Thioflavin-based molecular probes for application in Alzheimer's disease: from in silico to in vitro models

Alzheimer{'}s disease (AD) is a neurological disease of confusing causation with no cure or prevention available. The definitive diagnosis is made postmortem{,} in part through the presence of amyloid-beta plaques in the brain tissue{,} which can be done with the small molecule thioflavin-T (ThT). Plaques are also found to contain elevated amounts of metal ions Cu(ii) and Zn(ii) that contribute to the neurotoxicity of amyloid-beta (A[small beta]). In this paper{,} we report in silico{,} in vitro{,} and ex vivo studies with ThT-derived metal binders 2-(2-hydroxyphenyl)benzoxazole (HBX){,} 2-(2-hydroxyphenyl)benzothiazole (HBT) and their respective iodinated counterparts{,} HBXI and HBTI. They exhibit low cytotoxicity in a neuronal cell line{,} potential blood-brain barrier penetration{,} and interaction with A[small beta] fibrils from senile plaques present in human and transgenic mice AD models. Molecular modelling studies have also been undertaken to understand the prospective ligand-A[small beta] complexes as well as to rationalize the experimental findings. Overall{,} our studies demonstrate that HBX{,} HBT{,} HBXI{,} and HBTI are excellent agents for future use in in vivo models of AD{,} as they show in vitro efficacy and biological compatibility. In addition to this{,} we present the glycosylated form of HBX (GBX){,} which has been prepared to take advantage of the benefits of the prodrug approach. Overall{,} the in vitro and ex vivo assays presented in this work validate the use of the proposed ThT-based drug candidate series as chemical tools for further in vivo development.