Safety, Tolerability, and Pharmacokinetics of the β-Site Amyloid Precursor Protein-Cleaving Enzyme 1 Inhibitor Verubecestat (MK-8931) in Healthy Elderly Male and Female Subjects

Brain macrophage senescence in glioma

Gliomas are a diverse group of primary central nervous system neoplasms with no curative therapies available. Brain macrophages comprise microglia in the brain parenchyma, border-associated macrophages in the meningeal-choroid plexus-perivascular space and monocyte-derived macrophages infiltrating the brain. With the great improvement of our recognition of brain macrophages, diverse macrophage populations have been found in the context of glioma, which exhibit functional and phenotypic heterogeneity. We have long thought that brain macrophage senescence is detrimental, manifested by specialized forms of persistent cell cycle arrest and chronic low-grade inflammation. Persistent senescence of macrophages may result in immune dysfunction, potentially contributing to glioma initiation and development. Given the crucial roles played by brain macrophages in glioma, we unravel how brain macrophages undergo reprogramming and their contribution to glioma. We outline general molecular alterations and specific biomarkers in senescent brain macrophages, as well as functional changes (such as metabolism, autophagy, phagocytosis, antigen presentation, and infiltration and recruitment). In addition, recent advances in genetic regulation and mechanisms linked to senescent brain macrophages are discussed. In particular, this review emphasizes the contribution of senescent brain macrophages to glioma, which may drive translational efforts to utilize brain macrophages as a prognostic marker or/and treatment target in glioma. An in-depth comprehending of how brain macrophage senescence functionally influences the tumor microenvironment will be key to our development of innovative therapeutics for glioma.

BACE1 Inhibitors for Alzheimer's Disease: Current Challenges and Future Perspectives

Disease-modifying therapies (DMT) for Alzheimer's disease (AD) are highly longed-for. In this quest, anti-amyloid therapies take center stage supported by genetic facts that highlight an imbalance between production and clearance of amyloid-β peptide (Aβ) in AD patients. Indeed, evidence from basic research, human genetic and biomarker studies, suggests the accumulation of Aβ as a driver of AD pathogenesis and progression. The aspartic protease β-site AβPP cleaving enzyme (BACE1) is the initiator for Aβ production. Underpinning a critical role for BACE1 in AD pathophysiology are the elevated BACE1 concentration and activity observed in the brain and body fluids of AD patients. Therefore, BACE1 is a prime drug target for reducing Aβ levels in early AD. Small-molecule BACE1 inhibitors have been extensively developed for the last 20 years. However, clinical trials with these molecules have been discontinued for futility or safety reasons. Most of the observed adverse side effects were due to other aspartic proteases cross-inhibition, including the homologue BACE2, and to mechanism-based toxicity since BACE1 has substrates with important roles for synaptic plasticity and synaptic homeostasis besides amyloid-β protein precursor (AβPP). Despite these setbacks, BACE1 persists as a well-validated therapeutic target for which a specific inhibitor with high substrate selectivity may yet to be found. In this review we provide an overview of the evolution in BACE1 inhibitors design pinpointing the molecules that reached advanced phases of clinical trials and the liabilities that precluded adequate trial effects. Finally, we ponder on the challenges that anti-amyloid therapies must overcome to achieve clinical success.

Amyloid Pathology Modulates the Associations of Neuropsychiatric Symptoms with Cognitive Impairments and Neurodegeneration in Non-Demented Elderly

BACKGROUND

The associations between neuropsychiatric symptoms (NPSs) and Alzheimer's disease (AD) have been well-studied, yet gaps remain.

OBJECTIVE

We aimed to examine the associations of four subsyndromes (hyperactivity, psychosis, affective symptoms, and apathy) of NPSs with cognition, neurodegeneration, and AD pathologies.

METHODS

Totally 1,040 non-demented elderly (48.07% males) from the Alzheimer's Disease Neuroimaging Initiative (ADNI) were included. We assessed the relationships between NPSs and AD neuropathologies, cognition, neurodegeneration, and clinical correlates in cross-sectional and longitudinal via multiple linear regression, linear mixed effects, and Cox proportional hazard models. Causal mediation analyses were conducted to explore the mediation effects of AD pathologies on cognition and neurodegeneration.

RESULTS

We found that individuals with hyperactivity, psychosis, affective symptoms, or apathy displayed a poorer cognitive status, a lower CSF amyloid-β (Aβ) level and a higher risk of clinical conversion (p < 0.05). Hyperactivity and affective symptoms were associated with increasing cerebral Aβ deposition (p < 0.05). Except psychosis, the other three subsyndromes accompanied with faster atrophy of hippocampal volume (p < 0.05). Specific NPSs were predominantly associated with different cognitive domains decline through an 8-year follow-up (p < 0.05). Moreover, the relationships between NPSs and cognitive decline, neurodegeneration might be associated with Aβ, the mediation percentage varied from 6.05% to 17.51% (p < 0.05).

CONCLUSIONS

NPSs could be strongly associated with AD. The influences of NPSs on cognitive impairments, neurodegeneration might be partially associated with Aβ.

BACE1 Inhibitors for Alzheimer's Disease: The Past, Present and Any Future?

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder and the most common cause of dementia in the elderly. The complexity of AD has hindered the development of either a cure or a disease-modifying therapy to halt the disease progression. Numerous hypotheses were presented in order to explain the mechanisms underlying the pathogenesis of AD. Introduced in 1992, the "Amyloid Cascade Hypothesis" had a huge impact on the field and inspired the rise of various drug candidates, especially amyloid-beta (Aβ)-directed drugs; including beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) inhibitors. Adopted by a number of pharmaceutical companies, the development of BACE1 inhibitors has gained momentum in the past decade with promising results from experimental and early clinical-phase studies. Nevertheless, nearly all BACE1 inhibitors failed in later phases of clinical trials, due to safety and/or efficacy issues, and others were discontinued early in favor of second-generation small-molecule candidates. This paper aims to provide a comprehensive review of all BACE1 inhibitors to ever reach clinical trials, and we discuss the challenges and different perspectives on whether BACE1 inhibitors are to be reconsidered or revitalized in the future.

Evaluation of 18F-flutemetamol amyloid PET image analysis parameters on the effect of verubecestat on brain amlyoid load in Alzheimer's disease

PURPOSE

The BACE inhibitor verubecestat was previously found to reduce amyloid load as assessed by ¹⁸F-flutemetamol positron emission tomography (PET) composite cortical standard uptake value ratio (SUVr) in patients with mild-to-moderate Alzheimer's disease (AD) in a substudy of the EPOCH trial. Here, we report on additional analyses relevant to the EPOCH PET data, to help inform on the use of PET for assessing amlyloid load in AD clinical trials.

PROCEDURES

The analyses addressed (1) identification of an optimal ¹⁸F-flutemetamol reference region, (2) determination of the threshold to characterize the magnitude of the longitudinal change, and (3) the impact of partial volume correction (PVC). Pons and subcortical white matter were evaluated as reference regions. The SUVr cutoffs and final reference region choice were determined using 162 ¹⁸F-flutemetamol PET scans from the AIBL dataset. ¹⁸F-flutemetamol SUVrs were computed at baseline and at Week 78 in EPOCH participants who received verubecestat 12 mg (n = 14), 40 mg (n = 20), or placebo (n = 20). Drug effects on amyloid load were computed using either Meltzer (MZ), or symmetric geometric transfer matrix (SGTM) PVC and compared to uncorrected data.

RESULTS

The optimal subcortical white matter and pons SUVr cutoffs were determined to be 0.69 and 0.62, respectively. The effect size to detect longitudinal change was higher for subcortical white matter (1.20) than pons (0.45). Hence, subcortical white matter was used as the reference region for the EPOCH PET substudy. In EPOCH, uncorrected baseline SUVr values correlated strongly with MZ PVC (r² = 0.94) and SGTM PVC (r² = 0.92) baseline SUVr values, and PVC did not provide improvement for evaluating treatment effects on amyloid load at Week 78. No change from baseline was observed in the placebo group at Week 78, whereas a 0.02 and a 0.04 decrease in SUVr were observed in the 12 mg and 40 mg arms, with the latter representing a 22% reduction in the amyloid load above the detection threshold.

CONCLUSIONS

Treatment-related ¹⁸F-flutemetamol longitudinal changes in AD clinical trials can be quantified using a subcortical white matter reference region without PVC.

CLINICAL TRIAL REGISTRATION

clinicaltrials.gov NCT01739348.

Design, Synthesis, and Biological Evaluation of Notopterol Derivatives as Triple Inhibitors of AChE/BACE1/GSK3β for the Treatment of Alzheimer's Disease

The pathogenesis of Alzheimer's disease (AD) is very complex, and there are many hypotheses. Therefore, the development of a multi-target-directed-ligand may be an effective therapeutic strategy. Our previous study showed that notopterol (a natural product from Notopterygium) is a dual BACE1/GSK3β inhibitor. In this study, we designed and synthesized 48 notopterol derivatives with furacoumarin as a scaffold in order to enhance their balanced AChE/BACE1/GSK3β inhibitory activity. Fortunately, 1c showed effective inhibitory activity against AChE (58.7% at 1.0 μM), BACE1 (48.3% at 20 μM), and GSK3β (40.3% at 10 μM). Furthermore, 1c showed good blood-brain barrier penetrability, suitable bioavailability, and oral safety. More importantly, 1c could ameliorate the impaired learning and memory in Aβ-induced AD mice. In conclusion, we reported the triple inhibitor of AChE/BACE1/GSK3β lead compounds based on a furocoumarin scaffold of notopterol for the first time, which provides a potential new strategy for the treatment of AD.

A Model-Based Approach to Bridging Plasma and Dried Blood Spot Concentration Data for Phase 3 Verubecestat Trials

In-clinic venous dried blood spot (DBS) pharmacokinetic (PK) sampling was incorporated into two phase 3 studies of verubecestat for Alzheimer's disease (EPOCH [NCT01739348] and APECS [NCT01953601]), as a potential alternative to plasma PK sampling. Initially, plasma and DBS PK samples were collected concurrently to better understand the DBS-plasma verubecestat concentration relationship, with the intention of discontinuing DBS or plasma sampling following interim analysis. Following initial analyses and comparison of results with prespecified selection criteria, plasma PK sampling was discontinued; however, a stability issue resulting in generally lower DBS verubecestat concentrations with longer collection-to-assay times was subsequently discovered (associated with non-compliance in DBS sample handling), prompting reintroduction of plasma sampling. To enable inclusion of DBS data in population PK analyses, a conversion algorithm for calculating plasma-equivalent concentrations (accounting for DBS sample instability) was developed using paired (time-matched) plasma and DBS data from the EPOCH study. Verubecestat population PK models developed from pooled phase 1/1b and EPOCH data using either (1) plasma-only data or (2) plasma and plasma-equivalent concentrations (calculated from non-paired DBS samples) yielded similar results. The algorithm robustness was demonstrated using DBS data from paired samples from the APECS study and comparison between plasma and plasma-equivalent concentrations. The population PK model was updated with APECS data (both plasma and, if no plasma sample available, plasma equivalents). The results demonstrated similar PK in the two phase 3 populations and exposures consistent with expectations from phase 1 data. This case study illustrates challenges with employing new sampling techniques in large, global trials and describes lessons learned.

An Investigation of Instability in Dried Blood Spot Samples for Pharmacokinetic Sampling in Phase 3 Trials of Verubecestat

In-clinic dried blood spot (DBS) pharmacokinetic (PK) sampling was incorporated into two phase 3 studies of verubecestat for Alzheimer's disease (EPOCH [NCT01739348] and APECS [NCT01953601]), as a potential alternative to plasma PK sampling for improved logistical feasibility and decreased blood volume burden. However, an interim PK analysis revealed verubecestat concentrations in DBS samples declined with time to assay in both trials. An investigation revealed wide variation in implementation practices for DBS sample handling procedures resulting in insufficient desiccation which caused verubecestat instability. High-resolution mass spectrometry evaluations of stressed and aged verubecestat DBS samples revealed the presence of two hydrolysis degradants. To minimize instability, new DBS handling procedures were implemented that provided additional desiccant and minimized the time to analysis. Both verubecestat hydrolysis products were previously discovered and synthesized during active pharmaceutical ingredient stability characterization. A liquid chromatography-mass spectrometry assay to quantitate the dominant verubecestat degradant in DBS samples was developed and validated. The application of this method to stressed and aged verubecestat DBS samples confirmed that degradant concentrations accounted for the observed decreases in the verubecestat concentration. Furthermore, after increasing desiccant amounts, degradant concentrations accounted for approximately 7% of the verubecestat concentration in DBS clinical samples, indicating that issues with sample handling were minimized with new storage and shipping conditions. This case study illustrates the challenges with employing new sampling techniques in large, global trials, and the importance of anticipating and mitigating implementation risks.

Alzheimer's Disease: Key Insights from Two Decades of Clinical Trial Failures

Given the acknowledged lack of success in Alzheimer’s disease (AD) drug development over the past two decades, the objective of this review was to derive key insights from the myriad failures to inform future drug development. A systematic and exhaustive review was performed on all failed AD compounds for dementia (interventional phase II and III clinical trials from ClinicalTrials.gov) from 2004 to the present. Starting with the initial ∼2,700 AD clinical trials, ∼550 trials met our initial criteria, from which 98 unique phase II and III compounds with various mechanisms of action met our criteria of a failed compound. The two recent reported phase III successes of aducanumab and oligomannate are very encouraging; however, we are awaiting real-world validation of their effectiveness. These two successes against the 98 failures gives a 2.0% phase II and III success rate since 2003, when the previous novel compound was approved. Potential contributing methodological factors for the clinical trial failures were categorized into 1) insufficient evidence to initiate the pivotal trials, and 2) pivotal trial design shortcomings. Our evaluation found that rational drug development principles were not always followed for AD therapeutics development, and the question remains whether some of the failed compounds may have shown efficacy if the principles were better adhered to. Several recommendations are made for future AD therapeutic development. The whole database of the 98 failed compounds is presented in the Supplementary Material.

Selective Secretase Targeting for Alzheimer's Disease Therapy

Alzheimer's disease (AD) is associated with marked atrophy of the cerebral cortex and accumulation of amyloid plaques and neurofibrillary tangles. Amyloid plaques are formed by oligomers of amyloid-β (Aβ) in the brain, with a length of 42 and 40 amino acids. α-secretase cleaves amyloid-β protein precursor (AβPP) producing the membrane-bound fragment CTFα and the soluble fragment sAβPPα with neuroprotective activity; β-secretase produces membrane-bound fragment CTFβ and a soluble fragment sAβPPβ. After α-secretase cleavage of AβPP, γ-secretase cleaves CTFα to produce the cytoplasmic fragment AICD and P3 in the non-amyloidogenic pathway. CTFβ is cleaved by γ-secretase producing AICD as well as Aβ in amyloidogenic pathways. In the last years, the study of natural products and synthetic compounds, such as α-secretase activity enhancers, β-secretase inhibitors (BACE-1), and γ-secretase activity modulators, have been the focus of pharmaceuticals and researchers. Drugs were improved regarding solubility, blood-brain barrier penetration, selectivity, and potency decreasing Aβ42. In this regard, BACE-1 inhibitors, such as Atabecestat, NB-360, Umibecestat, PF-06751979 Verubecestat, LY2886721, Lanabecestat, LY2811376 and Elenbecestat, were submitted to phase I-III clinical trials. However, inhibition of Aβ production did not recover cognitive functions or reverse disease progress. Novel strategies are being developed, aiming at a partial reduction of Aβ production, such as the development of γ-secretase modulators or α-secretase activity enhancers. Such therapeutic tools shall focus on slowing down or minimizing the progression of neuronal damage. Here, we summarize structures and activities of the latest compounds designed for AD treatment, with remarkable in vitro, in vivo, and clinical phase activities.

Targeting for Success: Demonstrating Proof-of-Concept with Mechanistic Early Phase Clinical Pharmacology Studies for Disease-Modification in Neurodegenerative Disorders

The clinical failure rate for disease-modifying treatments (DMTs) that slow or stop disease progression has been nearly 100% for the major neurodegenerative disorders (NDDs), with many compounds failing in expensive and time-consuming phase 2 and 3 trials for lack of efficacy. Here, we critically review the use of pharmacological and mechanistic biomarkers in early phase clinical trials of DMTs in NDDs, and propose a roadmap for providing early proof-of-concept to increase R&D productivity in this field of high unmet medical need. A literature search was performed on published early phase clinical trials aimed at the evaluation of NDD DMT compounds using MESH terms in PubMed. Publications were selected that reported an early phase clinical trial with NDD DMT compounds between 2010 and November 2020. Attention was given to the reported use of pharmacodynamic (mechanistic and physiological response) biomarkers. A total of 121 early phase clinical trials were identified, of which 89 trials (74%) incorporated one or multiple pharmacodynamic biomarkers. However, only 65 trials (54%) used mechanistic (target occupancy or activation) biomarkers to demonstrate target engagement in humans. The most important categories of early phase mechanistic and response biomarkers are discussed and a roadmap for incorporation of a robust biomarker strategy for early phase NDD DMT clinical trials is proposed. As our understanding of NDDs is improving, there is a rise in potentially disease-modifying treatments being brought to the clinic. Further increasing the rational use of mechanistic biomarkers in early phase trials for these (targeted) therapies can increase R&D productivity with a quick win/fast fail approach in an area that has seen a nearly 100% failure rate to date.

The Ups and Downs of BACE1: Walking a Fine Line between Neurocognitive and Other Psychiatric Symptoms of Alzheimer's Disease

Although neurocognitive deficit is the best-recognized indicator of Alzheimer's disease (AD), psychotic and other noncognitive symptoms are the prime cause of institutionalization. BACE1 is the rate-limiting enzyme in the production of Aβ of AD, and one of the promising therapeutic targets in countering cognitive decline and amyloid pathology. Changes in BACE1 activity have also emerged to cause significant noncognitive neuropsychiatric symptoms and impairments of circadian rhythms, as evident from clinical trials and reports in transgenic models. In this study, we consider key characteristics of BACE1 with its contribution to neurocognitive deficit and other psychiatric symptoms of AD. We argue that a growing list of noncognitive mental impairments related to pharmacological modulation of BACE1 might present a major obstacle in clinical translation of emerging therapeutic leads targeting this protease. The adverse effects of BACE1 inhibition on mental health call for a revision of treatment strategies that assume indiscriminate inhibition of this key protease, and stress the need for further mechanistic and translational studies.

Quantification and pharmacokinetic property of verubecestat an BACE1 inhibitor in rat plasma

In the present study, an ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) approach was designed to measure the rat plasma levels of verubecestat with diazepam as the internal standard. Acetonitrile-based protein precipitation was applied for sample preparation, then the analyte verubecestat was subjected to gradient elution chromatography with a mobile phase composed of acetonitrile (A) and 0.1% formic acid in water (B). Verubecestat was monitored by m/z 410.1 → 124.0 transition for quantification by multiple reaction monitoring (MRM) in positive ion electrospray ionization (ESI) source. When the concentration of verubecestat ranged from 1 to 2500 ng/mL, the method exhibited good linearity. For verubecestat, the intra- and inter-day precision were determined with the values of 2.9-9.0% and 0.4-6.5%, respectively; and the accuracy ranged from -2.2% to 10.4%. Matrix effect, extraction recovery, and stability data were in line with the standard FDA guidelines for validating a bioanalytical method. The validity of the developed method was confirmed through the pharmacokinetic study.