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Kong L, Ning K, Liu X, Lu J, Chen B, Ye R, Li Z, Jiang S, Tang S, Chai JR, Fang Y, Lan Y, Mai X, Xie Q, Liu J, Shao L, Fu W, Wang Y, Li W. Reversal of subtype-selectivity and function by the introduction of a para-benzamidyl substituent to N-cyclopropylmethyl nornepenthone. Eur J Med Chem 2023; 258:115589. [PMID: 37413884 DOI: 10.1016/j.ejmech.2023.115589] [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: 05/11/2023] [Revised: 06/19/2023] [Accepted: 06/21/2023] [Indexed: 07/08/2023]
Abstract
The discovery and development of novel μ-opioid receptor (MOR) antagonists is a significant area to combat Opioid Use Disorder (OUD). In this work, a series of para-substituted N-cyclopropylmethyl-nornepenthone derivatives were designed and synthesized and pharmacologically assayed. Compound 6a was identified as a selective MOR antagonist both in vitro and in vivo. Its molecular basis was elucidated using molecular docking and MD simulations. A subpocket on the extracellular side of the TM2 domain of MOR, in particular the residue Y2.64, was proposed to be responsible for the reversal of subtype selectivity and functional reversal of this compound.
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Affiliation(s)
- Linghui Kong
- Department of Medicinal Chemistry, School of Pharmacy, Fudan University, No. 826 Zhangheng Road, Shanghai, 201203, China
| | - Kuan Ning
- School of Chinese Materia Medica, Nanjing University of Chinese Medicine, Nanjing, 210023, China; CAS Key Laboratory of Receptor Research and State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, No. 555 Zuchongzhi Road, Shanghai, 201203, China
| | - Xiao Liu
- Department of Medicinal Chemistry, School of Pharmacy, Fudan University, No. 826 Zhangheng Road, Shanghai, 201203, China
| | - Jiashuo Lu
- Department of Pharmacy, Dalian Medical University, Dalian, 116044, China
| | - Baiyu Chen
- Department of Medicinal Chemistry, School of Pharmacy, Fudan University, No. 826 Zhangheng Road, Shanghai, 201203, China
| | - Rongrong Ye
- CAS Key Laboratory of Receptor Research and State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, No. 555 Zuchongzhi Road, Shanghai, 201203, China; School of Chemical and Environmental Engineering, Shanghai Institute of Technology, Shanghai, 201418, China
| | - Zixiang Li
- Department of Medicinal Chemistry, School of Pharmacy, Fudan University, No. 826 Zhangheng Road, Shanghai, 201203, China
| | - Shuang Jiang
- School of Chinese Materia Medica, Nanjing University of Chinese Medicine, Nanjing, 210023, China; CAS Key Laboratory of Receptor Research and State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, No. 555 Zuchongzhi Road, Shanghai, 201203, China
| | - Siyuan Tang
- Department of Medicinal Chemistry, School of Pharmacy, Fudan University, No. 826 Zhangheng Road, Shanghai, 201203, China
| | - Jing-Rui Chai
- CAS Key Laboratory of Receptor Research and State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, No. 555 Zuchongzhi Road, Shanghai, 201203, China
| | - Yun Fang
- Department of Medicinal Chemistry, School of Pharmacy, Fudan University, No. 826 Zhangheng Road, Shanghai, 201203, China
| | - Yingjie Lan
- Department of Medicinal Chemistry, School of Pharmacy, Fudan University, No. 826 Zhangheng Road, Shanghai, 201203, China
| | - Xiaobo Mai
- Department of Medicinal Chemistry, School of Pharmacy, Fudan University, No. 826 Zhangheng Road, Shanghai, 201203, China
| | - Qiong Xie
- Department of Medicinal Chemistry, School of Pharmacy, Fudan University, No. 826 Zhangheng Road, Shanghai, 201203, China
| | - Jinggen Liu
- School of Chinese Materia Medica, Nanjing University of Chinese Medicine, Nanjing, 210023, China; CAS Key Laboratory of Receptor Research and State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, No. 555 Zuchongzhi Road, Shanghai, 201203, China.
| | - Liming Shao
- Department of Medicinal Chemistry, School of Pharmacy, Fudan University, No. 826 Zhangheng Road, Shanghai, 201203, China; State Key Laboratory of Medical Neurobiology, Fudan University, No. 138 Yixueyuan Road, Shanghai, 200032, China.
| | - Wei Fu
- Department of Medicinal Chemistry, School of Pharmacy, Fudan University, No. 826 Zhangheng Road, Shanghai, 201203, China
| | - Yujun Wang
- CAS Key Laboratory of Receptor Research and State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, No. 555 Zuchongzhi Road, Shanghai, 201203, China; Shandong Laboratory of Yantai Drug Discovery, Bohai Rim Advanced Research Institute for Drug Discovery, Yantai, Shandong, 264117, China.
| | - Wei Li
- Department of Medicinal Chemistry, School of Pharmacy, Fudan University, No. 826 Zhangheng Road, Shanghai, 201203, China.
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Ligand-Free Signaling of G-Protein-Coupled Receptors: Relevance to μ Opioid Receptors in Analgesia and Addiction. Molecules 2022; 27:molecules27185826. [PMID: 36144565 PMCID: PMC9503102 DOI: 10.3390/molecules27185826] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2022] [Revised: 09/04/2022] [Accepted: 09/06/2022] [Indexed: 11/17/2022] Open
Abstract
Numerous G-protein-coupled receptors (GPCRs) display ligand-free basal signaling with potential physiological functions, a target in drug development. As an example, the μ opioid receptor (MOR) signals in ligand-free form (MOR-μ*), influencing opioid responses. In addition, agonists bind to MOR but can dissociate upon MOR activation, with ligand-free MOR-μ* carrying out signaling. Opioid pain therapy is effective but incurs adverse effects (ADRs) and risk of opioid use disorder (OUD). Sustained opioid agonist exposure increases persistent basal MOR-μ* activity, which could be a driving force for OUD and ADRs. Antagonists competitively prevent resting MOR (MOR-μ) activation to MOR-μ*, while common antagonists, such as naloxone and naltrexone, also bind to and block ligand-free MOR-μ*, acting as potent inverse agonists. A neutral antagonist, 6β-naltrexol (6BN), binds to but does not block MOR-μ*, preventing MOR-μ activation only competitively with reduced potency. We hypothesize that 6BN gradually accelerates MOR-μ* reversal to resting-state MOR-μ. Thus, 6BN potently prevents opioid dependence in rodents, at doses well below those blocking antinociception or causing withdrawal. Acting as a ‘retrograde addiction modulator’, 6BN could represent a novel class of therapeutics for OUD. Further studies need to address regulation of MOR-μ* and, more broadly, the physiological and pharmacological significance of ligand-free signaling in GPCRs.
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Cooper AH, Hedden NS, Prasoon P, Qi Y, Taylor BK. Postsurgical Latent Pain Sensitization Is Driven by Descending Serotonergic Facilitation and Masked by µ-Opioid Receptor Constitutive Activity in the Rostral Ventromedial Medulla. J Neurosci 2022; 42:5870-5881. [PMID: 35701159 PMCID: PMC9337598 DOI: 10.1523/jneurosci.2038-21.2022] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2021] [Revised: 05/22/2022] [Accepted: 05/27/2022] [Indexed: 01/29/2023] Open
Abstract
Following tissue injury, latent sensitization (LS) of nociceptive signaling can persist indefinitely, kept in remission by compensatory µ-opioid receptor constitutive activity (MORCA) in the dorsal horn of the spinal cord. To demonstrate LS, we conducted plantar incision in mice and then waited 3-4 weeks for hypersensitivity to resolve. At this time (remission), systemic administration of the opioid receptor antagonist/inverse agonist naltrexone reinstated mechanical and heat hypersensitivity. We first tested the hypothesis that LS extends to serotonergic neurons in the rostral ventral medulla (RVM) that convey pronociceptive input to the spinal cord. We report that in male and female mice, hypersensitivity was accompanied by increased Fos expression in serotonergic neurons of the RVM, abolished on chemogenetic inhibition of RVM 5-HT neurons, and blocked by intrathecal injection of the 5-HT3R antagonist ondansetron; the 5-HT2AR antagonist MDL-11 939 had no effect. Second, to test for MORCA, we microinjected the MOR inverse agonist d-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2 (CTAP) and/or neutral opioid receptor antagonist 6β-naltrexol. Intra-RVM CTAP produced mechanical hypersensitivity at both hindpaws; 6β-naltrexol had no effect by itself, but blocked CTAP-induced hypersensitivity. This indicates that MORCA, rather than an opioid ligand-dependent mechanism, maintains LS in remission. We conclude that incision establishes LS in descending RVM 5-HT neurons that drives pronociceptive 5-HT3R signaling in the dorsal horn, and this LS is tonically opposed by MORCA in the RVM. The 5-HT3 receptor is a promising therapeutic target for the development of drugs to prevent the transition from acute to chronic postsurgical pain.SIGNIFICANCE STATEMENT Surgery leads to latent pain sensitization and a compensatory state of endogenous pain control that is maintained long after tissue healing. Here, we show that either chemogenetic inhibition of serotonergic neuron activity in the RVM or pharmacological inhibition of 5-HT3 receptor signaling at the spinal cord blocks behavioral signs of postsurgical latent sensitization. We conclude that MORCA in the RVM opposes descending serotonergic facilitation of LS and that the 5-HT3 receptor is a promising therapeutic target for the development of drugs to prevent the transition from acute to chronic postsurgical pain.
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Affiliation(s)
- Andrew H Cooper
- Department of Anesthesiology and Perioperative Medicine, Pittsburgh Center for Pain Research, Pittsburgh Project to End Opioid Misuse, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213
| | - Naomi S Hedden
- Department of Anesthesiology and Perioperative Medicine, Pittsburgh Center for Pain Research, Pittsburgh Project to End Opioid Misuse, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213
| | - Pranav Prasoon
- Department of Anesthesiology and Perioperative Medicine, Pittsburgh Center for Pain Research, Pittsburgh Project to End Opioid Misuse, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213
| | - Yanmei Qi
- Department of Anesthesiology and Perioperative Medicine, Pittsburgh Center for Pain Research, Pittsburgh Project to End Opioid Misuse, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213
| | - Bradley K Taylor
- Department of Anesthesiology and Perioperative Medicine, Pittsburgh Center for Pain Research, Pittsburgh Project to End Opioid Misuse, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213
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Zhang Y, Jeske NA. GRK2 Dictates a Functional Switch of the Peripheral Mu-Opioid Receptor. ACS Chem Neurosci 2020; 11:4376-4386. [PMID: 33174729 DOI: 10.1021/acschemneuro.0c00622] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
The peripheral mu-opioid receptor (MOR) has been recognized as a potential target to provide safer analgesia with reduced central side effects. Although analgesic incompetence of the peripheral MOR in the absence of inflammation was initially identified more than a decade ago, there has been very limited investigation into the underlying signaling mechanisms. Here we identify that G protein-coupled receptor kinase 2 (GRK2) constitutively interacts with the MOR in peripheral sensory neurons to suppress peripheral MOR activity. Brief exposure to bradykinin (BK) causes uncoupling of GRK2 from the MOR and subsequent restoration of MOR functionality in dorsal root ganglion (DRG) neurons. Interestingly, prolonged BK treatment induces constitutive activation of the MOR through a mechanism that involves protein kinase C (PKC) activation. After silencing Raf kinase inhibitory protein (RKIP) by RNA interference, BK-induced constitutive MOR activation is completely abrogated, which agrees with previous findings that BK activates PKC signaling to initiate GRK2 sequestration by RKIP. Furthermore, we demonstrate that constitutive, peripheral MOR activity requires GRK2 uncoupling and that the FDA-approved SSRI paroxetine promotes this state of uncoupling. Collectively, these results indicate that GRK2 tightly regulates MOR functional states and controls constitutive MOR activity in peripheral sensory neurons, supporting the potential for targeting the kinase to provide safer analgesia.
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Golovko AI, Ivanov MB, Golovko ES, Dolgo-Saburov VB, Zatsepin EP. The Neurochemical Mechanisms of the Pharmacological Activities of Inverse Agonists of the Benzodiazepine Binding Site. NEUROCHEM J+ 2018. [DOI: 10.1134/s1819712418030042] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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6
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Madapa S, Gadhiya S, Kurtzman T, Alberts IL, Ramsey S, Reith M, Harding WW. Synthesis and evaluation of C9 alkoxy analogues of (-)-stepholidine as dopamine receptor ligands. Eur J Med Chem 2016; 125:255-268. [PMID: 27688181 DOI: 10.1016/j.ejmech.2016.09.036] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2016] [Revised: 09/09/2016] [Accepted: 09/10/2016] [Indexed: 01/01/2023]
Abstract
Tetrahydroprotoberberine alkaloids have shown interesting polypharmacological actions at dopamine receptors and are a unique template from which to mine novel molecules with dual selective actions at D1 and D3 receptors. Such compounds will be valuable to evaluate as anti-cocaine therapeutics. Towards that eventual goal, we engaged an SAR study in which a series of C9 alkoxy analogues of the D1/D2/D3 ligand (-)-stepholidine that possessed or lacked a C12 bromo functionality, were synthesized and evaluated for affinity at dopamine D1, D2 and D3 receptors. We found that the analogues are generally selective for the D1 receptor. Small n-alkoxy substituents (up to 4 carbons in length) were generally well tolerated for high D1 affinity but such groups reduced D3 affinity. In the case of C12 brominated analogues, C9 alkoxylation also had little effect on D1 affinity for the smaller alkoxy groups, but reduced D2 and D3 affinities significantly. C12 bromination tends to increase D1 receptor selectivity. A number of compounds were identified that retain affinity for D1 and D3 receptors but lack D2 receptor affinity. Among them, compound 22a was found to be a selective D1/D3 dual antagonist (Ki = 5.3 and 106 nM at D1 and D3 receptors). Docking studies performed on the analogues at the D3 receptor revealed a number of interactions that are important for affinity including a critical N - Asp110 salt bridge motif, H-bonds to Ser192 and Cys181 and hydrophobic interactions between the aryl rings and Phe106 and Phe345. The analogues adopt an orientation in which ring A is located in the orthosteric binding site while the C9 alkoxy substituents attached to ring D project into the secondary binding pocket of the D3 receptor.
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Affiliation(s)
- Sudharshan Madapa
- Department of Chemistry, Hunter College, City University of New York, 695 Park Avenue, NY 10065, USA
| | - Satishkumar Gadhiya
- Department of Chemistry, Hunter College, City University of New York, 695 Park Avenue, NY 10065, USA; Ph.D. Program in Chemistry, CUNY Graduate Center, 365 5th Avenue, New York, NY 10016, USA
| | - Thomas Kurtzman
- Ph.D. Program in Chemistry, CUNY Graduate Center, 365 5th Avenue, New York, NY 10016, USA; Ph.D. Program in Biochemistry, CUNY Graduate Center, 365 5th Avenue, New York, NY 10016, USA; Department of Chemistry, Lehman College, The City University of New York, Bronx, NY 10468, USA
| | - Ian L Alberts
- Department of Natural Sciences, LaGuardia Community College, City University of New York, New York, NY 11101, USA
| | - Steven Ramsey
- Ph.D. Program in Biochemistry, CUNY Graduate Center, 365 5th Avenue, New York, NY 10016, USA; Department of Chemistry, Lehman College, The City University of New York, Bronx, NY 10468, USA
| | - Maarten Reith
- Department of Psychiatry, New York University, New York, NY 10016, USA
| | - Wayne W Harding
- Department of Chemistry, Hunter College, City University of New York, 695 Park Avenue, NY 10065, USA; Ph.D. Program in Chemistry, CUNY Graduate Center, 365 5th Avenue, New York, NY 10016, USA; Ph.D. Program in Biochemistry, CUNY Graduate Center, 365 5th Avenue, New York, NY 10016, USA.
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Zhen J, Antonio T, Jacob JC, Grandy DK, Reith MEA, Dutta AK, Selley DE. Efficacy of Hybrid Tetrahydrobenzo[d]thiazole Based Aryl Piperazines D-264 and D-301 at D₂ and D₃ Receptors. Neurochem Res 2015; 41:328-339. [PMID: 26718829 DOI: 10.1007/s11064-015-1808-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2015] [Revised: 12/08/2015] [Accepted: 12/14/2015] [Indexed: 01/15/2023]
Abstract
In elucidating the role of pharmacodynamic efficacy at D3 receptors in therapeutic effectiveness of dopamine receptor agonists, the influence of study system must be understood. Here two compounds with D3 over D2 selectivity developed in our earlier work, D-264 and D-301, are compared in dopamine receptor-mediated G-protein activation in striatal regions of wild-type and D2 receptor knockout mice and in CHO cells expressing D2 or D3 receptors. In caudate-putamen of D2 knockout mice, D-301 was ~3-fold more efficacious than D-264 in activating G-proteins as assessed by [(35)S]GTPγS binding; in nucleus accumbens, D-301 stimulated G-protein activation whereas D-264 did not. In contrast, the two ligands exerted similar efficacy in both regions of wild-type mice, suggesting both ligands activate D2 receptors with similar efficacy. In D2 and D3 receptor-expressing CHO cells, D-264 and D-301 appeared to act in the [(35)S]GTPγS assay as full agonists because they produced maximal stimulation equal to dopamine. Competition for [(3)H]spiperone binding was then performed to determine Ki/EC50 ratios as an index of receptor reserve for each ligand. Action of D-301, but not D-264, showed receptor reserve in D3 but not in D2 receptor-expressing cells, whereas dopamine showed receptor reserve in both cell lines. Gαo1 is highly expressed in brain and is important in D2-like receptor-G protein coupling. Transfection of Gαo1 in D3- but not D2-expressing CHO cells led to receptor reserve for D-264 without altering receptor expression levels. D-301 and dopamine exhibited receptor reserve in D3-expressing cells both with and without transfection of Gαo1. Altogether, these results indicate that D-301 has greater intrinsic efficacy to activate D3 receptors than D-264, whereas the two compounds act on D2 receptors with similar intrinsic efficacy. These findings also suggest caution in interpreting Emax values from functional assays in receptor-transfected cell models without accounting for receptor reserve.
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Affiliation(s)
- Juan Zhen
- Department of Psychiatry, New York University School of Medicine, New York, NY, USA
| | - Tamara Antonio
- Department of Psychiatry, New York University School of Medicine, New York, NY, USA
| | - Joanna C Jacob
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA, USA
| | - David K Grandy
- DKG Department of Physiology & Pharmacology, School of Medicine and the Knight Cardiovascular Institute, Oregon Health & Science University, Portland, OR, USA
| | - Maarten E A Reith
- Department of Psychiatry, New York University School of Medicine, New York, NY, USA.,Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY, USA
| | - Aloke K Dutta
- Department of Pharmaceutical Sciences, Wayne State University, Detroit, MI, USA
| | - Dana E Selley
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, VA, USA
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Das B, Vedachalam S, Luo D, Antonio T, Reith MEA, Dutta AK. Development of a Highly Potent D2/D3 Agonist and a Partial Agonist from Structure-Activity Relationship Study of N(6)-(2-(4-(1H-Indol-5-yl)piperazin-1-yl)ethyl)-N(6)-propyl-4,5,6,7-tetrahydrobenzo[d]thiazole-2,6-diamine Analogues: Implication in the Treatment of Parkinson's Disease. J Med Chem 2015; 58:9179-95. [PMID: 26555041 PMCID: PMC6250127 DOI: 10.1021/acs.jmedchem.5b01031] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Our structure-activity relationship studies with N(6)-(2-(4-(1H-indol-5-yl)piperazin-1-yl)ethyl)-N(6)-propyl-4,5,6,7-tetrahydrobenzo[d]thiazole-2,6-diamine derivatives led to development of a lead compound (-)-21a which exhibited very high affinity (Ki, D2 = 16.4 nM, D3 = 1.15 nM) and full agonist activity (EC50 (GTPγS); D2 = 3.23 and D3 = 1.41 nM) at both D2 and D3 receptors. A partial agonist molecule (-)-34 (EC50 (GTPγS); D2 = 21.6 (Emax = 27%) and D3 = 10.9 nM) was also identified. In a Parkinson's disease (PD) animal model, (-)-21a was highly efficacious in reversing hypolocomotion in reserpinized rats with a long duration of action, indicating its potential as an anti-PD drug. Compound (-)-34 was also able to elevate locomotor activity in the above PD animal model significantly, implying its potential application in PD therapy. Furthermore, (-)-21a was shown to be neuroprotective in protecting neuronal PC12 from toxicity of 6-OHDA. This report, therefore, underpins the notion that a multifunctional drug like (-)-21a might have the potential not only to ameliorate motor dysfunction in PD patients but also to modify disease progression by protecting DA neurons from progressive degeneration.
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Affiliation(s)
- Banibrata Das
- Department of Pharmaceutical Sciences, Wayne State University, Detroit, Michigan 48202, United States
| | - Seenuvasan Vedachalam
- Department of Pharmaceutical Sciences, Wayne State University, Detroit, Michigan 48202, United States
| | - Dan Luo
- Department of Pharmaceutical Sciences, Wayne State University, Detroit, Michigan 48202, United States
| | - Tamara Antonio
- Department of Psychiatry, New York University, New York, New York 10016, United States
| | - Maarten E. A. Reith
- Department of Psychiatry, New York University, New York, New York 10016, United States
- Department of Biochemistry and Molecular Pharmacology, New York University, New York, New York 10016, United States
| | - Aloke K. Dutta
- Department of Pharmaceutical Sciences, Wayne State University, Detroit, Michigan 48202, United States
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9
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Reply to Wang and Sadée. Psychopharmacology (Berl) 2015; 232:1495-6. [PMID: 25757674 DOI: 10.1007/s00213-015-3900-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/17/2015] [Accepted: 02/21/2015] [Indexed: 10/23/2022]
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Kelly E, Mundell SJ, Sava A, Roth AL, Felici A, Maltby K, Nathan PJ, Bullmore ET, Henderson G. The opioid receptor pharmacology of GSK1521498 compared to other ligands with differential effects on compulsive reward-related behaviours. Psychopharmacology (Berl) 2015; 232:305-14. [PMID: 24973897 PMCID: PMC4281354 DOI: 10.1007/s00213-014-3666-3] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/18/2014] [Accepted: 06/12/2014] [Indexed: 12/02/2022]
Abstract
RATIONALE The novel opioid receptor antagonist, GSK1421498, has been shown to attenuate reward-driven compulsive behaviours, such as stimulant drug seeking or binge eating, in animals and humans. Here, we report new data on the receptor pharmacology of GSK121498, in comparison to naltrexone, naloxone, 6-β-naltrexol and nalmefene. OBJECTIVES To determine whether the novel opioid antagonist, GSK1521498, is an orthosteric or allosteric antagonist at the μ opioid receptor (MOPr) and whether it has neutral antagonist or inverse agonist properties. METHODS A combination of radioligand binding assays and [(35)S]GTPγS binding assays was employed. RESULTS GSK1521498 completely displaced [(3)H]naloxone binding to MOPr and did not alter the rate of [(3)H]naloxone dissociation from MOPr observations compatible with it binding to the orthosteric site on MOPr. GSK1521498 exhibited inverse agonism when MOPr was overexpressed but not when the level of MOPr expression was low. In parallel studies under conditions of high receptor expression density, naloxone, naltrexone, 6-β-naltrexol and nalmefene exhibited partial agonism, not inverse agonism as has been reported previously for naloxone and naltrexone. In brain tissue from mice receiving a prolonged morphine pre-treatment, GSK1521498 exhibited slight inverse agonism. CONCLUSIONS Differences between GSK1521498 and naltrexone in their effects on compulsive reward seeking are arguably linked to the more selective and complete MOPr antagonism of GSK1521498 versus the partial MOPr agonism of naltrexone. GSK1521498 is also pharmacologically differentiated by its inverse agonist efficacy at high levels of MOPr expression, but this may be less likely to contribute to behavioural differentiation at patho-physiological levels of expression.
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Affiliation(s)
- Eamonn Kelly
- School of Physiology and Pharmacology, University of Bristol, Bristol, BS8 1TD UK
| | - Stuart J. Mundell
- School of Physiology and Pharmacology, University of Bristol, Bristol, BS8 1TD UK
| | - Anna Sava
- Aptuit Centre for Drug Discovery & Development, Aptuit Srl., Verona, Italy
| | - Adelheid L. Roth
- Aptuit Centre for Drug Discovery & Development, Aptuit Srl., Verona, Italy
| | - Antonio Felici
- Aptuit Centre for Drug Discovery & Development, Aptuit Srl., Verona, Italy
| | - Kay Maltby
- Medicines Discovery and Development, GlaxoSmithKline, Clinical Unit Cambridge, Cambridge, UK ,Brain Mapping Unit, Department of Psychiatry, University of Cambridge, Cambridge, UK
| | - Pradeep J. Nathan
- Medicines Discovery and Development, GlaxoSmithKline, Clinical Unit Cambridge, Cambridge, UK ,Brain Mapping Unit, Department of Psychiatry, University of Cambridge, Cambridge, UK
| | - Edward T. Bullmore
- Medicines Discovery and Development, GlaxoSmithKline, Clinical Unit Cambridge, Cambridge, UK ,Brain Mapping Unit, Department of Psychiatry, University of Cambridge, Cambridge, UK
| | - Graeme Henderson
- School of Physiology and Pharmacology, University of Bristol, Bristol, BS8 1TD UK
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11
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Taylor BK, Corder G. Endogenous analgesia, dependence, and latent pain sensitization. Curr Top Behav Neurosci 2014; 20:283-325. [PMID: 25227929 PMCID: PMC4464817 DOI: 10.1007/7854_2014_351] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Endogenous activation of µ-opioid receptors (MORs) provides relief from acute pain. Recent studies have established that tissue inflammation produces latent pain sensitization (LS) that is masked by spinal MOR signaling for months, even after complete recovery from injury and re-establishment of normal pain thresholds. Disruption with MOR inverse agonists reinstates pain and precipitates cellular, somatic, and aversive signs of physical withdrawal; this phenomenon requires N-methyl-D-aspartate receptor-mediated activation of calcium-sensitive adenylyl cyclase type 1 (AC1). In this review, we present a new conceptual model of the transition from acute to chronic pain, based on the delicate balance between LS and endogenous analgesia that develops after painful tissue injury. First, injury activates pain pathways. Second, the spinal cord establishes MOR constitutive activity (MORCA) as it attempts to control pain. Third, over time, the body becomes dependent on MORCA, which paradoxically sensitizes pain pathways. Stress or injury escalates opposing inhibitory and excitatory influences on nociceptive processing as a pathological consequence of increased endogenous opioid tone. Pain begets MORCA begets pain vulnerability in a vicious cycle. The final result is a silent insidious state characterized by the escalation of two opposing excitatory and inhibitory influences on pain transmission: LS mediated by AC1 (which maintains the accelerator) and pain inhibition mediated by MORCA (which maintains the brake). This raises the prospect that opposing homeostatic interactions between MORCA analgesia and latent NMDAR-AC1-mediated pain sensitization creates a lasting vulnerability to develop chronic pain. Thus, chronic pain syndromes may result from a failure in constitutive signaling of spinal MORs and a loss of endogenous analgesic control. An overarching long-term therapeutic goal of future research is to alleviate chronic pain by either (a) facilitating endogenous opioid analgesia, thus restricting LS within a state of remission, or (b) extinguishing LS altogether.
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Affiliation(s)
- Bradley K Taylor
- Department of Physiology, School of Medicine, University of Kentucky Medical Center, Lexington, KY, 40536-0298, USA,
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Ananthan S, Saini SK, Zhou G, Hobrath JV, Padmalayam I, Zhai L, Bostwick JR, Antonio T, Reith MEA, McDowell S, Cho E, McAleer L, Taylor M, Luedtke RR. Design, synthesis, and structure-activity relationship studies of a series of [4-(4-carboxamidobutyl)]-1-arylpiperazines: insights into structural features contributing to dopamine D3 versus D2 receptor subtype selectivity. J Med Chem 2014; 57:7042-60. [PMID: 25126833 PMCID: PMC4148173 DOI: 10.1021/jm500801r] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
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Antagonist and partial agonist modulators
of the dopamine D3 receptor
(D3R) have emerged as promising therapeutics for the treatment of
substance abuse and neuropsychiatric disorders. However, development
of druglike lead compounds with selectivity for the D3 receptor has
been challenging because of the high sequence homology between the
D3R and the dopamine D2 receptor (D2R). In this effort, we synthesized
a series of acylaminobutylpiperazines incorporating aza-aromatic units
and evaluated their binding and functional activities at the D3 and
D2 receptors. Docking studies and results from evaluations against
a set of chimeric and mutant receptors suggest that interactions at
the extracellular end of TM7 contribute to the D3R versus D2R selectivity
of these ligands. Molecular insights from this study could potentially
enable rational design of potent and selective D3R ligands.
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Affiliation(s)
- Subramaniam Ananthan
- Organic Chemistry Department, Southern Research Institute , Birmingham, Alabama 35205, United States
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13
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The vital role of constitutive GPCR activity in the mesolimbic dopamine system. Transl Psychiatry 2014; 4:e361. [PMID: 24518399 PMCID: PMC3944632 DOI: 10.1038/tp.2013.130] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/06/2013] [Revised: 11/13/2013] [Accepted: 12/07/2013] [Indexed: 12/28/2022] Open
Abstract
The midbrain dopamine system has an important role in processing rewards and the stimuli associated with them, and is implicated in various psychiatric disorders. This system is tightly regulated by various G protein-coupled receptors (GPCRs). It is becoming increasingly clear that these receptors are not only activated by (endogenous) agonists but that they also exhibit agonist-independent intrinsic constitutive activity. In this review we highlight the evidence for the physiological role of such constitutive GPCR activity (in particular for cannabinoid 1, serotonin 2C and mu-opioid receptors) in the ventral tegmental area and in its output regions like the nucleus accumbens. We also address the behavioral relevance of constitutive GPCR signaling and discuss the repercussions of its abolition in dopamine-related psychiatric diseases.
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14
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Yuan Y, Zaidi SA, Elbegdorj O, Aschenbach LCK, Li G, Stevens DL, Scoggins KL, Dewey WL, Selley DE, Zhang Y. Design, synthesis, and biological evaluation of 14-heteroaromatic-substituted naltrexone derivatives: pharmacological profile switch from mu opioid receptor selectivity to mu/kappa opioid receptor dual selectivity. J Med Chem 2013; 56:9156-69. [PMID: 24144240 PMCID: PMC4373589 DOI: 10.1021/jm4012214] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
On the basis of a mu opioid receptor (MOR) homology model and the isosterism concept, three generations of 14-heteroaromatically substituted naltrexone derivatives were designed, synthesized, and evaluated as potential MOR-selective ligands. The first-generation ligands appeared to be MOR-selective, whereas the second and the third generation ones showed MOR/kappa opioid receptor (KOR) dual selectivity. Docking of ligands 2 (MOR selective) and 10 (MOR/KOR dual selective) to the three opioid receptor crystal structures revealed a nonconserved-residue-facilitated hydrogen-bonding network that could be responsible for their distinctive selectivity profiles. The MOR/KOR dual-selective ligand 10 showed no agonism and acted as a potent antagonist in the tail-flick assay. It also produced less severe opioid withdrawal symptoms than naloxone in morphine-dependent mice. In conclusion, ligand 10 may serve as a novel lead compound to develop MOR/KOR dual-selective ligands, which might possess unique therapeutic value for opioid addiction treatment.
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MESH Headings
- Animals
- Behavior, Animal/drug effects
- CHO Cells
- Chemistry Techniques, Synthetic
- Cricetinae
- Cricetulus
- Drug Design
- Male
- Mice
- Models, Molecular
- Naltrexone/chemical synthesis
- Naltrexone/chemistry
- Naltrexone/metabolism
- Naltrexone/pharmacology
- Protein Conformation
- Receptors, Opioid, kappa/chemistry
- Receptors, Opioid, kappa/metabolism
- Receptors, Opioid, mu/chemistry
- Receptors, Opioid, mu/metabolism
- Substrate Specificity
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Affiliation(s)
- Yunyun Yuan
- Department of Medicinal Chemistry, Virginia Commonwealth University, 800 East Leigh Street, Richmond, VA 23298, USA
| | - Saheem A. Zaidi
- Department of Medicinal Chemistry, Virginia Commonwealth University, 800 East Leigh Street, Richmond, VA 23298, USA
| | - Orgil Elbegdorj
- Department of Medicinal Chemistry, Virginia Commonwealth University, 800 East Leigh Street, Richmond, VA 23298, USA
| | - Lindsey C. K. Aschenbach
- Department of Medicinal Chemistry, Virginia Commonwealth University, 800 East Leigh Street, Richmond, VA 23298, USA
| | - Guo Li
- Department of Medicinal Chemistry, Virginia Commonwealth University, 800 East Leigh Street, Richmond, VA 23298, USA
| | - David L. Stevens
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, 410 North 12th Street, Richmond, VA 23298, USA
| | - Krista L. Scoggins
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, 410 North 12th Street, Richmond, VA 23298, USA
| | - William L. Dewey
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, 410 North 12th Street, Richmond, VA 23298, USA
| | - Dana E. Selley
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, 410 North 12th Street, Richmond, VA 23298, USA
| | - Yan Zhang
- Department of Medicinal Chemistry, Virginia Commonwealth University, 800 East Leigh Street, Richmond, VA 23298, USA
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15
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Morphine withdrawal enhances constitutive μ-opioid receptor activity in the ventral tegmental area. J Neurosci 2013; 32:16120-8. [PMID: 23152596 DOI: 10.1523/jneurosci.1572-12.2012] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
μ-Opioid receptors (MORs) in the ventral tegmental area (VTA) are pivotally involved in addictive behavior. While MORs are typically activated by opioids, they can also become constitutively active in the absence of any agonist. In the current study, we present evidence that MOR constitutive activity is highly relevant in the mouse VTA, as it regulates GABAergic input to dopamine neurons. Specifically, suppression of MOR constitutive activity with the inverse agonist KC-2-009 enhanced GABAergic neurotransmission onto VTA dopamine neurons. This inverse agonistic effect was fully blocked by the specific MOR neutral antagonist CTOP, which had no effect on GABAergic transmission itself. We next show that withdrawal from chronic morphine further increases the magnitude of inverse agonistic effects at the MOR, suggesting enhanced MOR constitutive activity. We demonstrate that this increase can be an adaptive response to the detrimental elevation in cAMP levels known to occur during morphine withdrawal. These findings offer important insights in the physiological occurrence and function of MOR constitutive activity, and have important implications for therapeutic strategies aimed at normalizing MOR signaling during addiction and opioid overdose.
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16
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Williams JT, Ingram SL, Henderson G, Chavkin C, von Zastrow M, Schulz S, Koch T, Evans CJ, Christie MJ. Regulation of μ-opioid receptors: desensitization, phosphorylation, internalization, and tolerance. Pharmacol Rev 2013; 65:223-54. [PMID: 23321159 DOI: 10.1124/pr.112.005942] [Citation(s) in RCA: 577] [Impact Index Per Article: 52.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Morphine and related µ-opioid receptor (MOR) agonists remain among the most effective drugs known for acute relief of severe pain. A major problem in treating painful conditions is that tolerance limits the long-term utility of opioid agonists. Considerable effort has been expended on developing an understanding of the molecular and cellular processes that underlie acute MOR signaling, short-term receptor regulation, and the progression of events that lead to tolerance for different MOR agonists. Although great progress has been made in the past decade, many points of contention and controversy cloud the realization of this progress. This review attempts to clarify some confusion by clearly defining terms, such as desensitization and tolerance, and addressing optimal pharmacological analyses for discerning relative importance of these cellular mechanisms. Cellular and molecular mechanisms regulating MOR function by phosphorylation relative to receptor desensitization and endocytosis are comprehensively reviewed, with an emphasis on agonist-biased regulation and areas where knowledge is lacking or controversial. The implications of these mechanisms for understanding the substantial contribution of MOR signaling to opioid tolerance are then considered in detail. While some functional MOR regulatory mechanisms contributing to tolerance are clearly understood, there are large gaps in understanding the molecular processes responsible for loss of MOR function after chronic exposure to opioids. Further elucidation of the cellular mechanisms that are regulated by opioids will be necessary for the successful development of MOR-based approaches to new pain therapeutics that limit the development of tolerance.
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Affiliation(s)
- John T Williams
- Vollum Institute, Oregon Health Sciences University, Portland, Oregon, USA
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17
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An efficient synthesis of 3-OBn-6β,14-epoxy-bridged opiates from naltrexone and identification of a related dual MOR inverse agonist/KOR agonist. Bioorg Med Chem Lett 2012; 22:6801-5. [DOI: 10.1016/j.bmcl.2012.06.056] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2012] [Revised: 06/08/2012] [Accepted: 06/11/2012] [Indexed: 12/14/2022]
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18
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Abstract
This paper is the thirty-third consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2010 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration (Section 16); and immunological responses (Section 17).
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Affiliation(s)
- Richard J Bodnar
- Department of Psychology and Neuropsychology Doctoral Sub-Program, Queens College, City University of New York, Flushing, NY 11367, USA.
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19
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Cunningham CW, Rothman RB, Prisinzano TE. Neuropharmacology of the naturally occurring kappa-opioid hallucinogen salvinorin A. Pharmacol Rev 2011; 63:316-47. [PMID: 21444610 DOI: 10.1124/pr.110.003244] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Salvia divinorum is a perennial sage native to Oaxaca, Mexico, that has been used traditionally in divination rituals and as a treatment for the "semimagical" disease panzón de borrego. Because of the intense "out-of-body" experiences reported after inhalation of the pyrolized smoke, S. divinorum has been gaining popularity as a recreational hallucinogen, and the United States and several other countries have regulated its use. Early studies isolated the neoclerodane diterpene salvinorin A as the principal psychoactive constituent responsible for these hallucinogenic effects. Since the finding that salvinorin A exerts its potent psychotropic actions through the activation of KOP receptors, there has been much interest in elucidating the underlying mechanisms behind its effects. These effects are particularly remarkable, because 1) salvinorin A is the first reported non-nitrogenous opioid receptor agonist, and 2) its effects are not mediated by the 5-HT(2A) receptor, the classic target of hallucinogens such as lysergic acid diethylamide and mescaline. Rigorous investigation into the structural features of salvinorin A responsible for opioid receptor affinity and selectivity has produced numerous receptor probes, affinity labels, and tools for evaluating the biological processes responsible for its observed psychological effects. Salvinorin A has therapeutic potential as a treatment for pain, mood and personality disorders, substance abuse, and gastrointestinal disturbances, and suggests that nonalkaloids are potential scaffolds for drug development for aminergic G-protein coupled receptors.
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Cheng K, Lee YS, Rothman RB, Dersch CM, Bittman RW, Jacobson AE, Rice KC. Probes for narcotic receptor mediated phenomena. 41. Unusual inverse μ-agonists and potent μ-opioid antagonists by modification of the N-substituent in enantiomeric 5-(3-hydroxyphenyl)morphans. J Med Chem 2011; 54:957-69. [PMID: 21247164 DOI: 10.1021/jm1011676] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Conformational restraint in the N-substituent of enantiomeric 5-(3-hydroxyphenyl)morphans was conferred by the addition of a cyclopropane ring or a double bond. All of the possible enantiomers and isomers of the N-substituted compounds were synthesized. Opioid receptor binding assays indicated that some of them had about 20-fold higher μ-affinity than the compound with an N-phenylpropyl substituent (K(i) = 2-450 nM for the examined compounds with various N-substituents). Most of the compounds acted unusually as inverse agonists in the [(35)S]GTP-γ-S functional binding assay using nondependent cells that stably express the cloned human μ-opioid receptor. Two of the N-substituted compounds with a cyclopropane ring were very potent μ-opioid antagonists ((+)-29, K(e) = 0.17 and (-)-30, K(e) =0.3) in the [(35)S]GTP-γ-S functional binding assay. By comparison of the geometry-optimized structures of the newly synthesized compounds, an attempt was made to rationalize their μ-opioid receptor affinity in terms of the spatial position of N-substituents.
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Affiliation(s)
- Kejun Cheng
- Drug Design and Synthesis Section, Chemical Biology Research Branch, National Institute on Drug Abuse, National Institutes of Health, Department of Health and Human Services, 5625 Fishers Lane, Room 4N03, Bethesda, Maryland 20892-9415, United States
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21
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Hsin LW, Chang LT, Rothman RB, Dersch CM, Fishback JA, Matsumoto RR. Synthesis and opioid activity of enantiomeric N-substituted 2,3,4,4a,5,6,7,7a-octahydro-1H-benzofuro[3,2-e]isoquinolines. J Med Chem 2010; 53:1392-6. [PMID: 20055417 DOI: 10.1021/jm901503e] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A series of enantiomeric N-substituted 2,3,4,4a,5,6,7,7a-octahydro-1H-benzofuro[3,2-e]isoquinolines was synthesized. The (-)-enantiomers had much greater kappa-, mu-, and delta-opioid receptor binding affinity than the corresponding (+)-enantiomers. Compounds (-)-1a, (-)-1b, and (-)-1c displayed subnanomolar binding affinity for the mu-receptor, and (-)-1b had a high affinity for the kappa-receptor. Compound (-)-1a was a mu-partial agonist and kappa-antagonist. Compound (-)-1b was a potent neutral mu-antagonist (K(d) = 0.22 nM) and a kappa-partial agonist.
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Affiliation(s)
- Ling-Wei Hsin
- School of Pharmacy, College of Medicine, National Taiwan University, Number 1, Jen-Ai Road, Taipei, Taiwan 10018, ROC.
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22
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23
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Bilsky EJ, Giuvelis D, Osborn MD, Dersch CM, Xu H, Rothman RB. In vitro and in vivo assessment of mu opioid receptor constitutive activity. Methods Enzymol 2010; 484:413-43. [PMID: 21036244 DOI: 10.1016/b978-0-12-381298-8.00021-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Constitutive (basal) signaling has been described and characterized for numerous G protein coupled receptors (GPCRs). The relevance of this activity to disease, drug discovery and development, and to clinical pharmacotherapy is just beginning to emerge. Opioid receptors were the first GPCR systems for which there was definitive evidence presented for constitutive activity, with numerous studies now published on the regulation of this activity (e.g., structure/activity of the receptor as it relates to basal activity, pharmacology of ligands that act as agonists, inverse agonists and "neutral antagonists," etc.). This chapter summarizes some of the methods used to characterize constitutive activity at the mu opioid receptor (MOR) in preclinical in vitro and in vivo model systems. This includes cell-based systems that are useful for higher throughput screening of novel ligands and for studying variables that can impact basal tone in a system. In vivo assays are also described in which constitutive activity is increased in response to acute or chronic opioid agonist exposure and where withdrawal is precipitated with antagonists that may function as inverse agonists or "neutral" antagonists. The methods described have inherent advantages and disadvantages that need to be considered in any drug discovery/development program. A brief discussion of progress toward understanding the clinical implications of MOR constitutive activity in the management of opioid addiction and chronic pain is also included in this chapter.
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Affiliation(s)
- Edward J Bilsky
- Department of Biomedical Sciences, College of Osteopathic Medicine, University of New England, Biddeford, Maine, USA
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