Synthetic amyloids as a new generic platform for PET imaging. From infectious disease to cancer imaging

Experimental data demonstrated that amyloid-like aggregation of proteins is induced by short amyloidogenic Aggregation Prone Regions (APRs) within a protein sequence. These APRs are able to self-assemble into β-sheets, resulting in the typical cross-β structured backbone of amyloids. These amyloidogenic sequence segments normally consist of 5-15 amino acids and contain hydrophobic amino acids of low net charge. It was demonstrated that such APRs are sufficient to induce amyloid-like aggregation and are present in the vast majority of naturally occurring proteins, often buried inside the hydrophobic core of the folded protein. When APRs are solvent-exposed, self-assembly takes places via intermolecular association of APRs. The inclusion of non-homologous sequences into the densely in-register stacking of otherwise identical side chains is sterically impeded. Proteins will therefore usually aggregate predominantly with identical proteins because of this sequence specificity of amyloid aggregation. The β-sheet propensity of a certain peptide segment can be determined by APR prediction algorithms, such as the TANGO algorithm. Previously, it was established that APRs can be used to develop synthetic amyloidogenic peptides called Pept-insTM. Pept-in stands for "Peptide Interferor" and they have a maximum length of around 20 amino acids. Their sequences are based on APRs present in a target protein, which are identified via the TANGO algorithm. Instead of ligand-receptor interaction or epitope-antibody binding, Pept-ins interact with their target through their APR via highly specific β-sheet aggregation interactions. Pept-ins have previously been investigated for target-specific knockdown by inducing the aggregation of the target protein, suitable for agricultural and therapeutic applications in plants, prokaryotes and eukaryotes and for in vitro detection purposes. In this Doctoral Thesis, the potential of Pept-ins for in vivo diagnostic imaging was explored. More specifically, the use of Pept-ins radiolabelled with positron-emitting radionuclides for positron emission tomography (PET) imaging of cancer and infection was evaluated. Radionuclide imaging methods such as PET enable non-invasive imaging of biological processes and diseases, employing the high affinity and high selectivity interaction of radiolabelled compounds with their target in vivo. Radiolabelled vascin, [68Ga]Ga-NODAGA-PEG4-vascin, and radiolabelled P2, [68Ga]Ga-NODAGA-PEG2-P2, were evaluated a