Abstract by Ida Vang Andersen

Parkinson’s disease (PD) is the second most common neurodegenerative disease, but the pathogenesis remains to be fully elucidated. Diagnosing patients with PD is based on neurological examination. This examination is unprecise and is usually only able to detect very late stages of PD. Even up-to-date molecular imaging methods such as Positron emission tomography (PET) is not much of a help as state-of-the-art PET tracers target the loss of dopaminergic neurons. As PD symptoms appear when around 70-90% of the dopaminergic neurons are lost, such measurements are not optimal and may be even too late for a meaningful treatment. One of the hallmarks of PD is the accumulation of the intrinsically disordered protein alpha-synuclein (aSyn) inside the neurons of the brain. This accumulation starts much earlier than dopaminergic neuron loss and is as such a valuable target to image PD at stages that might allow to prevent disease progression before the brain is damaged to such extent that treatment approaches appear to be useless. 

In this PhD study, the overall aim was to develop a peptide with high affinity and selectivity to intracellularly located aSyn. To develop such a peptide several challenges has been addressed. Firstly, a peptide with sufficient affinity for aSyn had to be identified. We investigated several peptide sequences based on the protein lymphocyte-activation gene 3 and were able to identify several promising lead structures. Further studies are now needed, using specific tracers with high binding affinity and selectivity, to investigate aSyn pathology, which hopefully could contribute to elucidate the pathogenesis of PD. Secondly, we aimed to identify possibilities to guide peptides over the blood-brain barrier (BBB). Usually, these structures cannot enter in the brain. For this purpose, we investigated two possibilities. I) We aimed to open the BBB with the bee venom melittin, which unfortunately was unsuccessful. II) We aimed to develop a pretargeted approach. Such an approach would have the advantage that transporter-guided BBB passage could be a way to by-passing conventional direct labeling approaches of peptides, that lead to very limited brain uptake. In this project, we developed a tetrazine that was able cross the BBB and was able to ligate in vivo to a target beyond the BBB. We optimized a radiolabeling procedure to reach acceptable radiochemical yields. Furthermore, we developed a model peptide based on [⁶⁴Cu]DOTATATE to verify if pretargeted imaging beyond the BBB was feasible. We confirmed first that the click-adducts of the Trans-cyclooctene-modified peptide and tetrazine were still able to bind to their target with high affinity. Future in vivo studies are needed to demonstrate the possibility of peptides to be used for imaging aSyn.

With this PhD study, I hope to have developed some new tools and methods that will allow us in the future to better understand PD and allow to develop effective treatments.