Development of a novel β-secretase binding assay using the AlphaScreen platform

Alzheimer's disease (AD) is a devastating neurodegenerative disease affecting millions of people. β-secretase-1 (BACE1), an enzyme involved in the processing of the amyloid precursor protein (APP) to form Aβ is a validated target for AD. Herein, the authors develop and validate a novel binding assay for BACE1 using the AlphaScreen platform that is amenable for high-throughput screening (HTS). Small-molecule BACE1 inhibitors of the hydroxyethylamine, hydantoin, and sulfamide classes were functionalized by biotin PEG linkers of varying lengths forming probes that were bound to streptavidin donor beads. BACE1 was coupled to nickel-chelate acceptor beads. Upon mixing, probes designed from all three classes registered high signal-to-background values in the AlphaScreen binding assay, where the interaction between probe and BACE1 was completely blocked by free parent compound. A probe from the hydantoin class was chosen for further optimization, where the final assay conditions of 50 nM BACE and 250 nM probe were used and Z(') values >0.75 were commonly observed. IC50 values determined by the AlphaScreen assay format exhibited ~10-fold greater sensitivity when compared with a fluorescence polarization-based activity assay. The assay was miniaturized to a 1536-well format for HTS, in which 525 000 compounds were screened.