Deposition of β-amyloid (Aβ) is considered an important early event in the pathogenesis of Alzheimer's disease (AD), and reduction of Aβ levels in the brain could be a viable therapeutic approach. A potentially noninflammatory route to facilitate clearance and reduce toxicity of Aβ is to degrade the peptide using proteolytic nanobodies. Here we show that a proteolytic nanobody engineered to cleave Aβ at its α-secretase site has potential therapeutic value. The Asec-1A proteolytic nanobody, derived from a parent catalytic light chain antibody, prevents aggregation of monomeric Aβ, inhibits further aggregation of preformed Aβ aggregates, and reduces Aβ-induced cytotoxicity toward a human neuroblastoma cell line. The nanobody also reduces toxicity induced by overexpression of the human amyloid precursor protein (APP) in a Chinese hamster ovary (CHO) cell line by cleaving APP at the α-secretase site which precludes formation of Aβ. Targeted proteolysis of APP and Aβ with catalytic nanobodies represents a novel therapeutic approach for treating AD where potentially harmful side effects can be minimized.
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