Assay to screen for molecules that associate with Alzheimer's related beta-amyloid fibrils

Small molecules that bind to aggregated forms of Abeta peptides show promise as potential in vivo labeling agents for the diagnosis and monitoring of Alzheimer's disease. A major challenge in developing potential imaging agents that target Abeta is to rapidly identify and evaluate the association of molecules with insoluble deposits of aggregated Abeta peptides. This paper describes a simple, parallel method to rapidly screen libraries of molecules for their ability to associate with fibrils formed from synthetic Abeta peptides by monitoring their ability to inhibit the interaction of a monoclonal anti-Abeta IgG with these fibrils. We demonstrate that this assay can detect the association of small molecules with Abeta fibrils at concentrations of small molecule in the nanomolar to millimolar range. By comparing results from the screening of a small set of 30 compounds, we illustrated that this assay can rapidly analyze the relative affinity of small molecules for Abeta fibrils and identified eight compounds that can bind to Abeta fibrils at <20 microM concentrations. Significant advantages of this assay are (1) the ability to screen structurally diverse molecules without requiring them to have specific spectroscopic or radiolabeled properties, (2) the ability to estimate the percentage of the surface of the fibrils covered by the small molecules, and (3) the ability to detect the association of small molecules that potentially bind to different sites along the fibril axis. This assay also has minimal requirements for equipment or specialized facilities and should, therefore, be useful for both academic and industrial laboratories.