Biophysical Tools; Binding Assay; Organic Chemistry; Post-photoaffinity Modifications; Ligand-gated Ion Channels; Neuroscience; Serotonin 5-HT3 Receptor; Fluorescence Spectroscopy
Thompson Andrew J., Metzger Simon, Lochner Martin, Ruepp Marc-David (2017), The Binding Orientation of Epibatidine at α7 nACh Receptors, in Neuropharmacology
, 116, 421-428.
Marc-David Ruepp, Hao Wei, Michele Leuenberger, Martin Lochner, Andrew J. Thompson (2017), The Binding Orientations of Structurally-related Ligands Can Differ; A Cautionary Note, in Neuropharmacology
, 119, 48-61.
Leuenberger Michele, Ritler Andreas, Simonin Alexandre, Hediger Matthias A., Lochner Martin (2016), Concise Asymmetric Synthesis and Pharmacological Characterization of All Stereoisomers of Glutamate Transporter Inhibitor TFB-TBOA and Synthesis of EAAT Photoaffinity Probes, in ACS Chemical Neuroscience
, 7, 534-539.
Mu Linjing, Müller Herde Adrienne, Rüefli Pascal M., Sladojevich Filippo, Milicevic Sephton Selena, Krämer Stefanie D., Thompson Andrew J., Schibli Roger, Ametamey Simon M., Lochner Martin (2016), Synthesis and Pharmacological Evaluation of [11C]Granisetron and [18F]Fluoropalonosetron as PET Probes for 5-HT3 Receptor Imaging, in ACS Chemical Neuroscience
, 7(11), 1552-1564.
Lochner Martin, Thompson Andrew J. (2016), The Muscarinic Antagonists Scopolamine and Atropine are Competitive Antagonists at 5-HT3 Receptors, in Neuropharmacology
, 108, 220-228.
Lochner Martin, Thompson Andrew J. (2015), A Review of Fluorescent Ligands for Studying 5-HT3 Receptors, in Neuropharmacology
, 98, 31-40.
Jack Thomas, Simonin Jonathan, Ruepp Marc-David, Thompson Andrew J., Gertsch Jürg, Lochner Martin (corresponding author) (2015), Characterizing New Fluorescent Tools for Studying 5-HT3 Receptor Pharmacology, in Neuropharmacology
, 90, 63-73.
Lochner Martin, Thompson Andrew J. (2015), Lighting up Neuroscience
, Elsevier, London.
Barden A. O., Goler A. S., Humphreys S. C., Tabatabaei S., Lochner Martin, Ruepp Marc-David, Jack Thomas, Simonin Jonathan, Thompson Andrew J., Jones J. P., Brozik James A. (2015), Tracking Individual Membrane Proteins and Their Biochemistry: The Power of Direct Observation, in Neuropharmacology
, 98, 22-30.
Jack Thomas, Ruepp Marc-David, Thompson Andrew J., Mühlemann Oliver, Lochner Martin (corresponding author) (2014), Synthesis and Characterization of Photoaffinity Probes that Target the 5-HT3 Receptor, in Chimia
, 68(4), 239-242.
Lochner Martin, Thompson Andrew J. (corresponding author) (2014), The Antimalarial Drug Proguanil Is an Antagonist at 5-HT3 Receptors, in Journal of Pharmacology and Experimental Therapeutics
, 351(3), 674-684.
Knight Anthony, Hemmings Jennifer L., Winfield Ian, Leuenberger Michele, Frattini Eugenia, Frenguelli Bruno G., Dowell Simon J., Lochner Martin, Ladds Graham, Discovery of Novel Adenosine Receptor Agonists that Exhibit Subtype Selectivity, in Journal of Medicinal Chemistry
The aim of this proposal is the design and synthesis of molecular tools which will allow the study of ligand- and voltage-gated ion channels (LGICs and VGICs) and G-protein coupled receptors (GPCRs) in cells, and thus aid our understanding of the function of these multi-subunit, transmembrane proteins. In addition to probes that monitor the function and cellular localisation of the target proteins by using fluorescence we also propose to develop probes which will facilitate their site-specific covalent modification. We anticipate that such modification probes provide the means to specifically modify the wild-type target receptors and ion channels and endow them with new properties (e.g. fluorescence) which in turn can be utilised to study their function in the cellular environment. What is more, we believe that such fluorescent probes and chemically modified receptors or ion channels can be used in binding assays for small molecules. The flux of ions across the cell membrane in both directions is vital for numerous physiological processes but cells need to control these events tightly. Charged particles like ions are not able to diffuse freely through the lipid bilayer which forms the plasma membrane and therefore ion channels represent transmembrane gates which open and close in response to external or internal stimuli. Ligand-gated ion channels (LGICs) are mostly located at nerve terminals, also called synapses, and are responsible for the fast transmission of action potentials between neurons. LGICs are assembled from several subunits and activated by small compounds (e.g. neurotransmitters) that bind to particular clefts which induces a conformational change from a non-conducting «closed» state to a conducting «open» state. Voltage-gated ion channels (VGICs) are opened and closed due to changes in membrane potential. LGICs and VGICs often work in accord in neurons: high influx of cations through opened LGICs for instance will change the membrane potential of the cell (i.e. depolarise the cell) to a certain threshold which in turn will cause VGICs to open and this is ultimately leading to the generation of an new action potential. G-protein coupled receptors (GPCRs) are also mostly activated by an external stimulus (e.g. small molecules) but they don’t possess a pore for ions to pass. Instead, activation of GPCRs triggers intracellular signalling cascades which are initiated by the associated G-proteins.Numerous mutations in ion channels genes are known to cause human diseases (so-called channelopathies). This not only demonstrates the crucial physiological importance of ion channels but it also makes them formidable drug targets. Small molecules can activate (agonists), block (antagonists) or enhance (positive allosteric modulators) ion channel function. Despite considerable achievements in the past ten or so years to solve high-resolution crystal structures of homologous prokaryotic and eukaryotic proteins, in some cases in complex with small molecules, we still have a poor understanding as to where most of the small compounds bind and how they are able to activate these complex macromolecular machines. A high-resolution crystal structure of the 5-HT3 receptor is not known for instance. Structures which have been determined for homologous proteins have allowed construction of 5-HT3R homology models with ambiguous accuracy. It should be noted that, albeit informative, crystal structures only reveal snap shots of a highly dynamic system and many structures in complex with small compounds represent thermodynamically stable states rather than real intermediates. We believe that small molecular probes that interact with these dynamic receptors and ion channels can deliver information about their function and to some extend their structure, and thus they can complement current molecular biology and structural biology techniques. We have already contributed to the field by developing fluorescent ligands that specifically bind to the 5 HT3 receptor on the surface of live cells.With regards to the discovery of new drugs it is still very challenging to design compounds with desired properties (antagonist, (partial) agonist, positive allosteric modulator) from scratch and one ends up with synthesising large compound libraries that are tested using low- to medium-throughput biological assays.This present proposal is an extension of the current SNSF Professorship and we will focus on the projects that in our mind have the most solid basis and greatest prospect of success. More precisely, (i) we shall develop fluorescent probes for the in vivo imaging of the serotonin 5-HT3 receptor, a LGIC, in cells, native tissue or whole organisms. In addition, (ii) the fluorescent ligands should also be used in fluorescence-based binding assays (fluorescence polarisation) for small compounds that target this receptor. Furthermore, (iii) multi-functional probes containing the ligand moiety, a photo-inducible crosslinking tag and a fluorophore will be synthesised and used to covalently attach a fluorophore near the ligand binding site of the 5-HT3 receptor. This strategy is novel in that it avoids the necessity of introducing mutations in the target receptor in order to achieve conjugation with fluorophores. We propose to apply the same methodology and (iv) use our multi-functional probes to chemically label hERG, a cardiac voltage-gated potassium channel, with a small organic fluorophore. Finally, (v) fluorescent agonists acting on the adenosine A1 receptor (AA1R), a GPCR that regulates numerous physiological processes in the central nervous system, will be synthesised and used to study the activation and subsequent cellular internalisation of the AA1R.