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

Adriana Di Nanni; Ran Sing Saw; Umberto M Battisti; Gregory D Bowden; Adam Boeckermann; Kaare Bjerregaard-Andersen; Bernd J Pichler; Kristina Herfert; Matthias M Herth; Andreas Maurer

doi:10.1021/acsomega.3c04292

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

ACS Omega. 2023 Aug 15;8(34):31450-31467. doi: 10.1021/acsomega.3c04292. eCollection 2023 Aug 29.

Authors

Adriana Di Nanni¹, Ran Sing Saw¹, Umberto M Battisti², Gregory D Bowden^{1

3}, Adam Boeckermann¹, Kaare Bjerregaard-Andersen⁴, Bernd J Pichler^{1

3}, Kristina Herfert¹, Matthias M Herth^{2

5}, Andreas Maurer^{1

3}

Affiliations

¹ Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard Karls University Tübingen, Röntgenweg 13, 72076 Tübingen, Germany.
² Department of Drug Design and Pharmacology, Faculty of Health and Medicinal Sciences, University of Copenhagen, Jagtvej 160, 2100 Copenhagen, Denmark.
³ Cluster of Excellence iFIT (EXC 2180) "Image-Guided and Functionally Instructed Tumor Therapies", Eberhard Karls University Tübingen, 72076 Tübingen, Germany.
⁴ Department of Antibody Engineering and Biochemistry, H. Lundbeck A/S, Ottiliavej 9, 2500 Valby, Denmark.
⁵ Department of Clinical Physiology, Nuclear Medicine & PET, Rigshospitalet, Blegdamsvej 9, 2100 Copenhagen, Denmark.

Abstract

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 (K_i = 25.4 ± 2.3 nM) and its less lipophilic analogue MFSB, which exhibited enhanced affinity to αSYN (K_i = 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.