Jack D. Scott

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.

MLi-2, a potent, selective and centrally active compound for exploring the therapeutic potential and safety of LRRK2 kinase inhibition

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most common genetic cause of familial and sporadic Parkinson’s disease (PD). That the most prevalent mutation, G2019S, leads to increased kinase activity has led to a concerted effort to identify LRRK2 kinase inhibitors as a potential disease-modifying therapy for PD. An internal medicinal chemistry effort identified several potent and highly selective compounds with favorable drug-like properties. Here, we characterize the pharmacological properties of cis-2,6-dimethyl-4-(6-(5-(1-methylcyclopropoxy)-1H-indazol-3-yl)pyrimidin-4-yl)morpholine (MLi-2), a structurally novel, highly potent, and selective LRRK2 kinase inhibitor with central nervous system activity. MLi-2 exhibits exceptional potency in a purified LRRK2 kinase assay in vitro (IC50 = 0.76 nM), a cellular assay monitoring dephosphorylation of LRRK2 pSer935 LRRK2 (IC50 = 1.4 nM), and a radioligand competition binding assay (IC50 = 3.4 nM). MLi-2 has greater than 295-fold selectivity for over 300 kinases in addition to a diverse panel of receptors and ion channels. Acute oral and subchronic dosing in MLi-2 mice resulted in dose-dependent central and peripheral target inhibition over a 24-hour period as measured by dephosphorylation of pSer935 LRRK2. Treatment of MitoPark mice with MLi-2 was well tolerated over a 15-week period at brain and plasma exposures >100× the in vivo plasma IC50 for LRRK2 kinase inhibition as measured by pSer935 dephosphorylation. Morphologic changes in the lung, consistent with enlarged type II pneumocytes, were observed in MLi-2-treated MitoPark mice. These data demonstrate the suitability of MLi-2 as a compound to explore LRRK2 biology in cellular and animal models.

Characterization of a novel vasopressin V1b receptor antagonist, V1B-30N, in animal models of anxiety-like and depression-like behavior

Overactivity of the hypothalamic-pituitary-adrenal (HPA) axis has been linked to affective disorders such as anxiety and depression. Dampening HPA activity has, therefore, been considered as a possible means of treating affective disorders. Given the important role of vasopressin in modulating the HPA axis, one strategy has focused on inhibiting activity of the vasopressin 1b (V1b) receptor. In animals, V1b receptor antagonists reduce plasma stress hormone levels and have been shown to have an anxiolytic-like effect. Recently, V1B-30N was identified as a highly potent V1b receptor antagonist with selectivity over other vasopressin receptors, which is evaluated here in rodent models of anxiety-like and depression-like behaviors. V1B-30N (1-30mg/kg, IP) dose-dependently reduced separation-induced vocalizations in rat pups without producing any sedative effects in the animals. Similarly, V1B-30N (3-30mg/kg, IP) dose-dependently reduced separation-induced vocalizations in guinea pig pups. In a conflict assay, conditioned lick suppression, V1B-30N (3-30mg/kg, IP) increased punished licking. To assess antidepressive-like properties, V1B-30N (1-30mg/kg) was tested in the mouse and rat forced-swim tests but was found to be inactive. These results are consistent with previous findings with other V1b antagonists, which suggest that acute pharmacological antagonism of the V1b receptor has anxiolytic-like but not antidepressant-like properties.

Chronic BACE inhibition dramatically slows the rate of Aß accumulation and the development of amyloid plaques in young TgCRND8 mice

decrease the beta-amyloid load and restore cognitive impairment. However, since only a small fraction of IgG can penetrate the blood-brain barrier (BBB), successful transport of antibodies across the BBB provides a challenging issue for both active and passive Ab immunotherapy. Magnetic resonance (MR) imaging guided focused ultrasound has shown promising results for the induced disruption of the BBB for the delivery of antibodies. Noninvasive MRI-guided focal delivery of energy may allow for low doses of antibodies to enter the brain. Methods: Animals were fixed on top of a transducer that is positioned within a waterbath for noisefree sonication. We chose specific focus points for BBB opening according to localization MR images. Microbubble injection was given i.v during sonication at a 0.41MPa peak pressure threshold. Antibody was inserted into the blood stream prior to BBB opening. With MR imaging we then monitored extravasation of previously i.v. injected gadolinium as an in vivo BBB opening control agent. Antibody distribution, side effects and treatment effect were examined using immunohistological and immunohistochemical methods. Results: We successfully performed drug delivery via magnetic resonance guided opening of the BBB in transgenic and control animals. Sonication of a mouse cortex or choroid plexus has lead to extravasation of gadolinium and entry of the therapeutic antibody into the target area. The delivered antibody distribution, treatment effect and safety aspects have been investigated in terms of plaque load, inflammation, vascular changes and cerebral microhemorrhages. Conclusions: Focused ultrasound facilitates a safe, noninvasive, precise and reproductive therapeutic antibody entry into the brain of an Alzheimer’s mouse model. This targeted drug delivery opens new perspectives for therapeutic approaches for brain diseases by allowing high-molecular weight substances to be delivered across the BBB.

Diaryl piperidines as CB1 receptor antagonists.

The syntheses and SAR investigations of novel CB(1) receptor antagonists based on a 1,2-diaryl piperidine core have been described. Optimization of this core afforded a compound with robust in vivo potency by reducing food intake in a mouse DIO model.

Discovery of novel, potent BACE inhibitors with central activity for the treatment of Alzheimer's disease

Lynn A. Hyde, Prescott T. Leach, Qi Zhang, Giuseppe Terracina, Bonnie J. Werner, Robert A. Hodgson, Cinzia Cantu, Xia Chen, Maxine Chen, Jeffrey Misiaszek, Yusheng Wu, Suresh Babu, Tao Guo, Dawit Tadesse, Jack Scott, Wei Li, Lili Zhang, Eric M. Parker, Andrew W. Stamford, Matthew E. Kennedy, Merck Research Laboratories, Kenilworth, NJ, USA; Ligand Pharmaceuticals, Inc, Cranbury, NJ, USA. Contact e-mail: lynn.hyde@spcorp.com