Emerging paradigms in GPCR allostery: implications for drug discovery
TL;DR: New findings have the potential to alter how screening for allosteric drugs is performed and may increase the chances of success in the development ofallosteric modulators as clinical lead compounds.
Abstract: Allosteric ligands bind to G protein-coupled receptors (GPCRs; also known as seven-transmembrane receptors) at sites that are distinct from the sites to which endogenous ligands bind. The existence of allosteric ligands has enriched the ways in which the functions of GPCRs can be manipulated for potential therapeutic benefit, yet the complexity of their actions provides both challenges and opportunities for drug screening and development. Converging avenues of research in areas such as biased signalling by allosteric ligands and the mechanisms by which allosteric ligands modulate the effects of diverse endogenous ligands have provided new insights into how interactions between allosteric ligands and GPCRs could be exploited for drug discovery. These new findings have the potential to alter how screening for allosteric drugs is performed and may increase the chances of success in the development of allosteric modulators as clinical lead compounds.
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TL;DR: An up-to-date analysis of all GPCR drugs and agents in clinical trials is reported, which reveals current trends across molecule types, drug targets and therapeutic indications, including showing that 475 drugs act at 108 unique GPCRs.
Abstract: G protein-coupled receptors (GPCRs) are the most intensively studied drug targets, mostly due to their substantial involvement in human pathophysiology and their pharmacological tractability. Here, we report an up-to-date analysis of all GPCR drugs and agents in clinical trials, which reveals current trends across molecule types, drug targets and therapeutic indications, including showing that 475 drugs (~34% of all drugs approved by the US Food and Drug Administration (FDA)) act at 108 unique GPCRs. Approximately 321 agents are currently in clinical trials, of which ~20% target 66 potentially novel GPCR targets without an approved drug, and the number of biological drugs, allosteric modulators and biased agonists has increased. The major disease indications for GPCR modulators show a shift towards diabetes, obesity and Alzheimer disease, although several central nervous system disorders are also highly represented. The 224 (56%) non-olfactory GPCRs that have not yet been explored in clinical trials have broad untapped therapeutic potential, particularly in genetic and immune system disorders. Finally, we provide an interactive online resource to analyse and infer trends in GPCR drug discovery.
1,588 citations
TL;DR: It is hypothesized that cannabidiol would inhibit cannabinoid agonist activity through negative allosteric modulation of CB1 receptors through positive allosterics modulation ofCB1 receptors.
Abstract: Background and Purpose
Cannabidiol has been reported to act as an antagonist at cannabinoid CB1 receptors. We hypothesized that cannabidiol would inhibit cannabinoid agonist activity through negative allosteric modulation of CB1 receptors.
Experimental Approach
Internalization of CB1 receptors, arrestin2 recruitment, and PLCβ3 and ERK1/2 phosphorylation, were quantified in HEK 293A cells heterologously expressing CB1 receptors and in the STHdhQ7/Q7 cell model of striatal neurons endogenously expressing CB1 receptors. Cells were treated with 2-arachidonylglycerol or Δ9-tetrahydrocannabinol alone and in combination with different concentrations of cannabidiol.
Key Results
Cannabidiol reduced the efficacy and potency of 2-arachidonylglycerol and Δ9-tetrahydrocannabinol on PLCβ3- and ERK1/2-dependent signalling in cells heterologously (HEK 293A) or endogenously (STHdhQ7/Q7) expressing CB1 receptors. By reducing arrestin2 recruitment to CB1 receptors, cannabidiol treatment prevented internalization of these receptors. The allosteric activity of cannabidiol depended upon polar residues being present at positions 98 and 107 in the extracellular amino terminus of the CB1 receptor.
Conclusions and Implications
Cannabidiol behaved as a non-competitive negative allosteric modulator of CB1 receptors. Allosteric modulation, in conjunction with effects not mediated by CB1 receptors, may explain the in vivo effects of cannabidiol. Allosteric modulators of CB1 receptors have the potential to treat CNS and peripheral disorders while avoiding the adverse effects associated with orthosteric agonism or antagonism of these receptors.
689 citations
Cites background from "Emerging paradigms in GPCR alloster..."
...All class A, B and C GPCRs investigated to date possess allosteric binding sites (Wootten et al., 2013)....
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...…orthosteric ligands, allosteric modulators of CB1 receptors may not produce these undesirable side effects because their efficacy depends on the presence of orthosteric ligands, such as the two major endocannabinoids, anandamide and 2-arachidonylglycerol (2-AG) (Ross, 2007; Wootten et al., 2013)....
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...Therefore, the effect ceiling of an allosteric modulator is determined by the endogenous or exogenous orthosteric ligand (Wootten et al., 2013)....
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...In contrast, exogenous orthosteric ligands may produce adverse effects through supraphysiological over-activation or downregulation of a receptor (Wootten et al., 2013)....
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...An allosteric binding site is a distinct domain from the orthosteric site that can bind to small molecules or other proteins in order to modulate receptor activity (Wootten et al., 2013)....
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TL;DR: An emphasis is placed on describing research efforts to overcome the inherent weaknesses of peptide drugs, in particular their poor pharmacokinetic properties, and how these efforts have been critical to the discovery, design, and subsequent development of novel therapeutics.
Abstract: Over the past decade, peptide drug discovery has experienced a revival of interest and scientific momentum, as the pharmaceutical industry has come to appreciate the role that peptide therapeutics can play in addressing unmet medical needs and how this class of compounds can be an excellent complement or even preferable alternative to small molecule and biological therapeutics. In this Perspective, we give a concise description of the recent progress in peptide drug discovery in a holistic manner, highlighting enabling technological advances affecting nearly every aspect of this field: from lead discovery, to synthesis and optimization, to peptide drug delivery. An emphasis is placed on describing research efforts to overcome the inherent weaknesses of peptide drugs, in particular their poor pharmacokinetic properties, and how these efforts have been critical to the discovery, design, and subsequent development of novel therapeutics.
651 citations
TL;DR: What is currently known about the flexibility and dynamics of GPCRs, as determined through crystallography, spectroscopy, and computer simulations is reviewed.
Abstract: The function of G protein-coupled receptors (GPCRs)—which represent the largest class of both human membrane proteins and drug targets—depends critically on their ability to change shape, transitioning among distinct conformations. Determining the structural dynamics of GPCRs is thus essential both for understanding the physiology of these receptors and for the rational design of GPCR-targeted drugs. Here we review what is currently known about the flexibility and dynamics of GPCRs, as determined through crystallography, spectroscopy, and computer simulations. We first provide an overview of the types of motion exhibited by a GPCR and then discuss GPCR dynamics in the context of ligand binding, activation, allosteric modulation, and biased signaling. Finally, we discuss the implications of GPCR conformational plasticity for drug design.
500 citations
TL;DR: The data establish the molecular basis for allosteric sodium ion control in opioid signalling, revealing that sodium-coordinating residues act as ‘efficacy switches’ at a prototypic G-protein-coupled receptor.
Abstract: Opioids represent widely prescribed and abused medications, although their signal transduction mechanisms are not well understood. Here we present the 1.8 A high-resolution crystal structure of the human δ-opioid receptor (δ-OR), revealing the presence and fundamental role of a sodium ion in mediating allosteric control of receptor functional selectivity and constitutive activity. The distinctive δ-OR sodium ion site architecture is centrally located in a polar interaction network in the seven-transmembrane bundle core, with the sodium ion stabilizing a reduced agonist affinity state, and thereby modulating signal transduction. Site-directed mutagenesis and functional studies reveal that changing the allosteric sodium site residue Asn 131 to an alanine or a valine augments constitutive β-arrestin-mediated signalling. Asp95Ala, Asn310Ala and Asn314Ala mutations transform classical δ-opioid antagonists such as naltrindole into potent β-arrestin-biased agonists. The data establish the molecular basis for allosteric sodium ion control in opioid signalling, revealing that sodium-coordinating residues act as ‘efficacy switches’ at a prototypic G-protein-coupled receptor. The 1.8 A high-resolution X-ray crystal structure of the human δ-opioid receptor is presented, with site-directed mutagenesis and functional studies revealing a crucial role for a sodium ion in mediating allosteric control in this receptor. Opioid receptors mediate the actions of endogenous and exogenous opioids for many physiological processes, including analgesia, consciousness, motor control and mood. This paper reports the X-ray crystal structure of the human δ-opioid receptor at 1.8 A resolution, revealing the presence of a sodium ion that seems to mediate allosteric control of this G-protein-coupled receptor. Site-directed mutagenesis and functional studies show that mutating key amino acids in the allosteric sodium site to alanine transforms the antagonist naltrindole into a potent β-arrestin-biased agonist. Also apparent is an allosteric sodium-binding pocket that could aid the development of subtype-selective δ-opioid receptor agonists and antagonists — the extension of orthosteric ligands into the pocket could generate 'bitopic' orthosteric/allosteric compounds with more favourable pharmacological properties.
434 citations
Cites background from "Emerging paradigms in GPCR alloster..."
...4 Å); and (3) calculations of ion valence (Table S2)....
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...S1a); (3) a distinct conformation of the human third extracellular loop (ECL3) (Fig....
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References
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TL;DR: This issue of Pharmacological Reviews includes a new venture in the collaboration between the International Union of Pharmacology (IUPHAR) and the American Society for Pharmacology and Experimental Therapeutics (ASPET), in that a new classification of voltage-gated ion channels is outlined.
Abstract: This issue of Pharmacological Reviews includes a new venture in the collaboration between the International Union of Pharmacology (IUPHAR) and the American Society for Pharmacology and Experimental Therapeutics (ASPET), in that a new classification of voltage-gated ion channels is outlined in this
7,389 citations
TL;DR: This article determined the structure of rhodopsin from diffraction data extending to 2.8 angstroms resolution and found that the highly organized structure in the extracellular region, including a conserved disulfide bridge, forms a basis for the arrangement of the sevenhelix transmembrane motif.
Abstract: Heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs) respond to a variety of different external stimuli and activate G proteins. GPCRs share many structural features, including a bundle of seven transmembrane alpha helices connected by six loops of varying lengths. We determined the structure of rhodopsin from diffraction data extending to 2.8 angstroms resolution. The highly organized structure in the extracellular region, including a conserved disulfide bridge, forms a basis for the arrangement of the seven-helix transmembrane motif. The ground-state chromophore, 11-cis-retinal, holds the transmembrane region of the protein in the inactive conformation. Interactions of the chromophore with a cluster of key residues determine the wavelength of the maximum absorption. Changes in these interactions among rhodopsins facilitate color discrimination. Identification of a set of residues that mediate interactions between the transmembrane helices and the cytoplasmic surface, where G-protein activation occurs, also suggests a possible structural change upon photoactivation.
5,357 citations
TL;DR: This crystal structure represents the first high-resolution view of transmembrane signalling by a GPCR and the most surprising observation is a major displacement of the α-helical domain of Gαs relative to the Ras-like GTPase domain.
Abstract: G protein-coupled receptors (GPCRs) are responsible for the majority of cellular responses to hormones and neurotransmitters as well as the senses of sight, olfaction and taste. The paradigm of GPCR signalling is the activation of a heterotrimeric GTP binding protein (G protein) by an agonist-occupied receptor. The b2 adrenergic receptor (b2AR) activation of Gs, the stimulatory G protein for adenylyl cyclase, has long been a model system for GPCR signalling. Here we present the crystal structure of the active state ternary complex composed of agonist-occupied monomericb2AR and nucleotide-free Gs heterotrimer. The principal interactions between the b2AR and Gs involve the amino- and carboxy-terminal a-helices of Gs, with conformational changes propagating to the nucleotide-binding pocket. The
2,676 citations
TL;DR: The properties of chemokines and their receptors are discussed and the roles of these chemoattractants in selected clinical disorders are highlighted.
Abstract: In this review, the authors discuss the properties of chemokines and their receptors and highlight the roles of these chemoattractants in selected clinical disorders.
2,368 citations
TL;DR: Five independent crystal structures of CXCR4 bound to an antagonist small molecule IT1t and a cyclic peptide CVX15 at 2.5 to 3.2 angstrom resolution reveal a consistent homodimer with an interface including helices V and VI that may be involved in regulating signaling.
Abstract: Chemokine receptors are critical regulators of cell migration in the context of immune surveillance, inflammation, and development. The G protein-coupled chemokine receptor CXCR4 is specifically implicated in cancer metastasis and HIV-1 infection. Here we report five independent crystal structures of CXCR4 bound to an antagonist small molecule IT1t and a cyclic peptide CVX15 at 2.5 to 3.2 angstrom resolution. All structures reveal a consistent homodimer with an interface including helices V and VI that may be involved in regulating signaling. The location and shape of the ligand-binding sites differ from other G protein-coupled receptors and are closer to the extracellular surface. These structures provide new clues about the interactions between CXCR4 and its natural ligand CXCL12, and with the HIV-1 glycoprotein gp120.
1,682 citations