[In vivo imaging of amyloid plaques in the brain]

The pathological hallmark of Alzheimer's disease (AD) is the deposition of senile plaques (SPs) and neurofibrillary tangles. The deposition of SPs, which initially occurs in the neocortex, is regarded as the critical event for the pathogenesis of AD. Previous pathological studies indicated that the earliest deposition of SPs is suspected to occur before any detectable cognitive decline. Therefore, noninvasive imaging of brain SPs is considered to be an ideal diagnostic method for presymptomatic detection of AD. For in vivo detection of SPs in the brain, a lipophilic probe that can selectively binds SPs is indispensable to the examination using positron emission tomography (PET) or single photon emission computed tomography (SPECT). For this purpose, many kinds of amyloid binding agents have been developed, such as FDDNP, BTA-1, IMPY. We have also developed a series of promising compounds for in vivo imaging of amyloid deposits. One of these compounds, compound-A, achieves high binding affinity for A beta fibrils. This agent also showed abundant initial brain uptake and short brain clearance half-life in normal mice. Furthermore, to investigate the in vivo binding property of compound-A to amyloid plaques, compound-A was intravenously administered to APP transgenic mice. Brain slices at 120 min post injection demonstrated specific binding of compound-A to amyloid plaques in the brain. These data emphasize the potential usefulness of compound-A as in vivo imaging probe for early diagnosis of AD.