Is abeta a sufficient biomarker for monitoring anti-abeta clinical studies? A critical review

Molecular dynamics simulation of the brain-isolated single-domain antibody/nanobody from camels through in vivo phage display screening

Introduction

During the last decade, there has been a significant rise in the use of therapeutic antibodies or passive immunotherapy for treating various conditions like inflammation and cancer. However, these proteins face challenges reaching the brain and often require specialized delivery methods such as single-domain antibodies (sdAbs). Traditional antibodies struggle to efficiently cross the blood-brain barrier (BBB), hindering their effectiveness. Receptor-mediated transcytosis (RMT) offers a promising pathway for transporting large molecules essential for brain function and treatment across the BBB.

Methods

SdAbs and peptide ligands with an affinity for RMT receptors are commonly employed to enhance the transport of biotherapeutics compounds across the BBB. This research used a sdAbs phage-displayed library from 13 camelus dromedarius samples to identify sdABs that specifically bind to and are internalized by human BBB endothelial cells (ECs) through in vivo panning.

Results and discussion

One sdAb, defined as FB24, was isolated, sequenced, translated into an open reading frame (ORF), and subjected to three-dimensional (3D) modeling. Molecular docking and molecular dynamics simulations were carried out by the HADDOCK web server and GROMACS, respectively, to evaluate the interaction between FB24 and EC receptors in silico. The docking results revealed that FB24 exhibited binding activity against potential EC receptors with -1.7 to -2.7 ranged z score and maintained a stable structure. The docked complex of FB24-RAGE (receptor for advanced glycation end products, also known as advanced glycation end product receptor [AGER]) showed 18 hydrogen bonds and 213 non-bonded contacts. It was chosen for further analysis by molecular dynamics simulations by GROMACS. This complex showed a stable condition, and its root mean square deviation (RMSD) was 0.218 nm. The results suggest that FB24 could serve as a suitable carrier vector for transporting therapeutic and diagnostic agents across the BBB to the brain through a non-invasive route.

AuNPs- Aβ-Ni-HRP sandwich assay: A new sensitive colorimetric method for the detection of Aβ 1-40

Amyloid β-peptide (Aβ) is a key predictor for preclinical diagnosis of Alzheimer's disease (AD) and vascular diseases. In this work, we propose a gold nanoparticle (AuNPs)-Aβ-nickel (Ni)-horseradish peroxidase (HRP) based colorimetric assay for the detection of Aβ_1-40. The consecutive binding of Aβ_1-40 to AuNPs and metal ions is designed and examined for Aβ-specific aggregation of AuNPs and the generation of quantitative colorimetric signals. The affinity of Aβ_1-40 towards various metal ions was studied first, and two metal ions, Cu and Ni, were specifically tested with Metal Ion-Binding Site Prediction (MIB) and High-resolution Electrospray Ionization Mass Spectrometry (HR-ESI-MS). Subsequently, the binding of Aβ_1-40 and AuNPs was examined, and the binding between Aβ-AuNPs and Ni-HRP was finally analyzed by UV-Vis and nano-zetasizer. Based on the characterized dual binding of Aβ_1-40, a colorimetric sandwich assay was developed and the analytical performance of the developed assay has been evaluated with standard solutions and human serum samples. Good linearity within a range from 0 nM to 10 nM was found. The detection limits of 0.22 nM in the standard sample and 0.23 nM in the human serum sample have been demonstrated. The newly developed colorimetric sandwich assay is a short, simple, antibody-free assay and achieves high sensitivity with only 100 μL Aβ_1-40 samples. The assay has immense potential for the detection of Aβ_1-40 in biological or biomedical diagnosis.

Central Nervous System Delivery of Antibodies and Their Single-Domain Antibodies and Variable Fragment Derivatives with Focus on Intranasal Nose to Brain Administration

IgG antibodies are some of the most important biopharmaceutical molecules with a high market volume. In spite of the fact that clinical therapies with antibodies are broadly utilized in oncology, immunology and hematology, their delivery strategies and biodistribution need improvement, their limitations being due to their size and poor ability to penetrate into tissues. In view of their small size, there is a rising interest in derivatives, such as single-domain antibodies and single-chain variable fragments, for clinical diagnostic but also therapeutic applications. Smaller antibody formats combine several benefits for clinical applications and can be manufactured at reduced production costs compared with full-length IgGs. Moreover, such formats have a relevant potential for targeted drug delivery that directs drug cargo to a specific tissue or across the blood–brain barrier. In this review, we give an overview of the challenges for antibody drug delivery in general and focus on intranasal delivery to the central nervous system with antibody formats of different sizes.

Alzheimer's disease: from basic science to precision medicine approach

Alzheimer’s disease (AD) is the most common form of dementia in the elderly. Together with cerebral amyloid accumulation, several factors contribute to AD pathology including vascular alterations, systemic inflammation, genetic/epigenetic status and mitochondrial dysfunction. Much is now being devoted to neuroinflammation. However, anti-inflammatory drugs as numerous other therapies, mainly targeted on β-amyloid, have failed to show efficacious effects in AD. Timing, proper selection of patients, and the need for a multitarget approach appear to be the main weak points of current therapeutic efforts. The efficacy of a treatment could be better evaluate if efficient biomarkers are available. We propose here the application of precision medicine principles in AD to simultaneously verify the efficacy of a treatment and the reliability of specific biomarkers according to individually tailored biomarker-guided targeted therapies. People at risk of developing AD or in the very early phase of the disease should be stratified according to: (1) neuropsychological tests; (2) apolipoprotein E (ApoE) genotyping; (3) biochemical analysis of plasma and cerebrospinal fluid (CSF); (4) MRI and positron emission tomography and (5) assessment of their inflammatory profile by an integration of various genetic and biochemical parameters in plasma, CSF and an analysis of microbiota composition. The selected population should be treated with antiamyloidogenic and anti-inflammatory drugs in randomised, longitudinal, placebo-controlled studies using ad hoc profiles (eg, vascular profile, mitochondrial profile, etc…) If these criteria are adopted widely and the results shared, it may be possible to rapidly develop innovative and personalised drug treatment protocols with more realistic chances of being efficacious.

Challenges in Alzheimer's Disease Drug Discovery and Development: The Role of Modeling, Simulation, and Open Data

Alzheimer's disease (AD) is the leading cause of dementia worldwide. With 35 million people over 60 years of age with dementia, there is an urgent need to develop new treatments for AD. To streamline this process, it is imperative to apply insights and learnings from past failures to future drug development programs. In the present work, we focus on how modeling and simulation tools can leverage open data to address drug development challenges in AD.

Peripheral complement interactions with amyloid β peptide in Alzheimer's disease: 2. Relationship to amyloid β immunotherapy

INTRODUCTION

Our previous studies have shown that amyloid β peptide (Aβ) is subject to complement-mediated clearance from the peripheral circulation, and that this mechanism is deficient in Alzheimer's disease. The mechanism should be enhanced by Aβ antibodies that form immune complexes (ICs) with Aβ, and therefore may be relevant to current Aβ immunotherapy approaches.

METHODS

Multidisciplinary methods were employed to demonstrate enhanced complement-mediated capture of Aβ antibody immune complexes compared with Aβ alone in both erythrocytes and THP1-derived macrophages.

RESULTS

Aβ antibodies dramatically increased complement activation and opsonization of Aβ, followed by commensurately enhanced Aβ capture by human erythrocytes and macrophages. These in vitro findings were consistent with enhanced peripheral clearance of intravenously administered Aβ antibody immune complexes in nonhuman primates.

DISCUSSION

Together with our previous results, showing significant Alzheimer's disease deficits in peripheral Aβ clearance, the present findings strongly suggest that peripheral mechanisms should not be ignored as contributors to the effects of Aβ immunotherapy.

Synthesis and Evaluation of [(18)F]RAGER: A First Generation Small-Molecule PET Radioligand Targeting the Receptor for Advanced Glycation Endproducts

The receptor for advanced glycation endproducts (RAGE) is a 35 kDa transmembrane receptor that belongs to the immunoglobulin superfamily of cell surface molecules. Its role in Alzheimer's disease (AD) is complex, but it is thought to mediate influx of circulating amyloid-β into the brain as well as amplify Aβ-induced pathogenic responses. RAGE is therefore of considerable interest as both a diagnostic and a therapeutic target in AD. Herein we report the synthesis and preliminary preclinical evaluation of [(18)F]RAGER, the first small molecule PET radiotracer for RAGE (Kd = 15 nM). Docking studies proposed a likely binding interaction between RAGE and RAGER, [(18)F]RAGER autoradiography showed colocalization with RAGE identified by immunohistochemistry in AD brain samples, and [(18)F]RAGER microPET confirmed CNS penetration and increased uptake in areas of the brain known to express RAGE. This first generation radiotracer represents initial proof-of-concept and a promising first step toward quantifying CNS RAGE activity using PET. However, there were high levels of nonspecific [(18)F]RAGER binding in vitro, likely due to its high log P (experimental log P = 3.5), and rapid metabolism of [(18)F]RAGER in rat liver microsome studies. Therefore, development of second generation ligands with improved imaging properties would be advantageous prior to anticipated translation into clinical PET imaging studies.

Oligomeric α-synuclein and β-amyloid variants as potential biomarkers for Parkinson's and Alzheimer's diseases

Oligomeric forms of α-synuclein and β-amyloid are toxic protein variants that are thought to contribute to the onset and progression of Parkinson's disease (PD) and Alzheimer's disease (AD), respectively. The detection of toxic variants in human cerebrospinal fluid (CSF) and blood has great promise for facilitating early and accurate diagnoses of these devastating diseases. Two hurdles that have impeded the use of these protein variants as biomarkers are the availability of reagents that can bind the different variants and a sensitive assay to detect their very low concentrations. We previously isolated antibody-based reagents that selectively bind two different oligomeric variants of α-synuclein and two of β-amyloid, and developed a phage-based capture enzyme-linked immunosorbent assay (ELISA) with subfemtomolar sensitivity to quantify their presence. Here, we used these reagents to show that these oligomeric α-synuclein variants are preferentially present in PD brain tissue, CSF and serum, and that the oligomeric β-amyloid variants are preferentially present in AD brain tissue, CSF, and serum. Some AD samples also had α-synuclein pathology and some PD samples also had β-amyloid pathology, and, very intriguingly, these PD cases also had a history of dementia. Detection of different oligomeric α-synuclein and β-amyloid species is an effective method for identifying tissue, CSF and sera from PD and AD samples, respectively, and samples that also contained early stages of other protein pathologies, indicating their potential value as blood-based biomarkers for neurodegenerative diseases.

Clearing the amyloid in Alzheimer's: progress towards earlier diagnosis and effective treatments – an update for clinicians

SUMMARY 

A beta (Aβ or β-amyloid) is a key molecule in Alzheimer's disease (AD) pathogenesis. According to the ‘amyloid hypothesis’, the gradual accumulation of Aβ triggers events which results in neuronal loss in regions of the brain involved with memory and learning. Diverse agents have been developed to reduce brain Aβ accumulation or to enhance its clearance. Some have progressed to human trials, however all have failed to improve cognition in patients. This has led researchers to question whether Aβ is really the problem. However, the trials have been targeting end stages of AD, by which stage extensive irreversible neuronal damage has already occurred. Intervention is required preclinically, therefore preclinical AD biomarkers are needed. In this regard, amyloid imaging and cerebrospinal fluid biomarkers are leading the way, with plasma biomarkers and eye tests also being investigated. This review covers the current state of knowledge of Aβ as an early diagnostic biomarker and as a therapeutic target in AD.

Intravenous immunoglobulin for the treatment of Alzheimer's disease: current evidence and considerations

Alzheimer's disease (AD) is a devastating neurodegenerative form of dementia with increasing incidence rates in most countries. AD is characterized by amyloid plaques and neurofibrillary tangles in the brains of AD individuals accompanied by global neuronal loss. The peptide amyloid-β (Aβ) aggregates to amyloid plaques in AD brains. As a result, many therapeutic approaches target Aβ. Human plasma and the plasma product intravenous immunoglobulin (IVIG) contain naturally-occurring anti-Aβ antibodies (Nabs-Aβ) that appear to reduce risks of developing AD. IVIG sequesters Aβ and thus interferes with AD progression. This study reviews the role of different Aβ species, Nabs-Aβ, preclinical data, and clinical studies of IVIG as potential AD treatments. The focus of this study is the outcomes of a recent Gammaglobulin Alzheimer's Partnership Phase III trial that did not reach primary endpoints, as well as efforts to compare IVIG with current anti-Aβ monoclonals such as bapineuzumab, solanezumab, and BIIB037. Moreover, this study critically examines current market and ethical consequences of potential off-label uses of IVIG, limits in IVIG supply, and subsequent challenges.

Interpreting Alzheimer's disease clinical trials in light of the effects on amyloid-β

The failure of several potential Alzheimer’s disease therapeutics in mid- to late-stage clinical development has provoked significant discussion regarding the validity of the amyloid hypothesis. In this review, we propose a minimum criterion of 25% for amyloid-β (Aβ) lowering to achieve clinically meaningful slowing of disease progression. This criterion is based on genetic, risk factor, clinical and preclinical studies. We then compare this minimum criterion with the degree of Aβ lowering produced by the potential therapies that have failed in clinical trials. If the proposed minimum Aβ lowering criterion is used, then the amyloid hypothesis has yet to be adequately tested in the clinic. Therefore, we believe that the amyloid hypothesis remains valid and remains to be confirmed or refuted in future clinical trials.