Susanne Gustavsson

Discovery of AZD3839, a Potent and Selective BACE1 Inhibitor Clinical Candidate for the Treatment of Alzheimer Disease

Background: BACE1 inhibitors target the first step in Aβ formation and are tractable drugs for halting disease progression in Alzheimer disease. Results: AZD3839 is a novel BACE1 inhibitor that effectively reduces brain and CSF Aβ levels in several preclinical species. Conclusion: Based on the preclinical profile, AZD3839 was progressed into Phase I. Significance: AZD3839 may have disease-modifying potential in the treatment of Alzheimer disease. β-Site amyloid precursor protein cleaving enzyme1 (BACE1) is one of the key enzymes involved in the processing of the amyloid precursor protein (APP) and formation of amyloid β peptide (Aβ) species. Because cerebral deposition of Aβ species might be critical for the pathogenesis of Alzheimer disease, BACE1 has emerged as a key target for the treatment of this disease. Here, we report the discovery and comprehensive preclinical characterization of AZD3839, a potent and selective inhibitor of human BACE1. AZD3839 was identified using fragment-based screening and structure-based design. In a concentration-dependent manner, AZD3839 inhibited BACE1 activity in a biochemical fluorescence resonance energy transfer (FRET) assay, Aβ and sAPPβ release from modified and wild-type human SH-SY5Y cells and mouse N2A cells as well as from mouse and guinea pig primary cortical neurons. Selectivity against BACE2 and cathepsin D was 14 and >1000-fold, respectively. AZD3839 exhibited dose- and time-dependent lowering of plasma, brain, and cerebrospinal fluid Aβ levels in mouse, guinea pig, and non-human primate. Pharmacokinetic/pharmacodynamic analyses of mouse and guinea pig data showed a good correlation between the potency of AZD3839 in primary cortical neurons and in vivo brain effects. These results suggest that AZD3839 effectively reduces the levels of Aβ in brain, CSF, and plasma in several preclinical species. It might, therefore, have disease-modifying potential in the treatment of Alzheimer disease and related dementias. Based on the overall pharmacological profile and its drug like properties, AZD3839 has been progressed into Phase 1 clinical trials in man.

Aminoimidazoles as Bace-1 Inhibitors: The Challenge to Achieve in Vivo Brain Efficacy

The evaluation of a series of bicyclic aminoimidazoles as potent BACE-1 inhibitors is described. The crystal structures of compounds 14 and 23 in complex with BACE-1 reveal hydrogen bond interactions with the protein important for achieving potent inhibition. The optimization of permeability and efflux properties of the compounds is discussed as well as the importance of these properties for attaining in vivo brain efficacy. Compound (R)-25 was selected for evaluation in vivo in wild type mice and 1.5h after oral co-administration of 300μmol/kg (R)-25 and efflux inhibitor GF120918 the brain Aβ40 level was reduced by 17% and the plasma Aβ40 level by 76%.

Sulfonimidamides as Sulfonamides Bioisosteres: Rational Evaluation through Synthetic, in Vitro, and in Vivo Studies with γ-Secretase Inhibitors

The proof of the pudding: A proof-of-concept study using γ-secretase inhibitors as a model has shown that sulfonimidamides act as bioisosteres for sulfonamides. Detailed in vitro and in vivo profiling reveal that the sulfonimidamide motif imparts desirable properties such as decreased lipophilicity and plasma protein binding, accompanied by increased solubility. Our data support a wider use of this unique functional group in the design of new pharmacologically active agents.

AZ-4217: a high potency BACE inhibitor displaying acute central efficacy in different in vivo models and reduced amyloid deposition in Tg2576 mice.

Aβ, the product of APP (amyloid precursor protein), has been implicated in the pathophysiology of Alzheimers disease (AD). β-Site APP cleaving enzyme1 (BACE1) is the enzyme initiating the processing of the APP to Aβ peptides. Small molecule BACE1 inhibitors are expected to decrease Aβ-peptide generation and thereby reduce amyloid plaque formation in the brain, a neuropathological hallmark of AD. BACE1 inhibition thus addresses a key mechanism in AD and its potential as a therapeutic target is currently being addressed in clinical studies. Here, we report the discovery and the pharmacokinetic and pharmacodynamic properties of BACE1 inhibitor AZ-4217, a high potency compound (IC50 160 pm in human SH-SY5Y cells) with an excellent in vivo efficacy. Central efficacy of BACE1 inhibition was observed after a single dose in C57BL/6 mice, guinea pigs, and in an APP transgenic mouse model of cerebral amyloidosis (Tg2576). Furthermore, we demonstrate that in a 1 month treatment paradigm BACE1 inhibition of Aβ production does lower amyloid deposition in 12-month-old Tg2576 mice. These results strongly support BACE1 inhibition as concretely impacting amyloid deposition and therefore potentially an important approach for therapeutic intervention in AD.

Alzheimer's Disease: Presenilin 2-Sparing γ-Secretase Inhibition Is a Tolerable Aβ Peptide-Lowering Strategy

γ-Secretase inhibition represents a major therapeutic strategy for lowering amyloid β (Aβ) peptide production in Alzheimers disease (AD). Progress toward clinical use of γ-secretase inhibitors has, however, been hampered due to mechanism-based adverse events, primarily related to impairment of Notch signaling. The γ-secretase inhibitor MRK-560 represents an exception as it is largely tolerable in vivo despite displaying only a small selectivity between Aβ production and Notch signaling in vitro. In exploring the molecular basis for the observed tolerability, we show that MRK-560 displays a strong preference for the presenilin 1 (PS1) over PS2 subclass of γ-secretases and is tolerable in wild-type mice but causes dose-dependent Notch-related side effect in PS2-deficient mice at drug exposure levels resulting in a substantial decrease in brain Aβ levels. This demonstrates that PS2 plays an important role in mediating essential Notch signaling in several peripheral organs during pharmacological inhibition of PS1 and provide preclinical in vivo proof of concept for PS2-sparing inhibition as a novel, tolerable and efficacious γ-secretase targeting strategy for AD.

Revisiting the peripheral sink hypothesis: inhibiting BACE1 activity in the periphery does not alter β‐amyloid levels in the CNS

Aggregation of amyloid beta (Aβ) peptides and the subsequent neural plaque formation is a central aspect of Alzheimers disease. Various strategies to reduce Aβ load in the brain are therefore intensely pursued. It has been hypothesized that reducing Aβ peptides in the periphery, that is in organs outside the brain, would be a way to diminish Aβ levels and plaque load in the brain. In this report, we put this peripheral sink hypothesis to test by investigating how selective inhibition of Aβ production in the periphery using a β‐secretase (BACE)1 inhibitor or reduced BACE1 gene dosage affects Aβ load in the brain. Selective inhibition of peripheral BACE1 activity in wild‐type mice or mice over‐expressing amyloid precursor protein (APPswe transgenic mice; Tg2576) reduced Aβ levels in the periphery but not in the brain, not even after chronic treatment over several months. In contrast, a BACE1 inhibitor with improved brain disposition reduced Aβ levels in both brain and periphery already after acute dosing. Mice heterozygous for BACE1, displayed a 62% reduction in plasma Aβ40, whereas brain Aβ40 was only lowered by 11%. These data suggest that reduction of Aβ in the periphery is not sufficient to reduce brain Aβ levels and that BACE1 is not the rate‐limiting enzyme for Aβ processing in the brain. This provides evidence against the peripheral sink hypothesis and suggests that a decrease in Aβ via BACE1 inhibition would need to be carried out in the brain.

In vivo reduction of beta-amyloid peptides in the brain of Tg2576 mice after oral administration of a novel BACE1 inhibitor

daily for 7 days, then 16 mg daily for 7 days, followed by a co-administration period of 10 days with 125 mg avagacestat.Results: 32 and 34 subjects were randomized in the donepezil and galantamine study, respectively. Coadministration of avagacestat and donepezil or galantamine was associated with an increase in the geometric mean Cmax (14-21%) and AUC(TAU) (24-26%) of donepezil and/or galantamine; an increase not likely to be clinically relevant. One serious adverse event (SAE) was reported in healthy subjects co-administered avagacestat and galantamine for 10 days. On Day 25, a subject was found to have elevated lipase (5x ULN) and amylase (2x ULN) and was diagnosed with pancreatitis. The subject, who also had multiple gall stones, was admitted to the hospital, was treated, and recovered fully. Co-administration of avagacestat with either donepezil or galantamine in healthy subjects for short periods of timewas associated with a higher frequency of AEs than administration of donepezil or galantamine alone. The most common AEs in either study included headache, nausea, and epistaxis. Most AEs were mild in nature and all, except nasal congestion, resolved prior to study discharge. Conclusions: Co-administration of multiple 125 mg doses of avagacestat (the highest dose tested in phase IIb studies) and either donepezil or galantamine at steady-state appeared to be generally well tolerated in healthy subjects. Co-administration of avagacestat was not associated with clinically relevant increases in Cmax or AUC for either donepezil or galantamine.