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Development of PET tracers for aggregated alpha-synuclein - towards imaging of Parkinson’s disease
1  1. Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University Tübingen, Röntgenweg 11-17, 72076 Tübingen, Germany
2  2. Cluster of Excellence iFIT (EXC 2180) “Image-Guided and Functionally Instructed Tumor Therapies”, Eberhard Karls University Tübingen, Germany
Academic Editor: Alfredo Berzal-Herranz (registering DOI)

Abstract: Aggregation of alpha-synuclein into fibrils and their deposition in Lewy-bodies is a characteristic hallmark of Parkinson’s disease, multiple system atrophy and various other neurodegenerative diseases. Better understanding of the spatiotemporal development of these aggregates would greatly facilitate diagnosis and therapy development and is thus desperately awaited. However, despite great efforts from different research groups in academia and industry no PET tracer for synuclein has reached clinical application yet. The need for high selectivity and optimal pharmacokinetic properties due to frequent presence of Aß and Tau co-pathologies, the intracellular localization and the low abundance of the target are critical challenges in the development of synuclein PET tracers. We are currently pursuing several libraries on independent scaffolds and assessing their binding to recombinant synuclein, Aß and Tau in direct or competitive assays. Automated radiolabeling procedures with 18F or 11C at high specific radioactivity are developed for promising tracer candidates. Furthermore, the compounds’ binding to human brain slices harboring defined pathology is measured using in vitro autoradiography. Blood-brain barrier penetration, pharmacokinetics and metabolism are assessed in healthy mice to ensure suitability for brain imaging with low non-specific retention. Using this strategy, we were able to achieve a diverse set of radiotracers with promising characteristics. While most of the compounds in literature suffer from suboptimal selectivity, we were able to identify a candidate with virtually absent Aß binding in our in vitro competition assay. While the pharmacokinetics of this candidate will need further optimization, the obtained data represent a promising starting point for future work.

Keywords: Radiotracer; PET imaging; Alpha-Synuclein; Parkinson’s disease