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Amyloid beta (Aβ) peptides, which aggregate to form neocortical plaques in Alzheimer's disease, exist in states that range from soluble monomers and oligomers/protofibrils to insoluble fibrillar amyloid. The present study evaluated the effects of mAb158, a mouse monoclonal antibody version of lecanemab that preferentially binds to soluble Aβ protofibrils, in aged transgenic mice (Tg2576) with Aβ pathology. Female Tg2576 mice (12 months old) received weekly intraperitoneal mAb158 (35 mg/kg) or vehicle for 4 weeks or for 18 weeks, with or without a subsequent 12-week off-treatment period. Aβ protofibril levels were significantly lower in mAb158-treated animals at both 4 and 18 weeks, while longer treatment duration (18 weeks) was required to observe significantly lower Aβ42 levels in insoluble brain fractions and lower Aβ plaque load. Following the off-treatment period, comparison of the vehicle- and mAb158-treated mice demonstrated that the Aβ protofibril levels, insoluble Aβ42 levels and Aβ plaque load remained significantly lower in mAb158-treated animals, as compared with age-matched controls. However, there was a significant increase of brain accumulation of both the Aβ protofibril levels, insoluble Aβ42 levels and Aβ plaque load after treatment cessation. Thus, repeated mAb158 treatment of aged Tg2576 mice first reduced Aβ protofibril levels within 4 weeks of treatment, which then was followed by a reduction of amyloid plaque pathology within 18 weeks of treatment. These effects were maintained 12 weeks after the final dose, indicating that mAb158 had a disease-modifying effect on the Aβ pathology in this mouse model. In addition, brain accumulation of both Aβ protofibril levels and amyloid pathology progressed after discontinuation of the treatment which supports the importance of continued treatment with mAb158 to maintain the effects on Aβ pathology., Competing Interests: Declaration of competing interest BR, OZ, PA, EB, MB, AR, EG, HK, LS, PN, FE, GO, LL and CM are employees of BioArctic. LL is a co-founder and board member of BioArctic. YI, TF and AK are employees of Eisai., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Recent advances in immunotherapeutic approaches to the treatment of Alzheimer's disease (AD) have increased the importance of understanding the exact binding preference of each amyloid-beta (Aβ) antibody employed, since this determines both efficacy and risk for potentially serious adverse events known as amyloid-related imaging abnormalities. Lecanemab is a humanized IgG1 antibody that was developed to target the soluble Aβ protofibril conformation. The present study prepared extracts of post mortem brain samples from AD patients and non-demented elderly controls, characterized the forms of Aβ present, and investigated their interactions with lecanemab. Brain tissue samples were homogenized and extracted using tris-buffered saline. Aβ levels and aggregation states in soluble and insoluble extracts, and in fractions prepared using size-exclusion chromatography or density gradient ultracentrifugation, were analyzed using combinations of immunoassay, immunoprecipitation (IP), and mass spectrometry. Lecanemab immunohistochemistry was also conducted in temporal cortex. The majority of temporal cortex Aβ (98 %) was in the insoluble extract. Aβ42 was the most abundant form present, particularly in AD subjects, and most soluble Aβ42 was in soluble aggregated protofibrillar structures. Aβ protofibril levels were much higher in AD subjects than in controls. Protofibrils captured by lecanemab-IP contained high levels of Aβ42 and lecanemab bound to large, medium, and small Aβ42 protofibrils in a concentration-dependent manner. Competitive IP showed that neither Aβ40 monomers nor Aβ40-enriched fibrils isolated from cerebral amyloid angiopathy reduced lecanemab's binding to Aβ42 protofibrils. Immunohistochemistry showed that lecanemab bound readily to Aβ plaques (diffuse and compact) and to intraneuronal Aβ in AD temporal cortex. Taken together, these findings indicate that while lecanemab binds to Aβ plaques, it preferentially targets soluble aggregated Aβ protofibrils. These are largely composed of Aβ42, and lecanemab binds less readily to the Aβ40-enriched fibrils found in the cerebral vasculature. This is a promising binding profile because Aβ42 protofibrils represent a key therapeutic target in AD, while a lack of binding to monomeric Aβ and cerebral amyloid deposits should reduce peripheral antibody sequestration and minimize risk for adverse events., Competing Interests: Declaration of competing interest Malin Johannesson, Linda Söderberg, Olof Zachrisson, Nicolas Fritz, Helen Kylefjord, Eleni Gkanatsiou, Emily Button, Anne-Sophie Svensson, Adeline Rachalski, Patrik Nygren, Gunilla Osswald, Lars Lannfelt, and Christer Möller are employees and shareholders of BioArctic. Lars Lannfelt is a co-founder and board member of BioArctic., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

γ-Secretase inhibitors have been considered promising drug candidates against Alzheimer's disease (AD) due to their ability to reduce amyloid-β (Aβ) production. However, clinical trials have been halted due to lack of clinical efficacy and/or side effects. Recent in vitro studies suggest that low doses of γ-secretase inhibitors may instead increase Aβ production. Using a stem cell-derived human model of cortical neurons and low doses of the γ-secretase inhibitor DAPT, the effects on a variety of Aβ peptides were studied using mass spectrometry. One major focus was to develop a novel method for specific detection of oligomeric Aβ (oAβ), and this was used to study the effects of low-dose γ-secretase inhibitor treatment on intracellular oAβ accumulation. Low-dose treatment (2 and 20nM) with DAPT increased the secretion of several Aβ peptides, especially Aβx-42. Furthermore, using the novel method for oAβ detection, we found that 2nM DAPT treatment of cortical neurons resulted in increased oAβ accumulation. Thus, low dose-treatment with DAPT causes both increased production of long, aggregation-prone Aβ peptides and accumulation of intracellular Aβ oligomers, both believed to contribute to AD pathology., (Copyright © 2017 Elsevier Inc. All rights reserved.)