Mechanisms of allosteric modulation at GABA receptors by CGP7930 and GS39783: effects on affinities and efficacies of orthosteric ligands with distinct intrinsic properties

Urwyler, Stephan; Gjoni, Tina; Koljatić, Jelena; Dupuis, Delphine S.

doi:10.1016/j.neuropharm.2004.10.013

Cited by 67 publications

(55 citation statements)

References 33 publications

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“…Thus, PAMs have recently been proposed as therapeutically superior drugs with respect to undesired side effects Koek et al, 2010). In fact, GS-39783 (novel GABA B receptor PAM) was shown to increase in vitro the GABA B receptor agonist affinity and potency, as well as the capacity of GABA to reduce cAMP production (Urwyler et al, 2005). In our hands, this compound exerted the same anxiolyticlike responses on the behavioral level as described elsewhere Cryan et al, 2004;Jacobson and Cryan, 2008).…”

Section: Discussionsupporting

confidence: 70%

Biphasic Effects of Cannabinoids in Anxiety Responses: CB1 and GABAB Receptors in the Balance of GABAergic and Glutamatergic Neurotransmission

Rey

Purrio

Viveros

et al. 2012

Neuropsychopharmacol

282

198

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Biphasic effects of cannabinoids have been shown in processes such as feeding behavior, motor activity, motivational processes and anxiety responses. Using two different tests for the characterization of anxiety-related behavior (elevated plus-maze and holeboard), we first identified in wild-type C57BL/6N mice, two doses of the synthetic CB1 cannabinoid receptor agonist CP-55,940 with anxiolytic (1 mg/kg) and anxiogenic properties (50 mg/kg), respectively. To clarify the role of CB1 receptors in this biphasic effect, both doses were applied to two different conditional CB1 receptor knockout (KO) mouse lines, GABA-CB1-KO (CB1 receptor inactivation in forebrain GABAergic neurons) and Glu-CB1-KO (CB1 receptor inactivation in cortical glutamatergic neurons). We found that the anxiolytic-like effects of the low dose of cannabinoids are mediated via the CB1 receptor on cortical glutamatergic terminals, because this anxiolytic-like response was abrogated only in Glu-CB1-KO mice. On the contrary, the CB1 receptor on the GABAergic terminals is required to induce an anxiogenic-like effect under a high-dose treatment because of the fact that this effect was abolished specifically in GABA-CB1-KO mice. These experiments were carried out in both sexes, and no differences occurred with the doses tested in the mutant mice. Interestingly, the positive allosteric modulation of GABA B receptor with GS-39783 was found to largely abrogate the anxiogenic-like effect of the high dose of CP-55,940. Our results shed new light in further understanding the biphasic effects of cannabinoids at the molecular level and, importantly, pave the way for the development of novel anxiolytic cannabinoid drugs, which may have favorable effect profiles targeting the CB1 receptor on glutamatergic terminals.

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Section: Discussionsupporting

confidence: 70%

Biphasic Effects of Cannabinoids in Anxiety Responses: CB1 and GABAB Receptors in the Balance of GABAergic and Glutamatergic Neurotransmission

Rey

Purrio

Viveros

et al. 2012

Neuropsychopharmacol

282

198

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“…It is likely that apparent partial agonistic activity of positive modulator compounds depends on the expression systems used and requires assays with considerable receptor reserve, such as the inositol phosphate production assay used by Binet et al (2004). Similar observations have been made for both CGP7930 and GS39783 in a cAMP assay using a cell line stably expressing GABA B receptors (Urwyler et al, 2005). However, the lack of significant agonistic activity of GS39783 observed in the present study is in agreement with in vitro assays (Urwyler et al, 2003) and with in vivo experiments in which orally applied GS39783 lacked effects on its own but, together with a threshold concentration of the agonist baclofen, significantly decreased cAMP formation in the rat striatum in a dose-dependent fashion (Gjoni et al, 2006).…”

Section: Discussionmentioning

confidence: 59%

Point Mutations in the Transmembrane Region of GABA_B2 Facilitate Activation by the Positive Modulator N,N′-Dicyclopentyl-2-methylsulfanyl-5-nitro-pyrimidine-4,6-diamine (GS39783) in the Absence of the GABA_B1 Subunit

Dupuis

Relkovic²,

Lhuillier³

et al. 2006

Mol Pharmacol

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GABA B receptors are heterodimers of two subunits, GABA B1 (GB1) and GABA B2 (GB2). Agonists such as GABA and baclofen bind to the GB1 subunit only, whereas GB2 is essential for G protein activation. Positive allosteric modulators enhance the potency and efficacy of agonists at GABA B receptors and are of particular interest because they lack the sedative and muscle relaxant properties of agonists. In this study, we aimed to characterize the interaction of the positive modulator N,NЈ-dicyclopentyl-2-methylsulfanyl-5-nitro-pyrimidine-4,6-diamine (GS39783) with the GABA B receptor heterodimer. Using functional guanosine 5Ј-O-(3-[35 S]thio)triphosphate binding assays, we observed positive modulation by GS39783 in different vertebrate species but not in Drosophila melanogaster. However, coexpression of D. melanogaster GB1 with rat GB2 yielded functional receptors positively modulated by GS39783. Together with data from rat/D. melanogaster GB2 subunit chimeras, this pointed to a critical role of the GB2 transmembrane region for positive modulation. We further characterized GS39783 function using point mutations. GS39783 positively modulated GABA responses but also showed considerable agonistic activity at heterodimers containing a mutant rat GB2 subunit with three amino acid substitutions in transmembrane domain VI. It was surprising that in contrast to wild-type rat GB2, this mutant subunit was also activated by GS39783 when expressed without GB1. The mutations of both G706T and A708P are necessary and sufficient for activation and identify a key region for the effect of GS39783 in the GB2 transmembrane region. Our data show that mutations of specific amino acids in GB2 can induce agonism in addition to positive modulation and facilitate GB2 activation in the absence of GB1.GABA B receptors are the metabotropic receptors for GABA and modulate inhibitory and excitatory neurotransmission . Presynaptic GABA B receptors, via inhibition of Ca 2ϩ channels, inhibit the release of several neurotransmitters and neuropeptides whereas postsynaptically located receptors activate potassium channels and induce slow inhibitory postsynaptic potentials. GABA B receptors belong to the family C of G protein-coupled receptors (GPCRs) with the agonist binding pocket being constituted by the large N-terminal extracellular domain (ECD). Native GABA B receptors are heterodimers composed of two subunits, GABA B1 (GB1) and GABA B2 (GB2). The receptors are exceptional among GPCR heterodimers in that only one subunit, GB1, constitutes the GABA binding domain, whereas activation of G proteins is mediated only through the second subunit, GB2. Mutagenesis studies and the lack of evolutionary conservation suggest that the ECD of GB2 does not form a binding pocket for a natural ligand (Kniazeff et al., 2002).

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“…This model treats the allosteric interactions in purely numerical terms; i.e., the constants ␥ and ␦ are independent of the qualitative nature of the orthosteric ligand. Thus, this model predicts that partial or full agonists or inverse agonists, as 64 URWYLER well as competitive antagonists, should be equally amenable to modulation by allosteric drugs (for examples and further discussion, see Urwyler et al, 2005). The model of Hall was extended in a further step to a "quaternary complex model" by Christopoulos and Kenakin (2002), to include allosteric modulation of the orthosteric site not only by low molecular weight compounds, but at the same time also by receptor-G-protein interactions.…”

Section: Allosteric Receptor Modulation In the Light Of Theoreticamentioning

confidence: 99%

“…For example, inverse agonism can only be detected in the presence of a measurable degree of constitutive activity, and the measurement of low-efficacy partial agonism depends on the availability of an assay system sufficiently sensitive to detect small responses (Binet et al, 2004;Urwyler et al, 2005;Langmead and Christopoulos, 2006). In this context, it should be noted that in sensitive, highly expressing recombinant systems with a high degree of receptor reserve, the apparent efficacy of partial agonists will increase and can even reach seemingly full agonism.…”

Section: Allosteric Modulation Of Family C Gpcrsmentioning

confidence: 99%

Allosteric Modulation of Family C G-Protein-Coupled Receptors: from Molecular Insights to Therapeutic Perspectives

2011

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Mechanisms of allosteric modulation at GABA receptors by CGP7930 and GS39783: effects on affinities and efficacies of orthosteric ligands with distinct intrinsic properties

Cited by 67 publications

References 33 publications

Biphasic Effects of Cannabinoids in Anxiety Responses: CB1 and GABAB Receptors in the Balance of GABAergic and Glutamatergic Neurotransmission

Biphasic Effects of Cannabinoids in Anxiety Responses: CB1 and GABAB Receptors in the Balance of GABAergic and Glutamatergic Neurotransmission

Point Mutations in the Transmembrane Region of GABA_B2 Facilitate Activation by the Positive Modulator N,N′-Dicyclopentyl-2-methylsulfanyl-5-nitro-pyrimidine-4,6-diamine (GS39783) in the Absence of the GABA_B1 Subunit

Allosteric Modulation of Family C G-Protein-Coupled Receptors: from Molecular Insights to Therapeutic Perspectives

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Mechanisms of allosteric modulation at GABA receptors by CGP7930 and GS39783: effects on affinities and efficacies of orthosteric ligands with distinct intrinsic properties

Cited by 67 publications

References 33 publications

Biphasic Effects of Cannabinoids in Anxiety Responses: CB1 and GABAB Receptors in the Balance of GABAergic and Glutamatergic Neurotransmission

Biphasic Effects of Cannabinoids in Anxiety Responses: CB1 and GABAB Receptors in the Balance of GABAergic and Glutamatergic Neurotransmission

Point Mutations in the Transmembrane Region of GABAB2 Facilitate Activation by the Positive Modulator N,N′-Dicyclopentyl-2-methylsulfanyl-5-nitro-pyrimidine-4,6-diamine (GS39783) in the Absence of the GABAB1 Subunit

Allosteric Modulation of Family C G-Protein-Coupled Receptors: from Molecular Insights to Therapeutic Perspectives

Contact Info

Product

Resources

About

Point Mutations in the Transmembrane Region of GABA_B2 Facilitate Activation by the Positive Modulator N,N′-Dicyclopentyl-2-methylsulfanyl-5-nitro-pyrimidine-4,6-diamine (GS39783) in the Absence of the GABA_B1 Subunit