Benzothiazole‐Based Neutral Ratiometric Fluorescence Sensor for Amyloid Fibrils

Abstract

Early detection of amyloid fibrils is very important for the timely diagnosis of several neurological diseases. Thioflavin-T (ThT) is a gold standard fluorescent probe for amyloid fibrils and has been used for the last few decades. However, due to its positive charge, ThT is incapable of crossing the blood-brain barrier and cannot be used for in vivo imaging of fibrils. In the present work, we synthesized a neutral ThT derivative, 2-[2'-Me,4'-(dimethylamino)phenyl]benzothiazole (2Me-DABT), which showed a strong affinity towards the amyloid fibrils. On association with the amyloid fibrils, 2Me-DABT not only showed a large increase in its emission intensity, but also, unlike ThT, a large blueshift in its emission spectrum was observed. Thus, unlike ThT, 2Me-DABT is a potential candidate for the ratiometric sensor of the amyloid fibrils. Detailed photophysical properties of 2Me-DABT in amyloid fibrils and different solvent media were studied to understand its sensory activity. Fluorescence resonance energy transfer (FRET) studies suggested that the sites of localization for ThT and 2Me-DABT in amyloid fibrils are not same and their average distance of separation in amyloid fibrils was determined. The experimental data was nicely supported by molecular docking studies, which confirmed the binding of 2Me-DABT in the inner core of the amyloid fibrils.

A Comparative Photophysical Study of Structural Modifications of Thioflavin T-Inspired Fluorophores

“…mPAP_5 and ThT showed the same K D value ( K D (ThT) = 79.4 ± 6.1 μM, K D (mPAP_5) = 72.3 ± 6.7 μM) suggesting that the dye–amyloid interaction is tolerant against the benzothiazole methoxy substituent, further implying that the poorer photophysical properties of mPAP_5 compared to ThT do not originate from weaker binding. All PAP derivatives outperformed ThT as well as their corresponding mPAP partners by more than an order of magnitude, which was in agreement with the literature. ,, …”

“…Despite these advantages, ThT fluorescence in the context of amyloid aggregation is poorly understood. The optical and binding properties of some derivatives of ThT have been studied previously, including the cationic ICT dyes and neutral BTA − and 2Me-DABT. , Pittsburgh compound B (PiB), a structurally similar but neutral benzothiazole, has an affinity for amyloid approximately 300-fold greater than ThT, due to the increased lipophilicity which results in stronger interactions with hydrophobic residues . As a consequence, PiB does not undergo the enhancement of Φ Fl upon amyloid binding, rendering it a poor fluorescence reporter of amyloid.…”

Structural Analogue of Thioflavin T, DMASEBT, as a Tool for Amyloid Fibrils Study

“…The search for fluorescent dyes, with photophysical characteristics lying within the spectral region of the “biological transparency window”, is now an urgent task. In recent years, several different dyes were proposed for this aim (see, for example, refs − ), but the majority of these probes are currently poorly studied. It is not possible to make an unequivocal conclusion about whether their photophysical properties meet the main requirements of fluorescent probes for detecting amyloid fibrils, which tasks can be solved with their use, are there any limitations in these dyes application, and how versatile they are, etc.…”

Fluorescence Lifetime and Intensity of Thioflavin T as Reporters of Different Fibrillation Stages: Insights Obtained from Fluorescence Up-Conversion and Particle Size Distribution Measurements

“…The nanoparticle tracking analysis experiments with fluorescence detection were carried out with the use of ThT analog 2M-DMASEBT (trans2-(′-(dimethylamino)-2,6-dimethyl styryl)-3-ethyl-1,3- benzothiazole tosylate) ( Scheme 1 ) [ 42 ]. The 2M-DMASEBT was used in this experiment because of the red shift of its absorption and fluorescence spectra by approximately 100 nm compared to ThT [ 43 ], which allowed to excite it with 488 nm laser used in the NTA setup.…”