Valant C


Full name : Valant Celine

First name : Celine

Mail : Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville VIC 3052

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Country : Australia

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References (9)

Title : Probing structural requirements of positive allosteric modulators of the m4 muscarinic receptor - Huynh_2013_J.Med.Chem_56_8196
Author(s) : Huynh T , Valant C , Crosby IT , Sexton PM , Christopoulos A , Capuano B
Ref : Journal of Medicinal Chemistry , 56 :8196 , 2013
Abstract : The M4 mAChR is implicated in several CNS disorders and possesses an allosteric binding site for which ligands modulating the affinity and/or efficacy of ACh may be exploited for selective receptor targeting. We report the synthesis of a focused library of putative M4 PAMs derived from VU0152100 and VU10005. These compounds investigate the pharmacological effects of previously identified methoxy and fluoro substituents, providing useful estimates of affinity (KB), cooperativity (alphabeta), and direct agonist properties (tauB).
ESTHER : Huynh_2013_J.Med.Chem_56_8196
PubMedSearch : Huynh_2013_J.Med.Chem_56_8196
PubMedID: 24074052

Title : Reverse engineering of the selective agonist TBPB unveils both orthosteric and allosteric modes of action at the M(1) muscarinic acetylcholine receptor - Keov_2013_Mol.Pharmacol_84_425
Author(s) : Keov P , Valant C , Devine SM , Lane JR , Scammells PJ , Sexton PM , Christopoulos A
Ref : Molecular Pharmacology , 84 :425 , 2013
Abstract : Recent interest in the M(1) muscarinic acetylcholine (ACh) receptor (mAChR) has led to the discovery of various selective agonists for the receptor. The novel selective agonist 1-(1'-(2-methylbenzyl)-1,4'-bipiperidin-4-yl)-1H-benzo[d]imidazol-2(3H)-1 (TBPB) displays unprecedented functional selectivity at the M(1) mAChR. This functional selectivity has been described to stem from sole interaction with an allosteric site, although the evidence for such a mechanism is equivocal. To delineate TBPB's mechanism of action, several truncated variants of TBPB were synthesized and characterized. Binding experiments with [(3)H]N-methylscopolamine at the M(1), M(2), M(3), and M(4) mAChRs revealed radioligand displacement in a manner consistent with a competitive binding mode at the orthosteric site by TBPB and fragment derivatives. Cell-based functional assays of fragment derivatives of TBPB identified both agonistic and antagonistic moieties, one of which, 1-(1-cyclohexylpiperidin-4-yl)-1H-benzo[d]imidazol-2(3H)-1 (VCP794), lost agonistic selectivity for the M(1) mAChR. Further interaction experiments between TBPB or its antagonist fragments with ACh also indicated a mechanism consistent with competitive binding at mAChRs. However, interaction with an allosteric site by an antagonist fragment of TBPB was demonstrated via its ability to retard radioligand dissociation. To reconcile this dual orthosteric/allosteric pharmacological behavior, we propose that TBPB is a bitopic ligand, interacting with both the orthosteric site and an allosteric site, at the M(1) mAChR. This mechanism may also be the case for other selective agonists for mAChRs, and should be taken into consideration in the profiling and classification of new novel selective agonists for this receptor family.
ESTHER : Keov_2013_Mol.Pharmacol_84_425
PubMedSearch : Keov_2013_Mol.Pharmacol_84_425
PubMedID: 23798605

Title : Structural basis for modulation of a G-protein-coupled receptor by allosteric drugs - Dror_2013_Nature_503_295
Author(s) : Dror RO , Green HF , Valant C , Borhani DW , Valcourt JR , Pan AC , Arlow DH , Canals M , Lane JR , Rahmani R , Baell JB , Sexton PM , Christopoulos A , Shaw DE
Ref : Nature , 503 :295 , 2013
Abstract : The design of G-protein-coupled receptor (GPCR) allosteric modulators, an active area of modern pharmaceutical research, has proved challenging because neither the binding modes nor the molecular mechanisms of such drugs are known. Here we determine binding sites, bound conformations and specific drug-receptor interactions for several allosteric modulators of the M2 muscarinic acetylcholine receptor (M2 receptor), a prototypical family A GPCR, using atomic-level simulations in which the modulators spontaneously associate with the receptor. Despite substantial structural diversity, all modulators form cation-pi interactions with clusters of aromatic residues in the receptor extracellular vestibule, approximately 15 A from the classical, 'orthosteric' ligand-binding site. We validate the observed modulator binding modes through radioligand binding experiments on receptor mutants designed, on the basis of our simulations, either to increase or to decrease modulator affinity. Simulations also revealed mechanisms that contribute to positive and negative allosteric modulation of classical ligand binding, including coupled conformational changes of the two binding sites and electrostatic interactions between ligands in these sites. These observations enabled the design of chemical modifications that substantially alter a modulator's allosteric effects. Our findings thus provide a structural basis for the rational design of allosteric modulators targeting muscarinic and possibly other GPCRs.
ESTHER : Dror_2013_Nature_503_295
PubMedSearch : Dror_2013_Nature_503_295
PubMedID: 24121438

Title : Activation and allosteric modulation of a muscarinic acetylcholine receptor - Kruse_2013_Nature_504_101
Author(s) : Kruse AC , Ring AM , Manglik A , Hu J , Hu K , Eitel K , Hubner H , Pardon E , Valant C , Sexton PM , Christopoulos A , Felder CC , Gmeiner P , Steyaert J , Weis WI , Garcia KC , Wess J , Kobilka BK
Ref : Nature , 504 :101 , 2013
Abstract : Despite recent advances in crystallography and the availability of G-protein-coupled receptor (GPCR) structures, little is known about the mechanism of their activation process, as only the beta2 adrenergic receptor (beta2AR) and rhodopsin have been crystallized in fully active conformations. Here we report the structure of an agonist-bound, active state of the human M2 muscarinic acetylcholine receptor stabilized by a G-protein mimetic camelid antibody fragment isolated by conformational selection using yeast surface display. In addition to the expected changes in the intracellular surface, the structure reveals larger conformational changes in the extracellular region and orthosteric binding site than observed in the active states of the beta2AR and rhodopsin. We also report the structure of the M2 receptor simultaneously bound to the orthosteric agonist iperoxo and the positive allosteric modulator LY2119620. This structure reveals that LY2119620 recognizes a largely pre-formed binding site in the extracellular vestibule of the iperoxo-bound receptor, inducing a slight contraction of this outer binding pocket. These structures offer important insights into the activation mechanism and allosteric modulation of muscarinic receptors.
ESTHER : Kruse_2013_Nature_504_101
PubMedSearch : Kruse_2013_Nature_504_101
PubMedID: 24256733

Title : Synthesis and pharmacological profiling of analogues of benzyl quinolone carboxylic acid (BQCA) as allosteric modulators of the M1 muscarinic receptor - Mistry_2013_J.Med.Chem_56_5151
Author(s) : Mistry SN , Valant C , Sexton PM , Capuano B , Christopoulos A , Scammells PJ
Ref : Journal of Medicinal Chemistry , 56 :5151 , 2013
Abstract : Established therapy in Alzheimer's disease involves potentiation of the endogenous orthosteric ligand, acetylcholine, at the M1 muscarinic receptors found in higher concentrations in the cortex and hippocampus. Adverse effects, due to indiscriminate activation of other muscarinic receptor subtypes, are common. M1 muscarinic positive allosteric modulators/allosteric agonists such as BQCA offer an attractive solution, being exquisitely M1-selective over other muscarinic subtypes. A common difficulty with allosteric ligands is interpreting SAR, based on composite potency values derived in the presence of fixed concentration of agonist. In reality these values encompass multiple pharmacological parameters, each potentially and differentially sensitive to structural modification of the ligand. We report novel BQCA analogues which appear to augment ligand affinity for the receptor (pK(B)), intrinsic efficacy (tauB), and both binding (alpha) and functional (beta) cooperativity with acetylcholine. Ultimately, development of such enriched SAR surrounding allosteric modulators will provide insight into their mode of action.
ESTHER : Mistry_2013_J.Med.Chem_56_5151
PubMedSearch : Mistry_2013_J.Med.Chem_56_5151
PubMedID: 23718562

Title : Allosteric modulation of endogenous metabolites as an avenue for drug discovery - Wootten_2012_Mol.Pharmacol_82_281
Author(s) : Wootten D , Savage EE , Valant C , May LT , Sloop KW , Ficorilli J , Showalter AD , Willard FS , Christopoulos A , Sexton PM
Ref : Molecular Pharmacology , 82 :281 , 2012
Abstract : G protein-coupled receptors (GPCRs) are the largest family of cell surface receptors and a key drug target class. Recently, allosteric drugs that can co-bind with and modulate the activity of the endogenous ligand(s) for the receptor have become a major focus of the pharmaceutical and biotechnology industry for the development of novel GPCR therapeutic agents. This class of drugs has distinct properties compared with drugs targeting the endogenous (orthosteric) ligand-binding site that include the ability to sculpt cellular signaling and to respond differently in the presence of discrete orthosteric ligands, a behavior termed "probe dependence." Here, using cell signaling assays combined with ex vivo and in vivo studies of insulin secretion, we demonstrate that allosteric ligands can cause marked potentiation of previously "inert" metabolic products of neurotransmitters and peptide hormones, a novel consequence of the phenomenon of probe dependence. Indeed, at the muscarinic M(2) receptor and glucagon-like peptide 1 (GLP-1) receptor, allosteric potentiation of the metabolites, choline and GLP-1(9-36)NH(2), respectively, was ~100-fold and up to 200-fold greater than that seen with the physiological signaling molecules acetylcholine and GLP-1(7-36)NH(2). Modulation of GLP-1(9-36)NH(2) was also demonstrated in ex vivo and in vivo assays of insulin secretion. This work opens up new avenues for allosteric drug discovery by directly targeting modulation of metabolites, but it also identifies a behavior that could contribute to unexpected clinical outcomes if interaction of allosteric drugs with metabolites is not part of their preclinical assessment.
ESTHER : Wootten_2012_Mol.Pharmacol_82_281
PubMedSearch : Wootten_2012_Mol.Pharmacol_82_281
PubMedID: 22576254

Title : Probe dependence in the allosteric modulation of a G protein-coupled receptor: implications for detection and validation of allosteric ligand effects - Valant_2012_Mol.Pharmacol_81_41
Author(s) : Valant C , Felder CC , Sexton PM , Christopoulos A
Ref : Molecular Pharmacology , 81 :41 , 2012
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.
ESTHER : Valant_2012_Mol.Pharmacol_81_41
PubMedSearch : Valant_2012_Mol.Pharmacol_81_41
PubMedID: 21989256

Title : Determination of adenosine A1 receptor agonist and antagonist pharmacology using Saccharomyces cerevisiae: implications for ligand screening and functional selectivity - Stewart_2009_J.Pharmacol.Exp.Ther_331_277
Author(s) : Stewart GD , Valant C , Dowell SJ , Mijaljica D , Devenish RJ , Scammells PJ , Sexton PM , Christopoulos A
Ref : Journal of Pharmacology & Experimental Therapeutics , 331 :277 , 2009
Abstract : The budding yeast, Saccharomyces cerevisiae, is a convenient system for coupling heterologous G protein-coupled receptors (GPCRs) to the pheromone response pathway to facilitate empirical ligand screening and/or GPCR mutagenesis studies. However, few studies have applied this system to define GPCR-G protein-coupling preferences and furnish information on ligand affinities, efficacies, and functional selectivity. We thus used different S. cerevisiae strains, each expressing a specific human Galpha/yeast Gpa1 protein chimera, and determined the pharmacology of various ligands of the coexpressed human adenosine A(1) receptor. These assays, in conjunction with the application of quantitative models of agonism and antagonism, revealed that (-)-N(6)-(2-phenylisopropyl)adenosine was a high-efficacy agonist that selectively coupled to Gpa/1Galpha(o), Gpa1/Galpha(i1/2), and Gpa1/Galpha(i3), whereas the novel compound, 5'-deoxy-N(6)-(endo-norborn-2-yl)-5'-(2-fluorophenylthio)adenosine (VCP-189), was a lower-efficacy agonist that selectively coupled to Gpa1/Galpha(i) proteins; the latter finding suggested that VCP-189 might be functionally selective. The affinity of the antagonist, 8-cyclopentyl-1,3-dipropylxanthine, was also determined at the various strains. Subsequent experiments performed in mammalian Chinese hamster ovary cells monitoring cAMP formation/inhibition, intracellular calcium mobilization, phosphorylation of extracellular signal-regulated kinase 1 and 2 or (35)S-labeled guanosine 5'-(gamma-thio)triphosphate binding, were in general agreement with the yeast data regarding agonist efficacy estimation and antagonist affinity estimation, but revealed that the apparent functional selectivity of VCP-189 could be explained by differences in stimulus-response coupling between yeast and mammalian cells. Our results suggest that this yeast system is a useful tool for quantifying ligand affinity and relative efficacy, but it may lack the sensitivity required to detect functional selectivity of low-efficacy agonists.
ESTHER : Stewart_2009_J.Pharmacol.Exp.Ther_331_277
PubMedSearch : Stewart_2009_J.Pharmacol.Exp.Ther_331_277
PubMedID: 19641164

Title : A novel mechanism of G protein-coupled receptor functional selectivity. Muscarinic partial agonist McN-A-343 as a bitopic orthosteric\/allosteric ligand - Valant_2008_J.Biol.Chem_283_29312
Author(s) : Valant C , Gregory KJ , Hall NE , Scammells PJ , Lew MJ , Sexton PM , Christopoulos A
Ref : Journal of Biological Chemistry , 283 :29312 , 2008
Abstract : Many G protein-coupled receptors (GPCRs) possess allosteric binding sites distinct from the orthosteric site utilized by their cognate ligands, but most GPCR allosteric modulators reported to date lack signaling efficacy in their own right. McN-A-343 (4-(N-(3-chlorophenyl)carbamoyloxy)-2-butynyltrimethylammonium chloride) is a functionally selective muscarinic acetylcholine receptor (mAChR) partial agonist that can also interact allosterically at the M(2) mAChR. We hypothesized that this molecule simultaneously utilizes both an allosteric and the orthosteric site on the M(2) mAChR to mediate these effects. By synthesizing progressively truncated McN-A-343 derivatives, we identified two, which minimally contain 3-chlorophenylcarbamate, as pure allosteric modulators. These compounds were positive modulators of the orthosteric antagonist N-[(3)H]methylscopolamine, but in functional assays of M(2) mAChR-mediated ERK1/2 phosphorylation and guanosine 5'-3-O-([(35)S]thio)triphosphate binding, they were negative modulators of agonist efficacy. This negative allosteric effect was diminished upon mutation of Y177A in the second extracellular (E2) loop of the M(2) mAChR that is known to reduce prototypical allosteric modulator potency. Our results are consistent with McN-A-343 being a bitopic orthosteric/allosteric ligand with the allosteric moiety engendering partial agonism and functional selectivity. This finding suggests a novel and largely unappreciated mechanism of "directed efficacy" whereby functional selectivity may be engendered in a GPCR by utilizing an allosteric ligand to direct the signaling of an orthosteric ligand encoded within the same molecule.
ESTHER : Valant_2008_J.Biol.Chem_283_29312
PubMedSearch : Valant_2008_J.Biol.Chem_283_29312
PubMedID: 18723515