Development of alkoxy styrylchromone derivatives for imaging of cerebral amyloid-b plaques with SPECT

We report here the development of radioiodinated styrylchromone derivatives with alkoxy groups as single photon emission computed tomography (SPECT) imaging probes for cerebral amyloid-b (Ab) plaques. Among the derivatives, the methoxy derivative 14 and the dimethoxy derivative 15 displayed relatively high affinity for the Ab(1–42) aggregates with Ki values of 22 and 46 nM, respectively. Fluorescent imaging demonstrated that 14 and 15 clearly labeled thioflavin-S positive Ab plaques in the brain sections of Tg2576 transgenic mice. In the in vivo studies, [125I]14 and [125I]15 showed high initial brain uptake expressed as the percentage of the injected dose per gram (2.25% and 2.49% ID/g at 2 min, respectively) with favorable clearance (0.12% and 0.20% ID/g at 180 min, respectively) from the brain tissue of normal mice. Furthermore, in vitro autoradiography confirmed that [125I]15 binds thioflavin-S positive regions in Tg2576 mouse brain sections. The derivative 15 may be a potential scaffold for the development of in vivo imaging probes targeting Ab plaques in the brain. In particular, further structural modifications are required to improve the compounds binding affinity for Ab.