Brian Scott Bronk

Optimization of a natural product-based class of γ-secretase modulators.

A series of triterpene-based γ-secretase modulators is optimized. An acetate present at the C24 position of the natural product was replaced with either carbamates or ethers to provide compounds with better metabolic stability. With one of those pharmacophores in place at C24, morpholines or carbamates were installed at the C3 position to refine the physicochemical properties of the analogues. This strategy gave compounds with low clearance and good distribution into the central nervous system (CNS) of CD-1 mice. Two of these compounds, 100 and 120, were tested for a pharmacodynamic effect in the strain and lowered brain Aβ42 levels.

Efficacy of SPI-1865, a novel gamma-secretase modulator, in multiple rodent models

IntroductionModulation of the gamma-secretase enzyme, which reduces the production of the amyloidogenic Aβ42 peptide while sparing the production of other Aβ species, is a promising therapeutic approach for the treatment of Alzheimers disease. Satori has identified a unique class of small molecule gamma-secretase modulators (GSMs) capable of decreasing Aβ42 levels in cellular and rodent model systems. The compound class exhibits potency in the nM range in vitro and is selective for lowering Aβ42 and Aβ38 while sparing Aβ40 and total Aβ levels. In vivo, a compound from the series, SPI-1865, demonstrates similar pharmacology in wild-type CD1 mice, Tg2576 mice and Sprague Dawley rats.MethodsAnimals were orally administered either a single dose of SPI-1865 or dosed for multiple days. Aβ levels were measured using a sensitive plate-based ELISA system (MSD) and brain and plasma exposure of drug were assessed by LC/MS/MS.ResultsIn wild-type mice using either dosing regimen, brain Aβ42 and Aβ38 levels were decreased upon treatment with SPI-1865 and little to no statistically meaningful effect on Aβ40 was observed, reflecting the changes observed in vitro. In rats, brain Aβ levels were examined and similar to the mouse studies, brain Aβ42 and Aβ38 were lowered. Comparable changes were also observed in the Tg2576 mice, where Aβ levels were measured in brain as well as plasma and CSF.ConclusionsTaken together, these data indicate that SPI-1865 is orally bioavailable, brain penetrant, and effective at lowering Aβ42 in a dose responsive manner. With this unique profile, the class of compounds represented by SPI-1865 may be a promising new therapy for Alzheimers disease.

Initial Optimization of a New Series of γ-Secretase Modulators Derived from a Triterpene Glycoside

The discovery of a new series of γ-secretase modulators is disclosed. Starting from a triterpene glycoside γ-secretase modulator that gave a very low brain-to-plasma ratio, initial SAR and optimization involved replacement of a pendant sugar with a series of morpholines. This modification led to two compounds with significantly improved central nervous system (CNS) exposure.

Modulation of Gamma-Secretase for the Treatment of Alzheimer's Disease

The Amyloid Hypothesis states that the cascade of events associated with Alzheimers disease (AD)—formation of amyloid plaques, neurofibrillary tangles, synaptic loss, neurodegeneration, and cognitive decline—are triggered by Aβ peptide dysregulation (Kakuda et al., 2006, Sato et al., 2003, Qi-Takahara et al., 2005). Since γ-secretase is critical for Aβ production, many in the biopharmaceutical community focused on γ-secretase as a target for therapeutic approaches for Alzheimers disease. However, pharmacological approaches to control γ-secretase activity are challenging because the enzyme has multiple, physiologically critical protein substrates. To lower amyloidogenic Aβ peptides without affecting other γ-secretase substrates, the epsilon (ε) cleavage that is essential for the activity of many substrates must be preserved. Small molecule modulators of γ-secretase activity have been discovered that spare the ε cleavage of APP and other substrates while decreasing the production of Aβ 42. Multiple chemical classes of γ-secretase modulators have been identified which differ in the pattern of Aβ peptides produced. Ideally, modulators will allow the ε cleavage of all substrates while shifting APP cleavage from Aβ 42 and other highly amyloidogenic Aβ peptides to shorter and less neurotoxic forms of the peptides without altering the total Aβ pool. Here, we compare chemically distinct modulators for effects on APP processing and in vivo activity.

Design, synthesis, and in vivo characterization of a novel series of tetralin amino imidazoles as γ-secretase inhibitors: Discovery of PF-3084014

A novel series of tetralin containing amino imidazoles, derived from modification of the corresponding phenyl acetic acid derivatives is described. Replacement of the amide led to identification of a potent series of tetralin-amino imidazoles with robust central efficacy. The reduction of brain Aβ in guinea pigs in the absence of changes in B-cells suggested a potential therapeutic index with respect to APP processing compared with biomarkers of notch related toxicity. Optimization of the FTOC to plasma concentrations at the brain Aβ EC(50) lead to the identification of compound 14f (PF-3084014) which was selected for clinical development.

SAR investigations on a novel class of gamma-secretase modulators based on a unique scaffold

In this communication we present details of our analog efforts within a novel series of gamma-secretase modulating compounds. Esters and carbamates were investigated as bioisosteres for a glycoside moiety present in an initial hit isolated from black cohosh extract. We identified elements within each series that retain the potency and selectivity of the initial lead while improving physicochemical properties.

Minimization of drug–drug interaction risk and candidate selection in a natural product-based class of gamma-secretase modulators

Early lead compounds in this gamma secretase modulator series were found to potently inhibit CYP3A4 and other human CYP isoforms increasing their risk of causing drug-drug-interactions (DDIs). Using structure-activity relationships and CYP3A4 structural information, analogs were developed that minimized this DDI potential. Three of these new analogs were further characterized by rat PK, rat PK/PD and rat exploratory toxicity studies resulting in selection of SPI-1865 (14) as a preclinical development candidate.

Diamide amino-imidazoles: a novel series of γ-secretase inhibitors for the treatment of Alzheimer's disease.

The synthesis and structure-activity relationship (SAR) of a novel series of di-substituted imidazoles, derived from modification of DAPT, are described. Subsequent optimization led to identification of a highly potent series of inhibitors that contain a β-amine in the imidazole side-chain resulting in a robust in vivo reduction of plasma and brain Aβ in guinea pigs. The therapeutic index between Aβ reductions and changes in B-cell populations were studied for compound 10 h.

Classification of γ-secretase modulators and their effect on pharmacological profiles of amyloid β peptides

MALDI-TOF profiling enables rapid P2-513 Introduction γ-Secretase modulators (GSMs) decrease the cleavage of amyloid precursor protein (APP) at the site that generates 42-amino acid amyloid β protein (Aβ42) while sparing the normal cleavage of Notch. However, the mechanism by which GSMs modulate γ-secretase is not clear and may not proceed through a single mechanism, as evidenced by the differential effects GSMs can have on other A peptides. The objective of this study was to determine the pharmacologic profiles of literature GSMs and novel Satori SPI compounds by examining the effect on various A peptides using two different MS-based detection methods. We have examined the cleavage profile of APP in the presence of various GSMs by immunoprecipitation/MALDI-TOF and quantified key Aβ peptides by LC/MS/MS. While all GSMs reduce A1-42 production, structurally distinct classes of GSMs affected Aβ1-38 and Aβ1-39 in opposite directions, i.e., Aβ38-increasing GSMs decreased Aβ39 production while characterization of multiple A peptides 4331.15 4132.93 2463.30 4330.75 2463.15 3153.02 3263.71 4132.64 3712.45 2316.29 3868.85 2897.94 2645.34 4515.39 3457.22 A1-20 A11-38 A11-39 A11-37 A11-40 A1-28 A1-33 A1-34 A1-38 A1-39 A1-37 A1-40 A1-42 Vehicle Aβ38-decreasing GSMs increased Aβ39 production. These two classes of GSMs did not dramatically change the levels of total Aβ (Aβ1-x) at the concentrations that reduced Aβ1-42, presumably because increases in the production of shorter peptides compensate for the loss of longer peptides like Aβ1-42. Quantification of individual peptides (Aβ37, 38, 39, 40 and 42) by LC/MS/MS revealed significant perturbations in the concentrations of the shorter Aβ species. GSMs may slightly shift γ-secretase along the -helical domain of APP transmembrane domain without changing total γ-secretase activity by shifting the cleavage from longer to shorter peptides. Method 4330.55

Gamma—secretase modulators do not show a potency shift in high expressing model systems

ubiquitin-positive inclusion bodies. Besides aggregation of TDP-43, ubiquitination, hyperphosphorylation, fragmentation and loss of nuclear localization was observed in diseases. However, it remains to be clarified whether TDP-43 aggregates are toxic or not, and how abnormality of TDP-43 mediates neuronal degeneration. Methods: We show here that the cells with TDP-43 inclusions suppressed cell-growth, using BrdU up-take analysis. And morphological relationship between TDP-43 inclusion and several transcription factors were detected in immunocytochemical analysis. Results: We report here that cell-growth is strongly suppressed in the cells with TDP-43 inclusions compared to the cells without inclusions. In these cells, RNA polymerase II and several transcription factors are co-localized with TDP-43 aggregates. Furthermore, accumulation of RNA polymerase II with phosphorylated TDP-43 inclusions was detected in FTLD brains. These results suggested that abnormal TDP-43 inclusions cause growth arrest in SH-SY5Y cells by recruiting general transcription factors and leading to toxicity or cellular dysfunction. Conclusions: In TDP-43 proteinopathy, transcriptional dysregulation may also contribute to neuronal degeneration.