Affinity-based inhibition of β-amyloid toxicity

Strategies for interfering with protein aggregation are important for elucidating and controlling the pathologies of amyloid diseases. We have previously identified compounds that block the cellular toxicity of the beta-amyloid peptide, but the relationship between their ability to inhibit toxicity and their affinity for Ad is unknown. To elucidate this relationship, we have developed an assay capable of measuring the affinities of small molecules for beta-amyloid peptide. Our approach employs immobilized beta-amyloid peptide at low density to minimize the problems that arise from variability in the beta-amyloid aggregation state. We found that low-molecular weight (MW of 700-1700) ligands for beta-amyloid can be identified readily by using surface plasmon resonance. The best of these bound effectively (K-d similar to 40 muM) to beta-amyloid. The affinities measured for peptides in the SPR assay correspond to results from Abeta cell toxicity assays. The most potent ligands for immobilized beta-amyloid are the most potent inhibitors of the neuronal cell toxicity of beta-amyloid. Compounds with dissocation constants above similar to100 muM did not show significant activity in the cell toxicity assays. Our data support the hypothesis that ligands exhibiting greater affinity for the beta-amyloid peptide are effective at altering its aggregation and inhibiting cell toxicity.