P1-420: Novel fluorene compounds bind A-Beta amyloid aggregates and neutralize their toxicity

Abstract

Aβ protein is the major protein constituent of the amyloid plaques seen in the brains of patients with Alzheimer's disease (AD). Recent evidence suggests that Aβ-oligomers (AβO), rather than fibrils, play an important role in the early pathogenesis of AD. The discovery of small molecule inhibitors of neurotoxicity induced by AβO, either applied extracellularly or accumulated intraneuronally, is an important goal of drug development for AD. However, 98% of small molecules fail to pass the blood-brain barrier (BBB). Here we tested the neuroprotective effect of several established amyloid ligands developed for amyloid imaging. The advantage of these compounds is that they can penetrate BBB and bind to various cerebral Aβ aggregates with high affinity and selectivity. MC65 protection assay, Surface plasmon resonance spectroscopy (SPR), Electron paramagnetic resonance (EPR) spectroscopy, Atomic force icroscopy (AFM), Electron microscopy (EM), in vivo tests using the 5xFAD mouse model. Out of several pharmacophores developed for amyloid imaging purpose, we selected two fluorenes using our previously published MC65 protection assay. The two fluorenes, K-01–162 and K-01–186, showed promising activity for protection against cytotoxicity induced by intracellular AβO. They showed wide therapeutic windows and little toxicity. SPR studies showed that these compounds bound AβO with an affinity comparable to that of Congo red. EPR spectroscopy studies demonstrated an increase in motional freedom of spin-labled peptides in AβO upon exposure to K01–162 and K01–186. Via binding to AβO, these compounds decreased the binding of AβO to synapses, therefore may prevent the synaptotoxicity induced by AβO. Studies using AFM and EM revealed the ability of K01–162 and K01–186 to disaggregate AβO and prevent the progressive Aβ aggregation. Our initial in vivo tests using the 5xFAD mouse model showed that the soluble Aβ species and amyloid plaque burden were decreased by the short-term intracerebroventricular infusion of K01–162. These results indicate that direct binding of K01–162 and K-01–186 to AβO can alter AβO structure and neutralize AβO toxicity. They are also effective in reducing the brain amyloid load. Based on our results, K01–162 and K01–186 have potential therapeutic value for AD.