DEVELOPMENT OF A MULTI-MODALITY PLATFORM FOR OLIGOMERIC PROTEIN AGGREGATE IMAGING

Abstract

The accumulation of misfolded β-amyloid and tau protein deposits is the histopathological landmark for a variety of diseases of the central nervous system. Luminescent conjugated oligo- and polythiophenes (LCOs and LCPs) were recently identified as being able to distinguish between different types and morphologies of protein deposits, enabling the diagnosis of a broader subset of diseases (Klingstedt, T.; Chem.Eur.J.; 2013; 19: 10179). The aim of this work was to modify previously reported LCO pFTAA and optimize its pharmacokinetic properties to be compatible with in vivo application using positron emission tomography (PET), while retaining affinity and selectivity profiles for oligomeric morphologies of b-amyloid and tau protein. To this end, carboxylic acid groups which form an integral part of the pFTAA structure were replaced with 2,2,2-trifluoroethanol (TFE) groups to synthesize novel compound pTP-TFE (Fig. 1). Binding of pTP-TFE to synthetic oligomers and fibrils of b-amyloid and tau protein was evaluated using fluorescence spectrophotometry and transmission electron microscopy (TEM). The interaction of pTP-TFE with aggregates of b-amyloid was further evaluated using 19F-NMR spectroscopy. The synthesis of pTP-TFE was achieved in 9 steps, with an overall yield 1.5%. Fluorescence spectrophotometry revealed that pTP-TFE binds to earlier forms of b-amyloid aggregates in comparison to pFTAA, while the binding affinity for tau aggregates is similar between the two compounds. pTP-TFE shows a blue-shift in its spectra when bound to oligomeric aggregates of tau in comparison to fibril binding. Furthermore, studies using pTP-TFE and b-amyloid fibrils show that their interaction can be monitored by 19F-NMR, where binding leads to a downfield shift of both fluorine signals.