Synthesis and biological evaluation of novel radioiodinated benzimidazole derivatives for imaging α-synuclein aggregates.

α-Synuclein (α-syn) aggregates are commonly found in the brains of patients with Parkinson's disease (PD), dementia with Lewy bodies (DLB), and some other diseases. Therefore, in vivo imaging of α-syn aggregates would aid in drug development, early diagnosis, and monitoring of disease status. In order to develop imaging probes targeting α-syn aggregates, we synthesized and evaluated three novel radioiodinated benzimidazole (BI) derivatives for selective imaging of α-syn aggregates. In binding experiments, BI-2 exhibited the highest selective binding affinity for α-syn aggregates among the BI derivatives. In addition, BI-2 clearly stained Lewy bodies in PD brain sections, but did not label senile plaques deposited in AD brain sections. However, in the biodistribution study using normal mice, [I]BI-2 did not demonstrate high brain uptake (0.56%ID/g at 2-min post-injection). Further structural modifications of the BI derivatives are needed, but the BI scaffold may be an attractive candidate for developing α-syn imaging probes.