Detection and Imaging of Aβ1‐42 and Tau Fibrils by Redesigned Fluorescent X‐34 Analogues

• Published in: Chemistry : a European journal 2018-05, Vol.24 (28), p.7210-7216
• Main Authors: Zhang, Jun, Sandberg, Alexander, Konsmo, Audun, Wu, Xiongyu, Nyström, Sofie, Nilsson, K. Peter R., Konradsson, Peter, LeVine, Harry, Lindgren, Mikael, Hammarström, Per
• Format: Article
• Language: English
• Subjects: Affinity; Alzheimer's disease; Amyloid; amyloid ligands; Benzene; Binding sites; Brain; Chemistry; dyes/pigments; Fibrils; Fluorescence; Hydrocarbons; Ligands; microscopy; Neurodegenerative diseases; Neuroimaging; Optical properties; Pathology; Proteins; Tau protein
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201800501

We revisited the Congo red analogue 2,5‐bis(4′‐hydroxy‐3′‐carboxy‐styryl)benzene (X‐34) to develop this highly fluorescent amyloid dye for imaging Alzheimer's disease (AD) pathology comprising Aβ and Tau fibrils. A selection of ligands with distinct optical properties were synthesized by replacing the central benzene unit of X‐34, with other heterocyclic moieties. Full photophysical characterization was performed, including recording absorbance and fluorescence spectra, Stokes shift, quantum yield and fluorescence lifetimes. All ligands displayed high affinity towards recombinant amyloid fibrils of Aβ1‐42 (13–300 nm Kd) and Tau (16–200 nm Kd) as well as selectivity towards the corresponding disease‐associated protein aggregates in AD tissue. We observed that these ligands efficiently displaced X‐34, but not Pittsburgh compound B (PiB) from recombinant Aβ1‐42 amyloid fibrils, arguing for retained targeting of the Congo red type binding site. We foresee that the X‐34 scaffold offers the possibility to develop novel high‐affinity ligands for Aβ pathology found in human AD brain in a different mode compared with PiB, potentially recognizing different polymorphs of Aβ fibrils. New dyes from old: Four new fluorescent amyloid ligands based on the 2,5‐bis(4′‐hydroxy‐3′‐carboxystyryl)benzene (X‐34) scaffold with new optical properties are reported (see figure).