Cebranopadol, a Novel First-in-Class Analgesic Drug Candidate: First Experience With Cancer-Related Pain for up to 26 Weeks

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.

Naturally Inspired Molecules for Neuropathic Pain Inhibition-Effect of Mirogabalin and Cebranopadol on Mechanical and Thermal Nociceptive Threshold in Mice

BACKGROUND

Neuropathic pain is drug-resistant to available analgesics and therefore novel treatment options for this debilitating clinical condition are urgently needed. Recently, two drug candidates, namely mirogabalin and cebranopadol have become a subject of interest because of their potential utility as analgesics for chronic pain treatment. However, they have not been investigated thoroughly in some types of neuropathic pain, both in humans and experimental animals.

METHODS

This study used the von Frey test, the hot plate test and the two-plate thermal place preference test supported by image analysis and machine learning to assess the effect of intraperitoneal mirogabalin and subcutaneous cebranopadol on mechanical and thermal nociceptive threshold in mouse models of neuropathic pain induced by streptozotocin, paclitaxel and oxaliplatin.

RESULTS

Mirogabalin and cebranopadol effectively attenuated tactile allodynia in models of neuropathic pain induced by streptozotocin and paclitaxel. Cebranopadol was more effective than mirogabalin in this respect. Both drugs also elevated the heat nociceptive threshold in mice. In the oxaliplatin model, cebranopadol and mirogabalin reduced cold-exacerbated pain.

CONCLUSIONS

Since mirogabalin and cebranopadol are effective in animal models of neuropathic pain, they seem to be promising novel therapies for various types of neuropathic pain in patients, in particular those who are resistant to available analgesics.

IUPHAR Review - Bivalent and bifunctional opioid receptor ligands as novel analgesics

Though efficacious in managing chronic, severe pain, opioid analgesics are accompanied by significant adverse effects including constipation, tolerance, dependence, and respiratory depression. The life-threatening risks associated with µ opioid receptor agonist-based analgesics challenges their use in clinic. A rational approach to combatting these adverse effects is to develop agents that incorporate activity at a second pharmacologic target in addition to µ opioid receptor activation. The promise of such bivalent or bifunctional ligands is the development of an analgesic with an improved side effect profile. In this review, we highlight ongoing efforts in the development of bivalent and bifunctional analgesics that combine µ agonism with efficacy at κ and δ opioid receptors, the nociceptin opioid peptide (NOP) receptor, σ receptors, and cannabinoid receptors. Several examples of bifunctional analgesics in preclinical and clinical development are highlighted, as are strategies being employed toward the rational design of novel agents.

Opioids and opioid receptors; understanding pharmacological mechanisms as a key to therapeutic advances and mitigation of the misuse crisis

Opioids are a mainstay in acute pain management and produce their effects and side effects (e.g., tolerance, opioid-use disorder and immune suppression) by interaction with opioid receptors. I will discuss opioid pharmacology in some controversial areas of enquiry of anaesthetic relevance. The main opioid target is the µ (mu,MOP) receptor but other members of the opioid receptor family, δ (delta; DOP) and κ (kappa; KOP) opioid receptors also produce analgesic actions. These are naloxone-sensitive. There is important clinical development relating to the Nociceptin/Orphanin FQ (NOP) receptor, an opioid receptor that is not naloxone-sensitive. Better understanding of the drivers for opioid effects and side effects may facilitate separation of side effects and production of safer drugs. Opioids bind to the receptor orthosteric site to produce their effects and can engage monomer or homo-, heterodimer receptors. Some ligands can drive one intracellular pathway over another. This is the basis of biased agonism (or functional selectivity). Opioid actions at the orthosteric site can be modulated allosterically and positive allosteric modulators that enhance opioid action are in development. As well as targeting ligand-receptor interaction and transduction, modulating receptor expression and hence function is also tractable. There is evidence for epigenetic associations with different types of pain and also substance misuse. As long as the opioid narrative is defined by the 'opioid crisis' the drive to remove them could gather pace. This will deny use where they are effective, and access to morphine for pain relief in low income countries.

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.

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.

Fixed Dose Versus Loose Dose: Analgesic Combinations

Combinations of drugs may be fixed (two or more entities in a single product) or loose (two or more agents taken together but as individual agents) to help address multimechanistic pain. The use of opioids plus nonopioids can result in lower opioid consumption without sacrificing analgesic benefits. Drug combinations may offer additive or synergistic benefits. A variety of fixed-dose combination products are available on the market such as diclofenac plus thiocolchicoside, acetaminophen and caffeine, acetaminophen and opioid, ibuprofen and acetaminophen, tramadol and acetaminophen, and others. Fixed-dose combination products offer predictable pharmacokinetics and pharmacodynamics, known adverse events, and can reduce the pill burden. However, they are limited to certain drug combinations and doses; loose dosing allows prescribers the versatility to meet individual patient requirements as well as the ability to titrate as needed. Not all drug combinations offer synergistic benefits, which depend on the drugs and their doses. Certain drugs offer dual mechanisms of action in a single molecule, such as tapentadol, and these may further be used in combination with other analgesics. New technology allows for co-crystal productions of analgesic agents which may further improve drug characteristics, such as bioavailability. Combination analgesics are important additions to the analgesic armamentarium and may offer important benefits at lower doses than monotherapy.

A systematic review on the kappa opioid receptor and its ligands: New directions for the treatment of pain, anxiety, depression, and drug abuse

Kappa opioid receptor (KOR) is a member of the opioid receptor system, the G protein-coupled receptors that are expressed throughout the peripheral and central nervous systems and play crucial roles in the modulation of antinociception and a variety of behavioral states like anxiety, depression, and drug abuse. KOR agonists are known to produce potent analgesic effects and have been used clinically for the treatment of pain, while KOR antagonists have shown efficacy in the treatment of anxiety and depression. This review summarizes the history, design strategy, discovery, and development of KOR ligands. KOR agonists are classified as non-biased, G protein-biased, and β-arrestin recruitment-biased, according to their degrees of bias. The mechanisms and associated effects of the G protein signaling pathway and β-arrestin recruitment signaling pathway are also discussed. Meanwhile, KOR antagonists are classified as long-acting and short-acting, based on their half-lives. In addition, we have special sections for mixed KOR agonists and selective peripheral KOR agonists. The mechanisms of action and pharmacokinetic, pharmacodynamic, and behavioral studies for each of these categories are also discussed in this review.

Cebranopadol as a Novel Promising Agent for the Treatment of Pain

Opioids are used to treat pain, but despite their effectiveness, they possess several side effects such as respiratory depression, tolerance and physical dependence. Cebranopadol has been evaluated as a solution to this problem. The compound acts on the mu opioid receptor and the nociceptin/orphanin receptor and these receptors co-activation can reduce opioid side-effects without compromising analgesia. In the present review, we have compiled information on the effects of cebranopadol, its pharmacokinetics, and clinical trials involving cebranopadol, to further explore its promise in pain management.

Current and Future Therapeutic Options in Pain Management: Multi-mechanistic Opioids Involving Both MOR and NOP Receptor Activation

Opioids are widely used in chronic pain management, despite major concerns about their risk of adverse events, particularly abuse, misuse, and respiratory depression from overdose. Multi-mechanistic opioids, such as tapentadol and buprenorphine, have been widely studied as a valid alternative to traditional opioids for their safer profile. Special interest was focused on the role of the nociceptin opioid peptide (NOP) receptor in terms of analgesia and improved tolerability. Nociceptin opioid peptide receptor agonists were shown to reinforce the antinociceptive effect of mu opioid receptor (MOR) agonists and modulate some of their adverse effects. Therefore, multi-mechanistic opioids involving both MOR and NOP receptor activation became a major field of pharmaceutical and clinical investigations. Buprenorphine was re-discovered in a new perspective, as an atypical analgesic and as a substitution therapy for opioid use disorders; and buprenorphine derivatives have been tested in animal models of nociceptive and neuropathic pain. Similarly, cebranopadol, a full MOR/NOP receptor agonist, has been clinically evaluated for its potent analgesic efficacy and better tolerability profile, compared with traditional opioids. This review overviews pharmacological mechanisms of the NOP receptor system, including its role in pain management and in the development of opioid tolerance. Clinical data on buprenorphine suggest its role as a safer alternative to traditional opioids, particularly in patients with non-cancer pain; while data on cebranopadol still require phase III study results to approve its introduction on the market. Other bifunctional MOR/NOP receptor ligands, such as BU08028, BU10038, and AT-121, are currently under pharmacological investigations and could represent promising analgesic agents for the future.

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.

New pharmacological perspectives and therapeutic options for opioids: Differences matter

Opioids remain the major drug class for the treatment of acute, chronic and cancer pain, but have major harmful effects such as dependence and opioid-induced ventilatory impairment. Although no new typical opioids have come onto the market in the past almost 50 years, a plethora of new innovative formulations has been developed to meet the clinical need. This review is intended to shed light on new understanding of the molecular pharmacology of opioids, which has arisen largely due to the genomic revolution, and what new drugs may become available in the coming years. Atypical opioids have and are being developed which not only target the mu opioid receptor but other targets in the pain pathway. Biased mu agonists have been developed but remain 'unbiased' clinically. The contribution of drugs targeting non-mu opioid receptors either alone or as heterodimers shows potential promise but remains understudied. That gene splice variants of the mu opioid receptor produce multiple receptor isoforms in different brain regions, and may change with pain chronicity and phenotype, presents new challenges but also opportunities for precision pain medicine. Finally, that opioids also have pro-inflammatory effects not aligned with mu opioid receptor binding affinity implicates a fresh understanding of their role in chronic pain, whether cancer or non-cancer. Hopefully, a new understanding of opioid analgesic drug action may lead to new drug development and better precision medicine in acute and chronic pain relief with less patient harm.

Spotlight on Nociceptin/Orphanin FQ Receptor in the Treatment of Pain

In our society today, pain has become a main source of strain on most individuals. It is crucial to develop novel treatments against pain while focusing on decreasing their adverse effects. Throughout the extent of development for new pain therapies, the nociceptin/orphanin FQ receptor (NOP receptor) has appeared to be an encouraging focal point. Concentrating on NOP receptor to treat chronic pain with limited range of unwanted effects serves as a suitable alternative to prototypical opioid morphine that could potentially lead to life-threatening effects caused by respiratory depression in overdose, as well as generate abuse and addiction. In addition to these harmful effects, the uprising opioid epidemic is responsible for becoming one of the most disastrous public health issues in the US. In this article, the contributing molecular and cellular structure in controlling the cellular trafficking of NOP receptor and studies that support the role of NOP receptor and its ligands in pain management are reviewed.

Non-Opioid Peptides Targeting Opioid Effects

Opioids are the most potent widely used analgesics, primarily, but not exclusively, in palliative care. However, they are associated with numerous side effects, such as tolerance, addiction, respiratory depression, and cardiovascular events. This, in turn, can result in their overuse in cases of addiction, the need for dose escalation in cases of developing tolerance, and the emergence of dose-related opioid toxicity, resulting in respiratory depression or cardiovascular problems that can even lead to unintentional death. Therefore, a very important challenge for researchers is to look for ways to counteract the side effects of opioids. The use of peptides and their related compounds, which have been shown to modulate the effects of opioids, may provide such an opportunity. This short review is a compendium of knowledge about the most important and recent findings regarding selected peptides and their modulatory effects on various opioid actions, including cardiovascular and respiratory responses. In addition to the peptides more commonly reported in the literature in the context of their pro- and/or anti-opioid activity-such as neuropeptide FF (NPFF), cholecystokinin (CCK), and melanocyte inhibiting factor (MIF)-we also included in the review nociceptin/orphanin (N/OFQ), ghrelin, oxytocin, endothelin, and venom peptides.

Pharmaceutical therapeutics for articular regeneration and restoration: state-of-the-art technology for screening small molecular drugs

Articular cartilage damage caused by sports injury or osteoarthritis (OA) has gained increased attention as a worldwide health burden. Pharmaceutical treatments are considered cost-effective means of promoting cartilage regeneration, but are limited by their inability to generate sufficient functional chondrocytes and modify disease progression. Small molecular chemical compounds are an abundant source of new pharmaceutical therapeutics for cartilage regeneration, as they have advantages in design, fabrication, and application, and, when used in combination, act as powerful tools for manipulating cellular fate. In this review, we present current achievements in the development of small molecular drugs for cartilage regeneration, particularly in the fields of chondrocyte generation and reversion of chondrocyte degenerative phenotypes. Several clinically or preclinically available small molecules, which have been shown to facilitate chondrogenesis, chondrocyte dedifferentiation, and cellular reprogramming, and subsequently ameliorate cartilage degeneration by targeting inflammation, matrix degradation, metabolism, and epigenetics, are summarized. Notably, this review introduces essential parameters for high-throughput screening strategies, including models of different chondrogenic cell sources, phenotype readout methodologies, and transferable advanced systems from other fields. Overall, this review provides new insights into future pharmaceutical therapies for cartilage regeneration.

Opioid Receptor Regulation of Neuronal Voltage-Gated Calcium Channels

Neuronal voltage-gated calcium channels play a pivotal role in the conversion of electrical signals into calcium entry into nerve endings that is required for the release of neurotransmitters. They are under the control of a number of cellular signaling pathways that serve to fine tune synaptic activities, including G-protein coupled receptors (GPCRs) and the opioid system. Besides modulating channel activity via activation of second messengers, GPCRs also physically associate with calcium channels to regulate their function and expression at the plasma membrane. In this mini review, we discuss the mechanisms by which calcium channels are regulated by classical opioid and nociceptin receptors. We highlight the importance of this regulation in the control of neuronal functions and their implication in the development of disease conditions. Finally, we present recent literature concerning the use of novel μ-opioid receptor/nociceptin receptor modulators and discuss their use as potential drug candidates for the treatment of pain.

Novel bifunctional hybrid compounds designed to enhance the effects of opioids and antagonize the pronociceptive effects of nonopioid peptides as potent analgesics in a rat model of neuropathic pain

ABSTRACT

The purpose of our work was to determine the role of nonopioid peptides derived from opioid prohormones in sensory hypersensitivity characteristics of neuropathic pain and to propose a pharmacological approach to restore the balance of these endogenous opioid systems. Nonopioid peptides may have a pronociceptive effect and therefore contribute to less effective opioid analgesia in neuropathic pain. In our study, we used unilateral chronic constriction injury (CCI) of the sciatic nerve as a neuropathic pain model in rats. We demonstrated the pronociceptive effects of proopiomelanocortin- and proenkephalin-derived nonopioid peptides assessed by von Frey and cold plate tests, 7 to 14 days after injury. The concentration of proenkephalin-derived pronociceptive peptides was increased more robustly than that of Met-enkephalin in the ipsilateral lumbar spinal cord of CCI-exposed rats, as shown by mass spectrometry, and the pronociceptive effect of one of these peptides was blocked by an antagonist of the melanocortin 4 (MC4) receptor. The above results confirm our hypothesis regarding the possibility of creating an analgesic drug for neuropathic pain based on enhancing opioid activity and blocking the pronociceptive effect of nonopioid peptides. We designed and synthesized bifunctional hybrids composed of opioid (OP) receptor agonist and MC4 receptor antagonist (OP-linker-MC4). Moreover, we demonstrated that they have potent and long-lasting antinociceptive effects after a single administration and a delayed development of tolerance compared with morphine after repeated intrathecal administration to rats subjected to CCI. We conclude that the bifunctional hybrids OP-linker-MC4 we propose are important prototypes of drugs for use in neuropathic pain.

Medications Development for Treatment of Opioid Use Disorder

This review describes methods for preclinical evaluation of candidate medications to treat opioid use disorder (OUD). The review is founded on the propositions that (1) drug self-administration procedures provide the most direct method for assessment of medication effectiveness, (2) procedures that assess choice between opioid and nondrug reinforcers are especially useful, and (3) states of opioid dependence and withdrawal profoundly influence both opioid reinforcement and effects of candidate medications. Effects of opioid medications and vaccines on opioid choice in nondependent and opioid-dependent subjects are reviewed. Various nonopioid medications have also been examined, but none yet have been identified that safely and reliably reduce opioid choice. Future research will focus on (1) strategies for increasing safety and/or effectiveness of opioid medications (e.g., G-protein-biased μ-opioid agonists), and (2) continued development of nonopioid medications (e.g., clonidine) that might serve as adjunctive agents to current opioid medications.

Strategies for Developing κ Opioid Receptor Agonists for the Treatment of Pain with Fewer Side Effects

There is significant need to find effective, nonaddictive pain medications. κ Opioid receptor (KOPr) agonists have been studied for decades but have recently received increased attention because of their analgesic effects and lack of abuse potential. However, a range of side effects have limited the clinical development of these drugs. There are several strategies currently used to develop safer and more effective KOPr agonists. These strategies include identifying G-protein-biased agonists, developing peripherally restricted KOPr agonists without centrally mediated side effects, and developing mixed opioid agonists, which target multiple receptors at specific ratios to balance side-effect profiles and reduce tolerance. Here, we review the latest developments in research related to KOPr agonists for the treatment of pain. SIGNIFICANCE STATEMENT: This review discusses strategies for developing safer κ opioid receptor (KOPr) agonists with therapeutic potential for the treatment of pain. Although one strategy is to modify selective KOPr agonists to create peripherally restricted or G-protein-biased structures, another approach is to combine KOPr agonists with μ, δ, or nociceptin opioid receptor activation to obtain mixed opioid receptor agonists, therefore negating the adverse effects and retaining the therapeutic effect.

Cebranopadol reduces cocaine self-administration in male rats: Dose, treatment and safety consideration

As a novel first-in-class potent analgesic acting as an agonist of multiple opioid receptors, cebranopadol showed high efficacy and good tolerability in a broad range of preclinical models and clinical trials related to pain. In the present study, to evaluate the efficacy and safety of cebranopadol as a potential treatment of cocaine dependence, we tested the effects of cebranopadol with single and repeated doses (25, 50, 75, or 100 μg/kg, oral gavage) using rat models of cocaine fixed-ratio (FR) self-administration (SA), cocaine progressive-ratio (PR) SA, and sucrose pellet SA. In single-dosing treatment paradigm, cebranopadol significantly and dose-dependently reduced cocaine SA under FR and PR schedules and suppressed food intake under FR schedule without causing apparent side effects. In repeated-dosing treatment scheme, i.e. daily administration of 25, 50, 75, or 100 μg/kg cebranopadol for a week, the similar reduction in cocaine intake was detected, while non-negligible complications/side effects were observed at repeated high doses (75 and 100 μg/kg). The observed side effects were similar to the common toxic signs elicited by heroin at high doses, although cebranopadol did not fully substitute heroin's discriminative stimulant effects in our drug discriminative tests. These results demonstrated that the most appropriate oral dose of cebranopadol to balance the efficacy and safety is 50 μg/kg. Collectively, although cebranopadol may serve as a new treatment for cocaine dependence, more consideration, cautiousness, and a clear optimal dose window to dissociate its therapeutic effects from opioid side effects/complications in male and female subjects will be necessary to increase its practical clinical utility.