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-beta 42 (A beta 42) 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-A beta 42 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 A beta 42 (scFv9 and scFV42.2, respectively) that decrease insoluble A beta 42 in CRND mice are neuroprotective in Drosophila models of A beta 42 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 co-expression of both anti-A beta scFvs display synergistic neuroprotective activities, suggesting that combined therapies targeting distinct A beta 42 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-A beta scFvs in vivo and identifying scFv combinations with synergistic neuroprotective activities.