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GABA B Receptor Chemistry and Pharmacology: Agonists, Antagonists, and Allosteric Modulators. Curr Top Behav Neurosci 2021; 52:81-118. [PMID: 34036555 DOI: 10.1007/7854_2021_232] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
The GABAB receptors are metabotropic G protein-coupled receptors (GPCRs) that mediate the actions of the primary inhibitory neurotransmitter, γ-aminobutyric acid (GABA). In the CNS, GABA plays an important role in behavior, learning and memory, cognition, and stress. GABA is also located throughout the gastrointestinal (GI) tract and is involved in the autonomic control of the intestine and esophageal reflex. Consequently, dysregulated GABAB receptor signaling is associated with neurological, mental health, and gastrointestinal disorders; hence, these receptors have been identified as key therapeutic targets and are the focus of multiple drug discovery efforts for indications such as muscle spasticity disorders, schizophrenia, pain, addiction, and gastroesophageal reflex disease (GERD). Numerous agonists, antagonists, and allosteric modulators of the GABAB receptor have been described; however, Lioresal® (Baclofen; β-(4-chlorophenyl)-γ-aminobutyric acid) is the only FDA-approved drug that selectively targets GABAB receptors in clinical use; undesirable side effects, such as sedation, muscle weakness, fatigue, cognitive deficits, seizures, tolerance and potential for abuse, limit their therapeutic use. Here, we review GABAB receptor chemistry and pharmacology, presenting orthosteric agonists, antagonists, and positive and negative allosteric modulators, and highlight the therapeutic potential of targeting GABAB receptor modulation for the treatment of various CNS and peripheral disorders.
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Kniazeff J. The different aspects of the GABAB receptor allosteric modulation. FROM STRUCTURE TO CLINICAL DEVELOPMENT: ALLOSTERIC MODULATION OF G PROTEIN-COUPLED RECEPTORS 2020; 88:83-113. [DOI: 10.1016/bs.apha.2020.02.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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Cunningham JJ, Orr E, Lothian BC, Morgen J, Brebner K. Effects of fendiline on cocaine-seeking behavior in the rat. Psychopharmacology (Berl) 2015; 232:4401-10. [PMID: 26345344 DOI: 10.1007/s00213-015-4061-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/27/2015] [Accepted: 08/27/2015] [Indexed: 11/26/2022]
Abstract
RATIONALE L-type Ca(2+) channels (LTCC) and GABAB receptors are both possible targets in the development of new pharmacological compounds for cocaine addiction. Drugs that target either receptor attenuate a wide range of cocaine-seeking behaviors in the rat. However, there is no current human-approved pharmacotherapeutic intervention for psychostimulant addiction. OBJECTIVES This study examined the effects of a human-approved LTCC blocker, fendiline, on cocaine-taking and cocaine-seeking behavior in rats. The effects of combining fendiline with the GABAB receptor agonist baclofen on cocaine self-administration were also tested. METHODS Male Wistar rats were trained to self-administer cocaine, and the effects of fendiline pretreatment (vehicle, 1.78, 3.16, 5.62 mg/kg, intraperitoneal (IP)) were tested on progressive ratio responding and cue- and drug-induced reinstatement. The effects of baclofen (vehicle, 0.56, 1.78, 3.16, 5.62 mg/kg, IP) combined with fendiline (5.62 mg/kg, IP) were tested on progressive ratio responding. Control experiments measured locomotor activity and lever pressing for food in rats that received both baclofen and fendiline prior to the test session. RESULTS Acute injections of fendiline prior to cue- or drug-induced reinstatement significantly attenuated lever-pressing behavior (p < 0.05). Fendiline and baclofen, but not fendiline alone, not only significantly attenuated breakpoints, but also impaired general motor behavior and naturalistic reinforcement (p < 0.05). CONCLUSION These data suggest that the LTCC blocker fendiline may represent a novel pharmacotherapeutic intervention to prevent reinstatement to cocaine seeking. Also, co-administration of fendiline and baclofen not only can attenuate the motivation to take cocaine, but also impairs general motor behavior and naturalistic reinforcement.
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Affiliation(s)
- Jonathan J Cunningham
- Department of Psychiatry, University of British Columbia, Detwiller Pavilion, 2255 Wesbrook Mall, Vancouver, British Columbia, V6T 2A1, Canada.
| | - Erin Orr
- Department of Psychology, St. Francis Xavier University, 2320 Notre Dame Blvd., Antigonish, Nova Scotia, B2G 2W5, Canada
| | - Barbara C Lothian
- Department of Psychology, St. Francis Xavier University, 2320 Notre Dame Blvd., Antigonish, Nova Scotia, B2G 2W5, Canada
| | - Jennifer Morgen
- Department of Psychology, St. Francis Xavier University, 2320 Notre Dame Blvd., Antigonish, Nova Scotia, B2G 2W5, Canada
| | - Karen Brebner
- Department of Psychology, St. Francis Xavier University, 2320 Notre Dame Blvd., Antigonish, Nova Scotia, B2G 2W5, Canada.
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Brown KM, Roy KK, Hockerman GH, Doerksen RJ, Colby DA. Activation of the γ-Aminobutyric Acid Type B (GABA(B)) Receptor by Agonists and Positive Allosteric Modulators. J Med Chem 2015; 58:6336-47. [PMID: 25856547 DOI: 10.1021/jm5018913] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Since the discovery of the GABA(B) agonist and muscle relaxant baclofen, there have been substantial advancements in the development of compounds that activate the GABA(B) receptor as agonists or positive allosteric modulators. For the agonists, most of the existing structure-activity data apply to understanding the role of substituents on the backbone of GABA as well as replacing the carboxylic acid and amine groups. In the cases of the positive allosteric modulators, the allosteric binding site(s) and structure-activity relationships are less well-defined; however, multiple classes of molecules have been discovered. The recent report of the X-ray structure of the GABA(B) receptor with bound agonists and antagonists provides new insights for the development of compounds that bind the orthosteric site of this receptor. From a therapeutic perspective, these data have enabled efforts in drug discovery in areas of addiction-related behavior, the treatment of anxiety, and the control of muscle contractility.
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Affiliation(s)
- Katie M Brown
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University , West Lafayette, Indiana 47907, United States
| | - Kuldeep K Roy
- Department of Biomolecular Sciences, University of Mississippi , University, Mississippi 38677, United States
| | - Gregory H Hockerman
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University , West Lafayette, Indiana 47907, United States
| | - Robert J Doerksen
- Department of Biomolecular Sciences, University of Mississippi , University, Mississippi 38677, United States
| | - David A Colby
- Department of Biomolecular Sciences, University of Mississippi , University, Mississippi 38677, United States
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van der Westhuizen ET, Valant C, Sexton PM, Christopoulos A. Endogenous Allosteric Modulators of G Protein–Coupled Receptors. J Pharmacol Exp Ther 2015; 353:246-60. [DOI: 10.1124/jpet.114.221606] [Citation(s) in RCA: 106] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
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Effect of fendiline on the maintenance and expression of methamphetamine-induced conditioned place preference in Sprague-Dawley rats. Psychopharmacology (Berl) 2014; 231:2019-29. [PMID: 24264565 PMCID: PMC3988275 DOI: 10.1007/s00213-013-3347-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/20/2013] [Accepted: 10/25/2013] [Indexed: 01/30/2023]
Abstract
RATIONALE Fendiline is a GABAB receptor-positive allosteric modulator and L-type Ca²⁺ channel blocker that is safe for human use. Based on these pharmacological properties, fendiline may be useful to disrupt associative memories that can drive relapse to drug use in drug-addicted individuals OBJECTIVE The current study evaluated the potential of fendiline to inhibit the maintenance and expression of learned associations between methamphetamine (meth) and an environmental context using conditioned place preference (CPP) in rats, to model for the associative learning that occurs during drug abuse by humans METHODS Following meth conditioning (1 mg/kg), fendiline (5 mg/kg) was administered at various post-conditioning times to ascertain if there was a temporal window during which fendiline would be effective. RESULTS Two once-daily injections of fendiline did not influence the maintenance of CPP regardless of the post-conditioning treatment time while 10 once-daily fendiline treatments inhibited CPP maintenance (p < 0.05). Fendiline administered immediately prior to the CPP test inhibited expression of meth-induced CPP in rats with a fendiline treatment history of 10 once-daily injections (p < 0.05) or those that received two injections that corresponded to the last 2 days of the 10-day treatment (p < 0.05). Fendiline did not produce preference or aversion on its own, nor did it alter motivated motor behavior. CONCLUSION Maintenance and expression of meth CPP is mitigated by repeated fendiline treatments when administered during the days that precede CPP testing. Reduction in the significance of meth-associated cues can reduce relapse; therefore, fendiline may be of value for addiction therapy in abstinent, meth-addicted humans.
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Urwyler S. Allosteric modulation of family C G-protein-coupled receptors: from molecular insights to therapeutic perspectives. Pharmacol Rev 2011; 63:59-126. [PMID: 21228259 DOI: 10.1124/pr.109.002501] [Citation(s) in RCA: 164] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Allosteric receptor modulation is an attractive concept in drug targeting because it offers important potential advantages over conventional orthosteric agonism or antagonism. Allosteric ligands modulate receptor function by binding to a site distinct from the recognition site for the endogenous agonist. They often have no effect on their own and therefore act only in conjunction with physiological receptor activation. This article reviews the current status of allosteric modulation at family C G-protein coupled receptors in the light of their specific structural features on the one hand and current concepts in receptor theory on the other hand. Family C G-protein-coupled receptors are characterized by a large extracellular domain containing the orthosteric agonist binding site known as the "venus flytrap module" because of its bilobal structure and the dynamics of its activation mechanism. Mutational analysis and chimeric constructs have revealed that allosteric modulators of the calcium-sensing, metabotropic glutamate and GABA(B) receptors bind to the seven transmembrane domain, through which they modify signal transduction after receptor activation. This is in contrast to taste-enhancing molecules, which bind to different parts of sweet and umami receptors. The complexity of interactions between orthosteric and allosteric ligands is revealed by a number of adequate biochemical and electrophysiological assay systems. Many allosteric family C GPCR modulators show in vivo efficacy in behavioral models for a variety of clinical indications. The positive allosteric calcium sensing receptor modulator cinacalcet is the first drug of this type to enter the market and therefore provides proof of principle in humans.
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Affiliation(s)
- Stephan Urwyler
- Department of Chemistry and Biochemistry, University of Berne, P/A Weissensteinweg 3, CH-3303 Jegenstorf, Berne, Switzerland.
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Pin JP, Prézeau L. Allosteric modulators of GABA(B) receptors: mechanism of action and therapeutic perspective. Curr Neuropharmacol 2010; 5:195-201. [PMID: 19305802 PMCID: PMC2656813 DOI: 10.2174/157015907781695919] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2007] [Accepted: 04/05/2007] [Indexed: 12/19/2022] Open
Abstract
γ-aminobutyric acid (GABA) plays important roles in the central nervous system, acting as a neurotransmitter on both ionotropic ligand-gated Cl--channels, and metabotropic G-protein coupled receptors (GPCRs). These two types of receptors called GABAA (and C) and GABAB are the targets of major therapeutic drugs such as the anxiolytic benzodiazepines, and antispastic drug baclofen (lioresal®), respectively. Although the multiplicity of GABAA receptors offer a number of possibilities to discover new and more selective drugs, the molecular characterization of the GABAB receptor revealed a unique, though complex, heterodimeric GPCR. High throughput screening strategies carried out in pharmaceutical industries, helped identifying new compounds positively modulating the activity of the GABAB receptor. These molecules, almost devoid of apparent activity when applied alone, greatly enhance both the potency and efficacy of GABAB agonists. As such, in contrast to baclofen that constantly activates the receptor everywhere in the brain, these positive allosteric modulators induce a large increase in GABAB-mediated responses only WHERE and WHEN physiologically needed. Such compounds are then well adapted to help GABA to activate its GABAB receptors, like benzodiazepines favor GABAA receptor activation. In this review, the way of action of these molecules will be presented in light of our actual knowledge of the activation mechanism of the GABAB receptor. We will then show that, as expected, these molecules have more pronounced in vivo responses and less side effects than pure agonists, offering new potential therapeutic applications for this new class of GABAB ligands.
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Huang C, Huang C, Cheng J, Liu S, Chen I, Tsai J, Chou C, Tseng P, Jan C. Fendiline-evoked [Ca2+]i rises and non-Ca2+-triggered cell death in human oral cancer cells. Hum Exp Toxicol 2009; 28:41-8. [PMID: 19411560 DOI: 10.1177/0960327108097436] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The effect of fendiline on cytosolic free Ca(2+) concentrations ([Ca(2+)](i)) and proliferation has not been explored in human oral cancer cells. This study examined whether fendiline altered Ca(2+) levels and caused cell death in OC2 human oral cancer cells. [Ca(2+)](i) and cell viability were measured using the fluorescent dyes fura-2 and WST-1, respectively. Fendiline at concentrations above 10 microM increased [Ca(2+)](i) in a concentration-dependent manner. The Ca(2+) signal was reduced partly by removing extracellular Ca(2+). The fendiline-induced Ca(2+) influx was sensitive to blockade of L-type Ca(2+) channel blockers. In Ca(2+)-free medium, after pretreatment with 50 microM fendiline, 1 microM thapsigargin (an endoplasmic reticulum Ca(2+) pump inhibitor)-induced [Ca(2+)](i) rises were inhibited; and conversely, thapsigargin pretreatment nearly abolished fendiline-induced [Ca(2+)](i) rises. Inhibition of phospholipase C with 2 microM U73122 did not change fendiline-induced [Ca(2+)](i) rises. At concentrations between 5 and 25 microM, fendiline killed cells in a concentration-dependent manner. The cytotoxic effect of 15 microM fendiline was not reversed by prechelating cytosolic Ca(2+) with BAPTA/AM. Collectively, in OC2 cells, fendiline induced [Ca(2+)](i) rises by causing Ca(2+) release from the endoplasmic reticulum and Ca(2+) influx from L-type Ca(2+) channels. Furthermore, fendiline-caused cytotoxicity was not via a preceding [Ca(2+)](i) rise.
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Affiliation(s)
- Cc Huang
- Department of Nursery, Tzu Hui Institute of Technology; Pingtung, Taiwan
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Abstract
CGP7930 (3-(3',5'-Di-tert-butyl-4'-hydroxy)phenyl-2,2-dimethylpropanol) is a positive allosteric modulator of the metabotropic GABAB receptor. CGP7930 has been found to modulate the GABAB receptor in the open, or high affinity, state increasing agonist affinity for the receptor and signal transduction efficacy following agonist stimulation. The GABAB heteromeric subunit B2, involved in signal transduction but not ligand binding, seems to be the site of action of CGP7930 and similar allosteric modulators. When administered alone in naïve animals, CGP7930 acts as an anxiolytic in rodents without other overt behavioral effects and has also been demonstrated to reduce self-administration of nicotine, cocaine, or alcohol in rodents, suggesting that "fine tuning" of the GABAB receptor by positive allosteric modulators may be able to regulate abuse of these drugs. Baclofen, the GABAB agonist, is currently finding use in treating addiction and various other disorders, but this can result in off-target effects and tolerance. CGP7930 when co-administered with baclofen enhances its potency, which could in theory minimize deleterious effects. Further study of CGP7930 is required, but this compound, and others like it, holds potential in a clinical setting.
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Affiliation(s)
- C L Adams
- Department of Pharmaceutical Biology, Victorian College of Pharmacy, Monash University, Australia
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Mannoury la Cour C, Herbelles C, Pasteau V, de Nanteuil G, Millan MJ. Influence of positive allosteric modulators on GABA(B) receptor coupling in rat brain: a scintillation proximity assay characterisation of G protein subtypes. J Neurochem 2007; 105:308-23. [PMID: 18021295 DOI: 10.1111/j.1471-4159.2007.05131.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Little is known concerning coupling of cerebral GABA(B) receptors to G protein subtypes, and the influence of positive allosteric modulators (PAMs) has not been evaluated. These questions were addressed by an antibody-capture/scintillation proximity assay strategy. GABA concentration-dependently enhanced the magnitude of [(35)S]GTPgammaS binding to Galphao and, less markedly, Galphai(1/3) in cortex, whereas Gq and Gs/olf were unaffected. (R)-baclofen and SKF97581 likewise activated Galphao and Galphai(1/3), expressing their actions more potently than GABA. Similar findings were acquired in hippocampus and cerebellum, and the GABA(B) antagonist, CGP55845A, abolished agonist-induced activation of Galphao and Galphai(1/3) in all structures. The PAMs, GS39783, CGP7930 and CGP13501, inactive alone, enhanced efficacy and potency of agonist-induced [(35)S]GTPgammaS binding to Galphao in all regions, actions abolished by CGP55845A. In contrast, they did not modify efficacies at Galphai(1/3). Similarly, in human embryonic kidney cells expressing GABA(B(1a+2)) or GABA(B(1b+2)) receptors, allosteric modulators did not detectably enhance efficacy of GABA at Galphai(1/3), though they increased its potency. To summarise, GABA(B) receptors coupled both to Galphao and to Galphai, but not Gq and Gs/olf, in rat brain. PAMs more markedly enhanced efficacy of coupling to Go versus Gi(1/3). It will be of interest to confirm these observations employing complementary techniques and to evaluate their potential therapeutic significance.
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Abstract
The past decade has witnessed a significant growth in the identification of allosteric modulators of G protein-coupled receptors (GPCRs), i.e., ligands that interact with binding sites that are topographically distinct from the orthosteric site recognized by the receptor's endogenous agonist. Because of their ability to modulate receptor conformations in the presence of orthosteric ligand, allosteric modulators can "fine-tune" classical pharmacological responses. This is advantageous in terms of a potential for engendering greater GPCR subtype-selectivity, but represents a significant challenge for detecting and validating allosteric behaviors. Although allosteric sites need not have evolved to accommodate endogenous ligands, there are a number of examples of where such modulators have been shown to contribute to physiological or pathophysiological processes. Studies are also beginning to unravel the structural basis of allosteric modulation of GPCRs. It remains to be determined whether such modulation represents interactions within monomers versus across dimers.
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Affiliation(s)
- Lauren T May
- Department of Pharmacology, University of Melbourne, 3010 Parkville, Victoria
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Asay MJ, Boyd SK. Characterization of the binding of [3H]CGP54626 to GABAB receptors in the male bullfrog (Rana catesbeiana). Brain Res 2006; 1094:76-85. [PMID: 16725130 DOI: 10.1016/j.brainres.2006.03.008] [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: 11/07/2005] [Revised: 03/06/2006] [Accepted: 03/07/2006] [Indexed: 10/24/2022]
Abstract
Gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the vertebrate brain. GABA activates both ionotropic (GABA(A)) and metabotropic (GABA(B)) receptors in mammals. Whether non-mammalian vertebrates possess receptors with similar characteristics is not well understood. We used a mammalian GABA(B)-specific antagonist to determine the pharmacology of putative receptors in the brain of an anuran amphibian, the male bullfrog (Rana catesbeiana). Receptor binding assays with the antagonist [(3)H]CGP54626 revealed a single class of high affinity binding sites (with a K(D) of 2.97 nM and a B(max) of 2619 fmol/mg protein). Binding was time- and temperature-dependent, saturable and specific. Specific binding of [(3)H]CGP54626 was inhibited by several mammalian GABA(B) receptor agonists and antagonists. The rank order potency of agonists was: GABA = SKF97541 > (R)-Baclofen > 3-APPA. The rank order for antagonists was: CGP54626 = CGP55845 > CGP52432 > CGP35348. The GABA(A) receptor ligands muscimol and SR95531 had very low affinity for [(3)H]CGP54626 binding sites, while bicuculline compounds had no affinity. Binding of GABA was positively modulated by CGP7930. Taurine did not allosterically modulate GABA binding but did inhibit [(3)H]CGP54626 binding in a linear fashion. Bullfrog brain thus possesses binding sites with significant similarity to mammalian GABA(B) receptors. These receptors differ from mammalian receptors, however, in dissociation kinetics, ligand specificity and allosteric modulation.
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Affiliation(s)
- Matthew J Asay
- Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA.
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Christiansen B, Wellendorph P, Bräuner-Osborne H. Activity of L-alpha-amino acids at the promiscuous goldfish odorant receptor 5.24. Eur J Pharmacol 2006; 536:98-101. [PMID: 16546162 DOI: 10.1016/j.ejphar.2006.02.015] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2006] [Accepted: 02/10/2006] [Indexed: 10/24/2022]
Abstract
The goldfish odorant receptor 5.24 is a member of family C of G protein-coupled receptors and is closely related to the human receptor GPRC6A. Receptor 5.24 has previously been shown to have binding affinity for L-alpha-amino acids, especially the basic amino acids arginine and lysine. Here we report the agonist activities of the 20 proteinogenic L-alpha-amino acids, and L-ornithine and L-citrulline, measured in an intracellular calcium release assay in mammalian tsA cells. The results show that receptor 5.24 is broadly activated by 19 of the tested L-alpha-amino acids and displays a preference for basic amino acids.
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Affiliation(s)
- Bolette Christiansen
- Department of Medicinal Chemistry, Danish University of Pharmaceutical Sciences, 2 Universitetsparken, DK-2100 Copenhagen, Denmark
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Abstract
Metabotropic gamma-aminobutyric acid(B) (GABAB) receptors for the major inhibitory transmitter GABA, together with metabotropic glutamate (mGLuRs) receptors, the extracellular calcium-sensing receptors (CaSRs), some V2R pheromone receptors and T1R taste receptors, belong to the family of 3 G-protein-coupled receptors (GPCRs). GABAB receptors are known to control neuronal excitability and modulate synaptic neurotransmission, playing a very important role in many physiological activities. These receptors are widely expressed and distributed in the nervous system and have been implicated in a variety of neurodegenerative and pathophysiological disorders including epilepsy, spasticity, chronic pain, depression, schizophrenia and drug addiction. To form a functional receptor entity, GABAB receptors must exist as a heterodimer consisting of GABAB1 and GABAB2 receptor subtypes with two 7-transmembrane proteins, and these subunits arise from distinct genes. The GABAB1 subunit binds the endogenous ligand within its extracellular N-terminus, whilst the GABAB2 subunit is not only essential for the correct trafficking of the GABAB1 subunit to the cell surface, but is also responsible for the interaction of the receptor with its cognate G-protein. Allosteric modulation has recently been recognized as an alternative pharmacological approach to gain selectivity in drug action. It is now generally accepted that modulators acting at the allosteric sites provide a novel perspective for the development of subtype-selective agents acting at GPCRs. These agents interact with allosteric binding sites quite separate from the highly conserved agonist binding region. In this review, we present a new class of phenylalkylamines, based on the lead compound fendiline, that are potent positive potentiators of GABAB receptor-mediated function and discuss their putative clinical applications. It is proposed that these new modulators may have therapeutic value in GABAB receptor pharmacology and are capable of selectively modifying GABAB receptor function. The allosteric modulators are offering an attractive and novel means to identify new leads, that are devoid of side effects associated with GABAB receptor agonists, and may, therefore, represent a major advance in the drug discovery process.
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Affiliation(s)
- Jennifer Ong
- Department of Anaesthesia and Intensive Care, The University of Adelaide, Australia.
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Chen Y, Phillips K, Minton G, Sher E. GABA(B) receptor modulators potentiate baclofen-induced depression of dopamine neuron activity in the rat ventral tegmental area. Br J Pharmacol 2005; 144:926-32. [PMID: 15711597 PMCID: PMC1576072 DOI: 10.1038/sj.bjp.0706100] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
2,6-Di-tert-butyl-4-(3-hydroxy-2,2-dimethyl-propyl)-phenol (CGP7930) is a recently reported positive allosteric modulator of gamma-aminobutyric acid (GABA)(B) receptors. In this study, we assessed the ability of CGP7930 to modulate the baclofen-induced depression of dopamine (DA) neuron activity via the activation of GABA(B) receptors in the ventral tegmental area in rat midbrain slices. The selective GABA(B) receptor agonist, baclofen, depressed the spontaneous firing rate of DA neurons in a concentration-dependent manner (EC50 = 0.27 microM, n = 11). CGP7930 (30 microM) significantly (P < 0.05) shifted the baclofen concentration-response curve to the left (EC50 = 0.15 microM, n = 5). The effects of baclofen alone or baclofen coapplied with CGP7930 were fully blocked by 1 microM (2S)-3-[[(1S)-1-(3,4-dichloropheny)ethyl]amino-2-hydroxypropyl] (phenylmethyl) phosphinic acid (CGP55845), a potent and selective GABA(B) receptor antagonist. In similar experiments, N-[3,3-diphenylpropyl]-alpha-methylbenzylamine (fendiline) (30 or 50 microM), a compound shown to potentiate GABA(B) receptor-mediated cortical hyperpolarisation, also significantly enhanced the inhibitory effect of baclofen. It is therefore concluded that the recently reported GABA(B) receptor modulators, CGP7930 and fendiline, can enhance GABA(B) receptor-mediated depression of DA neuronal activity. This finding suggests a therapeutic potential for GABA(B) potentiators for the treatment of diseases associated with a hyperfunctional mesocorticolimbic system.
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Affiliation(s)
- Ying Chen
- Eli Lilly & Co. Ltd, Erl Wood Manor, Sunninghill Road, Windlesham, Surrey GU20 6PH.
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Olianas MC, Ambu R, Garau L, Onali P. Allosteric modulation of GABA(B) receptor function in human frontal cortex. Neurochem Int 2005; 46:149-58. [PMID: 15627515 DOI: 10.1016/j.neuint.2004.08.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2004] [Accepted: 08/06/2004] [Indexed: 12/01/2022]
Abstract
In the present study, the effects of different allosteric modulators on the functional activity of gamma-aminobutyric acid (GABA)B receptors in membranes of post-mortem human frontal cortex were examined. Western blot analysis indicated that the tissue preparations expressed both GABA(B1) and GABA(B2) subunits of the GABA(B) receptor heterodimer. In [35S]-GTPgammaS binding assays, Ca2+ ion (1 mM) enhanced the potency of the agonists GABA and 3-aminopropylphosphinic acid (3-APA) and that of the antagonist CGP55845, but not that of the GABA(B) receptor agonist (-)-baclofen. CGP7930 (2,6-di-t-Bu-4-(3-hydroxy-2,2-dimethyl-propyl)-phenol), a positive allosteric modulator of GABA(B) receptors, potentiated both GABA(B) receptor-mediated stimulation of [35S]-GTPgammaS binding and inhibition of forskolin (FSK)-stimulated adenylyl cyclase activity. Chelation of Ca2+ ion by EGTA reduced the CGP7930 enhancement of GABA potency in stimulating [35S]-GTPgammaS binding by two-fold. Fendiline, also reported to act as a positive allosteric modulator of GABA(B) receptors, failed to enhance GABA stimulation of [35S]-GTPgammaS binding but inhibited the potentiating effect of CGP7930. The inhibitory effect was mimicked by the phenothiazine antipsychotic trifluoperazine (TFP), but not by other compounds, such as verapamil or diphenydramine (DPN). These data demonstrate that the function of GABA(B) receptors of human frontal cortex is positively modulated by Ca2+ ion and CGP7930, which interact synergistically. Conversely, fendiline and trifluoperazine negatively affect the allosteric regulation by CGP7930.
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Affiliation(s)
- Maria C Olianas
- Department of Neuroscience, Section of Biochemical Pharmacology, University of Cagliari, 09042 Monserrato, CA, Italy
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