Drug Targets

A selection of articles from European Pharmaceutical Review covering Drug Targets, GPCRs, Ion Channels and Kinase:

 

Microfluidics in cell-to-cell signalling measurements

Microfluidics in cell-to-cell signalling measurements

30 June 2016  •  Laura D. Casto and Christopher A. Baker, University of Tennessee

Hormones are secreted molecules that carry biological information between cells. This type of cell-to-cell communication is vital to human life, and its dysregulation often underlies disease. In fact, the largest known class of cell surface receptors involved in hormone communication, G-protein coupled receptors, are also the largest class of known drug targets. Understanding these communication processes and their dysregulation requires an ability to ‘listen in’ on hormone communications with high fidelity. To do this, highly sensitive and specific measurements of often challenging-to-detect chemical species – for example, peptides and proteins – must be made from within complex matrices such as biological fluids and tissues. This challenge has given rise to sophisticated analytical techniques for in vivo hormone measurements, including implanted microelectrodes for in situ detection of electrochemically active hormones from model organisms, and microdialysis for in situ sampling of electrically inactive molecules for ex vivo measurements...

Chloride ion channels and transporters

Chloride ion channels and transporters: from curiosities of nature and source of human disease to drug targets

20 August 2013  •  Jonathan D. Lippiat, School of Biomedical Sciences, University of Leeds

Early in their undergraduate education, the student is introduced to various types of integral membrane protein: receptors, adhesion proteins, ion channels, ion pumps and ion transporters. As they progress through their studies, they find out that discrete gene families and protein structures are responsible for these different protein classes and there is never any reason to consider that there might be any ambiguity in assigning any particular protein to its appropriate protein class.

Cell based label-free assays in GPCR drug discovery

GPCRs: Cell based label-free assays in GPCR drug discovery

20 August 2013  •  Niklas Larsson, Linda Sundström, Erik Ryberg and Lovisa Frostne (AstraZeneca)

G protein-coupled receptors are one of the major classes of therapeutic targets for a broad range of diseases. The most commonly used assays in GPCR drug discovery measure production of second messengers such as cAMP or IP3 that are the result of activation of individual signalling pathways. Such specific assays are unable to provide a holistic view of the cell response after GPCR activation. This is now changing as label-free technologies and assays on whole cells have been developed that are unbiased towards the specific downstream pathways and capture the integrated cell response. In this mini-review, we focus on the application of one of these technologies, namely resonant waveguide grating (RWG) for measurements of dynamic mass redistribution (DMR) in intact cells upon GPCR activation. Since the technology is sensitive and non-invasive, it is applicable to most cell types, including primary cells with native receptor expression levels. We discuss how DMR assays have become an important component of GPCR drug discovery screening cascades and may have the potential to improve the ability to predict if compounds will be efficacious in vivo.

Table 1 Three generations of BCR-ABL inhibitor mentioned in this review

Getting to grips with drug resistance in the human protein kinase superfamily

21 February 2013  •  Patrick A Eyers, Department of Oncology, Sheffield Cancer Research Centre, University of Sheffield

Protein kinases represent a vast, partially untapped resource of drug targets for therapeutic intervention in human disease. The remarkable success of the tyrosine kinase inhibitor Imatinib, which is now the first-line therapy in Philadelphia-positive tyrosine kinase inhibitor Imatinibhas galvanised biomedical researchers in an attempt to repeat the landmark success of this ‘bench-to-bedside’ approach to therapy[1]. Imatinib inhibits the BCR-ABL fusion kinases responsible for driving these cancers, and its clinical efficacy provides compelling molecular evidence that this drug elicits life-extending clinical responses through an ‘on-target’ mechanism. Interestingly, Imatinib has several additional (non-ABL) protein kinase targets including oncogenic KIT, which also allows it to be employed for the treatment of high-risk Gastro Intestinal Stromal Tumours...

Drug Targets Supplement 2012

Drug Targets: In-depth focus 2012

11 December 2012  •  Patricia McDonald / Emmanuel Sturchler / Dayue Darrel Duan

GPCR allosteric modulation: new opportunities and challenges for drug discovery.
Chloride channels and cardiac arrhythmia: novel therapeutic targets?

Figure 1: Classification Scheme of GPCRs. R (Rhodopsin-like), S (Secretin-like), G (Glutamate-like), Others (Adhesion, Frizzled, Taste type-2, unclassified)

G protein coupled receptors – exploiting flexible conformations

3 September 2012  •  Kathryn L. Chapman, Imperial Drug Discovery Centre, Imperial College London and John B.C. Findlay & Gemma K. Kinsella, Department of Biology, National University of Ireland Maynooth

G-protein coupled receptors (GPCRs) are a diverse super-family of proteins located within the plasma membrane of eukaryotic cells which have a common architecture consisting of seven-transmembrane (7-TM) segments, connected by extracellular (ECL) and intracellular (ICL) loops. They differ from other 7-TM proteins in their ability to activate guanine-nucleotide binding proteins or β-arrestin and so initiate a signalling cascade. They have a wide range of physiological roles and provide many successful drug targets, playing a role in disorders including allergies, cardiovascular dysfunction, depression, obesity, cancer, pain, diabetes and a variety of central nervous system conditions. This review will give a general overview of GPCRs and how their structures and activities can be used in drug discovery...

GPCR screening and drug discovery: Challenges and latest trends

26 April 2012  •  Sofia M.A. Martins, João R.C. Trabuco, Gabriel A. Monteiro and Duarte Miguel Prazeres, Institute for Biotechnology and Bioengineering, Instituto Superior Técnico, Technical University of Lisbon

G-protein coupled receptors (GPCRs) are one of the most popular drug targets today. Almost one third of the approved drugs currently available rely on some kind of interaction with these receptors. The annual revenues are around USD 30 billion (109) and the fact that one quarter of the top US selling drugs are GPCR-related puts this drug target under the drug discovery spotlight. Also, GPCRs are one of the largest families in the human genome, with nearly 1,000 sequences identified as likely to be GPCRs. Among these, around 100 sequences have been confirmed as receptors, but have no known ligand or function. These so-called orphan receptors harbour the highest drug discovery potential. Still, even amongst the non-orphan receptors, only a handful are actually targeted by drugs...

Conformational Bias: A key concept for protein kinase inhibition

28 February 2012  •  Henrik Möbitz, Global Discovery Chemistry, Computer Aided Drug Design, Novartis Institutes for Biomedical Research and Doriano Fabbro, Expertise Platform Kinases, Novartis Institutes for Biomedical Research

Protein kinases act as molecular switches with remarkable plasticity and dynamics upon interaction with specific regulatory domains as well as modulators. Conformation provides a conceptual framework for understanding many aspects of kinase biology. The kinase domain has precise structural prerequisites for signal transfer and can oscillate between two major conformations: an on state with maximal kinase activity (active kinase) and an off state with minimal activity on the other extreme. Conformational bias, i.e. a shift in the equilibrium between active and inactive conformations is a key determinant in kinase regulation and can be brought about by many factors including post-translational modifications, regulatory proteins, ligand binding etc. Kinase inhibitors can be viewed as particular ligands to protein kinases. As the mode of action is linked to the binding mode, the selectivity as well as the kinetics of kinase inhibitors can often be rationalised based on the target conformation. Pathologic kinase deregulation often involves a shift towards the active conformation, leading to constitutive signalling. In this review, we discuss how mutations act as a conformational bias and depending on the mode of action can lead to activation of the protein kinase that can either result in resistance or contribute to the efficacy of kinase inhibitors. Deregulation of protein kinase activities by mutations and/or amplification are associated with a variety of pathologies ranging from cancer to inflammatory diseases, diabetes, infectious diseases and cardiovascular and metabolic disorders...

FIGURE 1 Schematic overview of a typical homology modelling procedure that is used to build threedimensional coordinates for a protein of unknown structure

Status and challenges in structure-based drug discovery for G protein-coupled receptors

13 December 2011  •  Henri Xhaard, Head of Computational Drug Discovery Group, Centre for Drug Research, University of Helsinki

The central location of G protein-coupled receptors (GPCRs) at the interface between the interior and exterior of cells, as well as their key role in signalling events, make GPCRs a prominent class of pharmaceutical targets. To date, approximately 40 per cent of known drugs are thought to act on GPCRs either directly or indirectly. GPCRs are for the most part inaccessible to structural determination due to difficulties to express, purify and crystallise them; however, progress of structure determination has led to seven new structures in the last decade. This number is still insufficient to conduct structure-based drug discovery on all available targets. Computational modelling is therefore a very useful surrogate and in this paper I discuss the reliability of atomistic three-dimensional models that are obtained through molecular modelling in light of the GPCRdock 2008 and 2010 competitions organised by the Scripps Institute. G protein coupled receptors (GPCRs) are key proteins involved in signalling and as such are prominent drug targets. Ligands that bind to GPCRs include small aminergic neuro - transmitters or hormones such as noradrenaline and adrenaline, dopamine, histamine, small peptides, nucleic acids, lipids or even opsins that contain light-reactive retinal chromophores. Altogether, in the human genome project, about 390 non-olfactory GPCRs have been identified; of which about 100 are orphan proteins without an identified ligand or cellular function...

FIGURE 1 Structures of active and inactive conformations of the β2 adrenoceptor Structures of the β2 adrenoceptor (light grey) in an inactive conformation with the antagonist carazolol bound (left33), and in an active conformation in complex with Gs (dark grey) and the agonist BI-167107 bound (right41). In both cases, the ligand is represented by black spheres to show the location of the orthosteric binding site within the membrane-spanning region of the protein. T4 lysozyme (black) is inserted in the third intracellular loop between helices 5 and 6 in the inactive structure (bottom left), and fused in the extracellular N-terminus for the active structure (top right), to remove flexibility and to provide polar surfaces for crystallisation. The nanobody (black, bottom right) served to stabilise the open conformation of Gs and also provided crystallisation contacts

Lead discovery for targeting G protein-coupled receptors

19 October 2011  •  Sandra Siehler and Sandra W. Cowan-Jacob, Novartis Institutes for BioMedical Research

G protein-coupled receptors (GPCRs) control a plethora of key physiological functions in every cell of an organism. GPCRs are therefore involved in many diseases, since altered ligand or receptor levels and genetic or epigenetic modifications can lead to GPCR dysfunction and hence a pathophysiological phenotype. About one third of currently marketed drugs target GPCRs. The human genome contains 720-800 predicted GPCRs, and about half of them respond to olfactory/sensory signals, whereas the others are known or predicted to be activated by endogenous ligands and many of these represent potential drug targets. Seventy seven per cent of these non-sensory GPCRs belong to the class A (rhodopsin-like) family, whereas 14 per cent represent class B (secretin-like) GPCRs, less than one per cent belong to the class C (metabotropic receptor-like) or the atypical frizzled-/smoothened receptor class, and the remaining 25 per cent are orphan receptors...

Figure 1 Process to obtain UV Scans of standards and assay samples. Solid compound samples are weighed

UV-Vis scan-based quality control of assay-ready plates for improved data integrity

19 April 2011  •  Gary K Smith, M Anthony Leesnitzer, Lois L Wright, Iona Popa-Burke, Trevor Casserly, Luke Miller, Melissa Gomez & Iris Scherer, GlaxoSmithKline

Quality biological data requires both a high quality assay and a high quality compound. While assay quality is very closely monitored and has been intensively studied in the past, the quality of the final compound solutions being tested in an assay has received little attention. Quality of these samples is critical to the screening process, especially for XC50 determinations used in structureactivity relationship (SAR) analyses. Many laboratories have implemented routine analytical quality control (QC) on the stock solutions of all compounds, as well as quality assurance (QA) procedures for the weighing and liquid handling instrumentation used to produce the final assay-ready plates. Unfortunately, the stock sample QC and instrumentation QA together do not address the issues of assay plate production; indeed, stock sample QC does not address what happens to the sample once it has entered a compound management solution store at all...

Figure 1 Cardiac safety schematic integrating indirect ion channel modulation analysis

Indirect modulation of cardiac ion channels and implications for preclinical safety assessment

19 August 2010  •  Gül Erdemli & Dmitri Mikhailov, Center for Proteomic Chemistry, Novartis Institutes for BioMedical Sciences and Albert M Kim, Translational Medicine, Novartis Institutes for BioMedical Sciences

The preclinical assessment of a small molecule’s liability for QT interval prolongation is an essential part of the drug discovery process. Patch clamp assays for heterologously expressed recombinant cardiac ion channels are widely used in the pharmaceutical industry to evaluate potential drug-channel interactions. These assays are generally acute assessments and are not designed to detect indirect channel modulations that may result in QT prolongation. Despite the abundant literature demonstrating potential transcriptional, translational and post-translational mechanisms for indirect ion channel modulation, contribution of these mechanisms to drug-induced QT prolongation and/or arrhythmia propensity is not well understood. In this brief review, we discuss some potential mechanisms through which indirect ion channel modulation can produce QT prolongation and strategies for their early detection and mitigation.

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