Gamma Secretase Inhibitors in Cancer: A Current Perspective on Clinical Performance

Gamma secretase inhibitors (GSIs), initially developed as Alzheimer''s therapies, have been repurposed as anticancer agents given their inhibition of Notch receptor cleavage. The success of GSIs in preclinical models has been ascribed to induction of cancer stem‐like cell differentiation and apoptosis, while also impairing epithelial‐to‐mesenchymal transition and sensitizing cells to traditional chemoradiotherapies. The promise of these agents has yet to be realized in the clinic, however, as GSIs have failed to demonstrate clinical benefit in most solid tumors with the notable exceptions of CNS malignancies and desmoid tumors. Disappointing clinical performance to date reflects important questions that remain to be answered. For example, what is the net impact of these agents on antitumor immune responses, and will they require concurrent targeting of tumor‐intrinsic compensatory pathways? Addressing these limitations in our current understanding of GSI mechanisms will undoubtedly facilitate their rational incorporation into combinatorial strategies and provide a valuable tool with which to combat Notch‐dependent cancers. In the present review, we provide a current understanding of GSI mechanisms, discuss clinical performance to date, and suggest areas for future investigation that might maximize the utility of these agents.Implications for PracticeThe performance of gamma secretase inhibitors (GSIs) in clinical trials generally has not reflected their encouraging performance in preclinical studies. This review provides a current perspective on the clinical performance of GSIs across various solid tumor types alongside putative mechanisms of antitumor activity. Through exploration of outstanding gaps in knowledge as well as reasons for success in certain cancer types, the authors identify areas for future investigation that will likely enable incorporation of GSIs into rational combinatorial strategies for superior tumor control and patient outcomes.     

Critical role of notch signaling in osteosarcoma invasion and metastasis.

PURPOSE: Notch signaling is an important mediator of growth and survival in several cancer types, with Notch pathway genes functioning as oncogenes or tumor suppressors in different cancers. However, the role of Notch in osteosarcoma is unknown. EXPERIMENTAL DESIGN: We assessed the expression of Notch pathway genes in human osteosarcoma cell lines and patient samples. We then used pharmacologic and retroviral manipulation of the Notch pathway and studied the effect on osteosarcoma cell proliferation, survival, anchorage-independent growth, invasion, and metastasis in vitro and in vivo. RESULTS: Notch pathway genes, including Notch ligand DLL1, Notch1 and Notch2, and the Notch target gene HES1, were expressed in osteosarcoma cells, and expression of HES1 was associated with invasive and metastatic potential. Blockade of Notch pathway signaling with a small molecule inhibitor of gamma secretase eliminated invasion in Matrigel without affecting cell proliferation, survival, or anchorage-independent growth. Manipulation of Notch and HES1 signaling showed a crucial role for HES1 in osteosarcoma invasiveness and metastasis in vivo. CONCLUSION: These studies identify a new invasion and metastasis-regulating pathway in osteosarcoma and define a novel function for the Notch pathway: regulation of metastasis. Because the Notch pathway can be inhibited pharmacologically, these findings point toward possible new treatments to reduce invasion and metastasis in osteosarcoma.     

姜黄素调控Notch信号通路对肺癌干细胞增殖及凋亡的影响

目的:研究姜黄素对肺癌干细胞增殖及凋亡的影响。方法:利用免疫磁珠标记肺癌表面标记物乙醛脱氢酶1(ALDH1)，从肺癌A549细胞系中分离肺癌干细胞；MTT实验检测姜黄素对肺癌干细胞增殖的影响；流式细胞仪检测姜黄素对肺癌干细胞凋亡的影响；Western blot检测Notch1和Hes1蛋白的表达情况；抑制剂γ-分泌酶抑制Notch信号通路研究对肺癌干细胞增殖及凋亡的影响。结果:利用免疫磁珠分选法分选出肺癌细胞系A549中ALDH1+肺癌干细胞。MTT检测结果显示，姜黄素能够呈浓度依赖性的抑制肺癌干细胞的增殖；经姜黄素处理后的肺癌干细胞，与对照组相比，凋亡率明显升高，Notch1和Hes1蛋白的表达明显下降。经γ-分泌酶抑制剂处理肺癌干细胞后，实验结果显示，γ-分泌酶抑制剂通过下调Notch1和Hes1蛋白的表达调控Notch信号通路抑制肺癌干细胞的增殖，诱导其凋亡。结论:姜黄素抑制肺癌干细胞的增殖，诱导其凋亡与Notch信号通路有关。     

Alterations in cellular metabolome after pharmacological inhibition of Notch in glioblastoma cells

Notch signaling can promote tumorigenesis in the nervous system and plays important roles in stem‐like cancer cells. However, little is known about how Notch inhibition might alter tumor metabolism, particularly in lesions arising in the brain. The gamma‐secretase inhibitor MRK003 was used to treat glioblastoma neurospheres, and they were subdivided into sensitive and insensitive groups in terms of canonical Notch target response. Global metabolomes were then examined using proton magnetic resonance spectroscopy, and changes in intracellular concentration of various metabolites identified which correlate with Notch inhibition. Reductions in glutamate were verified by oxidation‐based colorimetric assays. Interestingly, the alkylating chemotherapeutic agent temozolomide, the mTOR‐inhibitor MLN0128, and the WNT inhibitor LGK974 did not reduce glutamate levels, suggesting that changes to this metabolite might reflect specific downstream effects of Notch blockade in gliomas rather than general sequelae of tumor growth inhibition. Global and targeted expression analyses revealed that multiple genes important in glutamate homeostasis, including glutaminase, are dysregulated after Notch inhibition. Treatment with an allosteric inhibitor of glutaminase, compound 968, could slow glioblastoma growth, and Notch inhibition may act at least in part by regulating glutaminase and glutamate.     

Gamma-secretase inhibitors target tumor-initiating cells in a mouse model of ERBB2 breast cancer

Human breast tumors comprise a minor sub-population of tumor-initiating cells (TICs), commonly termed cancer stem cells. TICs are thought to sustain tumor growth and to confer resistance to current anticancer therapies. Hence, targeting TIC may be essential to achieving durable cancer cures. To identify molecular targets in breast TIC, we employed a transgenic mouse model of ERBB2 breast cancer; tumors arising in this model comprise a very high frequency of TIC, which is maintained in tumor cell populations propagated in vitro as non-adherent tumorspheres. The Notch pathway is dysregulated in human breast tumors and overexpression of constitutively active Notch proteins induces mammary tumors in mice. The Notch pathway has also been implicated in stem cell processes including those of mammary epithelial stem cells. Hence, we investigated the potential that the Notch pathway is required for TIC activity. We found that an antagonist of Notch signaling, a gamma (γ)-secretase inhibitor termed MRK-003, inhibited the survival of tumorsphere-derived cells in vitro and eliminated TIC as assessed by cell transplantation into syngeneic mice. Whereas MRK-003 also inhibited the self-renewal and/or proliferation of mammosphere-resident cells, this effect of the inhibitor was reversible thus suggesting that it did not compromise the survival of these cells. MRK-003 administration to tumor-bearing mice eliminated tumor-resident TIC and resulted in rapid and durable tumor regression. MRK-003 inhibited the proliferation of tumor cells, and induced their apoptosis and differentiation. These findings suggest that MRK-003 targets breast TIC and illustrate that eradicating these cells in breast tumors ensures long-term, recurrence-free survival.     

Inhibition of Tumor Angiogenesis and Tumor Growth by the DSL Domain of Human Delta-Like 1 Targeted to Vascular Endothelial Cells

The growth of solid tumors depends on neovascularization. Several therapies targeting tumor angiogenesis have been developed. However, poor response in some tumors and emerging resistance necessitate further investigations of new drug targets. Notch signal pathway plays a pivotal role in vascular development and tumor angiogenesis. Either blockade or forced activation of this pathway can inhibit angiogenesis. As blocking Notch pathway results in the formation of vascular neoplasm, activation of Notch pathway to prevent tumor angiogenesis might be an alternative choice. However, an in vivo deliverable reagent with highly efficient Notch-activating capacity has not been developed. Here, we generated a polypeptide, hD1R, which consists of the Delta-Serrate-Lag-2 fragment of the human Notch ligand Delta-like 1 and an arginine-glycine-aspartate (RGD) motif targeting endothelial cells (ECs). We showed that hD1R could bind to ECs specifically through its RGD motif and effectively triggered Notch signaling in ECs. We demonstrated both in vitro and in vivo that hD1R inhibited angiogenic sprouting and EC proliferation. In tumor-bearing mice, the injection of hD1R effectively repressed tumor growth, most likely through increasing tumor hypoxia and tissue necrosis. The amount and width of vessels reduced remarkably in tumors of mice treated with hD1R. Moreover, vessels in tumors of mice treated with hD1R recruited more NG2⁺ perivascular cells and were better perfused. Combined application of hD1R and chemotherapy with cisplatin and teniposide revealed that these two treatments had additive antitumor effects. Our study provided a new strategy for antiangiogenic tumor therapy.     

Long-term results with radiation therapy for pediatric desmoid tumors

Purpose: To retrospectively review the treatment and outcome of pediatric patients with desmoid tumor who received radiation therapy at a single institution.

Materials and Methods: Thirteen pediatric patients received radiation therapy for desmoid tumor at St. Jude Children’s Research Hospital between 1962 and 1998. Only 2 of the patients reviewed received treatment prior to 1976. The median dose of external beam irradiation was 50 Gy.

Results: At the time of this report, 10 of 13 patients have had tumors that recurred after radiation therapy and 3 have died from their disease. One additional patient was harboring a recurrence, and 1 had not been followed long enough to suggest that the patient had achieved disease control. One patient remained locally controlled after radiation therapy with long-term follow-up (196 months). The median time to recurrence following radiation therapy was 19 months (range, 3–135 months). Eight of the 13 patients suffered substantial tumor and treatment-related morbidity.

Conclusions: Desmoid tumors in pediatric patients are locally aggressive tumors that are likely to recur after radiation therapy. Alternatives to radiation therapy should be sought for the treatment of these tumors, and efforts should focus on low-morbidity therapies aimed at inhibiting the growth of these unique tumors.     

WNT signaling enhances breast cancer cell motility and blockade of the WNT pathway by sFRP1 suppresses MDA-MB-231 xenograft growth

Introduction  

In breast cancer, deregulation of the WNT signaling pathway occurs by autocrine mechanisms. WNT ligands and Frizzled receptors are coexpressed in primary breast tumors and cancer cell lines. Moreover, many breast tumors show hypermethylation of the secreted Frizzled-related protein 1 (sFRP1) promoter region, causing low expression of this WNT antagonist. We have previously shown that the WNT pathway influences proliferation of breast cancer cell lines via activation of canonical signaling and epidermal growth factor receptor transactivation, and that interference with WNT signaling reduces proliferation. Here we examine the role of WNT signaling in breast tumor cell migration and on xenograft outgrowth.     

High-grade soft tissue sarcoma arising in a desmoid tumor: case report and review of the literature

Desmoid tumors are rare benign monoclonal fibroblastic tumors. Their aggressiveness is local with no potential for metastasis or dedifferentiation. Here we report on a 61-year-old patient who presented a locally advanced breast desmoid tumor diagnosed 20 years after post-operative radiotherapy for breast carcinoma. After 2 years of medical treatment, a high-grade undifferentiated pleomorphic soft tissue sarcoma arose within the desmoid tumor. Despite extensive surgery removing both tumors, the patient showed locoregional relapse by the sarcoma, followed by multimetastatic progression, then death 25 months after the surgery. The arising of a soft tissue sarcoma in a desmoid tumor is an exceptional event since our case is the fourth one reported so far in literature. It reinforces the need for timely and accurate diagnosis when a new mass develops in the region of a preexisting desmoid tumor, and more generally when a desmoid tumor modifies its clinical or radiological aspect.     

Autocrine WNT signaling contributes to breast cancer cell proliferation via the canonical WNT pathway and EGFR transactivation

Background  

De-regulation of the wingless and integration site growth factor (WNT) signaling pathway via mutations in APC and Axin, proteins that target β-catenin for destruction, have been linked to various types of human cancer. These genetic alterations rarely, if ever, are observed in breast tumors. However, various lines of evidence suggest that WNT signaling may also be de-regulated in breast cancer. Most breast tumors show hypermethylation of the promoter region of secreted Frizzled-related protein 1 (sFRP1), a negative WNT pathway regulator, leading to downregulation of its expression. As a consequence, WNT signaling is enhanced and may contribute to proliferation of human breast tumor cells. We previously demonstrated that, in addition to the canonical WNT/β-catenin pathway, WNT signaling activates the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway in mouse mammary epithelial cells via epidermal growth factor receptor (EGFR) transactivation.     

Therapeutic potential of replication-selective oncolytic adenoviruses on cells from familial and sporadic desmoid tumors

PURPOSE: Constitutive activation of the Wnt signaling pathway is a hallmark of many cancers and has been associated with familial and sporadic desmoid tumors. The aim of the present study is to assess the therapeutic potential of oncolytic adenoviruses selectively replicating in cells in which the Wnt signaling pathway is active on primary cells from desmoid tumors. EXPERIMENTAL DESIGN: Primary cells extracted from familial (n = 3) or sporadic (n = 3) desmoid tumors were cultured short term. Cancer cell survival and viral replication were measured in vitro upon infection with two different oncolytic adenoviruses targeting a constitutive activation of the Wnt signaling pathway. Adenoviral infectivity was also assessed. RESULTS: Although cells extracted from one sporadic desmoid tumor responded very well to the oncolytic action of the adenoviruses (<20% of viable cells upon infection at a multiplicity of infection of 10), cells from two tumor samples were totally resistant to the viral action. Cells from the remaining samples showed intermediate sensitivity to the oncolytic viruses. These effects were correlated to the level of infectivity of the cells. Finally, in responder cells, evidences of viral replication was observed. CONCLUSIONS: Our experimental data suggest that the response of desmoid tumor cells to oncolytic adenovirus is neither correlated to the type of mutation activating the Wnt signaling pathway nor to the familial or sporadic nature of the tumor. In addition, they highlight the variability of infectivity of individual tumors and predict a great variability in the response to oncolytic adenoviruses.     

Notch1-Snail1-E-cadherin pathway in metastatic hepatocellular carcinoma

Notch signaling, a critical pathway for tissue development, also contributes to tumorigenesis in many cancers, but its pathological function in liver cancer is not well defined. In our study, Notch1 expression and its clinicopathological parameters were evaluated in 82 human hepatocellular carcinoma (HCC) patients. Plasmid-based siNotch1 shRNA was transiently or stably transfected into metastatic HCC cells and subsequently evaluated for the effects on orthotopic liver tumor metastasis in a mouse model as well as the effects on downstream pathways. Aberrant high expression of Notch1 was significantly associated with metastatic disease parameters in HCC patients, such as tumor-node-metastasis Stages III-IV and tumor venous invasion. Knocking-down Notch1 reduced cell motility in vitro and orthotopic tumor metastasis from the liver to the lung in vivo in a mouse model. In metastatic HCC cells, abnormal expression of Notch1 was associated with increased expression of Snail1 and repressed expression of E-cadherin; the Notch1-Snail1-E-cadherin association can also be found in HCC patient tumors. Inhibition of Notch1 by shRNA abolished Snail1 expression, which further resulted in the re-establishment of repressed E-cadherin in metastatic HCC cells. Thus, abnormal Notch1 expression was strongly associated with HCC metastatic disease, which might be mediated through the Notch1-Snail1-E-cadherin pathway. Knock-down of Notch1 reversed HCC tumor metastasis in a mouse model. Therefore, these data suggest that effective targeting of Notch signaling might also inhibit tumor metastasis.     

Role of Notch signaling in cell-fate determination of human mammary stem/progenitor cells

Introduction

Notch signaling has been implicated in the regulation of cell-fate decisions such as self-renewal of adult stem cells and differentiation of progenitor cells along a particular lineage. Moreover, depending on the cellular and developmental context, the Notch pathway acts as a regulator of cell survival and cell proliferation. Abnormal expression of Notch receptors has been found in different types of epithelial metaplastic lesions and neoplastic lesions, suggesting that Notch may act as a proto-oncogene. The vertebrate Notch1 and Notch4 homologs are involved in normal development of the mammary gland, and mutated forms of these genes are associated with development of mouse mammary tumors.

Methods

In order to determine the role of Notch signaling in mammary cell-fate determination, we have utilized a newly described in vitro system in which mammary stem/progenitor cells can be cultured in suspension as nonadherent 'mammospheres'. Notch signaling was activated using exogenous ligands, or was inhibited using previously characterized Notch signaling antagonists.

Results

Utilizing this system, we demonstrate that Notch signaling can act on mammary stem cells to promote self-renewal and on early progenitor cells to promote their proliferation, as demonstrated by a 10-fold increase in secondary mammosphere formation upon addition of a Notch-activating DSL peptide. In addition to acting on stem cells, Notch signaling is also able to act on multipotent progenitor cells, facilitating myoepithelial lineage-specific commitment and proliferation. Stimulation of this pathway also promotes branching morphogenesis in three-dimensional Matrigel cultures. These effects are completely inhibited by a Notch4 blocking antibody or a gamma secretase inhibitor that blocks Notch processing. In contrast to the effects of Notch signaling on mammary stem/progenitor cells, modulation of this pathway has no discernable effect on fully committed, differentiated, mammary epithelial cells.

Conclusion

These studies suggest that Notch signaling plays a critical role in normal human mammary development by acting on both stem cells and progenitor cells, affecting self-renewal and lineage-specific differentiation. Based on these findings we propose that abnormal Notch signaling may contribute to mammary carcinogenesis by deregulating the self-renewal of normal mammary stem cells.