Methocinnamox has affinity values for the opioid receptors of 0.6nM for the μ-opioid receptor, 2.2nM for the δ-opioid receptor, and 4.9nM for the κ-opioid receptor.[2] Hence, it has about 3.7-fold preferential affinity for the μ-opioid receptor over the δ-opioid receptor and about 8.2-fold higher affinity for the μ-opioid receptor over the κ-opioid receptor.[2]
The antagonism of the μ-opioid receptor by methocinnamox is not irreversible as the drug does not form a covalent bond with the receptor.[2] This is in contrast to prototypical μ-opioid receptor alkylating agents like β-funaltrexamine and β-chlornaltrexamine.[2][4] However, in spite of its lack of covalent binding to the μ-opioid receptor, methocinnamox appears to not dissociate from the μ-opioid receptor or dissociates from it extremely slowly.[2] Hence, methocinnamox has been described as a pseudo-irreversible antagonist of the μ-opioid receptor or as a "functionally irreversible" antagonist.[2] The mechanism underlying the pseudo-irreversible antagonism of methocinnamox hasn't been fully elucidated.[1] Also unlike irreversible μ-opioid receptor antagonists like β-funaltrexamine and β-chlornaltrexamine, methocinnamox lacks κ-opioid receptor agonism and is more selective for the μ-opioid receptor in its actions.[4]
Methocinnamox has been found to bind to two distinct sites on the μ-opioid receptor.[1] It binds to the orthosteric site as a pseudo-irreversible and non-competitive antagonist, thereby directly blocking opioid binding.[1] In addition, methocinnamox has been found to bind to and act as an antagonist of an unknown allosteric site on the μ-opioid receptor with lower affinity that modulates the affinity and/or intrinsic activity of orthosteric μ-opioid receptor agonists.[1]
The μ-opioid receptor antagonism of methocinnamox is non-competitive and insurmountable by μ-opioid receptor agonists like morphine and fentanyl.[2][1] It has been found to completely block the effects of morphine at morphine doses of up to 1,000mg/kg in animals, with the dose–response curve of morphine being shifted rightward by up to 100-fold.[2][8] Doses of morphine of 1,000mg/kg are normally often fatal.[2] The insurmountability of methocinnamox's μ-opioid receptor antagonism is in contrast to that with competitive μ-opioid receptor antagonists like naloxone and naltrexone, which can be overcome with higher doses of μ-opioid receptor agonists.[1][2]
In contrast to the μ-opioid receptor, the antagonism of the κ- and δ-opioid receptors by methocinnamox is competitive and reversible.[1] Moreover, methocinnamox shows a short duration in the body.[1] The actions of methocinnamox in vivo are selective for μ-opioid receptor antagonism, with a lack of significant antagonism of the effects of κ-opioid receptor agonists like bremazocine or δ-opioid receptor agonists like BW373U86.[2]
The actions of methocinnamox are dose-dependent.[2] A single dose of 3.2mg/kg blocked the effects of morphine for approximately 2weeks in animals whereas a single 10mg/kg dose blocked the effects of morphine for over 2months.[2]
Pharmacokinetics
In animals, methocinnamox reached peak concentrations 15 to 45minutes following injection and had an elimination half-life of approximately 70minutes.[1] In spite of this short duration in the body however, the μ-opioid receptor antagonist effects of methocinnamox persist for up to months with a single injection.[1][2] These findings suggest that the long-lasting effects of methocinnamox are not due to pharmacokinetic factors but rather its pharmacodynamic properties and pseudo-irreversible antagonism.[1]
Methocinnamox has not yet been tested in humans as of 2022.[1] However, it has been tested in rodents and monkeys.[2] It was reported in March 2020 that clinical trials of methocinnamox were expected to begin within 18 to 24months.[3] In March 2023, it was reported that a phase 1 clinical trial of methocinnamox funded by the National Institutes of Health (NIH) would possibly start in 2024.[5]
^ abcdMoss L (4 March 2020). "New drug blocks the fatal effects of opioids?". wndu.com. Retrieved 9 August 2024. Researchers say they hope to have [methocinnamox] in human clinical trials within the next 18 to 24 months.
^ abAlvarez-Hernandez J (7 March 2023). "UT Health San Antonio Professor France leads novel drug discovery research". UT Health San Antonio. Retrieved 9 August 2024. Charles P. France, PhD, the Robert A. Welch Distinguished University Chair in Chemistry, professor of pharmacology and professor of psychiatry in the Joe R. and Teresa Lozano Long School of Medicine at The University of Texas Health Science Center at San Antonio (UT Health San Antonio), recently received a $4.12 million award from the U.S. National Institutes of Health (NIH) to investigate innovative drug development research of the compound methocinnamox (MCAM) to help combat the opioid epidemic. [...] This NIH funding mechanism, specifically UG3/UH3, has one precise objective to advance the discovery into the clinical setting. "We want to get this into the clinic," France said. [...] "Under the best of conditions, we hope to have this compound into a phase one clinical trial sometime in 2024."
^"Methoclocinnamox". PubChem. U.S. National Library of Medicine. Retrieved 9 August 2024.
^ abcGerak LR, Maguire DR, France CP (2019). "Behavioral Pharmacology of Drugs Acting at Mu Opioid Receptors". Substance Use Disorders. Handbook of Experimental Pharmacology. Vol. 258. Cham: Springer International Publishing. pp. 127–145. doi:10.1007/164_2019_265. ISBN978-3-030-33678-3. PMID31451969. Given the advantages of buprenorphine as a treatment for opioid use disorder, additional compounds related to buprenorphine were synthesized in an attempt to reduce its adverse effects (Broadbear et al. 2000). These efforts resulted in the discovery of the mu opioid receptor antagonist methocinnamox (MCAM). Like buprenorphine, MCAM binds pseudoirreversibly to mu opioid receptors; however, it does not appear to produce agonist effects at mu opioid receptors under any conditions. Instead, MCAM produces long-lasting antagonism at mu opioid receptors, as evidenced by attenuation of the antinociceptive effects of morphine in rodents, with the morphine dose-effect curve shifted up to hundredfold rightward (Peckham et al. 2005) and antagonist effects evident for at least 2 days after administration (Broadbear et al. 2000).
^Hiranita T, Ho NP, France CP (2023). "Comparison of the mu-opioid receptor antagonists methocinnamox (MCAM) and naloxone to reverse the ventilatory-depressant effects of fentanyl and heroin in male rats". ASPET 2023 Annual Meeting Abstract - Central Nervous System Pharmacology - Neuropharmacology. American Society for Pharmacology and Experimental Therapeutics. p. 544. doi:10.1124/jpet.122.155410.