Alternative drug discovery approaches for orphan GPCRs

G protein-coupled receptors (GPCRs) are well-known drug targets. However, a question mark remains for the more than 100 orphan GPCRs as current deorphanisation strategies failed to identify specific ligands for these receptors. Recent advances have shown that orphan GPCRs may have important functions that are ligand-independent. Orphan GPCRs can modulate the function of well-defined drug targets such as GPCRs with identified ligands and neurotransmitter transporters though physical association with those molecules. Thus, compounds that bind to orphan GPCRs and allosterically regulate the function of the interacting partner or even disrupt the interaction with the latter could become new drugs.     

Dependence of molecular properties on proteomic family for marketed oral drugs

An association of drugs with their proteomic family reveals that molecular properties of drugs targeting proteases, lipid and peptide G-protein-coupled receptors (GPCRs), and nuclear hormone receptors significantly exceed limits for some properties in the "rule of five", while drugs targeting cytochrome P450s, biogenic amine GPCRs, and transporters have significantly lower values for certain properties. Also, the variation in drug targets appears to be a factor explaining increasing molecular weight over time.     

Nonpeptide ligands that target peptide-activated GPCRs in inflammation

The focus of this review is on G protein-coupled receptors (GPCRs) for which nonpeptidic ligands are known and have been evaluated for the treatment of inflammatory conditions. GPCRs are the most prevalent class of cell surface proteins in pharmaceutical research today, and GPCR-targeting drugs account for one tenth of worldwide pharmaceutical sales. Of over 800 human GPCRs identified to date, several hundred are activated by peptides/proteins and just over 30 of these have been identified so far as potential therapeutic targets for the treatment of inflammatory diseases. This review highlights those GPCRs and over 60 structurally diverse nonpeptidic compounds that interact with them and display pro- or anti- inflammatory properties. Among these GPCR targets are the receptors for peptides like bradykinin, chemokines, complement anaphylatoxins, corticotropin releasing factor, endothelins, melanocortins, tachykinins, urocortins, as well as the protease activated receptors (PARs). Other peptide activated GPCRs implicated in inflammation, like those that bind angiotensin II, N-formyl peptides, galanin, neuropeptide Y, opioids and oxytocin, are only briefly discussed because there is either less direct association with inflammation or few/no nonpeptidic antiinflammatory ligands known. While it is still very early in the development of antiinflammatory drugs that target GPCRs, there is already a wealth of information supporting their important roles as cellular sentries in inflammatory diseases. New opportunities are emerging to evaluate antiinflammatory activities of potent and selective GPCR-binding ligands, including those being developed for other disease indications. In summary, GPCRs deserve a great deal more attention as potential therapeutic targets in inflammatory diseases.     

Constitutively activated G protein-coupled receptors: a novel approach to CNS drug discovery

G protein-coupled receptors (GPCRs) represent a major class of signal transduction proteins that modulate various biological functions. GPCRs are one of the most common targets for drug development-currently, 39 of the top 100 marketed drugs in use act directly or indirectly through activation or blockade of GPCR-mediated receptors. Nearly 160 GPCRs have been identified based on their gene sequence and their ability to interact with known endogenous ligands. However, an estimated 500-800 additional GPCRs have been classified as "orphan" receptors (oGPCRs) because their endogenous ligands have not yet been identified. Given that known GPCRs have proven to be such clinically useful drug targets, these oGPCRs represent a rich group of receptor targets for the development of novel and improved medicines. To develop ligands for these potential drug targets requires the ability to identify groups or pools of GPCRs that are likely to be involved in a specific disease process (obesity, schizophrenia, depression, etc.) and to dissect out the pharmacological and signal transduction differences between these GPCR subtypes. It also requires the development of assays to detect ligands of GPCRs even when the endogenous ligands are unidentified. This paper will review novel strategies to identify clinically interesting oGPCRs and to screen for small molecules that act as ligands without prior knowledge of endogenous ligands. This involves the use of constitutively activated GPCRs, a technology that provides a unique opportunity to identify several classes of pharmacological agents, including agonists, inverse agonists and allosteric modulators.     

G protein-coupled receptors as therapeutic targets for obesity and type 2 diabetes

The prevalence of obesity and type 2 diabetes, two strongly correlated disorders, is increasing worldwide. Weight loss can reduce the risk of developing type 2 diabetes and the pharmacological treatments normally required to manage this disorder. Even though dietary and lifestyle changes may eventually reduce obesity for some individuals, new safe and more efficacious drugs are required for successful weight reduction and treatment of type 2 diabetes in a large proportion of obese individuals. In addition to targeting known G protein-coupled receptors (GPCRs), several orphan GPCRs expressed in central nervous system areas known to regulate feeding may provide new targets for the treatment of obesity. Similarly, the pancreas contains numerous islet GPCRs as well as an abundance of orphan GPCRs that potentially could emerge as targets for future antidiabetic compounds. One of the major challenges facing the pharmaceutical industry is how to rapidly establish the function and therapeutic relevance of orphan GPCRs, some of which may represent novel targets for the discovery of the next generation of drugs to effectively treat obesity and type 2 diabetes. This review will focus on the significant potential of known and orphan GPCRs as targets for the discovery of new drugs to successfully treat these serious disorders.     

G蛋白偶联受体二聚化在药物开发中所发挥的特异性作用(英文)

G蛋白偶联受体(GPCRs)是与G蛋白相偶联的七次跨膜受体,其成员有上千种,是重要的药物靶点之一。目前,GPCRs相关药物占市场上药物的40%-50%。在过去的十年中,对GPCRs主要以单体的形式存在着的这一假说做出了重新评估,大量事实证明GPCRs也能以同源或异源二聚体,甚至是高阶寡聚体的形式存在,比较热门的领域是GPCRs二聚化。最近研究表明同源或异源二聚化有不同于单体的特异功能特征,包括配体识别、信号转导、运输等。同时,在较少副作用治疗疾病的新药开发上,具有不同病理和信号转导途径的二聚体的出现开辟了新的领域。本综述主要介绍二聚体的特异结构及其特异的信号转导途径,从而有助于在GPCRs药物开发中取得丰硕的成果。     

What makes a good anti-inflammatory drug target?

This review focuses on the major, 'successful' target families in inflammation and attempts to identify some of the key features of what makes a good anti-inflammatory target. The review is based on a systematic analysis of approved anti-inflammatory drugs grouped according to their drug-target family. The cytokine family is a drug-dense area. They have yielded and continue to yield a rich stream of drugs. As in other therapeutic areas, G-protein-coupled receptors (GPCRs), also known as seven-transmembrane pass receptors, have provided significant drug targets. In addition, the superfamilies of cell adhesion molecules and co-stimulatory molecules, which have special relevance to immune processes, have begun to provide the first approved drugs and might yield many more. The recent, rapid increase in the number of defined targets in the immune system -- leukocyte surface antigens, cytokines, GPCRs, adhesion molecules and co-stimulatory molecules -- will ensure a rich stream of future anti-inflammatory drug targets.     

Heterodimerization and surface localization of G protein coupled receptors

G protein coupled receptors (GPCRs) are one of the largest human gene families, and are targets for many important therapeutic drugs. Over the last few years, there has been a major paradigm shift in our understanding of how these receptors function. Formerly, GPCRs were thought to exist as monomers that, upon agonist occupation, activated a heterotrimeric G protein to alter the concentrations of specific second messengers. Until recently, this relatively linear cascade has been the standard paradigm for signaling by these molecules. However, it is now clear that this model is not adequate to explain many aspects of GPCR function. We now know that many, if not most, GPCRs form homo- and/or hetero-oligomeric complexes and interact directly with intracellular proteins in addition to G proteins. It now appears that many GPCRs may not function independently, but might more accurately be described as subunits of large multi-protein signaling complexes. These observations raise many important new questions; some of which include: (1) how many functionally and pharmacologically distinct receptor subtypes exist in vivo? (2) Which GPCRs physically associate, and in what stochiometries? (3) What are the roles of individual subunits in binding ligand and activating responses? (4) Are the pharmacological or signaling properties of GPCR heterodimers different from monomers? Since these receptors are the targets for a large number of clinically useful compounds, such information is likely to be of direct therapeutic importance, both in understanding how existing drugs work, but also in discovering novel compounds to treat disease.     

Heterodimerization of g protein-coupled receptors: specificity and functional significance

G protein-coupled receptors (GPCRs) are cell surface receptors that mediate physiological responses to a diverse array of stimuli. GPCRs have traditionally been thought to act as monomers, but recent evidence suggests that GPCRs may form dimers (or higher-order oligomers) as part of their normal trafficking and function. In fact, certain GPCRs seem to have a strict requirement for heterodimerization to attain proper surface expression and functional activity. Even those GPCRs that do not absolutely require heterodimerization may still specifically associate with other GPCR subtypes, sometimes resulting in dramatic effects on receptor pharmacology, signaling, and/or internalization. Understanding the specificity and functional significance of GPCR heterodimerization is of tremendous clinical importance since GPCRs are the molecular targets for numerous therapeutic drugs.     

Receptorome screening for CNS drug discovery

An estimated 50% of currently marketed drugs target G protein-coupled receptors (GPCRs) for a wide variety of indications, including central nervous system (CNS) disorders. Although drug discovery efforts have focused on GPCRs, less than 10% of GPCRs are currently used as drug targets. Thus, GPCRs continue to represent a significant opportunity for future CNS drug development. Identifying the molecular targets of psychoactive compounds may result in the elucidation of novel targets for CNS drug discovery. This commentary will describe discovery-based approaches and provide several recent examples of novel ligand-receptor interactions discovered through systematic screening of the 'receptorome'.     

Structure-based drug screening for G-protein-coupled receptors

G-protein-coupled receptors (GPCRs) represent a large family of signaling proteins that includes many therapeutic targets; however, progress in identifying new small molecule drugs has been disappointing. The past 4 years have seen remarkable progress in the structural biology of GPCRs, raising the possibility of applying structure-based approaches to GPCR drug discovery efforts. Of the various structure-based approaches that have been applied to soluble protein targets, such as proteases and kinases, in silico docking is among the most ready applicable to GPCRs. Early studies suggest that GPCR binding pockets are well suited to docking, and docking screens have identified potent and novel compounds for these targets. This review will focus on the current state of in silico docking for GPCRs.     

Coupling mode of receptors and G proteins

Signaling via G-protein-coupled receptors (GPCRs) is crucial to many physiological and pathophysiological processes in multicellular organisms, and GPCRs themselves are targets for important drugs. Classical cell supplementation experiments suggest a collision coupling model, in which receptors and G proteins diffuse randomly within the cell membrane and interact only if receptors are activated. This model is also backed by kinetic and live cell imaging data. According to the challenging theory, receptors and G proteins are precoupled—meaning they are forming stable complexes in the absence of agonist, which prevail during signaling. This model has been favored on the basis of copurification and coimmunoprecipitation of inactive receptors with G proteins and more recently by some approaches measuring energy transfer between labeled receptors and G proteins. This article reviews key findings regarding the receptor/G protein coupling mode, including most recent findings obtained by optical techniques.     

G蛋白偶联受体固有活性研究进展与新药开发

G蛋白偶联受体(G-prote in-coup led receptor,GPCR)是与G蛋白有信号连接的一大类受体家族,是人体内最大的膜受体蛋白家族,是一类具有7个跨膜螺旋的跨膜蛋白受体。GPCR的结构特征和在信号传导中的重要作用决定了其可以作为很好的药物靶标。目前世界药物市场上有三分之一的小分子药物是GPCR的激活剂(agon ist)或拮抗剂(antagon ist)。以其为靶点的药物在医药产业中占据显著地位。在当今前50种最畅销的上市药物中,20%属于G蛋白受体相关药物。近来的研究发现,大多数G蛋白偶联受体具有一个很重要的特性,就是具有固有活性(Constitutive ac-tivity),即无激动剂条件受体自发的维持激活并维持下游信号传导通路的活性。固有活性涉及受体、G蛋白及下游信号通路之间的关系。该文就G蛋白偶联受体固有活性概念、研究进展、反相激动剂与固有活性研究、固有活性与新药开发4个方面,进行以下论述。     

The structure and dynamics of GPCR oligomers: a new focus in models of cell-signaling mechanisms and drug design

G protein-coupled receptors (GPCRs) represent approximately half of the potential pharmaceutical targets for current drugs, and thus the way in which these receptors assemble into dimeric/oligomeric structures is of vital interest in practical as well as conceptual aspects of current drug discovery efforts. The significance of such structures is based on the recent realization that ligand-dependent signaling by GPCRs is not necessarily transduced to the G protein by receptor monomers, but possibly by GPCR dimers or even oligomers that function as dynamic macromolecular assemblies. In addition, recent evidence that GPCR hetero-oligomerization can produce signaling units with unexpected combinations of pharmacological properties suggests entirely new methods for developing successful drugs. The dynamic mechanisms of these signaling assemblies remain to be elucidated. The development of increasingly accurate dynamic molecular models of GPCR dimers is expected to produce a more complete structural context for understanding the molecular mechanisms of GPCR function, and to aid in drug discovery.     

G-protein-coupled receptor heteromers: function and ligand pharmacology

Almost all existing models for G-protein-coupled receptors (GPCRs) are based on the occurrence of monomers. Recent studies show that many GPCRs are dimers. Therefore for some receptors dimers and not monomers are the main species interacting with hormones/neurotransmitters/drugs. There are reasons for equivocal interpretations of the data fitting to receptor dimers assuming they are monomers. Fitting data using a dimer-based model gives not only the equilibrium dissociation constants for high and low affinity binding to receptor dimers but also a 'cooperativity index' that reflects the molecular communication between monomers within the dimer. The dimer cooperativity index (D(C)) is a valuable tool that enables to interpret and quantify, for instance, the effect of allosteric regulators. For different receptors heteromerization confers a specific functional property for the receptor heteromer that can be considered as a 'dimer fingerprint'. The occurrence of heteromers with different pharmacological and signalling properties opens a complete new field to search for novel drug targets useful to combat a variety of diseases and potentially with fewer side effects. Antagonists, which are quite common marketed drugs targeting GPCRs, display variable affinities when a given receptor is expressed with different heteromeric partners. This fact should be taken into account in the development of new drugs.     

孤儿G蛋白偶联受体及其作为新药靶点的重要意义

作为膜受体最大的一个家族,G蛋白偶联受体(GPCRs)参与了广泛的生理与病理过程,因而一直是新药发现及研究的最重要靶点。孤儿GPCRs(oGPCRs)是一类内源性配基未定、功能未知的GPCRs,作为创新药物的靶点具有重要的地位和意义。     

G蛋白偶联受体/分泌酶复合体调节阿尔兹海默症发病进程的新机制

目的目前对于特异性调控分泌酶剪切淀粉样蛋白前体蛋白的分子机制尚不十分清楚,而临床上抗阿尔兹海默症(A lzhe im ers′D isease,AD)药物的疗效也不足以从根本上缓解病理症状的恶化。对G-蛋白偶联受体(G-prote in coup led receptors,GPCR s)在AD疾病进程的调节机制相关研究进展予以总结,对于以GPCR作为药物靶点的潜在可能性进行讨论。方法对于特异性调控分泌酶剪切淀粉样蛋白前体蛋白的分子机制相关的细胞生物学领域以及AD疾病模型上对于发病机制的研究进展进行总结归纳,并针对该领域的几个重要科学问题进行讨论。结果与结论GPCR对于AD疾病进程的调节机制,尤其是其与分泌酶形成的复合体对于β-淀粉样蛋白(amyloid-,βAβ)产生以及AD发病的调节机制,具有理想的特异性,可成为抗AD药物的新型潜在靶点。     

Emerging concepts of guanine nucleotide-binding protein-coupled receptor (GPCR) function and implications for high throughput screening

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.     

Techniques: Recent developments in computer-aided engineering of GPCR ligands using the human adenosine A3 receptor as an example

G-protein-coupled receptors (GPCRs) represent the largest known family of signal-transducing molecules, and convey signals for light and many extracellular regulatory molecules. GPCRs are dysfunctional or dysregulated in several human diseases and are estimated to be the targets of >40% of the drugs used in clinical medicine today. The crystal structure of rhodopsin provides the first information on the three-dimensional structure of GPCRs, which now supports homology modeling studies and structure-based drug-design approaches. In this article, we review recent work on adenosine receptors, a family of GPCRs, and, in particular, on adenosine A(3) receptor antagonists. We focus on an iterative, bi-directional approach in which models are used to generate hypotheses that are tested by experimentation; the experimental findings are, in turn, used to refine the model. The success of this approach is due to the synergistic interaction between theory and experimentation.     

Ligand-based homology modeling as attractive tool to inspect GPCR structural plasticity

G protein-coupled receptors (GPCRs) represent the largest family known of signal-transducing molecules. They convey signals for light and many extracellular regulatory molecules. GPCRs have been found to be dysfunctional/dysregulated in a growing number of human diseases and they have been estimated to be the targets of more than 40% of the drugs used in clinical medicine today. The crystal structure of rhodopsin provides the first three-dimensional GPCR information, which now supports homology modeling studies and structure-based drug design approaches. Here, we review our recent work on adenosine receptors, a family of GPCRs and, in particular, on A(3) adenosine receptor subtype antagonists. We will focus on an alternative approach to computationally explore the multi-conformational space of the antagonist-like state of the human A(3) receptor. We define ligand-based homology modeling as new approach to simulate the reorganization of the receptor induced by the ligand binding. The success of this approach is due to the synergic interaction between theory and experiment.