Jack Tseng

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.

Hourly variability of cerebrospinal fluid biomarkers in Alzheimer's disease subjects and healthy older volunteers.

Large hour-to-hour variability has previously been demonstrated in the cerebrospinal fluid (CSF) concentrations of Alzheimers disease (AD) biomarkers amyloid β(42) (Aβ(42)) and Aβ(40) in healthy younger subjects. We investigated the within-subject variability over 36 hours in CSF Aβ and tau proteins, in older subjects and AD patients. Six patients with mild stage AD (59-85 years, Mini Mental State Examination (MMSE) 16-26) and 6 healthy older volunteers (64-77 years) received an intrathecal catheter from which, during 36 hours, each hour 6 mL of CSF was drawn. Concentrations of Aβ(42), Aβ(40), total tau, and phosphorylated tau were determined and the variability was analyzed. Within-subject variability within 3-hour periods was assessed as the coefficient of variation, which was comparable for these 4 biomarkers in controls (4.2%-4.6%) and AD (3.1%-5.8%). Variability over 12 hour periods was 5.3% to 9.5%. These findings suggest that CSF biomarker variability is relatively low in healthy older controls and AD patients. Furthermore, continuous sampling of CSF proved to be a useful and robust method, which may also be used to investigate AD pathogenesis and to evaluate pharmacotherapeutic interventions.

CSF α-synuclein concentrations do not fluctuate over hours and are not correlated to amyloid β in humans.

Reports on the value of cerebrospinal fluid (CSF) α-synuclein as a biomarker for dementia with Lewy bodies and Parkinson disease are contradicting. This may be explained by fluctuating CSF α-synuclein concentrations over time. Such fluctuations have been suggested for CSF amyloid β concentrations. Furthermore, a physiological relationship between α-synuclein and amyloid β has been suggested based on in vitro research. We performed repeated CSF sampling in healthy elderly and AD patients and showed that sinusoidal fluctuations in CSF α-synuclein concentrations were not present. Furthermore, we did not find evidence for an interaction between amyloid β and α-synuclein concentrations in CSF.

Effect of Food, Antacid, and Age on the Pharmacokinetics of the Oral Thrombin Receptor Antagonist Vorapaxar (SCH 530348) in Healthy Volunteers

This randomized, open‐label, parallel group study examined the effects of food, antacid, and age on the pharmacokinetics of vorapaxar. In total, 101 subjects were enrolled including 83 young adults (18–45 years) and 18 elderly subjects (>65 years). Subjects received single‐dose vorapaxar 40 mg after a 10‐hour fast (young and elderly) or with extra‐strength antacid, food, or 1 or 2 hours after food (young only). Vorapaxar 40 mg was rapidly absorbed after a fast (median Tmax: 1 hour). Administration with food or 1 or 2 hours post‐meal modestly increased vorapaxar mean area under the curve (AUC) and Cmax and prolonged median Tmax by 1 hour. Concomitant food modestly increased vorapaxar AUC from time zero to infinity [AUC(I)] and Cmax 43% and 31%, respectively. Antacid modestly decreased vorapaxar AUC(I) by 15% and Cmax by 38%, and increased median Tmax by 1 hour. Vorapaxar AUC(I) and Cmax were 41% and 29% higher, respectively, in elderly versus young subjects. Concomitant food and older age were associated with modest increases, and antacid was associated with a small decrease in vorapaxar exposure, which are not expected to affect the drugs safety or efficacy.

Safety and pharmacokinetics of the novel BACE inhibitor MK-8931 in healthy subjects following single- and Multiple-Dose administration

Background:Alzheimer’s disease (AD) is a common, debilitating neurodegenerative disorder afflicting the aging population. Synaptic accumulation of Aß-protein oligomers and tau might be responsible for the neurological damage in AD. Thus, special interest has emerged in developing treatments that reduce the formation or facilitate the clearance of these oligomers. Utilizing molecular modeling and structure based design techniques we generated a series of novel organic heterocyclic compounds that are capable of recognizing the aggregated Aß-protein molecule and promoting clearance. Using cell-free and cell-based assays, a compound denominated NPT-400 with activity in the high nanomolar range was identified for pharmacokinetic (PK) and preliminary efficacy studies in APP transgenic (tg) mice. Methods: The mThy1-hAPP751 transgenic mouse was utilized for efficacy studies. This mouse combines the Swedish (K670M/N671L) and London (V717I) APPmutations, and these animals develop AD-like neuropathology and behavioral deficits starting at 3-4 months of age. Female non-tg and tg mice (w5 mo of age) received a single injection of vehicle or NPT-400-3 (IP, 10 mg/kg) three times per week for 6.5 weeks. Behavioral assessments were conducted during week 4 of treatment including locomotor activity and water maze. At the completion of treatment, brains were hemisected and tissue sections were processed for immunolabeling and confocal analysis, and homogenates were analyzed for levels of Abeta-protein by ELISA and immunoblot. For PK studies, wildtype C57Bl6 mice received IVor PO NPT-400-3 compound at 10 mg/kg and blood and plasma levels were analyzed at 0-24 hrs. Results: Treatment with NPT-400-3 resulted in a statistically significant normalization of locomotor activity accompanied by amelioration of the synaptic and dendritic pathology in the neocortex and hippocampus. By immunoblot and ELISA the levels of monomeric and oligomeric Aß-protein were statistically significantly reduced in the brains of the APP tg mice. PK studies showed that NPT400-3 is stable in plasma, is orally bioavailable and penetrates the brain with a B/P ratio of 0.8. Conclusions:NPT-400-3 is an orally bioavailable, brain penetrating Aß-protein stabilizing organic compound that reduces the accumulation of Aß-protein oligomers and ameliorates behavioral deficits and neuropathology in APP tg mice without overt adverse effects.

The effects of the CXCR2 antagonist, MK-7123, on bone marrow functions in healthy subjects.

The CXCR2 antagonist MK-7123 causes dose-dependent reductions in absolute neutrophil counts (ANC) and decreases neutrophil tissue responses, but its effects on bone marrow functions are not yet known. We conducted a double-blind, randomized study in 18 healthy subjects comparing the effects of either MK-7123 (30mg, po, daily for 28days) or placebo on peripheral blood counts and bone marrow myeloid cell populations. MK-7123 caused a reversible decrease (approximately 50%) in the ANC as demonstrated on days 1 and 28, the first and last days of the treatment period. Bone marrow aspirate smears and biopsy imprints did not differ in the proportion of mature neutrophils in pretreatment, day 28, day 56 or placebo samples. There were no treatment effects on biopsy or aspirate clot cellularity, myeloid to erythroid or myeloid post-mitotic to mitotic ratios; flow-cytometric analyses of aspirate cells; or bone marrow fat to cell balance as assessed by MRI. MK-7123 was generally well tolerated with neutropenia being the most common adverse event; however, there were no clinical symptoms associated with decreased ANCs. These findings indicate that the CXCR2 antagonist MK-7123 causes rapidly reversible decrease in the ANC without measurable myelosuppressive effects. The results support the development of CXCR2 antagonists as potentially useful anti-inflammatory agents, primarily interrupting neutrophil trafficking.

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.