A Fluorescent Probe as a Lead Compound for a Selective α‑Synuclein PET Tracer: Development of a Library of 2‑Styrylbenzothiazoles and Biological Evaluation of [18F]PFSB and [18F]MFSB

• Published in: ACS omega Vol. 8; no. 34; pp. 31450 - 31467
• Main Authors: Di Nanni, Adriana, Saw, Ran Sing, Battisti, Umberto M., Bowden, Gregory D., Boeckermann, Adam, Bjerregaard-Andersen, Kaare, Pichler, Bernd J., Herfert, Kristina, Herth, Matthias M., Maurer, Andreas
• Format: Journal Article
• Language: English
• Published: American Chemical Society 29.08.2023
• ISSN: 2470-1343; 2470-1343
• DOI: 10.1021/acsomega.3c04292

A method to detect and quantify aggregated α-synuclein (αSYN) fibrils in vivo would drastically impact the current understanding of multiple neurodegenerative diseases, revolutionizing their diagnosis and treatment. Several efforts have produced promising scaffolds, but a notable challenge has hampered the establishment of a clinically successful αSYN positron emission tomography (PET) tracer: the requirement of high selectivity over the other misfolded proteins amyloid β (Aβ) and tau. By designing and screening a library of 2-styrylbenzothiazoles based on the selective fluorescent probe RB1, this study aimed at developing a selective αSYN PET tracer. [3H]­PiB competition binding assays identified PFSB (Ki = 25.4 ± 2.3 nM) and its less lipophilic analogue MFSB, which exhibited enhanced affinity to αSYN (Ki = 10.3 ± 4.7 nM) and preserved selectivity over Aβ. The two lead compounds were labeled with fluorine-18 and evaluated using in vitro autoradiography on human brain slices, where they demonstrated up to 4-fold increased specific binding in MSA cases compared to the corresponding control, reasonably reflecting selective binding to αSYN pathology. In vivo PET imaging showed [18F]MFSB successfully crosses the blood–brain barrier (BBB) and is taken up in the brain (SUV = 1.79 ± 0.02). Although its pharmacokinetic profile raises the need for additional structural optimization, [18F]MFSB represents a critical step forward in the development of a successful αSYN PET tracer by overcoming the major challenge of αSYN/Aβ selectivity.