A Placebo-Controlled, Multiple Ascending Dose Study to Evaluate the Safety, Pharmacokinetics and Pharmacodynamics of Avagacestat (BMS-708163) in Healthy Young and Elderly Subjects

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.

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.

Effects of DDT on Amyloid Precursor Protein Levels and Amyloid Beta Pathology: Mechanistic Links to Alzheimer's Disease Risk

BACKGROUND

The interaction of aging-related, genetic, and environmental factors is thought to contribute to the etiology of late-onset, sporadic Alzheimer's disease (AD). We previously reported that serum levels of p,p'-dichlorodiphenyldichloroethylene (DDE), a long-lasting metabolite of the organochlorine pesticide dichlorodiphenyltrichloroethane (DDT), were significantly elevated in patients with AD and associated with the risk of AD diagnosis. However, the mechanism by which DDT may contribute to AD pathogenesis is unknown.

OBJECTIVES

This study sought to assess effects of DDT exposure on the amyloid pathway in multiple in vitro and in vivo models.

METHODS

Cultured cells (SH-SY5Y and primary neurons), transgenic flies overexpressing amyloid beta (Aβ), and C57BL/6J and 3xTG-AD mice were treated with DDT to assess impacts on the amyloid pathway. Real time quantitative polymerase chain reaction, multiplex assay, western immunoblotting and immunohistochemical methods were used to assess the effects of DDT on amyloid precursor protein (APP) and other contributors to amyloid processing and deposition.

RESULTS

Exposure to DDT revealed significantly higher APP mRNA and protein levels in immortalized and primary neurons, as well as in wild-type and AD-models. This was accompanied by higher levels of secreted Aβ in SH-SY5Y cells, an effect abolished by the sodium channel antagonist tetrodotoxin. Transgenic flies and 3xTG-AD mice had more Aβ pathology following DDT exposure. Furthermore, loss of the synaptic markers synaptophysin and PSD95 were observed in the cortex of the brains of 3xTG-AD mice.

DISCUSSION

Sporadic Alzheimer's disease risk involves contributions from genetic and environmental factors. Here, we used multiple model systems, including primary neurons, transgenic flies, and mice to demonstrate the effects of DDT on APP and its pathological product Aβ. These data, combined with our previous epidemiological findings, provide a mechanistic framework by which DDT exposure may contribute to increased risk of AD by impacting the amyloid pathway. https://doi.org/10.1289/EHP10576.

Advances in PPARs Molecular Dynamics and Glitazones as a Repurposing Therapeutic Strategy through Mitochondrial Redox Dynamics against Neurodegeneration

Peroxisome proliferator-activated receptors (PPARs) activity has significant implications for the development of novel therapeutic modalities against neurodegenerative diseases. Although PPAR-α, PPAR-β/δ, and PPAR-γ nuclear receptor expressions are significantly reported in the brain, their implications in brain physiology and other neurodegenerative diseases still require extensive studies. PPAR signaling can modulate various cell signaling mechanisms involved in the cells contributing to on- and off-target actions selectively to promote therapeutic effects as well as the adverse effects of PPAR ligands. Both natural and synthetic ligands for the PPARα, PPARγ, and PPARβ/δ have been reported. PPARα (WY 14.643) and PPARγ agonists can confer neuroprotection by modulating mitochondrial dynamics through the redox system. The pharmacological effect of these agonists may deliver effective clinical responses by protecting vulnerable neurons from Aβ toxicity in Alzheimer's disease (AD) patients. Therefore, the current review delineated the ligands' interaction with 3D-PPARs to modulate neuroprotection, and also deciphered the efficacy of numerous drugs, viz. Aβ aggregation inhibitors, vaccines, and γ-secretase inhibitors against AD; this review elucidated the role of PPAR and their receptor isoforms in neural systems, and neurodegeneration in human beings. Further, we have substantially discussed the efficacy of PPREs as potent transcription factors in the brain, and the role of PPAR agonists in neurotransmission, PPAR gamma coactivator-1α (PGC-1α) and mitochondrial dynamics in neuroprotection during AD conditions. This review concludes with the statement that the development of novel PPARs agonists may benefit patients with neurodegeneration, mainly AD patients, which may help mitigate the pathophysiology of dementia, subsequently improving overall the patient's quality of life.

Conformational Models of APP Processing by Gamma Secretase Based on Analysis of Pathogenic Mutations

Proteolytic processing of amyloid precursor protein (APP) plays a critical role in the pathogenesis of Alzheimer's disease (AD). Sequential cleavage of APP by β and γ secretases leads to the generation of Aβ40 (non-amyloidogenic) and Aβ42 (amyloidogenic) peptides. Presenilin-1 (PS1) or presenilin-2 (PS2) play the role of a catalytic subunit of γ-secretase. Multiple familial AD (FAD) mutations in APP, PS1, or PS2 result in an increased Aβ42:Aβ40 ratio and the accumulation of toxic Aβ42 oligomers and plaques in patient brains. In this study, we perform molecular modeling of the APP complex with γ-secretase and analyze potential effects of FAD mutations in APP and PS1. We noticed that all FAD mutations in the APP transmembrane domain are predicted to cause an increase in the local disorder of its secondary structure. Based on structural analysis of known γ-secretase structures, we propose that APP can form a complex with γ-secretase in 2 potential conformations-M1 and M2. In conformation, the M1 transmembrane domain of APP forms a contact with the perimembrane domain that follows transmembrane domain 6 (TM6) in the PS1 structure. In conformation, the M2 transmembrane domain of APP forms a contact with transmembrane domain 7 (TM7) in the PS1 structure. By analyzing the effects of PS1-FAD mutations on the local protein disorder index, we discovered that these mutations increase the conformational flexibility of M2 and reduce the conformational flexibility of M1. Based on these results, we propose that M2 conformation, but not M1 conformation, of the γ secretase complex with APP leads to the amyloidogenic (Aβ42-generating) processing of APP. Our model predicts that APP processing in M1 conformation is favored by curved membranes, such as the membranes of early endosomes. In contrast, APP processing in M2 conformation is likely to be favored by relatively flat membranes, such as membranes of late endosomes and plasma membranes. These predictions are consistent with published biochemical analyses of APP processing at different subcellular locations. Our results also suggest that specific inhibitors of Aβ42 production could be potentially developed by selectively targeting the M2 conformation of the γ secretase complex with APP.

Past, present and future of therapeutic strategies against amyloid-β peptides in Alzheimer's disease: a systematic review

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease in ageing, affecting around 46 million people worldwide but few treatments are currently available. The etiology of AD is still puzzling, and new drugs development and clinical trials have high failure rates. Urgent outline of an integral (multi-target) and effective treatment of AD is needed. Accumulation of amyloid-β (Aβ) peptides is considered one of the fundamental neuropathological pillars of the disease, and its dyshomeostasis has shown a crucial role in AD onset. Therefore, many amyloid-targeted therapies have been investigated. Here, we will systematically review recent (from 2014) investigational, follow-up and review studies focused on anti-amyloid strategies to summarize and analyze their current clinical potential. Combination of anti-Aβ therapies with new developing early detection biomarkers and other therapeutic agents acting on early functional AD changes will be highlighted in this review. Near-term approval seems likely for several drugs acting against Aβ, with recent FDA approval of a monoclonal anti-Aβ oligomers antibody -aducanumab- raising hopes and controversies. We conclude that, development of oligomer-epitope specific Aβ treatment and implementation of multiple improved biomarkers and risk prediction methods allowing early detection, together with therapies acting on other factors such as hyperexcitability in early AD, could be the key to slowing this global pandemic.

Use of Zebrafish Genetic Models to Study Etiology of the Amyloid-Beta and Neurofibrillary Tangle Pathways in Alzheimer's Disease

The prevalence of neurodegenerative diseases is increasing globally, with an imperative need to identify and expand the availability of pharmaceutical treatment strategies. Alzheimer's disease is the most common neurodegenerative disease for which there is no cure or has limited treatments. Rodent models are primarily used in Alzheimer's disease research to investigate causes, pathology, molecular mechanisms, and pharmaceutical therapies. However, there is a lack of a comprehensive understanding of Alzheimer's disease causes, pathogenesis, and optimal treatments due in part to some limitations of using rodents, including higher economic cost, which can influence sample size and ultimately statistical power. It is necessary to expand our animal model toolbox to provide alternative strategies in Alzheimer's disease research. The zebrafish application in neurodegenerative disease research and neuropharmacology is greatly expanding due to several vital strengths spanning lower economic costs, the smaller size of the organism, a sequenced characterized genome, and well described anatomical structures. These characteristics are coupled to the conserved molecular function and disease pathways in humans. The existence of orthologs for genes associated with Alzheimer's disease in zebrafish is also confirmed. While wild-type zebrafish appear to lack some of the neuropathological features of Alzheimer's disease, the advent of genetic editing technologies has expanded evaluation of the amyloid and neurofibrillary tangle hypotheses using the zebrafish and exploration of pharmaceutical molecular targets. An overview of how genetic editing technologies are being used with the zebrafish to create models to investigate the causes, pathology, molecular mechanisms, and pharmaceutical targets of Alzheimer's disease is detailed.

Alzheimer Disease Clinical Trials Targeting Amyloid: Lessons Learned From Success in Mice and Failure in Humans

BACKGROUND

The goal of slowing or halting the development of Alzheimer disease (AD) has resulted in the huge allocation of resources by academic institutions and pharmaceutical companies to the development of new treatments. The etiology of AD is elusive, but the aggregation of amyloid-β and tau peptide and oxidative processes are considered critical pathologic mechanisms. The failure of drugs with multiple mechanisms to meet efficacy outcomes has caused several companies to decide not to pursue further AD studies and has left the field essentially where it has been for the past 15 years. Efforts are underway to develop biomarkers for detection and monitoring of AD using genetic, imaging, and biochemical technology, but this is of minimal use if no intervention can be offered.

REVIEW SUMMARY

In this review, we consider the natural progression of AD and how it continues despite present attempts to modify the amyloid-related machinery to alter the disease trajectory. We describe the mechanisms and approaches to AD treatment targeting amyloid, including both passive and active immunotherapy as well as inhibitors of enzymes in the amyloidogenic pathway.

CONCLUSION

Lessons learned from clinical trials of amyloid reduction strategies may prove crucial for the leap forward toward novel therapeutic targets to treat AD.

Recent advances on drug development and emerging therapeutic agents for Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative old age disease that is complex, multifactorial, unalterable, and progressive in nature. The currently approved therapy includes cholinesterase inhibitors, NMDA-receptor antagonists and their combination therapy provides only temporary symptomatic relief. Sincere efforts have been made by the researchers globally to identify new targets, discover, and develop novel therapeutic agents for the treatment of AD. This brief review article is intended to cover the recent advances in drug development and emerging therapeutic agents for AD acting at different targets. The article is compiled using various scientific online databases and by referring to clinicaltrials.gov and ALZFORUM (alzforum.org) websites. The upcoming therapies act on one or more targets including amyloids (secretases, Aβ₄₂ production, amyloid deposition, and immunotherapy), tau proteins (tau phosphorylation/aggregation and immunotherapy) and neuroinflammation in addition to other miscellaneous targets. Despite the tremendous improvement in our understanding of the underlying pathophysiology of AD, only aducanumab was approved by FDA for the treatment of AD in 18 years i.e., since 2003. Hence, it is concluded that novel therapeutic strategies are required to discover and develop therapeutic agents to fight against the century old AD.

Bridging the Gap Between Fluid Biomarkers for Alzheimer's Disease, Model Systems, and Patients

Alzheimer’s disease (AD) is a debilitating neurodegenerative disease characterized by the accumulation of two proteins in fibrillar form: amyloid-β (Aβ) and tau. Despite decades of intensive research, we cannot yet pinpoint the exact cause of the disease or unequivocally determine the exact mechanism(s) underlying its progression. This confounds early diagnosis and treatment of the disease. Cerebrospinal fluid (CSF) biomarkers, which can reveal ongoing biochemical changes in the brain, can help monitor developing AD pathology prior to clinical diagnosis. Here we review preclinical and clinical investigations of commonly used biomarkers in animals and patients with AD, which can bridge translation from model systems into the clinic. The core AD biomarkers have been found to translate well across species, whereas biomarkers of neuroinflammation translate to a lesser extent. Nevertheless, there is no absolute equivalence between biomarkers in human AD patients and those examined in preclinical models in terms of revealing key pathological hallmarks of the disease. In this review, we provide an overview of current but also novel AD biomarkers and how they relate to key constituents of the pathological cascade, highlighting confounding factors and pitfalls in interpretation, and also provide recommendations for standardized procedures during sample collection to enhance the translational validity of preclinical AD models.

Therapeutic Strategies Targeting Amyloid-β in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder linked to protein misfolding and aggregation. AD is pathologically characterized by senile plaques formed by extracellular Amyloid-β (Aβ) peptide and Intracellular Neurofibrillary Tangles (NFT) formed by hyperphosphorylated tau protein. Extensive synaptic loss and neuronal degeneration are responsible for memory impairment, cognitive decline and behavioral dysfunctions typical of AD. Amyloidosis has been implicated in the depression of acetylcholine synthesis and release, overactivation of N-methyl-D-aspartate (NMDA) receptors and increased intracellular calcium levels that result in excitotoxic neuronal degeneration. Current drugs used in AD treatment are either cholinesterase inhibitors or NMDA receptor antagonists; however, they provide only symptomatic relief and do not alter the progression of the disease. Aβ is the product of Amyloid Precursor Protein (APP) processing after successive cleavage by β- and γ-secretases while APP proteolysis by α-secretase results in non-amyloidogenic products. According to the amyloid cascade hypothesis, Aβ dyshomeostasis results in the accumulation and aggregation of Aβ into soluble oligomers and insoluble fibrils. The former are synaptotoxic and can induce tau hyperphosphorylation while the latter deposit in senile plaques and elicit proinflammatory responses, contributing to oxidative stress, neuronal degeneration and neuroinflammation. Aβ-protein-targeted therapeutic strategies are thus a promising disease-modifying approach for the treatment and prevention of AD. This review summarizes recent findings on Aβ-protein targeted AD drugs, including β-secretase inhibitors, γ-secretase inhibitors and modulators, α-secretase activators, direct inhibitors of Aβ aggregation and immunotherapy targeting Aβ, focusing mainly on those currently under clinical trials.

Practical Method for Preparation of (S)-2-Amino-5,5,5-trifluoropentanoic Acid via Dynamic Kinetic Resolution

This work reports an operationally convenient ∼20 g scale synthesis of (S)-2-amino-5,5,5-trifluoropentanoic acid and its Fmoc-derivative via dynamic kinetic resolution of the corresponding racemate.

Investigations on the Relationship between Ovarian, Endocrine, and Renal Findings in Nonclinical Safety Studies of the γ-secretase Inhibitor Avagacestat

Avagacestat, a gamma (γ)-secretase inhibitor that was in development for treatment of Alzheimer's disease, produced ovarian granulosa-thecal cell tumors in rats and dogs and a glomerulopathy with profound proteinuria in female rats. This report describes the results of follow-up investigative studies, including the use of ovariectomized (OVX) rats, to further characterize these findings and determine their mechanism(s). Ovarian proliferative changes in rats likely resulted from: 1) inhibition of Notch signaling pathways regulating ovarian follicular differentiation/development, characterized microscopically as altered ovarian cyclicity and/or ovarian follicular degeneration; 2) subsequent disruption of the hypothalamic-pituitary-ovarian axis due to ovarian atrophy with decreases in serum estrogen and progesterone (as low as 0.45× and 0.21× controls, respectively); and 3) chronic gonadotropin stimulation and pituitary hypertrophy/hyperplasia in response to the absence of negative feedback. Gonadotropin stimulation in rats was confirmed by increases in serum follicle-stimulating hormone (FSH; up to 7.75× controls) and luteinizing hormone (LH; up to 5.84×). A similar non-genotoxic mechanism was likely responsible for the ovarian findings in dogs although changes in serum hormone levels were not detected. The dose- and time-dependent glomerulopathy with progression to chronic progressive nephropathy in female rats appears to be a direct effect of avagacestat and was not ameliorated with co-administration of 17β-estradiol or an antihypertensive (enalapril) and was not present in control OVX rats. In contrast, adrenocortical hypertrophy in female rats was considered secondary to ovarian changes based on the absence of this finding in avagacestat-treated OVX rats and no increase in ACTH staining in the pituitary.

Activation of microglia and astrocytes: a roadway to neuroinflammation and Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease that is of high importance to the neuroscience world, yet the complex pathogenicity is not fully understood. Inflammation is usually observed in AD and could implicate both beneficial or detrimental effects depending on the severity of the disease. During initial AD pathology, microglia and astrocyte activation is beneficial since they are involved in amyloid-beta clearance. However, with the progression of the disease, activated microglia elicit detrimental effects by the overexpression of pro-inflammatory cytokines such as interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF-α) bringing forth neurodegeneration in the surrounding brain regions. This results in decline in Aβ clearance by microglia; Aβ accumulation thus increases in the brain resulting in neuroinflammation. Thus, Aβ accumulation is the effect of increased release of pro-inflammatory molecules. Reactive astrocytes acquire gain of toxic function and exhibits neurotoxic effects with loss of neurotrophic functions. Astrocyte dysfunctioning results in increased release of cytokines and inflammatory mediators, neurodegeneration, decreased glutamate uptake, loss of neuronal synapses, and ultimately cognitive deficits in AD. We discuss the role of intracellular signaling pathways in the inflammatory responses produced by astrocytes and microglial activation, including the glycogen synthase kinase-3β, nuclear factor kappa B cascade, mitogen-activated protein kinase pathways and c-Jun N-terminal kinase. In this review, we describe the role of neuroinflammation in the chronicity of AD pathogenesis and an overview of the recent research towards the development of new therapies to treat this disorder.

γ-Secretase and its modulators: Twenty years and beyond

Twenty years ago, Wolfe, Xia, and Selkoe identified two aspartate residues in Alzheimer's presenilin protein that constitute the active site of the γ-secretase complex. Mutations in the genes encoding amyloid precursor protein (APP) or presenilin (PS) cause early onset familial Alzheimer's disease (AD), and sequential cleavages of the APP by β-secretase and γ-secretase/presenilin generate amyloid β protein (Aβ), the major component of pathological hallmark, neuritic plaques, in brains of AD patients. Therapeutic strategies centered on targeting γ-secretase/presenilin to reduce amyloid were implemented and led to several high profile clinical trials. This review article focuses on the studies of γ-secretase and its inhibitors/modulators since the discovery of presenilin as the γ-secretase. While a lack of complete understanding of presenilin biology renders failure of clinical trials, the lessons learned from some γ-secretase modulators, while premature for human testing, provide new directions to develop potential therapeutics. Imbalanced Aβ homeostasis is an upstream event of neurodegenerative processes. Exploration of γ-secretase modulators for their roles in these processes is highly significant, e.g., decreasing neuroinflammation and levels of phosphorylated tau, the component of the other AD pathological hallmark, neurofibrillary tangles. Agents with excellent human pharmacology hold great promise in suppressing neurodegeneration in pre-symptomatic or early stage AD patients.

Drug Development for Alzheimer's Disease: Microglia Induced Neuroinflammation as a Target?

Alzheimer's disease (AD) is one of the most common causes of dementia. Its pathogenesis is characterized by the aggregation of the amyloid-β (Aβ) protein in senile plaques and the hyperphosphorylated tau protein in neurofibrillary tangles in the brain. Current medications for AD can provide temporary help with the memory symptoms and other cognitive changes of patients, however, they are not able to stop or reverse the progression of AD. New medication discovery and the development of a cure for AD is urgently in need. In this review, we summarized drugs for AD treatments and their recent updates, and discussed the potential of microglia induced neuroinflammation as a target for anti-AD drug development.

Dosing, collection, and quality control issues in cerebrospinal fluid research using animal models

Cerebrospinal fluid (CSF) is a complex fluid filling the ventricular system and surrounding the brain and spinal cord. Although the bulk of CSF is created by the choroid plexus, a significant fraction derives from the interstitial fluid in the brain and spinal cord parenchyma. For this reason, CSF can often be used as a source of pharmacodynamic and prognostic biomarkers to reflect biochemical changes occurring within the brain. For instance, CSF biomarkers can be used to diagnose and track progression of disease as well as understand pharmacokinetic and pharmacodynamic relationships in clinical trials. To facilitate the use of these biomarkers in humans, studies in preclinical species are often valuable. This review summarizes methods for preclinical CSF collection for biomarkers from mice, rats, and nonhuman primates. In addition, dosing directly into CSF is increasingly being used to improve drug levels in the brain. Therefore, this review also summarizes the state of the art in CSF dosing in these preclinical species.

Targeting Tumor Necrosis Factor Alpha for Alzheimer's Disease

Alzheimer's disease (AD) affects an estimated 44 million individuals worldwide, yet no therapeutic intervention is available to stop the progression of the dementia. Neuropathological hallmarks of AD are extracellular deposits of amyloid beta (Aβ) peptides assembled in plaques, intraneuronal accumulation of hyperphosphorylated tau protein forming tangles, and chronic inflammation. A pivotal molecule in inflammation is the pro-inflammatory cytokine TNF-α. Several lines of evidence using genetic and pharmacological manipulations indicate that TNF-α signaling exacerbates both Aβ and tau pathologies in vivo. Interestingly, preventive and intervention anti-inflammatory strategies demonstrated a reduction in brain pathology and an amelioration of cognitive function in rodent models of AD. Phase I and IIa clinical trials suggest that TNF-α inhibitors might slow down cognitive decline and improve daily activities in AD patients. In the present review, we summarize the evidence pointing towards a beneficial role of anti-TNF-α therapies to prevent or slow the progression of AD. We also present possible physical and pharmacological interventions to modulate TNF-α signaling in AD subjects along with their limitations.

Inhibition of γ-Secretase Leads to an Increase in Presenilin-1

γ-Secretase inhibitors (GSIs) are potential therapeutic agents for Alzheimer’s disease (AD); however, trials have proven disappointing. We addressed the possibility that γ-secretase inhibition can provoke a rebound effect, elevating the levels of the catalytic γ-secretase subunit, presenilin-1 (PS1). Acute treatment of SH-SY5Y cells with the GSI LY-374973 (N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester, DAPT) augments PS1, in parallel with increases in other γ-secretase subunits nicastrin, presenilin enhancer 2, and anterior pharynx-defective 1, yet with no increase in messenger RNA expression. Over-expression of the C-terminal fragment (CTF) of APP, C99, also triggered an increase in PS1. Similar increases in PS1 were evident in primary neurons treated repeatedly (4 days) with DAPT or with the GSI BMS-708163 (avagacestat). Likewise, rats examined after 21 days administered with avagacestat (40 mg/kg/day) had more brain PS1. Sustained γ-secretase inhibition did not exert a long-term effect on PS1 activity, evident through the decrease in CTFs of APP and ApoER2. Prolonged avagacestat treatment of rats produced a subtle impairment in anxiety-like behavior. The rebound increase in PS1 in response to GSIs must be taken into consideration for future drug development.

A Translational Systems Pharmacology Model for Aβ Kinetics in Mouse, Monkey, and Human

A mechanistic model of amyloid beta production, degradation, and distribution was constructed for mouse, monkey, and human, calibrated and externally verified across multiple datasets. Simulations of single‐dose avagacestat treatment demonstrate that the Aβ₄₂ brain inhibition may exceed that in cerebrospinal fluid (CSF). The dose that achieves 50% CSF Aβ₄₀ inhibition for humans (both healthy and with Alzheimer's disease (AD)) is about 1 mpk, one order of magnitude lower than for mouse (10 mpk), mainly because of differences in pharmacokinetics. The predicted maximal percent of brain Aβ₄₂ inhibition after single‐dose avagacestat is higher for AD subjects (about 60%) than for healthy individuals (about 45%). The probability of achieving a normal physiological level for Aβ₄₂ in brain (1 nM) during multiple avagacestat dosing can be increased by using a dosing regimen that achieves higher exposure. The proposed model allows prediction of brain pharmacodynamics for different species given differing dosing regimens.

Pharmacological Agents Targeting γ-Secretase Increase Risk of Cancer and Cognitive Decline in Alzheimer's Disease Patients: A Systematic Review and Meta-Analysis

BACKGROUND

Drugs targeting γ-secretase in Alzheimer's disease (AD) have failed to demonstrate efficacy in clinical trials.

OBJECTIVE

To perform a meta-analysis of randomized controlled trials (RCTs) to evaluate the efficacy and safety of drugs targeting γ-secretase in AD.

METHODS

Ten trials were identified involving 5,227 patients using electronic databases and manual review of reference lists. RCTs of at least two weeks duration involving a drug targeting γ-secretase were eligible. The main outcomes examined were adverse events and cognitive measures (ADAS-cog, MMSE, ADCS-ADL, and CDR-sb). A sub-group analysis was performed, excluding the γ-secretase modulator tarenflurbil, to evaluate the safety and efficacy of γ-secretase inhibitors only.

RESULTS

There was an increased risk of adverse events (Odds Ratio (OR) 1.38, 95% CI 1.09-1.73; p = 0.01), serious adverse events (OR 1.50, 95% CI 1.22-1.84; p < 0.001), and skin cancers (OR 4.77, 95% CI 2.83-8.06; p < 0.001). There was significantly increased risk of infections (OR 1.36, 95% CI 1.13-1.63; p < 0.001) in the subgroup analysis excluding tarenflurbil. Pooled results also revealed a worsening in ADAS-cog (difference in means 1.33, 95% CI 0.58-2.08; p < 0.001) and MMSE (difference in means -0.66, 95% CI -0.96 to 0.35; p < 0.001), but not ADCS-ADL or CDR-sb.

CONCLUSION

The use of γ-secretase inhibitors is associated with significantly increased risk of serious adverse events including skin cancers, and worsening in cognitive indicators. This evidence indicates that γ-secretase may not be an appropriate target for clinical treatment of AD.

Highly sensitive ligand-binding assays in pre-clinical and clinical applications: immuno-PCR and other emerging techniques

Recombinant DNA technology and corresponding innovations in molecular biology, chemistry and medicine have led to novel therapeutic biomacromolecules as lead candidates in the pharmaceutical drug development pipelines. While monoclonal antibodies and other proteins provide therapeutic potential beyond the possibilities of small molecule drugs, the concomitant demand for supportive bioanalytical sample testing creates multiple novel challenges. For example, intact macromolecules can usually not be quantified by mass-spectrometry without enzymatic digestion and isotopically labeled internal standards are costly and/or difficult to prepare. Classical ELISA-type immunoassays, on the other hand, often lack the sensitivity required to obtain pharmacokinetics of low dosed drugs or pharmacodynamics of suitable biomarkers. Here we summarize emerging state-of-the-art ligand-binding assay technologies for pharmaceutical sample testing, which reveal enhanced analytical sensitivity over classical ELISA formats. We focus on immuno-PCR, which combines antibody specificity with the extremely sensitive detection of a tethered DNA marker by quantitative PCR, and alternative nucleic acid-based technologies as well as methods based on electrochemiluminescence or single-molecule counting. Using case studies, we discuss advantages and drawbacks of these methods for preclinical and clinical sample testing.

Advances in recent patent and clinical trial drug development for Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease, involving a large number of genes, proteins and their complex interactions. Currently, no effective therapeutic agents are available to either stop or reverse the progression of this disease, likely due to its polygenic nature. The complicated pathophysiology of AD remains unresolved. Although it has been hypothesized that the amyloid β cascade and the hyper-phosphorylated tau protein may be primarily involved, other mechanisms, such as oxidative stress, deficiency of central cholinergic neurotransmitter, mitochondrial dysfunction and inflammation have also been implicated. The main focus of this review is to document current therapeutic agents in clinical trials and patented candidate compounds under development based on their main mechanisms of action. It also discusses the relationship between the recent understanding of key targets and the development of potential therapeutic agents for the treatment of AD.

Current Research Therapeutic Strategies for Alzheimer's Disease Treatment

Alzheimer's disease (AD) currently presents one of the biggest healthcare issues in the developed countries. There is no effective treatment capable of slowing down disease progression. In recent years the main focus of research on novel pharmacotherapies was based on the amyloidogenic hypothesis of AD, which posits that the beta amyloid (Aβ) peptide is chiefly responsible for cognitive impairment and neuronal death. The goal of such treatments is (a) to reduce Aβ production through the inhibition of β and γ secretase enzymes and (b) to promote dissolution of existing cerebral Aβ plaques. However, this approach has proven to be only modestly effective. Recent studies suggest an alternative strategy centred on the inhibition of the downstream Aβ signalling, particularly at the synapse. Aβ oligomers may cause aberrant N-methyl-D-aspartate receptor (NMDAR) activation postsynaptically by forming complexes with the cell-surface prion protein (PrPC). PrPC is enriched at the neuronal postsynaptic density, where it interacts with Fyn tyrosine kinase. Fyn activation occurs when Aβ is bound to PrPC-Fyn complex. Fyn causes tyrosine phosphorylation of the NR2B subunit of metabotropic glutamate receptor 5 (mGluR5). Fyn kinase blockers masitinib and saracatinib have proven to be efficacious in treating AD symptoms in experimental mouse models of the disease.

Harnessing Cerebrospinal Fluid Biomarkers in Clinical Trials for Treating Alzheimer's and Parkinson's Diseases: Potential and Challenges

No disease-modifying therapies (DMT) for neurodegenerative diseases (NDs) have been established, particularly for Alzheimer's disease (AD) and Parkinson's disease (PD). It is unclear why candidate drugs that successfully demonstrate therapeutic effects in animal models fail to show disease-modifying effects in clinical trials. To overcome this hurdle, patients with homogeneous pathologies should be detected as early as possible. The early detection of AD patients using sufficiently tested biomarkers could demonstrate the potential usefulness of combining biomarkers with clinical measures as a diagnostic tool. Cerebrospinal fluid (CSF) biomarkers for NDs are being incorporated in clinical trials designed with the aim of detecting patients earlier, evaluating target engagement, collecting homogeneous patients, facilitating prevention trials, and testing the potential of surrogate markers relative to clinical measures. In this review we summarize the latest information on CSF biomarkers in NDs, particularly AD and PD, and their use in clinical trials. The large number of issues related to CSF biomarker measurements and applications has resulted in relatively few clinical trials on CSF biomarkers being conducted. However, the available CSF biomarker data obtained in clinical trials support the advantages of incorporating CSF biomarkers in clinical trials, even though the data have mostly been obtained in AD trials. We describe the current issues with and ongoing efforts for the use of CSF biomarkers in clinical trials and the plans to harness CSF biomarkers for the development of DMT and clinical routines. This effort requires nationwide, global, and multidisciplinary efforts in academia, industry, and regulatory agencies to facilitate a new era.

Peripheral and central effects of γ-secretase inhibition by semagacestat in Alzheimer's disease

INTRODUCTION

The negative efficacy study examining the γ-secretase inhibitor semagacestat in mild to moderate Alzheimer's disease (AD) included a number of biomarkers of the disease as well as safety outcomes. We analyzed these data to explore relationships between drug exposure and pharmacodynamic effects and to examine the correlations among outcome measures.

METHODS

The study was a multicenter, randomized, placebo-controlled trial of two dose regimens of semagacestat and a placebo administered for 18 months to individuals with mild to moderate AD. Changes in measures of central and peripheral drug activity were compared between the three treatment groups using one-way analysis of variance. The relationship between changes in each of the outcome measures and measures of drug exposure and peripheral pharmacodynamic effect were assessed using Spearman's correlation coefficient.

RESULTS

Assignment to the active treatment arms was associated with reduction in plasma amyloid-β (Aβ) peptides, increase in ventricular volume, decrease in cerebrospinal fluid phosphorylated tau (p-tau) and several other laboratory measures and adverse event categories. Within the active arms, exposure to drug, as indicated by area under the concentration curve (AUC) of blood concentration, was associated with reduction in plasma Aβ peptides and a subset of laboratory changes and adverse event rates. Ventricular volume increase, right hippocampal volume loss and gastrointestinal symptoms were related to change in plasma Aβ peptide but not AUC, supporting a link to inhibition of γ-secretase cleavage of the amyloid precursor protein. Cognitive decline correlated with ventricular expansion and reduction in p-tau.

CONCLUSION

These findings may inform future studies of drugs targeting secretases involved in Aβ generation.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT00594568. Registered 11 January 2008.

Alzheimer's Disease: Lessons Learned from Amyloidocentric Clinical Trials

Alzheimer's disease (AD) is one of the most debilitating neurodegenerative diseases and is predicted to affect 1 in 85 people by 2050. Despite much effort to discover a therapeutic strategy to prevent progression or to cure AD, to date no effective disease-modifying agent is available that can prevent, halt, or reverse the cognitive and functional decline of patients with AD. Several underlying etiologies to this failure are proposed. First, accumulating evidence from past trials suggests a preventive as opposed to therapeutic paradigm, and the precise temporal and mechanistic relationship of β-amyloid (Aβ) and tau protein should be elucidated to confirm this hypothesis. Second, we are in urgent need of revised diagnostic criteria to support future trials. Third, various technical and methodological improvements are required, based on the lessons learned from previous failed trials.

Role of cerebrospinal fluid biomarkers in clinical trials for Alzheimer's disease modifying therapies

Until now, a disease-modifying therapy (DMT) that has an ability to slow or arrest Alzheimer's disease (AD) progression has not been developed, and all clinical trials involving AD patients enrolled by clinical assessment alone also have not been successful. Given the growing consensus that the DMT is likely to require treatment initiation well before full-blown dementia emerges, the early detection of AD will provide opportunities to successfully identify new drugs that slow the course of AD pathology. Recent advances in early detection of AD and prediction of progression of the disease using various biomarkers, including cerebrospinal fluid (CSF) Aβ_1-42, total tau and p-tau₁₈₁ levels, and imagining biomarkers, are now being actively integrated into the designs of AD clinical trials. In terms of therapeutic mechanisms, monitoring these markers may be helpful for go/no-go decision making as well as surrogate markers for disease severity or progression. Furthermore, CSF biomarkers can be used as a tool to enrich patients for clinical trials with prospect of increasing statistical power and reducing costs in drug development. However, the standardization of technical aspects of analysis of these biomarkers is an essential prerequisite to the clinical uses. To accomplish this, global efforts are underway to standardize CSF biomarker measurements and a quality control program supported by the Alzheimer's Association. The current review summarizes therapeutic targets of developing drugs in AD pathophysiology, and provides the most recent advances in the

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.

Disease-modifying drugs in Alzheimer's disease

Alzheimer's disease (AD) is an age-dependent neurodegenerative disorder and the most common cause of dementia. The early stages of AD are characterized by short-term memory loss. Once the disease progresses, patients experience difficulties in sense of direction, oral communication, calculation, ability to learn, and cognitive thinking. The median duration of the disease is 10 years. The pathology is characterized by deposition of amyloid beta peptide (so-called senile plaques) and tau protein in the form of neurofibrillary tangles. Currently, two classes of drugs are licensed by the European Medicines Agency for the treatment of AD, ie, acetylcholinesterase inhibitors for mild to moderate AD, and memantine, an N-methyl-D-aspartate receptor antagonist, for moderate and severe AD. Treatment with acetylcholinesterase inhibitors or memantine aims at slowing progression and controlling symptoms, whereas drugs under development are intended to modify the pathologic steps leading to AD. Herein, we review the clinical features, pharmacologic properties, and cost-effectiveness of the available acetylcholinesterase inhibitors and memantine, and focus on disease-modifying drugs aiming to interfere with the amyloid beta peptide, including vaccination, passive immunization, and tau deposition.

Therapeutics of Alzheimer's disease: Past, present and future

Alzheimer's disease (AD) is the most common cause of dementia worldwide. The etiology is multifactorial, and pathophysiology of the disease is complex. Data indicate an exponential rise in the number of cases of AD, emphasizing the need for developing an effective treatment. AD also imposes tremendous emotional and financial burden to the patient's family and community. The disease has been studied over a century, but acetylcholinesterase inhibitors and memantine are the only drugs currently approved for its management. These drugs provide symptomatic improvement alone but do less to modify the disease process. The extensive insight into the molecular and cellular pathomechanism in AD over the past few decades has provided us significant progress in the understanding of the disease. A number of novel strategies that seek to modify the disease process have been developed. The major developments in this direction are the amyloid and tau based therapeutics, which could hold the key to treatment of AD in the near future. Several putative drugs have been thoroughly investigated in preclinical studies, but many of them have failed to produce results in the clinical scenario; therefore it is only prudent that lessons be learnt from the past mistakes. The current rationales and targets evaluated for therapeutic benefit in AD are reviewed in this article. This article is part of the Special Issue entitled 'The Synaptic Basis of Neurodegenerative Disorders'.

Pharmacodynamics of selective inhibition of γ-secretase by avagacestat

A hallmark of Alzheimer's disease (AD) pathology is the accumulation of brain amyloid β-peptide (Aβ), generated by γ-secretase-mediated cleavage of the amyloid precursor protein (APP). Therefore, γ-secretase inhibitors (GSIs) may lower brain Aβ and offer a potential new approach to treat AD. As γ-secretase also cleaves Notch proteins, GSIs can have undesirable effects due to interference with Notch signaling. Avagacestat (BMS-708163) is a GSI developed for selective inhibition of APP over Notch cleavage. Avagacestat inhibition of APP and Notch cleavage was evaluated in cell culture by measuring levels of Aβ and human Notch proteins. In rats, dogs, and humans, selectivity was evaluated by measuring plasma blood concentrations in relation to effects on cerebrospinal fluid (CSF) Aβ levels and Notch-related toxicities. Measurements of Notch-related toxicity included goblet cell metaplasia in the gut, marginal-zone depletion in the spleen, reductions in B cells, and changes in expression of the Notch-regulated hairy and enhancer of split homolog-1 from blood cells. In rats and dogs, acute administration of avagacestat robustly reduced CSF Aβ40 and Aβ42 levels similarly. Chronic administration in rats and dogs, and 28-day, single- and multiple-ascending-dose administration in healthy human subjects caused similar exposure-dependent reductions in CSF Aβ40. Consistent with the 137-fold selectivity measured in cell culture, we identified doses of avagacestat that reduce CSF Aβ levels without causing Notch-related toxicities. Our results demonstrate the selectivity of avagacestat for APP over Notch cleavage, supporting further evaluation of avagacestat for AD therapy.

Interplay between α-, β-, and γ-secretases determines biphasic amyloid-β protein level in the presence of a γ-secretase inhibitor

Amyloid-β (Aβ) is produced by the consecutive cleavage of amyloid precursor protein (APP) first by β-secretase, generating C99, and then by γ-secretase. APP is also cleaved by α-secretase. It is hypothesized that reducing the production of Aβ in the brain may slow the progression of Alzheimer disease. Therefore, different γ-secretase inhibitors have been developed to reduce Aβ production. Paradoxically, it has been shown that low to moderate inhibitor concentrations cause a rise in Aβ production in different cell lines, in different animal models, and also in humans. A mechanistic understanding of the Aβ rise remains elusive. Here, a minimal mathematical model has been developed that quantitatively describes the Aβ dynamics in cell lines that exhibit the rise as well as in cell lines that do not. The model includes steps of APP processing through both the so-called amyloidogenic pathway and the so-called non-amyloidogenic pathway. It is shown that the cross-talk between these two pathways accounts for the increase in Aβ production in response to inhibitor, i.e. an increase in C99 will inhibit the non-amyloidogenic pathway, redirecting APP to be cleaved by β-secretase, leading to an additional increase in C99 that overcomes the loss in γ-secretase activity. With a minor extension, the model also describes plasma Aβ profiles observed in humans upon dosing with a γ-secretase inhibitor. In conclusion, this mechanistic model rationalizes a series of experimental results that spans from in vitro to in vivo and to humans. This has important implications for the development of drugs targeting Aβ production in Alzheimer disease.