In Vitro and In Vivo Characterization of Novel Small-Molecule Alzheimer's Disease Amyloid-Beta Therapies

In recent years, studies have indicated that the presence of neurotoxic forms of aggregated amyloid-beta peptide have a strong correlation with the pathological progression of Alzheimer’s Disease. Therefore, the inhibition, modulation, and/or reduction of targeted amyloid-beta aggregates formation are considered promising therapeutic strategies to treat this disease. In order to search for novel small molecule modulators with good biocompatibility, our research group screened various FDA-approved food dyes and their close structural analogs. We recently reported that Brilliant Blue G and Erythrosin B are novel modulators of amyloid-beta monomer in vitro aggregation and cytotoxicity in a dose-dependent manner.
This dissertation details four additional characterization investigations (three in vitro and one in vivo) to further develop Brilliant Blue G, Erythrosin B, and their structural analogs as potential Alzheimer’s Disease therapeutics. First, we performed a structure-activity relationship analysis on Erythrosin B and its analogs and discovered the placement of heavy halogen atoms on the xanthene benzoate backbone structure to be a critical feature for the amyloid-beta monomer binding, aggregation, and cytotoxicity modulating activity observed. Second, having seen the potent effect of halogenation at generating effective amyloid-beta binding ligands, we then sought to explore the specific binding sites of Erythrosin B and its structural analogs on the amyloid-beta monomer target peptide. After creating a novel method for identifying ligand binding sites using dot blotting with a sequence-specific antibody panel, the technique revealed amino acids 10-16 of amyloid-beta as a common strong binding site for Erythrosin B and its analogs. Third, since we had thus far characterized the effects of Brilliant Blue G and Erythrosin B on amyloid-beta aggregation from the monomer state, we wanted to also investigate if these molecules could perturb pre-existing aggregates from a different side of the thermodynamic spectrum. To this end, we performed comparative structural studies on the different fates of very stable amyloid-beta fibrils remodeled by the two compounds, finding that Brilliant Blue G- and Erythrosin B-treatment generate fragmented amyloid-beta fibrils and protofibrils, respectively. Fourth, we sought to further evaluate these novel modulators in a more therapeutically-relevant Alzheimer’s Disease mouse model. Brilliant Blue G was selected to be tested first and administered to mice for three months. The results revealed that administration of Brilliant Blue G to the transgenic Alzheimer’s Disease mouse was well-tolerated, crossed the blood-brain barrier, rescued neuronal loss, and reduced intraneuronal amyloid-beta loading.