P4–411: Clinical study of E2609, a novel BACE1 inhibitor, demonstrates target engagement and inhibition of BACE1 activity in CSF

Small-molecule drugs development for Alzheimer's disease

Alzheimer's disease (AD) is an irreversible, progressive neurodegenerative brain disorder with no effective therapeutic drugs currently. The complicated pathophysiology of AD is not well understood, although beta-amyloid (Aβ) cascade and hyperphosphorylated tau protein were regarded as the two main causes of AD. Other mechanisms, such as oxidative stress, deficiency of central cholinergic neurotransmitters, mitochondrial dysfunction, and inflammation, were also proposed and studied as targets in AD. This review aims to summarize the small-molecule drugs that were developed based on the pathogenesis and gives a deeper understanding of the AD. We hope that it could help scientists find new and better treatments to gradually conquer the problems related to AD in future.

CSF and Blood Biomarkers in Neuroinflammatory and Neurodegenerative Diseases: Implications for Treatment

Neuroinflammatory and neurodegenerative diseases are characterized by the interplay of a number of molecular pathways that can be assessed through biofluids, especially cerebrospinal fluid and blood. Accordingly, the definition and classification of these disorders will move from clinical and pathological to biological criteria. The consequences of this biomarker-based diagnostic and prognostic approach are highly relevant to the field of drug development. Indeed, in view of the availability of disease-modifying drugs, fluid biomarkers offer a unique opportunity for improving the quality and applicability of results from clinical trials. Herein, we discuss the benefits of using fluid biomarkers for patient stratification, target engagement, and outcome assessment, as well as the most recent developments in neuroinflammatory and neurodegenerative diseases.

Targeting Amyloidogenic Processing of APP in Alzheimer's Disease

Alzheimer's disease (AD) is the most common type of senile dementia, characterized by neurofibrillary tangle and amyloid plaque in brain pathology. Major efforts in AD drug were devoted to the interference with the production and accumulation of amyloid-β peptide (Aβ), which plays a causal role in the pathogenesis of AD. Aβ is generated from amyloid precursor protein (APP), by consecutive cleavage by β-secretase and γ-secretase. Therefore, β-secretase and γ-secretase inhibition have been the focus for AD drug discovery efforts for amyloid reduction. Here, we review β-secretase inhibitors and γ-secretase inhibitors/modulators, and their efficacies in clinical trials. In addition, we discussed the novel concept of specifically targeting the γ-secretase substrate APP. Targeting amyloidogenic processing of APP is still a fundamentally sound strategy to develop disease-modifying AD therapies and recent advance in γ-secretase/APP complex structure provides new opportunities in designing selective inhibitors/modulators for AD.

Recent Studies on Design and Development of Drugs Against Alzheimer's Disease (AD) Based on Inhibition of BACE-1 and Other AD-causative Agents

BACKGROUND

Alzheimer's disease (AD) is one of the neurodegenerative diseases and has been hypothesized to be a protein misfolding disease. In the generation of AD, β-secretase, γ-secretase, and tau protein play an important role. A literature search reflects ever increasing interest in the design and development of anti-AD drugs targeting β-secretase, γ-secretase, and tau protein.

OBJECTIVE

The objective is to explore the structural aspects and role of β-secretase, γ-secretase, and tau protein in AD and the efforts made to exploit them for the design of effective anti-AD drugs.

METHODS

The manuscript covers the recent studies on design and development of anti-AD drugs exploiting amyloid and cholinergic hypotheses.

RESULTS

Based on amyloid and cholinergic hypotheses, effective anti-AD drugs have been searched out in which non-peptidic BACE1 inhibitors have been most prominent.

CONCLUSION

Further exploitation of the structural aspects and the inhibition mechanism for β-secretase, γ-secretase, and tau protein and the use of cholinergic hypothesis may lead still more potent anti-AD drugs.

Hybrid approach to sieve out natural compounds against dual targets in Alzheimer's Disease

Excess Aβ production by the key protease BACE1, results in Aβ aggregation, forming amyloid plaques, all of which contribute to the pathogenesis of Alzheimer’s disease. Besides the multi-factorial nature of the disease, the diversity in the size and shape of known ligands that bind to the active site of BACE1, that is the flexibility of the enzyme, pose a serious challenge for the identification of drug candidates. To address the issue of receptor flexibility we have carried out ensemble docking with multiple receptor conformations. Therein, two representative structures each from closed and semi-open BACE1 conformations were selected for virtual screening to identify compounds that bind to the active site of both the conformations. These outperformed compounds were ranked using pharmacophore models generated by a ligand-based approach, for the identification of BACE1 inhibitors. The inhibitors were further predicted for anti-amyloidogenic activity using a QSAR model already established by our group thus enlisting compounds with dual potency. BACE1 inhibitory and anti-amyloidogenic activity for the commercially available compounds were validated using in vitro studies. Thus, incorporation of receptor flexibility in BACE1 through ensemble docking in conjunction with structure and ligand-based approach for screening might act as an effective protocol for obtaining promising scaffolds against AD.

Future Therapeutics in Alzheimer's Disease: Development Status of BACE Inhibitors

Alzheimer's disease (AD) is the primary cause of dementia in the elderly. It remains incurable and poses a huge socio-economic challenge for developed countries with an aging population. AD manifests by progressive decline in cognitive functions and alterations in behaviour, which are the result of the extensive degeneration of brain neurons. The AD pathogenic mechanism involves the accumulation of amyloid beta peptide (Aβ), an aggregating protein fragment that self-associates to form neurotoxic fibrils that trigger a cascade of cellular events leading to neuronal injury and death. Researchers from academia and the pharmaceutical industry have pursued a rational approach to AD drug discovery and targeted the amyloid cascade. Schemes have been devised to prevent the overproduction and accumulation of Aβ in the brain. The extensive efforts of the past 20 years have been translated into bringing new drugs to advanced clinical trials. The most progressed mechanism-based therapies to date consist of immunological interventions to clear Aβ oligomers, and pharmacological drugs to inhibit the secretase enzymes that produce Aβ, namely β-site amyloid precursor-cleaving enzyme (BACE) and γ-secretase. After giving an update on the development and current status of new AD therapeutics, this review will focus on BACE inhibitors and, in particular, will discuss the prospects of verubecestat (MK-8931), which has reached phase III clinical trials.

Two decades of new drug discovery and development for Alzheimer's disease

Alzheimer's disease is a progressive and irreversible neurodegenerative disease, associated with a decreased cognitive function and severe behavioral abnormalities.

Amyloid beta modulators and neuroprotection in Alzheimer's disease: a critical appraisal

Multiple cellular changes have been identified as being involved in Alzheimer's disease (AD) pathogenesis, including mitochondrial damage, synaptic loss, amyloid beta (Aβ) production and/or accumulation, inflammatory responses, and phosphorylated tau formation and/or accumulation. Studies have established that Aβ-induced synaptic dysfunction is dependent on abnormal amyloid precursor protein (APP) processing caused by β- and γ-secretases, resulting in the generation of Aβ. The Aβ formed as a result of abnormal APP processing induces phosphorylated tau and activates glycogen synthase kinase-3β (GSK3β) and cyclin-dependent kinase-5 (CDK5). Here, we review the latest research on the development of Aβ modulators for neuroprotection in AD. We also review the use of molecular inhibitors as therapeutic targets in AD.

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.

Slowing the progression of Alzheimer's disease; what works?

Alzheimer's disease (AD) is an age-related progressive dementia, which is increasing in prevalence world-wide. Typically affecting short-term memory at onset, this devastating illness advances to impair all aspects of cognition, as well as non-cognitive domains. Although much effort has been made in recent years to develop disease-modifying treatments, medications which provided promising results in pre-clinical research have so far faltered in human clinical trials. Attention has recently shifted into trying to identify preventative measures that may delay the onset of the illness. Preventative factors include physical activity, proper diet, cognitive stimulation and the management of conditions such as hypertension, diabetes and obesity. However, it remains imperative to identify approaches that may help patients already diagnosed with the illness. Alongside pharmacological research, much work has been done on uncovering strategies which may slow down the progression of AD. This review aims to summarize evidence supporting or refuting methods impacting on the progression of the disease. AD remains a chronic and serious condition, therefore any intervention delaying the onset of moderate/severe symptoms will have a significant impact on patients and their families.

Prospects of β-Secretase Inhibitors for the Treatment of Alzheimer's Disease

β-Secretase continues to be an attractive drug discovery target for the therapeutic intervention of Alzheimer's disease (AD). This enzyme plays a critical role in the production of neurotoxic β-amyloid (Aβ) peptides in the brain. Over the years, extensive research efforts have led to the development of many promising classes of inhibitors against this protease. Many small-molecule, peptidomimetic, and nonpeptide β-secretase inhibitors have now overcome the key challenging development hurdles such as selectivity and brain penetration. A number of inhibitors have also shown further promise in reducing brain Aβ and rescuing cognitive decline in animal models. Recently, several β-secretase inhibitors have entered into preclinical and phase I studies, and at least one of these inhibitors has advanced to phase II/III human trials. The outlook on β-secretase inhibitor drugs for the treatment of AD patients is discussed herein.

BACE1 inhibitor drugs in clinical trials for Alzheimer's disease

β-site amyloid precursor protein cleaving enzyme 1 (BACE1) is the β-secretase enzyme required for the production of the neurotoxic β-amyloid (Aβ) peptide that is widely considered to have a crucial early role in the etiology of Alzheimer’s disease (AD). As a result, BACE1 has emerged as a prime drug target for reducing the levels of Aβ in the AD brain, and the development of BACE1 inhibitors as therapeutic agents is being vigorously pursued. It has proven difficult for the pharmaceutical industry to design BACE1 inhibitor drugs that pass the blood–brain barrier, however this challenge has recently been met and BACE1 inhibitors are now in human clinical trials to test for safety and efficacy in AD patients and individuals with pre-symptomatic AD. Initial results suggest that some of these BACE1 inhibitor drugs are well tolerated, although others have dropped out because of toxicity and it is still too early to know whether any will be effective for the prevention or treatment of AD. Additionally, based on newly identified BACE1 substrates and phenotypes of mice that lack BACE1, concerns have emerged about potential mechanism-based side effects of BACE1 inhibitor drugs with chronic administration. It is hoped that a therapeutic window can be achieved that balances safety and efficacy. This review summarizes the current state of progress in the development of BACE1 inhibitor drugs and the evaluation of their therapeutic potential for AD.

Cerebrospinal fluid biomarkers in trials for Alzheimer and Parkinson diseases

Alzheimer disease (AD) and Parkinson disease (PD) are the most common neurodegenerative disorders. For both diseases, early intervention is thought to be essential to the success of disease-modifying treatments. Cerebrospinal fluid (CSF) can reflect some of the pathophysiological changes that occur in the brain, and the number of CSF biomarkers under investigation in neurodegenerative conditions has grown rapidly in the past 20 years. In AD, CSF biomarkers are increasingly being used in clinical practice, and have been incorporated into the majority of clinical trials to demonstrate target engagement, to enrich or stratify patient groups, and to find evidence of disease modification. In PD, CSF biomarkers have not yet reached the clinic, but are being studied in patients with parkinsonism, and are being used in clinical trials either to monitor progression or to demonstrate target engagement and downstream effects of drugs. CSF biomarkers might also serve as surrogate markers of clinical benefit after a specific therapeutic intervention, although additional data are required. It is anticipated that CSF biomarkers will have an important role in trials aimed at disease modification in the near future. In this Review, we provide an overview of CSF biomarkers in AD and PD, and discuss their role in clinical trials.

Targeting the β secretase BACE1 for Alzheimer's disease therapy

The β secretase, widely known as β-site amyloid precursor protein cleaving enzyme 1 (BACE1), initiates the production of the toxic amyloid β (Aβ) that plays a crucial early part in Alzheimer's disease pathogenesis. BACE1 is a prime therapeutic target for lowering cerebral Aβ concentrations in Alzheimer's disease, and clinical development of BACE1 inhibitors is being intensely pursued. Although BACE1 inhibitor drug development has proven challenging, several promising BACE1 inhibitors have recently entered human clinical trials. The safety and efficacy of these drugs are being tested at present in healthy individuals and patients with Alzheimer's disease, and will soon be tested in individuals with presymptomatic Alzheimer's disease. Although hopes are high that BACE1 inhibitors might be efficacious for the prevention or treatment of Alzheimer's disease, concerns have been raised about potential mechanism-based side-effects of these drugs. The potential of therapeutic BACE1 inhibition might prove to be a watershed in the treatment of Alzheimer's disease.