Development of a Proteolytically Stable Retro-Inverso Peptide Inhibitor of β-Amyloid Oligomerization as a Potential Novel Treatment for Alzheimer's Disease

The formation of beta-amyloid (A beta) deposits in the brain is likely to be a seminal step in the development of Alzheimer's disease. Recent studies support the hypothesis that A beta soluble oligomers are toxic to cells and have potent effects on memory and learning. Inhibiting the early stages of A beta aggregation could, therefore, provide a novel approach to treating the underlying cause of AD. We have designed a retro-inverso peptide (RI-OR2, H2N-r <- G <- k <- l <- v <- f <- f <- G <- r-Ac), based on a previously described inhibitor of A beta oliaomer formation (OR2, H2N-R-G-K-L-V-F-F-G-R-NH2). Unlike OR2, RI-OR2 was highly stable to proteolysis and completely resisted breakdown in human plasma and brain extracts. RI-OR2 blocked the formation of A beta oligomers and fibrils from extensively deseeded preparations of A beta(1-40) and A beta(1-42), as assessed by thioflavin T binding, an immunoassay method for A beta oligomers, SDS-PAGE separation of stable oligomers, and atomic force microscopy, and was more effective against A beta(1-42) than A beta(1-40). In surface plasmon resonance experiments, RI-OR2 was shown to bind to immobilized A beta(1-42) monomers and fibrils, with an apparent K-d of 9-12 mu M, and also acted as an inhibitor of A beta(1-42) fibril extension. In two different cell toxicity assays, RI-OR2 significantly reversed the toxicity of A beta(1-42) toward cultured SH-SY5Y neuroblastoma cells. Thus, RI-OR2 represents a strong candidate for further development as a novel treatment for Alzheimer's disease.