Jared N. Cumming

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.

Structure based design of iminohydantoin BACE1 inhibitors: Identification of an orally available, centrally active BACE1 inhibitor

From an initial lead 1, a structure-based design approach led to identification of a novel, high-affinity iminohydantoin BACE1 inhibitor that lowers CNS-derived Aβ following oral administration to rats. Herein we report SAR development in the S3 and F subsites of BACE1 for this series, the synthetic approaches employed in this effort, and in vivo data for the optimized compound.

Piperazine sulfonamide BACE1 inhibitors: design, synthesis, and in vivo characterization.

With collaboration between chemistry, X-ray crystallography, and molecular modeling, we designed and synthesized a series of novel piperazine sulfonamide BACE1 inhibitors. Iterative exploration of the non-prime side and S2 sub-pocket of the enzyme culminated in identification of an analog that potently lowers peripheral Abeta(40) in transgenic mice with a single subcutaneous dose.

Structure-Based Design of an Iminoheterocyclic β-Site Amyloid Precursor Protein Cleaving Enzyme (BACE) Inhibitor that Lowers Central Aβ in Nonhuman Primates

We describe successful efforts to optimize the in vivo profile and address off-target liabilities of a series of BACE1 inhibitors represented by 6 that embodies the recently validated fused pyrrolidine iminopyrimidinone scaffold. Employing structure-based design, truncation of the cyanophenyl group of 6 that binds in the S3 pocket of BACE1 followed by modification of the thienyl group in S1 was pursued. Optimization of the pyrimidine substituent that binds in the S2-S2″ pocket of BACE1 remediated time-dependent CYP3A4 inhibition of earlier analogues in this series and imparted high BACE1 affinity. These efforts resulted in the discovery of difluorophenyl analogue 9 (MBi-4), which robustly lowered CSF and cortex Aβ40 in both rats and cynomolgus monkeys following a single oral dose. Compound 9 represents a unique molecular shape among BACE inhibitors reported to potently lower central Aβ in nonrodent preclinical species.

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.