On the development of novel cocaine-analogues for in vivo imaging of the dopamine transporter status [Elektronische Ressource] / Patrick J. Riß

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• Publié par: johannes_gutenberg-universitat_mainz
• Publié le: 01 janvier 2008
• Nombre de lectures: 19
• Langue: English
• Poids de l'ouvrage: 3 Mo

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On the development
of novel cocaine-analogues
for in vivo imaging of the
dopamine transporter status.

Dissertation

zur Erlangung des Grades

"Doktor der Naturwissenschaften"

im Promotionsfach Chemie

am Fachbereich Chemie, Pharmazie und Geowissenschaften
der Johannes Gutenberg-Universität in Mainz

Patrick J. Riß
geb. in Aachen

Mainz, den 21.11.08 1 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
18probes, suitable for multi-injection studies. Therefore, labelling with longer-lived F-fluoride
68and in particular the generator nuclide Ga is worthwhile for clinical routine imaging. In
11contrast, the introduction of a C-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
18 11subsequently labelled with F and C 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 >PET. Furthermore, the radioactivity uptake into the DAT-
rich brain regions was rapid and indicated fast binding equilibrium. No radioactive metabolite
18 11was found in the rat brain. [ F]PR04.MZ and [ C]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
68Ga-characteristics of PR04.MZ as a selective ligand of the neuronal DAT. To pursue
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 N S -type 3 3
BFCs for biomolecule-chelator conjugates of sufficient lipophilicity for the penetration of the
blood-brain-barrier was elucidated.
12 Table of Contents

1Abstract 1
2 Table of Contents 2
3Introduction 3
4Manuscripts 16
18A convenient chemo-enzymatic synthesis and F-labelling of both 4.1 17
enantiomers of trans-1-toluenesulfonyloxymethyl-2-fluoromethyl-
cyclopropane
4.2 Synthesis and monoamine uptake inhibition of conformationally restricted 34
2-carbomethoxy-3-phenyl tropanes
184.3 In vitro, ex vivo and in vivo characterisation of [ F]PR04.MZ in rodents: 58
A selective dopamine transporter ligand for low concentration imaging.
114.4 Efficient [ C]MeI methylation of PR04.MZ: A DAT-ligand for low 76
concentration imaging
11 18Comparison of [ C]PR04.MZ and [ F]PR04.MZ in anubis papio baboons: 4.5 83
A selective high-affinity DAT-ligand for low concentration imaging of the
extra-striate dopamine transporter
184.6 Efficient microwave-assisted direct fluorination of [ F]PRD04 and 96
18[ F]LBT999: Highly selective dopamine transporter ligands for PET
684.7 NODAPA-OH and NODAPA-(NCS) : Synthesis, Ga-radiolabelling 108n
and in vitro characterisation of novel versatile bifunctional chelators
for molecular imaging
684.8 Studies towards the synthesis of lipophilic bifunctional chelators for Ga 115
4.9 Radioaktiv-markierte Cyclopropan-Derivate DAT-affiner Tropane 125
5 Summary and Conclusions 137
6References 145

23 Introduction

The present thesis is concerned with design, preparation and biological evaluation of novel
cocaine derivatives for the non-invasive exploration of the functionality of the human
dopamine-transporter in high and low densities in the mammalian brain.

A historic progress in the methodological development of neuroscience has been made since
1Otto Loewi has discovered chemical neurotransmission in 1921. In these days quantitative
studies in vivo were mainly complicated due to the absence of a non-invasive method for
quantitative monitoring of compounds within the living subject. Until the discovery of single
photon emission computed tomography (SPECT) and the introduction of positron emission
2,3tomography (PET) by Michael Phelps and Ter-Pogossian in 1975, these examinations were
restricted to invasive postmortem, ex vivo and in vitro studies. In contrast, the new imaging
methods allowed the non invasive tracking and quantification of radioactive molecules in
non-toxic, non-pharmacodynamic concentrations according to the tracer principle defined by
4Georg de Hevesy. Since then, the advances in technical, hardware and software equipment,
the development of modern, non-invasive imaging techniques as well as the significant efforts
in the development of radioactive probes for this purpose have contributed to impressive
insights into the tissue distribution, metabolic rates and mechanisms of action of many
5biomolecules. In these terms, expanding George de Hevesy's tracer principle to living
systems may be one of the greatest advances since Otto Loewi's days.

Although the modern radiological in vivo imaging modalities computer tomography (CT) and
nuclear magnetic resonance imaging (MRI) provide superior lateral resolution (MRI, CT) and
tissue contrast (MRI), their application is limited (today) to primary morphologic information.
In contrast, the nuclear imaging methods SPECT and in particular PET provide quantitative
information on the biochemical and physiological function of molecules, cells and tissues
within the subject. Recently, this has led to the development of combined „multi-modality“
imaging approaches wherein nuclear and radiological imaging is fused (eg. PET/CT).
Thereby, quantitative PET data and structural alignment information is collected in a single
scanning procedure. Up to date PET/CT-scanners are prone to reliability, diagnostic
information and time-effectivity of any given examination (Figure 1).

At this point the physico-technical equipment has evolved to a highly technical routine
7modality. However, this expensive equipment is completely useless without the continued
influx of approppriate molecular probes, labelled with positron-emitting radionuclides, to
meet the medicinal challenges of the present century.

The most versatile representative among these molecular imaging probes / tracers is the
18 18glucose surrogate 2-desoxy-2-[ F]fluoro-D-glucose ([ F]FDG), a fluorine labelled non-
natural sugar derivative that can be applied as indicator for glucose transport and the glucose
phosphorylation rate, based on the Sokoloff-correlation between metabolic trapping of 2-
8 9 18desoxyglucose and natural glucose metabolism inside the body. [ F]FDG is not only the
most available and most cost-effective radiotracer for PET, but also provides the broad
molecular diagnosis of a variety