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De Vrieze LM, Walton SE, Pottie E, Papsun D, Logan BK, Krotulski AJ, Stove CP, Vandeputte MM. In vitro structure-activity relationships and forensic case series of emerging 2-benzylbenzimidazole 'nitazene' opioids. Arch Toxicol 2024; 98:2999-3018. [PMID: 38877156 PMCID: PMC11324687 DOI: 10.1007/s00204-024-03774-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2024] [Accepted: 04/24/2024] [Indexed: 06/16/2024]
Abstract
2-Benzylbenzimidazole 'nitazene' opioids are presenting a growing threat to public health. Although various nitazenes were previously studied, systematic comparisons of the effects of different structural modifications to the 2-benzylbenzimidazole core structure on μ-opioid receptor (MOR) activity are limited. Here, we assessed in vitro structure-activity relationships of 9 previously uncharacterized nitazenes alongside known structural analogues. Specifically, we focused on MOR activation by 'ring' substituted analogues (i.e., N-pyrrolidino and N-piperidinyl modifications), 'desnitazene' analogues (lacking the 5-nitro group), and N-desethyl analogues. The results from two in vitro MOR activation assays (β-arrestin 2 recruitment and inhibition of cAMP accumulation) showed that 'ring' modifications overall yield highly active drugs. With the exception of 4'-OH analogues (which are metabolites), N-pyrrolidino substitutions were generally more favorable for MOR activation than N-piperidine substitutions. Furthermore, removal of the 5-nitro group on the benzimidazole ring consistently caused a pronounced decrease in potency. The N-desethyl modifications showed important MOR activity, and generally resulted in a slightly lowered potency than comparator nitazenes. Intriguingly, N-desethyl isotonitazene was the exception and was consistently more potent than isotonitazene. Complementing the in vitro findings and demonstrating the high harm potential associated with many of these compounds, we describe 85 forensic cases from North America and the United Kingdom involving etodesnitazene, N-desethyl etonitazene, N-desethyl isotonitazene, N-pyrrolidino metonitazene, and N-pyrrolidino protonitazene. The low-to-sub ng/mL blood concentrations observed in most cases underscore the drugs' high potencies. Taken together, by bridging pharmacology and case data, this study may aid to increase awareness and guide legislative and public health efforts.
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Affiliation(s)
- Liam M De Vrieze
- Laboratory of Toxicology, Department of Bioanalysis, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium
| | - Sara E Walton
- Center for Forensic Science Research and Education, Fredric Rieders Family Foundation, Willow Grove, PA, 19090, USA
| | - Eline Pottie
- Laboratory of Toxicology, Department of Bioanalysis, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium
| | | | - Barry K Logan
- Center for Forensic Science Research and Education, Fredric Rieders Family Foundation, Willow Grove, PA, 19090, USA
- NMS Labs, Horsham, PA, 19044, USA
| | - Alex J Krotulski
- Center for Forensic Science Research and Education, Fredric Rieders Family Foundation, Willow Grove, PA, 19090, USA
| | - Christophe P Stove
- Laboratory of Toxicology, Department of Bioanalysis, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium.
| | - Marthe M Vandeputte
- Laboratory of Toxicology, Department of Bioanalysis, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium.
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2
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Syrjanen R, Schumann JL, Castle JW, Sharp L, Griffiths A, Blakey K, Dutch M, Maplesden J, Greene SL. Protonitazene detection in two cases of opioid toxicity following the use of tetrahydrocannabinol vape products in Australia. Clin Toxicol (Phila) 2024:1-3. [PMID: 39078080 DOI: 10.1080/15563650.2024.2383692] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2023] [Revised: 07/15/2024] [Accepted: 07/18/2024] [Indexed: 07/31/2024]
Abstract
INTRODUCTION Protonitazene is an opioid belonging to the 2-benzylbenzimidazole structural class. We describe two cases of opioid toxicity involving the reported inhalation of a delta-9-tetrahydrocannabinol vape product in which protonitazene was detected. CASE REPORTS Case 1 was a young male found unconscious after the reported use of a delta-9-tetrahydrocannabinol vape. He suffered two subsequent apnoeic episodes requiring bag-valve-mask ventilation before eventual recovery. Only protonitazene was detected in blood at a concentration of 0.74 µg/L. Case 2 was a young male who died shortly after being found unresponsive. The postmortem femoral blood concentrations of protonitazene and delta-9-tetrahydrocannabinol were 0.33 µg/L and 2 µg/L, respectively. Analysis of a pod vaping device found in the decedent's hand and a separate e-liquid bottle labelled as delta-9-tetrahydrocannabinol showed a mixture of protonitazene and delta-9-tetrahydrocannabinol. DISCUSSION The opioid effects of protonitazene are mediated through β-arrestin2 and mu opioid receptor signalling pathways. Benzimidazole opioids are lipophilic and, when mixed with a suitable solvent, can be used in a vape device. It is anticipated that naloxone would have provided effective reversal of toxicity in our cases. CONCLUSIONS Novel routes of opioid administration, like vaping, may appear relatively innocuous in comparison to intravenous administration, but opioids may still be absorbed at high concentrations, resulting in severe opioid toxicity or death.
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Affiliation(s)
- Rebekka Syrjanen
- Department of Forensic Medicine, Monash University, Southbank, Australia
- Austin Health, Victorian Poisons Information Centre, Austin Hospital, Heidelberg, Australia
| | - Jennifer L Schumann
- Department of Forensic Medicine, Monash University, Southbank, Australia
- Toxicology Department, Victorian Institute of Forensic Medicine, Southbank, Australia
- Monash University, Monash Addiction Research Centre, Frankston, Australia
| | - Jared W Castle
- Toxicology Department, Victorian Institute of Forensic Medicine, Southbank, Australia
| | - Lesley Sharp
- Forensic Toxicology, Forensic and Scientific Services, Coopers Plains, Australia
| | - Andrew Griffiths
- Forensic Toxicology, Forensic and Scientific Services, Coopers Plains, Australia
| | - Karen Blakey
- Forensic Chemistry, Forensic Science Queensland, Coopers Plains, Australia
| | - Martin Dutch
- Event Health Services, St John Ambulance Victoria, Notting Hill, Australia
- Department of Critical Care, The University of Melbourne, Melbourne Medical School, Parkville, Australia
| | | | - Shaun L Greene
- Austin Health, Victorian Poisons Information Centre, Austin Hospital, Heidelberg, Australia
- Department of Critical Care, The University of Melbourne, Melbourne Medical School, Parkville, Australia
- Emergency Department, Austin Health, Austin Hospital, Heidelberg, Australia
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3
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Jadhav GR, Fasinu PS. Metabolic characterization of the new benzimidazole synthetic opioids - nitazenes. Front Pharmacol 2024; 15:1434573. [PMID: 39092223 PMCID: PMC11291330 DOI: 10.3389/fphar.2024.1434573] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2024] [Accepted: 06/19/2024] [Indexed: 08/04/2024] Open
Abstract
The recent re-emergence and the increasing popularity of nitazenes, a group of new synthetic opioids (NSO) that belong to the benzimidazole chemical class, has raised public health concerns. As a class of potential opioid analgesic agents whose development was discontinued in the 1960s due to their high potential for abuse, very little is known about their metabolism and physiologic disposition. In the current study, three nitazenes-butonitazene, isotonitazene and protonitaze were incubated in human liver microsomes (HLM), human S9 (HS9) fractions and recombinant cytochrome P450 enzymes. All three nitazenes were rapidly metabolized in both HLM and HS9 with over 95% depletion within 60 min. In HLM, butonitazene, isotonitazene and protonitazene had in vitro intrinsic clearance (CLint) (µL/min/mg protein) values of 309, 221 and 216 respectively compared to 150 of verapamil, the positive control. In HS9, CLint values were 217, 139, and 150 for butonitazene, isotonitazene and protonitazene respectively compared to only 35 for testosterone, the control probe substrate. Putative metabolite identified from this study include products of hydroxylation, desethylation, dealkylation, desethylation followed by dealkylation, and desethylation followed by hydroxylation. The metabolic phenotyping showed CYP2D6, CYP2B6 and CYP2C8 and the major hepatic enzymes responsible for the metabolism of nitazenes. Within 30 min of incubation, CYP2D6 depleted butonitazene (99%), isotonitazene (72%) and butonitazene (100%) significantly. The rapid metabolism of nitazenes may be an important factor in accurate and timely detections and quantitation of the unchanged drugs in human matrices following intoxication or in forensic analysis. The involvement of multiple polymorphic CYPs in their metabolism may play important roles in the susceptibility to intoxication and/or addiction, depending on the activity of the metabolites.
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Affiliation(s)
| | - Pius S. Fasinu
- Department of Pharmacology and Toxicology, Heersink School of Medicine, The University of Alabama at Birmingham, Birmingham, AL, United States
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Kozell LB, Eshleman AJ, Wolfrum KM, Swanson TL, Bloom SH, Benware S, Schmachtenberg JL, Schutzer KA, Schutzer WE, Janowsky A, Abbas AI. Pharmacologic Characterization of Substituted Nitazenes at μ, κ, and Δ Opioid Receptors Suggests High Potential for Toxicity. J Pharmacol Exp Ther 2024; 389:219-228. [PMID: 38453524 PMCID: PMC11026150 DOI: 10.1124/jpet.123.002052] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2023] [Revised: 02/22/2024] [Accepted: 02/27/2024] [Indexed: 03/09/2024] Open
Abstract
The benzimidazole opioids (substituted nitazenes) are highly potent μ opiod receptor (MOR) agonists with heroin- or fentanyl-like effects. These compounds have caused hospitalizations and fatal overdoses. We characterized the in vitro pharmacology and structure-activity relationships of 19 nitazenes with substitutions at three positions of the benzimidazole core. Affinities were assessed using agonist radioligand binding assays at human μ, κ, and Δ opioid receptors (MOR, KOR, and DOR, respectively) heterologously expressed in CHO cells. Notably, for MOR binding, nine substituted nitazenes had significantly higher affinities than fentanyl including N-pyrrolidino etonitazene, N-pyrrilidino isonitazene, and N-desethyl isotonitazene; 13 had subnanomolar affinities. Only metodesnitazene and flunitazene had significantly lower affinities than fentanyl. Affinities for the substituted nitazenes at KOR and DOR relative to MOR were 46- to 2580-fold and 180- to 1280-fold lower, respectively. Functional activities were assessed using [35S]GTPγS binding assays. Four nitazenes had subnanomolar potencies at MOR: N-pyrrolidino etonitazene, N-pyrrilidino isonitazene, N-pyrrilidino protonitazene and N-desethyl isotonitazene. Ten substituted nitazenes had significantly higher potencies than fentanyl. All tested nitazenes were full MOR agonists. Potencies at KOR and DOR relative to MOR were 7.3- to 7920-fold and 24- to 9400-fold lower, respectively. Thus, many of these compounds are high affinity/high potency MOR agonists with elevated potential to elicit toxicity and overdose at low doses. SIGNIFICANCE STATEMENT: Substituted nitazenes are a growing public health threat. Although the 19 nitazenes tested vary in their opioid receptor pharmacology, a number are very high affinity, high potency, and high efficacy compounds- higher than fentanyl. Their pharmacology suggests high potential for harm.
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Affiliation(s)
- Laura B Kozell
- VA Portland Health Care System (L.B.K., A.J.E., K.M.W., T.L.S., S.H.B., S.B., J.L.S., K.A.S., W.E.S., A.J., A.I.A.), Departments of Psychiatry (L.B.K., A.J.E., T.L.S., W.E.S., A.J., A.I.A.), and Behavioral Neuroscience (L.B.K., A.J., A.I.A.), Oregon Health and Science University, Portland, Oregon
| | - Amy J Eshleman
- VA Portland Health Care System (L.B.K., A.J.E., K.M.W., T.L.S., S.H.B., S.B., J.L.S., K.A.S., W.E.S., A.J., A.I.A.), Departments of Psychiatry (L.B.K., A.J.E., T.L.S., W.E.S., A.J., A.I.A.), and Behavioral Neuroscience (L.B.K., A.J., A.I.A.), Oregon Health and Science University, Portland, Oregon
| | - Katherine M Wolfrum
- VA Portland Health Care System (L.B.K., A.J.E., K.M.W., T.L.S., S.H.B., S.B., J.L.S., K.A.S., W.E.S., A.J., A.I.A.), Departments of Psychiatry (L.B.K., A.J.E., T.L.S., W.E.S., A.J., A.I.A.), and Behavioral Neuroscience (L.B.K., A.J., A.I.A.), Oregon Health and Science University, Portland, Oregon
| | - Tracy L Swanson
- VA Portland Health Care System (L.B.K., A.J.E., K.M.W., T.L.S., S.H.B., S.B., J.L.S., K.A.S., W.E.S., A.J., A.I.A.), Departments of Psychiatry (L.B.K., A.J.E., T.L.S., W.E.S., A.J., A.I.A.), and Behavioral Neuroscience (L.B.K., A.J., A.I.A.), Oregon Health and Science University, Portland, Oregon
| | - Shelley H Bloom
- VA Portland Health Care System (L.B.K., A.J.E., K.M.W., T.L.S., S.H.B., S.B., J.L.S., K.A.S., W.E.S., A.J., A.I.A.), Departments of Psychiatry (L.B.K., A.J.E., T.L.S., W.E.S., A.J., A.I.A.), and Behavioral Neuroscience (L.B.K., A.J., A.I.A.), Oregon Health and Science University, Portland, Oregon
| | - Sheila Benware
- VA Portland Health Care System (L.B.K., A.J.E., K.M.W., T.L.S., S.H.B., S.B., J.L.S., K.A.S., W.E.S., A.J., A.I.A.), Departments of Psychiatry (L.B.K., A.J.E., T.L.S., W.E.S., A.J., A.I.A.), and Behavioral Neuroscience (L.B.K., A.J., A.I.A.), Oregon Health and Science University, Portland, Oregon
| | - Jennifer L Schmachtenberg
- VA Portland Health Care System (L.B.K., A.J.E., K.M.W., T.L.S., S.H.B., S.B., J.L.S., K.A.S., W.E.S., A.J., A.I.A.), Departments of Psychiatry (L.B.K., A.J.E., T.L.S., W.E.S., A.J., A.I.A.), and Behavioral Neuroscience (L.B.K., A.J., A.I.A.), Oregon Health and Science University, Portland, Oregon
| | - Kamryn A Schutzer
- VA Portland Health Care System (L.B.K., A.J.E., K.M.W., T.L.S., S.H.B., S.B., J.L.S., K.A.S., W.E.S., A.J., A.I.A.), Departments of Psychiatry (L.B.K., A.J.E., T.L.S., W.E.S., A.J., A.I.A.), and Behavioral Neuroscience (L.B.K., A.J., A.I.A.), Oregon Health and Science University, Portland, Oregon
| | - William E Schutzer
- VA Portland Health Care System (L.B.K., A.J.E., K.M.W., T.L.S., S.H.B., S.B., J.L.S., K.A.S., W.E.S., A.J., A.I.A.), Departments of Psychiatry (L.B.K., A.J.E., T.L.S., W.E.S., A.J., A.I.A.), and Behavioral Neuroscience (L.B.K., A.J., A.I.A.), Oregon Health and Science University, Portland, Oregon
| | - Aaron Janowsky
- VA Portland Health Care System (L.B.K., A.J.E., K.M.W., T.L.S., S.H.B., S.B., J.L.S., K.A.S., W.E.S., A.J., A.I.A.), Departments of Psychiatry (L.B.K., A.J.E., T.L.S., W.E.S., A.J., A.I.A.), and Behavioral Neuroscience (L.B.K., A.J., A.I.A.), Oregon Health and Science University, Portland, Oregon
| | - Atheir I Abbas
- VA Portland Health Care System (L.B.K., A.J.E., K.M.W., T.L.S., S.H.B., S.B., J.L.S., K.A.S., W.E.S., A.J., A.I.A.), Departments of Psychiatry (L.B.K., A.J.E., T.L.S., W.E.S., A.J., A.I.A.), and Behavioral Neuroscience (L.B.K., A.J., A.I.A.), Oregon Health and Science University, Portland, Oregon
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5
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Tsai MHM, Chen L, Baumann MH, Canals M, Javitch JA, Lane JR, Shi L. In Vitro Functional Profiling of Fentanyl and Nitazene Analogs at the μ-Opioid Receptor Reveals High Efficacy for Gi Protein Signaling. ACS Chem Neurosci 2024; 15:854-867. [PMID: 38345920 DOI: 10.1021/acschemneuro.3c00750] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/22/2024] Open
Abstract
Novel synthetic opioids (NSOs), including both fentanyl and non-fentanyl analogs that act as μ-opioid receptor (MOR) agonists, are associated with serious intoxication and fatal overdose. Previous studies proposed that G-protein-biased MOR agonists are safer pain medications, while other evidence indicates that low intrinsic efficacy at MOR better explains the reduced opioid side effects. Here, we characterized the in vitro functional profiles of various NSOs at the MOR using adenylate cyclase inhibition and β-arrestin2 recruitment assays, in conjunction with the application of the receptor depletion approach. By fitting the concentration-response data to the operational model of agonism, we deduced the intrinsic efficacy and affinity for each opioid in the Gi protein signaling and β-arrestin2 recruitment pathways. Compared to the reference agonist [d-Ala2,N-MePhe4,Gly-ol5]enkephalin, we found that several fentanyl analogs were more efficacious at inhibiting cAMP production, whereas all fentanyl analogs were less efficacious at recruiting β-arrestin2. In contrast, the non-fentanyl 2-benzylbenzimidazole (i.e., nitazene) analogs were highly efficacious and potent in both the cAMP and β-arrestin2 assays. Our findings suggest that the high intrinsic efficacy of the NSOs in Gi protein signaling is a common property that may underlie their high risk of intoxication and overdose, highlighting the limitation of using in vitro functional bias to predict the adverse effects of opioids. In addition, the extremely high potency of many NSOs now infiltrating illicit drug markets further contributes to the danger posed to public health.
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Affiliation(s)
- Meng-Hua M Tsai
- Computational Chemistry and Molecular Biophysics Section, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland 21224, United States
| | - Li Chen
- Computational Chemistry and Molecular Biophysics Section, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland 21224, United States
| | - Michael H Baumann
- Designer Drug Research Unit, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland 21224, United States
| | - Meritxell Canals
- Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, Queen's Medical Centre, University of Nottingham, Nottingham NG7 2UH, U.K
- Centre of Membrane Proteins and Receptors, Universities of Birmingham and Nottingham, Midlands NG7 2UH, U.K
| | - Jonathan A Javitch
- Division of Molecular Therapeutics, New York State Psychiatric Institute, New York, New York 10032, United States
- Department of Molecular Pharmacology and Therapeutics, Vagelos College of Physicians and Surgeons, Columbia University, New York, New York 10032, United States
- Department of Psychiatry, Vagelos College of Physicians and Surgeons, Columbia University, New York, New York 10032, United States
| | - J Robert Lane
- Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, Queen's Medical Centre, University of Nottingham, Nottingham NG7 2UH, U.K
- Centre of Membrane Proteins and Receptors, Universities of Birmingham and Nottingham, Midlands NG7 2UH, U.K
| | - Lei Shi
- Computational Chemistry and Molecular Biophysics Section, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland 21224, United States
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6
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Glatfelter GC, Vandeputte MM, Chen L, Walther D, Tsai MHM, Shi L, Stove CP, Baumann MH. Alkoxy chain length governs the potency of 2-benzylbenzimidazole 'nitazene' opioids associated with human overdose. Psychopharmacology (Berl) 2023; 240:2573-2584. [PMID: 37658878 DOI: 10.1007/s00213-023-06451-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/29/2023] [Accepted: 08/15/2023] [Indexed: 09/05/2023]
Abstract
RATIONALE Novel synthetic opioids (NSOs) are emerging in recreational drug markets worldwide. In particular, 2-benzylbenzimidazole 'nitazene' compounds are problematic NSOs associated with serious clinical consequences, including fatal respiratory depression. Evidence from in vitro studies shows that alkoxy chain length can influence the potency of nitazenes at the mu-opioid receptor (MOR). However, structure-activity relationships (SARs) of nitazenes for inducing opioid-like effects in animal models are not well understood compared to relevant opioids contributing to the ongoing opioid crisis (e.g., fentanyl). OBJECTIVES Here, we examined the in vitro and in vivo effects of nitazene analogues with varying alkoxy chain lengths (i.e., metonitazene, etonitazene, isotonitazene, protonitazene, and butonitazene) as compared to reference opioids (i.e., morphine and fentanyl). METHODS AND RESULTS Nitazene analogues displayed nanomolar affinities for MOR in rat brain membranes and picomolar potencies to activate MOR in transfected cells. All compounds induced opioid-like effects on locomotor activity, hot plate latency, and body temperature in male mice, and alkoxy chain length markedly influenced potency. Etonitazene, with an ethoxy chain, was the most potent analogue in MOR functional assays (EC50 = 30 pM, Emax = 103%) and across all in vivo endpoints (ED50 = 3-12 μg/kg). In vivo SARs revealed that ethoxy, isopropoxy, and propoxy chains engendered higher potencies than fentanyl, whereas methoxy and butoxy analogues were less potent. MOR functional potencies, but not MOR affinities, were positively correlated with in vivo potencies to induce opioid effects. CONCLUSIONS Overall, our data show that certain nitazene NSOs are more potent than fentanyl as MOR agonists in mice, highlighting concerns regarding the high potential for overdose in humans who are exposed to these compounds.
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Affiliation(s)
- Grant C Glatfelter
- Designer Drug Research Unit, National Institute On Drug Abuse, Intramural Research Program, Baltimore, MD, USA.
| | - Marthe M Vandeputte
- Laboratory of Toxicology, Department of Bioanalysis, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium
| | - Li Chen
- Computational Chemistry and Molecular Biophysics Section, National Institute On Drug Abuse, Intramural Research Program, Baltimore, MD, USA
| | - Donna Walther
- Designer Drug Research Unit, National Institute On Drug Abuse, Intramural Research Program, Baltimore, MD, USA
| | - Meng-Hua M Tsai
- Computational Chemistry and Molecular Biophysics Section, National Institute On Drug Abuse, Intramural Research Program, Baltimore, MD, USA
| | - Lei Shi
- Computational Chemistry and Molecular Biophysics Section, National Institute On Drug Abuse, Intramural Research Program, Baltimore, MD, USA
| | - Christophe P Stove
- Laboratory of Toxicology, Department of Bioanalysis, Faculty of Pharmaceutical Sciences, Ghent University, Ghent, Belgium
| | - Michael H Baumann
- Designer Drug Research Unit, National Institute On Drug Abuse, Intramural Research Program, Baltimore, MD, USA
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7
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Tsai MHM, Chen L, Baumann MH, Canals M, Javitch JA, Lane JR, Shi L. The in vitro functional profiles of fentanyl and nitazene analogs at the μ-opioid receptor - high efficacy is dangerous regardless of signaling bias. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.11.10.566672. [PMID: 38014284 PMCID: PMC10680598 DOI: 10.1101/2023.11.10.566672] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2023]
Abstract
Novel synthetic opioids (NSOs), including both fentanyl and non-fentanyl analogs that act as the μ-opioid receptor (MOR) agonists, are associated with serious intoxication and fatal overdose. Previous studies proposed that G protein biased MOR agonists are safer pain medications, while other evidence indicates that low intrinsic efficacy at MOR better explains reduced opioid side effects. Here, we characterized the in vitro functional profiles of various NSOs at MOR using adenylate cyclase inhibition and β-arrestin2 recruitment assays, in conjunction with the application of the receptor depletion approach. By fitting the concentration-response data to the operational model of agonism, we deduced the intrinsic efficacy and affinity for each opioid in the Gi protein signaling and β-arrestin2 recruitment pathways. Compared to the reference agonist DAMGO, we found that several fentanyl analogs were more efficacious at inhibiting cAMP production, whereas all fentanyl analogs were less efficacious at recruiting β-arrestin2. In contrast, the non-fentanyl 2-benzylbenzimidazole (i.e., nitazene) analogs were highly efficacious and potent in both the cAMP and β-arrestin2 assays. Our findings suggest that the high intrinsic efficacy of the NSOs in Gi protein signaling is a common property that may underlie their high risk of intoxication and overdose, highlighting the limitation of using in vitro functional bias to predict the adverse effects of opioids. Instead, our results show that, regardless of bias, opioids with sufficiently high intrinsic efficacy can be lethal, especially given the extremely high potency of many of these compounds that are now pervading the illicit drug market.
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Affiliation(s)
- Meng-Hua M. Tsai
- Computational Chemistry and Molecular Biophysics Section, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland 21224, USA
| | - Li Chen
- Computational Chemistry and Molecular Biophysics Section, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland 21224, USA
| | - Michael H. Baumann
- Designer Drug Research Unit, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland 21224, USA
| | - Meritxell Canals
- Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, Queen’s Medical Centre, University of Nottingham, Nottingham, UK
- Centre of Membrane Proteins and Receptors, Universities of Birmingham and Nottingham, Midlands, UK
| | - Jonathan A. Javitch
- Division of Molecular Therapeutics, New York State Psychiatric Institute, New York, NY 10032, USA
- Department of Molecular Pharmacology and Therapeutics, Vagelos College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA
- Department of Psychiatry, Vagelos College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA
| | - J. Robert Lane
- Division of Physiology, Pharmacology and Neuroscience, School of Life Sciences, Queen’s Medical Centre, University of Nottingham, Nottingham, UK
- Centre of Membrane Proteins and Receptors, Universities of Birmingham and Nottingham, Midlands, UK
| | - Lei Shi
- Computational Chemistry and Molecular Biophysics Section, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland 21224, USA
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8
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Malcolm NJ, Palkovic B, Sprague DJ, Calkins MM, Lanham JK, Halberstadt AL, Stucke AG, McCorvy JD. Mu-opioid receptor selective superagonists produce prolonged respiratory depression. iScience 2023; 26:107121. [PMID: 37416459 PMCID: PMC10320493 DOI: 10.1016/j.isci.2023.107121] [Citation(s) in RCA: 12] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2022] [Revised: 03/17/2023] [Accepted: 06/09/2023] [Indexed: 07/08/2023] Open
Abstract
Synthetic opioids are increasingly challenging to combat the opioid epidemic and act primarily at opioid receptors, chiefly the G protein-coupled receptor (GPCR) μ-opioid receptor (MOR), which signals through G protein-dependent and β-arrestin pathways. Using a bioluminescence resonance energy transfer (BRET) system, we investigate GPCR-signaling profiles by synthetic nitazenes, which are known to cause overdose and death due to respiratory depression. We show that isotonitazene and its metabolite, N-desethyl isotonitazene, are very potent MOR-selective superagonists, surpassing both DAMGO G protein and β-arrestin recruitment activity, which are properties distinct from other conventional opioids. Both isotonitazene and N-desethyl isotonitazene show high potency in mouse analgesia tail-flick assays, but N-desethyl isotonitazene shows longer-lasting respiratory depression compared to fentanyl. Overall, our results suggest that potent MOR-selective superagonists may be a pharmacological property predictive of prolonged respiratory depression resulting in fatal consequences and should be examined for future opioid analgesics.
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Affiliation(s)
- Nicholas J. Malcolm
- Department of Cell Biology, Neurobiology, and Anatomy, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Barbara Palkovic
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Daniel J. Sprague
- Department of Cell Biology, Neurobiology, and Anatomy, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Maggie M. Calkins
- Department of Cell Biology, Neurobiology, and Anatomy, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Janelle K. Lanham
- Department of Cell Biology, Neurobiology, and Anatomy, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Adam L. Halberstadt
- Department of Psychiatry, University of California San Diego, La Jolla, CA 92093, USA
- Research Service, VA San Diego Healthcare System, San Diego, CA 92108, USA
| | - Astrid G. Stucke
- Department of Anesthesiology, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - John D. McCorvy
- Department of Cell Biology, Neurobiology, and Anatomy, Medical College of Wisconsin, Milwaukee, WI 53226, USA
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