Authors:	Riss, Patrick J.
Title:	On the development of novel cocaine-analogues for in vivo imaging of the dopamine transporter status
Online publication date:	27-Apr-2009
Year of first publication:	2009
Language:	english
Abstract:	The present thesis is concerned with the development of novel cocaine-derived dopamine transporter ligands for the non-invasive exploration of the striatal and extra-striatal dopamine transporter (DAT) in living systems. The presynaptic dopamine transporter acquires an important function within the mediation of dopaminergic signal transduction. Its availability can serve as a measure for the overall integrity of the dopaminergic system. The DAT is upregulated in early Parkinson’s disease (PD), resulting in an increased availability of DAT-binding sites in the striatal DAT domains. Thereby, DAT imaging has become an important routine diagnostic tool for the early diagnosis of PD in patients, as well as for the differentiation of PD from symptomatically similar medical conditions. Furthermore, the dopaminergic system is involved in a variety of psychiatric diseases. In this regard, DAT-selective imaging agents may provide detailed insights into the scientific understanding of the biochemical background of both, the progress as well as the origins of the symptoms. DAT-imaging may also contribute to the determination of the dopaminergic therapeutic response for a given medication and thereby contribute to more convenient conditions for the patient. From an imaging point of view, the former demands a high availability of the radioactive probe to facilitate broad application of the modality, whereas the latter profits from short-lived probes, suitable for multi-injection studies. Therefore, labelling with longer-lived 18F-fluoride and in particular the generator nuclide 68Ga is worthwhile for clinical routine imaging. In contrast, the introduction of a 11C-label is a prerequisite for detailed scientific studies of neuronal interactions. The development of suitable DAT-ligands for medical imaging has often been complicated by the mixed binding profile of many compounds that that interact with the DAT. Other drawbacks have included high non-specific binding, extensive metabolism and slow accumulation in the DAT-rich brain areas. However, some recent examples have partially overcome the mentioned complications. Based on the structural speciality of these leads, novel ligand structures were designed and successfully synthesised in the present work. A structure activity relationship (SAR) study was conducted wherein the new structural modifications were examined for their influence on DAT-affinity and selectivity. Two of the compounds showed improvements in in vitro affinity for the DAT as well as selectivity versus the serotonin transporter (SERT) and norepinephrine transporter (NET). The main effort was focussed on the high-affinity candidate PR04.MZ, which was subsequently labelled with 18F and 11C in high yield. An initial pharmacological characterisation of PR04.MZ in rodents revealed highly specific binding to the target brain structures. As a result of low non-specific binding, the DAT-rich striatal area was clearly visualised by autoradiography and µPET. Furthermore, the radioactivity uptake into the DAT-rich brain regions was rapid and indicated fast binding equilibrium. No radioactive metabolite was found in the rat brain. [18F]PR04.MZ and [11C]PR04.MZ were compared in the primate brain and the plasma metabolism was studied. It was found that the ligands specifically visualise the DAT in high and low density in the primate brain. The activity uptake was rapid and quantitative evaluation by Logan graphical analysis and simplified reference tissue model was possible after a scanning time of 30 min. These results further reflect the good characteristics of PR04.MZ as a selective ligand of the neuronal DAT. To pursue 68Ga-labelling of the DAT, initial synthetic studies were performed as part of the present thesis. Thereby, a concept for the convenient preparation of novel bifunctional chelators (BFCs) was developed. Furthermore, the suitability of novel 1,4,7-triazacyclononane based N3S3-type BFCs for biomolecule-chelator conjugates of sufficient lipophilicity for the penetration of the blood-brain-barrier was elucidated. Der präsynaptische Dopamintransporter (DAT) besitzt eine Schlüsselrolle in der Regulation der Dopaminkonzentration im synaptischen Spalt. Aus diesem Grund lässt die Messung der Dopamintransporter-Verfügbarkeit mit Hilfe der Positronen Emissions Tomographie (PET) detaillierte Rückschlüsse auf die Integrität des dopaminergen Systems zu. Dopaminerge Signalwege sind an einer Reihe von neurodegenerativen und psychiatrischen Erkrankungen, z.B. Morbus Parkinson oder Psychosen, beteiligt. Daher besitzt die Messung der DAT-Verfügbarkeit eine hohe Relevanz in der medizinischen Diagnostik und der Forschung. Zu diesem Zweck werden mit Positronen-emittierenden Radionukliden markierte, hochaffine und selektive Liganden des Dopamintransporters benötigt. Die vorliegende Arbeit befasst sich mit der Entwicklung neuer Dopamintransporterliganden für die PET. Zunächst wurde die Struktur-Aktivitäts-Beziehung einer neuen Generation von DAT-selektiven Kokainanaloga untersucht, die die Möglichkeit bieten sowohl mit Fluor-18 als auch mit Kohlenstoff-11 markiert zu werden. Aus dieser Studie gingen zwei neuartige, hochselektive und hochaffine Liganden des DAT hervor. Der Ligand mit der höchsten in vitro Affinität (PR04.MZ) wurde sowohl mit Fluor-18 als auch mit Kohlenstoff-11 markiert. Im Anschluss an die Markierung wurde PR04.MZ in vitro, ex vivo und in vivo in Nagetieren und Primaten evaluiert. Dabei konnte im lebenden Tier gezeigt werden, dass PR04.MZ hochspezifisch, selektiv und reversibel and den präsynaptischen DAT bindet. Zusätzlich ermöglicht der Ligand die Visualisierung und Quantifizierung striataler und extrastriataler Dopamintransporter, wodurch Studien der gesamten dopaminergen Nervenbahnen ermöglicht werden. Aufgrund der hohen klinischen Relevanz von DAT-Liganden, wurden außerdem Studien zur Entwicklung eines Gallium-68 markierten Analogons durchgeführt. Im Rahmen dieser Studien wurden schließlich neue bifunktionelle Chelatoren entwickelt, die die Einbringungen eines Galliumkomplexes in ein biologisch Relevantes Molekül ermöglichen. Des Weiteren wurde eine Gallium-68 markierte Modellverbindung hinsichtlich ihrer Fähigkeit die Blut-Hirn-Schranke zu überwinden untersucht.
DDC:	500 Naturwissenschaften 500 Natural sciences and mathematics
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 09 Chemie, Pharmazie u. Geowissensch.
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-4330
URN:	urn:nbn:de:hebis:77-19806
Version:	Original work
Publication type:	Dissertation
License:	In Copyright
Information on rights of use:	https://rightsstatements.org/vocab/InC/1.0/
Appears in collections:	JGU-Publikationen