A randomized, double-blind, placebo-controlled study of the kappa opioid receptor antagonist, CERC-501, in a human laboratory model of smoking behavior

A review of kappa opioid receptor antagonists and their clinical trial landscape

Myriad signaling pathways are implicated in neuropsychiatric disorders, yet many mechanisms are unknown and current treatment options are limited. The intriguing dynorphin/kappa opioid receptor (KOR) system that is widely distributed throughout the brain appears to be essential in regulating many physiological and pathophysiological processes. This review explores up to date advances on the relationship between the dynorphin/KOR system with a particular focus on the KOR antagonist compounds tested as clinical candidates that could offer potential treatment options for CNS disorders.

Interaction between corticotropin-releasing factor, orexin, and dynorphin in the infralimbic cortex may mediate exacerbated alcohol-seeking behavior

A major challenge for the treatment of alcohol use disorder (AUD) is relapse to alcohol use, even after protracted periods of self-imposed abstinence. Stress significantly contributes to the chronic relapsing nature of AUD, given its long-lasting ability to elicit intense craving and precipitate relapse. As individuals transition to alcohol dependence, compensatory allostatic mechanisms result in insults to hypothalamic-pituitary-adrenal axis function, mediated by corticotropin-releasing factor (CRF), which is subsequently hypothesized to alter brain reward pathways, influence affect, elicit craving, and ultimately perpetuate problematic drinking and relapse vulnerability. Orexin (OX; also called hypocretin) plays a well-established role in regulating diverse physiological processes, including stress, and has been shown to interact with CRF. Interestingly, most hypothalamic cells that express Ox mRNA also express Pdyn mRNA. Both dynorphin and OX are located in the same synaptic vesicles, and they are co-released. The infralimbic cortex (IL) of the medial prefrontal cortex (mPFC) has emerged as being directly involved in the compulsive nature of alcohol consumption during dependence. The IL is a CRF-rich region that receives OX projections from the hypothalamus and where OX receptor mRNA has been detected. Although not thoroughly understood, anatomical and behavioral pharmacology data suggest that CRF, OX, and dynorphin may interact, particularly in the IL, and that functional interactions between these three systems in the IL may be critical for the etiology and pervasiveness of compulsive alcohol seeking in dependent subjects that may render them vulnerable to relapse. The present review presents evidence of the role of the IL in AUD and discusses functional interactions between CRF, OX, and dynorphin in this structure and how they are related to exacerbated alcohol drinking and seeking.

Preclinical and clinical efficacy of kappa opioid receptor antagonists for depression: A systematic review

BACKGROUND

Approximately 30 % of persons with Major Depressive Disorder (MDD) inadequately respond to conventional antidepressants. Kappa opioid receptor (KOR) antagonists, aticaprant and navacaprant, are in development as treatments for MDD. Herein, we aim to comprehensively evaluate the safety, efficacy and pharmacology of aticaprant and navacaprant for MDD.

METHODS

We performed a systematic review of primary research investigating aticaprant and navacaprant on PubMed, OVID, and Scopus databases from inception to April 2024. Studies that reported on the pharmacological profile and/or safety and efficacy of aticaprant and navacaprant were included.

RESULTS

Navacaprant monotherapy and aticaprant adjunctive therapy are in development for MDD. Navacaprant exhibits 300-fold selectivity for the KOR compared to the mu-opioid receptor, while aticaprant exhibits 30-fold selectivity. At clinically-relevant doses, navacaprant and aticaprant occupy 87-95 % and 73-94 % of KORs, respectively. Clinical trials of the foregoing agents (navacaprant as monotherapy and actiprant as adjunctive therapy) reported significant improvement in depressive symptoms and may clinically benefit measures of anhedonia. Both agents appear well-tolerated, with most adverse events mild and no known safety concerns.

LIMITATIONS

Aticaprant and navacaprant treatment for MDD are in early stages of clinical trials and results from Phase 3 pivotal trials are not yet available.

CONCLUSIONS

Kappa opioid receptor antagonists may serve as mechanistically-novel treatments for MDD and persons who inadequately respond to index conventional antidepressants. Anhedonia is debilitating and insufficiently treated with conventional antidepressants. Future research vistas should establish the efficacy and safety of KORAs in phase 3 studies in both acute and maintenance paradigms.

Novel medications for problematic alcohol use

Alcohol-related harm, a major cause of disease burden globally, affects people along a spectrum of use. When a harmful pattern of drinking is present in the absence of significant behavioral pathology, low-intensity brief interventions that provide information about health consequences of continued use provide large health benefits. At the other end of the spectrum, profound behavioral pathology, including continued use despite knowledge of potentially fatal consequences, warrants a medical diagnosis, and treatment is strongly indicated. Available behavioral and pharmacological treatments are supported by scientific evidence but are vastly underutilized. Discovery of additional medications, with a favorable balance of efficacy versus safety and tolerability can improve clinical uptake of treatment, allow personalized treatment, and improve outcomes. Here, we delineate the clinical conditions when pharmacotherapy should be considered in relation to the main diagnostic systems in use and discuss clinical endpoints that represent meaningful clinical benefits. We then review specific developments in three categories of targets that show promise for expanding the treatment toolkit. GPCRs remain the largest category of successful drug targets across contemporary medicine, and several GPCR targets are currently pursued for alcohol-related indications. Endocrine systems are another established category, and several promising targets have emerged for alcohol indications. Finally, immune modulators have revolutionized treatment of multiple medical conditions, and they may also hold potential to produce benefits in patients with alcohol problems.

Comorbid alcohol use disorder and posttraumatic stress disorder: A proof-of-concept randomized placebo-controlled trial of buprenorphine and naltrexone combination treatment

BACKGROUND

Effective pharmacologic treatments for comorbid alcohol use disorder (AUD) and posttraumatic stress disorder (PTSD) are lacking. Kappa (κ) opioid receptor antagonists may address this unmet need. Buprenorphine is a κ-opioid antagonist and a partial agonist of mu (μ) opioid receptors. Whereas naltrexone blocks all μ-mediated effects combining it with buprenorphine yields a pharmacologic net effect of opioid receptor antagonism. Because no κ-opioid receptor antagonist it available for clinical use, we tested this combination in a proof-of-concept study.

METHODS

Consenting participants were enrolled in a Phase II, multisite, double-blind, randomized, placebo-controlled trial evaluating the effectiveness of sublingual (SL) buprenorphine combined with extended-release (XR) injectable naltrexone for the treatment of comorbid AUD and PTSD. Eligible participants (n = 75) were randomized (1:1:1) to receive either buprenorphine 2 mg/day plus naltrexone-XR (n = 35), buprenorphine 8 mg/day plus naltrexone-XR (n = 6) or SL plus injectable placebo (n = 34) for 12 weeks. The buprenorphine 8 mg/day plus naltrexone-XR arm was dropped early in the trial due to the negative impact of COVID-19 on enrollment. A binary primary outcome of response at week 8 was defined as a decrease from baseline of ≥10 points on the past week Clinician-Administered PTSD Scale (CAPS-5) and a reduction of ≥1 of past month alcohol risk level, as defined by the World Health Organization (WHO) and measured by the Timeline Follow-Back.

RESULTS

Based on the results of a futility analysis, enrollment was stopped prior to reaching the initial goal of 90 participants. At the week eight primary timepoint, there were no statistically significant differences between buprenorphine plus naltrexone-XR and placebo group for the primary composite outcome (OR = 0.63; p-value = 0.52), or the subcomponents of the PTSD outcome (OR = 0.76; p-value = 0.69) and AUD outcome (OR = 0.17; p-value = 0.08). The placebo arm had a significantly higher proportion of participants with ≥1 WHO risk level reduction than the buprenorphine plus naltrexone-XR arm (OR = 0.18, p value = 0.02).

CONCLUSIONS

This is the first study to evaluate the potential of κ-opioid receptor antagonism for the treatment of comorbid AUD and PTSD. The combination of buprenorphine and naltrexone-XR showed no significant improvement over placebo for the composite, PTSD, or alcohol measures.

Stress-related neuropeptide systems as targets for treatment of alcohol addiction: A clinical perspective

Alcohol use is a major cause of disability and death globally. These negative consequences disproportionately affect people who develop alcohol addiction, a chronic relapsing condition characterized by increased motivation to use alcohol, choice of alcohol over healthy, natural rewards, and continued use despite negative consequences. Available pharmacotherapies for alcohol addiction are few, have effect sizes in need of improvement, and remain infrequently prescribed. Research aimed at developing novel therapeutics has in large part focused on attenuating pleasurable or "rewarding" properties of alcohol, but this targets processes that primarily play a role as initiation factors. As clinical alcohol addiction develops, long-term changes in brain function result in a shift of affective homeostasis, and rewarding alcohol effects become progressively reduced. Instead, increased stress sensitivity and negative affective states emerge in the absence of alcohol and create powerful incentives for relapse and continued use through negative reinforcement, or "relief." Based on research in animal models, several neuropeptide systems have been proposed to play an important role in this shift, suggesting that these systems could be targeted by novel medications. Two mechanisms in this category, antagonism at corticotropin-releasing factor type 1, and neurokinin 1/substance P receptors, have been subject to initial evaluation in humans. A third, kappa-opioid receptor antagonism, has been evaluated in nicotine addiction and could soon be tested for alcohol. This paper discusses findings with these mechanisms to date, and their prospects as future targets for novel medications.

Alleviation of Cocaine Withdrawal and Pertinent Interactions between Salvinorin-Based Antagonists and Kappa Opioid Receptor

The kappa opioid receptor (KOR) is involved in the regulation of both the reward and mood processes. Recent reports find that the use of drugs of abuse increases the production of dynorphin and the overall activation of KOR. Long-acting KOR antagonists, such as norbinaltorphimine (nor-BNI), JDTic, and 5'-guanidinonaltrindole (GNTI), have been shown to stop depressive and anxiety-related disorders, which are the common side effects of withdrawal that can lead to a relapse in drug use. Unfortunately, these prototypical KOR antagonists are known to induce selective KOR antagonism that is delayed by hours and extremely prolonged, and their use in humans comes with serious safety concerns because they possess a large window for potential drug-drug interactions. Furthermore, their persistent pharmacodynamic activities can hinder the ability to reverse unanticipated side effects immediately. Herein, we report our studies of the lead selective, salvinorin-based KOR antagonist (1) as well as nor-BNI on C57BL/6N male mice for spontaneous cocaine withdrawal. Assessment of pharmacokinetics showed that 1 is a short-acting compound with an average half-life of 3.75 h across different compartments (brain, spinal cord, liver, and plasma). Both 1 (5 mg/kg) and nor-BNI (5 mg/kg) were shown to reduce spontaneous withdrawal behavior in mice, with 1 producing additional anti-anxiety-like behavior in a light-dark transition test (however, no mood-related effects of 1 or nor-BNI were observed at the current dosing in an elevated plus maze or a tail suspension test). Our results support the study of selective, short-acting KOR antagonists for the treatment of psychostimulant withdrawal and the associated negative mood states that contribute to relapse. Furthermore, we identified pertinent interactions between 1 and KOR via computational studies, including induced-fit docking, mutagenesis, and molecular dynamics simulations, to gain insight into the design of future selective, potent, and short-acting salvinorin-based KOR antagonists.

A novel human laboratory alcohol self-administration paradigm for medication screening: Modeling the ability to resist drinking and heavy drinking

Background

Human laboratory analogues of drinking behavior provide an efficient, cost-effective mechanistic evaluation of a medication signal on drinking. We developed a novel alcohol self-administration paradigm which models the ability to resist drinking and heavy drinking.

Methods

We compared a de-escalating schedule of monetary reinforcement (n=16, 50% female) to no schedule (n=16, 50% female) on the ability to resist drinking (i.e., latency to start drinking) and subsequent ad-libitum alcohol consumption of preferred alcoholic beverage in participants with alcohol use disorder (AUD). Participants completed two laboratory sessions designed to model the ability to resist drinking using stress (versus neutral imagery, within-subject factor) as a prime for drinking.

Results

Participants consumed more alcohol with no schedule (74.2%) versus with the de-escalating reinforcement schedule (40.3%,). The de-escalating schedule reduced alcohol consumption by 49%. Eighty-one percent of participants drank heavily with no schedule and this was reduced with the schedule. Use of the de-escalating schedule also increased the latency to pour and sip the first drink. Participants poured and sipped alcohol faster following stress imagery (vs. neutral), had greater craving, and consumed more alcohol in the first 30 minutes.

Conclusions

Our novel alcohol self-administration model generated heavy drinking. Over 80% of participants without reinforcement consumed more than 2/3 of their preferred alcoholic beverage designed to increase blood alcohol levels to 0.12 mg% within a 2-hour window. Our model was sensitive to stress, and the de-escalating schedule highlighted stress effects on drinking. Thus, this model is ideal for a cross-over design to test medications for AUD.

Traumatic Stress-Induced Vulnerability to Addiction: Critical Role of the Dynorphin/Kappa Opioid Receptor System

Substance use disorders (SUD) may emerge from an individual’s attempt to limit negative affective states and symptoms linked to stress. Indeed, SUD is highly comorbid with chronic stress, traumatic stress, or post-traumatic stress disorder (PTSD), and treatments approved for each pathology individually often failed to have a therapeutic efficiency in such comorbid patients. The kappa-opioid receptor (KOR) and its endogenous ligand dynorphin (DYN), seem to play a key role in the occurrence of this comorbidity. The DYN/KOR function is increased either in traumatic stress or during drug use, dependence acquisition and DYN is released during stress. The behavioural effects of stress related to the DYN/KOR system include anxiety, dissociative and depressive symptoms, as well as increased conditioned fear response. Furthermore, the DYN/KOR system is implicated in negative reinforcement after the euphoric effects of a drug of abuse ends. During chronic drug consumption DYN/KOR functions increase and facilitate tolerance and dependence. The drug-seeking behaviour induced by KOR activation can be retrieved either during the development of an addictive behaviour, or during relapse after withdrawal. DYN is known to be one of the most powerful negative modulators of dopamine signalling, notably in brain structures implicated in both reward and fear circuitries. KOR are also acting as inhibitory heteroreceptors on serotonin neurons. Moreover, the DYN/KOR system cross-regulate with corticotropin-releasing factor in the brain. The sexual dimorphism of the DYN/KOR system could be the cause of the gender differences observed in patients with SUD or/and traumatic stress-related pathologies. This review underlies experimental and clinical results emphasizing the DYN/KOR system as common mechanisms shared by SUD or/and traumatic stress-related pathologies, and suggests KOR antagonist as a new pharmacological strategy to treat this comorbidity.

Nicotine and opioid co-dependence: Findings from bench research to clinical trials

Concomitant use of tobacco and opioids represents a growing public health concern. In fact, the mortality rate due to smoking-related illness approaches 50% among SUD patients. Cumulative evidence demonstrates that the vulnerability to drugs of abuse is influenced by behavioral, environmental, and genetic factors. This review explores the contribution of genetics and neural mechanisms influencing nicotine and opioid reward, respiration, and antinociception, emphasizing the interaction of cholinergic and opioid receptor systems. Despite the substantial evidence demonstrating nicotine-opioid interactions within the brain and on behavior, the currently available pharmacotherapies targeting these systems have shown limited efficacy for smoking cessation on opioid-maintained smokers. Thus, further studies designed to identify novel targets modulating both nicotinic and opioid receptor systems may lead to more efficacious approaches for co-morbid nicotine dependence and opioid use disorder.

Optogenetic stimulation of dynorphinergic neurons within the dorsal raphe activate kappa opioid receptors in the ventral tegmental area and ablation of dorsal raphe prodynorphin or kappa receptors in dopamine neurons blocks stress potentiation of cocaine reward

Behavioral stress exposure increases the risk of drug-taking in individuals with substance use disorders by mechanisms involving the dynorphins, which are the endogenous neuropeptides for the kappa opioid receptor (KOR). KOR agonists have been shown to encode dysphoria, aversion, and changes in reward valuation, and kappa opioid antagonists are in clinical development for treating substance use disorders. In this study, we confirmed that KORs were expressed in dopaminergic neurons in the ventral tegmental area (VTA) of male C57BL6/J mice. Genetic ablation of KORs from dopamine neurons blocked the potentiating effects of repeated forced swim stress on cocaine conditioned place preference (CPP). KOR activation inhibited dopamine neuron GCaMP6m calcium activity in VTA during swim stress and caused a rebound enhancement during the period after stress exposure. Transient optogenetic inhibition of VTA dopamine neurons with AAV5-DIO-SwiChR was acutely aversive in a real time place preference assay and blunted cocaine CPP when inhibition was administered concurrently with cocaine conditioning. However, when inhibition preceded cocaine conditioning by 30 min, cocaine CPP was enhanced. Retrograde tracing with CAV2-DIO-ZsGreen identified a population of prodynorphin^Cre neurons in the dorsal raphe nucleus (DRN) projecting to the VTA. Optogenetic stimulation of dynorphinergic neurons within the DRN by Channelrhodopsin2 activated KOR in VTA and ablation of prodynorphin blocked stress potentiation of cocaine CPP. Together, these studies demonstrate the presence of a dynorphin/KOR midbrain circuit that projects from the DRN to VTA and is involved in altering the dynamic response of dopamine neuron activity to enhance drug reward learning.

Peptide Kappa Opioid Receptor Ligands and Their Potential for Drug Development

Ligands for kappa opioid receptors (KOR) have potential uses as non-addictive analgesics and for the treatment of pruritus, mood disorders, and substance abuse. These areas continue to have major unmet medical needs. Significant advances have been made in recent years in the preclinical development of novel opioid peptides, notably ones with structural features that inherently impart stability to proteases. Following a brief discussion of the potential therapeutic applications of KOR agonists and antagonists, this review focuses on two series of novel opioid peptides, all-D-amino acid tetrapeptides as peripherally selective KOR agonists for the treatment of pain and pruritus without centrally mediated side effects, and macrocyclic tetrapeptides based on CJ-15,208 that can exhibit different opioid profiles with potential applications such as analgesics and treatments for substance abuse.

Pleiotropic Effects of Kappa Opioid Receptor-Related Ligands in Non-human Primates

The kappa opioid receptor (KOR)-related ligands have been demonstrated in preclinical studies for several therapeutic potentials. This chapter highlights (1) how non-human primates (NHP) studies facilitate the research and development of ligands targeting the KOR, (2) effects of the endogenous opioid peptide, dynorphin A-(1-17), and its analogs in NHP, and (3) pleiotropic effects and therapeutic applications of KOR-related ligands. In particular, synthetic ligands targeting the KOR have been extensively studied in NHP in three therapeutic areas, i.e., the treatment for itch, pain, and substance use disorders. As the KORs are widely expressed in the peripheral and central nervous systems, pleiotropic effects of KOR-related ligands, such as discriminative stimulus effects, neuroendocrine effects (e.g., prolactin release and stimulation of hypothalamic-pituitary-adrenal axis), and diuresis, in NHP are discussed. Centrally acting KOR agonists are known to produce adverse effects including dysphoria, hallucination, and sedation. Nonetheless, with strategic advances in medicinal chemistry, three classes of KOR-related agonists, i.e., peripherally restricted KOR agonists, mixed KOR/mu opioid receptor partial agonists, and G protein-biased KOR agonists, warrant additional NHP studies to improve our understanding of their functional efficacy, selectivity, and tolerability. Pharmacological studies in NHP which carry high translational significance will facilitate future development of KOR-based medications.

Targeting the Opioid Receptors: A Promising Therapeutic Avenue for Treatment in “Heavy Drinking Smokers”

Aims

Despite a general decline in tobacco use in the last decades, the prevalence of tobacco smoking in individuals with alcohol use disorder (AUD) remains substantial (45–50%). Importantly, the co-use of both substances potentiates the adverse effects, making it a significant public health problem. Substantial evidence suggests that AUD and Tobacco use disorder (TUD) may share common mechanisms. Targeting these mechanisms may therefore provide more effective therapy. Numerous studies describe a potential role of the endogenous opioid system in both AUD and TUD. Reviewing this literature, we aim to evaluate the efficacy of molecules that target the opioid system as promising therapeutic interventions for treating alcohol and tobacco co-use disorders.

Methods

We provide a synthesis of the current epidemiological knowledge of alcohol and tobacco co-use disorders. We evaluate clinical and preclinical research that focuses on the regulation of the endogenous opioid system in alcohol, nicotine, and their interactions.

Results

The epidemiological data confirm that smoking stimulates heavy drinking and facilitates alcohol craving. Pharmacological findings suggest that treatments that are efficacious in the dual addiction provide a beneficial treatment outcome in comorbid AUD and TUD. In this regard, MOP, DOP and NOP-receptor antagonists show promising results, while the findings prompt caution when considering KOP-receptor antagonists as a treatment option in alcohol and tobacco co-use disorders.

Conclusions

Existing literature suggests a role of the opioid system in sustaining the high comorbidity rates of AUD and TUD. Molecules targeting opioid receptors may therefore represent promising therapeutic interventions in ‘heavy drinking smokers.’

Improving translation of animal models of addiction and relapse by reverse translation

Critical features of human addiction are increasingly being incorporated into complementary animal models, including escalation of drug intake, punished drug seeking and taking, intermittent drug access, choice between drug and non-drug rewards, and assessment of individual differences based on criteria in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV). Combined with new technologies, these models advanced our understanding of brain mechanisms of drug self-administration and relapse, but these mechanistic gains have not led to improvements in addiction treatment. This problem is not unique to addiction neuroscience, but it is an increasing source of disappointment and calls to regroup. Here we first summarize behavioural and neurobiological results from the animal models mentioned above. We then propose a reverse translational approach, whose goal is to develop models that mimic successful treatments: opioid agonist maintenance, contingency management and the community-reinforcement approach. These reverse-translated 'treatments' may provide an ecologically relevant platform from which to discover new circuits, test new medications and improve translation.

Nicotine increases alcohol self-administration in male rats via a μ-opioid mechanism within the mesolimbic pathway

Background and Purpose

Alcohol and nicotine use disorders are commonly comorbid. Both alcohol and nicotine can activate opioid systems in reward‐related brain regions, leading to adaptive changes in opioid signalling upon chronic exposure. The potential role of these adaptations for comorbidity is presently unknown. Here, we examined the contribution of μ and κ‐opioid receptors to nicotine‐induced escalation of alcohol self‐administration in rats.

Experimental Approach

Chronic nicotine was tested on alcohol self‐administration and motivation to obtain alcohol. We then tested the effect of the κ antagonist CERC‐501 and the preferential μ receptor antagonist naltrexone on basal and nicotine‐escalated alcohol self‐administration. To probe μ or κ receptor adaptations, receptor binding and G‐protein coupling assays were performed in reward‐related brain regions. Finally, dopaminergic activity in response to alcohol was examined, using phosphorylation of DARPP‐32 in nucleus accumbens as a biomarker.

Key Results

Nicotine robustly induced escalation of alcohol self‐administration and motivation to obtain alcohol. This was blocked by naltrexone but not by CERC‐501. Escalation of alcohol self‐administration was associated with decreased DAMGO‐stimulated μ receptor signalling in the ventral tegmental area (VTA) and decreased pDARPP‐32 in the nucleus accumbens shell in response to alcohol.

Conclusions and Implications

Collectively, these results suggest that nicotine contributes to escalate alcohol self‐administration through a dysregulation of μ receptor activity in the VTA. These data imply that targeting μ rather than κ receptors may be the preferred pharmacotherapeutic approach for the treatment of alcohol use disorder when nicotine use contributes to alcohol consumption.

The Rise and Fall of Kappa-Opioid Receptors in Drug Abuse Research

Substance use disorders represent a global public health issue. This mental health disorder is hypothesized to result from neurobiological changes as a result of chronic drug exposure and clinically manifests as inappropriate behavioral allocation toward the procurement and use of the abused substance and away from other behaviors maintained by more adaptive nondrug reinforcers (e.g., social relationships, work). The dynorphin/kappa-opioid receptor (KOR) is one receptor system that has been altered following chronic exposure to drugs of abuse (e.g., cocaine, opioids, alcohol) in both laboratory animals and humans, implicating the dynorphin/KOR system in the expression, mechanisms, and treatment of substance use disorders. KOR antagonists have reduced drug self-administration in laboratory animals under certain experimental conditions, but not others. Recently, several human laboratory and clinical trials have evaluated the effectiveness of KOR antagonists as candidate pharmacotherapies for cocaine or tobacco use disorder to test hypotheses generated from preclinical studies. KOR antagonists failed to significantly alter drug use metrics in humans suggesting translational discordance between some preclinical drug self-administration studies and consistent with other preclinical drug self-administration studies that provide concurrent access to an alternative nondrug reinforcer (e.g., food). The implications of this translational discordance and future directions for examining the therapeutic potential of KOR agonists or antagonists as candidate substance use disorder pharmacotherapies are discussed.

Kappa Opioid Receptor Antagonists as Potential Therapeutics for Mood and Substance Use Disorders

The kappa opioid receptor (KOR) and its primary cognate ligands, the dynorphin peptides, are involved in diverse physiological processes. Disruptions to the KOR/dynorphin system have been found to likely play a role in multiple neuropsychological disorders, and hence KOR has emerged as a potential therapeutic target. Targeting KOR is complicated by close homology to the mu and delta opioid receptors (MOR and DOR), and many KOR ligands have at least moderate affinity to MOR and/or DOR. Animal models utilizing primarily very long-lasting selective KOR antagonists (>3 weeks following a single dose) have demonstrated that KOR antagonism attenuates certain anxiety-like and depression-like behaviors and blocks stress- and cue-induced reinstatement to drug seeking. Recently, relatively selective KOR antagonists with medication-like pharmacokinetic and pharmacodynamic properties and durations of action have been developed. One of these, JNJ-67953964 (also referred to as CERC-501, LY2456302, OpraKappa or Aticaprant) has been studied in humans, and shown to be safe, relatively KOR selective, and able to substantially attenuate binding of a KOR PET tracer to CNS localized KOR for greater than 24 h. While animal studies have indicated that compounds of this structural class are capable of normalizing withdrawal signs in animal models of cocaine and alcohol dependence and reducing cocaine and alcohol intake/seeking, additional studies are needed to determine the value of these second generation KOR antagonists in treating mood disorders and substance use disorders in humans.