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Alwassil OI, Abdrakhmanova GR, Dukat M. Computational analysis of non-competitive antagonist arylguanidine-α7 nAChR complexes. J Mol Graph Model 2021; 107:107943. [PMID: 34058639 DOI: 10.1016/j.jmgm.2021.107943] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Revised: 04/07/2021] [Accepted: 05/11/2021] [Indexed: 10/21/2022]
Abstract
meta-Chlorophenylguanidine (1) is a non-competitive α7 nicotinic acetylcholine receptor (nAChR) antagonist. Here we examined the hydrogen bond donor role of the anilinic N1-H on the inhibitory effect of 1 by preparing its N1-CH3 counterpart 2. Analog 2 was found to be at least as potent as 1 as a non-competitive α7 nAChR antagonist in a patch-clamp assay. To establish a structural basis for the mode of interaction of guanidines 1 and 2, we generated 100 homology models of the hα7 nAChR. This was followed by Connolly surface (SYBYL-X2.1) and blind docking (AutoDock 4.1) studies to identify eight possible binding pockets, two of which were supported by empirical data and employed in our docking studies. The optimized model-ligand complexes were analyzed using a Hydropathic INTeractions (HINT) analysis in order to compare and contrast different binding pockets and modes. We identified a potential allosteric binding site and distinct rotameric binding modes for 1 and 2 at α7 nAChRs. These differences in the binding orientations minimized the importance of an anilinic NH function for the antagonist activity at nACh receptors.
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Affiliation(s)
- Osama I Alwassil
- Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, P.O. Box 980540, Richmond, VA, 23298-540, USA
| | - Galya R Abdrakhmanova
- Department of Pharmacology and Toxicology, School of Medicine, Virginia Commonwealth University, P.O. Box 980524, Richmond, VA, 23298, USA
| | - Małgorzata Dukat
- Department of Medicinal Chemistry, School of Pharmacy, Virginia Commonwealth University, P.O. Box 980540, Richmond, VA, 23298-540, USA.
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2
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Allosterism of Nicotinic Acetylcholine Receptors: Therapeutic Potential for Neuroinflammation Underlying Brain Trauma and Degenerative Disorders. Int J Mol Sci 2020; 21:ijms21144918. [PMID: 32664647 PMCID: PMC7404387 DOI: 10.3390/ijms21144918] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 07/06/2020] [Accepted: 07/10/2020] [Indexed: 12/21/2022] Open
Abstract
Inflammation is a key physiological phenomenon that can be pervasive when dysregulated. Persistent chronic inflammation precedes several pathophysiological conditions forming one of the critical cellular homeostatic checkpoints. With a steady global surge in inflammatory diseases, it is imperative to delineate underlying mechanisms and design suitable drug molecules targeting the cellular partners that mediate and regulate inflammation. Nicotinic acetylcholine receptors have a confirmed role in influencing inflammatory pathways and have been a subject of scientific scrutiny underlying drug development in recent years. Drugs designed to target allosteric sites on the nicotinic acetylcholine receptors present a unique opportunity to unravel the role of the cholinergic system in regulating and restoring inflammatory homeostasis. Such a therapeutic approach holds promise in treating several inflammatory conditions and diseases with inflammation as an underlying pathology. Here, we briefly describe the potential of cholinergic allosterism and some allosteric modulators as a promising therapeutic option for the treatment of neuroinflammation.
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Wilkerson JL, Deba F, Crowley ML, Hamouda AK, McMahon LR. Advances in the In vitro and In vivo pharmacology of Alpha4beta2 nicotinic receptor positive allosteric modulators. Neuropharmacology 2020; 168:108008. [PMID: 32113032 DOI: 10.1016/j.neuropharm.2020.108008] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2019] [Revised: 02/08/2020] [Accepted: 02/11/2020] [Indexed: 11/29/2022]
Abstract
Receptors containing α4 and β2 subunits are a major neuronal nicotinic acetylcholine receptor (nAChR) subtype in the brain. This receptor plays a critical role in nicotine addiction, with potential smoking cessation therapeutics producing modulation of α4β2 nAChR. In addition, compounds that act as agonists at α4β2 nAChR may be useful for the treatment of pathological pain. Further, as the α4β2 nAChR has been implicated in cognition, therapeutics that act as α4β2 nAChR agonists are also being examined as treatments for cognitive disorders and neurological diseases that impact cognitive function, such as Alzheimer's disease and schizophrenia. This review will cover the molecular in vitro evidence that allosteric modulators of the α4β2 neuronal nAChR provide several advantages over traditional α4β2 nAChR orthosteric ligands. Specifically, we explore the concept that nAChR allosteric modulators allow for greater pharmacological selectivity, while minimizing potential deleterious off-target effects. Further, here we discuss the development and preclinical in vivo behavioral assessment of allosteric modulators at the α4β2 neuronal nAChR as therapeutics for smoking cessation, pathological pain, as well as cognitive disorders and neurological diseases that impact cognitive function. This article is part of the special issue on 'Contemporary Advances in Nicotine Neuropharmacology'.
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Affiliation(s)
- Jenny L Wilkerson
- Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville, FL, 32610, United States.
| | - Farah Deba
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Texas at Tyler, Tyler, TX, 75799, United States
| | - Morgan L Crowley
- Department of Medicinal Chemistry, College of Pharmacy, University of Florida, Gainesville, FL, 32610, United States
| | - Ayman K Hamouda
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Texas at Tyler, Tyler, TX, 75799, United States.
| | - Lance R McMahon
- Department of Pharmacodynamics, College of Pharmacy, University of Florida, Gainesville, FL, 32610, United States.
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Ekins S, Mathews P, Saito EK, Diaz N, Naylor D, Chung J, McMurtray AM. α7-Nicotinic acetylcholine receptor inhibition by indinavir: implications for cognitive dysfunction in treated HIV disease. AIDS 2017; 31:1083-1089. [PMID: 28358738 DOI: 10.1097/qad.0000000000001488] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
OBJECTIVE The study set out to determine if the HIV protease inhibitor, indinavir, alters responsiveness of α7-nicotinic acetylcholine receptors to acetylcholine. DESIGN Treatment with HAART has dramatically reduced development of HIV-associated dementia and more severe forms of cognitive impairment. However, many individuals continue to experience cognitive decline of uncertain cause. Previous studies have failed to demonstrate significant alterations of functional brain connectivity, structural brain changes, or changes in cerebral blood flow sufficient to explain cognitive decline in virally suppressed individuals. This suggests that the mechanisms underlying development and progression of cognitive problems likely occurs at a micro rather than macro level, such as disruptions in neurotransmitter system signaling. MATERIALS AND METHODS Indinavir's effects on α7-nicotinic acetylcholine receptor activity was tested using a ScreenPatch IonWorks Barracuda-based assay in a mammalian cell model. RESULTS At low concentrations (0.0003-10 μmol/l) indinavir acts as a positive allosteric modulator (EC50 = 0.021 μmol/l), whereas at concentrations greater than 10 μmol/l (30-100 μmol/l) indinavir acts as an inhibitor of the α7-nicotinic acetylcholine receptor. CONCLUSION At concentrations greater than 10 μmol/l indinavir reduces synaptic transmission in the acetylcholine neurotransmitter system, which could possibly contribute to cognitive dysfunction. These results suggest that further experiments should be considered to assess whether patients might benefit from treatment with cholinesterase inhibitors that counteract the effects of indinavir.
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Reyes-Parada M, Iturriaga-Vasquez P. The development of novel polypharmacological agents targeting the multiple binding sites of nicotinic acetylcholine receptors. Expert Opin Drug Discov 2016; 11:969-81. [DOI: 10.1080/17460441.2016.1227317] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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Mohamed TS, Jayakar SS, Hamouda AK. Orthosteric and Allosteric Ligands of Nicotinic Acetylcholine Receptors for Smoking Cessation. Front Mol Neurosci 2015; 8:71. [PMID: 26635524 PMCID: PMC4658446 DOI: 10.3389/fnmol.2015.00071] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2015] [Accepted: 11/06/2015] [Indexed: 12/23/2022] Open
Abstract
Nicotine addiction, the result of tobacco use, leads to over six million premature deaths world-wide per year, a number that is expected to increase by a third within the next two decades. While more than half of smokers want and attempt to quit, only a small percentage of smokers are able to quit without pharmacological interventions. Therefore, over the past decades, researchers in academia and the pharmaceutical industry have focused their attention on the development of more effective smoking cessation therapies, which is now a growing 1.9 billion dollar market. Because the role of neuronal nicotinic acetylcholine receptors (nAChR) in nicotine addiction is well established, nAChR based therapeutics remain the leading strategy for smoking cessation. However, the development of neuronal nAChR drugs that are selective for a nAChR subpopulation is challenging, and only few neuronal nAChR drugs are clinically available. Among the many neuronal nAChR subtypes that have been identified in the brain, the α4β2 subtype is the most abundant and plays a critical role in nicotine addiction. Here, we review the role of neuronal nAChRs, especially the α4β2 subtype, in the development and treatment of nicotine addiction. We also compare available smoking cessation medications and other nAChR orthosteric and allosteric ligands that have been developed with emphasis on the difficulties faced in the development of clinically useful compounds with high nAChR subtype selectivity.
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Affiliation(s)
- Tasnim S Mohamed
- Department of Pharmaceutical Sciences, College of Pharmacy, Texas A&M Health Sciences Center Kingsville, TX, USA
| | - Selwyn S Jayakar
- Department of Neurobiology, Harvard Medical School Boston, MA, USA
| | - Ayman K Hamouda
- Department of Pharmaceutical Sciences, College of Pharmacy, Texas A&M Health Sciences Center Kingsville, TX, USA ; Department of Neuroscience and Experimental Therapeutics, College of Medicine, Texas A&M Health Sciences Center Bryan, TX, USA
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Multiple binding sites in the nicotinic acetylcholine receptors: An opportunity for polypharmacolgy. Pharmacol Res 2015; 101:9-17. [PMID: 26318763 DOI: 10.1016/j.phrs.2015.08.018] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/03/2015] [Revised: 08/20/2015] [Accepted: 08/20/2015] [Indexed: 12/21/2022]
Abstract
For decades, the development of selective compounds has been the main goal for chemists and biologists involved in drug discovery. However, diverse lines of evidence indicate that polypharmacological agents, i.e. those that act simultaneously at various protein targets, might show better profiles than selective ligands, regarding both efficacy and side effects. On the other hand, the availability of the crystal structure of different receptors allows a detailed analysis of the main interactions between drugs and receptors in a specific binding site. Neuronal nicotinic acetylcholine receptors (nAChRs) constitute a large and diverse family of ligand-gated ion channels (LGICs) that, as a product of its modulation, regulate neurotransmitter release, which in turns produce a global neuromodulation of the central nervous system. nAChRs are pentameric protein complexes in such a way that expression of compatible subunits can lead to various receptor assemblies or subtypes. The agonist binding site, located at the extracellular region, exhibits different properties depending on the subunits that conform the receptor. In the last years, it has been recognized that nAChRs could also contain one or more allosteric sites which could bind non-classical nicotinic ligands including several therapeutically useful drugs. The presence of multiple binding sites in nAChRs offers an interesting possibility for the development of novel polypharmacological agents with a wide spectrum of actions.
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8
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Allosteric modulation of nicotinic acetylcholine receptors. Biochem Pharmacol 2015; 97:408-417. [PMID: 26231943 DOI: 10.1016/j.bcp.2015.07.028] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Accepted: 07/24/2015] [Indexed: 12/12/2022]
Abstract
Nicotinic acetylcholine receptors (nAChRs) are receptors for the neurotransmitter acetylcholine and are members of the 'Cys-loop' family of pentameric ligand-gated ion channels (LGICs). Acetylcholine binds in the receptor extracellular domain at the interface between two subunits and research has identified a large number of nAChR-selective ligands, including agonists and competitive antagonists, that bind at the same site as acetylcholine (commonly referred to as the orthosteric binding site). In addition, more recent research has identified ligands that are able to modulate nAChR function by binding to sites that are distinct from the binding site for acetylcholine, including sites located in the transmembrane domain. These include positive allosteric modulators (PAMs), negative allosteric modulators (NAMs), silent allosteric modulators (SAMs) and compounds that are able to activate nAChRs via an allosteric binding site (allosteric agonists). Our aim in this article is to review important aspects of the pharmacological diversity of nAChR allosteric modulators and to describe recent evidence aimed at identifying binding sites for allosteric modulators on nAChRs.
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9
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Hamouda AK, Jayakar SS, Chiara DC, Cohen JB. Photoaffinity Labeling of Nicotinic Receptors: Diversity of Drug Binding Sites! J Mol Neurosci 2013; 53:480-6. [DOI: 10.1007/s12031-013-0150-1] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2013] [Accepted: 10/10/2013] [Indexed: 12/11/2022]
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10
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Xue SJ, Bu HF, Liu L, Xu X, Ma X, Zhu J. Optical Activity 1,5-Substituted-1,3,5-hexahydrotriazine-2- N-nitroimines: Synthesis and Insecticidal Activity. J Heterocycl Chem 2013. [DOI: 10.1002/jhet.920] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Si-Jia Xue
- College of Life and Environment Sciences; Shanghai Normal University; Shanghai; 200234; China
| | - Hong-Fei Bu
- College of Life and Environment Sciences; Shanghai Normal University; Shanghai; 200234; China
| | - Li Liu
- College of Life and Environment Sciences; Shanghai Normal University; Shanghai; 200234; China
| | - Xiao Xu
- College of Life and Environment Sciences; Shanghai Normal University; Shanghai; 200234; China
| | - XuBo Ma
- College of Life and Environment Sciences; Shanghai Normal University; Shanghai; 200234; China
| | - Jun Zhu
- College of Life and Environment Sciences; Shanghai Normal University; Shanghai; 200234; China
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Physostigmine and galanthamine bind in the presence of agonist at the canonical and noncanonical subunit interfaces of a nicotinic acetylcholine receptor. J Neurosci 2013; 33:485-94. [PMID: 23303929 DOI: 10.1523/jneurosci.3483-12.2013] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Galanthamine and physostigmine are clinically used cholinomimetics that both inhibit acetylcholinesterase and also interact directly with and potentiate nAChRs. As with most nAChR-positive allosteric modulators, the location and number of their binding site(s) within nAChRs are unknown. In this study, we use the intrinsic photoreactivities of [(3)H]physostigmine and [(3)H]galanthamine upon irradiation at 312 nm to directly identify amino acids contributing to their binding sites in the Torpedo californica nAChR. Protein sequencing of fragments isolated from proteolytic digests of [(3)H]physostigmine- or [(3)H]galanthamine-photolabeled nAChR establish that, in the presence of agonist (carbamylcholine), both drugs photolabeled amino acids on the complementary (non-α) surface of the transmitter binding sites (γTyr-111/γTyr-117/δTyr172). They also photolabeled δTyr-212 at the δ-β subunit interface and γTyr-105 in the vestibule of the ion channel, with photolabeling of both residues enhanced in the presence of agonist. Furthermore, [(3)H]physostigmine photolabeling of γTyr-111, γTyr-117, δTyr-212, and γTyr-105 was inhibited in the presence of nonradioactive galanthamine. The locations of the photolabeled amino acids in the nAChR structure and the results of computational docking studies provide evidence that, in the presence of agonist, physostigmine and galanthamine bind to at least three distinct sites in the nAChR extracellular domain: at the α-γ interface (1) in the entry to the transmitter binding site and (2) in the vestibule of the ion channel near the level of the transmitter binding site, and at the δ-β interface (3) in a location equivalent to the benzodiazepine binding site in GABA(A) receptors.
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12
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Rohde LAH, Ahring PK, Jensen ML, Nielsen EØ, Peters D, Helgstrand C, Krintel C, Harpsøe K, Gajhede M, Kastrup JS, Balle T. Intersubunit bridge formation governs agonist efficacy at nicotinic acetylcholine α4β2 receptors: unique role of halogen bonding revealed. J Biol Chem 2011; 287:4248-59. [PMID: 22170047 DOI: 10.1074/jbc.m111.292243] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The α4β2 subtype of the nicotinic acetylcholine receptor has been pursued as a drug target for treatment of psychiatric and neurodegenerative disorders and smoking cessation aids for decades. Still, a thorough understanding of structure-function relationships of α4β2 agonists is lacking. Using binding experiments, electrophysiology and x-ray crystallography we have investigated a consecutive series of five prototypical pyridine-containing agonists derived from 1-(pyridin-3-yl)-1,4-diazepane. A correlation between binding affinities at α4β2 and the acetylcholine-binding protein from Lymnaea stagnalis (Ls-AChBP) confirms Ls-AChBP as structural surrogate for α4β2 receptors. Crystal structures of five agonists with efficacies at α4β2 from 21-76% were determined in complex with Ls-AChBP. No variation in closure of loop C is observed despite large efficacy variations. Instead, the efficacy of a compound appears tightly coupled to its ability to form a strong intersubunit bridge linking the primary and complementary binding interfaces. For the tested agonists, a specific halogen bond was observed to play a large role in establishing such strong intersubunit anchoring.
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Affiliation(s)
- Line Aagot Hede Rohde
- Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Copenhagen 2100, Denmark
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Pandya A, Yakel JL. Allosteric modulators of the α4β2 subtype of neuronal nicotinic acetylcholine receptors. Biochem Pharmacol 2011; 82:952-8. [PMID: 21596025 PMCID: PMC3162104 DOI: 10.1016/j.bcp.2011.04.020] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Revised: 04/28/2011] [Accepted: 04/29/2011] [Indexed: 02/07/2023]
Abstract
Nicotinic acetylcholine receptors are ligand-gated ion conducting transmembrane channels from the Cys-loop receptor super-family. The α4β2 subtype is the predominant heteromeric subtype of nicotinic receptors found in the brain. Allosteric modulators for α4β2 receptors interact at a site other than the orthosteric site where acetylcholine binds. Many compounds which act as allosteric modulators of the α4β2 receptors have been identified, with both positive and negative effects. Such allosteric modulators either increase or decrease the response induced by agonist on the α4β2 receptors. Here we discuss the concept of allosterism as it pertains to the α4β2 receptors and summarize the important features of allosteric modulators for this nicotinic receptor subtype.
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Affiliation(s)
- Anshul Pandya
- Laboratory of Neurobiology, National Institute of Environmental Health Sciences, National Institutes of Health, Department of Health and Human Services, Research Triangle Park, NC 27709, USA.
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14
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Atkinson AP, Baguet E, Galland N, Le Questel JY, Planchat A, Graton J. Structural Features and Hydrogen-Bond Properties of Galanthamine and Codeine: An Experimental and Theoretical Study. Chemistry 2011; 17:11637-49. [DOI: 10.1002/chem.201100475] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2011] [Revised: 06/21/2011] [Indexed: 11/07/2022]
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15
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Taly A, Colas C, Malliavin T, Blondel A, Nilges M, Corringer PJ, Joseph D. Discrimination of agonists versus antagonists of nicotinic ligands based on docking onto AChBP structures. J Mol Graph Model 2011; 30:100-9. [PMID: 21764343 DOI: 10.1016/j.jmgm.2011.06.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2011] [Revised: 05/27/2011] [Accepted: 06/22/2011] [Indexed: 11/26/2022]
Abstract
Numerous high-resolution crystallographic structures of the acetylcholine binding protein (AChBP), a molluscan cholinergic protein, homologous to the extracellular domain of nicotinic acetylcholine receptors, are available. This offers opportunities to model the interaction between various ligands and the acetylcholine binding site. Herein we present a study of the interplay between ligand binding and motions of the C-loop capping the binding site. Nicotinic agonists and antagonists were docked on AChBP X-ray structures. It is shown that the studied agonists and antagonists can be discriminated according to their higher affinities for structures respectively obtained in the presence of agonists or antagonists, highlighting the fact that AChBP structures retain a pharmacological footprint of the compound used in crystallography experiments. A detailed analysis of the binding site cavities suggests that this property is mainly related to the shape of the cavities.
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Affiliation(s)
- Antoine Taly
- Laboratoire de Conception et Application de Molécules Bioactives, UMR 7199 CNRS-Université de Strasbourg, 74 Route du Rhin-BP 60024, 67401 Illkirch Cedex, France.
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Arias HR, Gu RX, Feuerbach D, Guo BB, Ye Y, Wei DQ. Novel positive allosteric modulators of the human α7 nicotinic acetylcholine receptor. Biochemistry 2011; 50:5263-78. [PMID: 21510634 DOI: 10.1021/bi102001m] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The pharmacological activity of a series of novel amide derivatives was characterized on several nicotinic acetylcholine receptors (AChRs). Ca(2+) influx results indicate that these compounds are not agonists of the human (h) α4β2, α3β4, α7, and α1β1γδ AChRs; compounds 2-4 are specific positive allosteric modulators (PAMs) of hα7 AChRs, whereas compounds 1-4, 7, and 12 are noncompetitive antagonists of the other AChRs. Radioligand binding results indicate that PAMs do not inhibit binding of [(3)H]methyllycaconitine but enhance binding of [(3)H]epibatidine to hα7 AChRs, indicating that these compounds do not directly, but allosterically, interact with the hα7 agonist sites. Additional competition binding results indicate that the antagonistic action mediated by these compounds is produced by direct interaction with neither the phencyclidine site in the Torpedo AChR ion channel nor the imipramine and the agonist sites in the hα4β2 and hα3β4 AChRs. Molecular dynamics and docking results suggest that the binding site for compounds 2-4 is mainly located in the inner β-sheet of the hα7-α7 interface, ∼12 Å from the agonist locus. Hydrogen bond interactions between the amide group of the PAMs and the hα7 AChR binding site are found to be critical for their activity. The dual PAM and antagonistic activities elicited by compounds 2-4 might be therapeutically important.
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Affiliation(s)
- Hugo R Arias
- College of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China
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17
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Williams DK, Wang J, Papke RL. Positive allosteric modulators as an approach to nicotinic acetylcholine receptor-targeted therapeutics: advantages and limitations. Biochem Pharmacol 2011; 82:915-30. [PMID: 21575610 DOI: 10.1016/j.bcp.2011.05.001] [Citation(s) in RCA: 208] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2011] [Revised: 04/28/2011] [Accepted: 05/02/2011] [Indexed: 11/16/2022]
Abstract
Neuronal nicotinic acetylcholine receptors (nAChR), recognized targets for drug development in cognitive and neuro-degenerative disorders, are allosteric proteins with dynamic interconversions between multiple functional states. Activation of the nAChR ion channel is primarily controlled by the binding of ligands (agonists, partial agonists, competitive antagonists) at conventional agonist binding sites, but is also regulated in either negative or positive ways by the binding of ligands to other modulatory sites. In this review, we discuss models for the activation and desensitization of nAChR, and the discovery of multiple types of ligands that influence those processes in both heteromeric nAChR, such as the high-affinity nicotine receptors of the brain, and homomeric α7-type receptors. In recent years, α7 nAChRs have been identified as a potential target for therapeutic indications leading to the development of α7-selective agonists and partial agonists. However, unique properties of α7 nAChR, including low probability of channel opening and rapid desensitization, may limit the therapeutic usefulness of ligands binding exclusively to conventional agonist binding sites. New enthusiasm for the therapeutic targeting of α7 has come from the identification of α7-selective positive allosteric modulators (PAMs) that work effectively on the intrinsic factors that limit α7 ion channel activation. While these new drugs appear promising for therapeutic development, we also consider potential caveats and possible limitations for their use, including PAM-insensitive forms of desensitization and cytotoxicity issues.
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Affiliation(s)
- Dustin K Williams
- Department of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville, FL Neurocypres, United States
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18
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Dallanoce C, Magrone P, Matera C, Frigerio F, Grazioso G, De Amici M, Fucile S, Piccari V, Frydenvang K, Pucci L, Gotti C, Clementi F, De Micheli C. Design, synthesis, and pharmacological characterization of novel spirocyclic quinuclidinyl-Δ2-isoxazoline derivatives as potent and selective agonists of α7 nicotinic acetylcholine receptors. ChemMedChem 2011; 6:889-903. [PMID: 21365765 DOI: 10.1002/cmdc.201000514] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2010] [Revised: 01/13/2011] [Indexed: 11/08/2022]
Abstract
A set of racemic spirocyclic quinuclidinyl-Δ(2)-isoxazoline derivatives was synthesized using a 1,3-dipolar cycloaddition-based approach. Target compounds were assayed for binding affinity toward rat neuronal homomeric (α7) and heteromeric (α4β2) nicotinic acetylcholine receptors. Δ(2) -Isoxazolines 3 a (3-Br), 6 a (3-OMe), 5 a (3-Ph), 8 a (3-OnPr), and 4 a (3-Me) were the ligands with the highest affinity for the α7 subtype (K(i) values equal to 13.5, 14.2, 25.0, 71.6, and 96.2 nM, respectively), and showed excellent α7 versus α4β2 subtype selectivity. These compounds, tested in electrophysiological experiments against human α7 and α4β2 receptors stably expressed in cell lines, behaved as partial α7 agonists with varying levels of potency. The two enantiomers of (±)-3-methoxy-1-oxa-2,7-diaza-7,10-ethanospiro[4.5]dec-2-ene sesquifumarate 6 a were prepared using (+)-dibenzoyl-L- or (-)-dibenzoyl-D-tartaric acid as resolving agents. Enantiomer (R)-(-)-6 a was found to be the eutomer, with K(i) values of 4.6 and 48.7 nM against rat and human α7 receptors, respectively.
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Affiliation(s)
- Clelia Dallanoce
- Dipartimento di Scienze Farmaceutiche Pietro Pratesi, Università degli Studi di Milano, Milan, Italy
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Chiral 1,5-disubstituted 1,3,5-hexahydrotriazine-2-N-nitroimine analogues as novel potent neonicotinoids: Synthesis, insecticidal evaluation and molecular docking studies. Eur J Med Chem 2011; 46:11-20. [DOI: 10.1016/j.ejmech.2010.09.047] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2010] [Revised: 08/18/2010] [Accepted: 09/19/2010] [Indexed: 11/19/2022]
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Ludwig J, Höffle-Maas A, Samochocki M, Luttmann E, Albuquerque EX, Fels G, Maelicke A. Localization by site-directed mutagenesis of a galantamine binding site on α7 nicotinic acetylcholine receptor extracellular domain. J Recept Signal Transduct Res 2010; 30:469-83. [PMID: 21062106 DOI: 10.3109/10799893.2010.505239] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Galantamine is an approved drug treatment for Alzheimer's disease. Initially identified as a weak cholinesterase inhibitor, we have established that galantamine mainly acts as an 'allosterically potentiating ligand (APL)' of nicotinic acetylcholine receptors (nAChR). Meanwhile other 'positive allosteric modulators (PAM)' of nAChR channel activity have been discovered, and for one of them a binding site within the transmembrane domain has been proposed. Here we show, by performing site-directed mutagenesis studies of ectopically expressed chimeric chicken α7/mouse 5-hydroxytryptamine 3 receptor-channel complex, in combination with whole-cell current measurements, in the presence and absence of galantamine, that the APL binding site is different from the proposed PAM binding site. We demonstrate that residues T197, I196, and F198 of ß-strand 10 represent major elements of the galantamine binding site. Residue K123, earlier suggested as being 'close to' the APL binding site, is not part of this site but rather appears to play a role in coupling of agonist binding to channel opening and closing. Our data confirm our earlier results that the galantamine binding site is different from the ACh binding site. Both sites are in close proximity and hence may influence each other in a synergistic fashion. Other interesting areas identified in the present study are a 'hinge' region around and containing residues F122, K123, and K143 possibly being involved in relaying the signal of agonist binding to gating of the transmembrane channel, and a 'folding centre', with P119 as the dominating residue, that crucially positions the agonist binding site with respect to the hinge region.
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Arias HR. Positive and negative modulation of nicotinic receptors. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2010; 80:153-203. [PMID: 21109220 DOI: 10.1016/b978-0-12-381264-3.00005-9] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Nicotinic acetylcholine receptors (AChRs) are one of the best characterized ion channels from the Cys-loop receptor superfamily. The study of acetylcholine binding proteins and prokaryotic ion channels from different species has been paramount for the understanding of the structure-function relationship of the Cys-loop receptor superfamily. AChR function can be modulated by different ligand types. The neurotransmitter ACh and other agonists trigger conformational changes in the receptor, finally opening the intrinsic cation channel. The so-called gating process couples ligand binding, located at the extracellular portion, to the opening of the ion channel, located at the transmembrane region. After agonist activation, in the prolonged presence of agonists, the AChR becomes desensitized. Competitive antagonists overlap the agonist-binding sites inhibiting the pharmacological action of agonists. Positive allosteric modulators (PAMs) do not bind to the orthostetic binding sites but allosterically enhance the activity elicited by agonists by increasing the gating process (type I) and/or by decreasing desensitization (type II). Instead, negative allosteric modulators (NAMs) produce the opposite effects. Interestingly, this negative effect is similar to that found for another class of allosteric drugs, that is, noncompetitive antagonists (NCAs). However, the main difference between both categories of drugs is based on their distinct binding site locations. Although both NAMs and NCAs do not bind to the agonist sites, NACs bind to sites located in the ion channel, whereas NAMs bind to nonluminal sites. However, this classification is less clear for NAMs interacting at the extracellular-transmembrane interface where the ion channel mouth might be involved. Interestingly, PAMs and NAMs might be developed as potential medications for the treatment of several diseases involving AChRs, including dementia-, skin-, and immunological-related diseases, drug addiction, and cancer. More exciting is the potential combination of specific agonists with specific PAMs. However, we are still in the beginning of understanding how these compounds act and how these drugs can be used therapeutically.
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Affiliation(s)
- Hugo R Arias
- Department of Pharmaceutical Sciences, Midwestern University, Glendale, AZ, USA
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