Feasibility of targeted alpha therapy for Alzheimer's disease using 211At-labeled agent targeting amyloid-β aggregates

Abstract

Objective: Amyloid-β (Aβ) aggregates have been recognized as therapeutic targets for Alzheimer's disease (AD). Targeted alpha therapy (TAT) using α-particles has the potential to be applied as a novel treatment approach for AD by reducing the quantity of Aβ aggregates. In this study, we developed a novel astatine-211-labeled pyridyl benzofuran (PBF) derivative, [²¹¹At]APBF-2, as a small molecule-based Aβ-TAT agent and evaluated its potential for in vivo use.

Methods: [²¹¹At]APBF-2 was synthesized in a one-step astatination process using the tributyltin precursor. In the Aβ aggregation inhibition assay, [²¹¹At]APBF-2 was added to a sample containing Aβ_1-42 monomers and thioflavin-T (ThT) and the mixture was incubated for 24 h. The quantity of Aβ aggregates was evaluated by measuring ThT fluorescence intensity. The biodistribution of [²¹¹At]APBF-2 (25 kBq/100 μL) was evaluated using ddY mice (n = 5).

Results: [²¹¹At]APBF-2 was synthesized in radiochemical yield of 57% with a radiochemical purity of over 95%. In the in vitro assay, [²¹¹At]APBF-2 showed a dose-dependent decrease in ThT fluorescence intensity, suggesting the ability of [²¹¹At]APBF-2 to inhibit Aβ aggregation. In the biodistribution study using normal mice, the initial brain uptake of [²¹¹At]APBF-2 was observed (2.95% injected dose/g at 2 min), demonstrating favorable Blood-brain barrier permeability.

Conclusions: These results suggest the feasibility of using [²¹¹At]APBF-2 as an Aβ-TAT agent for in vivo applications.

Keywords: Amyloid-β (Aβ); Astatine-211 (211At); Blood–brain barrier permeability; Pyridyl benzofuran (PBF); Targeted alpha therapy (TAT).