Pentameric Thiophene‐Based Ligands that Spectrally Discriminate Amyloid‐β and Tau Aggregates Display Distinct Solvatochromism and Viscosity‐Induced Spectral Shifts

Abstract

A wide range of neurodegenerative diseases are characterized by the deposition of multiple protein aggregates. Ligands for molecular characterization and discrimination of these pathological hallmarks are thus important for understanding their potential role in pathogenesis as well as for clinical diagnosis of the disease. In this regard, luminescent conjugated oligothiophenes (LCOs) have proven useful for spectral discrimination of amyloid-beta (Aβ) and tau neurofibrillary tangles (NFTs), two of the pathological hallmarks associated with Alzheimer’s disease. Herein, the solvatochromism of a library of anionic pentameric thiophene-based ligands, as well as their ability to spectrally discriminate Aβ and tau aggregates, were investigated. Overall, the results from this study identified distinct solvatochromic and viscosity-dependent behavior of thiophene-based ligands that can be applied as indices to direct the chemical design of improved LCOs for spectral separation of Aβ and tau aggregates in brain tissue sections. The results also suggest that the observed spectral transitions of the ligands are due to their ability to conform by induced fit to specific microenvironments within the binding interface of each particular protein aggregate. We foresee that these findings might aid in the chemical design of thiophene-based ligands that are increasingly selective for distinct disease-associated protein aggregates.

A Palette of Fluorescent Thiophene‐Based Ligands for the Identification of Protein Aggregates

“…By applying general synthetic routes, including Suzuki cross-coupling of this building block with di-brominated phenylene, selenophene, quinoxaline, or benzodithiazole, followed by de-protection of the anionic side chains, four pentameric thiohene-based ligands, HS-163, HS-165, HS-167, and HS-169 with distinct central heterocyclic moieties were synthesized. In addition, the previously reported pentameric oligothiophene, HS-84 (Scheme1), [13] was included in the study.…”

“…All of the ligandsr evealed distinct excitation and emission characteristics when bound to recombinant Ab fibrils (Figure 2). When mixed with the amyloid-like fibrils, HS-84 (Figure 2A), HS-163 (Figure 2B), and HS-165 ( Figure 2C [12,13] PEPPSI = pyridine-enhanced precatalyst preparation stabilization and initiation.…”

“…Eur.J.2015, 21,15133 -15137 www.chemeurj.org emission spectra with enhanced intensity and the characteristic double peaks reported for anionic oligothiophenes bound to recombinant amyloid-like fibrils. [10][11][12][13] HS-167 and HS-169 also display redshifted excitation maximaa nd blueshifted emission maximaw hen bound to Ab 1-42 amyloid-like fibrils ( Table S2 in the Supporting Information). In addition, am ore pronounced enhancement of the emission intensity was observed from these D-A-D compounds upon interaction with the fibrils (Figure 2D,E).…”

Both lipopolysaccharide and lipoteichoic acids potently induce anomalous fibrin amyloid formation: assessment with novel Amytracker™stains

“…It is known that the Amytracker TM dyes are spectrally richer, can discriminate different forms of amyloid, and that their staining properties clearly differ from those of ThT [68,70,[77][78][79].…”

“…Some of these are referred to as luminescent conjugated oligothiophenes (LCOs) [68][69][70][71][72][73][74][75][76] and are marketed as Amytracker™ 480 and 680 (derived, respectively, from HS163 and hFTAA HS169 in the literature [71,74]), but proprietary structures that are not identical to them; (see Figure 1 for the chemical structures of HS163 and HS169). Although they too show strong selectivity for, and enhanced fluorescence when binding to, classical amyloid proteins, their staining properties clearly differ from those of ThT [68,70,[77][78][79]. In some cases, their binding affects prion formation itself [80,81] (and even ThT has anti-ageing properties at low concentrations [82]).…”