Multiple-peptide conjugates for binding β-amyloid plaques of Alzheimer's disease

Formation of β-amyloid plaques in Alzheimer's disease is initiated by intermolecular contact of the 5-amino acid sequence, KLVFF, in β-amyloid peptides ranging in size from 40 to 43 residues. Through optimization of binding avidity using structure/function studies, we have found that the retro-inverso peptide, ffvlk, binds artificial fibrils made from Aβ^1-40 with moderate affinity (K_d = 5 × 10^-10 M). Conjugates having two copies of this peptide, whether connected by a long poly(ethylene glycol) (PEG) spacer or just two amino acids, display about 100-fold greater affinity for fibrils. Placing six copies of ffvlk on a branched PEG resulted in a 10 000-fold greater affinity (K_d = 1 × 10^-10 M) than the monomer peptide. This increased affinity was accompanied by more effective inhibition of the thioflavin T fluorescence signal, which correlates with neurotoxicity of plaques and fibrils. We propose that conjugates bearing several copies of ffvlk may be useful as diagnostic and therapeutic agents for Alzheimer's disease.