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Burger WAC, Sexton PM, Christopoulos A, Thal DM. Toward an understanding of the structural basis of allostery in muscarinic acetylcholine receptors. J Gen Physiol 2018; 150:1360-1372. [PMID: 30190312 PMCID: PMC6168235 DOI: 10.1085/jgp.201711979] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2018] [Accepted: 08/14/2018] [Indexed: 01/16/2023] Open
Abstract
Burger et al. summarize our mechanistic understanding of allostery in the prototypical GPCR, the muscarinic acetylcholine receptor. Recent breakthroughs and developments in structural biology have led to a spate of crystal structures for G protein–coupled receptors (GPCRs). This is the case for the muscarinic acetylcholine receptors (mAChRs) where inactive-state structures for four of the five subtypes and two active-state structures for one subtype are available. These mAChR crystal structures have provided new insights into receptor mechanisms, dynamics, and allosteric modulation. This is highly relevant to the mAChRs given that these receptors are an exemplar model system for the study of GPCR allostery. Allosteric mechanisms of the mAChRs are predominantly consistent with a two-state model, albeit with some notable recent exceptions. Herein, we discuss the mechanisms for positive and negative allosteric modulation at the mAChRs and compare and contrast these to evidence offered by pharmacological, biochemical, and computational approaches. This analysis provides insight into the fundamental pharmacological properties exhibited by GPCR allosteric modulators, such as enhanced subtype selectivity, probe dependence, and biased modulation while highlighting the current challenges that remain. Though complex, enhanced molecular understanding of allosteric mechanisms will have considerable influence on our understanding of GPCR activation and signaling and development of therapeutic interventions.
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Affiliation(s)
- Wessel A C Burger
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia
| | - Patrick M Sexton
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia
| | - Arthur Christopoulos
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia
| | - David M Thal
- Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia
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2
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Livingston KE, Stanczyk MA, Burford NT, Alt A, Canals M, Traynor JR. Pharmacologic Evidence for a Putative Conserved Allosteric Site on Opioid Receptors. Mol Pharmacol 2017; 93:157-167. [PMID: 29233847 DOI: 10.1124/mol.117.109561] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2017] [Accepted: 11/27/2017] [Indexed: 11/22/2022] Open
Abstract
Allosteric modulators of G protein-coupled receptors, including opioid receptors, have been proposed as possible therapeutic agents with enhanced selectivity. BMS-986122 is a positive allosteric modulator (PAM) of the μ-opioid receptor (µ-OR). BMS-986187 is a structurally distinct PAM for the δ-opioid receptor (δ-OR) that has been reported to exhibit 100-fold selectivity in promoting δ-OR over μ-OR agonism. We used ligand binding and second-messenger assays to show that BMS-986187 is an effective PAM at the μ-OR and at the κ-opioid receptor (κ-OR), but it is ineffective at the nociceptin receptor. The affinity of BMS-986187 for δ-ORs and κ-ORs is approximately 20- to 30-fold higher than for μ-ORs, determined using an allosteric ternary complex model. Moreover, we provide evidence, using a silent allosteric modulator as an allosteric antagonist, that BMS-986187 and BMS-986122 bind to a similar region on all three traditional opioid receptor types (µ-OR, δ-OR, and κ-OR). In contrast to the dogma surrounding allosteric modulators, the results indicate a possible conserved allosteric binding site across the opioid receptor family that can accommodate structurally diverse molecules. These findings have implications for the development of selective allosteric modulators.
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Affiliation(s)
- Kathryn E Livingston
- Department of Pharmacology and Edward F. Domino Research Center, University of Michigan, Ann Arbor, Michigan (K.E.L., M.A.S., J.R.T.); Research and Development/Discovery, Bristol-Myers Squibb Company, Wallingford, Connecticut (N.T.B., A.A.); and Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (M.C.)
| | - M Alexander Stanczyk
- Department of Pharmacology and Edward F. Domino Research Center, University of Michigan, Ann Arbor, Michigan (K.E.L., M.A.S., J.R.T.); Research and Development/Discovery, Bristol-Myers Squibb Company, Wallingford, Connecticut (N.T.B., A.A.); and Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (M.C.)
| | - Neil T Burford
- Department of Pharmacology and Edward F. Domino Research Center, University of Michigan, Ann Arbor, Michigan (K.E.L., M.A.S., J.R.T.); Research and Development/Discovery, Bristol-Myers Squibb Company, Wallingford, Connecticut (N.T.B., A.A.); and Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (M.C.)
| | - Andrew Alt
- Department of Pharmacology and Edward F. Domino Research Center, University of Michigan, Ann Arbor, Michigan (K.E.L., M.A.S., J.R.T.); Research and Development/Discovery, Bristol-Myers Squibb Company, Wallingford, Connecticut (N.T.B., A.A.); and Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (M.C.)
| | - Meritxell Canals
- Department of Pharmacology and Edward F. Domino Research Center, University of Michigan, Ann Arbor, Michigan (K.E.L., M.A.S., J.R.T.); Research and Development/Discovery, Bristol-Myers Squibb Company, Wallingford, Connecticut (N.T.B., A.A.); and Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (M.C.)
| | - John R Traynor
- Department of Pharmacology and Edward F. Domino Research Center, University of Michigan, Ann Arbor, Michigan (K.E.L., M.A.S., J.R.T.); Research and Development/Discovery, Bristol-Myers Squibb Company, Wallingford, Connecticut (N.T.B., A.A.); and Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia (M.C.)
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3
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Schober DA, Croy CH, Xiao H, Christopoulos A, Felder CC. Development of a radioligand, [(3)H]LY2119620, to probe the human M(2) and M(4) muscarinic receptor allosteric binding sites. Mol Pharmacol 2014; 86:116-23. [PMID: 24807966 DOI: 10.1124/mol.114.091785] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
In this study, we characterized a muscarinic acetylcholine receptor (mAChR) potentiator, LY2119620 (3-amino-5-chloro-N-cyclopropyl-4-methyl-6-[2-(4-methylpiperazin-1-yl)-2-oxoethoxy]thieno[2,3-b]pyridine-2-carboxamide) as a novel probe of the human M2 and M4 allosteric binding sites. Since the discovery of allosteric binding sites on G protein-coupled receptors, compounds targeting these novel sites have been starting to emerge. For example, LY2033298 (3-amino-5-chloro-6-methoxy-4-methyl-thieno(2,3-b)pyridine-2-carboxylic acid cyclopropylamid) and a derivative of this chemical scaffold, VU152100 (3-amino-N-(4-methoxybenzyl)-4,6-dimethylthieno[2,3-b]pyridine carboxamide), bind to the human M4 mAChR allosteric pocket. In the current study, we characterized LY2119620, a compound similar in structure to LY2033298 and binds to the same allosteric site on the human M4 mAChRs. However, LY2119620 also binds to an allosteric site on the human M2 subtype. [(3)H]NMS ([(3)H]N-methylscopolamine) binding experiments confirm that LY2119620 does not compete for the orthosteric binding pocket at any of the five muscarinic receptor subtypes. Dissociation kinetic studies using [(3)H]NMS further support that LY2119620 binds allosterically to the M2 and M4 mAChRs and was positively cooperative with muscarinic orthosteric agonists. To probe directly the allosteric sites on M2 and M4, we radiolabeled LY2119620. Cooperativity binding of [(3)H]LY2119620 with mAChR orthosteric agonists detects significant changes in Bmax values with little change in Kd, suggesting a G protein-dependent process. Furthermore, [(3)H]LY2119620 was displaced by compounds of similar chemical structure but not by previously described mAChR allosteric compounds such as gallamine or WIN 62,577 (17-β-hydroxy-17-α-ethynyl-δ-4-androstano[3,2-b]pyrimido[1,2-a]benzimidazole). Our results therefore demonstrate the development of a radioligand, [(3)H]LY2119620 to probe specifically the human M2 and M4 muscarinic receptor allosteric binding sites.
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Affiliation(s)
- Douglas A Schober
- Lilly Neuroscience, Lilly Research Laboratories, Eli Lilly and Co., Lilly Corporate Center, Indianapolis, Indiana (D.A.S., C.H.C., H.X., C.C.F.); and Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Parkville, Victoria, Australia (A.C.)
| | - Carrie H Croy
- Lilly Neuroscience, Lilly Research Laboratories, Eli Lilly and Co., Lilly Corporate Center, Indianapolis, Indiana (D.A.S., C.H.C., H.X., C.C.F.); and Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Parkville, Victoria, Australia (A.C.)
| | - Hongling Xiao
- Lilly Neuroscience, Lilly Research Laboratories, Eli Lilly and Co., Lilly Corporate Center, Indianapolis, Indiana (D.A.S., C.H.C., H.X., C.C.F.); and Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Parkville, Victoria, Australia (A.C.)
| | - Arthur Christopoulos
- Lilly Neuroscience, Lilly Research Laboratories, Eli Lilly and Co., Lilly Corporate Center, Indianapolis, Indiana (D.A.S., C.H.C., H.X., C.C.F.); and Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Parkville, Victoria, Australia (A.C.)
| | - Christian C Felder
- Lilly Neuroscience, Lilly Research Laboratories, Eli Lilly and Co., Lilly Corporate Center, Indianapolis, Indiana (D.A.S., C.H.C., H.X., C.C.F.); and Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Parkville, Victoria, Australia (A.C.)
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Khurana L, Ali HI, Olszewska T, Ahn KH, Damaraju A, Kendall DA, Lu D. Optimization of chemical functionalities of indole-2-carboxamides to improve allosteric parameters for the cannabinoid receptor 1 (CB1). J Med Chem 2014; 57:3040-52. [PMID: 24635495 PMCID: PMC4203403 DOI: 10.1021/jm5000112] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
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5-Chloro-3-ethyl-N-(4-(piperidin-1-yl)phenethyl)-1H-indole-2-carboxamide
(1; ORG27569) is a prototypical
allosteric modulator for the cannabinoid type 1 receptor (CB1). Here,
we reveal key structural requirements of indole-2-carboxamides for
allosteric modulation of CB1: a critical chain length at the C3-position,
an electron withdrawing group at the C5-position, the length of the
linker between the amide bond and the phenyl ring B, and the amino
substituent on the phenyl ring B. These significantly impact the binding
affinity (KB) and the binding cooperativity
(α). A potent CB1 allosteric modulator 5-chloro-N-(4-(dimethylamino)phenethyl)-3-propyl-1H-indole-2-carboxamide
(12d) was identified. It exhibited a KB of 259.3 nM with a strikingly high binding α of
24.5. We also identified 5-chloro-N-(4-(dimethylamino)phenethyl)-3-hexyl-1H-indole-2-carboxamide (12f) with a KB of 89.1 nM, which is among the lowest KB values obtained for any allosteric modulator
of CB1. These positive allosteric modulators of orthosteric agonist
binding nonetheless antagonized the agonist-induced G-protein coupling
to the CB1 receptor, yet induced β-arrestin mediated ERK1/2
phosphorylation.
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Affiliation(s)
- Leepakshi Khurana
- Department of Pharmaceutical Sciences, University of Connecticut , Storrs, Connecticut, United States
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Keov P, Valant C, Devine SM, Lane JR, Scammells PJ, Sexton PM, Christopoulos A. Reverse Engineering of the Selective Agonist TBPB Unveils Both Orthosteric and Allosteric Modes of Action at the M1 Muscarinic Acetylcholine Receptor. Mol Pharmacol 2013; 84:425-37. [DOI: 10.1124/mol.113.087320] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
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Daval SB, Valant C, Bonnet D, Kellenberger E, Hibert M, Galzi JL, Ilien B. Fluorescent derivatives of AC-42 to probe bitopic orthosteric/allosteric binding mechanisms on muscarinic M1 receptors. J Med Chem 2012; 55:2125-43. [PMID: 22329602 DOI: 10.1021/jm201348t] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Two fluorescent derivatives of the M1 muscarinic selective agonist AC-42 were synthesized by coupling the lissamine rhodamine B fluorophore (in ortho and para positions) to AC42-NH(2). This precursor, prepared according to an original seven-step procedure, was included in the study together with the LRB fluorophore (alone or linked to an alkyl chain). All these compounds are antagonists, but examination of their ability to inhibit or modulate orthosteric [(3)H]NMS binding revealed that para-LRB-AC42 shared several properties with AC-42. Carefully designed experiments allowed para-LRB-AC42 to be used as a FRET tracer on EGFP-fused M1 receptors. Under equilibrium binding conditions, orthosteric ligands, AC-42, and the allosteric modulator gallamine behaved as competitors of para-LRB-AC42 binding whereas other allosteric compounds such as WIN 51,708 and N-desmethylclozapine were noncompetitive inhibitors. Finally, molecular modeling studies focused on putative orthosteric/allosteric bitopic poses for AC-42 and para-LRB-AC42 in a 3D model of the human M1 receptor.
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Affiliation(s)
- Sandrine B Daval
- Unité Biotechnologie et Signalisation Cellulaire, UMR 7242 CNRS, Ecole Supérieure de Biotechnologie de Strasbourg, Université de Strasbourg, BP 10413, 67412 Illkirch, France
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7
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Valant C, Felder CC, Sexton PM, Christopoulos A. Probe dependence in the allosteric modulation of a G protein-coupled receptor: implications for detection and validation of allosteric ligand effects. Mol Pharmacol 2011; 81:41-52. [PMID: 21989256 DOI: 10.1124/mol.111.074872] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We recently described 3-amino-5-chloro-6-methoxy-4-methylthieno[2,3-b]pyridine-2-carboxylic acid cyclopropylamide (LY2033298) as a novel allosteric modulator of M(4) muscarinic acetylcholine (ACh) receptors (mAChRs) on the basis of its ability to preferentially potentiate the actions of ACh at the M(4) mAChR subtype. In the current study, we show that LY2033298 can also bind to the M(2) mAChR and mediate robust positive or negative allosteric effects, depending on the orthosteric ligand used as a probe of receptor activity. This finding of striking "probe dependence" indicates that the previously described selectivity of the modulator does not arise as a consequence of selective affinity for a poorly conserved allosteric site but rather is due to subtype-selective cooperativity with ACh upon interaction with a common allosteric binding site. Moreover, a comparison of the effects of the modulator on orthosteric ligand affinity relative to signaling through a [(35)S]guanosine 5'-O-(3-thio)triphosphate or extracellular signal-regulated kinase 1/2 phosphorylation assay at the M(2) mAChR revealed that, although the effects on binding were positive in all instances, the effects on signaling were either positive or strongly negative, depending on the agonist and the pathway. Mutational analysis identified residues Tyr177 and Trp99(3.28) (Ballesteros and Weinstein numbers are provided in superscript to indicate relative position of residues within the transmembrane domain) as contributing to the binding of LY2033298, whereas the orthosteric site residues, Tyr104(3.33) and Tyr403(6.51), contributed to the ability of the ligand to impose pathway-biased modulation. Taken together, these findings have important implications for the detection and validation of allosteric modulators of G protein-coupled receptors (GPCRs), because they highlight the potential for ligand misclassification or lack of appreciation of off-target allosteric activities.
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Affiliation(s)
- Celine Valant
- Drug Discovery Biology and Department of Pharmacology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia
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De Amici M, Dallanoce C, Holzgrabe U, Tränkle C, Mohr K. Allosteric ligands for G protein-coupled receptors: a novel strategy with attractive therapeutic opportunities. Med Res Rev 2010; 30:463-549. [PMID: 19557759 DOI: 10.1002/med.20166] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Allosteric receptor ligands bind to a recognition site that is distinct from the binding site of the endogenous messenger molecule. As a consequence, allosteric agents may attach to receptors that are already transmitter-bound. Ternary complex formation opens an avenue to qualitatively new drug actions at G protein-coupled receptors (GPCRs), in particular receptor subtype selective potentiation of endogenous transmitter action. Consequently, suitable exploitation of allosteric recognition sites as alternative molecular targets could pave the way to a drug discovery paradigm different from those aimed at mimicking or blocking the effects of endogenous (orthosteric) receptor activators. The number of allosteric ligands reported to modulate GPCR function is steadily increasing and some have already reached routine clinical use. This review aims at introducing into this fascinating field of drug discovery and at providing an overview about the achievements that have already been made. Various case examples will be discussed in the framework of GPCR classification (family A, B, and C receptors). In addition, the behavior at muscarinic receptors of hybrid derivatives incorporating both an allosteric and an orthosteric fragment in a common molecular skeleton will be illustrated.
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Affiliation(s)
- Marco De Amici
- Department of Pharmaceutical Sciences Pietro Pratesi, University of Milan, via Mangiagalli 25, 20133 Milano, Italy.
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Molecular mechanisms of action and in vivo validation of an M4 muscarinic acetylcholine receptor allosteric modulator with potential antipsychotic properties. Neuropsychopharmacology 2010; 35:855-69. [PMID: 19940843 PMCID: PMC3055367 DOI: 10.1038/npp.2009.194] [Citation(s) in RCA: 132] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
We recently identified LY2033298 as a novel allosteric potentiator of acetylcholine (ACh) at the M(4) muscarinic acetylcholine receptor (mAChR). This study characterized the molecular mode of action of this modulator in both recombinant and native systems. Radioligand-binding studies revealed that LY2033298 displayed a preference for the active state of the M(4) mAChR, manifested as a potentiation in the binding affinity of ACh (but not antagonists) and an increase in the proportion of high-affinity agonist-receptor complexes. This property accounted for the robust allosteric agonism displayed by the modulator in recombinant cells in assays of [(35)S]GTPgammaS binding, extracellular regulated kinase 1/2 phosphorylation, glycogen synthase kinase 3beta phosphorylation, and receptor internalization. We also found that the extent of modulation by LY2033298 differed depending on the signaling pathway, indicating that LY2033298 engenders functional selectivity in the actions of ACh. This property was retained in NG108-15 cells, which natively express rodent M(4) mAChRs. Functional interaction studies between LY2033298 and various orthosteric and allosteric ligands revealed that its site of action overlaps with the allosteric site used by prototypical mAChR modulators. Importantly, LY2033298 reduced [(3)H]ACh release from rat striatal slices, indicating retention of its ability to allosterically potentiate endogenous ACh in situ. Moreover, its ability to potentiate oxotremorine-mediated inhibition of condition avoidance responding in rodents was significantly attenuated in M(4) mAChR knockout mice, validating the M(4) mAChR as a key target of action of this novel allosteric ligand.
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Noetzel MJ, Grant MKO, El-Fakahany EE. Mechanisms of M3 muscarinic receptor regulation by wash-resistant xanomeline binding. Pharmacology 2009; 83:301-17. [PMID: 19401618 DOI: 10.1159/000214843] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2008] [Accepted: 02/12/2009] [Indexed: 11/19/2022]
Abstract
BACKGROUND/AIMS Xanomeline has been shown to bind in a unique manner at M1 and M3 muscarinic receptors, with interactions at both the orthosteric site and an allosteric site. We have previously shown that brief exposure of Chinese hamster ovary cells that express the M3 receptor to xanomeline followed by removal of free agonist results in a delayed decrease in radioligand binding and receptor response to agonists. In the current study, we were interested in determining the mechanisms of this effect. METHODS Cells were treated with carbachol, pilocarpine or xanomeline for 1 h followed by washing and either used immediately or after waiting for 23 h. Control groups included cells that were not exposed to agonists and cells that were treated with agonists for 24 h. Radioligand binding and functional assays were conducted to determine the effects of agonist treatments. RESULTS The above treatment protocol with xanomeline resulted in similar effects of the binding of [(3)H]NMS and [(3)H]QNB. When receptor function is blocked using a variety of methods, the long-term effects of xanomeline binding were absent. CONCLUSION Our data indicate that xanomeline wash-resistant binding at the receptor allosteric site leads to receptor downregulation and that receptor activation is necessary for these effects.
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Affiliation(s)
- Meredith J Noetzel
- Division of Neuroscience Research in Psychiatry, University of Minnesota Medical School, Minneapolis, MN 55455, USA
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Navarro HA, Howard JL, Pollard GT, Carroll FI. Positive allosteric modulation of the human cannabinoid (CB) receptor by RTI-371, a selective inhibitor of the dopamine transporter. Br J Pharmacol 2009; 156:1178-84. [PMID: 19226282 DOI: 10.1111/j.1476-5381.2009.00124.x] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND AND PURPOSE In our search for an indirect dopamine agonist as therapy for cocaine addiction, several selective inhibitors of the dopamine transporter (DAT), which are 3-phenyltropane analogues, were assayed for their effect on locomotor activity in mice. Interestingly, several of the compounds showed a poor correlation between stimulation of locomotion and DAT inhibition. One of the compounds, 3beta-(4-methylphenyl)-2beta-[3-(4-chlorophenyl)isoxazol-5-yl]tropane (RTI-371), was shown to cross the blood-brain barrier, by binding studies in vivo, and block cocaine-induced locomotor stimulation. As poor pharmacokinetics could not explain the behavioural effects of RTI-371, this compound was screened through our functional assays for activity at other CNS receptors. Initial screening identified RTI-371 as a positive allosteric modulator of the human CB(1) (hCB(1)) receptor. EXPERIMENTAL APPROACH The effect of RTI-371 and other DAT-selective inhibitors on CP55940-stimulated calcium mobilization was characterized in a calcium mobilization-based functional assay for the hCB(1) receptor. Selected compounds were also characterized in a similar assay for human mu opioid receptor activation to assess the specificity of their effects. KEY RESULTS RTI-371 and several other DAT-selective inhibitors with atypical actions on locomotor behaviour increased the efficacy of CP55940 in a concentration-dependent manner. CONCLUSIONS AND IMPLICATIONS These results suggest that the lack of correlation between the DAT-binding affinity and locomotor stimulation of RTI-371 could be due at least in part to its activity as a positive modulator of the hCB(1) receptor.
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Abstract
G protein-coupled receptors (GPCRs) are a large family of proteins that represent targets for approximately 40% of all approved drugs. They possess unique structural motifs that allow them to interact with a diverse series of extracellular ligands, as well as intracellular signaling proteins, such as G proteins, RAMPs, arrestins, and indeed other receptors. Extensive efforts are under way to discover new generations of drugs against GPCRs with unique targeted therapeutic uses, including "designer" drugs such as allosteric regulators, inverse agonists, and drugs targeting hetero-oligomeric complexes. This has been facilitated by the development of new screening technologies to identify novel drugs against both known and orphan GPCRs.
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Gregory KJ, Sexton PM, Christopoulos A. Allosteric modulation of muscarinic acetylcholine receptors. Curr Neuropharmacol 2007; 5:157-67. [PMID: 19305798 PMCID: PMC2656816 DOI: 10.2174/157015907781695946] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2007] [Accepted: 04/05/2007] [Indexed: 11/22/2022] Open
Abstract
Muscarinic acetylcholine receptors (mAChRs) are prototypical Family A G protein coupled-receptors. The five mAChR subtypes are widespread throughout the periphery and the central nervous system and, accordingly, are widely involved in a variety of both physiological and pathophysiological processes. There currently remains an unmet need for better therapeutic agents that can selectively target a given mAChR subtype to the relative exclusion of others. The main reason for the lack of such selective mAChR ligands is the high sequence homology within the acetylcholine-binding site (orthosteric site) across all mAChRs. However, the mAChRs possess at least one, and likely two, extracellular allosteric binding sites that can recognize small molecule allosteric modulators to regulate the binding and function of orthosteric ligands. Extensive studies of prototypical mAChR modulators, such as gallamine and alcuronium, have provided strong pharmacological evidence, and associated structure-activity relationships (SAR), for a "common" allosteric site on all five mAChRs. These studies are also supported by mutagenesis experiments implicating the second extracellular loop and the interface between the third extracellular loop and the top of transmembrane domain 7 as contributing to the common allosteric site. Other studies are also delineating the pharmacology of a second allosteric site, recognized by compounds such as staurosporine. In addition, allosteric agonists, such as McN-A-343, AC-42 and N-desmethylclozapine, have also been identified. Current challenges to the field include the ability to effectively detect and validate allosteric mechanisms, and to quantify allosteric effects on binding affinity and signaling efficacy to inform allosteric modulator SAR.
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Affiliation(s)
| | | | - Arthur Christopoulos
- Drug Discovery Biology Laboratory, Department of Pharmacology, Monash University, Clayton, Victoria, 3800, Australia
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Eglen RM, Bosse R, Reisine T. Emerging concepts of guanine nucleotide-binding protein-coupled receptor (GPCR) function and implications for high throughput screening. Assay Drug Dev Technol 2007; 5:425-51. [PMID: 17638542 DOI: 10.1089/adt.2007.062] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Guanine nucleotide binding protein (G protein) coupled receptors (GPCRs) comprise one of the largest families of proteins in the human genome and are a target for 40% of all approved drugs. GPCRs have unique structural motifs that allow them to interact with a wide and diverse series of extracellular ligands, as well as intracellular proteins, G proteins, receptor activity-modifying proteins, arrestins, and indeed other receptors. This distinctive structure has led to numerous efforts to discover drugs against GPCRs with targeted therapeutic uses. Such "designer" drugs currently include allosteric regulators, inverse agonists, and drugs targeting hetero-oligomeric complexes. Moreover, the large family of orphan GPCRs provides a rich and novel field of targets to discover drugs with unique therapeutic properties. The numerous technologies to discover GPCR drugs have also greatly advanced over the years, facilitating compound screening against known and orphan GPCRs, as well as in the identification of unique designer GPCR drugs. Indeed, high throughput screening (HTS) technologies employing functional cell-based approaches are now widely used. These include measurement of second messenger accumulation such as cyclic AMP, calcium ions, and inositol phosphates, as well as mitogen-activated protein kinase activation, protein-protein interactions, and GPCR oligomerization. This review focuses on how the improved understanding of the molecular pharmacology of GPCRs, coupled with a plethora of novel HTS technologies, is leading to the discovery and development of an entirely new generation of GPCR-based therapeutics.
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Affiliation(s)
- Richard M Eglen
- Discovery and Research Reagents, PerkinElmer Life and Analytical Sciences, Waltham, MA 02451, USA.
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15
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Vistoli G, Pedretti A, Testa B, Matucci R. The conformational and property space of acetylcholine bound to muscarinic receptors: An entropy component accounts for the subtype selectivity of acetylcholine. Arch Biochem Biophys 2007; 464:112-21. [PMID: 17544360 DOI: 10.1016/j.abb.2007.04.022] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2007] [Accepted: 04/17/2007] [Indexed: 11/21/2022]
Abstract
The conformational behavior of receptor-bound acetylcholine (ACh) was investigated by molecular dynamics simulations. Based on the great similarity among muscarinic receptors, the study was focused on the human M(1), M(2), and M(5) receptors as previously modeled by us. The results showed that receptor-bound ACh was not frozen in a single preferred conformation but preserved an unexpected fraction of its conformational space. However, there were marked differences between the three receptors since the ligand was mostly trans in the M(1) receptor, equally distributed among trans and gauche conformers in M(2), and exclusively gauche in the M(5); the greater flexibility of M(2)-bound ACh was paralleled by the greater flexibility of the occupied M(2) binding site. By contrast, the property space of receptor-bound ACh, and particularly its virtual (computed, conformation-dependent) lipophilicity, was restricted to relatively narrow ranges optimal for successful interaction. Experimental binding investigations to the individual human M(1), M(2), and M(5) muscarinic receptors showed ACh to have a 10-fold higher affinity for the M(2) compared to the M(1) and M(5) receptors. This selectivity was not confirmed by the calculated binding scores, a fact postulated to be caused by the absence of an entropy component in such binding scores. Indeed, the Shannon entropy of all geometric and physicochemical properties monitored were markedly higher in M(2)-bound ACh compared to M(1)-bound and M(5)-bound ACh. This finding suggests that the selectivity profile of acetylcholine for the M(2) receptor is largely entropy-driven, a fact that might explain the intrinsic difficulty to design subtype-selective muscarinic agonists.
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Affiliation(s)
- Giulio Vistoli
- Istituto di Chimica Farmaceutica Pietro Pratesi, Facoltà di Farmacia, Università di Milano, Viale Abruzzi 42, I-20131 Milano, Italy.
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16
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Lanzafame AA, Sexton PM, Christopoulos A. Interaction Studies of Multiple Binding Sites on M4 Muscarinic Acetylcholine Receptors. Mol Pharmacol 2006; 70:736-46. [PMID: 16709648 DOI: 10.1124/mol.106.024711] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This study investigated the reciprocal cross-interactions between two distinct allosteric sites on the M(4) muscarinic acetylcholine receptor (mAChR) in the absence or presence of different orthosteric ligands. Initial studies revealed that two novel benzimidazole allosteric modulators, 17-beta-hydroxy-17-alpha-ethy nyl-delta(4)-androstano[3,2-b]pyrimido[1,2-a]benzimidazole (WIN 62,577) and 17-beta-hydroxy-17-alpha-ethynyl-5-alpha-androstano[3,2-b]pyrimido[1,2-a]benzimidazole (WIN 51,708), exhibited different degrees of positive, negative, or close-to-neutral cooperativity with the orthosteric site on M(1) or M(4) mAChRs, depending on the chemical nature of the orthosteric radioligand that was used [[(3)H]N-methylscopolamine ([(3)H]NMS) versus [(3)H]quinuclidinylbenzilate ([(3)H]QNB)]. The largest window for observing an effect (negative cooperativity) was noted for the combination of WIN 62,577 and [(3)H]QNB at the M(4) mAChR. Experiments involving the combination of these two ligands with unlabeled agonists [acetylcholine, 4-(m-chlorophenylcarbamoyloxy)-2-butynyltrimethylammonium (McN-A-343), or xanomeline] revealed low degrees of negative cooperativity between WIN 62,577 and each agonist, whereas stronger negative cooperativity was observed against atropine. It is interesting that when these experiments were repeated using the prototypical modulators heptane-1,7-bis-(dimethyl-3'-phthalimidopropyl)-ammonium bromide (C(7)/3-phth), alcuronium, or brucine (which act at a separate allosteric site), WIN 62,577 exhibited negative cooperativity with each modulator when the orthosteric site was unoccupied, but this switched to neutral cooperativity when the receptor was occupied by [(3)H]QNB. Dissociation kinetic experiments using [(3)H]NMS and combination of C(7)/3-phth with WIN 62,577 also provided evidence for neutral cooperativity between the two allosteric sites when the orthosteric site is occupied. Together, these results provide insight into the nature of the interaction between two distinct allosteric sites on the M(4) mAChR and how this interaction is perturbed upon occupancy of the orthosteric site.
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Affiliation(s)
- Alfred A Lanzafame
- Drug Discovery Biology Laboratory, Department of Pharmacology, Building 13E, Monash University, Clayton 3800, Victoria, Australia
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17
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Langmead CJ, Fry VAH, Forbes IT, Branch CL, Christopoulos A, Wood MD, Herdon HJ. Probing the Molecular Mechanism of Interaction between 4-n-Butyl-1-[4-(2-methylphenyl)-4-oxo-1-butyl]-piperidine (AC-42) and the Muscarinic M1 Receptor: Direct Pharmacological Evidence That AC-42 Is an Allosteric Agonist. Mol Pharmacol 2005; 69:236-46. [PMID: 16207821 DOI: 10.1124/mol.105.017814] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
4-n-Butyl-1-[4-(2-methylphenyl)-4-oxo-1-butyl]-piperidine hydrogen chloride (AC-42) is a selective agonist of the muscarinic M(1) receptor previously suggested to interact with an "ectopic" site on this receptor. However, the pharmacological properties of this site (i.e., whether it overlaps to any extent with the classic orthosteric site or represents a novel allosteric site) remain undetermined. In the present study, atropine or pirenzepine significantly inhibited the ability of either carbachol or AC-42 to stimulate inositol phosphate accumulation or intracellular calcium mobilization in Chinese hamster ovary (CHO) cells stably expressing the human M(1) receptor. However, the interaction between either of these antagonists and AC-42 was characterized by Schild slopes significantly less than unity. Increasing the concentrations of atropine revealed that the Schild regression was curvilinear, consistent with a negative allosteric interaction. More direct evidence for an allosteric mode of action of AC-42 was obtained in [(3)H]N-methylscopolamine ([(3)H]NMS) binding studies, in that both AC-42 and the prototypical modulator gallamine failed to fully inhibit specific [(3)H]NMS binding in a manner that was quantitatively described by an allosteric model applied to both modulator data sets. Furthermore, AC-42 and gallamine significantly retarded the rate of [(3)H]NMS dissociation from CHO-hM(1) cell membranes, conclusively demonstrating their ability to bind to a topographically distinct site to change M(1) receptor conformation. These data provide the first direct evidence that AC-42 is an allosteric agonist that activates M(1) receptors in the absence of the orthosteric agonist.
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Affiliation(s)
- Christopher J Langmead
- Psychiatry Centre of Excellence for Drug Discovery, GlaxoSmithKline, Third Ave., Harlow, Essex, CM19 5AW, UK.
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18
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Dei S, Angeli P, Bellucci C, Buccioni M, Gualtieri F, Marucci G, Manetti D, Matucci R, Romanelli MN, Scapecchi S, Teodori E. Muscarinic subtype affinity and functional activity profile of 1-methyl-2-(2-methyl-1,3-dioxolan-4-yl)pyrrolidine and 1-methyl-2-(2-methyl-1,3-oxathiolan-5-yl)pyrrolidine derivatives. Biochem Pharmacol 2005; 69:1637-45. [PMID: 15896343 DOI: 10.1016/j.bcp.2005.03.009] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2005] [Revised: 03/11/2005] [Accepted: 03/11/2005] [Indexed: 11/20/2022]
Abstract
Starting from two previously studied muscarinic full agonists, characterized by a 1,3-dioxolane ((+)-1) and a 1,3-oxathiolane ((+)-2) cycle, two new series of muscarinic ligands were designed, obtained by the steric complication of the parent compounds produced by freezing the aminoalkyl chain into a pyrrolidine ring. Both tertiary amines and the corresponding iodomethyl derivatives were synthesised and studied, and several compounds of the series which behaved as muscarinic agonists have been selected, on the basis of preliminary binding experiments on rat cortex homogenates, for the present work. Results are presented obtained from testing the affinity of the selected compounds against cloned human muscarinic receptors expressed in CHO cells, in order to evaluate subtype selectivity. Their functional activity on classical models of M1-M4 receptors, in guinea pig and rabbit tissues is also reported. With respect to parent compounds, the new molecules present some selectivity toward hm2 receptors; fair M2 selectivity is also evident in functional studies, where these compounds behave as partial agonists. Among the other compounds of the series (2S, 4'R, 2'S)-1,1-dimethyl-2-(2-methyl-1,3-dioxolan-4-yl)pyrrolidinium iodide (-)-3 and (2R, 5'S, 2'S)-1-methyl-2-(2-methyl-1,3-oxathiolan-5-yl)pyrrolidine (+)-5 present a promising pharmacological profile. Compound (-)-3 shows modest hm2 selectivity in binding experiments but a clearcut M2 selectivity in functional tests, where it behaves as a weak antagonist on M1 and M4 subtypes, as a weak full agonist on the M3 subtype and as a potent partial agonist on M2 subtype. Tertiary amine (+)-5 presents a quite similar profile but appears more interesting since, lacking a permanent charge on the nitrogen atom, it may represent an interesting tool to study CNS muscarinic receptors. Our results confirm that sterical complication of parent compounds (+)-1 and (+)-2 produces more selective muscarinic agonists.
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Affiliation(s)
- Silvia Dei
- Dipartimento di Scienze Farmaceutiche, Università di Firenze, via U. Schiff 6, 50019 Sesto Fiorentino (FI), Italy.
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19
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Jakubík J, Krejcí A, Dolezal V. Asparagine, Valine, and Threonine in the Third Extracellular Loop of Muscarinic Receptor Have Essential Roles in the Positive Cooperativity of Strychnine-Like Allosteric Modulators. J Pharmacol Exp Ther 2005; 313:688-96. [PMID: 15647330 DOI: 10.1124/jpet.104.080358] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We have investigated allosteric interactions of four closely related strychnine-like substances: Wieland-Gumlich aldehyde (WGA), propargyl Wieland-Gumlich aldehyde, strychnine, and brucine with N-methylscopolamine (NMS) on M(3) subtype of muscarinic receptor genetically modified in the second or the third extracellular loop to corresponding loops of M(2) subtype (M(3)o2 and M(3)o3 chimera). The M(3)o2 chimeric receptor The exhibited no change in either affinity of strychnine, brucine, and WGA or in cooperativity of brucine or WGA, whereas both parameters for propargyl-WGA changed. In contrast, there was a change in affinity of all tested modulators (except for brucine) and in their cooperativity in the M(3)o3 chimera. Directions of affinity changes in both chimeras were always toward values of the donor M(2) subtype, but changes in cooperativity were variable. Compared with the native M(3) receptor, strychnine displayed a slight increase in positive cooperativity and propargyl-WGA a robust decrease in negative cooperativity at M(3)o2 chimera. Similar changes were found in the M(3)o3 chimera. Interestingly, cooperativity of brucine and WGA at the M(3)o3 chimera changed from negative to positive. This is the first evidence of constitution of positive cooperativity of WGA by switching sequences of two parental receptors, both exhibiting negative cooperativity. Gradual replacement of individual amino acids revealed that only three residues (NVT of the o3 loop of the M(2) receptor) are involved in this effect. Data suggest that these amino acids are essential for propagation of a conformation change resulting in positive cooperativity induced by these modulators.
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Affiliation(s)
- J Jakubík
- Department of Neurochemistry, Institute of Physiology, Czech Academy Sciences, Prague.
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20
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Christopoulos A, May LT, Avlani VA, Sexton PM. G-protein-coupled receptor allosterism: the promise and the problem(s). Biochem Soc Trans 2004; 32:873-7. [PMID: 15494038 DOI: 10.1042/bst0320873] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Allosteric modulators of G-protein-coupled receptors interact with binding sites that are topographically distinct from the orthosteric site recognized by the receptor's endogenous agonist. Allosteric ligands offer a number of advantages over orthosteric drugs, including the potential for greater receptor subtype selectivity and a more ‘physiological’ regulation of receptor activity. However, the manifestations of allosterism at G-protein-coupled receptors are quite varied, and significant challenges remain for the optimization of screening methods to ensure the routine detection and validation of allosteric ligands.
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Affiliation(s)
- A Christopoulos
- Department of Pharmacology, University of Melbourne, Grattan St., Parkville, 3010, Victoria, Australia
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21
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Dambrova M, Chlopicki S, Liepinsh E, Kirjanova O, Gorshkova O, Kozlovski VI, Uhlen S, Liepina I, Petrovska R, Kalvinsh I. The methylester of gamma-butyrobetaine, but not gamma-butyrobetaine itself, induces muscarinic receptor-dependent vasodilatation. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 2004; 369:533-9. [PMID: 15060760 DOI: 10.1007/s00210-004-0925-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2003] [Accepted: 02/24/2004] [Indexed: 11/24/2022]
Abstract
Gamma-butyrobetaine (GBB) is known mostly as a bio-precursor of carnitine, a key molecule in the regulation of myocardial energy metabolism. The metabolites of carnitine and GBB were investigated for acetylcholine-like activity decades ago. The present study shows that the methylester of GBB (GBB-ME) exerts its biological activity by binding to muscarinic acetylcholine receptors. GBB-ME dose-dependently decreased the blood pressure in anaesthetised rats and also produced endothelium-dependent vasodilation in the isolated guinea-pig heart. The biological effects of GBB-ME were inhibited partially by the NOS inhibitor N(omega)-nitro-L-arginine methylester (L-NAME) and abolished by the acetylcholine receptor antagonist atropine, thus supporting the hypothesis that GBB-ME acts as muscarinic agonist. Moreover, we have shown here for the first time that GBB-ME binds directly to transfected human muscarinic (m) acetylcholine receptors, the potency order being m2>m5> or =m4> or =m1>m3. GBB itself showed neither biological activity nor significant affinity for the m1-5 receptors. We conclude that GBB-ME, but not the parent GBB, possesses acetylcholine-like activity in vivo and in vitro.
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Affiliation(s)
- Maija Dambrova
- Department of Medicinal Chemistry, Latvian Institute of Organic Synthesis, Aizkraukles 21, LV1006 Riga, Latvia.
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22
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Lanzafame A, Christopoulos A. Investigation of the interaction of a putative allosteric modulator, N-(2,3-diphenyl-1,2,4-thiadiazole-5-(2H)-ylidene) methanamine hydrobromide (SCH-202676), with M1 muscarinic acetylcholine receptors. J Pharmacol Exp Ther 2003; 308:830-7. [PMID: 14617684 DOI: 10.1124/jpet.103.060590] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The interaction between a novel G protein-coupled receptor modulator, N-(2,3-diphenyl-1,2,4-thiadiazole-5-(2H)-ylidene) methanamine hydrobromide (SCH-202676), and the M(1) muscarinic acetylcholine receptor (mAChR) was investigated. In contrast to the prototypical mAChR allosteric modulator, heptane 1,7-bis-(dimethyl-3'-phthalimidopropyl)-ammonium bromide (C(7)/3-phth), SCH-202676 had no effect on the dissociation kinetics of [(3)H]N-methylscopolamine ([(3)H]NMS) at M(1) mAChRs stably expressed in Chinese hamster ovary (CHO) cell membranes. However, SCH-202676 completely inhibited the binding of [(3)H]NMS in membrane preparations, with a Hill slope significantly greater than unity, indicative of positive cooperativity in the binding of the inhibitor. Moreover, SCH-202676 caused dextral shifts of the [(3)H]NMS saturation binding curve that were greater than expected for a competitive interaction. The addition of C(7)/3-phth (100 microM) had no significant effect on the inhibitory potency of SCH-202676. In contrast to the findings in cell membranes, the interaction between SCH-202676 and [(3)H]NMS in intact M(1) CHO cells yielded saturation and inhibition isotherms that were compatible with the predictions for a competitive interaction. Intact cell assays of acetylcholine-mediated phosphoinositide hydrolysis in the absence or presence of SCH-202676 revealed a mixed competitive/noncompetitive mode of interaction that was dependent on the concentration of SCH-202676. These data reveal that the nature of the interaction between SCH-202676 and the M(1) mAChR is dependent on whether it is studied using intact versus broken cell preparations. It is proposed that SCH-202676 uses a dual mode of ligand-receptor interaction involving both extra- and intracellular attachment points on the M(1) mAChR that are distinct from the allosteric binding site recognized by prototypical mAChR modulators such as C(7)/3-phth.
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Affiliation(s)
- Alfred Lanzafame
- Department of Pharmacology, University of Melbourne, Parkville, Victoria, Australia
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23
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Gharagozloo P, Lazareno S, Miyauchi M, Popham A, Birdsall NJM. Substituted pentacyclic carbazolones as novel muscarinic allosteric agents: synthesis and structure-affinity and cooperativity relationships. J Med Chem 2002; 45:1259-74. [PMID: 11881995 DOI: 10.1021/jm010946z] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Two series of pentacyclic carbazolones, 22 and 23, have been synthesized utilizing a facile intramolecular Dielsminus signAlder reaction and are allosteric modulators at muscarinic acetylcholine receptors. Their affinities and cooperativities with acetylcholine and the antagonist N-methylscopolamine (NMS) at M(1)minus signM(4) receptors have been analyzed and compared. All of the synthesized compounds are negatively cooperative with acetylcholine. In contrast, the majority of the compounds exhibit positive cooperativity with NMS, particularly at M(2) and M(4) receptors. The subtype selectivity, in terms of affinity, was in general M(2) > M(1) > M(4) > M(3). The largest increases in affinity produced by a single substitution of the core structure were given by the 1-OMe (22b) and 1-Cl (22d) derivatives. The position of the N in the ring did not appear to be important for binding affinity or cooperativity. Two compounds 22y and 23i, both trisubstituted analogues, were the most potent compounds synthesized, with dissociation constants of 30minus sign100 nM for the M(2) NMS-liganded and unliganded receptor, respectively. The results indicate that the allosteric site, like the primary binding site, is capable of high-affinity interactions with molecules of relatively low molecular weight.
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Affiliation(s)
- Parviz Gharagozloo
- MRC Technology Research Division, 1-3 Burtonhole Lane, Mill Hill, London, NW7 1AD, UK.
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24
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Christopoulos A. Allosteric binding sites on cell-surface receptors: novel targets for drug discovery. Nat Rev Drug Discov 2002; 1:198-210. [PMID: 12120504 DOI: 10.1038/nrd746] [Citation(s) in RCA: 493] [Impact Index Per Article: 22.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Cell-surface receptors are the targets for more than 60% of current drugs. Traditionally, optimizing the interaction of lead molecules with the binding site for the endogenous agonist (orthosteric site) has been viewed as the best means of achieving selectivity of action. However, recent developments have highlighted the fact that drugs can interact with binding sites on the receptor molecule that are distinct from the orthosteric site, known as allosteric sites. Allosteric modulators could offer several advantages over orthosteric ligands, including greater selectivity and saturability of their effect.
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Affiliation(s)
- Arthur Christopoulos
- Department of Pharmacology, University of Melbourne, Grattan Street, Parkville, Victoria 3010, Australia.
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25
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Christopoulos A. Quantification of Allosteric Interactions at G Protein Coupled Receptors Using Radioligand Binding Assays. ACTA ACUST UNITED AC 2001. [DOI: 10.1002/0471141755.ph0122s11] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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26
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Miyoshi S, Tu AT. A snake venom inhibitor to muscarinic acetylcholine receptor (mAChR): isolation and interaction with cloned human mAChR. Arch Biochem Biophys 2000; 377:290-5. [PMID: 10845706 DOI: 10.1006/abbi.2000.1784] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
An inhibitor to the muscarinic acetylcholine receptor (mAChR) was purified from the venom of Crotalus atrox (western diamondback rattlesnake). The inhibitor was found to be a 30-kDa homodimer protein with phospholipase A2 activity. In order to determine the subtype selectivity of the purified inhibitor, the inhibitory effect on the binding of two orthosteric antagonists, [3H]quinuclidinyl benzilate ([3H]QNB) and [3H]N-methylscopolamine methyl chloride ([3H]NMS), to five subtypes of cloned human mAChR was tested. The purified inhibitor reduced the binding of [3H]QNB and/or [3H]NMS to all subtypes of the mAChR while showing the highest inhibitory effect on the M5 subtype. The Kd values of the receptors for the antagonists were increased in the presence of the inhibitor; however, the Bmax values were not changed. The effects of the purified inhibitor on the dissociation of [3H]NMS from the receptors were also investigated. Dissociation of the antagonist was remarkably slowed down by addition of the inhibitor. These findings may suggest an allosteric action of the purified inhibitor. In addition, the present study indicates that the presence of mAChR inhibitors is quite common in snake venoms.
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Affiliation(s)
- S Miyoshi
- Department of Biochemistry and Molecular Biology, Colorado State University, Fort Collins 80523, USA
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27
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Grant MK, Christopoulos A, El-Fakahany EE. Regulation of acetylcholine binding by ATP at the muscarinic M(1) receptor in intact CHO cells. Brain Res 1999; 839:94-9. [PMID: 10482803 DOI: 10.1016/s0006-8993(99)01720-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
ATP may have a modulatory effect on cholinergic transmission, as it is known that ATP is released as a co-transmitter with acetylcholine from nerve terminals. The ability of ATP to influence the binding of acetylcholine to the M(1) muscarinic acetylcholine receptor expressed in intact CHO cells was investigated. In competition binding experiments, acetylcholine completely inhibited the binding of [3H]N-methylscopolamine, but yielded a shallow competition isotherm that was best described in terms of two affinity states. When these experiments were repeated in the presence of 1 mM ATP, the acetylcholine competition curve was better described in terms of a single, low-affinity state with a Hill slope not significantly different from unity. This modulatory effect of ATP was completely reversed by the addition of the P(2) purinoceptor antagonist, suramin, to the assay medium. When the competition between the muscarinic receptor antagonist, atropine, and [3H]N-methylscopolamine was investigated, however, ATP was unable to modulate the binding of atropine, which was consistent with a one-site binding model in each instance. In contrast to the intact cell studies, ATP did not affect either affinity state of acetylcholine binding when studied in homogenate preparations. The results of the present study indicate that ATP, acting via endogenously expressed purinoceptors, is able to influence agonist binding to the M(1) muscarinic acetylcholine receptor via a cross-talk that requires the functional integrity of intact CHO cells.
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Affiliation(s)
- M K Grant
- Department of Psychiatry, Pharmacology and Neuroscience, University of Minnesota Medical School, Minneapolis, MN 55455, USA
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