Gantenerumab reduces amyloid-β plaques in patients with prodromal to moderate Alzheimer's disease: a PET substudy interim analysis

Circadian rhythm disruption and retinal dysfunction: a bidirectional link in Alzheimer's disease?

Dysfunction in circadian rhythms is a common occurrence in patients with Alzheimer's disease. A predominant function of the retina is circadian synchronization, carrying information to the brain through the retinohypothalamic tract, which projects to the suprachiasmatic nucleus. Notably, Alzheimer's disease hallmarks, including amyloid-β, are present in the retinas of Alzheimer's disease patients, followed/associated by structural and functional disturbances. However, the mechanistic link between circadian dysfunction and the pathological changes affecting the retina in Alzheimer's disease is not fully understood, although some studies point to the possibility that retinal dysfunction could be considered an early pathological process that directly modulates the circadian rhythm.

The role of macrophage plasticity in neurodegenerative diseases

Tissue-resident macrophages and recruited macrophages play pivotal roles in innate immunity and the maintenance of brain homeostasis. Investigating the involvement of these macrophage populations in eliciting pathological changes associated with neurodegenerative diseases has been a focal point of research. Dysregulated states of macrophages can compromise clearance mechanisms for pathological proteins such as amyloid-β (Aβ) in Alzheimer's disease (AD) and TDP-43 in Amyotrophic lateral sclerosis (ALS). Additionally, recent evidence suggests that abnormalities in the peripheral clearance of pathological proteins are implicated in the pathogenesis and progression of neurodegenerative diseases. Furthermore, numerous genome-wide association studies have linked genetic risk factors, which alter the functionality of various immune cells, to the accumulation of pathological proteins. This review aims to unravel the intricacies of macrophage biology in both homeostatic conditions and neurodegenerative disorders. To this end, we initially provide an overview of the modifications in receptor and gene expression observed in diverse macrophage subsets throughout development. Subsequently, we outlined the roles of resident macrophages and recruited macrophages in neurodegenerative diseases and the progress of targeted therapy. Finally, we describe the latest advances in macrophage imaging methods and measurement of inflammation, which may provide information and related treatment strategies that hold promise for informing the design of future investigations and therapeutic interventions.

α-Tocotrienol Protects Neurons by Preventing Tau Hyperphosphorylation via Inhibiting Microtubule Affinity-Regulating Kinase Activation

In the pathological process of Alzheimer's disease, neuronal cell death is closely related to the accumulation of reactive oxygen species. Our previous studies have found that oxidative stress can activate microtubule affinity-regulating kinases, resulting in elevated phosphorylation levels of tau protein specifically at the Ser262 residue in N1E-115 cells that have been subjected to exposure to hydrogen peroxide. This process may be one of the pathogenic mechanisms of Alzheimer's disease. Vitamin E is a fat-soluble, naturally occurring antioxidant that plays a crucial role in biological systems. This study aimed to examine the probable processes that contribute to the inhibiting effect on the abnormal phosphorylation of tau protein and the neuroprotective activity of a particular type of vitamin E, α-tocotrienol. The experimental analysis revealed that α-tocotrienol showed significant neuroprotective effects in the N1E-115 cell line. Our data further suggest that one of the mechanisms underlying the neuroprotective effects of α-tocotrienol may be through the inhibition of microtubule affinity-regulated kinase activation, which significantly reduces the oxidative stress-induced aberrant elevation of p-Tau (Ser262) levels. These results indicate that α-tocotrienol may represent an intriguing strategy for treating or preventing Alzheimer's disease.

Harmonizing tau positron emission tomography in Alzheimer's disease: The CenTauR scale and the joint propagation model

INTRODUCTION

Tau-positron emission tomography (PET) outcome data of patients with Alzheimer's disease (AD) cannot currently be meaningfully compared or combined when different tracers are used due to differences in tracer properties, instrumentation, and methods of analysis.

METHODS

Using head-to-head data from five cohorts with tau PET radiotracers designed to target tau deposition in AD, we tested a joint propagation model (JPM) to harmonize quantification (units termed "CenTauR" [CTR]). JPM is a statistical model that simultaneously models the relationships between head-to-head and anchor point data. JPM was compared to a linear regression approach analogous to the one used in the amyloid PET Centiloid scale.

RESULTS

A strong linear relationship was observed between CTR values across brain regions. Using the JPM approach, CTR estimates were similar to, but more accurate than, those derived using the linear regression approach.

DISCUSSION

Preliminary findings using the JPM support the development and adoption of a universal scale for tau-PET quantification.

HIGHLIGHTS

Tested a novel joint propagation model (JPM) to harmonize quantification of tau PET. Units of common scale are termed "CenTauRs". Tested a Centiloid-like linear regression approach. Using five cohorts with head-to-head tau PET, JPM outperformed linearregressionbased approach. Strong linear relationship was observed between CenTauRs values across brain regions.

Transcranial blood-brain barrier opening in Alzheimer's disease patients using a portable focused ultrasound system with real-time 2-D cavitation mapping

Background : Focused ultrasound (FUS) in combination with microbubbles has recently shown great promise in facilitating blood-brain barrier (BBB) opening for drug delivery and immunotherapy in Alzheimer's disease (AD). However, it is currently limited to systems integrated within the MRI suites or requiring post-surgical implants, thus restricting its widespread clinical adoption. In this pilot study, we investigate the clinical safety and feasibility of a portable, non-invasive neuronavigation-guided FUS (NgFUS) system with integrated real-time 2-D microbubble cavitation mapping. Methods : A phase 1 clinical study with mild to moderate AD patients (N = 6) underwent a single session of microbubble-mediated NgFUS to induce transient BBB opening (BBBO). Microbubble activity under FUS was monitored with real-time 2-D cavitation maps and dosing to ensure the efficacy and safety of the NgFUS treatment. Post-operative MRI was used for BBB opening and closure confirmation as well as safety assessment. Changes in AD biomarker levels in both blood serum and extracellular vesicles (EVs) were evaluated, while changes in amyloid-beta (Aβ) load in the brain were assessed through 18F-florbetapir PET. Results : BBBO was achieved in 5 out of 6 subjects with an average volume of 983 ± 626 mm3 following FUS at the right frontal lobe both in white and gray matter regions. The outpatient treatment was completed within 34.8 ± 10.7 min. Cavitation dose significantly correlated with the BBBO volume (R 2 > 0.9, N = 4), demonstrating the portable NgFUS system's capability of predicting opening volumes. The cavitation maps co-localized closely with the BBBO location, representing the first report of real-time transcranial 2-D cavitation mapping in the human brain. Larger opening volumes correlated with increased levels of AD biomarkers, including Aβ42 (R 2 = 0.74), Tau (R 2 = 0.95), and P-Tau181 (R 2 = 0.86), assayed in serum-derived EVs sampled 3 days after FUS (N = 5). From PET scans, subjects showed a lower Aβ load increase in the treated frontal lobe region compared to the contralateral region. Reduction in asymmetry standardized uptake value ratios (SUVR) correlated with the cavitation dose (R 2 > 0.9, N = 3). Clinical changes in the mini-mental state examination over 6 months were within the expected range of cognitive decline with no additional changes observed as a result of FUS. Conclusion : We showed the safety and feasibility of this cost-effective and time-efficient portable NgFUS treatment for BBBO in AD patients with the first demonstration of real-time 2-D cavitation mapping. The cavitation dose correlated with BBBO volume, a slowed increase in pathology, and serum detection of AD proteins. Our study highlights the potential for accessible FUS treatment in AD, with or without drug delivery.

Monoclonal antibodies and aptamers: The future therapeutics for Alzheimer's disease

Alzheimer's disease (AD) is considered the most common and prevalent form of dementia of adult-onset with characteristic progressive impairment in cognition and memory. The cure for AD has not been found yet and the treatments available until recently were only symptomatic. Regardless of multidisciplinary approaches and efforts made by pharmaceutical companies, it was only in the past two years that new drugs were approved for the treatment of the disease. Amyloid beta (Aβ) immunotherapy is at the core of this therapy, which is one of the most innovative approaches looking to change the course of AD. This technology is based on synthetic peptides or monoclonal antibodies (mAb) to reduce Aβ levels in the brain and slow down the advance of neurodegeneration. Hence, this article reviews the state of the art about AD neuropathogenesis, the traditional pharmacologic treatment, as well as the modern active and passive immunization describing approved drugs, and drug prototypes currently under investigation in different clinical trials. In addition, future perspectives on immunotherapeutic strategies for AD and the rise of the aptamer technology as a non-immunogenic alternative to curb the disease progression are discussed.

Engineered Antibodies to Improve Efficacy against Neurodegenerative Disorders

Antibodies that can selectively remove rogue proteins in the brain are an obvious choice to treat neurodegenerative disorders (NDs), but after decades of efforts, only two antibodies to treat Alzheimer's disease are approved, dozens are in the testing phase, and one was withdrawn, and the other halted, likely due to efficacy issues. However, these outcomes should have been evident since these antibodies cannot enter the brain sufficiently due to the blood-brain barrier (BBB) protectant. However, all products can be rejuvenated by binding them with transferrin, preferably as smaller fragments. This model can be tested quickly and at a low cost and should be applied to bapineuzumab, solanezumab, crenezumab, gantenerumab, aducanumab, lecanemab, donanemab, cinpanemab, and gantenerumab, and their fragments. This paper demonstrates that conjugating with transferrin does not alter the binding to brain proteins such as amyloid-β (Aβ) and α-synuclein. We also present a selection of conjugate designs that will allow cleavage upon entering the brain to prevent their exocytosis while keeping the fragments connected to enable optimal binding to proteins. The identified products can be readily tested and returned to patients with the lowest regulatory cost and delays. These engineered antibodies can be manufactured by recombinant engineering, preferably by mRNA technology, as a more affordable solution to meet the dire need to treat neurodegenerative disorders effectively.

Mechanistic insights and emerging therapeutic stratagems for Alzheimer's disease

Alzheimer's disease (AD), a multi-factorial neurodegenerative disorder has affected over 30 million individuals globally and these numbers are expected to increase in the coming decades. Current therapeutic interventions are largely ineffective as they focus on a single target. Development of an effective drug therapy requires a deep understanding of the various factors influencing the onset and progression of the disease. Aging and genetic factors exert a major influence on the development of AD. Other factors like post-viral infections, iron overload, gut dysbiosis, and vascular dysfunction also exacerbate the onset and progression of AD. Further, post-translational modifications in tau, DRP1, CREB, and p65 proteins increase the disease severity through triggering mitochondrial dysfunction, synaptic loss, and differential interaction of amyloid beta with different receptors leading to impaired intracellular signalling. With advancements in neuroscience tools, new inter-relations that aggravate AD are being discovered including pre-existing diseases and exposure to other pathogens. Simultaneously, new therapeutic strategies involving modulation of gene expression through targeted delivery or modulation with light, harnessing the immune response to promote clearance of amyloid deposits, introduction of stem cells and extracellular vesicles to replace the destroyed neurons, exploring new therapeutic molecules from plant, marine and biological sources delivered in the free state or through nanoparticles and use of non-pharmacological interventions like music, transcranial stimulation and yoga. Polypharmacology approaches involving combination of therapeutic agents are also under active investigation for superior therapeutic outcomes. This review elaborates on various disease-causing factors, their underlying mechanisms, the inter-play between different disease-causing players, and emerging therapeutic options including those under clinical trials, for treatment of AD. The challenges involved in AD therapy and the way forward have also been discussed.

Anti-amyloid Antibody Therapies for Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia, which is characterized by a progressive neurodegenerative disorder that is extremely difficult to treat and severely reduces quality of life. Amyloid beta (Aβ) has been the primary target of experimental therapies owing to the neurotoxicity of Aβ and the brain Aβ load detected in humans by amyloid positron emission tomography (PET) imaging. Recently completed phase 2 and 3 trials of third-generation anti-amyloid immunotherapies indicated clinical efficacy in significantly reducing brain Aβ load and inhibiting the progression of cognitive decline. Anti-amyloid immunotherapies are the first effective disease-modifying therapies for AD, and aducanumab and lecanemab were recently approved through the US Food and Drug Administration's accelerated approval pathway. However, these therapies still exhibit insufficient clinical efficacy and are associated with amyloid-related imaging abnormalities. Further advances in the field of AD therapeutics are required to revolutionize clinical AD treatment, dementia care, and preventive cognitive healthcare.

Immunotherapy in Alzheimer's disease: focusing on the efficacy of gantenerumab on amyloid-β clearance and cognitive decline

Gantenerumab, a human monoclonal antibody (mAb), has been thought of as a potential agent to treat Alzheimer's disease (AD) by specifically targeting regions of the amyloid-β (Aβ) peptide sequence. Aβ protein accumulation in the brain leads to amyloid plaques, causing neuroinflammation, oxidative stress, neuronal damage, and neurotransmitter dysfunction, thereby causing cognitive decline in AD. Gantenerumab involves disrupting Aβ aggregation and promoting the breakdown of larger Aβ aggregates into smaller fragments, which facilitates the action of Aβ-degrading enzymes in the brain, thus slowing down the progression of AD. Moreover, Gantenerumab acts as an opsonin, coating Aβ plaques and enhancing their recognition by immune cells, which, combined with its ability to improve the activity of microglia, makes it an intriguing candidate for promoting Aβ plaque clearance. Indeed, the multifaceted effects of Gantenerumab, including Aβ disaggregation, enhanced immune recognition, and improved microglia activity, may position it as a promising therapeutic approach for AD. Of note, reports suggest that Gantenerumab, albeit its capacity to reduce or eliminate Aβ, has not demonstrated effectiveness in reducing cognitive decline. This review, after providing an overview of immunotherapy approaches that target Aβ in AD, explores the efficacy of Gantenerumab in reducing Aβ levels and cognitive decline.

Amyloid-beta antibody binding to cerebral amyloid angiopathy fibrils and risk for amyloid-related imaging abnormalities

Therapeutic antibodies have been developed to target amyloid-beta (Aβ), and some of these slow the progression of Alzheimer's disease (AD). However, they can also cause adverse events known as amyloid-related imaging abnormalities with edema (ARIA-E). We investigated therapeutic Aβ antibody binding to cerebral amyloid angiopathy (CAA) fibrils isolated from human leptomeningeal tissue to study whether this related to the ARIA-E frequencies previously reported by clinical trials. The binding of Aβ antibodies to CAA Aβ fibrils was evaluated in vitro using immunoprecipitation, surface plasmon resonance, and direct binding assay. Marked differences in Aβ antibody binding to CAA fibrils were observed. Solanezumab and crenezumab showed negligible CAA fibril binding and these antibodies have no reported ARIA-E cases. Lecanemab showed a low binding to CAA fibrils, consistent with its relatively low ARIA-E frequency of 12.6%, while aducanumab, bapineuzumab, and gantenerumab all showed higher binding to CAA fibrils and substantially higher ARIA-E frequencies (25-35%). An ARIA-E frequency of 24% was reported for donanemab, and its binding to CAA fibrils correlated with the amount of pyroglutamate-modified Aβ present. The findings of this study support the proposal that Aβ antibody-CAA interactions may relate to the ARIA-E frequency observed in patients treated with Aβ-based immunotherapies.

Monoclonal antibody therapy for Alzheimer's disease focusing on intracerebral targets

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases. Due to the complexity of the disorder and the presence of the blood-brain barrier (BBB), its drug discovery and development are facing enormous challenges, especially after several failures of monoclonal antibody (mAb) trials. Nevertheless, the Food and Drug Administration's approval of the mAb aducanumab has ushered in a new day. As we better understand the disease's pathogenesis and identify novel intracerebral therapeutic targets, antibody-based therapies have advanced over the past few years. The mAb drugs targeting β-amyloid or hyperphosphorylated tau protein are the focus of the current research. Massive neuronal loss and glial cell-mediated inflammation are also the vital pathological hallmarks of AD, signaling a new direction for research on mAb drugs. We have elucidated the mechanisms by which AD-specific mAbs cross the BBB to bind to targets. In order to investigate therapeutic approaches to treat AD, this review focuses on the promising mAbs targeting intracerebral dysfunction and related strategies to cross the BBB.

Recent trends in treatment strategies for Alzheimer's disease and the challenges: A topical advancement

Alzheimer's Disease (AD) is an irreversible and progressive neurological disease that has affected at least 50 million people around the globe. Considering the severity of the disease and the continuous increase in the number of patients, the development of new effective drugs or intervention strategies for AD has become urgent. AD is caused by a combination of genetic, environmental, and lifestyle factors, but its exact cause has not yet been clarified. Given the current challenges being faced in the clinical treatment of AD, such as complex AD pathological network and insufficient early diagnosis, herein, we have focused on the three core pathological features of AD, including amyloid-β (Aβ) aggregation, tau phosphorylation and tangles, and activation of inflammatory factors. In this review, we have briefly underscored the primary evidence supporting each pathology and discuss AD pathological network among Aβ, tau, and inflammation. We have also comprehensively summarized the most instructive drugs and their treatment strategies against Aβ, tau, or neuroinflammation used in basic research and clinical trials. Finally, we have discussed and outlined the pros and cons of each pathological approach and looked forward to potential personalized diagnosis and treatment strategies that are beneficial to AD patients.

Passive immunotherapy for Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease characterized by cognitive impairment with few therapeutic options. Despite many failures in developing AD treatment during the past 20 years, significant advances have been achieved in passive immunotherapy of AD very recently. Here, we review characteristics, clinical trial data, and mechanisms of action for monoclonal antibodies (mAbs) targeting key players in AD pathogenesis, including amyloid-β (Aβ), tau and neuroinflammation modulators. We emphasized the efficacy of lecanemab and donanemab on cognition and amyloid clearance in AD patients in phase III clinical trials and discussed factors that may contribute to the efficacy and side effects of anti-Aβ mAbs. In addition, we provided important information on mAbs targeting tau or inflammatory regulators in clinical trials, and indicated that mAbs against the mid-region of tau or pathogenic tau have therapeutic potential for AD. In conclusion, passive immunotherapy targeting key players in AD pathogenesis offers a promising strategy for effective AD treatment.

Clarity on the blazing trail: clearing the way for amyloid-removing therapies for Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with a complex pathogenesis. Senile plaques composed of the amyloid-β (Aβ) peptide in the brain are the core hallmarks of AD and a promising target for the development of disease-modifying therapies. However, over the past 20 years, the failures of clinical trials directed at Aβ clearance have fueled a debate as to whether Aβ is the principal pathogenic factor in AD and a valid therapeutic target. The success of the recent phase 3 trials of lecanemab (Clarity AD) and donanemab (Trailblazer Alz2), and lessons from previous Aβ clearance trials provide critical evidence to support the role of Aβ in AD pathogenesis and suggest that targeting Aβ clearance is heading in the right direction for AD treatment. Here, we analyze key questions relating to the efficacy of Aβ targeting therapies, and provide perspectives on early intervention, adequate Aβ removal, sufficient treatment period, and combinatory therapeutics, which may be required to achieve the best cognitive benefits in future trials in the real world.

Risk factors in developing amyloid related imaging abnormalities (ARIA) and clinical implications

Alzheimer's disease (AD) affects over 6 million people over the age of 65. The advent of new anti-amyloid monoclonal antibodies as treatment for early Alzheimer's disease these immunotherapeutics may slow disease progression but also pose significant risks. Amyloid related imaging abnormalities (ARIA) identified on MRI following administration of these new monoclonal antibodies can cause both brain edema (ARIA-E) and hemorrhage (ARIA-H). While most ARIA is asymptomatic, some patients can develop headache, confusion, nausea, dizziness, seizures and in rare cases death. By analyzing lecanemab, aducanumab, gantenerumab, donanemab, and bapineuzumab clinical trials; risk factors for developing ARIA can be identified to mitigate some of the ARIA risk. Risk factors for developing ARIA-E are a positive Apoε4 carrier status and prior multiple cerebral microhemorrhages. Risk factors for ARIA-H are age, antithrombotic use, and history of prior strokes. With lecanemab, ARIA-E and ARIA-H were seen at lower rates 12 and 17%, respectively, compared to aducanumab (ARIA-E 35% and ARIA-H 19%) in treated patients. ARIA risk factors have impacted inclusion and exclusion criteria, determining who can receive lecanemab. In some clinics, almost 90% of Alzheimer's patients are excluded from receiving these new anti-amyloid therapeutics. This review aims to discuss risk factors of ARIA and highlight important areas for further research. With more anti-amyloid monoclonal antibodies approved by the Food and Drug Administration, considering patient risk factors for developing ARIA is important to identify to minimize patient's risk while receiving these new therapies.

Targets, trials and tribulations in Alzheimer therapeutics

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by abnormal accumulation of extracellular amyloid beta senile plaques and intracellular neurofibrillary tangles in the parts of the brain responsible for cognition. The therapeutic burden for the management of AD relies solely on cholinesterase inhibitors that provide only symptomatic relief. The urgent need for disease-modifying drugs has resulted in intensive research in this domain, which has led to better understanding of the disease pathology and identification of a plethora of new pathological targets. Currently, there are over a hundred and seventy clinical trials exploring disease modification, cognitive enhancement, and reduction of neuro-psychiatric complications. However, the path to developing safe and efficacious AD therapeutics has not been without challenges. Several clinical trials have been terminated in advanced stages due to lack of therapeutic translation or increased incidence of adverse events. This review presents an in-depth look at the various therapeutic targets of AD and the lessons learnt during their clinical assessment. Comprehensive understanding of the implication of modulating various aspects of Alzheimer brain pathology is crucial for development of drugs with potential to halt disease progression in Alzheimer therapeutics.

Potential Impact of Slowing Disease Progression in Early Symptomatic Alzheimer's Disease on Patient Quality of Life, Caregiver Time, and Total Societal Costs: Estimates Based on Findings from GERAS-US Study

Background

Impact of Alzheimer's disease (AD) progression on patient health-related quality of life (HRQoL), caregiver time, and societal costs is not well characterized in early AD.

Objective

To assess the association of change in cognition with HRQoL, caregiver time, and societal costs over 36 months, and estimate the impact of slowing disease progression on these outcomes.

Methods

This post-hoc analysis included patients with amyloid-positive mild cognitive impairment (MCI) and mild AD dementia (MILD AD) from the 36-month GERAS-US study. Disease progression was assessed using the Mini-Mental State Examination score. Change in outcomes associated with slowing AD progression was estimated using coefficients from generalized linear models.

Results

At baseline, 300 patients had MCI and 317 had MILD AD. Observed natural progression over 36 months was associated with: 5.1 point decline in the Bath Assessment of Subjective Quality of Life in Dementia (BASQID) score (for HRQoL), increase in 1,050 hours of total caregiver time, and $8,504 total societal costs for MCI; 6.6 point decline in the BASQID score, increase in 1,929 hours of total caregiver time, and $12,795 total societal costs for MILD AD per person. Slowing AD progression by 30% could result in per person savings in HRQoL decline, total caregiver time, and total societal costs: for MCI: 1.5 points, 315 hours, and $2,638; for MILD AD: 2.0 points, 579 hours, and $3,974.

Conclusions

Slowing AD progression over 36 months could slow decline in HRQoL and save caregiver time and societal cost in patients with MCI and MILD AD.

Recent advancement in therapeutic strategies for Alzheimer's disease: Insights from clinical trials

Alzheimer's disease (AD) is the most prevalent form of dementia, characterized by the presence of plaques of amyloid beta and Tau proteins. There is currently no permanent cure for AD; the only medications approved by the FDA for mild to moderate AD are cholinesterase inhibitors, NMDA receptor antagonists, and immunotherapies against core pathophysiology, that provide temporary relief only. Researchers worldwide have made significant attempts to find new targets and develop innovative therapeutic molecules to treat AD. The FDA-approved drugs are palliative and couldn't restore the damaged neuron cells of AD. Stem cells have self-differentiation properties, making them prospective therapeutics to treat AD. The promising results in pre-clinical studies of stem cell therapy for AD seek attention worldwide. Various stem cells, mainly mesenchymal stem cells, are currently in different phases of clinical trials and need more advancements to take this therapy to the translational level. Here, we review research from the past decade that has identified several hypotheses related to AD pathology. Moreover, this article also focuses on the recent advancement in therapeutic strategies for AD treatment including immunotherapy and stem cell therapy detailing the clinical trials that are currently undergoing development.

A light at the end of the tunnel - from mutation identification to a potential treatment for Alzheimer's disease

Recent advances have driven the development of immunotherapies that act by either promoting or suppressing a patient's immune system to treat inflammation, autoimmune disease, cardiovascular disease, infectious diseases, and several cancers. In addition, research conducted over the past 25 years has identified therapeutic targets and indicated that immunotherapy could be used to treat Alzheimer's disease (AD). Despite a number of setbacks, this approach has now led to the development of the first disease-modifying treatments for this devastating disease. A key neuropathological feature of AD is the accumulation of a ~40-amino acid peptide known as amyloid β (Aβ) in the brain and cerebrovasculature. Our detection of an Aβ precursor protein mutation that caused early-onset AD in a Swedish family by enhancing Aβ protofibril formation sharpened the focus on soluble Aβ aggregates (oligomers and protofibrils) as viable therapeutic targets. Initial studies developed and tested a mouse monoclonal antibody (mAb158) with specific conformation-dependent binding to these soluble Aβ aggregates. Treatment with mAb158 selectively reduced Aβ protofibrils in the brain and cerebrospinal fluid of a transgenic mouse model of AD. A humanized version of mAb158 (lecanemab) subsequently entered clinical trials. Based on promising Phase 2 data showing plaque clearance and reduced cognitive decline, a Phase 3 trial found that lecanemab slowed decline on the primary cognitive endpoint by 27% over 18 months and also produced positive effects on secondary clinical endpoints and key biomarkers. In July 2023, the FDA granted lecanemab a full approval, and this therapeutic antibody will be marketed as Leqembi®. This represents a significant advance for patients with AD, although many challenges remain. In particular, it is now more important than ever to identify individuals who are vulnerable to AD, so that treatment can be initiated at an early stage in the disease process.

Evaluation of novel data-driven metrics of amyloid β deposition for longitudinal PET studies

PURPOSE

Positron emission tomography (PET) provides in vivo quantification of amyloid-β (Aβ) pathology. Established methods for assessing Aβ burden can be affected by physiological and technical factors. Novel, data-driven metrics have been developed to account for these sources of variability. We aimed to evaluate the performance of four of these amyloid PET metrics against conventional techniques, using a common set of criteria.

METHODS

Three cohorts were used for evaluation: Insight 46 (N=464, [18F]florbetapir), AIBL (N=277, [18F]flutemetamol), and an independent test-retest data (N=10, [18F]flutemetamol). Established metrics of amyloid tracer uptake included the Centiloid (CL) and where dynamic data was available, the non-displaceable binding potential (BPND). The four data-driven metrics computed were the amyloid load (Aβ load), the Aβ-PET pathology accumulation index (Aβ index), the Centiloid derived from non-negative matrix factorisation (CLNMF), and the amyloid pattern similarity score (AMPSS). These metrics were evaluated using reliability and repeatability in test-retest data, associations with BPND and CL, variability of the rate of change and sample size estimates to detect a 25% slowing in Aβ accumulation.

RESULTS

All metrics showed good reliability. Aβ load, Aβ index and CLNMF were strong associated with the BPND. The associations with CL suggest that cross-sectional measures of CLNMF, Aβ index and Aβ load are robust across studies. Sample size estimates for secondary prevention trial scenarios were the lowest for CLNMF and Aβ load compared to the CL.

CONCLUSION

Among the novel data-driven metrics evaluated, the Aβ load, the Aβ index and the CLNMF can provide comparable performance to more established quantification methods of Aβ PET tracer uptake. The CLNMF and Aβ load could offer a more precise alternative to CL, although further studies in larger cohorts should be conducted.

Implications of the Approval of Lecanemab for Alzheimer Disease Patient Care: Incremental Step or Paradigm Shift?

The amyloid cascade model of the pathogenesis of Alzheimer disease (AD) is well supported in observational studies. Its therapeutic corollary asserts that removal of amyloid-β peptide ("amyloid") would provide clinical benefits. After 2 decades of pursuing the strategy of amyloid removal without success, clinical trials of the antiamyloid monoclonal antibody (AAMA) donanemab and a phase 3 clinical trial of lecanemab have reported clinical benefits linked to amyloid removal. Lecanemab (trade name, Leqembi) is the first with published phase 3 trial results. When administered through IV every 2 weeks to patients with elevated brain amyloid and mild cognitive impairment or mild dementia, lecanemab delayed cognitive and functional worsening by approximately 5 months in an 18-month double-blind, placebo-controlled trial. The trial was well conducted, and the results favoring lecanemab were internally consistent. The demonstration that lecanemab treatment delayed clinical progression in persons with mild symptoms due to AD is a major conceptual achievement, but a better appreciation of the magnitude and durability of benefits for individual patients will require extended observations from clinical practice settings. Amyloid-related imaging abnormalities (ARIA) that were largely asymptomatic occurred in approximately 20%, slightly more than half of which were attributable to treatment and the rest to underlying AD-related amyloid angiopathy. Persons who were homozygous for the APOE ε4 allele had greater ARIA risks. Hemorrhagic complications with longer-term lecanemab use need to be better understood. Administration of lecanemab will place unprecedented pressures on dementia care personnel and infrastructure, both of which need to grow exponentially to meet the challenge.

Recent diagnostic techniques for the detection of Alzheimer's disease: a short review

Alzheimer's disease (AD) is a neurological condition that affects millions of individuals around the world and for which there are few effective therapies. Dementia is characterized by the formation of senile plaques and neurofibrillary tangles, which is followed by neurotoxicity, which results in memory loss and mortality. Pathogenesis occurs several years before the onset of disease. As the disease-modifying drugs are most effective in the early stages of Alzheimer's disease, biomarkers for early detection of disease and their development are crucial. This review discusses the diagnostic utility, benefits, and limitations of traditional techniques such as neuroimaging, cognitive testing, positron emission tomography, and biomarkers, as well as the novel techniques such as artificial intelligence, machine learning, immunotherapy, and blood test approaches for early detection, understanding, and treatment of AD.

Validation of 3- and 5-point severity scales to assess ARIA-E

INTRODUCTION

Anti-amyloid-β (Aβ) monoclonal antibodies (mAbs) offer the promise of disease modification and are emerging treatment options in Alzheimer's disease. Anti-Aβ mAbs require brain magnetic resonance imaging (MRI) examinations to detect anti-amyloid-induced amyloid-related imaging abnormalities (ARIA), important adverse drug reactions associated with some anti-Aβ mAbs currently available in the United States and in clinical development. We present a simple rating system for ARIA-edema (ARIA-E) that can assess severity on a 3- or 5-point scale based upon a single linear measurement of the largest area of lesion, and dissemination in space, termed the 3-point Severity Scale of ARIA-E (SSAE-3) and the 5-point Severity Scale of ARIA-E (SSAE-5), respectively.

METHODS

MRI results were collected from 75 participants from the SCarlet RoAD (NCT01224106) and Marguerite RoAD (NCT02051608) studies of gantenerumab. Three neuroradiologists experienced with the detection of ARIA-E were selected to read all cases independently. One rater was then chosen for a second read to assess intra-reader reproducibility.

RESULTS

The three raters had high agreement in identifying and grading ARIA-E. The Cohen/Fleiss kappa (κ) scores (95% confidence interval [CI]) for the inter- and intra-reader comparisons for SSAE-3 and SSAE-5 were 0.79 (0.70-1.00), 0.94 (0.94-1.00), 0.73 (0.66-1.00), and 0.90 (0.90-1.00), respectively.

DISCUSSION

Our study suggests that SSAE-3 and SSAE-5 are valid ARIA-E rating scales for use in routine clinical practice by experienced radiologists in specialized settings. The application of these scales in everyday use in clinical practice will support the expansion of anti-Aβ mAbs as a treatment option for people living with Alzheimer's disease.

Highlights

A simple rating scale is needed to rate severity of amyloid-related imaging abnormalities-edema (ARIA-E) in both research and clinical settings.The 3- and 5-point Severity Scales of ARIA-E (SSAE-3/-5) have good inter- and intra-reader agreement.The SSAE-3/-5 have been used in most major Alzheimer's disease (AD) trials to date and are suitable for large-scale use in routine clinical practice, which may help support the expansion of anti-amyloid antibodies as treatment options for AD.

Impact of therapeutic and low volume plasma exchange on clinical laboratory parameters in patients treated for Alzheimer's disease from the AMBAR study

INTRODUCTION

Little is known about the impact of plasma exchange (PE) on clinical laboratory parameters in Alzheimer's disease (AD) patients.

METHODS

AD patients in the AMBAR trial (N = 322) received weekly therapeutic PE (TPE) for 6 weeks followed by monthly low-volume PE (LVPE) for12 months. Treatment were placebo (sham PE), low-albumin, low-albumin + IVIG (i.e., albumin alternated with intravenous immunoglobulin) and high-albumin + IVIG.

RESULTS

Coagulation parameters transiently increased post-TPE. Blood calcium, platelets, and albumin levels decreased but remained within the reference range. Leukocyte counts increased. Fibrinogen, hemoglobin, total protein, gamma globulin, and IgG, transiently dipped below the reference range. Hypogammaglobulinemia (7.2 g/L) persisted in pre-TPE measurements. No changes were observed during the LVPE period. Cerebrospinal fluid parameters and vital signs were unchanged throughout.

CONCLUSION

Laboratory parameters of AD patients were affected by TPE similarly to effects of PE-treatment for other pathologies. These effects were less pronounced or non-existent for LVPE.

Anti-Amyloid Therapies for Alzheimer's Disease and the Amyloid Cascade Hypothesis

Over the past 30 years, the majority of (pre)clinical efforts to find an effective therapy for Alzheimer's disease (AD) focused on clearing the β-amyloid peptide (Aβ) from the brain since, according to the amyloid cascade hypothesis, the peptide was (and it is still considered by many) the pathogenic determinant of this neurodegenerative disorder. However, as reviewed in this article, results from the numerous clinical trials that have tested anti-Aβ therapies to date indicate that this peptide plays a minor role in the pathogenesis of AD. Indeed, even Aducanumab and Lecanemab, the two antibodies recently approved by the FDA for AD therapy, as well as Donanemab showed limited efficacy on cognitive parameters in phase III clinical trials, despite their capability of markedly lowering Aβ brain load. Furthermore, preclinical evidence demonstrates that Aβ possesses several physiological functions, including memory formation, suggesting that AD may in part be due to a loss of function of this peptide. Finally, it is generally accepted that AD could be the result of many molecular dysfunctions, and therefore, if we keep chasing only Aβ, it means that we cannot see the forest for the trees.

Passive Alzheimer's immunotherapy: A promising or uncertain option?

The US Food and Drug Administration (FDA)'s recent accelerated approval of two anti-amyloid antibodies for treatment of Alzheimer's disease (AD), aducanumab and lecanemab, has caused substantial debate. To inform this debate, we reviewed the literature on randomized clinical trials conducted with eight such antibodies focusing on clinical efficacy, cerebral amyloid removal, amyloid-related imaging abnormalities (ARIAs) and cerebral volumes to the extent such measurements have been reported. Two antibodies, donanemab and lecanemab, have demonstrated clinical efficacy, but these results remain uncertain. We further argue that the decreased amyloid PET signal in these trials is unlikely to be a one-to-one reflection of amyloid removal, but rather a reflection of increased therapy-related brain damage, as supported by the increased incidence of ARIAs and reported loss of brain volume. Due to these uncertainties of benefit and risk, we recommend that the FDA pauses existing approvals and approval of new antibodies until results of phase 4 studies with these drugs are available to inform on these risk-benefit uncertainties. We recommend that the FDA prioritize FDG PET and detection of ARIAs and accelerated brain volume loss with MRI in all trial patients, and neuropathological examination of all patients who die in these phase 4 trials.

Validation of quantitative assessment of florbetaben PET scans as an adjunct to the visual assessment across 15 software methods

PURPOSE

Amyloid positron emission tomography (PET) with [18F]florbetaben (FBB) is an established tool for detecting Aβ deposition in the brain in vivo based on visual assessment of PET scans. Quantitative measures are commonly used in the research context and allow continuous measurement of amyloid burden. The aim of this study was to demonstrate the robustness of FBB PET quantification.

METHODS

This is a retrospective analysis of FBB PET images from 589 subjects. PET scans were quantified with 15 analytical methods using nine software packages (MIMneuro, Hermes BRASS, Neurocloud, Neurology Toolkit, statistical parametric mapping (SPM8), PMOD Neuro, CapAIBL, non-negative matrix factorization (NMF), AmyloidIQ) that used several metrics to estimate Aβ load (SUVR, centiloid, amyloid load, and amyloid index). Six analytical methods reported centiloid (MIMneuro, standard centiloid, Neurology Toolkit, SPM8 (PET only), CapAIBL, NMF). All results were quality controlled.

RESULTS

The mean sensitivity, specificity, and accuracy were 96.1 ± 1.6%, 96.9 ± 1.0%, and 96.4 ± 1.1%, respectively, for all quantitative methods tested when compared to histopathology, where available. The mean percentage of agreement between binary quantitative assessment across all 15 methods and visual majority assessment was 92.4 ± 1.5%. Assessments of reliability, correlation analyses, and comparisons across software packages showed excellent performance and consistent results between analytical methods.

CONCLUSION

This study demonstrated that quantitative methods using both CE marked software and other widely available processing tools provided comparable results to visual assessments of FBB PET scans. Software quantification methods, such as centiloid analysis, can complement visual assessment of FBB PET images and could be used in the future for identification of early amyloid deposition, monitoring disease progression and treatment effectiveness.

Current and future therapeutic strategies for Alzheimer's disease: an overview of drug development bottlenecks

Alzheimer's disease (AD) is the most common chronic neurodegenerative disease worldwide. It causes cognitive dysfunction, such as aphasia and agnosia, and mental symptoms, such as behavioral abnormalities; all of which place a significant psychological and economic burden on the patients' families. No specific drugs are currently available for the treatment of AD, and the current drugs for AD only delay disease onset and progression. The pathophysiological basis of AD involves abnormal deposition of beta-amyloid protein (Aβ), abnormal tau protein phosphorylation, decreased activity of acetylcholine content, glutamate toxicity, autophagy, inflammatory reactions, mitochondria-targeting, and multi-targets. The US Food and Drug Administration (FDA) has approved five drugs for clinical use: tacrine, donepezil, carbalatine, galantamine, memantine, and lecanemab. We have focused on the newer drugs that have undergone clinical trials, most of which have not been successful as a result of excessive clinical side effects or poor efficacy. Although aducanumab received rapid approval from the FDA on 7 June 2021, its long-term safety and tolerability require further monitoring and confirmation. In this literature review, we aimed to explore the possible pathophysiological mechanisms underlying the occurrence and development of AD. We focused on anti-Aβ and anti-tau drugs, mitochondria-targeting and multi-targets, commercially available drugs, bottlenecks encountered in drug development, and the possible targets and therapeutic strategies for future drug development. We hope to present new concepts and methods for future drug therapies for AD.

FDG PET (and MRI) for Monitoring Immunotherapy in Alzheimer Disease

ABSTRACT

Passive immunotherapy for Alzheimer disease has been tried for over 10 years without success. However, in 2021 and most recently in January 2023, the US Food and Drug Administration granted accelerated approval of 2 antibodies for this purpose, aducanumab and lecanemab. In both cases, the approval was based on a presumed therapy-related removal of amyloid deposits from the brain and, in the case of lecanemab, also some delay in cognitive decline. We question the validity of the evidence for the removal of amyloid in particular as assessed by amyloid PET imaging, believing that what is observed is more likely a large nonspecific amyloid PET signal in the white matter that diminishes during immunotherapy-in line with dose-dependent increases in amyloid-related imaging abnormalities and increased loss of cerebral volume in treated compared with placebo patients. To investigate this further, we recommend repeat FDG PET and MRI in all future immunotherapy trials.

siRNA drug delivery across the blood-brain barrier in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease with a few FDA-approved drugs that provide modest symptomatic benefits and only two FDA-approved disease-modifying treatments for AD. The advancements in understanding the causative genes and non-coding sequences at the molecular level of the pathophysiology of AD have resulted in several exciting research papers that employed small interfering RNA (siRNA)-based therapy. Although siRNA is being sought by academia and biopharma industries, several challenges still need to be addressed. We comprehensively report the latest advances in AD pathophysiology, druggable targets, ongoing clinical trials, and the siRNA-based approaches across the blood-brain barrier for addressing AD. This review describes the latest delivery systems employed to address this barrier. Critical insights and future perspectives on siRNA therapy for AD are also provided.

FDG-PET versus Amyloid-PET Imaging for Diagnosis and Response Evaluation in Alzheimer's Disease: Benefits and Pitfalls

In June 2021, the US Federal Drug and Food Administration (FDA) granted accelerated approval for the antibody aducanumab and, in January 2023, also for the antibody lecanemab, based on a perceived drug-induced removal of cerebral amyloid-beta as assessed by amyloid-PET and, in the case of lecanemab, also a presumption of limited clinical efficacy. Approval of the antibody donanemab is awaiting further data. However, published trial data indicate few, small and uncertain clinical benefits, below what is considered "clinically meaningful" and similar to the effect of conventional medication. Furthermore, a therapy-related decrease in the amyloid-PET signal may also reflect increased cell damage rather than simply "amyloid removal". This interpretation is more consistent with increased rates of amyloid-related imaging abnormalities and brain volume loss in treated patients, relative to placebo. We also challenge the current diagnostic criteria for AD based on amyloid-PET imaging biomarkers and recommend that future anti-AD therapy trials apply: (1) diagnosis of AD based on the co-occurrence of cognitive decline and decreased cerebral metabolism assessed by FDA-approved FDG-PET, (2) therapy efficacy determined by favorable effect on cognitive ability, cerebral metabolism by FDG-PET, and brain volumes by MRI, and (3) neuropathologic examination of all deaths occurring in these trials.

Longitudinal head-to-head comparison of 11C-PiB and 18F-florbetapir PET in a Phase 2/3 clinical trial of anti-amyloid-β monoclonal antibodies in dominantly inherited Alzheimer's disease

PURPOSE

Pittsburgh Compound-B (11C-PiB) and 18F-florbetapir are amyloid-β (Aβ) positron emission tomography (PET) radiotracers that have been used as endpoints in Alzheimer's disease (AD) clinical trials to evaluate the efficacy of anti-Aβ monoclonal antibodies. However, comparing drug effects between and within trials may become complicated if different Aβ radiotracers were used. To study the consequences of using different Aβ radiotracers to measure Aβ clearance, we performed a head-to-head comparison of 11C-PiB and 18F-florbetapir in a Phase 2/3 clinical trial of anti-Aβ monoclonal antibodies.

METHODS

Sixty-six mutation-positive participants enrolled in the gantenerumab and placebo arms of the first Dominantly Inherited Alzheimer Network Trials Unit clinical trial (DIAN-TU-001) underwent both 11C-PiB and 18F-florbetapir PET imaging at baseline and during at least one follow-up visit. For each PET scan, regional standardized uptake value ratios (SUVRs), regional Centiloids, a global cortical SUVR, and a global cortical Centiloid value were calculated. Longitudinal changes in SUVRs and Centiloids were estimated using linear mixed models. Differences in longitudinal change between PET radiotracers and between drug arms were estimated using paired and Welch two sample t-tests, respectively. Simulated clinical trials were conducted to evaluate the consequences of some research sites using 11C-PiB while other sites use 18F-florbetapir for Aβ PET imaging.

RESULTS

In the placebo arm, the absolute rate of longitudinal change measured by global cortical 11C-PiB SUVRs did not differ from that of global cortical 18F-florbetapir SUVRs. In the gantenerumab arm, global cortical 11C-PiB SUVRs decreased more rapidly than global cortical 18F-florbetapir SUVRs. Drug effects were statistically significant across both Aβ radiotracers. In contrast, the rates of longitudinal change measured in global cortical Centiloids did not differ between Aβ radiotracers in either the placebo or gantenerumab arms, and drug effects remained statistically significant. Regional analyses largely recapitulated these global cortical analyses. Across simulated clinical trials, type I error was higher in trials where both Aβ radiotracers were used versus trials where only one Aβ radiotracer was used. Power was lower in trials where 18F-florbetapir was primarily used versus trials where 11C-PiB was primarily used.

CONCLUSION

Gantenerumab treatment induces longitudinal changes in Aβ PET, and the absolute rates of these longitudinal changes differ significantly between Aβ radiotracers. These differences were not seen in the placebo arm, suggesting that Aβ-clearing treatments may pose unique challenges when attempting to compare longitudinal results across different Aβ radiotracers. Our results suggest converting Aβ PET SUVR measurements to Centiloids (both globally and regionally) can harmonize these differences without losing sensitivity to drug effects. Nonetheless, until consensus is achieved on how to harmonize drug effects across radiotracers, and since using multiple radiotracers in the same trial may increase type I error, multisite studies should consider potential variability due to different radiotracers when interpreting Aβ PET biomarker data and, if feasible, use a single radiotracer for the best results.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01760005. Registered 31 December 2012. Retrospectively registered.

Modeling Alzheimer's disease progression utilizing clinical trial and ADNI data to predict longitudinal trajectory of CDR-SB

There is strong interest in developing predictive models to better understand individual heterogeneity and disease progression in Alzheimer's disease (AD). We have built upon previous longitudinal AD progression models, using a nonlinear, mixed-effect modeling approach to predict Clinical Dementia Rating Scale - Sum of Boxes (CDR-SB) progression. Data from the Alzheimer's Disease Neuroimaging Initiative (observational study) and placebo arms from four interventional trials (N = 1093) were used for model building. The placebo arms from two additional interventional trials (N = 805) were used for external model validation. In this modeling framework, CDR-SB progression over the disease trajectory timescale was obtained for each participant by estimating disease onset time (DOT). Disease progression following DOT was described by both global progression rate (RATE) and individual progression rate (α). Baseline Mini-Mental State Examination and CDR-SB scores described the interindividual variabilities in DOT and α well. This model successfully predicted outcomes in the external validation datasets, supporting its suitability for prospective prediction and use in design of future trials. By predicting individual participants' disease progression trajectories using baseline characteristics and comparing these against the observed responses to new agents, the model can help assess treatment effects and support decision making for future trials.

Amyloid β-based therapy for Alzheimer's disease: challenges, successes and future

Amyloid β protein (Aβ) is the main component of neuritic plaques in Alzheimer's disease (AD), and its accumulation has been considered as the molecular driver of Alzheimer's pathogenesis and progression. Aβ has been the prime target for the development of AD therapy. However, the repeated failures of Aβ-targeted clinical trials have cast considerable doubt on the amyloid cascade hypothesis and whether the development of Alzheimer's drug has followed the correct course. However, the recent successes of Aβ targeted trials have assuaged those doubts. In this review, we discussed the evolution of the amyloid cascade hypothesis over the last 30 years and summarized its application in Alzheimer's diagnosis and modification. In particular, we extensively discussed the pitfalls, promises and important unanswered questions regarding the current anti-Aβ therapy, as well as strategies for further study and development of more feasible Aβ-targeted approaches in the optimization of AD prevention and treatment.

Detection and treatment of Alzheimer's disease in its preclinical stage

Longitudinal multimodal biomarker studies reveal that the continuum of Alzheimer's disease (AD) includes a long latent phase, referred to as preclinical AD, which precedes the onset of symptoms by decades. Treatment during the preclinical AD phase offers an optimal opportunity for slowing the progression of disease. However, trial design in this population is complex. In this Review, we discuss the recent advances in accurate plasma measurements, new recruitment approaches, sensitive cognitive instruments and self-reported outcomes that have facilitated the successful launch of multiple phase 3 trials for preclinical AD. The recent success of anti-amyloid immunotherapy trials in symptomatic AD has increased the enthusiasm for testing this strategy at the earliest feasible stage. We provide an outlook for standard screening of amyloid accumulation at the preclinical stage in clinically normal individuals, during which effective therapy to delay or prevent cognitive decline can be initiated.

Antibody-guided proteases enable selective and catalytic degradation of challenging therapeutic targets

The exquisite specificity, natural biological functions, and favorable development properties of antibodies make them highly effective agents as drugs. Monoclonal antibodies are particularly strong as inhibitors of systemically accessible targets where trough-level concentrations can sustain full target occupancy. Yet beyond this pharmacologic wheelhouse, antibodies perform suboptimally for targets of high abundance and those not easily accessible from circulation. Fundamentally, this restraint on broader application is due largely to the stoichiometric nature of their activity - one drug molecule is generally able to inhibit a maximum of two target molecules at a time. Enzymes in contrast are able to catalytically turnover multiple substrates, making them a natural sub-stoichiometric solution for targets of high abundance or in poorly accessible sites of action. However, enzymes have their own limitations as drugs, including, in particular the polypharmacology and broad specificity often seen with native enzymes. In this study, we introduce antibody-guided proteolytic enzymes to enable selective sub-stoichiometric turnover of therapeutic targets. We demonstrate that antibody-mediated substrate targeting can enhance enzyme activity and specificity, with proof of concept for two challenging target proteins, amyloid-β (Aβ) and immunoglobulin G (IgG). This work advances a new biotherapeutic platform that combines the favorable properties of antibodies and proteolytic enzymes to more effectively suppress high-bar therapeutic targets.

Lessons from antiamyloid-β immunotherapies in Alzheimer's disease

The amyloid hypothesis, that established amyloid-β (Aβ) peptide as the primary cause of Alzheimer's disease (AD) and related dementia, has driven the development of treatments for neurodegeneration for 30 years. During the last decades, more than 200 clinical trials testing more than 30 anti-Aβ immunotherapies have been assessed as potential treatments for AD. A vaccine against Aβ was the first immunotherapy intended to avoid aggregation of Aβ into fibrils and senile plaques, but it dramatically failed. Several other vaccines have been proposed as potential AD treatments, targeting different domains or structural motifs of Aβ aggregates, but without clear clinical benefits or effectiveness. In contrast, anti-Aβ therapeutic antibodies have focused on recognizing and removing Aβ aggregates (oligomers, fibrils, or plaques) by eliciting immune clearance. In 2021, the first anti-Aβ antibody, aducanumab (branded as Aduhelm), received FDA approval under an accelerated approval process. The effectiveness and the overall processes regarding the approval of Aduhelm have been under major criticism and scrutiny, prompting a vote of no confidence by public and private health providers, limiting the coverage only to patients enrolled in clinical trials and not for the general elderly patients. Additionally, another three therapeutic anti-Aβ antibodies are following the same path for potential FDA approval. Here, we present the current status of anti-Aβ immunotherapies under evaluation in preclinical and clinical trials for the treatment of AD and related dementia, with a discussion of the main findings and critical lessons learned from the observations from Phase III, II, and I clinical trials of anti-Aβ vaccines and antibodies.

Disease-modifying vs symptomatic treatments: Splitting over lumping

Clinical trials of putative disease-modifying therapies in neurodegeneration have obeyed the century-old principle of convergence, or lumping, whereby any feature of a clinicopathologic disease entity is considered relevant to most of those affected. While this convergent approach has resulted in important successes in trials of symptomatic therapies, largely aimed at correcting common neurotransmitter deficiencies (e.g., cholinergic deficiency in Alzheimer's disease or dopaminergic deficiency in Parkinson's disease), it has been consistently futile in trials of neuroprotective or disease-modifying interventions. As individuals affected by the same neurodegenerative disorder do not share the same biological drivers, splitting such disease into small molecular/biological subtypes, to match people to therapies most likely to benefit them, is vital in the pursuit of disease modification. We here discuss three paths toward the splitting needed for future successes in precision medicine: (1) encourage the development of aging cohorts agnostic to phenotype in order to enact a biology-to-phenotype direction of biomarker development and validate divergence biomarkers (present in some, absent in most); (2) demand bioassay-based recruitment of subjects into disease-modifying trials of putative neuroprotective interventions in order to match the right therapies to the right recipients; and (3) evaluate promising epidemiologic leads of presumed pathogenetic potential using Mendelian randomization studies before designing the corresponding clinical trials. The reconfiguration of disease-modifying efforts for patients with neurodegenerative disorders will require a paradigm shift from lumping to splitting and from proteinopathy to proteinopenia.

Feasibility, safety, and tolerability of two modalities of plasma exchange with albumin replacement to treat elderly patients with Alzheimer's disease in the AMBAR study

BACKGROUND

In the Alzheimer Management by Albumin Replacement (AMBAR) study, mild-to-moderate Alzheimer's disease (AD) patients were treated with a plasma exchange (PE) program. Feasibility and safety of PE in this specific population are poorly understood and were analyzed in detail in this study.

METHODS

Qualified patients were treated with 6 weeks of weekly conventional therapeutic plasma exchange (TPE) with albumin replacement followed by monthly low-volume plasma exchange (LVPE) for 12 months. The patients were divided into four groups: placebo (sham PE treatment), low-albumin (20 g), low-albumin + intravenous immunoglobulin (IVIG) (10 g), and high-albumin (40 g) + IVIG (20 g). Adverse events (AEs) were recorded and analyzed for all PE treatment groups and PE modalities.

RESULTS

PE procedure-related AEs were more common in the active treatment groups (16.9% out of 1283 TPE and 12.5% out of 2203 LVPE were associated with at least one AE, a similar rate than in other PE indications) than in the placebo group (0.7% out of 1223 sham PE). Percentage of procedures with at least one AEs was higher with central venous access compared to peripheral venous access in all three active treatment groups (20.1% vs 13.1%, respectively).

CONCLUSION

The TPE and LVPE procedures used in the AMBAR study on mild-to-moderate AD population were as safe and feasible as in other therapeutic applications of PE or routine plasmapheresis.

Delivery of the Brainshuttle™ amyloid-beta antibody fusion trontinemab to non-human primate brain and projected efficacious dose regimens in humans

There are few treatments that slow neurodegeneration in Alzheimer's disease (AD), and while therapeutic antibodies are being investigated in clinical trials for AD treatment, their access to the central nervous system is restricted by the blood-brain barrier. This study investigates a bispecific modular fusion protein composed of gantenerumab, a fully human monoclonal anti- amyloid-beta (Aβ) antibody under investigation for AD treatment, with a human transferrin receptor 1-directed Brainshuttle™ module (trontinemab; RG6102, INN trontinemab). In vitro, trontinemab showed a similar binding affinity to fibrillar Aβ40 and Aβ plaques in human AD brain sections to gantenerumab. A single intravenous administration of trontinemab (10 mg/kg) or gantenerumab (20 mg/kg) to non-human primates (NHPs, Macaca fascicularis), was well tolerated in both groups. Immunohistochemistry indicated increased trontinemab uptake into the brain endothelial cell layer and parenchyma, and more homogeneous distribution, compared with gantenerumab. Brain and plasma pharmacokinetic (PK) parameters for trontinemab were estimated by nonlinear mixed-effects modeling with correction for tissue residual blood, indicating a 4-18-fold increase in brain exposure. A previously developed clinical PK/pharmacodynamic model of gantenerumab was adapted to include a brain compartment as a driver of plaque removal and linked to the allometrically scaled above model from NHP. The new brain exposure-based model was used to predict trontinemab dosing regimens for effective amyloid reduction. Simulations from these models were used to inform dosing of trontinemab in the first-in-human clinical trial.

Recent Updates on the Development of Therapeutics for the Targeted Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is a complicated, multifaceted, irreversible, and incurable neurotoxic old age illness. Although NMDA (N-methyl D-aspartate)-receptor antagonists, cholinesterase repressors, and their pairings have been approved for the treatment, they are useful for short symptomatic relief. Researchers throughout the globe have been constantly working to uncover the therapy of Alzheimer's disease as new candidates must be determined, and newer treatment medicines must be developed. The aim of this review is to address recent advances in medication research along with new Alzheimer's disease therapy for diverse targets. Information was gathered utilizing a variety of internet resources as well as websites, such as ALZFORUM (alzforum.org) and clinicaltrials.gov. In contrast to other domains, the proposed medicines target amyloids (secretases, A42 generation, neuroinflammation, amyloid precipitation, and immunization), tau proteins (tau phosphorylation/aggregation and immunotherapy), and amyloid deposition. Despite tremendous advancement in our understanding of the underlying pathophysiology of Alzheimer's disease, the FDA (Food and Drug Administration) only approved aducanumab for diagnosis and treatment in 2003. Hence, novel treatment tactics are needed to find and develop therapeutic medicines to combat Alzheimer's disease.

The neuroprotective effects of targeting key factors of neuronal cell death in neurodegenerative diseases: The role of ER stress, oxidative stress, and neuroinflammation

Neuronal loss is one of the striking causes of various central nervous system (CNS) disorders, including major neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and Amyotrophic lateral sclerosis (ALS). Although these diseases have different features and clinical manifestations, they share some common mechanisms of disease pathology. Progressive regional loss of neurons in patients is responsible for motor, memory, and cognitive dysfunctions, leading to disabilities and death. Neuronal cell death in neurodegenerative diseases is linked to various pathways and conditions. Protein misfolding and aggregation, mitochondrial dysfunction, generation of reactive oxygen species (ROS), and activation of the innate immune response are the most critical hallmarks of most common neurodegenerative diseases. Thus, endoplasmic reticulum (ER) stress, oxidative stress, and neuroinflammation are the major pathological factors of neuronal cell death. Even though the exact mechanisms are not fully discovered, the notable role of mentioned factors in neuronal loss is well known. On this basis, researchers have been prompted to investigate the neuroprotective effects of targeting underlying pathways to determine a promising therapeutic approach to disease treatment. This review provides an overview of the role of ER stress, oxidative stress, and neuroinflammation in neuronal cell death, mainly discussing the neuroprotective effects of targeting pathways or molecules involved in these pathological factors.

Protein misfolding and related human diseases: A comprehensive review of toxicity, proteins involved, and current therapeutic strategies

Most of the cell's chemical reactions and structural components are facilitated by proteins. But proteins are highly dynamic molecules, where numerous modifications or changes in the cellular environment can affect their native conformational fold leading to protein aggregation. Various stress conditions, such as oxidative stress, mutations and metal toxicity may cause protein misfolding and aggregation by shifting the conformational equilibrium towards more aggregation-prone states. Most of the protein misfolding diseases (PMDs) involve aggregation of protein. We have discussed such proteins like Aβ peptide, α-synuclein, amylin and lysozyme involved in Alzheimer's, Parkinson's, type II diabetes and non-neuropathic systemic amyloidosis respectively. Till date, all advances in PMDs therapeutics help symptomatically but do not prevent the root cause of the disease, i.e., the aggregation of protein involved in the diseases. Current efforts focused on developing therapies for PMDs have employed diverse strategies; repositioning pre-existing drugs as it saves time and money; natural compounds that are touted as potential drug candidates have an advantage of being taken in diet normally and will induce lesser side effects. This review also covers recently developed therapeutic strategies like antisense drugs and disaggregases which has yielded therapeutic agents that have transitioned from preclinical studies into human clinical trials.

Aβ42 oligomer-specific antibody ALZ-201 reduces the neurotoxicity of Alzheimer's disease brain extracts

BACKGROUND

In Alzheimer's disease (AD), amyloid-β 1-42 (Aβ42) neurotoxicity stems mostly from its soluble oligomeric aggregates. Studies of such aggregates have been hampered by the lack of oligomer-specific research tools and their intrinsic instability and heterogeneity. Here, we developed a monoclonal antibody with a unique oligomer-specific binding profile (ALZ-201) using oligomer-stabilising technology. Subsequently, we assessed the etiological relevance of the Aβ targeted by ALZ-201 on physiologically derived, toxic Aβ using extracts from post-mortem brains of AD patients and controls in primary mouse neuron cultures.

METHODS

Mice were immunised with stable oligomers derived from the Aβ42 peptide with A21C/A30C mutations (AβCC), and ALZ-201 was developed using hybridoma technology. Specificity for the oligomeric form of the Aβ42CC antigen and Aβ42 was confirmed using ELISA, and non-reactivity against plaques by immunohistochemistry (IHC). The antibody's potential for cross-protective activity against pathological Aβ was evaluated in brain tissue samples from 10 individuals confirmed as AD (n=7) and non-AD (n=3) with IHC staining for Aβ and phosphorylated tau (p-Tau) aggregates. Brain extracts were prepared and immunodepleted using the positive control 4G8 antibody, ALZ-201 or an isotype control to ALZ-201. Fractions were biochemically characterised, and toxicity assays were performed in primary mouse neuronal cultures using automated high-content microscopy.

RESULTS

AD brain extracts proved to be more toxic than controls as demonstrated by neuronal loss and morphological determinants (e.g. synapse density and measures of neurite complexity). Immunodepletion using 4G8 reduced Aβ levels in both AD and control samples compared to ALZ-201 or the isotype control, which showed no significant difference. Importantly, despite the differential effect on the total Aβ content, the neuroprotective effects of 4G8 and ALZ-201 immunodepletion were similar, whereas the isotype control showed no effect.

CONCLUSIONS

ALZ-201 depletes a toxic species in post-mortem AD brain extracts causing a positive physiological and protective impact on the integrity and morphology of mouse neurons. Its unique specificity indicates that a low-abundant, soluble Aβ42 oligomer may account for much of the neurotoxicity in AD. This critical attribute identifies the potential of ALZ-201 as a novel drug candidate for achieving a true, clinical therapeutic effect in AD.

Enhanced delivery of antibodies across the blood-brain barrier via TEMs with inherent receptor-mediated phagocytosis

BACKGROUND

The near impermeability of the blood-brain barrier (BBB) and the unique neuroimmune environment of the CNS prevents the effective use of antibodies in neurological diseases. Delivery of biotherapeutics to the brain can be enabled through receptor-mediated transcytosis via proteins such as the transferrin receptor, although limitations such as the ability to use Fc-mediated effector function to clear pathogenic targets can introduce safety liabilities. Hence, novel delivery approaches with alternative clearance mechanisms are warranted.

METHODS

Binders that optimized transport across the BBB, known as transcytosis-enabling modules (TEMs), were identified using a combination of antibody discovery techniques and pharmacokinetic analyses. Functional activity of TEMs were subsequently evaluated by imaging for the ability of myeloid cells to phagocytose target proteins and cells.

FINDINGS

We demonstrated significantly enhanced brain exposure of therapeutic antibodies using optimal transferrin receptor or CD98 TEMs. We found that these modules also mediated efficient clearance of tau aggregates and HER2+ tumor cells via a non-classical phagocytosis mechanism through direct engagement of myeloid cells. This mode of clearance potentially avoids the known drawbacks of FcγR-mediated antibody mechanisms in the brain such as the neurotoxic release of proinflammatory cytokines and immune cell exhaustion.

CONCLUSIONS

Our study reports a new brain delivery platform that harnesses receptor-mediated transcytosis to maximize brain uptake and uses a non-classical phagocytosis mechanism to efficiently clear pathologic proteins and cells. We believe these findings will transform therapeutic approaches to treat CNS diseases.

FUNDING

This research was funded by Janssen, Pharmaceutical Companies of Johnson & Johnson.