Anti-Aβ single-chain variable fragment antibodies exert synergistic neuroprotective activities in Drosophila models of Alzheimer's disease

Both active and passive immunotherapy protocols decrease insoluble amyloid-ß42 (Aß42) peptide in animal models, suggesting potential therapeutic applications against the main pathological trigger in Alzheimer's disease (AD). However, recent clinical trials have reported no significant benefits from humanized anti-Aß42 antibodies. Engineered single-chain variable fragment antibodies (scFv) are much smaller and can easily penetrate the brain, but identifying the most effective scFvs in murine AD models is slow and costly. We show here that scFvs against the N- and C-terminus of Aß42 (scFv9 and scFV42.2, respectively) that decrease insoluble Aß42 in CRND mice are neuroprotective in Drosophila models of Aß42 and amyloid precursor protein neurotoxicity. Both scFv9 and scFv42.2 suppress eye toxicity, reduce cell death in brain neurons, protect the structural integrity of dendritic terminals in brain neurons and delay locomotor dysfunction. Additionally, we show for the first time that coexpression of both anti-Aß scFvs display synergistic neuroprotective activities, suggesting that combined therapies targeting distinct Aß42 epitopes can be more effective than targeting a single epitope. Overall, we demonstrate the feasibility of using Drosophila as a first step for characterizing neuroprotective anti-Aß scFvs in vivo and identifying scFv combinations with synergistic neuroprotective activities.