Methocinnamox (MCAM) antagonizes the behavioral suppressant effects of morphine without impairing delayed matching-to-sample accuracy in rhesus monkeys

Structure-activity relationship analysis of meta-substituted N-cyclopropylmethyl-nornepenthones with mixed KOR/MOR activities

Substance Use Disorder (SUD) remains a significant global challenge, with current treatment options offering limited efficacy. Agonists targeting the kappa opioid receptor (KOR), especially those with additional mu opioid receptor (MOR) antagonistic activity, have shown promise in addressing SUD. In this study, a series of meta-substituted N-cyclopropylmethyl-nornepenthone derivatives were designed and synthesized, and their biological activities were assessed, leading to the identification of a KOR/MOR dual modulator, compound 10a. Unlike its para-positional isomer SLL-1062, where KOR activity is completely abolished, compound 10a displayed a single-digit nanomolar affinity for KOR, while its binding profiles for MOR and delta opioid receptor (DOR) were comparable to those of SLL-1062. Functional assays in vitro confirmed that compound 10a exhibited agonistic activity at KOR and antagonistic activity at MOR. The molecular basis for the introduction of a KOR component into compound 10a was further elucidated. Although compound 10a did not produce apparent antinociception in vivo, it effectively blocked morphine-induced antinociception and intestinal motility inhibition in rodent models. This study provides valuable insights into the development of MOR/KOR dual modulators and presents new lead compounds for potential treatments for SUD.

Daily methocinnamox treatment dose-dependently attenuates fentanyl self-administration in rhesus monkeys

Opioid use disorder and opioid overdose continue to be significant public health challenges despite the availability of effective treatments. Methocinnamox (MCAM) is a novel, long-acting opioid receptor antagonist that might be an effective treatment for opioid use disorder (i.e., preventing relapse and overdose). In nonhuman primates, MCAM selectively blocks the positive reinforcing effects of mu opioid receptor agonists, including heroin, fentanyl, and its ultra-potent analogs (e.g., carfentanil) with a single administration of MCAM being effective for up to two weeks. Because treatment of opioid use disorder would involve repeated administration of a medication, MCAM was studied in rhesus monkeys (3 males and 2 females) responding under a fixed-ratio self-administration procedure for a range of doses of fentanyl (0.000032-0.1 mg/kg/infusion). The fentanyl self-administration dose-effect curve was determined before and during treatment with progressively increasing daily doses of MCAM (0.001-0.1 mg/kg) given subcutaneously 1 h before the session. MCAM dose-dependently shifted the fentanyl dose-effect curve rightward and then, at larger doses, downward. The largest treatment dose of MCAM (0.1 mg/kg/day) shifted the curve more than 120-fold rightward with monkeys receiving doses much larger than the likely lethal dose of fentanyl with no adverse effect or observable change in behavior. This study demonstrates that MCAM reliably and dose-dependently decreases fentanyl self-administration and prevents opioid overdose, with no evidence of adverse effects over a broad dose range, further supporting the potential therapeutic utility of this novel antagonist.

Behavioral pharmacology of methocinnamox: A potential new treatment for opioid overdose and opioid use disorder

Opioid overdose and opioid use disorder continue to be significant public health challenges despite the availability of effective medications and significant efforts at all levels of society. The emergence of highly potent and efficacious opioids such as fentanyl and its derivatives over the last decade has only exacerbated what was already a substantial problem. Behavioral pharmacology research has proven invaluable for understanding the effects of drugs as well as developing and evaluating pharmacotherapies for disorders involving the central nervous system, including substance abuse disorders. This paper describes a program of research characterizing a potent, selective, and long-lasting mu opioid receptor antagonist, methocinnamox, and evaluating its potential for treating opioid overdose and opioid use disorder. Studies in rodents and nonhuman primates demonstrate that methocinnamox prevents and reverses opioid-induced ventilatory depression and selectively blocks opioid self-administration. This work, taken together with rigorous in vitro and ex vivo studies investigating methocinnamox neuropharmacology, lays a solid foundation for the therapeutic utility of this potentially life-saving medication. Moreover, these studies demonstrate how rigorous behavioral pharmacological studies can be integrated in a broader drug discovery and development research program.

Effects of Daily Methocinnamox Treatment on Fentanyl Self-Administration in Rhesus Monkeys

Methocinnamox (MCAM), a long-acting μ-opioid receptor antagonist, attenuates the positive reinforcing effects of opioids, such as heroin and fentanyl, suggesting it could be an effective treatment of opioid use disorder (OUD). Because treatment of OUD often involves repeated administration of a medication, this study evaluated effects of daily injections of a relatively small dose of MCAM on fentanyl self-administration and characterized the shift in the fentanyl dose-effect curve. Rhesus monkeys (3 males and 2 females) lever-pressed for intravenous infusions of fentanyl (0.032-10 μg/kg infusion) or cocaine (32-100 μg/kg infusion) under a fixed-ratio 30 schedule. MCAM (0.032 mg/kg) or naltrexone (0.0032-0.032 mg/kg) was administered subcutaneously 60 or 15 minutes, respectively, before sessions. When administered acutely, naltrexone and MCAM decreased fentanyl self-administration, with effects of naltrexone lasting less than 24 hours and effects of MCAM lasting for up to 3 days. Daily MCAM treatment attenuated responding for fentanyl, but not cocaine; effects were maintained for the duration of treatment with responding recovering quickly (within 2 days) following discontinuation of treatment. MCAM treatment shifted the fentanyl dose-effect curve in a parallel manner approximately 20-fold to the right. Naltrexone pretreatment decreased fentanyl intake with equal potency before and after MCAM treatment, confirming sensitivity of responding to antagonism by an opioid receptor antagonist. Although antagonist effects of treatment with a relatively small dose were surmountable, MCAM produced sustained and selective attenuation of opioid self-administration, supporting the view that it could be an effective treatment of OUD. SIGNIFICANCE STATEMENT: Opioid use disorder and opioid overdose continue to be significant public health challenges despite the availability of effective treatments. Methocinnamox (MCAM) is a long-acting μ-opioid receptor antagonist that blocks the reinforcing and ventilatory depressant effects of opioids in nonhuman subjects. This study demonstrates that daily treatment with MCAM reliably and selectively decreases fentanyl self-administration, further supporting the potential therapeutic utility of this novel antagonist.

The Potential of Methocinnamox as a Future Treatment for Opioid Use Disorder: A Narrative Review

The opioid epidemic is an ongoing public health crisis, and the United States health system is overwhelmed with increasing numbers of opioid-related overdoses. Methocinnamox (MCAM) is a novel mu opioid receptor antagonist with an extended duration of action. MCAM has potential to reduce the burden of the opioid epidemic by being used as an overdose rescue treatment and a long-term treatment for opioid use disorder (OUD). The currently available treatments for OUD include naloxone, naltrexone, and methadone. These treatments have certain limitations, which include short duration of action, patient non-compliance, and diversion. A narrative review was conducted using PubMed and Google Scholar databases covering the history of the opioid epidemic, pain receptors, current OUD treatments and the novel drug MCAM. MCAM could potentially be used as both a rescue and long-term treatment for opioid misuse. This is due to its pseudo-irreversible antagonism of the mu opioid receptor, abnormally long duration of action of nearly two weeks, and the possibility of using kappa or delta opioid receptor agonists for pain management during OUD treatment. MCAM’s novel pharmacokinetic and pharmacodynamic properties open a new avenue for treating opioid misuse.

Examining the effects of psychoactive drugs on complex behavioral processes in laboratory animals

Behavioral pharmacology has been aided significantly by the development of innovative cognitive tasks designed to examine complex behavioral processes in laboratory animals. Performance outcomes under these conditions have provided key metrics of drug action which serve to supplement traditional in vivo assays of physiologic and behavioral effects of psychoactive drugs. This chapter provides a primer of cognitive tasks designed to assay different aspects of complex behavior, including learning, cognitive flexibility, memory, attention, motivation, and impulsivity. Both capstone studies and recent publications are highlighted throughout to illustrate task value for two distinct but often interconnected translational strategies. First, task performance in laboratory animals can be utilized to elucidate how drugs of abuse affect complex behavioral processes. Here, the expectation is that adverse effects on such processes will have predictive relevance to consequences that will be experienced by humans. Second, these same task outcomes can be used to evaluate candidate therapeutics. In this case, the extent to which drug doses with medicinal value perturb task performance can contribute critical information for a more complete safety profile appraisal and advance the process of medications development. Methodological and theoretical considerations are discussed and include an emphasis on determining selectivity in drug action on complex behavioral processes.

Methocinnamox Reverses and Prevents Fentanyl-Induced Ventilatory Depression in Rats

Opioid use disorder affects over 2 million Americans with an increasing number of deaths due to overdose from the synthetic opioid fentanyl and its analogs. The Food and Drug Administration-approved opioid receptor antagonist naloxone (e.g., Narcan) is used currently to treat overdose; however, a short duration of action limits its clinical utility. Methocinnamox (MCAM) is a long-lasting opioid receptor antagonist that may reverse and prevent the ventilatory-depressant effects of fentanyl. This study compared the ability of naloxone (0.0001-10 mg/kg) and MCAM (0.0001-10 mg/kg) to reverse and prevent ventilatory depression by fentanyl and compared the duration of action of MCAM intravenously and subcutaneously in two procedures: ventilation and warm-water tail withdrawal. In male Sprague-Dawley rats (N = 8), fentanyl (0.0032-0.178 mg/kg, i.v.) decreased minute volume in a dose- and time-dependent manner with a dose of 0.178 mg/kg decreasing VE to less than 40% of control. MCAM and naloxone reversed the ventilatory-depressant effects of 0.178 mg/kg fentanyl in a dose-related manner. The day after antagonist administration, MCAM but not naloxone attenuated the ventilatory-depressant effects of fentanyl. The duration of action of MCAM lasted up to 3 days and at least 2 weeks after intravenous and subcutaneous administration, respectively. MCAM attenuated the antinociceptive effects of fentanyl, with antagonism lasting up to 5 days and more than 2 weeks after intravenous and subcutaneous administration, respectively. Reversal and prolonged antagonism by MCAM might provide an effective treatment option for the opioid crisis, particularly toxicity from fentanyl and related highly potent analogs. SIGNIFICANCE STATEMENT: This study demonstrates that like naloxone, methocinnamox (MCAM) reverses the ventilatory-depressant effects of fentanyl in a time- and dose-related manner. However, unlike naloxone, the duration of action of MCAM was greater than 2 weeks when administered subcutaneously and up to 5 days when administered intravenously. These data suggest that MCAM might be particularly useful for rescuing individuals from opioid overdose, including fentanyl overdose, as well as protecting against the reemergence of ventilatory depression (renarconization).

Countermeasures for Preventing and Treating Opioid Overdose

The only medication available currently to prevent and treat opioid overdose (naloxone) was approved by the US Food and Drug Administration (FDA) nearly 50 years ago. Because of its pharmacokinetic and pharmacodynamic properties, naloxone has limited utility under some conditions and would not be effective to counteract mass casualties involving large-scale deployment of weaponized synthetic opioids. To address shortcomings of current medical countermeasures for opioid toxicity, a trans-agency scientific meeting was convened by the US National Institute of Allergy and Infectious Diseases/National Institutes of Health (NIAID/NIH) on August 6 and 7, 2019, to explore emerging alternative approaches for treating opioid overdose in the event of weaponization of synthetic opioids. The meeting was initiated by the Chemical Countermeasures Research Program (CCRP), was organized by NIAID, and was a collaboration with the National Institute on Drug Abuse/NIH (NIDA/NIH), the FDA, the Defense Threat Reduction Agency (DTRA), and the Biomedical Advanced Research and Development Authority (BARDA). This paper provides an overview of several presentations at that meeting that discussed emerging new approaches for treating opioid overdose, including the following: (1) intranasal nalmefene, a competitive, reversible opioid receptor antagonist with a longer duration of action than naloxone; (2) methocinnamox, a novel opioid receptor antagonist; (3) covalent naloxone nanoparticles; (4) serotonin (5-HT)_1A receptor agonists; (5) fentanyl-binding cyclodextrin scaffolds; (6) detoxifying biomimetic "nanosponge" decoy receptors; and (7) antibody-based strategies. These approaches could also be applied to treat opioid use disorder.