Chemical modulation of the nociceptive receptor TRPV1: Synthetic, biological and computational studies

El canal iònic Receptor Vanil·loide Tipus 1 (sigles en anglès TRPV1) es considera un important integrador de diverses senyals de dolor. D'entre tots els productes que interaccionen amb TRPV1, aquells que bloquegen el senyal doloros de forma no competitiva han atret l'interès dels investigadors que treballen en el camp. A partir de resultats prèviament obtinguts per a diversos peptoides que van mostrar activitat com antagonistes no competitius de TRPV1 i que van permetre proposar una senzilla hipòtesi farmacoforica que incloïa un grup catiònic i dos aromàtics idèntics, la present tesi es va centrar en el disseny i preparació de productes amb estructures més rígides, no peptoides, capaços d'interaccionar amb TRPV1 com bloquejadors no competitius. L'avaluació biològica d'una col·lecció de nous antagonistes i un estudi en profunditat in vitro i in vivo del compost més actiu van proporcionar informació sobre el mode d'acció d'aquests compostos. Entre diferents alternatives considerades, l'esquelet d'1,3,5-triazina va ser seleccionat com el més adequat per albergar els requisits estructurals del farmacòfor proposat. Es van sintetitzar un total de 38 1,3,5-triazines-2,4,6-trisubstituidas amb estructures químicament diverses utilitzant un procediment prèviament optimitzat. Un estudi per RMN combinat amb càlculs teòrics va permetre determinar que moltes d'aquestes triazines presenten diferents confórmers en equilibri en solució, derivats de la rotació dels enllaços que uneixen les tres cadenes laterals a l'anell de triazina. Deu d'aquestes van resultar especialment actives, bloquejant el canal TRPV1 amb valors de IC50 en el rang submicromolar. D'entre les triazines sintetitzades destaca el compost 46 per la seva elevada potència (IC50 = 50 nM), trobant-se entre els bloquejadors de TRPV1 més potents descrits fins al moment. La triazina 46 presenta una activitat polimodal capaç d'inhibir l'activació de TRPV1 per capsaïcina i pH, una toxicitat reduïda tant en assajos in vitro com in vivo i actua de forma selectiva sobre TRPV1. Quant a la seva manera d'acció, 46 actua com un bloquejador de canal obert que s'uneix en una posició relativament profunda dins del porus aquós del canal. S'han construït models 3D-QSAR emprant la tècnica CoMSIA, que correlacionen les propietats estructurals de la col·lecció de compostos sintetitzats amb la seva activitat. Aquests models donen suport a la hipòtesi inicial sobre els determinants estructurals de l'activitat antagonista TRPV1, i constitueixen una eina per a la predicció de l'activitat de nous compostos. Emprant aquests models es va predir una activitat en el rang baix micromolar per membres d'una família de analegs basats en un esquelet central de pirrolidina. La síntesi i avaluació de l'activitat antagonista de TRPV1 d'alguns d'aquests anàlegs va confirmar les prediccions, validant els models 3D-QSAR i establint aquests compostos com un interessant punt de partida per al desenvolupament d'una nova família d'antagonistes.El canal iónico Receptor Vanilloide Tipo 1 (siglas en ingles TRPV1) se considera un importante integrador de diversas señales de dolor. De entre todos los productos que interaccionan con TRPV1, aquellos que bloquean la señal dolorosa de forma no competitiva han atraído el interés de los investigadores que trabajan en el campo. A partir de resultados previamente obtenidos para varios peptoides que mostraron actividad como antagonistas no competitivos de TRPV1 y que permitieron proponer una sencilla hipótesis farmacoforica que incluía un grupo catiónico y dos aromáticos idénticos, la presente tesis se centró en el diseño y preparación de productos con estructuras más rígidas, no peptoides, capaces de interaccionar con TRPV1 como bloqueadores no competitivos. La evaluación biológica de una colección de nuevos antagonistas y un estudio en profundidad in vitro e in vivo del compuesto más activo proporcionaron información sobre el modo de acción de estos compuestos. Entre diferentes alternativas consideradas, el esqueleto de 1,3,5-triazina fue seleccionado como el más adecuado para albergar los requisitos estructurales del farmacóforo propuesto. Se sintetizaron un total de 38 1,3,5-triazinas-2,4,6-trisubstituidas con estructuras químicamente diversas utilizando un procedimiento previamente optimizado. Un estudio por RMN combinado con cálculos teóricos permitió determinar que muchas de estas triazinas presentan diferentes conformeros en equilibrio en solución, derivados de la rotación de los enlaces que unen las tres cadenas laterales al anillo de triazina. Diez de de ellas resultaron especialmente activas, bloqueando el canal TRPV1 con valores de IC50 en el rango submicromolar. De entre las triazinas sintetizadas destaca el compuesto 46 por su elevada potencia (IC50 = 50 nM), encontrandose entre los bloqueadores de TRPV1 más potentes descritos hasta el momento. La triazina 46 presenta una actividad polimodal capaz de inhibir la activacion de TRPV1 por capsaicina y pH, una toxicidad reducida tanto en ensayos in vitro como in vivo y actúa de forma selectiva sobre TRPV1. En cuanto a su modo de acción, 46 actúa como un bloqueador de canal abierto que se une en una posición relativamente profunda dentro del poro acuoso del canal. Se han construido modelos 3D-QSAR empleando la técnica CoMSIA, que correlacionan las propiedades estructurales de la colección de compuestos sintetizados con su actividad. Estos modelos dan soporte a la hipótesis inicial sobre los determinantes estructurales de la actividad antagonista de TRPV1, y constituyen una herramienta para la predicción de la actividad de nuevos compuestos. Usando dichos modelos se predijo una actividad en el rango bajo micromolar para miembros de una familia de analogos basados en un esqueleto central de pirrolidina. La síntesis y evaluación de la actividad antagonista de TRPV1 de alguno de estos análogos confirmó las predicciones, validando dichos modelos 3D-QSAR y estableciendo dichos compuestos como un interesante punto de partida para el desarrollo de una nueva familia de antagonistas.The ion channel Vanilloid receptor type 1 (TRPV1) is considered an important integrator of various pain stimuli. Among the products that interact with TRPV1, the ones blocking the “pain signal” in an uncompetitive manner have attracted the attention of researchers working in the field. Based on previously obtained results for several peptoid hits that showed activity as uncompetitive TRPV1 antagonists, and that allowed to propose a basic pharmacophoric hypothesis consisting on one cationic and two identical aromatic moieties, this thesis focused on the design and synthesis of new antagonists with a more rigid non-peptoid structure. Biological evaluation of a collection of new blockers and an in depth in vitro and in vivo study of the most active one provided knowledge about their mode of action. In addition, a 3D-quantitative structure-activity relationship study (3D-QSAR) allowed to generate models that explain the observed biological activity and can help to predict the activities of new compounds. The 1,3,5-triazine skeleton was selected as rigid non-peptoid scaffold that can hold the three required pharmacophoric features. A total of 38 2,4,6-trisubstituted-1,3,5-triazines were synthesized using an optimized procedure. An in depth NMR study combined with theoretical calculations allowed to determine that most of these triazines present different conformers in equilibrium in solution, derived from the rotation of the bonds that joint the three side chains to the triazine ring. Ten of those triazines were particularly active blocking TRPV1 with submicromolar IC50 values. Triazine 46 exhibited a remarkably high activity (IC50 = 50 nM) being one of the most potent TRPV1 blockers described. It behaves as a polymodal antagonist against capsaicin and pH activation signals, exhibiting a low toxicity profile both in vitro and in vivo. Concerning its mechanism of action, 46 acts as an open channel blocker that locates relatively deep within the aqueous channel pore. Statistically significant 3D-QSAR models were generated, using the CoMSIA methodology, for the anti-TRPV1 activity of the newly synthesized compounds. Those models reinforced the initial hypothesis on the structural requirements for uncompetitive TRPV1 antagonists and provided a quantitative tool that could help to predict the activity of new compounds. Using these models, an activity in the low micromolar range was estimated for a few members of a new family of pyrrolidine based TRPV1 antagonists. The synthesis and biological evaluation of some of them confirmed the activity prediction, further validating the 3D-QSAR models and establishing these pyrrolidine analogues as an interesting starting point for further development of new anti-TRPV1 compounds.

Investigation of the Hsp90 C-terminal Binding Site, Novel Inhibitors and Isoform-Dependent Client Proteins

The heat shock proteins represent an important class of pro-survival proteins that are intimately involved in cell survival, adaptation to cellular stress, and protein management. Heat shock protein 90 kDa (Hsp90) is a molecular chaperone responsible for the post-translational maturation of nascent polypeptides. Many of the Hsp90-dependent client proteins are involved in oncogenic processes, and accordingly, Hsp90 has emerged as a promising target for anti-cancer therapies. Unfortunately, the clinical evaluation of Hsp90 inhibitors has been met with dosing, scheduling, and toxicity issues. The Hsp90 inhibitors that have reached clinical trials bind to the Hsp90 N-terminal ATP-binding site and demonstrate pan-Hsp90 inhibition, as they bind to and inhibit all four human Hsp90 isoforms. This characteristic may rationalize the undesired toxicities related to Hsp90 inhibition. Interestingly, the identification and characterization of isoform specific client proteins has not been extensively explored. In addition, N-terminal Hsp90 inhibition results in the induction of the heat shock response, whereby the expression of Hsp90 and other heat shock proteins is induced. This attribute of N-terminal inhibitors results in the clinically observed dosing and scheduling detriments as levels of Hsp90 increase with administration of the drug. Described herein is the design, synthesis and biological evaluation of novel Hsp90 inhibitors that avoid the above mentioned therapeutic liabilities of currently known Hsp90 inhibitors. The identification and characterization of an Hsp90-isoform dependent client protein and an Hsp90-isoform selective inhibitor is also presented

Preclinical tools in PET-tracer development

PET (Positronen Emmissions Tomographie) ist eine innovative Technik zur Visualisierung und Quantifizierung von Rezeptoren und Transportern in-vivo und erlaubt dadurch die Untersuchung von z.B. neurologischen, psychiatrischen und onkologischen Erkrankungen auf molekularem Level. Daher ist es notwendig, (neue) PET-Radiopharmaka zu entwickeln, um nähere Einblicke in die biochemischen Mechanismen pathologischer Veränderungen zu bekommen. Die Entwicklung eines PET-Tracers beginnt mit der Idee für ein Molekül mit geeigneter chemischer Struktur und mit guten Bindungseigenschaften zum gewünschten Target. Wenn das Molekül diese Voraussetzungen erfüllt, wird es synthetisiert, und mit einem PET-Nuklid radioaktiv markiert. Dann folgen verschiedene Untersuchungen zur Evaluierung der präklinischen Parameter des Radiopharmakons. Zwei Hauptaspekte im Entwicklungsprozess von neuen Radiopharmaka sind: 1) eine einfache und verlässliche Produktionsmethode für den PET-Tracer -im Optimalfall automatisiert- als Voraussetzung für alle weiteren Schritte 2) die präklinischen Evaluierungsparameter des Tracers zur Untersuchung auf dessen Eignung für eine gewünschte humane Applikation in der Zukunft. Beide Aspekte, die radiochemische Herstellung bzw. Automatisierung und die biopharmazeutische Evaluierung, werden im Rahmen von 5 verschiedenen Studien in dieser Doktorarbeit präsentiert. Die Entwicklung und präklinische Evaluierung von 4 verschiedenen PET-Tracern ([11C]DASB, [18F]FE@SUPPY, [18F]FE@SUPPY:2, und [18F]FE@CIT) für 3 unterschiedeliche Zielregionen: den Serontonintransporter (SERT), den Adenosin A3 Rezeptor (A3R) und den Dopamintransporter (DAT), sind wie folgt beschrieben: Die erste Studie präsentiert eine schnelle und voll-automatisierte Methode, die die verlässliche radiochemische Herstellung von [11C]DASB (ein Tracer für das Imaging des SERT z.B. bei Depressionspatienten) für klinische Untersuchungen (z.B. für die Universitätsklinik für Psychiatrie, Arbeitsgruppe Neuroimaging, der MedUni Wien) mit diesem Tracer in Zukunft vereinfachen wird. [18F]FE@SUPPY wurde kürzlich von der Arbeitsgruppe Radiopharmazeutische Wissenschaften als der erste PET-Tracer für den A3R vorgestellt. Der Adenosin A3 Rezeptor, der erst vor kurzem entdeckt worden ist, wird besonders hoch in verschiedenen pathologischen Prozessen, jedoch fast nicht in Zellen von gesunden Geweben exprimiert. Mögliche Einsatzgebiete von Tracern des A3R umfassen somit Entzündungsprozesse, onkologische Gegebenheiten wie solide Tumore und Brust-, Dickdarm-, Lungen-, Pankreas-, Prostata-, Melanom- und Hirnmetastasen; Herzkrankheiten wie Ischämie, und neurologische Erkrankungen wie zerebrale Ischämie, Glaukom und Epilepsie. [18F]FE@SUPPY:2 ist ein ganz neues 18F-radiomarkiertes Molekül, das als zusätzlicher potentieller Radiotracer für den A3R im Rahmen der These vorgestellt wird. In der Arbeit (in den Manuskripten 2 & 3) ist sowohl die radiochemische Herstellung von [18F]FE@SUPPY:2, die Optimierung der Radiosynthese von [18F]FE@SUPPY, und die Automatisierung von beiden A3R-Tracern enthalten. Weiters werden auch die präklinischen Parameter wie Affinität, Selektivität, unspezifische Bindung, Biodistribution, logP, Autoradiographien, in-vitro und ex-vivo Metabolitenstudien dieser neuen Radiopharmaka in der Arbeit (Manuskripten 3 und 4) untersucht. Der Tracer [18F]FE@CIT (ein potentieller Tracer für den DAT zum Imaging von z.B. Parkinson) wurde erfolgreich bezüglich seiner metabolischen Stabilität und autaradiographischen Verteilung in einem Tiermodell im Rahmen der fünften Studie evaluiert. Die hohe Selektivität von [18F]FE@CIT gegenüber dem SERT und dem NET (Norepinephrintransporter) konnte bewiesen werden und war sogar signifikant höher als die Selektivität der etablierten Radiopharmaka [123I]ß-CIT and [123I]FP-CIT. Basierend auf diesen Daten, soll [18F]FE@CIT in Zukunft zur Diagnose von neurologischen und psychiatrischen Erkrankungen des Menschen (z.B. Parkinson, Depression, Drogenmissbrauch, etc.) angewendet werden. Dieses Projekt wurde teilweise von der Österreichischen Akademie der Wissenschaften (ÖAW: DOC-fFORTE Nr. 22347 von D. Häusler) und dem Österreichischen Wissenschaftsfonds (FWF: P19383-B09 von M. Mitterhauser) gesponsert.Positron Emission Tomography (PET) is the first choice technology for the visualization and quantification of receptors and transporters, enabling examination of e.g. neurological, psychiatric and oncological diseases on a molecular level. Therefore, new and innovative PET-radiopharmaceuticals need to be developed to get further insights into the biochemical mechanisms involved in pathological changes. PET-tracer development starts with the idea or modelling of the chemical structure of a (new) molecule with (hopefully) good binding characteristics to the desired target site. As next steps, the compound needs to be synthesized and radiolabelled with a suitable PET-nuclide. Then it has to be evaluated regarding its parameters in various preclinical experimental settings. Hence, two major tools are crucial in the development-process of new PET-tracers: 1) a fast and reliable production method –most desirable and optimal in an automated set-up, and 2) proof of tracer suitability (high affinity, high selectivity and specificity, beside low unspecific binding) through preclinical evaluation in an animal model, prior to human application. Both aspects, the radiochemical preparation and automatisation, as well as the biopharmaceutical evaluation are presented in the thesis in 5 different manuscripts. In detail, the development and preclinical evaluation of 4 different PET-tracers ([11C]DASB, [18F]FE@SUPPY, [18F]FE@SUPPY:2, and [18F]FE@CIT) for 3 targets, the serotonin transporter (SERT), the adenosine A3 receptor (A3R) and the dopamine transporter (DAT), respectively, are covered in the present thesis. The first manuscript presents a method for a fast, reliable and fully-automated radiosynthesis of [11C]DASB (a tracer for the imaging of the SERT in human brain in e.g. depression patients) will facilitate further clinical investigations (e.g. for the department of psychiatry and psychotherapy of the medical university of Vienna) with this tracer. [18F]FE@SUPPY was introduced as the first A3R PET-tracer recently. The adenosine A3 receptor is expressed in high levels in tumor cells, but not in the majority of normal cells. Potential application of a tracer for the A3R will be inflammation processes, oncological diseases as solid tumors; breast-, colon-, lung-, pancreas-, prostate-, melanoma- and brain metastases, as well as ischemia (brain and heart) and neurological pathologies as glaucoma and epilepsy. [18F]FE@SUPPY:2, a completely new potential 18F-fluoroethylated radiotracer for the A3R, is presented in the thesis. The thesis covers the radiochemical preparation of [18F]FE@SUPPY:2 and the automation of the radiosyntheses of both radiotracers in manuscript 2 and 3. Moreover, preclinical evaluations (affinity, selectivity, unspecific binding, biodistribution, logP, autoradiography and in-vitro and ex-vivo metabolic stability) of the two tracers were conducted, and also a comparison of these parameters are given in manuscripts 3 and 4. [18F]FE@CIT, a potential new tracer for imaging of the DAT for e.g. Parkinson patients, was successfully further evaluated in terms of metabolic stability against CES and autoradiographic distribution on rat brain slices. The high selectivity of [18F]FE@CIT over SERT and NET was confirmed in this study, and furthermore, it was even significantly higher than the selectivity of the well known tracers [123I]ß-CIT and [123I]FP-CIT. Based on these results, we aim for the future diagnostic application of [18F]FE@CIT in humans with neurological and psychiatric diseases caused by changes in the dopaminergic system (e.g. Parkinson’s disease, depression, drug abuse). This project was partly sponsored by the Austrian Academy of Sciences (DOC-fFORTE Nr. 22347) awarded to D. Haeusler and by the Austrian Science Fund (FWF P19383-B09) awarded to M. Mitterhauser

QSAR METHODS DEVELOPMENT, VIRTUAL AND EXPERIMENTAL SCREENING FOR CANNABINOID LIGAND DISCOVERY

G protein coupled receptors (GPCRs) are the largest receptor family in mammalian genomes and are known to regulate wide variety of signals such as ions, hormones and neurotransmitters. It has been estimated that GPCRs represent more than 30% of current drug targets and have attracted many pharmaceutical industries as well as academic groups for potential drug discovery. Cannabinoid (CB) receptors, members of GPCR superfamily, are also involved in the activation of multiple intracellular signal transductions and their endogenous ligands or cannabinoids have attracted pharmacological research because of their potential therapeutic effects. In particular, the cannabinoid subtype-2 (CB2) receptor is known to be involved in immune system signal transductions and its ligands have the potential to be developed as drugs to treat many immune system disorders without potential psychotic side-effects. Therefore, this work was focused on discovering novel CB2 ligands by developing novel quantitative structure-activity relationship (QSAR) methods and performing virtual and experimental screenings. Three novel QSAR methods were developed to predict biological activities and binding affinities of ligands. In the first method, a traditional fragment-based approach was improved by introducing a fragment similarity concept that enhanced the prediction accuracy remarkably. In the second method, pharmacophoric and morphological descriptors were incorporated to derive a novel QSAR regression model with good prediction accuracy. In the third method, a novel fingerprint-based artificial neural network QSAR model was developed to overcome the similar scaffold requirement of many fragment-based and other 3D-QSAR methods. These methods provide a foundation for virtual screening and hit ranking of chemical ligands from large chemical space. In addition, several novel CB2 selective ligands within nM binding affinities were discovered. These ligands were proven to be inverse agonists as validated by functional assays and could be useful probes to study CB2 signaling as well as potential drug candidates for autoimmune disesases

Immune-Mediated Drug Induced Liver Injury: A Multidisciplinary Approach

This thesis presents an approach to expose relationships between immune mediated drug induced liver injury (IMDILI) and the three-dimensional structural features of toxic drug molecules and their metabolites. The series of analyses test the hypothesis that drugs which produce similar patterns of toxicity interact with targets within common toxicological pathways and that activation of the underlying mechanisms depends on structural similarity among toxic molecules. Spontaneous adverse drug reaction (ADR) reports were used to identify cases of IMDILI. Network map tools were used to compare the known and predicted protein interactions with each of the probe drugs to explore the interactions that are common between the drugs. The IMDILI probe set was then used to develop a pharmacophore model which became the starting point for identifying potential toxicity targets for IMDILI. Pharmacophore screening results demonstrated similarities between the probe IMDILI set of drugs and Toll-Like Receptor 7 (TLR7) agonists, suggesting TLR7 as a potential toxicity target. This thesis highlights the potential for multidisciplinary approaches in the study of complex diseases. Such approaches are particularly helpful for rare diseases where little knowledge is available, and may provide key insights into mechanisms of toxicity that cannot be gleaned from a single disciplinary study