Studies to investigate the in vivo therapeutic window of the gamma-secretase inhibitor N2-[(2S)-2-(3,5-difluorophenyl)-2-hydroxyethanoyl]-N1-[(7S)-5-methyl-6-oxo-6,7-dihydro-5H-dibenzo[b,d]azepin-7-yl]-L-alaninamide (LY411,575) in the CRND8 mouse

Mammalian Models in Alzheimer's Research: An Update

A form of dementia distinct from healthy cognitive aging, Alzheimer's disease (AD) is a complex multi-stage disease that currently afflicts over 50 million people worldwide. Unfortunately, previous therapeutic strategies developed from murine models emulating different aspects of AD pathogenesis were limited. Consequently, researchers are now developing models that express several aspects of pathogenesis that better reflect the clinical situation in humans. As such, this review seeks to provide insight regarding current applications of mammalian models in AD research by addressing recent developments and characterizations of prominent transgenic models and their contributions to pathogenesis as well as discuss the advantages, limitations, and application of emerging models that better capture genetic heterogeneity and mixed pathologies observed in the clinical situation.

Advances in Understanding the Notch Signaling Pathway in the Cochlea

The cochlear structure is highly complex and specific, and its development is regulated by multiple signaling pathways. Abnormalities in cochlear development can lead to different degrees of loss of function. Hair cells (HCs), which are difficult to regenerate in the mature mammalian cochlea, are susceptible to damage from noise and ototoxic drugs, and damage to HCs can cause hearing loss to varying degrees. Notch, a classical developmental signaling molecule, has been shown to be closely associated with embryonic cochlear development and plays an important role in HC regeneration in mammals, suggesting that the Notch signaling pathway may be a potential therapeutic target for cochlear development and hearing impairment due to HC damage. In recent years, the important role of the Notch signaling pathway in the cochlea has received increasing attention. In this paper, we review the role of Notch signaling in cochlear development and HC regeneration, with the aim of providing new research ideas for the prevention and treatment of related diseases.

Dbx1 controls the development of astrocytes of the intermediate spinal cord by modulating Notch signaling

Significant progress has been made in elucidating the basic principles that govern neuronal specification in the developing central nervous system. In contrast, much less is known about the origin of astrocytic diversity. Here, we demonstrate that a restricted pool of progenitors in the mouse spinal cord, expressing the transcription factor Dbx1, produces a subset of astrocytes, in addition to interneurons. Ventral p0-derived astrocytes (vA0 cells) exclusively populate intermediate regions of spinal cord with extraordinary precision. The postnatal vA0 population comprises gray matter protoplasmic and white matter fibrous astrocytes and a group of cells with strict radial morphology contacting the pia. We identified that vA0 cells in the lateral funiculus are distinguished by the expression of reelin and Kcnmb4. We show that Dbx1 mutants have an increased number of vA0 cells at the expense of p0-derived interneurons. Manipulation of the Notch pathway, together with the alteration in their ligands seen in Dbx1 knockouts, suggest that Dbx1 controls neuron-glial balance by modulating Notch-dependent cell interactions. In summary, this study highlights that restricted progenitors in the dorsal-ventral neural tube produce region-specific astrocytic subgroups and that progenitor transcriptional programs highly influence glial fate and are instrumental in creating astrocyte diversity.

Notch-ing up knowledge on molecular mechanisms of skin fibrosis: focus on the multifaceted Notch signalling pathway

Fibrosis can be defined as an excessive and deregulated deposition of extracellular matrix proteins, causing loss of physiological architecture and dysfunction of different tissues and organs. In the skin, fibrosis represents the hallmark of several acquired (e.g. systemic sclerosis and hypertrophic scars) and inherited (i.e. dystrophic epidermolysis bullosa) diseases. A complex series of interactions among a variety of cellular types and a wide range of molecular players drive the fibrogenic process, often in a context-dependent manner. However, the pathogenetic mechanisms leading to skin fibrosis are not completely elucidated. In this scenario, an increasing body of evidence has recently disclosed the involvement of Notch signalling cascade in fibrosis of the skin and other organs. Despite its apparent simplicity, Notch represents one of the most multifaceted, strictly regulated and intricate pathways with still unknown features both in health and disease conditions. Starting from the most recent advances in Notch activation and regulation, this review focuses on the pro-fibrotic function of Notch pathway in fibroproliferative skin disorders describing molecular networks, interplay with other pro-fibrotic molecules and pathways, including the transforming growth factor-β1, and therapeutic strategies under development.

Unlocking the Secrets of Cancer Stem Cells with γ-Secretase Inhibitors: A Novel Anticancer Strategy

The dysregulation of Notch signaling is associated with a wide variety of different human cancers. Notch signaling activation mostly relies on the activity of the γ-secretase enzyme that cleaves the Notch receptors and releases the active intracellular domain. It is well-documented that γ-secretase inhibitors (GSIs) block the Notch activity, mainly by inhibiting the oncogenic activity of this pathway. To date, several GSIs have been introduced clinically for the treatment of various diseases, such as Alzheimer's disease and various cancers, and their impacts on Notch inhibition have been found to be promising. Therefore, GSIs are of great interest for cancer therapy. The objective of this review is to provide a systematic review of in vitro and in vivo studies for investigating the effect of GSIs on various cancer stem cells (CSCs), mainly by modulation of the Notch signaling pathway. Various scholarly electronic databases were searched and relevant studies published in the English language were collected up to February 2020. Herein, we conclude that GSIs can be potential candidates for CSC-targeting therapy. The outcome of our study also indicates that GSIs in combination with anticancer drugs have a greater inhibitory effect on CSCs.

Translational animal models for Alzheimer's disease: An Alzheimer's Association Business Consortium Think Tank

Over 5 million Americans and 50 million individuals worldwide are living with Alzheimer's disease (AD). The progressive dementia associated with AD currently has no cure. Although clinical trials in patients are ultimately required to find safe and effective drugs, animal models of AD permit the integration of brain pathologies with learning and memory deficits that are the first step in developing these new drugs. The purpose of the Alzheimer's Association Business Consortium Think Tank meeting was to address the unmet need to improve the discovery and successful development of Alzheimer's therapies. We hypothesize that positive responses to new therapies observed in validated models of AD will provide predictive evidence for positive responses to these same therapies in AD patients. To achieve this goal, we convened a meeting of experts to explore the current state of AD animal models, identify knowledge gaps, and recommend actions for development of next-generation models with better predictability. Among our findings, we all recognize that models reflecting only single aspects of AD pathogenesis do not mimic AD. Models or combinations of new models are needed that incorporate genetics with environmental interactions, timing of disease development, heterogeneous mechanisms and pathways, comorbidities, and other pathologies that lead to AD and related dementias. Selection of the best models requires us to address the following: (1) which animal species, strains, and genetic backgrounds are most appropriate; (2) which models permit efficient use throughout the drug development pipeline; (3) the translatability of behavioral-cognitive assays from animals to patients; and (4) how to match potential AD therapeutics with particular models. Best practice guidelines to improve reproducibility also need to be developed for consistent use of these models in different research settings. To enhance translational predictability, we discuss a multi-model evaluation strategy to de-risk the successful transition of pre-clinical drug assets to the clinic.

A Review on Notch Signaling and Colorectal Cancer

Colorectal cancer (CRC) has one of the highest mortality rates despite the advancement of treatment options. Aggressive CRC remains difficult to treat owing to the activation of oncogenic signaling pathways such as the Notch signaling pathway. The role of Notch receptors varies according to the difference in their structures; in particular, aberrant activation of Notch1 has been attributed to the severity of CRC. Notch1 activation in CRC is inhibited by small molecule inhibitors that target γ-secretase, an enzyme responsible for the third and last cleavage step of Notch receptors. γ-Secretase also produces the intracellular domain that finally carries out cellular functions by activating downstream effectors. However, most inhibitors block γ-secretase non-selectively and cause severe toxicity. Plant-source-derived small molecules, monoclonal antibodies, biological molecules (such as SiRNAs), and compounds targeting the Notch1 receptor itself or the downstream molecules such as HES1 are some of the options that are in advanced stages of clinical trials. The Negative Regulatory Region (NRR), which plays a central role in the transduction of Notch1 signaling in the event of ligand-dependent and ligand-independent Notch1 processing is also being targeted specifically by monoclonal antibodies (mAbs) to prevent aberrant Notch1 activation. In this review, we discuss the role of Notch1 in CRC, particularly its metastatic phenotype, and how mutations in Notch1, specifically in its NRR region, contribute to the aberrant activation of Notch1 signaling, which, in turn, contributes to CRC pathogenesis. We also discuss prevailing and emerging therapies that target the Notch1 receptor and the NRR region, and we highlight the potential of these therapies in abrogating Notch signaling and, thus, CRC development and progression.

Identification of SPPL2a Inhibitors by Multiparametric Analysis of a High-Content Ultra-High-Throughput Screen

The intramembrane protease signal peptide peptidase-like 2a (SPPL2a) is a potential drug target for the treatment of autoimmune diseases due to an essential role in B cells and dendritic cells. To screen a library of 1.4 million compounds for inhibitors of SPPL2a, we developed an imaging assay detecting nuclear translocation of the proteolytically released cytosolic substrate fragment. The state-of-the-art hit calling approach based on nuclear translocation resulted in numerous false-positive hits, mainly interrupting intracellular protein trafficking. To filter the false positives, we extracted 340 image-based readouts and developed a novel multiparametric analysis method that successfully triaged the primary hit list. The identified scaffolds were validated by demonstrating activity on endogenous SPPL2a and substrate CD74/p8 in B cells. The multiparametric analysis discovered diverse cellular phenotypes and provided profiles for the whole library. The principle of the presented imaging assay, the screening strategy, and multiparametric analysis are potentially applicable in future screening campaigns.

Gamma secretase inhibitors: a patent review (2013 - 2015)

INTRODUCTION

Gamma secretase (GS) is an intricate and multi-subunits complex, and it can cut various transmembrane proteins. Now it is a therapeutic target for a number of diseases. However, due to some side effects, the clinical development of GSI is not successful. Therefore, searching for effective GSIs has become a key point in drug discovery. Areas covered: This review discusses the structure and function of GS and various types of GSIs. And this article seeks to give an overview of the patents or applications published from 2013 to 2015 in which novel chemical classes are claimed to inhibit the GS. Expert opinion: Firstly, further understanding the structure and function of GS to elucidate the disease mechanism and develop AD therapies is urgent. Secondly, if the bioequivalence, pharmacokinetics and selectivity can be improved greatly, some failed clinical inhibitors still can become the promising compounds for clinical trials. Thirdly, some weaknesses are exposed during the development of GSI, especially the insufficient potency, low brain penetration and poor selectivity. Finally, to find potent and selective GSI is the major direction in future. Moreover, to find new indications and dosing regimens in a trial of GSIs also can be seen as new ways.

Design and synthesis of water soluble β-aminosulfone analogues of SCH 900229 as γ-secretase inhibitors

In this paper we describe our strategy to improve the aqueous solubility of SCH 900229, a potent PS1-selective γ-secretase inhibitor for the treatment of Alzheimer's disease. Incorporation of ionizable amino groups into the side chain terminal generates water soluble β-aminosulfone analogues of SCH 900229 that maintain robust in vitro potency and in vivo efficacy.

Notch inhibitors for cancer treatment

Notch signaling is an evolutionarily conserved cell signaling pathway involved in cell fate during development, stem cell renewal and differentiation in postnatal tissues. Roles for Notch in carcinogenesis, in the biology of cancer stem cells and tumor angiogenesis have been reported. These features identify Notch as a potential therapeutic target in oncology. Based on the molecular structure of Notch receptor, Notch ligands and Notch activators, a set of Notch pathway inhibitors have been developed. Most of these inhibitors had shown anti-tumor effects in preclinical studies. At the same time, the combinatorial effect of these inhibitors with current chemotherapeutical drugs is still under study in different clinical trials. In this review, we describe the basics of Notch signaling and the role of Notch in normal and cancer stem cells as a logic way to develop different Notch inhibitors and their current stage of progress for cancer patient's treatment.

In Vivo Characterization of a Novel γ-Secretase Inhibitor SCH 697466 in Rodents and Investigation of Strategies for Managing Notch-Related Side Effects

Substantial evidence implicates β-amyloid (Aβ) peptides in the etiology of Alzheimer's disease (AD). Aβ is produced by the proteolytic cleavage of the amyloid precursor protein by β- and γ-secretase suggesting that γ-secretase inhibition may provide therapeutic benefit for AD. Although many γ-secretase inhibitors have been shown to be potent at lowering Aβ, some have also been shown to have side effects following repeated administration. All of these side effects can be attributed to altered Notch signaling, another γ-secretase substrate. Here we describe the in vivo characterization of the novel γ-secretase inhibitor SCH 697466 in rodents. Although SCH 697466 was effective at lowering Aβ, Notch-related side effects in the intestine and thymus were observed following subchronic administration at doses that provided sustained and complete lowering of Aβ. However, additional studies revealed that both partial but sustained lowering of Aβand complete but less sustained lowering of Aβ were successful approaches for managing Notch-related side effects. Further, changes in several Notch-related biomarkers paralleled the side effect observations. Taken together, these studies demonstrated that, by carefully varying the extent and duration of Aβ lowering by γ-secretase inhibitors, it is possible to obtain robust and sustained lowering of Aβ without evidence of Notch-related side effects.

Reducing available soluble β-amyloid prevents progression of cerebral amyloid angiopathy in transgenic mice

Cerebral amyloid angiopathy (CAA), the accumulation of β-amyloid (Aβ) in the walls of leptomeningeal and cortical blood vessels of the brain, is a major cause of intracerebral hemorrhage and cognitive impairment and is commonly associated with Alzheimer disease. The progression of CAA, as measured in transgenic mice by longitudinal imaging with multiphoton microscopy, occurs in a predictable linear manner. The dynamics of Aβ deposition in and clearance from vascular walls and their relationship to the concentration of Aβ in the brain are poorly understood. We manipulated Aβ levels in the brain using 2 approaches: peripheral clearance via administration of the amyloid binding "peripheral sink" protein gelsolin and direct inhibition of its formation via administration of LY-411575, a small-molecule γ-secretase inhibitor. We found that gelsolin and LY-411575 both reduced the rate of CAA progression in Tg2576 mice from untreated rates of 0.58% ± 0.15% and 0.52% ± 0.09% to 0.11% ± 0.18% (p = 0.04) and -0.17% ± 0.09% (p < 0.001) of affected vessel per day, respectively, in the absence of an immune response. The progression of CAA was also halted when gelsolin was combined with LY-411575 (-0.004% ± 0.10%, p < 0.003). These data suggest that CAA progression can be prevented with non-immune approaches that may reduce the availability of soluble Aβ but without evidence of substantial amyloid clearance from vessels.

Pharmacodynamics of selective inhibition of γ-secretase by avagacestat

A hallmark of Alzheimer's disease (AD) pathology is the accumulation of brain amyloid β-peptide (Aβ), generated by γ-secretase-mediated cleavage of the amyloid precursor protein (APP). Therefore, γ-secretase inhibitors (GSIs) may lower brain Aβ and offer a potential new approach to treat AD. As γ-secretase also cleaves Notch proteins, GSIs can have undesirable effects due to interference with Notch signaling. Avagacestat (BMS-708163) is a GSI developed for selective inhibition of APP over Notch cleavage. Avagacestat inhibition of APP and Notch cleavage was evaluated in cell culture by measuring levels of Aβ and human Notch proteins. In rats, dogs, and humans, selectivity was evaluated by measuring plasma blood concentrations in relation to effects on cerebrospinal fluid (CSF) Aβ levels and Notch-related toxicities. Measurements of Notch-related toxicity included goblet cell metaplasia in the gut, marginal-zone depletion in the spleen, reductions in B cells, and changes in expression of the Notch-regulated hairy and enhancer of split homolog-1 from blood cells. In rats and dogs, acute administration of avagacestat robustly reduced CSF Aβ40 and Aβ42 levels similarly. Chronic administration in rats and dogs, and 28-day, single- and multiple-ascending-dose administration in healthy human subjects caused similar exposure-dependent reductions in CSF Aβ40. Consistent with the 137-fold selectivity measured in cell culture, we identified doses of avagacestat that reduce CSF Aβ levels without causing Notch-related toxicities. Our results demonstrate the selectivity of avagacestat for APP over Notch cleavage, supporting further evaluation of avagacestat for AD therapy.

Discovery of SCH 900229, a Potent Presenilin 1 Selective γ-Secretase Inhibitor for the Treatment of Alzheimer's Disease

An exploration of the SAR of the side chain of a novel tricyclic series of γ-secretase inhibitors led to the identification of compound (-)-16 (SCH 900229), which is a potent and PS1 selective inhibitor of γ-secretase (Aβ40 IC50 = 1.3 nM). Compound (-)-16 demonstrated excellent lowering of Aβ after oral administration in preclinical animal models and was advanced to human clinical trials for further development as a therapeutic agent for the treatment of Alzheimer's disease.

Treatment strategies targeting amyloid β-protein

With the advent of the key discovery in the mid-1980s that the amyloid β-protein (Aβ) is the core constituent of the amyloid plaque pathology found in Alzheimer disease (AD), an intensive effort has been underway to attempt to mitigate its role in the hope of treating the disease. This effort fully matured when it was clarified that the Aβ is a normal product of cleavage of the amyloid precursor protein, and well-defined proteases for this process were identified. Further therapeutic options have been developed around the concept of anti-Aβ aggregation inhibitors and the surprising finding that immunization with Aβ itself leads to reduction of pathology in animal models of the disease. Here we review the progress in this field toward the goal of targeting Aβ for treatment and prevention of AD and identify some of the major challenges for the future of this area of medicine.

Targeting γ-secretase in breast cancer

γ-secretase complexes are multisubunit protease complexes that perform the intramembrane cleavage of more than 60 type-I transmembrane proteins, including Notch receptors. Since dysregulated Notch signaling has been implicated in the tumorigenesis and progression of breast cancer, small molecule γ-secretase inhibitors (GSIs) are being tested for their therapeutic potential in breast cancer treatment in several clinical trials. Here, the structure of γ-secretase complex and the development of GSIs are briefly reviewed, the roles of Notch and several other γ-secretase substrates in breast cancer are discussed, and the difference between γ-secretase inhibition and Notch inhibition, as well as the side effects associated with GSIs, are described. A better understanding of molecular mechanisms that affect the responsiveness of breast cancer to GSI might help to develop strategies to enhance the antitumor activity and, at the same time, alleviate the side effects of GSI.

γ-Secretase as a target for Alzheimer's disease

γ-Secretase is a protease complex responsible for cutting the transmembrane domain of the amyloid β-protein precursor (APP) to form the amyloid β-protein (Aβ), an aggregation-prone product that accumulates in the brain in Alzheimer's disease. As evidence suggests that Aβ is critical to Alzheimer pathogenesis, γ-secretase is considered a key target for the development of disease-modifying therapeutics. The protease complex cuts many other substrates, and some of these proteolytic events are part of signaling pathways or other important cellular functions. Among these, proteolysis of the Notch receptor is essential for signaling that is involved in a number of cell-fate determinations. Many inhibitors of γ-secretase have been identified, but it is clear that drug candidates for Alzheimer's disease should have minimal effects on the Notch signaling pathway, as serious safety issues have arisen with nonselective inhibitors. Two types of promising candidates that target this protease complex have emerged: the so-called "Notch-sparing" γ-secretase inhibitors, which block cleavage of APP selectively over that of Notch, and γ-secretase modulators, which shift the proportion of Aβ peptides produced in favor of shorter, less aggregation-prone species. The current status and prospects for these two general types of candidates will be discussed.

γ-Secretase inhibitors and modulators for Alzheimer's disease

γ-Secretase is a membrane embedded aspartyl protease complex with presenilin as the catalytic component. Along with β-secretase, this enzyme produces the amyloid β-protein of Alzheimer's disease (AD) from the amyloid β-protein precursor. Because of its key role in the pathogenesis of AD, γ-secretase has been a prime target for drug discovery, and many inhibitors of this protease have been developed. The therapeutic potential of these inhibitors is virtually negated by the fact that γ-secretase is an essential part of the Notch signaling pathway, rendering the compounds unacceptably toxic upon chronic exposure. However, these compounds have served as useful chemical tools for biological investigations. In contrast, γ-secretase modulators continue to be of keen interest as possible AD therapeutics. These modulators either shift amyloid β-protein production to shorter, less pathogenic peptides or inhibit the proteolysis of amyloid β-protein precursor selectively compared to that of Notch. The various chemical types of inhibitors and modulators will be discussed, along with their use as probes for basic biology and their potential as AD therapeutics.

BACE-1 inhibition prevents the γ-secretase inhibitor evoked Aβ rise in human neuroblastoma SH-SY5Y cells

Background

Accumulation of amyloid β-peptide (Aβ) in the plaques is one of the major pathological features in Alzheimer's disease (AD). Sequential cleavage of amyloid precursor protein (APP) by β-site APP cleaving enzyme 1 (BACE-1) and γ-secretase results in the formation of Aβ peptides. Preventing Aβ formation is believed to attenuate AD progression and BACE-1 and γ-secretase are thus attractive targets for AD drug development.

Methods

Combining BACE-1 and γ-secretase inhibition on Aβ secretion from human neuroblastoma SH-SY5Y cells was evaluated in this study. Secreted Aβ40 and Aβ42 levels were measured from SH-SY5Y cells stably transfected with APPwt or APPswe genes. A selective BACE inhibitor and the γ-secretase inhibitor LY450139 (semagacestat) were used to inhibit respective secretase.

Results

LY450139 increased Aβ40 and Aβ42 secretion from SH-SY5Y APPwt cells at low concentrations (by 60% at 3 nM) followed by subsequent inhibition at higher concentrations (IC₅₀ 90 nM). Washout studies showed that the Aβ increase evoked by 3 nM LY450139 was not due to enhanced cleavage following substrate accumulation but rather to activation of Aβ formation. By contrast, LY450139 inhibited Aβ formation from SH-SY5Y APPswe in a monophasic manner (IC₅₀ 18 nM). The BACE inhibitor per se inhibited Aβ secretion from both SH-SY5Y APPwt and SH-SY5Y APPswe cells with IC₅₀s ranging between 7 - 18 nM and also prevented the increased Aβ secretion evoked by 3 nM LY450139. Combining the BACE inhibitor with higher inhibitory concentrations of LY450139 failed to demonstrate any clear additive or synergistic effects.

Conclusion

BACE-1 inhibition attenuates the Aβ increase evoked by LY450139 while not providing any obvious synergistic effects on LY450139-mediated inhibition.

Discovery of a Potent Pyrazolopyridine Series of γ-Secretase Modulators

The synthesis and structure-activity relationship of a novel series of pyrazolopyridines are reported. These compounds represent a new class of γ-secretase modulators that demonstrate good in vitro potency in inhibiting Aβ42 production. Examples with statistically significant in vivo efficacy in reducing the production of rat cerebrospinal fluid Aβ42 were also identified.

Amyloid precursor protein selective gamma-secretase inhibitors for treatment of Alzheimer's disease

INTRODUCTION

Inhibition of gamma-secretase presents a direct target for lowering Aβ production in the brain as a therapy for Alzheimer's disease (AD). However, gamma-secretase is known to process multiple substrates in addition to amyloid precursor protein (APP), most notably Notch, which has limited clinical development of inhibitors targeting this enzyme. It has been postulated that APP substrate selective inhibitors of gamma-secretase would be preferable to non-selective inhibitors from a safety perspective for AD therapy.

METHODS

In vitro assays monitoring inhibitor potencies at APP γ-site cleavage (equivalent to Aβ40), and Notch ε-site cleavage, in conjunction with a single cell assay to simultaneously monitor selectivity for inhibition of Aβ production vs. Notch signaling were developed to discover APP selective gamma-secretase inhibitors. In vivo efficacy for acute reduction of brain Aβ was determined in the PDAPP transgene model of AD, as well as in wild-type FVB strain mice. In vivo selectivity was determined following seven days x twice per day (b.i.d.) treatment with 15 mg/kg/dose to 1,000 mg/kg/dose ELN475516, and monitoring brain Aβ reduction vs. Notch signaling endpoints in periphery.

RESULTS

The APP selective gamma-secretase inhibitors ELN318463 and ELN475516 reported here behave as classic gamma-secretase inhibitors, demonstrate 75- to 120-fold selectivity for inhibiting Aβ production compared with Notch signaling in cells, and displace an active site directed inhibitor at very high concentrations only in the presence of substrate. ELN318463 demonstrated discordant efficacy for reduction of brain Aβ in the PDAPP compared with wild-type FVB, not observed with ELN475516. Improved in vivo safety of ELN475516 was demonstrated in the 7d repeat dose study in wild-type mice, where a 33% reduction of brain Aβ was observed in mice terminated three hours post last dose at the lowest dose of inhibitor tested. No overt in-life or post-mortem indications of systemic toxicity, nor RNA and histological end-points indicative of toxicity attributable to inhibition of Notch signaling were observed at any dose tested.

CONCLUSIONS

The discordant in vivo activity of ELN318463 suggests that the potency of gamma-secretase inhibitors in AD transgenic mice should be corroborated in wild-type mice. The discovery of ELN475516 demonstrates that it is possible to develop APP selective gamma-secretase inhibitors with potential for treatment for AD.

Modulation of gamma-secretase reduces beta-amyloid deposition in a transgenic mouse model of Alzheimer's disease

Alzheimer's disease (AD) is characterized pathologically by the abundance of senile plaques and neurofibrillary tangles in the brain. We synthesized over 1200 novel gamma-secretase modulator (GSM) compounds that reduced Abeta(42) levels without inhibiting epsilon-site cleavage of APP and Notch, the generation of the APP and Notch intracellular domains, respectively. These compounds also reduced Abeta(40) levels while concomitantly elevating levels of Abeta(38) and Abeta(37). Immobilization of a potent GSM onto an agarose matrix quantitatively recovered Pen-2 and to a lesser degree PS-1 NTFs from cellular extracts. Moreover, oral administration (once daily) of another potent GSM to Tg 2576 transgenic AD mice displayed dose-responsive lowering of plasma and brain Abeta(42); chronic daily administration led to significant reductions in both diffuse and neuritic plaques. These effects were observed in the absence of Notch-related changes (e.g., intestinal proliferation of goblet cells), which are commonly associated with repeated exposure to functional gamma-secretase inhibitors (GSIs).

Amyloid-modifying therapies for Alzheimer's disease: therapeutic progress and its implications

Alzheimer's disease (AD) is the most prevalent form of dementia, affecting an estimated 4.8 million people in North America. For the past decade, the amyloid cascade hypothesis has dominated the field of AD research. This theory posits that the deposition of amyloid-beta protein (Abeta) in the brain is the key pathologic event in AD, which induces a series of neuropathological changes that manifest as cognitive decline and eventual dementia. Based on this theory, interventions that reduce Abeta burden in the brain would be expected to alleviate both the neuropathological changes and dementia, which characterize AD. Several diverse pharmacological strategies have been developed to accomplish this. These include inhibiting the formation of Abeta, preventing the aggregation of Abeta into insoluble aggregates, preventing the entry of Abeta into the brain from the periphery and enhancing the clearance of Abeta from the central nervous system. To date, no amyloid-modifying therapy has yet been successful in phase 3 clinical trials; however, several trials are currently underway. This article provides a review of the status of amyloid-modifying therapies and the implications for the amyloid cascade hypothesis.

The Discovery of Pyridone and Pyridazone Heterocycles as γ-Secretase Modulators

A series of novel pyridazone and pyridone compounds as γ-secretase modulators were discovered. Starting from the initial lead, structure-activity relationship studies were carried out in which an internal hydrogen bond was introduced to conformationally fix the side chain, and compounds with improved in vitro Aβ42 inhibition activity and good Aβtotal/Aβ42 selectivity were quickly discovered. Compound 35 displayed very good in vitro activity and excellent selectivity with good in vivo efficacy in both CRND8 mouse and nontransgenic rat models. This compound displayed a good overall profile in terms of rat pharmacokinetics and ancillary profile. No abnormal behavior and side effects were observed in all of the studies.

Pharmacodynamics and pharmacokinetics of the gamma-secretase inhibitor PF-3084014

PF-3084014 [(S)-2-((S)-5,7-difluoro-1,2,3,4-tetrahydronaphthalen-3-ylamino)-N-(1-(2-methyl-1-(neopentylamino)propan-2-yl)-1H-imidazol-4-yl)pentanamide] is a novel gamma-secretase inhibitor that reduces amyloid-beta (Abeta) production with an in vitro IC(50) of 1.2 nM (whole-cell assay) to 6.2 nM (cell-free assay). This compound inhibits Notch-related T- and B-cell maturation in an in vitro thymocyte assay with an EC(50) of 2.1 microM. A single acute dose showed dose-dependent reduction in brain, cerebrospinal fluid (CSF), and plasma Abeta in Tg2576 mice as measured by enzyme-linked immunosorbent assay and immunoprecipitation (IP)/mass spectrometry (MS). Guinea pigs were dosed with PF-3084014 for 5 days via osmotic minipump at 0.03 to 3 mg/kg/day and exhibited dose-dependent reduction in brain, CSF, and plasma Abeta. To further characterize Abeta dynamics in brain, CSF, and plasma in relation to drug exposure and Notch-related toxicities, guinea pigs were dosed with 0.03 to 10 mg/kg PF-3084014, and tissues were collected at regular intervals from 0.75 to 30 h after dose. Brain, CSF, and plasma all exhibited dose-dependent reductions in Abeta, and the magnitude and duration of Abeta lowering exceeded those of the reductions in B-cell endpoints. Other gamma-secretase inhibitors have shown high potency at elevating Abeta in the conditioned media of whole cells and the plasma of multiple animal models and humans. Such potentiation was not observed with PF-3084014. IP/MS analysis, however, revealed dose-dependent increases in Abeta11-40 and Abeta1-43 at doses that potently inhibited Abeta1-40 and Abeta1-42. PF-3084014, like previously described gamma-secretase inhibitors, preferentially reduced Abeta1-40 relative to Abeta1-42. Potency at Abeta relative to Notch-related endpoints in vitro and in vivo suggests that a therapeutic index can be achieved with this compound.

The large hydrophilic loop of presenilin 1 is important for regulating gamma-secretase complex assembly and dictating the amyloid beta peptide (Abeta) Profile without affecting Notch processing

Gamma-secretase is an enzyme complex that mediates both Notch signaling and beta-amyloid precursor protein (APP) processing, resulting in the generation of Notch intracellular domain, APP intracellular domain, and the amyloid beta peptide (Abeta), the latter playing a central role in Alzheimer disease (AD). By a hitherto undefined mechanism, the activity of gamma-secretase gives rise to Abeta peptides of different lengths, where Abeta42 is considered to play a particular role in AD. In this study we have examined the role of the large hydrophilic loop (amino acids 320-374, encoded by exon 10) of presenilin 1 (PS1), the catalytic subunit of gamma-secretase, for gamma-secretase complex formation and activity on Notch and APP processing. Deletion of exon 10 resulted in impaired PS1 endoproteolysis, gamma-secretase complex formation, and had a differential effect on Abeta-peptide production. Although the production of Abeta38, Abeta39, and Abeta40 was severely impaired, the effect on Abeta42 was affected to a lesser extent, implying that the production of the AD-related Abeta42 peptide is separate from the production of the Abeta38, Abeta39, and Abeta40 peptides. Interestingly, formation of the intracellular domains of both APP and Notch was intact, implying a differential cleavage activity between the epsilon/S3 and gamma sites. The most C-terminal amino acids of the hydrophilic loop were important for regulating APP processing. In summary, the large hydrophilic loop of PS1 appears to differentially regulate the relative production of different Abeta peptides without affecting Notch processing, two parameters of significance when considering gamma-secretase as a target for pharmaceutical intervention in AD.

Regulation of breast cancer stem cell activity by signaling through the Notch4 receptor

Notch receptor signaling pathways play an important role not only in normal breast development but also in breast cancer development and progression. We assessed the role of Notch receptors in stem cell activity in breast cancer cell lines and nine primary human tumor samples. Stem cells were enriched by selection of anoikis-resistant cells or cells expressing the membrane phenotype ESA(+)/CD44(+)/CD24(low). Using these breast cancer stem cell populations, we compared the activation status of Notch receptors with the status in luminally differentiated cells, and we evaluated the consequences of pathway inhibition in vitro and in vivo. We found that Notch4 signaling activity was 8-fold higher in stem cell-enriched cell populations compared with differentiated cells, whereas Notch1 signaling activity was 4-fold lower in the stem cell-enriched cell populations. Pharmacologic or genetic inhibition of Notch1 or Notch4 reduced stem cell activity in vitro and reduced tumor formation in vivo, but Notch4 inhibition produced a more robust effect with a complete inhibition of tumor initiation observed. Our findings suggest that Notch4-targeted therapies will be more effective than targeting Notch1 in suppressing breast cancer recurrence, as it is initiated by breast cancer stem cells.

Novel orally active morpholine N-arylsulfonamides gamma-secretase inhibitors with low CYP 3A4 liability

A new class of 2,6-disubstituted morpholine N-arylsulfonamide gamma-secretase inhibitors was designed based on the introduction of a morpholine core in lieu or piperidine in our lead series. This resulted in compounds with improved CYP 3A4 profiles. Several analogs that were active at lowering Abeta levels in Tg CRND8 mice upon oral administration were identified.

BACE and gamma-secretase characterization and their sorting as therapeutic targets to reduce amyloidogenesis

Secretases are named for enzymes processing amyloid precursor protein (APP), a prototypic type-1 membrane protein. This led directly to discovery of novel Aspartyl proteases (beta-secretases or BACE), a tetramer complex gamma-secretase (gamma-SC) containing presenilins, nicastrin, aph-1 and pen-2, and a new role for metalloprotease(s) of the ADAM family as a alpha-secretases. Recent advances in defining pathways that mediate endosomal-lysosomal-autophagic-exosomal trafficking now provide targets for new drugs to attenuate abnormal production of fibril forming products characteristic of AD. A key to success includes not only characterization of relevant secretases but mechanisms for sorting and transport of key metabolites to abnormal vesicles or sites for assembly of fibrils. New developments we highlight include an important role for an 'early recycling endosome' coated in retromer complex containing lipoprotein receptor LRP-II (SorLA) for switching APP to a non-amyloidogenic pathway for alpha-secretases processing, or to shuttle APP to a 'late endosome compartment' to form Abeta or AICD. LRP11 (SorLA) is of particular importance since it decreases in sporadic AD whose etiology otherwise is unknown.

Development of a high-throughput assay for screening of gamma-secretase inhibitor with endogenous human, mouse or Drosophila gamma-secretase

Selective lowering of amyloid-β levels with small-molecule γ-secretase inhibitors is a promising therapeutic approach for Alzheimer’s disease. In this work, we developed a high throughput assay for screening of γ-secretase inhibitors with endogenous γ-secretase and a fluorogenic substrate. The IC₅₀ values of known γ-secretase inhibitors generated with this method were comparable with reported values obtained by other methods. The assay was optimized and applied to a small-scale screening of 1,280 compounds. The discovery of several new inhibitors warrants further investigation. This assay was also proven to be easily adopted to test compounds for drosophila and mouse γ-secretase, which could be very useful to assess compounds activity against γ-secretase from different species before the in vivo test in animal models.

A gamma-secretase inhibitor decreases amyloid-beta production in the central nervous system

OBJECTIVE

Accumulation of amyloid-beta (Abeta) by overproduction or underclearance in the central nervous system (CNS) is hypothesized to be a necessary event in the pathogenesis of Alzheimer's disease. However, previously, there has not been a method to determine drug effects on Abeta production or clearance in the human CNS. The objective of this study was to determine the effects of a gamma-secretase inhibitor on the production of Abeta in the human CNS.

METHODS

We utilized a recently developed method of stable-isotope labeling combined with cerebrospinal fluid sampling to directly measure Abeta production during treatment of a gamma-secretase inhibitor, LY450139. We assessed whether this drug could decrease CNS Abeta production in healthy men (age range, 21-50 years) at single oral doses of 100, 140, or 280mg (n = 5 per group).

RESULTS

LY450139 significantly decreased the production of CNS Abeta in a dose-dependent fashion, with inhibition of Abeta generation of 47, 52, and 84% over a 12-hour period with doses of 100, 140, and 280mg, respectively. There was no difference in Abeta clearance.

INTERPRETATION

Stable isotope labeling of CNS proteins can be utilized to assess the effects of drugs on the production and clearance rates of proteins targeted as potential disease-modifying treatments for Alzheimer's disease and other CNS disorders. Results from this approach can assist in making decisions about drug dosing and frequency in the design of larger and longer clinical trials for diseases such as Alzheimer's disease, and may accelerate effective drug validation. Ann Neurol 2009.

Existing plaques and neuritic abnormalities in APP:PS1 mice are not affected by administration of the gamma-secretase inhibitor LY-411575

The gamma-secretase complex is a major therapeutic target for the prevention and treatment of Alzheimer's disease. Previous studies have shown that treatment of young APP mice with specific inhibitors of gamma-secretase prevented formation of new plaques. It has not yet been shown directly whether existing plaques would be affected by gamma-secretase inhibitor treatment. Similarly, alterations in neuronal morphology in the immediate vicinity of plaques represent a plaque-specific neurotoxic effect. Reversal of these alterations is an important endpoint of successful therapy whether or not a treatment affects plaque size. In the present study we used longitudinal imaging in vivo with multiphoton microscopy to study the effects of the orally active gamma-secretase inhibitor LY-411575 in 10-11 month old APP:PS1 mice with established amyloid pathology and neuritic abnormalities. Neurons expressed YFP allowing fluorescent detection of morphology whereas plaques were labelled with methoxy-XO4. The same identified neurites and plaques were followed in weekly imaging sessions in living mice treated daily (5 mg/kg) for 3 weeks with the compound. Although LY-411575 reduced Abeta levels in plasma and brain, it did not have an effect on the size of existing plaques. There was also no effect on the abnormal neuritic curvature near plaques, or the dystrophies in very close proximity to senile plaques. Our results suggest that therapeutics aimed at inhibition of Abeta generation are less effective for reversal of existing plaques than for prevention of new plaque formation and have no effect on the plaque-mediated neuritic abnormalities, at least under these conditions where Abeta production is suppressed but not completely blocked. Therefore, a combination therapy of Abeta suppression with agents that increase clearance of amyloid and/or prevent neurotoxicity might be needed for a more effective treatment in patients with pre-existing pathology.

gamma-Secretase inhibitor reduces diet-induced atherosclerosis in apolipoprotein E-deficient mice

Atherosclerosis is a chronic inflammatory disease resulting from interactions between lipids, macrophages and arterial wall cells. The Notch signaling pathway is involved in the activation of macrophages in atherosclerotic lesions. This study examined whether pharmacological inhibition of Notch signaling using a gamma-secretase inhibitor (GSI) can reduce atherosclerotic lesion formation. Notch-related molecules were significantly increased in aortas from apolipoprotein E-deficient (ApoE(-/-)) mice. In particular, macrophages in the plaques showed strong expression of Notch1 and a downstream transcriptional factor, Hes-1. A GSI (LY411,575, 0.2, and 1.0mg/kg/day) or vehicle control was then administered to ApoE(-/-) mice fed Western diet for 8 weeks before measuring the expression of Notch-related molecules. Systemic administration of GSI suppressed Notch signaling in vivo and reduced total plaque areas and fatty streak content in the aortic sinus in a dose-dependent manner without serious adverse effects. The GSI also suppressed the migratory activity of macrophages and reduced the expression of intercellular adhesion molecule-1, resulting in significantly decreased macrophage infiltration in the atherosclerotic plaques. These results provided new insight into the anti-atherogenic properties of GSI in Apo E(-/-) mice fed Western diet.

Committed neuronal precursors confer astrocytic potential on residual neural precursor cells

During midgestation, mammalian neural precursor cells (NPCs) differentiate only into neurons. Generation of astrocytes is prevented at this stage, because astrocyte-specific gene promoters are methylated. How the subsequent switch from suppression to expression of astrocytic genes occurs is unknown. We show in this study that Notch ligands are expressed on committed neuronal precursors and young neurons in mid-gestational telencephalon, and that neighboring Notch-activated NPCs acquire the potential to become astrocytes. Activation of the Notch signaling pathway in midgestational NPCs induces expression of the transcription factor nuclear factor I, which binds to astrocytic gene promoters, resulting in demethylation of astrocyte-specific genes. These findings provide a mechanistic explanation for why neurons come first: committed neuronal precursors and young neurons potentiate remaining NPCs to differentiate into the next cell lineage, astrocytes.

Novel molecular and cellular therapeutic targets in acute lymphoblastic leukemia and lymphoproliferative disease

While the outcome for pediatric patients with lymphoproliferative disorders (LPD) or lymphoid malignancies, such as acute lymphoblastic leukemia (ALL), has improved dramatically, patients often suffer from therapeutic sequelae. Additionally, despite intensified treatment, the prognosis remains dismal for patients with refractory or relapsed disease. Thus, novel biologically targeted treatment approaches are needed. These targets can be identified by understanding how a loss of lymphocyte homeostasis can result in LPD or ALL. Herein, we review potential molecular and cellular therapeutic strategies that (i) target key signaling networks (e.g., PI3K/AKT/mTOR, JAK/STAT, Notch1, and SRC kinase family-containing pathways) which regulate lymphocyte growth, survival, and function; (ii) block the interaction of ALL cells with stromal cells or lymphoid growth factors secreted by the bone marrow microenvironment; or (iii) stimulate innate and adaptive immune responses.