In a recent article published in the Journal of Alzheimer’s & Dementia, researchers introduced and characterized a novel platform based on monoclonal antibodies (mAbs).
Study: APOE Christchurch-mimetic therapeutic antibody reduces APOE-mediated toxicity and tau phosphorylation. Image Credit: SewCreamStudio/Shutterstock.com
This platform aims to inform future treatment approaches for Alzheimer’s disease (AD) and consists of apolipoprotein E (ApoE)-Christchurch (Ch)-inspired mAbs, anti-ApoE-heparan sulfate proteoglycans (HSPG), and anti-ApoE-group-specific antigens (GAGs). These components target the ApoE gene, a robust genetic risk factor for sporadic AD.
Specifically, these mAbs were designed to inhibit the interaction between ApoE and HSPGs, using recombinant constructs of the HSPG domain of ApoE3 and ApoE3Ch. The researchers also investigated whether these mAbs competed for heparin binding to reduce ApoE-derived cytotoxicity in vitro and tau phosphorylation in vivo. Notably, tau is a microtubule-associated protein (MAP) that forms insoluble filaments in AD, leading to neurofibrillary tangles, while heparin is a sulfated polysaccharide widely used in surgeries to prevent blood clot formation.
Previously, the researchers identified a unique case of a Colombian woman who carried an E280A mutation in the presenilin-1 (PSEN1) gene, making her genetically susceptible to AD dementia in her 40s. Surprisingly, she resisted AD dementia until her 70s. Despite high amyloid levels, she had lower-than-expected tau pathology and neurodegeneration. This woman was homozygous for a rare APOE3 variant called Christchurch (APOE3Ch), named after the city in New Zealand where it was discovered. Importantly, the Christchurch R136S mutation in the HSPG-binding domain was also involved in binding to low-density lipoprotein (LDL) receptors and LDL receptor-related protein (LRP).
About the study
In this study, the researchers conducted an extensive search of the PubMed and Medline databases to explore AD therapies targeting ApoE. They found various biologics designed to reduce ApoE levels but none specifically targeting the arginine (Arg) amino acid (AA) residue at position 136 of the mutated PSEN1 gene carrier (the Christchurch case). This mutation confers protection against autosomal dominant AD (ADAD), a more aggressive form of AD.
The researchers synthesized peptides corresponding to the N-terminal (amino acids 114-144) HSPG-binding region of wild-type (WT) and Ch variants of the ApoE3 gene. These peptides induced an immune response in mice, leading to the generation of hybridoma cell lines secreting highly specific anti-ApoE antibodies. Using enzyme-linked immunosorbent assay (ELISA), the researchers screened supernatants from these hybridoma clones, ultimately identifying 7C11.mAb and 1H4.mAb as the most promising antibodies.
Furthermore, the team examined the potency and selectivity of these antibodies for various ApoE variants and performed heparin affinity high-performance liquid chromatography (HPLC) to evaluate their affinity for heparin. They also assessed the cytotoxicity reduction and overall efficacy of these antibodies in vitro.
Binding assays revealed that the library of mAbs differentially targeted all ApoE variants tested. Anti-ApoE3-HSPG antibodies, particularly 7C11 and 1H4, exhibited high selectivity for ApoE2 and ApoE4 variants.
Biologics assays confirmed that 7C11 had the highest binding affinity for ApoE4. In vitro experiments showed that 7C11 effectively reduced ApoE4-HSPG binding, mitigating cytotoxicity, while introducing the Ch mutation on ApoE4 abolished cytotoxicity.
Affinity chromatography and far-western blotting assays confirmed that these mAbs competitively inhibited the interaction between ApoE and GAGs at the ApoECh site. Intravitreal injections of ApoE3 in P301S Tg mice resulted in tau filament accumulation in the retina, which was rescued by the anti-ApoE antibody 7C11.mAb, indicating a reduction in ApoE3-driven tauopathy in vivo.
Among the mAbs targeting the HSPG-binding domain of ApoE3/ApoE3Ch, 7C11.mAb emerged as the most relevant candidate due to its high affinity for ApoE4, the strongest risk factor for late-onset AD, and its clinical relevance to ApoE3.
Importantly, none of the mAbs bound to mouse ApoE, highlighting their specificity for human ApoE. However, this specificity also posed challenges in assessing their preclinical efficacy in mouse models.
The authors suggest that future studies should explore multiple ApoE-targeting approaches to enhance the chances of finding effective therapies for all AD patients.
Additionally, further research should investigate the effects of 7C11 in advanced tauopathy. While the researchers anticipated limited therapeutic potential for anti-ApoE3Ch mAbs, their approach, inspired by a case report of a delayed cognitive decline due to the ApoE Ch mutation, holds significant clinical promise.
ApoECh-specific antibodies may serve as valuable tools for detecting detrimental (ApoE4) and protective (ApoE3Ch) variants in vivo and potentially contribute to future AD-modifying therapies by reducing tau pathology.