Synthesis and biological evaluation of novel styryl benzimidazole derivatives as probes for imaging of neurofibrillary tangles in Alzheimer's disease.

This paper describes the synthesis and biological evaluation of styrylbenzimidazole (SBIM) derivatives as agents for imaging neurofibrillary tangles (NFT) in patients with Alzheimer's disease (AD). SBIM derivatives were prepared with 4-iodobenzene-1,2-diamine and substituted cinnamaldehydes. In binding experiments using recombinant tau and Aβ(1-42) aggregates, SBIM-3 showed higher affinity for the tau aggregates than Aβ(1-42) aggregates (ratio of K(d) values was 2.73). In in vitro autoradiography and fluorescent staining, [(125)I]SBIM-3 (or SBIM-3) bound NFT in sections of AD brain tissue. In biodistribution experiments using normal mice, all [(125)I]SBIM derivatives showed high initial uptake into (3.20-4.11%ID/g at 2 min after the injection) and rapid clearance from (0.12-0.33%ID/g at 60 min after the injection) the brain. In conclusion, appropriate structural modifications of SBIM derivatives could lead to more useful agents for the in vivo imaging of NFT in AD brains.