Huub Jan Kleijn

The BACE1 inhibitor verubecestat (MK-8931) reduces CNS β-amyloid in animal models and in Alzheimer’s disease patients

The BACE1 inhibitor verubecestat safely reduces β-amyloid deposition in rats, monkeys, healthy human subjects, and patients with Alzheimer’s disease. Getting to first BACE The discovery of BACE1 inhibitors that reduce β-amyloid peptides in Alzheimer’s disease (AD) patients has been an encouraging development in the quest for a disease-modifying therapy. Kennedy and colleagues now report the discovery of verubecestat, a structurally unique, orally bioavailable small molecule that potently inhibits brain BACE1 activity resulting in a reduction in Aβ peptides in the cerebrospinal fluid of animals, healthy volunteers, and AD patients. No dose-limiting toxicities were observed in chronic animal toxicology studies or in phase 1 human studies, thus reducing safety concerns raised by previous reports of BACE inhibitors and BACE1 knockout mice. β-Amyloid (Aβ) peptides are thought to be critically involved in the etiology of Alzheimer’s disease (AD). The aspartyl protease β-site amyloid precursor protein cleaving enzyme 1 (BACE1) is required for the production of Aβ, and BACE1 inhibition is thus an attractive target for the treatment of AD. We show that verubecestat (MK-8931) is a potent, selective, structurally unique BACE1 inhibitor that reduced plasma, cerebrospinal fluid (CSF), and brain concentrations of Aβ40, Aβ42, and sAPPβ (a direct product of BACE1 enzymatic activity) after acute and chronic administration to rats and monkeys. Chronic treatment of rats and monkeys with verubecestat achieved exposures >40-fold higher than those being tested in clinical trials in AD patients yet did not elicit many of the adverse effects previously attributed to BACE inhibition, such as reduced nerve myelination, neurodegeneration, altered glucose homeostasis, or hepatotoxicity. Fur hypopigmentation was observed in rabbits and mice but not in monkeys. Single and multiple doses were generally well tolerated and produced reductions in Aβ40, Aβ42, and sAPPβ in the CSF of both healthy human subjects and AD patients. The human data were fit to an amyloid pathway model that provided insight into the Aβ pools affected by BACE1 inhibition and guided the choice of doses for subsequent clinical trials.

Population pharmacokinetic-pharmacodynamic analysis for sugammadex-mediated reversal of rocuronium-induced neuromuscular blockade.

AIMS An integrated population pharmacokinetic-pharmacodynamic model was developed with the following aims: to simultaneously describe pharmacokinetic behaviour of sugammadex and rocuronium; to establish the pharmacokinetic-pharmacodynamic model for rocuronium-induced neuromuscular blockade and reversal by sugammadex; to evaluate covariate effects; and to explore, by simulation, typical covariate effects on reversal time. METHODS Data (n= 446) from eight sugammadex clinical studies covering men, women, non-Asians, Asians, paediatrics, adults and the elderly, with various degrees of renal impairment, were used. Modelling and simulation techniques based on physiological principles were applied to capture rocuronium and sugammadex pharmacokinetics and pharmacodynamics and to identify and quantify covariate effects. RESULTS Sugammadex pharmacokinetics were affected by renal function, bodyweight and race, and rocuronium pharmacokinetics were affected by age, renal function and race. Sevoflurane potentiated rocuronium-induced neuromuscular blockade. Posterior predictive checks and bootstrapping illustrated the accuracy and robustness of the model. External validation showed concordance between observed and predicted reversal times, but interindividual variability in reversal time was pronounced. Simulated reversal times in typical adults were 0.8, 1.5 and 1.4 min upon reversal with sugammadex 16 mg kg(-1) 3 min after rocuronium, sugammadex 4 mg kg(-1) during deep neuromuscular blockade and sugammadex 2 mg kg(-1) during moderate blockade, respectively. Simulations indicated that reversal times were faster in paediatric patients and slightly slower in elderly patients compared with adults. Renal function did not affect reversal time. CONCLUSIONS Simulations of the therapeutic dosing regimens demonstrated limited impact of age, renal function and sevoflurane use, as predicted reversal time in typical subjects was always <2 min.

Systems Pharmacology Analysis of the Amyloid Cascade after β-Secretase Inhibition Enables the Identification of an Aβ42 Oligomer Pool

The deposition of amyloid-β (Aβ) oligomers in brain parenchyma has been implicated in the pathophysiology of Alzheimer’s disease. Here we present a systems pharmacology model describing the changes in the amyloid precursor protein (APP) pathway after administration of three different doses (10, 30, and 125 mg/kg) of the β-secretase 1 (BACE1) inhibitor MBi-5 in cisterna magna ported rhesus monkeys. The time course of the MBi-5 concentration in plasma and cerebrospinal fluid (CSF) was analyzed in conjunction with the effect on the concentrations of the APP metabolites Aβ42, Aβ40, soluble β-amyloid precursor protein (sAPP) α, and sAPPβ in CSF. The systems pharmacology model contained expressions to describe the production, elimination, and brain-to-CSF transport for the APP metabolites. Upon administration of MBi-5, a dose-dependent increase of the metabolite sAPPα and dose-dependent decreases of sAPPβ and Aβ were observed. Maximal inhibition of BACE1 was close to 100% and the IC50 value was 0.0256 μM (95% confidence interval, 0.0137–0.0375). A differential effect of BACE1 inhibition on Aβ40 and Aβ42 was observed, with the Aβ40 response being larger than the Aβ42 response. This enabled the identification of an Aβ42 oligomer pool in the systems pharmacology model. These findings indicate that decreases in monomeric Aβ responses resulting from BACE1 inhibition are partially compensated by dissociation of Aβ oligomers and suggest that BACE1 inhibition may also reduce the putatively neurotoxic oligomer pool.

Early stage development of the glycine-1 re-uptake inhibitor SCH 900435: central nervous system effects compared with placebo in healthy men

AIMS To report the first three studies with SCH 900435, a selective glycine-1 re-uptake inhibitor in development for treating schizophrenia, using systematic evaluations of pharmacodynamics to understand the observed effects. METHODS Three double-blind, placebo-controlled studies (single, visual effect and multiple dose) were performed. In the single and multiple dose study SCH 900435 (0.5-30 mg) was given to healthy males and frequent pharmacokinetic and pharmacodynamic measurements were performed. The visual effects study incorporated visual electrophysiological measures of macular, retinal and intracranial visual pathway function. RESULTS In the single dose study (highest difference, 95% CI, P) increases in smooth pursuit eye movements (8, 12 mg (-6.09, 10.14, -2.04, 0.013), 30 mg), pupil : iris ratio (20 and 30 mg (-0.065, 0.09, -0.04, <0.0001)), VAS colour perception (30 mg (-9.48, 13.05, -5.91, <0.0001)) and changes in spontaneous reports of visual disturbance were found, while FSH (8 mg (0.42, 0.18, 0.66, 0.0015), 12, 20 mg), LH (8-30 mg (1.35, 0.65, 2.05, 0.0003)) and EEG alpha2 activity decreased (12, 20, 30 mg (0.27, 0.14, 0.41, 0.0002)). A subsequent dedicated visual effects study demonstrated that visual effects were transient without underlying electrophysiological changes. This provided enough safety information for starting a multiple ascending dose study, showing less visual symptoms after twice daily dosing and titration, possibly due to tolerance. CONCLUSIONS Several central nervous system (CNS) effects and gonadotropic changes resulted from administration of 8 mg and higher, providing evidence for CNS penetration and pharmacological activity of SCH 900435. Antipsychotic activity in patients, specificity of the reported effects for this drug class and possible tolerance to visual symptoms remain to be established.

Population PK Analyses of Ubrogepant (MK‐1602), a CGRP Receptor Antagonist: Enriching In‐Clinic Plasma PK Sampling With Outpatient Dried Blood Spot Sampling

Merck & Co., Inc. (Kenilworth, New Jersey) has recently published an integrated strategy for implementation of dried blood spots (DBS) in late‐stage trials for population pharmacokinetic (PK) modeling. We applied this strategy for another late‐stage clinical program: ubrogepant (MK‐1602), a novel oral calcitonin gene‐related peptide receptor antagonist for acute treatment of migraine. At the time of implementation, ubrogepant was entering phase 2 development. DBS was implemented to acquire PK information proximal to an acute migraine event to enable exposure–response modeling. The clinical endpoint was a spontaneous event, which generally occurs outside a clinic visit. Thus, an innovative feature of this trial was facilitating DBS in an outpatient setting. In vitro and bioanalytical tests established initial method feasibility and suitability for further evaluations in the clinic. A quantitative relationship was developed between blood and plasma concentrations from concurrently collected samples in a phase 1 (healthy subjects) and phase 2 (target patient population) study using graphical and population PK approaches. This integrated information was presented to the Food and Drug Administration for regulatory input. Following regulatory concurrence, DBS was poised for use in further clinical studies. Population PK modeling was used to dissect sources of variability contributing to DBS collection in the outpatient setting. What has been learned from this program has informed the broader integrated strategy of Merck & Co., Inc. (Kenilworth, NJ) for DBS implementation in clinical trials and research to improve the precision of PK data collected in an outpatient setting.

Extending a Systems Model of the APP Pathway: Separation of β- and γ-Secretase Sequential Cleavage Steps of APP

The abnormal accumulation of amyloid-β (Aβ) in the brain parenchyma has been posited as a central event in the pathophysiology of Alzheimer’s disease. Recently, we have proposed a systems pharmacology model of the amyloid precursor protein (APP) pathway, describing the Aβ APP metabolite responses (Aβ40, Aβ42, sAPPα, and sAPPβ) to β-secretase 1 (BACE1) inhibition. In this investigation this model was challenged to describe Aβ dynamics following γ-secretase (GS) inhibition. This led an extended systems pharmacology model, with separate descriptions to characterize the sequential cleavage steps of APP by BACE1 and GS, to describe the differences in Aβ response to their respective inhibition. Following GS inhibition, a lower Aβ40 formation rate constant was observed, compared with BACE1 inhibition. Both BACE1 and GS inhibition were predicted to lower Aβ oligomer levels. Further model refinement and new data may be helpful to fully understand the difference in Aβ dynamics following BACE1 versus GS inhibition.

IS THE PERIPHERAL SINK HYPOTHESIS PHYSIOLOGICALLY FEASIBLE? EVIDENCE FROM MODEL-BASED ASSESSMENT OF THE AMYLOID PATHWAY

Results:We quantified, using delta L*, a direct effect on pigmentation for a series of BACE2 inhibitors. After chronic administration of BACE2 inhibitors to pigmented mice, we observed a significant and robust effect on coat color as well as ultrastructural features of melanosomes. Ultrastructural abnormalities in melanosomes, both in the MelanoDermcultures as well as mouse skin included: incomplete pigmentation, irregular shape, loss of sharp margins, and variability in size. The ultrastructural changes in melanosome morphology observed following administration of BACE2 inhibitors were similar to those reported in BACE2 KO mice. Conclusions: Our preliminary in vitro / in vivo correlation analysis based on above results suggests that BACE2 plays a significant role in altering pigmentation in both MelanoDerm cultures and in vivo following chronic administration.

Development and application of a mathematical model of modulation of cerebrospinal fluid Aβ40 after treatment with gamma- and beta-secretase inhibitors

Background:A mathematical model representation of key amyloid pathway physiology to describe A b 40 modulation in CSF was developed to: (1) quantify clinical drug potency of g-secretase (GS) and b -secretase (BACE1) inhibitors; (2) enable benchmarking across compounds; (3) facilitate dose selection for efficacy trials. Methods: Lumbar CSF A b 40 concentration data in healthy adults treated with placebo; GS inhibitors MK-0752 or semagacestat (from literature); or BACE inhibitor MK8931 were available. Model-predicted drug brain concentrations were used as driver for CSFA b 40 modulation. An Emax relationship described inhibition of A b 40 production and a distribution delay between brain and lumbar CSFA b 40 was incorporated. An additive baseline drift model informed by study-specific placebo data allowed for drift correction. Data were fit using non-linear mixed effects modeling and model performance was qualified. This model was combined with population PK models to predicted dose response profiles for brain and CSFA b 40 inhibition. Trial performance predictions were made taking into account AD population demographics and knowledge on non-compliance. Results: An E max inhibition model combined with delay compartments best described the CSF A b 40 response upon inhibition of GS or BACE. Maximum inhibition (E max) estimates were 0.87, 0.86, 0.96 and for plasma concentration at 50% of maximum (EC 50) were 933 ng.mL -1, 6250 ng.mL -1, 10.2 ng.mL -1 for semagacestat, MK-0752, and MK-8931, respectively. Dose response profiles demonstrated greater potency and achievable CSFA b 40 suppression with MK-8931 compared to other compounds at clinically feasible doses. CSF A b 40 reductions between 50-75%, and between 75-100% from baseline were predicted to be achieved in 90% of the patients at doses of 12 and 40 mg MK-8931, respectively. Conclusions: CSF A b 40 response following placebo and GS or BACE inhibition were characterized by a common model framework. Comparative analysis among compounds suggests that semagacestat produces only limited (<11%) inhibition of Ab production. MK-8931 showed superior potency in the expected therapeutic dose range resulting in almost full suppression of CSFA b 40. Simulations indicate that 12 and 40 mgMK-8931 inhibit Ab production by>50% and >75%, respectively, suggesting that clinical trials in AD with MK8931 may provide a more robust test of the amyloid hypothesis, compared to semagacestat.

Pharmacokinetics and Pharmacodynamics of the BACE1 Inhibitor Verubecestat (MK-8931) in Healthy Japanese Adults: a Randomized, Placebo-Controlled Study

β‐site amyloid precursor protein cleaving enzyme 1 (BACE1) is required for the production of β‐amyloid (Aβ) peptides and is considered a potential treatment target for Alzheimers disease (AD). To support Japans participation in the global clinical development program, we characterized the safety, pharmacokinetics (PKs), and pharmacodynamics of the BACE1 inhibitor verubecestat (MK‐8931) in 24 healthy Japanese adults in a two‐part, single‐center, randomized, placebo‐controlled phase I trial (protocol MK‐8931‐007) and compared the results with historical data from non‐Japanese subjects. Both single (20, 100, and 450 mg) and multiple (80 and 150 mg once daily for 14 days) doses of verubecestat were well tolerated. Verubecestats PK profile was similar in Japanese and non‐Japanese subjects. Verubecestat also reduced mean cerebrospinal fluid concentrations of the Aβ proteins Aβ40, Aβ42, and soluble β fragment of amyloid precursor protein; the level of reduction was comparable between Japanese and non‐Japanese subjects. These results support the continued global development of verubecestat as a potential disease‐modifying agent for Japanese and non‐Japanese subjects who are at risk for developing AD.

VERUBECESTAT PHARMACOKINETIC AND EXPOSURE-RESPONSE RESULTS FROM EPOCH: A PHASE 3 TRIAL IN MILD-TO-MODERATE ALZHEIMER’S DISEASE

individuals. Incidences of this disease are expected to double every 20 years emphasizing an urgent need for a development of disease modifying therapeutic strategies. A substantial body of clinical evidence has framed AD in the context of metabolic dysfunction and its pathophysiological importance to disease progression, suggesting that modulation of cellular energetics could represent new therapeutic approach. In our previous research, we have demonstrated that modulation of mitochondrial complex I activity using a tricyclic pyrone compound CP2 is effective in clearing both amyloid beta (Ab) and phosphorylated Tau, augmenting mitochondrial bioenergetics, promoting resistance to oxidative stress and restoring mitochondrial transport, levels of BDNF and synaptic proteins in presymptomatic APP/PS1 mice. In parallel, these mice demonstrated an improved cognitive and behavioral phenotype over their untreated littermates. Methods: In our current study, we tested whether CP2 treatment could halt the disease progression in symptomatic APP/PS1 mice. We also evaluated treatment efficacy based on multiple parameters informative of healthy aging in chronologically aged non-transgenic (NTG) littermates. Results:Both APP/ PS1 and NTG mice displayed improved cognitive and motor performance following chronic CP2 treatment over 13 months, starting at 20 months of age compared to untreated counterparts. Treatment with CP2 improved metabolic outcomes related with aging such as glucose tolerance, lipid peroxidation, cellular senescence, weight loss and inflammation. Although NTG mice showed lower respiratory rate, long-term CP2 treatment did not affect the levels of available ATP in living mice of both genotypes. CP2-treated APP/PS1 mice showed trend for reduced levels of insoluble Ab. Moreover, CP2 treatment improved glucose uptake in the brain as observed by FDG-PET scan. Electrophysiological scans indicated that synaptic activity was restored in the hippocampal area of APP/PS1 mice. Electron microscopy imaging showed that modulation of mitochondrial complex I activity with CP2 increased the number of elongated mitochondria over small ones, suggesting that preservation of healthier mitochondria was essential for improved neuronal activity and survival. Conclusions: Therefore, treatment with mitochondrial complex I inhibitors represent a promising therapeutic approach to ameliorate AD and promote healthy aging.