Inhibition of HER2 Increases JAGGED1-dependent Breast Cancer Stem Cells: Role for Membrane JAGGED1

ErbB2-NOTCH1 axis controls autophagy in cardiac cells

Although the epidermal growth factor receptor 2 (ErbB2) and Notch1 signaling pathways have both significant roles in regulating cardiac biology, their interplay in the heart remains poorly investigated. Here, we present evidence of a crosstalk between ErbB2 and Notch1 in cardiac cells, with effects on autophagy and proliferation. Overexpression of ErbB2 in H9c2 cardiomyoblasts induced Notch1 activation in a post-transcriptional, p38-dependent manner, while ErbB2 inhibition with the specific inhibitor, lapatinib, reduced Notch1 activation. Moreover, incubation of H9c2 cells with lapatinib resulted in stalled autophagic flux and decreased proliferation, consistent with the established cardiotoxicity of this and other ErbB2-targeting drugs. Confirming the findings in H9c2 cells, exposure of primary neonatal mouse cardiomyocytes to exogenous neuregulin-1, which engages ErbB2, stimulated proliferation, and this effect was abrogated by concomitant inhibition of the enzyme responsible for Notch1 activation. Furthermore, the hearts of transgenic mice specifically overexpressing ErbB2 in cardiomyocytes had increased levels of active Notch1 and of Notch-related genes. These data expand the knowledge of ErbB2 and Notch1 functions in the heart and may allow better understanding the mechanisms of the cardiotoxicity of ErbB2-targeting cancer treatments.

The ubiquitin-proteasome system in the regulation of tumor dormancy and recurrence

Tumor recurrence is a mechanism triggered in sparse populations of cancer cells that usually remain in a quiescent state after strict stress and/or therapeutic factors, which is affected by a variety of autocrine and microenvironmental cues. Despite thorough investigations, the biology of dormant and/or cancer stem cells is still not fully elucidated, as for the mechanisms of their reawakening, while only the major molecular patterns driving the relapse process have been identified to date. These molecular patterns profoundly interfere with the elements of cellular proteostasis systems that support the efficiency of the recurrence process. As a major proteostasis machinery, we review the role of the ubiquitin-proteasome system (UPS) in tumor cell dormancy and reawakening, devoting particular attention to the functions of its components, E3 ligases, deubiquitinating enzymes and proteasomes in cancer recurrence. We demonstrate how UPS components functionally or mechanistically interact with the pivotal proteins implicated in the recurrence program and reveal that modulators of the UPS hold promise to become an efficient adjuvant therapy for eradicating refractory tumor cells to impede tumor relapse.

Inhibition of γ-secretase/Notch pathway as a potential therapy for reversing cancer drug resistance

The mechanism of tumor drug resistance is complex and may involve stem cell maintenance, epithelial-mesenchymal transition, the activation of survival signaling pathways, transporter protein expression, and tumor microenvironment remodeling, all of which are linked to γ-secretase/Notch signaling. Increasing evidence has shown that the activation of the γ-secretase/Notch pathway is a key driver of cancer progression and drug resistance development and that γ-secretase inhibitors (GSIs) may be the most promising agents for reversing chemotherapy resistance of tumors by targeting the γ-secretase/Notch pathway. Here, we systematically summarize the roles in supporting γ-secretase/Notch activation-associated transformation of cancer cells into cancer stem cells, promotion of the EMT process, PI3K/Akt, MEK/ERK and NF-κB activation, enhancement of ABC transporter protein expression, and TME alteration in mediating tumor drug resistance. Subsequently, we analyze the mechanism of GSIs targeting the γ-secretase/Notch pathway to reverse tumor drug resistance and propose the outstanding advantages of GSIs in treating breast cancer drug resistance over other tumors. Finally, we emphasize that the development of GSIs for reversing tumor drug resistance is promising.

Emerging insights into mechanisms of trastuzumab resistance in HER2-positive cancers

HER2 is an established therapeutic target in breast, gastric, and gastroesophageal junction carcinomas with HER2 overexpression or genomic alterations. The humanized monoclonal antibody trastuzumab targeting HER2 has substantially improved the clinical outcomes of HER2-positive patients, yet the inevitable intrinsic or acquired resistance to trastuzumab limits its clinical benefit, necessitating the elucidation of resistance mechanisms to develop alternate therapeutic strategies. This review presents an overview of trastuzumab resistance mechanisms involving signaling pathways, cellular metabolism, cell plasticity, and tumor microenvironment, particularly discussing the prospects of developing rational combinations to improve patient outcomes.

Pyrroline-5-Carboxylate Reductase-2 Promotes Colorectal Carcinogenesis by Modulating Microtubule-Associated Serine/Threonine Kinase-like/Wnt/β-Catenin Signaling

BACKGROUND

Despite significant progress in clinical management, colorectal cancer (CRC) remains the third most common cause of cancer-related deaths. A positive association between PYCR2 (pyrroline-5-carboxylate reductase-2), a terminal enzyme of proline metabolism, and CRC aggressiveness was recently reported. However, how PYCR2 promotes colon carcinogenesis remains ill understood.

METHODS

A comprehensive analysis was performed using publicly available cancer databases and CRC patient cohorts. Proteomics and biochemical evaluations were performed along with genetic manipulations and in vivo tumor growth assays to gain a mechanistic understanding.

RESULTS

PYCR2 expression was significantly upregulated in CRC and associated with poor patient survival, specifically among PYCR isoforms (PYCR1, 2, and 3). The genetic inhibition of PYCR2 inhibited the tumorigenic abilities of CRC cells and in vivo tumor growth. Coinciding with these observations was a significant decrease in cellular proline content. PYCR2 overexpression promoted the tumorigenic abilities of CRC cells. Proteomics (LC-MS/MS) analysis further demonstrated that PYCR2 loss of expression in CRC cells inhibits survival and cell cycle pathways. A subsequent biochemical analysis supported the causal role of PYCR2 in regulating CRC cell survival and the cell cycle, potentially by regulating the expression of MASTL, a cell-cycle-regulating protein upregulated in CRC. Further studies revealed that PYCR2 regulates Wnt/β-catenin-signaling in manners dependent on the expression of MASTL and the cancer stem cell niche.

CONCLUSIONS

PYCR2 promotes MASTL/Wnt/β-catenin signaling that, in turn, promotes cancer stem cell populations and, thus, colon carcinogenesis. Taken together, our data highlight the significance of PYCR2 as a novel therapeutic target for effectively treating aggressive colon cancer.

Autophagy, molecular chaperones, and unfolded protein response as promoters of tumor recurrence

Tumor recurrence is a paradoxical function of a machinery, whereby a small proportion of the cancer cell population enters a resistant, dormant state, persists long-term in this condition, and then transitions to proliferation. The dormant phenotype is typical of cancer stem cells, tumor-initiating cells, disseminated tumor cells, and drug-tolerant persisters, which all demonstrate similar or even equivalent properties. Cancer cell dormancy and its conversion to repopulation are regulated by several protein signaling systems that inhibit or induce cell proliferation and provide optimal interrelations between cancer cells and their special niche; these systems act in close connection with tumor microenvironment and immune response mechanisms. During dormancy and reawakening periods, cell proteostasis machineries, autophagy, molecular chaperones, and the unfolded protein response are recruited to protect refractory tumor cells from a wide variety of stressors and therapeutic insults. Proteostasis mechanisms functionally or even physically interfere with the main regulators of tumor relapse, and the significance of these interactions and implications in the tumor recurrence phases are discussed in this review.

Epigenetic regulation of Neuregulin 1 promotes breast cancer progression associated to hyperglycemia

Hyperglycemia is a risk factor for breast cancer-related morbidity and mortality. Hyperglycemia induces Neuregulin 1 (Nrg1) overexpression in breast cancer, which subsequently promotes tumor progression. However, molecular mechanisms underlying hyperglycemia-induced Nrg1 overexpression remain poorly understood. Here, we show that hyperglycemia causes active histone modifications at the Nrg1 enhancer, forming enhanceosome complexes where recombination signal binding protein for immunoglobulin kappa J region (RBPJ), E1A binding protein p300 (P300), and SET domain containing 1 A (SETD1A) are recruited to upregulate Nrg1 expression. Deletions in RBPJ-binding sites causes hyperglycemia-controlled Nrg1 levels to be downregulated, resulting in decreased tumor growth in vitro and in vivo. Mice with modest-temporary hyperglycemia, induced by low-dose short-exposure streptozotocin, display accelerated tumor growth and lapatinib resistance, whereas combining lapatinib with N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S42 phenylglycine t-butyl ester (DAPT) ameliorates tumor growth under these modest hyperglycemic conditions by inhibiting NOTCH and EGFR superfamilies. NOTCH activity is correlated with NRG1 levels, and high NRG1 levels predicts poor outcomes, particularly in HER2-positive breast cancer patients. Our findings highlight the hyperglycemia-linked epigenetic modulation of NRG1 as a potential therapeutic strategy for treating breast cancer patients with diabetes.

Trastuzumab resistance in HER2-positive breast cancer: Mechanisms, emerging biomarkers and targeting agents

Trastuzumab is a standard molecular targeted therapy for human epidermal growth factor receptor 2(HER2) -positive breast cancer, which can significantly improve the survival of patients with this molecular subtype of breast cancer. However, the clinical problem of onset or secondary resistance to trastuzumab has limited its efficacy. Therefore, it is very important to explore the mechanism of trastuzumab resistance and formulate countermeasures. Our study described the underlying molecular mechanism of trastuzumab resistance including ERBB2 mutations and nuclear localization, transcriptional and post-translational alterations of ERBB2, over-activation of bypass signaling pathways activation and so on. Then summarize the potential emerging predicting biomarkers and therapeutic strategies for trastuzumab resistance, in order to provide research direction for reversing trastuzumab resistance.

Fate decisions of breast cancer stem cells in cancer progression

Breast cancer has a marked recurrence and metastatic trait and is one of the most prevalent malignancies affecting women’s health worldwide. Tumor initiation and progression begin after the cell goes from a quiescent to an activated state and requires different mechanisms to act in concert to regulate t a specific set of spectral genes for expression. Cancer stem cells (CSCs) have been proven to initiate and drive tumorigenesis due to their capability of self-renew and differentiate. In addition, CSCs are believed to be capable of causing resistance to anti-tumor drugs, recurrence and metastasis. Therefore, exploring the origin, regulatory mechanisms and ultimate fate decision of CSCs in breast cancer outcomes has far-reaching clinical implications for the development of breast cancer stem cell (BCSC)-targeted therapeutic strategies. In this review, we will highlight the contribution of BCSCs to breast cancer and explore the internal and external factors that regulate the fate of BCSCs.

Notch Signaling in Breast Tumor Microenvironment as Mediator of Drug Resistance

Notch signaling dysregulation encourages breast cancer progression through different mechanisms such as stem cell maintenance, cell proliferation and migration/invasion. Furthermore, Notch is a crucial driver regulating juxtracrine and paracrine communications between tumor and stroma. The complex interplay between the abnormal Notch pathway orchestrating the activation of other signals and cellular heterogeneity contribute towards remodeling of the tumor microenvironment. These changes, together with tumor evolution and treatment pressure, drive breast cancer drug resistance. Preclinical studies have shown that targeting the Notch pathway can prevent or reverse resistance, reducing or eliminating breast cancer stem cells. In the present review, we will summarize the current scientific evidence that highlights the involvement of Notch activation within the breast tumor microenvironment, angiogenesis, extracellular matrix remodeling, and tumor/stroma/immune system interplay and its involvement in mechanisms of therapy resistance.

Notch signaling in female cancers: a multifaceted node to overcome drug resistance

Drug resistance is one of the main challenges in cancer therapy, including in the treatment of female-specific malignancies, which account for more than 60% of cancer cases among women. Therefore, elucidating the underlying molecular mechanisms is an urgent need in gynecological cancers to foster novel therapeutic approaches. Notably, Notch signaling, including either receptors or ligands, has emerged as a promising candidate given its multifaceted role in almost all of the hallmarks of cancer. Concerning the connection between Notch pathway and drug resistance in the afore-mentioned tumor contexts, several studies focused on the Notch-dependent regulation of the cancer stem cell (CSC) subpopulation or the induction of the epithelial-to-mesenchymal transition (EMT), both features implicated in either intrinsic or acquired resistance. Indeed, the present review provides an up-to-date overview of the published results on Notch signaling and EMT- or CSC-driven drug resistance. Moreover, other drug resistance-related mechanisms are examined such as the involvement of the Notch pathway in drug efflux and tumor microenvironment. Collectively, there is a long way to go before every facet will be fully understood; nevertheless, some small pieces are falling neatly into place. Overall, the main aim of this review is to provide strong evidence in support of Notch signaling inhibition as an effective strategy to evade or reverse resistance in female-specific cancers.

Anti-Jagged-1 immunotherapy in cancer

Notch signaling is a highly conserved pathway and it plays an essential role in regulating cellular proliferation, differentiation, and apoptosis. The human Notch family includes four receptors, Notch 1-4, and five ligands, delta-like ligand 1 (DLL1), delta-like ligand 3 (DLL3), delta-like ligand 4 (DLL4), Jagged-1 (JAG1), and Jagged-2 (JAG2). It is widely known, that Notch signaling components are often mutated and have deregulated expression in many types of cancer and other diseases. Thus, various therapeutic approaches targeting receptors and ligands of the Notch pathway are being investigated. Human JAG1 is closely related to tumor biology among the Notch ligands, and recent studies have shown potential for monoclonal antibodies targeting JAG1 in cancer therapy. Therefore, this review focuses on current reports on the significance of JAG1 directed cancer treatment, emphasizing immunotherapy.

ERBB Signaling Pathway in Cancer Stem Cells

The epidermal growth factor receptor (EGFR) was first tyrosine kinase receptor linked to human cancers. EGFR or ERBB1 is a member of ERBB subfamily, which consists of four type I transmembrane receptor tyrosine kinases, ERBB1, 2, 3 and 4. ERBBs form homo/heterodimers after ligand binding except ERBB2 and consequently becomes activated. Different signal pathways, such as phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT), RAS/RAF/MEK/ERK, phospholipase Cγ and JAK-STAT, are triggered by ERBB activation. Since ERBBs, through these pathways, regulate stemness and differentiation of cancer stem cells (CSCs), their roles in CSC tumorigenicity have extensively been investigated. The hyperactivation of ERBBs and its downstream pathways stimulated by either genetic and/or epigenetic factors are frequently described in many types of human cancers. Their dysregulations make cells acquiring CSC characters such as survival, tumorigenicity and stemness. Because of the roles in tumor growth and progress, ERBBs are considered to be one of the drug targets as cancer treatment strategy. In this chapter, we will summarize the structure, function and roles of ERBB subfamily along with their relative pathways regulating the stemness and tumorigenicity of CSCs. Finally, we will discuss the targeting therapy strategies of cancer along with ERBBs in addition to some challenges and future perspectives.

LncRNA FTX promotes the malignant progression of colorectal cancer by regulating the miR-214-5p-JAG1 axis

Background

Long non-coding RNAs (lncRNAs) have recently been found to be vital regulators of various cancers, including colorectal cancer (CRC). It has been previously reported that the dysregulated expression of lncRNA Five prime to Xist (FTX) is involved in carcinogenesis. However, the role of lncRNA FTX in the progression of CRC is still unclear.

Methods

Fluorescence in situ hybridization (FISH) was used to detect the expression of lncRNA FTX and miR-214-5p in CRC tissues. Cell Counting Kit-8 assay, transwell assay, wound-healing assay, and proliferation assay were used to explore the function of lncRNA FTX in CRC cells. Quantitative real-time polymerase chain reaction (qRT-PCR), western blotting, and luciferase reporter assay were used to confirm the relationship between lncRNA FTX and miR-214-5p-jagged canonical Notch ligand 1 (JAG1). We further explored the role of lncRNA FTX in vivo using xenograft tumor assay.

Results

lncRNA FTX was found to be upregulated in CRC tissues by FISH. The downregulation of endogenous lncRNA FTX expression inhibited CRC cell proliferation, migration, and invasion. Mechanistically, lncRNA FTX sequestered miR-214-5p and thus released its repression on JAG1, driving the malignant progression of CRC.

Conclusions

These findings give rise to a new perspective, the lncRNA FTX-miR-214-5p-JAG1 regulatory axis, in exploring the cancer-promoting mechanism of lncRNA FTX in CRC.

SOX12 Promotes Stem Cell-Like Phenotypes and Osteosarcoma Tumor Growth by Upregulating JAGGED1

SOX12 plays a role in promoting the growth of some tumors; however, its role in osteosarcoma remains unclear. From gene expression omnibus (GEO) and tumor alterations relevant for genomics-driven therapy (TARGET) databases, Kaplan–Meier analyses were conducted to establish relationships between SOX12 expression and osteosarcoma survival and recurrence in osteosarcoma patients. We also performed in vitro and in vivo assays to determine SOX12 function in osteosarcoma etiology. SOX12 expression was increased in osteosarcoma; high SOX12 expression levels were related to a poor prognosis and a high disease recurrence in patients. Moreover, SOX12 expression in osteosarcoma cell lines was increased, similar to osteosarcoma cancer stem cells. We also observed that SOX12 knockdown inhibited the spheroidization and expression of stemness markers in osteosarcoma cells and tumor formation in nude mice. In addition, SOX12 knockdown inhibited JAGGED1 and HES1 expression. Similarly, JAGGED1 knockdown also inhibited the formation of osteosarcoma cancer stem cells into pellets and reduced the expression of stemness markers and tumor formation capabilities in nude mice. Finally, during SOX12 knockdown, JAGGED1 overexpression rescued osteosarcoma cells from spheroidizing. SOX12 promotes stem cell-like phenotypes and osteosarcoma tumor growth by upregulating JAGGED1.

HER2 Signaling and Breast Cancer Stem Cells: The Bridge behind HER2-Positive Breast Cancer Aggressiveness and Therapy Refractoriness

Simple Summary

Breast cancer (BC) is not a single disease, but a group of different tumors, and altered HER2 expression defines a particularly aggressive subtype. Although HER2 pharmacological inhibition has dramatically improved the prognosis of HER2-positive BC patients, there is still an urgent need for improved knowledge of HER2 biology and mechanisms underlying HER2-driven aggressiveness and drug susceptibility. Emerging data suggest that the clinical efficacy of molecularly targeted therapies is related to their ability to target breast cancer stem cells (BCSCs), a population that is not only self-sustaining and able to differentiate into distinct lineages, but also contributes to tumor growth, aggressiveness, metastasis and treatment resistance. The aim of this review is to provide an overview of how the full-length HER2 receptor, the d16HER2 splice variant and the truncated p95HER2 variants are involved in the regulation and maintenance of BCSCs.

Abstract

HER2 overexpression/amplification occurs in 15–20% of breast cancers (BCs) and identifies a highly aggressive BC subtype. Recent clinical progress has increased the cure rates of limited-stage HER2-positive BC and significantly prolonged overall survival in patients with advanced disease; however, drug resistance and tumor recurrence remain major concerns. Therefore, there is an urgent need to increase knowledge regarding HER2 biology and implement available treatments. Cancer stem cells (CSCs) represent a subset of malignant cells capable of unlimited self-renewal and differentiation and are mainly considered to contribute to tumor onset, aggressiveness, metastasis, and treatment resistance. Seminal studies have highlighted the key role of altered HER2 signaling in the maintenance/enrichment of breast CSCs (BCSCs) and elucidated its bidirectional communication with stemness-related pathways, such as the Notch and Wingless/β-catenin cascades. d16HER2, a splice variant of full-length HER2 mRNA, has been identified as one of the most oncogenic HER2 isoform significantly implicated in tumorigenesis, epithelial-mesenchymal transition (EMT)/stemness and the response to targeted therapy. In addition, expression of a heterogeneous collection of HER2 truncated carboxy-terminal fragments (CTFs), collectively known as p95HER2, identifies a peculiar subgroup of HER2-positive BC with poor prognosis, with the p95HER2 variants being able to regulate CSC features. This review provides a comprehensive overview of the current evidence regarding HER2-/d16HER2-/p95HER2-positive BCSCs in the context of the signaling pathways governing their properties and describes the future prospects for targeting these components to achieve long-lasting tumor control.

Mammary Development and Breast Cancer: a Notch Perspective

Mammary gland development primarily occurs postnatally, and this unique process is complex and regulated by systemic hormones and local growth factors. The mammary gland is also a highly dynamic organ that undergoes profound changes at puberty and during the reproductive cycle. These changes are driven by mammary stem cells (MaSCs). Breast cancer is one of the most common causes of cancer-related death in women. Cancer stem cells (CSCs) play prominent roles in tumor initiation, drug resistance, tumor recurrence, and metastasis. The highly conserved Notch signaling pathway functions as a key regulator of the niche mediating mammary organogenesis and breast neoplasia. In this review, we discuss mechanisms by which Notch contributes to breast carcinoma pathology and suggest potentials for therapeutic targeting of Notch in breast cancer. In summary, we provide a comprehensive overview of Notch functions in regulating MaSCs, mammary development, and breast cancer.

The Role of Notch, Hedgehog, and Wnt Signaling Pathways in the Resistance of Tumors to Anticancer Therapies

Resistance to therapy is the major hurdle in the current cancer management. Cancer cells often rewire their cellular process to alternate mechanisms to resist the deleterious effect mounted by different therapeutic approaches. The major signaling pathways involved in the developmental process, such as Notch, Hedgehog, and Wnt, play a vital role in development, tumorigenesis, and also in the resistance to the various anticancer therapies. Understanding how cancer utilizes these developmental pathways in acquiring the resistance to the multi-therapeutic approach cancer can give rise to a new insight of the anti-therapy resistance mechanisms, which can be explored for the development of a novel therapeutic approach. We present a brief overview of Notch, Hedgehog, and Wnt signaling pathways in cancer and its role in providing resistance to various cancer treatment modalities such as chemotherapy, radiotherapy, molecular targeted therapy, and immunotherapy. Understanding the importance of these molecular networks will provide a rational basis for novel and safer combined anticancer therapeutic approaches for the improvement of cancer treatment by overcoming drug resistance.

Cancer stem cell-targeted therapeutic approaches for overcoming trastuzumab resistance in HER2-positive breast cancer

Application of the anti-HER2 drug trastuzumab has significantly improved the prognosis of patients with the HER2-positive subtype of breast cancer. However, 50% of patients with HER2 amplification relapse due to trastuzumab resistance. Accumulating evidence indicates that breast cancer is driven by a small subset of cancer-initiating cells or breast cancer stem cells (BCSCs), which have the capacity to self-renew and differentiate to regenerate the tumor cell hierarchy. Increasing data suggest that BCSCs are resistant to conventional therapy, including chemotherapy, radiotherapy, and endocrine therapy, which drives distant metastasis and breast cancer relapse. In recent years, the trastuzumab resistance of breast cancer has been closely related to the prevalence of BCSCs. Here, our primary focus is to discuss the role of epithelial-mesenchymal transition (EMT) of BCSCs in the setting of trastuzumab resistance and approaches of reducing or eradicating BCSCs in HER2-positive breast cancer.

Notch Signaling in Vascular Endothelial Cells, Angiogenesis, and Tumor Progression: An Update and Prospective

The Notch signaling pathway plays an essential role in a wide variety of biological processes including cell fate determination of vascular endothelial cells and the regulation of arterial differentiation and angiogenesis. The Notch pathway is also an essential regulator of tumor growth and survival by functioning as either an oncogene or a tumor suppressor in a context-dependent manner. Crosstalk between the Notch and other signaling pathways is also pivotal in tumor progression by promoting cancer cell growth, migration, invasion, metastasis, tumor angiogenesis, and the expansion of cancer stem cells (CSCs). In this review, we provide an overview and update of Notch signaling in endothelial cell fate determination and functioning, angiogenesis, and tumor progression, particularly in the development of CSCs and therapeutic resistance. We further summarize recent studies on how endothelial signaling crosstalk with the Notch pathway contributes to tumor angiogenesis and the development of CSCs, thereby providing insights into vascular biology within the tumor microenvironment and tumor progression.

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.

Dll1+ quiescent tumor stem cells drive chemoresistance in breast cancer through NF-κB survival pathway

Development of chemoresistance in breast cancer patients greatly increases mortality. Thus, understanding mechanisms underlying breast cancer resistance to chemotherapy is of paramount importance to overcome this clinical challenge. Although activated Notch receptors have been associated with chemoresistance in cancer, the specific Notch ligands and their molecular mechanisms leading to chemoresistance in breast cancer remain elusive. Using conditional knockout and reporter mouse models, we demonstrate that tumor cells expressing the Notch ligand Dll1 is important for tumor growth and metastasis and bear similarities to tumor-initiating cancer cells (TICs) in breast cancer. RNA-seq and ATAC-seq using reporter models and patient data demonstrated that NF-κB activation is downstream of Dll1 and is associated with a chemoresistant phenotype. Finally, pharmacological blocking of Dll1 or NF-κB pathway completely sensitizes Dll1⁺ tumors to chemotherapy, highlighting therapeutic avenues for chemotherapy resistant breast cancer patients in the near future.

Targeting Notch in oncology: the path forward

Notch signalling is involved in many aspects of cancer biology, including angiogenesis, tumour immunity and the maintenance of cancer stem-like cells. In addition, Notch can function as an oncogene and a tumour suppressor in different cancers and in different cell populations within the same tumour. Despite promising preclinical results and early-phase clinical trials, the goal of developing safe, effective, tumour-selective Notch-targeting agents for clinical use remains elusive. However, our continually improving understanding of Notch signalling in specific cancers, individual cancer cases and different cell populations, as well as crosstalk between pathways, is aiding the discovery and development of novel investigational Notch-targeted therapeutics.

Notch Signaling in Breast Cancer: A Role in Drug Resistance

Breast cancer is a heterogeneous disease that can be subdivided into unique molecular subtypes based on protein expression of the Estrogen Receptor, Progesterone Receptor, and/or the Human Epidermal Growth Factor Receptor 2. Therapeutic approaches are designed to inhibit these overexpressed receptors either by endocrine therapy, targeted therapies, or combinations with cytotoxic chemotherapy. However, a significant percentage of breast cancers are inherently resistant or acquire resistance to therapies, and mechanisms that promote resistance remain poorly understood. Notch signaling is an evolutionarily conserved signaling pathway that regulates cell fate, including survival and self-renewal of stem cells, proliferation, or differentiation. Deregulation of Notch signaling promotes resistance to targeted or cytotoxic therapies by enriching of a small population of resistant cells, referred to as breast cancer stem cells, within the bulk tumor; enhancing stem-like features during the process of de-differentiation of tumor cells; or promoting epithelial to mesenchymal transition. Preclinical studies have shown that targeting the Notch pathway can prevent or reverse resistance through reduction or elimination of breast cancer stem cells. However, Notch inhibitors have yet to be clinically approved for the treatment of breast cancer, mainly due to dose-limiting gastrointestinal toxicity. In this review, we discuss potential mechanisms of Notch-mediated resistance in breast cancer cells and breast cancer stem cells, and various methods of targeting Notch through γ-secretase inhibitors, Notch signaling biologics, or transcriptional inhibitors. We also discuss future plans for identification of novel Notch-targeted therapies, in order to reduce toxicity and improve outcomes for women with resistant breast cancer.

The oncogenic role of Jagged1/Notch signaling in cancer

Aberrant activation of Notch signaling plays an oncogenic role in cancer development. Jagged1 (JAG1) is an important Notch ligand that triggers Notch signaling through cell-cell interactions. JAG1 overexpression has been reported in many different types of cancer and correlates with a poor clinical prognosis. JAG1/Notch signaling controls oncogenic processes in different cell types and cellular contexts. Furthermore, JAG1/Notch signaling cascades activate a number of oncogenic factors that regulate cellular functions such as proliferation, metastasis, drug-resistance, and angiogenesis. To suppress the severe toxicity of pan-Notch inhibitors, JAG1 is attracting increasing attention as a source of therapeutic targets for cancers. In this review, the oncogenic role of JAG1/Notch signaling in cancer is discussed, as well as implications of strategies to inhibit JAG1/Notch signaling activity.

CAR T‑cell therapy for gastric cancer: Potential and perspective (Review)

Gastric cancer (GC) is one of the most frequently diagnosed digestive malignancies and is the third leading cause of cancer‑associated death worldwide. Delayed diagnosis and poor prognosis indicate the urgent need for new therapeutic strategies. The success of chimeric antigen receptor (CAR) T‑cell therapy for chemotherapy‑refractory hematological malignancies has inspired the development of a similar strategy for GC treatment. Although using CAR T‑cells against GC is not without difficulty, results from preclinical studies remain encouraging. The current review summarizes relevant preclinical studies and ongoing clinical trials for the use of CAR T‑cells for GC treatment and investigates possible toxicities, as well as current clinical experiences and emerging approaches. With a deeper understanding of the tumor microenvironment, novel target epitopes and scientific‑technical progress, the potential of CAR T‑cell therapy for GC is anticipated in the near future.

Antibody-drug conjugate T-DM1 treatment for HER2+ breast cancer induces ROR1 and confers resistance through activation of Hippo transcriptional coactivator YAP1

Background

A newly developed drug trastuzumab emtansine (T-DM1) has improved the survival of breast cancer (BC) patients. Despite an impressive initial clinical response, a subgroup of patient develop resistance and present therapeutic challenges. The underlying resistance mechanisms are not fully investigated. We report that T-DM1 treatment modulates the expression of ROR1 (type 1 receptor tyrosine kinase-like orphan receptor) and induces self-renewal of cancer stem cells (CSCs) leading to therapeutic resistance.

Methods

Using BC patient tumor samples, and BC cell lines we gained insight into the T-DM1 treatment induced ROR1 overexpression and resistance. In vitro sphere forming assays and in vivo extreme dilution assays were employed to analyze the stemness and self-renewal capacity of the cells. A series of molecular expression and protein assays including qRT-PCR, FACS-sorting, ELISA, immunostaining, Western blotting were used to provide evidence.

Findings

Exposure of cells to T-DM1 shifted ROR1 expression from low to high, enriched within the CSC subpopulation, coincident with increased Bmi1 and stemness factors. T-DM1 induced ROR1 cells showed high spheroid and tumor forming efficiency in vitro and in an animal model exhibiting shorter tumor-free time. Mechanistically, the overexpression of ROR1 is partly induced by the activation of YAP1 and its target genes. Silencing of ROR1 and YAP1 by pharmacologic inhibitors and/or sh/siRNA inhibited spheroid formation, the initiation of tumors and the capacity for self-renewal and ROR1 overexpression.

Interpretations

The results presented here indicate that simultaneous targeting of ROR1 and YAP1 may suppress CSC self-renewal efficacy and inhibit tumor progression in BC. In this manner such treatments may overcome the T-DM1 mediated therapeutic resistance and improve clinical outcome.

Fund

This study was supported by Neurogen Technologies for interdisciplinary research.

Estrogen-mediated protection against coronary heart disease: The role of the Notch pathway

Estrogen regulates a plethora of biological processes, under physiological and pathological conditions, by affecting key pathways involved in the regulation of cell proliferation, fate, survival and metabolism. The Notch receptors are mediators of communication between adjacent cells and are key determinants of cell fate during development and in postnatal life. Crosstalk between estrogen and the Notch pathway intervenes in many processes underlying the development and maintenance of the cardiovascular system. The identification of molecular mechanisms underlying the interaction between these types of endocrine and juxtacrine signaling are leading to a deeper understanding of physiological conditions regulated by these steroid hormones and, potentially, to novel therapeutic approaches to prevent pathologies linked to reduced levels of estrogen, such as coronary heart disease, and cardiotoxicity caused by hormone therapy for estrogen-receptor-positive breast cancer.

Re-establishing Apoptosis Competence in Bone Associated Cancers via Communicative Reprogramming Induced Through Notch Signaling Inhibition

Notch and its ligands on adjacent cells are key mediators of cellular communication during developmental choice in embryonic and adult tissues. This communication is frequently altered in the pathological interaction between cancer cells and healthy cells of the microenvironment due to the aberrant expression of tumor derived Notch receptors or ligands, that results in homotypic or heterotypic Notch signaling activation in tumor cells or surrounding stromal cells. A deadly consequence of this pathological communication is pharmacological resistance that results in patient's relapse. We will provide a survey of the role of Notch signaling in the bone marrow (BM), a microenvironment with a very high capacity to support several types of cancer, including primary cancers such as osteosarcoma or multiple myeloma and bone metastases from carcinomas. Moreover, in the BM niche several hematological malignancies maintain a reservoir of cancer stem cells, characterized by higher intrinsic drug resistance. Cell-cell communication in BM-tumor interaction triggers signaling pathways by direct contact and paracrine communication through soluble growth factors or extracellular vesicles, which can deliver specific molecules such as mRNAs, miRNAs, proteins, metabolites, etc. enabling tumor cells to reprogram the healthy cells of the microenvironment inducing them to support tumor growth. In this review we will explore how the dysregulated Notch activity contributes to tumor-mediated reprogramming of the BM niche and drug resistance, strengthening the rationale of a Notch-directed therapy to re-establish apoptosis competence in cancer.

Toward understanding cancer stem cell heterogeneity in the tumor microenvironment

The epithelial-mesenchymal transition (EMT) and cancer stem cell (CSC) formation are two paramount processes driving tumor progression, therapy resistance, and cancer metastasis. Recent experiments show that cells with varying EMT and CSC phenotypes are spatially segregated in the primary tumor. The underlying mechanisms generating such spatiotemporal dynamics in the tumor microenvironment, however, remain largely unexplored. Here, we show through a mechanism-based dynamical model that the diffusion of EMT-inducing signals such as TGF-β, together with noncell autonomous control of EMT and CSC decision making via the Notch signaling pathway, can explain experimentally observed disparate localization of subsets of CSCs with varying EMT phenotypes in the tumor. Our simulations show that the more mesenchymal CSCs lie at the invasive edge, while the hybrid epithelial/mesenchymal (E/M) CSCs reside in the tumor interior. Further, motivated by the role of Notch-Jagged signaling in mediating EMT and stemness, we investigated the microenvironmental factors that promote Notch-Jagged signaling. We show that many inflammatory cytokines such as IL-6 that can promote Notch-Jagged signaling can (i) stabilize a hybrid E/M phenotype, (ii) increase the likelihood of spatial proximity of hybrid E/M cells, and (iii) expand the fraction of CSCs. To validate the predicted connection between Notch-Jagged signaling and stemness, we knocked down JAG1 in hybrid E/M SUM149 human breast cancer cells in vitro. JAG1 knockdown significantly restricted tumor organoid formation, confirming the key role that Notch-Jagged signaling can play in tumor progression. Together, our integrated computational-experimental framework reveals the underlying principles of spatiotemporal dynamics of EMT and CSCs.