Rainer Martin Lueoend

Discovery of Cyclic Sulfone Hydroxyethylamines as Potent and Selective β-Site APP-Cleaving Enzyme 1 (BACE1) Inhibitors: Structure-Based Design and in Vivo Reduction of Amyloid β-Peptides

Structure-based design of a series of cyclic hydroxyethylamine BACE1 inhibitors allowed the rational incorporation of prime- and nonprime-side fragments to a central core template without any amide functionality. The core scaffold selection and the structure-activity relationship development were supported by molecular modeling studies and by X-ray analysis of BACE1 complexes with various ligands to expedite the optimization of the series. The direct extension from P1-aryl- and heteroaryl moieties into the S3 binding pocket allowed the enhancement of potency and selectivity over cathepsin D. Restraining the design and synthesis of compounds to a physicochemical property space consistent with central nervous system drugs led to inhibitors with improved blood-brain barrier permeability. Guided by structure-based optimization, we were able to obtain highly potent compounds such as 60p with enzymatic and cellular IC(50) values of 2 and 50 nM, respectively, and with >200-fold selectivity over cathepsin D. Pharmacodynamic studies in APP51/16 transgenic mice at oral doses of 180 μmol/kg demonstrated significant reduction of brain Aβ levels.

A novel BACE inhibitor NB-360 shows a superior pharmacological profile and robust reduction of amyloid-β and neuroinflammation in APP transgenic mice

BackgroundAlzheimer’s disease (AD) is the most common form of dementia, the number of affected individuals is rising, with significant impacts for healthcare systems. Current symptomatic treatments delay, but do not halt, disease progression. Genetic evidence points to aggregation and deposition of amyloid-β (Aβ) in the brain being causal for the neurodegeneration and dementia typical of AD. Approaches to target Aβ via inhibition of γ-secretase or passive antibody therapy have not yet resulted in substantial clinical benefits. Inhibition of BACE1 (β-secretase) has proven a challenging concept, but recent BACE1inhibitors can enter the brain sufficiently well to lower Aβ. However, failures with the first clinical BACE1 inhibitors have highlighted the need to generate compounds with appropriate efficacy and safety profiles, since long treatment periods are expected to be necessary in humans.ResultsTreatment with NB-360, a potent and brain penetrable BACE-1 inhibitor can completely block the progression of Aβ deposition in the brains of APP transgenic mice, a model for amyloid pathology. We furthermore show that almost complete reduction of Aβ was achieved also in rats and in dogs, suggesting that these findings are translational across species and can be extrapolated to humans. Amyloid pathology may be an initial step in a complex pathological cascade; therefore we investigated the effect of BACE-1 inhibition on neuroinflammation, a prominent downstream feature of the disease. NB-360 stopped accumulation of activated inflammatory cells in the brains of APP transgenic mice. Upon chronic treatment of APP transgenic mice, patches of grey hairs appeared.ConclusionsIn a rapidly developing field, the data on NB-360 broaden the chemical space and expand knowledge on the properties that are needed to make a BACE-1 inhibitor potent and safe enough for long-term use in patients. Due to its excellent brain penetration, reasonable oral doses of NB-360 were sufficient to completely block amyloid-β deposition in an APP transgenic mouse model. Data across species suggest similar treatment effects can possibly be achieved in humans. The reduced neuroinflammation upon amyloid reduction by NB-360 treatment supports the notion that targeting amyloid-β pathology can have beneficial downstream effects on the progression of Alzheimer’s disease.

Discovery of amino-1,4-oxazines as potent BACE-1 inhibitors.

New amino-1,4-oxazine derived BACE-1 inhibitors were explored and various synthetic routes developed. The binding mode of the inhibitors was elucidated by co-crystallization of 4 with BACE-1 and X-ray analysis. Subsequent optimization led to inhibitors with low double digit nanomolar activity in a biochemical and single digit nanomolar potency in a cellular assays. To assess the inhibitors for their permeation properties and potential to cross the blood-brain-barrier a MDR1-MDCK cell model was successfully applied. Compound 8a confirmed the in vitro results by dose-dependently reducing Aβ levels in mice in an acute treatment regimen.

THE BACE INHIBITOR NB-360 HAS EXCELLENT BRAIN PENETRATION AND EFFICACY ON AMYLOID-B LOAD IN ANIMAL MODELS

human APOE3 or APOE4) were treated with Bex, LG268 (a more selective RXR agonist), or vehicle control in 3 treatment paradigms: T1) 7-day oral gavage (5.75-6M); T2) 7-day hydrogel (5.75-6M); and T3) 30-day hydrogel (5-6M). Hydrogel provides a steady dosage of drug throughout the awake period of the mice. Brains were harvested, dissected, and homogenized by 3-step serial extraction.Results: In brain regions with lowAb levels at treatment, RXR agonists did not change soluble levels of Ab 42 and oAb in E3FAD or E4FAD mice. In brain regions with intermediate Ab levels, RXR agonist treatment induced an increase in soluble Ab 42 and oAb levels in E3FAD and E4FADmice. However, in the hippocampus of E4FADmice, with high Ab levels at treatment, RXR agonists induced a decrease in soluble Ab 42 and oAb levels and an increase in synaptic proteins. Importantly, total apoE levels were unaffected for all treatment groups, suggesting an alternate mechanism of action for RXR agonists. Our data further demonstrate that the beneficial effects of RXR agonists in E4FAD mice are mediated via: increased ABCA1 and ABCG1 expression, increased apoE4 association with lipoproteins, increased apoE/Ab complex levels, reduced oAb levels and enhanced synaptic viability. Conclusions: Collectively, our data demonstrate that RXR agonist efficacy is determined by the levels of Ab pathology at time of treatment, exhibiting no effect, or even an increase the levels of neurotoxic Ab in prevention paradigms where Ab levels are likely sub-pathological. However, in later stages of AD, RXR agonists may address the loss of function associated with APOE4 by increasing apoE4 lipidation and apoE4/Ab complex formation. Future studies are necessary to determine whether this pathway is relevant for APOE3 carriers with high Ab pathology, or if RXR agonists are an APOE4specific AD therapeutic.