furthermore, in a heroin self-administration training extinction/reinstatement paradigm, pretreatment with cebranopadol significantly attenuated yohimbine stress-induced reinstatement of drug seeking. Together, these data indicate that cebranopadol has limited abuse liability compared to heroin and is highly efficacious in attenuating opioid self-administration and stress-induced reinstatement, suggesting clinical potential of this compound for OUD treatment.

Nociceptin Receptor-Related Agonists as Safe and Non-addictive Analgesics

As clinical use of currently available opioid analgesics is often impeded by dose-limiting adverse effects, such as abuse liability and respiratory depression, new approaches have been pursued to develop safe, effective, and non-addictive pain medications. After the identification of the nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor more than 25 years ago, NOP receptor-related agonists have emerged as a promising target for developing novel and effective opioids that modulate the analgesic and addictive properties of mu-opioid peptide (MOP) receptor agonists. In this review, we highlight the effects of the NOP receptor-related agonists compared with those of MOP receptor agonists in experimental rodent and more translational non-human primate (NHP) models and the development status of key NOP receptor-related agonists as potential safe and non-addictive analgesics. Several lines of evidence demonstrated that peptidic and non-peptidic NOP receptor agonists produce potent analgesic effects by intrathecal delivery in NHPs. Moreover, mixed NOP/MOP receptor partial agonists (e.g., BU08028, BU10038, and AT-121) display potent analgesic effects when administered intrathecally or systemically, without eliciting adverse effects, such as respiratory depression, itch behavior, and signs of abuse liability. More importantly, cebranopadol, a mixed NOP/opioid receptor agonist with full efficacy at NOP and MOP receptors, produces robust analgesic efficacy with reduced adverse effects, conferring promising outcomes in clinical studies. A balanced coactivation of NOP and MOP receptors is a strategy that warrants further exploration and refinement for the development of novel analgesics with a safer and effective profile.

Endogenous opiates and behavior: 2021

This paper is the forty-fourth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2021 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonizts and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Multitargeted Opioid Ligand Discovery as a Strategy to Retain Analgesia and Reduce Opioid-Related Adverse Effects

The global "opioid crisis" has placed enormous pressure on the opioid ligand discovery community to produce novel opioid analgesics with superior opioid-related adverse-effect profiles compared with morphine. In this Perspective, the multitargeted opioid ligand strategy for the discovery of opioid analgesics with superior preclinical therapeutic indices relative to morphine is reviewed and discussed. Dual-targeted μ-opioid (MOP)/δ-opioid (DOP) ligands in which the in vitro DOP antagonist potency at least equals that of the MOP agonist activity, and are devoid of DOP or κ-opioid (KOP) agonist activity, are sufficiently promising candidates to warrant further investigation. Dual-targeted MOP/NOP partial agonists have superior preclinical therapeutic indices to morphine and/or fentanyl in nonhuman primates and are also considered promising. Based on the poor preclinical and clinical therapeutic indices of cebranopadol, which is a full agonist at MOP, DOP, and NOP receptors and a partial agonist at the KOP receptor, this pharmacologic template should be avoided.

PPL-103: A mixed opioid partial agonist with desirable anti-cocaine properties

Cocaine use disorder (CUD) is a persistent public health problem for which no effective medications are available. PPL-103 is an opioid receptor ligand with partial agonist activity at mu, kappa and delta opioid receptors, with a greater efficacy for kappa and low efficacy at mu receptors. Because chronic cocaine use induces changes in the kappa opioid receptor/dynorphin system, we hypothesized that a kappa partial agonist, such as PPL-103, would attenuate the aversive properties of the upregulated kappa system, resulting in effective treatment approach for CUD. We tested the effects of PPL-103 on cocaine self-administration models that recapitulate core aspects of CUD in humans. We found that PPL-103 reduced both long and short access cocaine self-administration, motivation to respond for cocaine, and binge-like cocaine taking, in rats. Operant responding for food, fentanyl and locomotor behavior were not altered at doses that decreased cocaine infusions. Repeated PPL-103 treatment did not lead to tolerance development. PPL-103 also reduced both priming- and cue-induced reinstatement of cocaine seeking, being more effective in the former. Surprisingly, PPL-103 reduced self-administration parameters and reinstatement in rats previously treated with the long-acting kappa receptor antagonist JDTic more potently than in non-JDTic treated animals, whereas naltrexone injected to rats subsequent to JDTic administration increased self-administration, suggesting that the partial mu agonist activity, rather than kappa agonism is important for reduction in cocaine taking and seeking. However, partial kappa activation seems to increase safety by limiting dysphoria, tolerance and addiction development. PPL-103 displays a desirable profile as a possible CUD pharmacotherapy.

Regulation of N-type calcium channels by nociceptin receptors and its possible role in neurological disorders

Activation of nociceptin opioid peptide receptors (NOP, a.k.a. opioid-like receptor-1, ORL-1) by the ligand nociceptin/orphanin FQ, leads to G protein-dependent regulation of Cav2.2 (N-type) voltage-gated calcium channels (VGCCs). This typically causes a reduction in calcium currents, triggering changes in presynaptic calcium levels and thus neurotransmission. Because of the widespread expression patterns of NOP and VGCCs across multiple brain regions, the dorsal horn of the spinal cord, and the dorsal root ganglia, this results in the alteration of numerous neurophysiological features. Here we review the regulation of N-type calcium channels by the NOP-nociceptin system in the context of neurological conditions such as anxiety, addiction, and pain.

Has the United States Reached a Plateau in Overdoses Caused by Synthetic Opioids After the Onset of the COVID-19 Pandemic? Examination of Centers for Disease Control and Prevention Data to November 2021

Background

Overdoses caused by synthetic mu-opioid receptor (MOR) agonists such as fentanyl are causing increasing mortality in the United States. The COVID-19 pandemic continues to have complex effects on public health, including opioid use disorders (OUD). It is unclear whether recent increases in mortality caused by synthetic opioids have reached a plateau (i.e., a stable period), after the onset of the COVID-19 pandemic.

Method

This study examined provisional overdose mortality data from the Centers for Disease Control and Prevention, for synthetic opioids excluding methadone (code T40.4; monthly data available from 39 States, plus New York City and Washington DC), for June 2019-November 2021. Data were first examined as crude mortality rates. The presence of a maximum plateau was analyzed for the last 4 months of available data. For authorities in which a plateau in mortality was detected, sigmoidal Boltzmann equations were used to model parameters of this phenomenon (e.g., level of the plateau).

Results

At the end of the study period, all but one authority (New Hampshire) reported increases in mortality rates for synthetic opioids, compared to the baseline month of June 2019 (range: 111-745% of baseline). A plateau was observed over the last 4 months of the study period (Aug 2021-Nov 2021) in 29 of the authorities. Ten other authorities had not reached a stable plateau at the end of the study period. For the authorities where a plateau was detected, a sigmoidal Boltzmann model revealed a fitted maximum of 262% rise in mortality over the study period, from the baseline month. The midpoint in the rise in mortality was fitted in September 2020. After separation of data into census regions, the highest plateau was observed in the West region, followed by South, Midwest, and Northeast (fitted plateau values were 409, 262, 204, and 149% of baseline, respectively).

Discussion

There were increases in overdose mortality due to synthetic opioids across most states, ranging considerably in magnitude. A plateau in overdose mortality was detected at the end of the study period in most of these authorities. The reasons for these plateaus should be explored, in order to develop optimized public health interventions.

Attenuated G protein signaling and minimal receptor phosphorylation as a biochemical signature of low side-effect opioid analgesics

Multi-receptor targeting has been proposed as a promising strategy for the development of opioid analgesics with fewer side effects. Cebranopadol and AT-121 are prototypical bifunctional ligands targeting the nociceptin/orphanin FQ peptide receptor (NOP) and µ-opioid receptor (MOP) that elicit potent analgesia in humans and nonhuman primates, respectively. Cebranopadol was reported to produce typical MOP-related side effects such as respiratory depression and reward, whereas AT-121 appeared to be devoid of these liabilities. However, the molecular basis underlying different side effect profiles in opioid analgesics remains unknown. Here, we examine agonist-induced receptor phosphorylation and G protein signaling profiles of a series of chemically diverse mixed MOP/NOP agonists, including cebranopadol and AT-121. We found that these compounds produce strikingly different MOP phosphorylation profiles. Cebranopadol, AT-034 and AT-324 stimulated extensive MOP phosphorylation, whereas AT-201 induced selective phosphorylation at S375 only. AT-121, on the other hand, did not promote any detectable MOP phosphorylation. Conversely, none of these compounds was able to elicit strong NOP phosphorylation and low NOP receptor phosphorylation correlated with partial agonism in a GIRK-channel assay. Our results suggest a close correlation between MOP receptor phosphorylation and side effect profile. Thus, bifunctional MOP/NOP opioid ligands combining low efficacy G protein signaling at both NOP and MOP with no detectable receptor phosphorylation appear to be devoid of side-effects such as respiratory depression, abuse liability or tolerance development, as with AT-121.

Functional roles of neuromedin B and gastrin-releasing peptide in regulating itch and pain in the spinal cord of non-human primates

Despite accumulating evidence in rodents, the functional role of neuromedin B (NMB) in regulating somatosensory systems in primate spinal cord is unknown. We aimed to compare the expression patterns of NMB and its receptor (NMBR) and the behavioral effects of intrathecal (i.t.) NMB with gastrin-releasing peptide (GRP) on itch or pain in non-human primates (NHPs). We used six adult rhesus monkeys. The mRNA or protein expressions of NMB, GRP, and their receptors were evaluated by quantitative reverse transcription polymerase chain reaction, immunohistochemistry, or in situ hybridization. We determined the behavioral effects of NMB or GRP via acute thermal nociception, capsaicin-induced thermal allodynia, and itch scratching response assays. NMB expression levels were greater than those of GRP in the dorsal root ganglia and spinal dorsal horn. Conversely, NMBR expression was significantly lower than GRP receptor (GRPR). I.t. NMB elicited only mild scratching responses, whereas GRP caused robust scratching responses. GRP- and NMB-elicited scratching responses were attenuated by GRPR (RC-3095) and NMBR (PD168368) antagonists, respectively. Moreover, i.t. NMB and GRP did not induce thermal hypersensitivity and GRPR and NMBR antagonists did not affect peripherally elicited thermal allodynia. Consistently, NMBR expression was low in both itch- and pain-responsive neurons in the spinal dorsal horn. Spinal NMB-NMBR system plays a minimal functional role in the neurotransmission of itch and pain in primates. Unlike the functional significance of the GRP-GRPR system in itch, drugs targeting the spinal NMB-NMBR system may not effectively alleviate non-NMBR-mediated itch.

Potential therapeutic targets for the treatment of opioid abuse and pain

Although μ-opioid peptide (MOP) receptor agonists are effective analgesics available in clinical settings, their serious adverse effects put limits on their use. The marked increase in abuse and misuse of prescription opioids for pain relief and opioid overdose mortality in the past decade has seriously impacted society. Therefore, safe analgesics that produce potent analgesic effects without causing MOP receptor-related adverse effects are needed. This review highlights the potential therapeutic targets for the treatment of opioid abuse and pain based on available evidence generated through preclinical studies and clinical trials. To ameliorate the abuse-related effects of opioids, orexin-1 receptor antagonists and mixed nociceptin/MOP partial agonists have shown promising results in translational aspects of animal models. There are several promising non-opioid targets for selectively inhibiting pain-related responses, including nerve growth factor inhibitors, voltage-gated sodium channel inhibitors, and cannabinoid- and nociceptin-related ligands. We have also discussed several emerging and novel targets. The current medications for opioid abuse are opioid receptor-based ligands. Although neurobiological studies in rodents have discovered several non-opioid targets, there is a translational gap between rodents and primates. Given that the neuroanatomical aspects underlying opioid abuse and pain are different between rodents and primates, it is pivotal to investigate the functional profiles of these non-opioid compounds compared to those of clinically used drugs in non-human primate models before initiating clinical trials. More pharmacological studies of the functional efficacy, selectivity, and tolerability of these newly discovered compounds in non-human primates will accelerate the development of effective medications for opioid abuse and pain.