Complexity of cancer stem cells

WNT5B drives osteosarcoma stemness, chemoresistance and metastasis

BACKGROUND

Treatment for osteosarcoma, a paediatric bone cancer with no therapeutic advances in over three decades, is limited by a lack of targeted therapies. Osteosarcoma frequently metastasises to the lungs, and only 20% of patients survive 5 years after the diagnosis of metastatic disease. We found that WNT5B is the most abundant WNT expressed in osteosarcoma tumours and its expression correlates with metastasis, histologic subtype and reduced survival.

METHODS

Using tumor-spheroids to model cancer stem-like cells, we performed qPCR, immunoblotting, and immunofluorescence to monitor changes in gene and protein expression. Additionally, we measured sphere size, migration and forming efficiency to monitor phenotypic changes. Therefore, we characterised WNT5B's relevance to cancer stem-like cells, metastasis, and chemoresistance and evaluated its potential as a therapeutic target.

RESULTS

In osteosarcoma cell lines and patient-derived spheres, WNT5B is enriched in stem cells and induces the expression of the stemness gene SOX2. WNT5B promotes sphere size, sphere-forming efficiency, and cell proliferation, migration, and chemoresistance to methotrexate (but not cisplatin or doxorubicin) in spheres formed from conventional cell lines and patient-derived xenografts. In vivo, WNT5B increased osteosarcoma lung and liver metastasis and inhibited the glycosaminoglycan hyaluronic acid via upregulation of hyaluronidase 1 (HYAL1), leading to changes in the tumour microenvironment. Further, we identified that WNT5B mRNA and protein correlate with the receptor ROR1 in primary tumours. Targeting WNT5B through inhibition of WNT/ROR1 signalling with an antibody to ROR1 reduced stemness properties, including chemoresistance, sphere size and SOX2 expression.

CONCLUSIONS

Together, these data define WNT5B's role in driving osteosarcoma cancer stem cell expansion and methotrexate resistance and provide evidence that the WNT5B pathway is a promising candidate for treating osteosarcoma patients.

KEY POINTS

WNT5B expression is high in osteosarcoma stem cells leading to increased stem cell proliferation and migration through SOX2. WNT5B expression in stem cells increases rates of osteosarcoma metastasis to the lungs and liver in vivo. The hyaluronic acid degradation enzyme HYAL1 is regulated by WNT5B in osteosarcoma contributing to metastasis. Inhibition of WNT5B with a ROR1 antibody decreases osteosarcoma stemness.

Ginseng-derived compounds as potential anticancer agents targeting cancer stem cells

Cancer stem cells (CSCs) are a rare subpopulation of cancer cells that exhibit stem cell-like characteristics, including self-renewal and differentiation in a multi-stage lineage state via symmetric or asymmetric division, causing tumor initiation, heterogeneity, progression, and recurrence and posing a major challenge to current anticancer therapy. Despite the importance of CSCs in carcinogenesis and cancer progression, currently available anticancer therapeutics have limitations for eradicating CSCs. Moreover, the efficacy and therapeutic windows of currently available anti-CSC agents are limited, suggesting the necessity to optimize and develop a novel anticancer agent targeting CSCs. Ginseng has been traditionally used for enhancing immunity and relieving fatigue. As ginseng's long history of use has demonstrated its safety, it has gained attention for its potential pharmacological properties, including anticancer effects. Several studies have identified the bioactive principles of ginseng, such as ginseng saponin (ginsenosides) and non-saponin compounds (e.g., polysaccharides, polyacetylenes, and phenolic compounds), and their pharmacological activities, including antioxidant, anticancer, antidiabetic, antifatigue, and neuroprotective effects. Notably, recent reports have shown the potential of ginseng-derived compounds as anti-CSC agents. This review investigates the biology of CSCs and efforts to utilize ginseng-derived components for cancer treatment targeting CSCs, highlighting their role in overcoming current therapeutic limitations.

Stem cell pathology: histogenesis of malignant fibrous histiocytoma and characterization of myofibroblasts appearing in fibrotic lesions

The concept of "stem cell pathology" is to establish the role of the stem cells by exploring their contribution to lesion development. The somatic stem cells are present in the body. Malignant fibrous histiocytoma (MFH; recently named "undifferentiated pleomorphic sarcoma") includes pluripotential undifferentiated mesenchymal stem cells as a cell element. An antibody (A3) generated by using rat MFH cells as the antigen labels somatic stem cells such as bone marrow stem cells and immature endothelial cells and pericytes, as well as immature epithelial cells in epithelialization. By using A3 and other antibodies recognizing somatic stem cells, it is considered that myofibroblasts appearing in rat fibrotic lesions are developed partly from immature hepatic stellate cells in hepatic fibrosis, immature pancreatic stellate cells in pancreatic fibrosis, pericytes/endothelial cells in neovascularization in injured tissues, as well as via the epithelial-mesenchymal transition. These progenitors may be in the stem cell lineage. In this review, the author introduces the histogenesis of MFH and the characteristics of myofibroblasts appearing in fibrosis, based mainly on the author's studies.

The Prognostic Value of Cancer Stem Cell Markers (CSCs) Expression-ALDH1A1, CD133, CD44-For Survival and Long-Term Follow-Up of Ovarian Cancer Patients

Recurrent disease and treatment-associated chemoresistance are the two main factors accounting for poor clinical outcomes of ovarian cancer (OC) patients. Both can be associated with cancer stem cells (CSCs), which contribute to cancer formation, progression, chemoresistance, and recurrence. Hence, this study investigated whether the expression of known CSC-associated markers ALDH1A, CD44, and CD133 may predict OC patient prognosis. We analyzed their expression in primary epithelial ovarian cancer (EOC) patients using immunohistochemistry and related them to clinicopathological data, including overall survival (OS) and progression-free survival (PFS). Expression of ALDH1A1 was detected in 32%, CD133 in 28%, and CD44 in 33% of cases. While Kaplan-Meier analysis revealed no association of the expression of CD133 and CD44 with PFS and OS, ALDH1A1-positive patients were characterized with both significantly shorter OS (p = 0.00022) and PFS (p = 0.027). Multivariate analysis demonstrated that the expression of ALDH1A1, FIGO stage III-IV, and residual disease after suboptimal debulking or neoadjuvant chemotherapy correlated with shorter OS. The results of this study identify ALDH1A1 as a potential independent prognostic factor of shorter OS and PFS in EOC patients. Therefore, targeting ALDH1A1-positive cancer cells may be a promising therapeutic strategy to influence the disease course and treatment response.

Pixel-Level Clustering of Hematoxylin-Eosin-Stained Sections of Mouse and Human Biliary Tract Cancer

We previously established mouse models of biliary tract cancer (BTC) based on the injection of cells with biliary epithelial stem cell properties derived from KRAS(G12V)-expressing organoids into syngeneic mice. The resulting mouse tumors appeared to recapitulate the pathological features of human BTC. Here we analyzed images of hematoxylin and eosin (H&E) staining for both the mouse tumor tissue and human cholangiocarcinoma tissue by pixel-level clustering with machine learning. A pixel-clustering model that was established via training with mouse images revealed homologies of tissue structure between the mouse and human tumors, suggesting similarities in tumor characteristics independent of animal species. Analysis of the human cholangiocarcinoma tissue samples with the model also revealed that the entropy distribution of cancer regions was higher than that of noncancer regions, with the entropy of pixels thus allowing discrimination between these two types of regions. Histograms of entropy tended to be broader for noncancer regions of late-stage human cholangiocarcinoma. These analyses indicate that our mouse BTC models are appropriate for investigation of BTC carcinogenesis and may support the development of new therapeutic strategies. In addition, our pixel-level clustering model is highly versatile and may contribute to the development of a new BTC diagnostic tool.

Fatty acid oxidation is a druggable gateway regulating cellular plasticity for driving metastasis in breast cancer

Cell state transitions control the functional behavior of cancer cells. Epithelial-to-mesenchymal transition (EMT) confers cancer stem cell-like properties, enhanced tumorigenicity and drug resistance to tumor cells, while mesenchymal-epithelial transition (MET) reverses these phenotypes. Using high-throughput chemical library screens, retinoids are found to be potent promoters of MET that inhibit tumorigenicity in basal-like breast cancer. Cell state transitions are defined by reprogramming of lipid metabolism. Retinoids bind cognate nuclear receptors, which target lipid metabolism genes, thereby redirecting fatty acids for β-oxidation in the mesenchymal cell state towards lipid storage in the epithelial cell state. Disruptions of key metabolic enzymes mediating this flux inhibit MET. Conversely, perturbations to fatty acid oxidation (FAO) rechannel fatty acid flux and promote a more epithelial cell phenotype, blocking EMT-driven breast cancer metastasis in animal models. FAO impinges on the epigenetic control of EMT through acetyl-CoA-dependent regulation of histone acetylation on EMT genes, thus determining cell states.

Cancer Stem Cell Assay for the Treatment of Platinum-Resistant Recurrent Ovarian Cancer

BACKGROUND

Disease recurrence and progression of ovarian cancer is a common event, which is accompanied by the development of platinum-resistant or refractory disease. The presence of chemo-resistant Cancer Stem Cells (CSCs) contribute to tumor propagation, maintenance, and treatment resistance of this difficult to treat disease. We have developed ChemoID, a cytotoxic synergy assay against CSCs that identifies the most effective chemotherapy treatment from a panel of FDA-approved chemotherapies using fresh cancer biopsies.

PATIENTS AND METHODS

Ascites or interventional radiology biopsies were collected under physician order from 78 consecutive patients affected by 3rd relapsed ovarian cancer. Test results from the assay were used when possible to treat patients with the highest cell kill drugs, taking into consideration their health status and using dose reductions, if needed. A chart analysis and review of CT and PET scans were performed to determine patients' outcomes for tumor response, Progression-Free Survival (PFS), and Overall Survival (OS).

RESULTS

We observed that recurrent ovarian cancer patients treated with high-cell kill chemotherapy agents guided by the CSCs drug response assay had an improvement in their median PFS and OS when compared to historical median PFS and OS and/or when compared to patients who could not receive high cell kill chemotherapies (PFS low cell kill 3.5 months vs. high cell kill 12.0 months; OS low cell kill 6.0 months vs. high cell kill 15.0 months).

CONCLUSION

This data indicates that the drug cytotoxicity assay aimed at targeting CSCs may be a useful tool for optimizing treatment selection when first-line therapy fails, and when there are multiple clinically-acceptable and -equivalent treatments available.

Cancer Stem Cells in Oropharyngeal Cancer

Oropharyngeal cancer (OPC), which is a common type of head and neck squamous cell carcinoma (HNSCC), is associated with tobacco and alcohol use, and human papillomavirus (HPV) infection. Underlying mechanisms and as a result prognosis of the HPV-positive and HPV-negative OPC patients are different. Like stem cells, the ability of self-renewal and differentiate, cancer stem cells (CSCs) have roles in tumor invasion, metastasis, drug resistance, and recurrence after therapy. Research revealed their roles to some extent in all of these processes but there are still many unresolved points to connect to CSC-targeted therapy. In this review, we will focus on what we currently know about CSCs of OPC and limitations of our current knowledge. We will present perspectives that will broaden our understanding and recent literature which may connect to therapy.

Mechanisms of the synergistic lung tumorigenic effect of arsenic and benzo(a)pyrene combined- exposure

Humans are often exposed to mixtures of environmental pollutants especially environmental chemical carcinogens, representing a significant environmental health issue. However, our understanding on the carcinogenic effects and mechanisms of environmental carcinogen mixture exposures is limited and mostly relies on the findings from studying individual chemical carcinogens. Both arsenic and benzo(a)pyrene (BaP) are among the most common environmental carcinogens causing lung cancer and other types of cancer in humans. Millions of people are exposed to arsenic via consuming arsenic-contaminated drinking water and even more people are exposed to BaP via cigarette smoking and consuming BaP-contaminated food. Thus arsenic and BaP combined-exposure in humans is common. Previous epidemiology studies indicated that arsenic-exposed people who were cigarette smokers had significantly higher lung cancer risk than those who were non-smokers. Since BaP is one of the major carcinogens in cigarette smoke, it has been speculated that arsenic and BaP combined-exposure may play important roles in the increased lung cancer risk observed in arsenic-exposed cigarette smokers. In this review, we summarize important findings and inconsistencies about the co-carcinogenic effects and underlying mechanisms of arsenic and BaP combined-exposure and propose new areas for future studies. A clear understanding on the mechanism of co-carcinogenic effects of arsenic and BaP combined exposure may identify novel targets to more efficiently treat and prevent lung cancer resulting from arsenic and BaP combined-exposure.

Thyroid Cancer Stem-Like Cells: From Microenvironmental Niches to Therapeutic Strategies

Thyroid cancer (TC) is the most common endocrine malignancy. Recent progress in thyroid cancer biology revealed a certain degree of intratumoral heterogeneity, highlighting the coexistence of cellular subpopulations with distinct proliferative capacities and differentiation abilities. Among those subpopulations, cancer stem-like cells (CSCs) are hypothesized to drive TC heterogeneity, contributing to its metastatic potential and therapy resistance. CSCs principally exist in tumor areas with specific microenvironmental conditions, the so-called stem cell niches. In particular, in thyroid cancer, CSCs' survival is enhanced in the hypoxic niche, the immune niche, and some areas with specific extracellular matrix composition. In this review, we summarize the current knowledge about thyroid CSCs, the tumoral niches that allow their survival, and the implications for TC therapy.

Molecular pathology underlying the robustness of cancer stem cells

Intratumoral heterogeneity is tightly associated with the failure of anticancer treatment modalities including conventional chemotherapy, radiation therapy, and molecularly targeted therapy. Such heterogeneity is generated in an evolutionary manner not only as a result of genetic alterations but also by the presence of cancer stem cells (CSCs). CSCs are proposed to exist at the top of a tumor cell hierarchy and are undifferentiated tumor cells that manifest enhanced tumorigenic and metastatic potential, self-renewal capacity, and therapeutic resistance. Properties that contribute to the robustness of CSCs include the abilities to withstand redox stress, to rapidly repair damaged DNA, to adapt to a hyperinflammatory or hyponutritious tumor microenvironment, and to expel anticancer drugs by the action of ATP-binding cassette transporters as well as plasticity with regard to the transition between dormant CSC and transit-amplifying progenitor cell phenotypes. In addition, CSCs manifest the phenomenon of metabolic reprogramming, which is essential for maintenance of their self-renewal potential and their ability to adapt to changes in the tumor microenvironment. Elucidation of the molecular underpinnings of these biological features of CSCs is key to the development of novel anticancer therapies. In this review, we highlight the pathological relevance of CSCs in terms of their hallmarks and identification, the properties of their niche—both in primary tumors and at potential sites of metastasis—and their resistance to oxidative stress dependent on system xc (−).

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Intratumoral heterogeneity driven by CSCs is responsible for therapeutic resistance.

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CTCs survive in the distant organs and achieve colonization, causing metastasis.

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E/M hybrid cancer cells due to partial EMT exhibit the highest metastatic potential.

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The CSC niche regulates stemness in metastatic disease as well as in primary tumor.

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Activation of system xc(-) by CD44 variant in CSCs is a promising therapeutic target.

Oncogenic KRAS-expressing organoids with biliary epithelial stem cell properties give rise to biliary tract cancer in mice

Biliary tract cancer (BTC) arises from biliary epithelial cells (BECs) and includes intrahepatic cholangiocarcinoma (IHCC), gallbladder cancer (GC), and extrahepatic cholangiocarcinoma (EHCC). Although frequent KRAS mutations and epigenetic changes at the INK4A/ARF locus have been identified, the molecular pathogenesis of BTC is unclear and the development of corresponding anticancer agents remains inadequate. We isolated epithelial cell adhesion molecule (EpCAM)–positive BECs from the mouse intrahepatic bile duct, gallbladder, and extrahepatic bile duct, and established organoids derived from these cells. Introduction of activated KRAS and homozygous deletion of Ink4a/Arf in the cells of each organoid type conferred the ability to form lethal metastatic adenocarcinoma with differentiated components and a pronounced desmoplastic reaction on cell transplantation into syngeneic mice, indicating that the manipulated cells correspond to BTC–initiating cells. The syngeneic mouse models recapitulate the pathological features of human IHCC, GC, and EHCC, and they should therefore prove useful for the investigation of BTC carcinogenesis and the development of new therapeutic strategies. Tumor cells isolated from primary tumors formed organoids in three‐dimensional culture, and serial syngeneic transplantation of these cells revealed that their cancer stem cell properties were supported by organoid culture, but not by adherent culture. Adherent culture thus attenuated tumorigenic activity as well as the expression of both epithelial and stem cell markers, whereas the expression of epithelial‐mesenchymal transition (EMT)–related transcription factor genes and mesenchymal cell markers was induced. Our data show that organoid culture is important for maintenance of epithelial cell characteristics, stemness, and tumorigenic activity of BTC–initiating cells.

YBX2 and cancer testis antigen 45 contribute to stemness, chemoresistance and a high degree of malignancy in human endometrial cancer

Y-box binding protein 2 (YBX2) has been associated with the properties of both germ cells and cancer cells. We hypothesized that YBX2 might contribute to the characteristics of cancer stem cells (CSCs). In this study, we clarified the function of YBX2 in endometrial cancer stem cells. We established a human YBX2-expressing Ishikawa (IK) cell line (IK-YBX2 cells). We analyzed gene expression associated with stemness and isolated SP cells from IK-YBX2 cells. The SP population of IK-YBX2 cells, the expression of ALDH1 and serial sphere-forming capacity were associated with levels of YBX2 expression. IK-YBX2 cells were resistant to anti-cancer drugs. In gene expression analysis, a gene for cancer testis antigen, CT45, was generally overexpressed in IK-YBX2 cells. YBX2-mediated CT45 expression was associated with increased levels of self-renewal capacity and paclitaxel resistance. The level of CT45 expression was enhanced in high-grade and/or advanced stages of human endometrial cancer tissues. We conclude that expression of YBX2 is essential for the stem cell-like phenotype. CT45 contributes to stemness associated with YBX2 and might be related to the progression of endometrial cancer.

Propagation and Maintenance of Cancer Stem Cells: A Major Influence of the Long Non-Coding RNA H19

Cancer stem cells (CSCs) represent a rare population of tumor cells that exhibit stem cell properties with the abilities of self-renewal and differentiation. These cells are now widely accepted to be responsible for tumor initiation, development, resistance to conventional therapies, and recurrence. Thus, a better understanding of the molecular mechanisms involved in the control of CSCs is essential to improve patient management in terms of diagnostics and therapies. CSCs are regulated by signals of the tumor microenvironment as well as intrinsic genetic and epigenetic modulators. H19, the first identified lncRNA is involved in the development and progression of many different cancer types. Recently, H19 has been demonstrated to be implicated in the regulation of CSCs in different types of cancers. The aim of this review is to provide an overview of the role and mechanisms of action of H19 in the regulation of CSCs. We summarize how H19 may regulate CSC division and cancer cell reprogramming, thus affecting metastasis and drug resistance. We also discuss the potential clinical implications of H19.

The acidic tumor microenvironment drives a stem-like phenotype in melanoma cells

Abstract

Acidosis characterizes the microenvironment of most solid tumors and is considered a new hallmark of cancer. It is mainly caused by both “aerobic” and “anaerobic” glycolysis of differently adapted cancer cells, with the final product lactic acid being responsible of the extracellular acidification. Many evidences underline the role of extracellular acidosis in tumor progression. Among the different findings, we demonstrated that acidosis-exposed cancer cells are characterized by an epithelial-to-mesenchymal transition phenotype with high invasive ability, high resistance to apoptosis, anchorage-independent growth, and drug therapy. Acidic melanoma cells over-express SOX2, which is crucial for the maintenance of their oxidative metabolism, and carbonic anhydrase IX, that correlates with poor prognosis of cancer patients. Considering these evidences, we realized that the profile outlined for acid cancer cells inevitably remind us the stemness profile. Therefore, we wondered whether extracellular acidosis might induce in cancer cells the acquisition of stem-like properties and contribute to the expansion of the cancer stem cell sub-population. We found that a chronic adaptation to acidosis stimulates in cancer cells the expression of stem-related markers, also providing a high in vitro/in vivo clonogenic and trans-differentiating ability. Moreover, we observed that the acidosis-induced stem-like phenotype of melanoma cells was reversible and related to the EMT induction. These findings help to characterize a further aspect of stem cell niche, contributing to the sustainment and expansion of cancer stem cell subpopulation. Thus, the usage of agents controlling tumor extracellular acidosis might acquire great importance in the clinic for the treatment of aggressive solid tumor.

Key messages

• Extracellular acidosis up-regulates EMT and stem-related markers in melanoma cells

• Acidic medium up-regulates in vitro self-renewal capacity of melanoma cells

• Chronic acidosis adaptation induces trans-differentiation ability in melanoma cells

• Melanoma cells adapted to acidosis show higher tumor-initiating potential than control cells

• Extracellular acidosis promotes a stem-like phenotype in prostate and colorectal carcinoma cells

Targeting of cancer stem cells by differentiation therapy

Chemoresistance is a hallmark of cancer stem cells (CSCs). To develop novel therapeutic strategies that target CSCs, we established osteosarcoma-initiating (OSi) cells by introducing the c-Myc gene into bone marrow stromal cells derived from Ink4a/Arf KO mice. These OSi cells include bipotent committed cells (similar to osteochondral progenitor cells) with a high tumorigenic activity as well as tripotent cells (similar to mesenchymal stem cells) of low tumorigenicity. We recently showed that the tripotent OSi cells are highly resistant to chemotherapeutic agents, and that depolymerization of the actin cytoskeleton in these cells induces their terminal adipocyte differentiation and suppresses their tumorigenicity. We here provide an overview of modulation of actin cytoskeleton dynamics associated with terminal adipocyte differentiation in osteosarcoma as well as discuss the prospects for new therapeutic strategies that target chemoresistant CSCs by inducing their differentiation.

Deubiquitinase USP7-mediated MCL-1 up-regulation enhances Arsenic and Benzo(a)pyrene co-exposure-induced Cancer Stem Cell-like property and Tumorigenesis

Rationale: MCL-1 is up-regulated in cancer and a target for cancer treatment. How MCL-1 is up-regulated and whether MCL-1 up-regulation plays a role in tumorigenic process is not well-known. Arsenic and benzo(a)pyrene (BaP) are well-recognized lung carcinogens and we recently reported that arsenic and BaP co-exposure acts synergistically in inducing cancer stem cell (CSC)-like property and lung tumorigenesis. This study was performed to further investigate the underlying mechanism focusing on the role of MCL-1. Methods: The spheroid formation assay and nude mouse tumorigenesis assay were used to determine the CSC-like property and tumorigenicity of arsenic plus BaP co-exposure-transformed human bronchial epithelial BEAS-2B cells, respectively. Biochemical, pharmacological and genetic approaches were used to manipulate gene expressions, dissect signaling pathways and determine protein-protein interactions. Both loss-of-function and gain-of-function approaches were used to validate the role of MCL-1 in arsenic plus BaP co-exposure-enhanced CSC-like property and tumorigenicity. Results: Arsenic plus BaP co-exposure-transformed cells express significantly higher protein levels of MCL-1 than the passage-matched control, arsenic or BaP exposure alone-transformed cells. Knocking down MCL-1 levels in arsenic plus BaP co-exposure-transformed cells significantly reduced their apoptosis resistance, CSC-like property and tumorigenicity in mice. Mechanistic studies revealed that arsenic plus BaP co-exposure up-regulates MCL-1 protein levels by synergistically activating the PI3K/Akt/mTOR pathway to increase the level of a deubiquitinase USP7, which in turn reduces the level of MCL-1 protein ubiquitination and prevents its subsequent proteasome degradation. Conclusions: The deubiquitinase USP7-mediated MCL-1 up-regulation enhances arsenic and BaP co-exposure-induced CSC-like property and tumorigenesis, providing the first evidence demonstrating that USP7 stabilizes MCL-1 protein during the tumorigenic process.

Arsenic and benzo[a]pyrene co-exposure acts synergistically in inducing cancer stem cell-like property and tumorigenesis by epigenetically down-regulating SOCS3 expression

Arsenic and benzo[a]pyrene (BaP) are among the most common environmental carcinogens causing lung cancer. Millions of people are exposed to arsenic through consuming arsenic-contaminated drinking water. High levels of BaP are found in well-done barbecued meat and other food in addition to cigarette smoke. Hence, arsenic and BaP co-exposure in humans is common. However, the combined health effect and the underlying mechanism of arsenic and BaP co-exposure have not been well-understood. In this study we investigate the combined tumorigenic effect of arsenic and BaP co-exposure and the mechanism using both cell culture and mouse models. It was found that arsenic (sodium arsenite, 1.0 µM) and BaP (2.5 µM) co-exposure for 30 weeks synergizes in inducing malignant transformation of immortalized non-tumorigenic human bronchial epithelial cells and cancer stem cell (CSC)-like property to enhance their tumorigenicity. In animal studies, A/J mice were exposed to arsenic in drinking water (sodium arsenite, 20 ppm) starting from gestation day 18. After birth, the dams continuously received arsenic water throughout lactation. At weaning (3 weeks of age), male offspring were exposed to either arsenic alone via drinking the same arsenic water or exposed to arsenic plus BaP. BaP was administered via oral gavage (3 µmol per mouse per week) once a week starting from 3 weeks of age for 8 weeks. All mice were euthanized 34-weeks after the first BaP exposure. It was found that mice in control and arsenic exposure alone group did not develop lung tumors. All mice in BaP exposure alone group developed lung adenomas. However, arsenic and BaP co-exposure synergized in increasing lung tumor multiplicity and tumor burden. Furthermore, 30% of mice in arsenic and BaP co-exposure group also developed lung adenocarcinomas. Mechanistic studies revealed that arsenic and BaP co-exposure does not produce more BPDE-DNA adducts than BaP exposure alone; but acts synergistically in activating aryl hydrocarbon receptor (AhR) to up-regulate the expression of a histone H3 lysine 9 methyltransferase SUV39H1 and increase the level of suppressive H3 lysine 9 dimethylation (H3K9me2), which down-regulates the expression of tumor suppressive SOCS3 leading to enhanced activation of Akt and Erk1/2 to promote cell transformation, CSC-like property and tumorigenesis. Together, these findings suggest that arsenic and BaP co-exposure synergizes in causing epigenetic dysregulation to enhance cell transformation, CSC-like property and tumorigenesis.

Stem Cell Therapy for Hepatocellular Carcinoma: Future Perspectives

Hepatocellular carcinoma (HCC) is one of the most common types of cancer and results in a high mortality rate worldwide. Unfortunately, most cases of HCC are diagnosed in an advanced stage, resulting in a poor prognosis and ineffective treatment. HCC is often resistant to both radiotherapy and chemotherapy, resulting in a high recurrence rate. Although the use of stem cells is evolving into a potentially effective approach for the treatment of cancer, few studies on stem cell therapy in HCC have been published. The administration of stem cells from bone marrow, adipose tissue, the amnion, and the umbilical cord to experimental animal models of HCC has not yielded consistent responses. However, it is possible to induce the apoptosis of cancer cells, repress angiogenesis, and cause tumor regression by administration of genetically modified stem cells. New alternative approaches to cancer therapy, such as the use of stem cell derivatives, exosomes or stem cell extracts, have been proposed. In this review, we highlight these experimental approaches for the use of stem cells as a vehicle for local drug delivery.

Chronic Hexavalent Chromium Exposure Induces Cancer Stem Cell-Like Property and Tumorigenesis by Increasing c-Myc Expression

Hexavalent chromium [Cr(VI)] is one of the most common environmental carcinogen causing lung cancer in humans; however, the mechanism of Cr(VI) carcinogenesis remains elusive. Cancer stem cells (CSCs) are considered as cancer initiating and maintaining cells. Ours and other recent studies showed that chronic Cr(VI) exposure induces CSC-like property representing an important mechanism of Cr(VI) carcinogenesis. However, how Cr(VI) exposure induces CSC-like property remains largely unknown. In this study, we found that stably knocking down the expression of c-Myc, a proto-oncogene and one of key stemness factors playing critical roles in cancer initiation and progression, in Cr(VI)-transformed human bronchial epithelial cells [BEAS-2B-Cr(VI)] significantly decreased their CSC-like property and tumorigenicity in mice. Moreover, stably knocking down c-Myc expression in parental nontransformed BEAS-2B cells significantly impaired the capability of chronic Cr(VI) exposure to induce CSC-like property and cell transformation. It was also found that stably overexpressing c-Myc alone in parental nontransformed BEAS-2B cells is capable of causing CSC-like property and cell transformation. Mechanistic studies showed that chronic Cr(VI) exposure increases c-Myc expression by down-regulating the level of microRNA-494 (miR-494). It was further determined that overexpressing miR-494 significantly reduces Cr(VI)-induced CSC-like property, cell transformation, and tumorigenesis mainly through down-regulating c-Myc expression. Together, these findings indicate that chronic low dose Cr(VI) exposure induces CSC-like property and tumorigenesis by increasing c-Myc expression through down-regulating the level of miR-494, revealing an important role of the proto-oncogene c-Myc in Cr(VI) carcinogenesis.

Hypoxia inducible factors in the tumor microenvironment as therapeutic targets of cancer stem cells

Cancer stem cells (CSC) constitute a small area of the tumor mass and are characterized by self-renewal, differentiation and the ability to promote the development of secondary chemo-resistant tumors. Self-renewal of CSCs is regulated through various signaling pathways including Hedgehog, Notch, and Wnt/β-catenin pathways. A few surface markers have been identified, which provide a means of targeting CSCs according to tumor type. Depending on the proximity of CSCs to the tumor hypoxic niche, hypoxia-inducible factors (HIFs) can play a critical role in modulating several CSC-related characteristics. For instance, the upregulation of HIF-1 and HIF-2 at tumor sites, which correlates with the expansion of CSCs and poor cancer prognosis, has been demonstrated. In this review, we will discuss the mechanisms by which hypoxia enhances the development of CSCs in the tumor microenvironment. Targeting HIFs in combination with other common therapeutics is pre-requisite for effective eradication of CSCs.

Sonic hedgehog pathway activation regulates cervical cancer stem cell characteristics during epithelial to mesenchymal transition

Resistance to therapy and metastasis remains one of the leading causes of mortality due to cervical cancer despite advances in detection and treatment. The mechanism of epithelial to mesenchymal transition (EMT) provides conceptual explanation to the invasiveness and metastatic spread of cancer but it has not been fully understood in cervical cancer. This study aims to investigate the mechanism by which silencing of E-cadherin gene regulates EMT leading to proliferation, invasion, and chemoresistance of cervical cancer cells through the Hedgehog (Hh) signaling pathway. We developed an in vitro EMT model by the knockdown of E-cadherin expression in cervical cancer cell lines. To understand the role of developmental pathway like Hh in the progression of cervical cancer, we investigated the expression of Hh pathway mediators by array in E-cadherin low cervical cancer cells and observed upregulation of Hh pathway. This was further validated on low passage patient-derived cell lines and cervical carcinoma tissue sections from cervical cancer patients. Further, we evaluated the role of two inhibitors (cyclopamine and GANT58) of the Hh pathway on invasiveness and apoptosis in E-cadherin low cervical cancer cells. In conclusion, we observed that inhibition of Hh pathway with GANT58 along with current therapeutic procedures could be more effective in targeting drug-resistant EMT cells and bulk tumor cells in cervical cancer.

Metal carcinogen exposure induces cancer stem cell-like property through epigenetic reprograming: A novel mechanism of metal carcinogenesis

Arsenic, cadmium, nickel and hexavalent chromium are among the most common environmental pollutants and potent carcinogens. Chronic exposure to these metals causes various types of cancer in humans, representing a significant environmental health issue. Although under active investigation, the mechanisms of metal carcinogenesis have not been clearly defined. One common feature of these metal carcinogens is that they are all able to cause various epigenetic dysregulations, which are believed to play important roles in their carcinogenicity. However, how metal carcinogen-caused epigenetic dysregulation contributes to metal carcinogenesis remains largely unknown. The evolution of cancer stem cell (CSC) theory has opened exciting new avenues for studying the mechanism of metal carcinogenesis. Increasing evidence indicates that chronic metal carcinogen exposure produces CSC-like cells through dysregulated epigenetic mechanisms. This review will first provide some brief introductions about CSC, epigenetics and epigenetic regulation of CSCs; then summarize progresses in recent studies on metal carcinogen-induced CSC-like property through epigenetic reprograming as a novel mechanism of metal carcinogenesis. Some perspectives for future studies in this field are also presented.

Multifaceted Mechanisms of Areca Nuts in Oral Carcinogenesis: the Molecular Pathology from Precancerous Condition to Malignant Transformation

Oral cancer is one of the most frequent malignant diseases worldwide, and areca nut is a primary carcinogen causing this cancer in Southeast Asia. It has been widely reported that areca nut induced several cytotoxic effects in oral cells, including ROS generation, inflammation, tissue hypoxia, DNA damage, and cell invasion. Recently, through chronic exposure model, more extensive pathological effects due to areca nut have been found. These include the induction of autophagy, promotion of epithelial- mesenchymal transition, and facilitation of cancer stemness conversion. Clinical findings support these adverse effects. Oral submucosal fibrosis, a premalignant condition, is prevalent in the area with habitual chewing of areca nuts. Consistently, oral cancer patients with habitual chewing areca nut exhibit more aggressive phenotypes, including resistance to chemo-radiotherapy. In this review, we comprehensively discuss and concisely summarize the up-to-date molecular and cellular mechanisms by which areca nuts contribute to malignant transformation. This review may provide critical information regarding clinical applications in risk assessment, disease prevention, diagnosis, and personalized therapeutics for areca nut-induced oral malignancy.

F-Box/WD Repeat Domain-Containing 7 Induces Chemotherapy Resistance in Colorectal Cancer Stem Cells

Although the cancer stem cell (CSC) concept has provided a reasonable explanation for cancer recurrence following chemotherapy, the relationship between CSCs and chemotherapy resistance has not been thoroughly investigated, especially in solid tumors. We aimed to identify the mechanism underlying colorectal cancer (CRC) chemoresistance focusing on the cell cycle mediator F-Box/WD repeat domain-containing 7 (FBXW7). From 55 consecutive CRC cases who underwent neoadjuvant chemotherapy (NAC) or neoadjuvant chemoradiotherapy (NACRT) at Kyoto University Hospital, pre-treatment endoscopic biopsy specimens were collected and divided into two groups upon immunohistochemical (IHC) analysis: 21 cases of FBXW7 high expression (FBXW7-high group) and 34 cases of low expression (FBXW7-low group). High FBXW7 expression in pre-treatment biopsy specimen was significantly associated with poor pathological therapeutic effect (p = 0.019). The proportion of FBXW7-positive cells in surgically resected CRC specimens from patients who underwent NAC or NACRT was significantly higher than that in the pre-treatment biopsy specimens (p < 0.001). The expression of FBXW7 was inversely correlated with that of Ki67 in both pre-treatment biopsy specimens and surgically resected specimens. FBXW7 expression in the EpCAM^high/CD44^high subpopulation isolated by flow cytometry from CRC samples was significantly higher than that in the EpCAM^high/CD44^low subpopulation. Cell-cycle analysis in CRC cell lines revealed that, upon FBXW7 silencing, the proportion of G0/G1 cells was significantly lower than that in control cells. Moreover, knockdown of FBXW7 in CRC cell lines increased the sensitivity to anti-cancer drugs in vitro and in vivo. A subset of CRC stem cells possesses chemoresistance through FBXW7 expression. Cell cycle arrest induced by FBXW7 expression should be considered as a potential therapeutic target to overcome chemoresistance in CRC stem cell subsets.

ROCK Inhibition Induces Terminal Adipocyte Differentiation and Suppresses Tumorigenesis in Chemoresistant Osteosarcoma Cells

Tumors comprise heterogeneous cell types including cancer stem cells (CSC), progenitor cells, and differentiated cells. Chemoresistance is a potential cause of relapse and a key characteristic of CSC, but the development of novel therapeutic approaches for targeting these cells has been limited. We previously established osteosarcoma-initiating (OSi) cells by introducing the gene for c-Myc into bone marrow stromal cells of Ink4a/Arf knockout mice. These OSi cells are composed of two distinct clones: highly tumorigenic cells (AX cells), similar to bipotent committed osteochondral progenitor cells, and tripotent cells of low tumorigenicity (AO cells), similar to mesenchymal stem cells. Here we show that depolymerization of the actin cytoskeleton induces terminal adipocyte differentiation and suppresses tumorigenesis in chemoresistant OSi cells. In contrast to AX cells, AO cells were highly resistant to conventional chemotherapeutic agents such as doxorubicin and were thus identified as chemoresistant cells. Inhibition of Rho-associated coiled-coil containing protein kinase (ROCK) elicited terminal adipocyte differentiation in chemoresistant AO cells through negative regulation of the transcriptional coactivator megakaryoblastic leukemia 1 associated with actin depolymerization. The clinically administered ROCK inhibitor fasudil significantly suppressed growth in vitro and tumorigenicity in vivo of chemoresistant AO cells as well as of OSi cells. Our findings thus suggest a new therapeutic strategy based on the induction of trans-terminal differentiation via modulation of actin cytoskeleton dynamics for therapy-resistant osteosarcoma stem cells. SIGNIFICANCE: These findings suggest that induction of trans-terminal differentiation through regulation of actin dynamics is a potential novel therapeutic approach for targeting chemoresistant stem-like tumor cells.

Norcantharidin inhibits the DDR of bladder cancer stem-like cells through cdc6 degradation

Introduction: Cancer stem cells (CSCs) are the main source of tumor resistance and recurrence. At present, the main treatment for patients with advanced or metastatic bladder cancer (BCa) is cisplatin-based combination chemotherapy. However, CSCs are not sensitive to DNA-damaging drugs due to their enhanced DNA damage response (DDR) activity. Materials and methods: Bladder cancer stem cell-like cells (BCSLCs) were obtained by treating UMUC3 cells with cisplatin. The characteristics of the BCSLCs were identified by qPCR, flow cytometry, scratch wound-healing assays, transwell assays, tumorigenic ability experiments, Edu assays and Western blot assays in vivo. After BCSLCs were treated with norcantharidin (NCTD), the expression of Cdc6 and activation of the ATR-Chk1 pathway were detected by Western blotting. A subcutaneous tumor model in nude mice was successfully established to assess the anti-tumor efficacy of NCTD and cisplatin either alone or in combination in vivo. The tumor tissues were detected by immunohistochemistry. Results: The derived BCSLCs showed higher expression of stemness markers, increased invasiveness, improved resistance to multiple chemotherapeutics, and higher tumorigenic capacity in vivo. The protein expression level of chromatin-binding Cdc6 was increased in BCSLCs; however, NCTD decreased the level of chromatin-binding Cdc6 and inhibited the activation of the ATR-Chk1 pathway, which ultimately led to reduction in DDR activity in BCSLCs. NCTD enhanced the killing effect of cisplatin on BCSLCs in vitro and vivo. NCTD combined with cisplatin enhanced cisplatin-induced DNA damage in BCSLCs. Conclusion: Long-term cisplatin treatment can enrich BCSLCs. However, NCTD enhanced the killing effect of cisplatin on BCSLCs in vitro and vivo. The mechanism is inhibiting the DDR activity by reducing the expression of chromatin-binding Cdc6.

Pinostrobin inhibits proliferation and induces apoptosis in cancer stem-like cells through a reactive oxygen species-dependent mechanism

Current treatments and targeted therapies for malignancies are limited due to their severe toxicity and the development of resistance against such treatments, which leads to relapse. Past evidence has indicated that a number of plant-derived dietary agents possess biological activity against highly tumorigenic and resistant cell populations associated with cancer relapse. These subpopulations, termed cancer stem-like cells (CSCs), have been targeted with plant-derived dietary flavonoids. The present study was undertaken to assess the anti-proliferative potential of pinostrobin, a dietary flavonoid, against CSCs. Sphere-forming cells were developed from HeLa cell lines using specific culture conditions. The existence of a CSC population was confirmed by the morphological examination and analysis of surface markers using confocal microscopy and flow cytometry. The effect of pinostrobin on the cell viability of the CSC population, evaluated through MTT reduction assays and the expression levels of surface markers (CD44⁺ and CD24⁺), was studied through various biological assays. HeLa-derived CSCs showed higher CD44⁺ and lower CD24⁺ expression. Pinostrobin inhibited the self-renewal capacity and sphere formation efficiency of CSCs in a dose-dependent manner. Increased ROS production, and decreased mitochondrial membrane potential and CD44⁺ expression indicated that pinostrobin promoted ROS-mediated apoptosis in CSCs. These results thus demonstrate the therapeutic potential and effectiveness of pinostrobin in the chemoprevention and relapse of cancer by targeting the CSC population. Thus, pinostrobin, in combination with currently available chemo and radiation therapies, could possibly be used as a safe strategy to alleviate adverse treatment effects, together with enhancing the efficacy.

The anti-proliferative potential of pinostrobin, a dietary flavonoid, is evaluated against cancer stem-like cells.

Dishevelled-3 phosphorylation is governed by HIPK2/PP1Cα/ITCH axis and the non-phosphorylated form promotes cancer stemness via LGR5 in hepatocellular carcinoma

Dishevelled-3 (Dvl3) is regarded as a binding hub with many different interacting partners. However, its regulation and mechanism on cancer stemness remain to be explored. In this study, we showed that Dvl3 was significantly overexpressed in human hepatocellular carcinomas (HCCs) and promoted cancer stemness both in vitro and in vivo. We found that the non-phosphorylated (NP)-Dvl3 was more stable than the phosphorylated form, more active in activating β-catenin transcriptional activity, and more potent in enhancing self-renewal ability in HCC cells. Mechanistically, we confirmed that the homeodomain-interacting protein kinase-2 (HIPK2) and E3 ubiquitin ligase ITCH were able to physically bind to Dvl3 protein. Knockdown of HIPK2 and the protein phosphatase regulatory unit C-alpha (PP1Cα) resulted in sustained Dvl3 phosphorylation and hence decrease in the NP form of Dvl3. On the other hand, knockdown of E3 ubiquitin ligase ITCH reduced the phosphorylation-induced degradation and stabilized the phosphorylated Dvl3 protein. Furthermore, the NP-Dvl3 enhanced the LGR5 promoter activity to upregulate LGR5 expression, which was associated with increased cancer stemness in HCC. Our findings established that HIPK2/PP1Cα/ITCH axis sustains the de-phosphorylation of Dvl3. This post-translational modification of Dvl3 in turn maintains LGR5 expression and enhances the cancer stemness properties in HCC.

An epidemiologic perspective on the stem cell hypothesis in human carcinogenesis

BACKGROUND

Tomasetti and Vogelstein have hypothesized that the patterns of cancer incidence in various cells and tissues are highly correlated with the estimated lifetime number of stem cell divisions. The authors reviewed the risks in tissues of 17 types of cancer from the United States and 69 additional countries. Positive correlations were observed consistently between the tissue - specific cancer incidence and the estimated lifetime number of stem cell divisions. The authors concluded that approximately two-thirds of global cancer incidence may be attributed to random DNA replication errors.

METHODS

An epidemiologic perspective is presented that may serve as a counterpoint in interpreting organ-specific cancer risks. The unifying nature of the Tomasetti/Vogelstein hypothesis must be viewed in the context of diverse and contrasting global trends and patterns of types and "causes" of cancers that are closely linked with economic development and cultural lifestyle practices. The presentation is organized by reviewing the global burden of cancer; concepts of causal inferences and counterfactual assumptions; multifactorial causes of hepatocellular carcinoma and a hierarchy of causes that varies internationally; tobacco carcinogenesis and the multiplex associations with 19 cancer sites and tissues; profile in contrasts in transit through the small and large intestine.

OBSERVATIONS AND CONCLUSIONS

It is readily recognized that DNA replication errors and number of stem cell divisions may vary in individuals and populations due to external environmental genotoxic chemicals and biologic agents, and internal hormonal and metabolic factors. There is a striking contrast in the risk of adenocarcinoma in the small intestine with that in the large intestine. Tomasetti and Vogelstein indicated that the cumulative number of divisions of stem cells over a lifetime in normal epithelial mucosal cells from colorectal cancer patients was 4 time greater than in the epithelial tissue from patients with adenocarcinoma of the small intestine. Their conclusion would suggest a "seed" and "soil" interaction rather than exclusively the independence of either component. Namely, that the contrasting physiological, biochemical, microbial and immunological features in the lumen and on the mucosal surface of the large intestine, in contrast to that in the small intestine, would foster molecular genetic and epigenetic events that are advantageous to neoplasia in the large intestine.

Development of a functional thyroid model based on an organoid culture system

The low turnover rate of thyroid follicular cells and the lack of a long-term thyroid cell culture system have hampered studies of thyroid carcinogenesis. We have now established a thyroid organoid culture system that supports thyroid cell proliferation in vitro. The established mouse thyroid organoids performed thyroid functions including thyroglobulin synthesis, iodide uptake, and the production and release of thyroid hormone. Furthermore, transplantation of the organoids into recipient mice resulted in the formation of normal thyroid-like tissue capable of iodide uptake and thyroglobulin production in vivo. Finally, forced expression of oncogenic NRAS (NRAS^Q61R) in thyroid organoids established from p53 knockout mice and transplantation of the manipulated organoids into mouse recipients generated a model of poorly differentiated thyroid cancer. Our findings suggest that this newly developed thyroid organoid culture system is a potential research tool for the study of thyroid physiology and pathology including thyroid cancer.

Metabolic features of cancer stem cells: the emerging role of lipid metabolism

Cancer stem cells (CSCs) are an uncommon subset of tumor cells capable of self-renewal, differentiating, and recreating the parental tumor when transplanted into the murine background. Over the past two decades, efforts toward understanding CSC biology culminated into identifying a set of signaling pathways sustaining "stemness". Nevertheless, while metabolic rewiring is nowadays considered a hallmark of cancer, no consensus has been reached on the metabolic features underlying the plastic nature of CSCs, which are capable of residing in a dormant state, and able to rapidly proliferate when the need to repopulate the tumor mass arises. An emerging concept in the field of CSC metabolism is that these cells are extremely reliant on the activity of enzymes involved in lipid metabolism, such as stearoyl-CoA desaturase 1 (SCD1) and 3-hydroxy-3-methylglutharyl-coenzyme A reductase (HMG-CoAR). Indeed, SCD1 and HMG-CoAR have been described as key factors for the correct function of a number of concatenated pathways involved in CSC fate decision, such as Hippo and Wnt. In the present review, we describe metabolic futures of CSCs with a special focus on lipid metabolism, which until now represents an underappreciated force in maintaining CSCs and an attractive therapeutic target.

Isolation and identification of tumor-initiating cell properties in human gallbladder cancer cell lines using the marker cluster of differentiation 133

The present study aimed to isolate and identify the properties of the cluster of differentiation (CD)133⁺ subset in human gallbladder cancer cells. The CD133⁺ and CD133⁻ subpopulations of the GBC-SD cell line were separated using immunomagnetic separation, and the biological features of the two subpopulations were analyzed in vitro and in vivo. In particular, the present study aimed to determine whether the two subpopulations were resistant to anti-tumor reagents and to identify the underlying molecular mechanisms involved. Following cell sorting of GBC-SD cells using immunomagnetic beads, 90.2±2% of cells were identified as CD133⁺. Immunofluorescence confirmed that CD133 was expressed at higher levels in the Cd133⁺ group compared with the CD133⁻ group. The proliferation of the CD133⁺ group was significantly increased compared with the CD133⁻ group in vitro and in vivo. Following treatment with fluorouracil or gemcitabine, cells in the CD133⁺ group exhibited a decreased sensitivity to these drugs. The number of transmembrane cells was significantly increased in the CD133⁺ group compared with the CD133⁻ group. In addition, the expression levels of ATP binding cassette subfamily G member 2, CD44, C-X-C motif chemokine receptor 4 (CXCR4), phosphorylated-protein kinase B (Akt) and CD133 in the CD133⁺ group were significantly increased, compared with those in the CD133⁻ group. In CD133⁺ GBC-SD cells, stromal cell-derived factor 1α (SDF-1α) or treatment with AMD3100, an inhibitor of CXCR4, promotes or suppresses the SDF-1α/CXCR4 axis, respectively, resulting in increased or decreased CD133 expression through the Akt signaling pathway. Inhibition of the Akt signaling pathway resulted in decreased CD133 expression in GBC-SD cells. Immunomagnetic beads were successfully used for isolation of the CD133⁺ subset from GBC-SD cells. Furthermore, the CD133⁺ subset revealed an increased potential for tumor formation, cell proliferation, invasion and resistance to chemotherapeutic agents with expression of stem cell-associated genes. Therefore, in GBC-SD cells, the CXCR4/Akt/CD133 signaling pathways may be activated.

Dynamic changes in CD44v-positive cells after preoperative anti-HER2 therapy and its correlation with pathologic complete response in HER2-positive breast cancer

Chemotherapy has been reported to increase the proportion of cancer stem cells (CSCs) and to promote epithelial-mesenchymal transition (EMT) phenotype changes. Anti-HER2 therapy may provide a strategy for eliminating CSC and EMT, which contribute to therapeutic resistance. No study has determined the changes in the quantity or characteristics of CSCs or circulating tumor cells (CTCs) with EMT phenotype during preoperative anti-HER2 therapy, and whether these changes correlate to response to dual anti-HER2 therapy. In a prospective clinical trial to evaluate pharmacodynamic biomarkers, 18 patients with operable primary HER2-positive breast cancer received dual anti-Her2 preoperative therapy with trastuzumab and lapatinib with paclitaxel. Proportions of tumor cells with CSC characteristics and EMT markers in CTC's were estimated at baseline, after 6 and 18 weeks of preoperative therapy to determine the quantitative cutoff value to predict pathologic complete response (pCR). Out of 18 patients, 8 (44%) had a pCR; 5 of these 8 patients (62%) were positive for CD44v at baseline and none were positive on the 6-week biopsy. In contrast, 6 of the 10 patients without pCR exhibited persistent levels, or enrichment of CD44v proportion and expression at 6 and 18 weeks (p=0.0128). Other biomarkers were not statistically significant predictors of pCR. Enrichment of CD44v-positive tumor cells after dual anti-HER2 therapy alone may predict poor response to dual anti-HER2 therapy plus chemotherapy.

Targeted molecular ablation of cancer stem cells for curing gastrointestinal cancers

Abundance of the ATPase-binding cassette (ABC) transporters and deranged self-renewal pathways characterize the presence of cancer stem cells (CSCs) in gastrointestinal cancers (GI cancers), which play crucial roles in tumorigenesis, chemotherapy resistance, tumor recurrence, and cancer metastasis. Therefore, in order to ensure high cure rates, chemoquiescence, CSCs should be ablated. Recent advances in either understanding CSCs or biomarker identification enable scientists to develop techniques for ablating CSCs and clinicians to provide cancer cure, especially in GI cancers characterized by inflammation-driven carcinogenesis. Areas covered: A novel approach to ablate CSCs in GI cancers, including esophageal, gastric, and colon cancers, is introduced along with explored underlying molecular mechanisms. Expert commentary: Though CSC ablation is still in the empirical stages and not in clinical practice, several strategies for ablating CSCs in GI cancers had been published, proton-pump inhibitors (PPIs) that regulate the membrane-bound ABC transporters, which underlie drug resistance; chloroquine (CQ) that inhibits autophagy, which is responsible for tumor survival; Hedgehog/Wnt/Notch inhibitors that influence the underlying stem-cell growth, and some natural products including Korean red ginseng, cancer-preventive kimchi, Artemisia extract, EGCG from green tea, and walnut extracts.

The Roles of ROS in Cancer Heterogeneity and Therapy

Cancer comprises a group of heterogeneous diseases encompassing high rates of morbidity and mortality. Heterogeneity, which is a hallmark of cancer, is one of the main factors related to resistance to chemotherapeutic agents leading to poor prognosis. Heterogeneity is profoundly affected by increasing levels of ROS. Under low concentrations, ROS may function as signaling molecules favoring tumorigenesis and heterogeneity, while under high ROS concentrations, these species may work as cancer modulators due to their deleterious, genotoxic or even proapoptotic effect on cancer cells. This double-edged sword effect represented by ROS relies on their ability to cause genetic and epigenetic modifications in DNA structure. Antitumor therapeutic approaches may use molecules that prevent the ROS formation precluding carcinogenesis or use chemical agents that promote a sudden increase of ROS causing considerable oxidative stress inside tumor mass. Therefore, herein, we review what ROS are and how they are produced in normal and in cancer cells while providing an argumentative discussion about their role in cancer pathophysiology. We also describe the various sources of ROS in cancer and their role in tumor heterogeneity. Further, we also discuss some therapeutic strategies from the current landscape of cancer heterogeneity, ROS modulation, or ROS production.

Human cancer stem cells are a target for cancer prevention using (-)-epigallocatechin gallate

Purpose

Our previous experiments show that the main constituent of green-tea catechins, (−)-epigallocatechin gallate (EGCG), completely prevents tumor promotion on mouse skin initiated with 7,12-dimethylbenz(a)anthracene followed by okadaic acid and that EGCG and green tea extract prevent cancer development in a wide range of target organs in rodents. Therefore, we focused our attention on human cancer stem cells (CSCs) as targets of cancer prevention and treatment with EGCG.

Methods

The numerous reports concerning anticancer activity of EGCG against human CSCs enriched from cancer cell lines were gathered from a search of PubMed, and we hope our review of the literatures will provide a broad selection for the effects of EGCG on various human CSCs.

Results

Based on our theoretical study, we discuss the findings as follows: (1) Compared with the parental cells, human CSCs express increased levels of the stemness markers Nanog, Oct4, Sox2, CD44, CD133, as well as the EMT markers, Twist, Snail, vimentin, and also aldehyde dehydrogenase. They showed decreased levels of E-cadherin and cyclin D1. (2) EGCG inhibits the transcription and translation of genes encoding stemness markers, indicating that EGCG generally inhibits the self-renewal of CSCs. (3) EGCG inhibits the expression of the epithelial-mesenchymal transition phenotypes of human CSCs. (4) The inhibition of EGCG of the stemness of CSCs was weaker compared with parental cells. (5) The weak inhibitory activity of EGCG increased synergistically in combination with anticancer drugs.

Conclusions

Green tea prevents human cancer, and the combination of EGCG and anticancer drugs confers cancer treatment with tissue-agnostic efficacy.

Aldehyde dehydrogenase 1A1 (ALDH1A1) expression by immunohistochemistry is associated with chemo-refractoriness in patients with high-grade ovarian serous carcinoma

Aldehyde dehydrogenase-1A1 (ALDH1A1), CD133, CD44, and CD24 have been reported as cancer stem cell markers in ovarian cancers. The goal of our study was to assess the prognostic significance of these markers in patients with advanced serous ovarian cancer. Formalin-fixed, paraffin-embedded tissues from 347 ovarian cancers were used to construct a microarray. Immunohistochemical studies for ALDH1A1, CD133, CD44, and CD24 were performed and scored semiquantitatively by 2 pathologists based on intensity and percent of positive immunoreactive cells. Immunohistochemistry was compared to clinical parameters and survival. Of the 347 cases, early stage disease, nonserous tumors, cases with incomplete therapy, and cores with no tumor were excluded. Immunohistochemistry was interpretable in 124 of the 136 stage III and IV ovarian serous carcinoma. ALDH1A1, CD24, and CD44 were variably detected in both tumor and stromal cells, and immunoreactivity in tumor was stronger than in stromal cells. CD133 immunoreactivity was not quantified due to nonspecific staining in tumor and stroma. Statistical analyses using χ² and Student t test revealed that ALDH1A1-positive (n=53) carcinoma were 3 times more likely to demonstrate platinum refractoriness than ALDH1A1-negative (n=71) tumors (17% vs. 6%, respectively; p=.04); however, neither progression free nor overall survival was influenced by ALDH1A1 status in this cohort. The expression of CD44 and CD24 had no clinicopathological associations in the present study. Our study supports that ALDH1A1 expression is associated with poor response to platinum-based therapy in patients with high-grade ovarian serous carcinoma. Further study of this relationship is needed to understand how this could impact clinical care.

Cancer stem cell research in Iran: potentials and challenges

Treatment modalities can reduce cancer-related mortality; however, a majority of patients develop drug resistance, metastasis and relapse. It has been proposed that tumorigenic characteristics of tumors are related to a proportion of cancer cells, termed cancer stem cells (CSCs). Following the first evidence regarding the existence of CSC population in acute myeloid leukemia in 1997, publications in CSCs field showed an explosive trend in all cancer types around the world. First research paper in the field of CSCs in Iran was published in 2004 on prostate cancer. Subsequently, an annual number of publications in the field of CSCs displayed a rapidly growing trend. Therefore, in the current review, we have presented a comprehensive evaluation of the CSCs research in Iran.

Cancer Stem Cells in Hepatocellular Carcinoma

BACKGROUND

Hepatocellular carcinoma is one of the most common cancers and the second leading cause of cancer-related deaths worldwide. Only a small proportion of patients benefit from curative treatment and the prognosis is very poor for the majority of cases due to late presentation, resistance to chemotherapy and high recurrence rate. In recent years, progress in stem cell biology allowed us to explain that hierarchically organized cancer stem cells (CSCs) drive histological and functional heterogeneity of hematological malignancies and solid tumors.

METHODS AND RESULTS

Also referred to as tumor-initiating cells, CSCs have been isolated from both hepatocellular carcinoma (HCC) cell lines and primary tumors by using hepatic progenitor markers. Although there is still no consensus on cancer stem cell phenotype in HCC, single or combined use of CSC markers defines a minor population of tumor cells with the capacity of self-renewing and the ability to recapitulate the original tumor heterogeneity.

CONCLUSIONS

This review focuses on the biological features of CSCs and their potential as diagnostic/prognostic tools and therapeutic targets in HCC.

Crucial role of carbonic anhydrase IX in tumorigenicity of xenotransplanted adult T-cell leukemia-derived cells

Carbonic anhydrase IX (CA9) is a membrane‐associated carbonic anhydrase that regulates cellular pH, is upregulated in various solid tumors, and is considered to be a therapeutic target. Here, we describe the essential role of CA9 in the tumorigenicity of cells derived from human adult T‐cell leukemia/lymphoma (ATL). We previously established the highly tumorigenic ST1‐N6 subline from the ATL‐derived ST1 cell line by serial xenotransplantation in NOG mice. In the present study, we first show that CA9 expression is strongly enhanced in ST1‐N6 cells. We then sorted ST1 cells by high or low CA9 expression and established ST1‐CA9^high and ST1‐CA9^low sublines. ST1‐CA9^high cells, like ST1‐N6 cells, were more strongly tumorigenic than ST1‐CA9^low or parental ST1 cells when injected into NOG mice. Knockdown of CA9 with shRNAs suppressed the ability of ST1‐CA9^high cells to initiate tumors, and the tumorigenicity of ST1 cells was significantly enhanced by introducing wild‐type CA9 or a CA9 mutant with deletion of an intracytoplasmic domain. However, a CA9 with point mutations in the catalytic site did not increase the tumorigenicity of ST1 cells. Furthermore, we detected a small population of CA9⁺CD25⁺ cells in lymph nodes of ATL patients. These findings suggest that CA9, and particularly its carbonic anhydrase activity, promotes the tumorigenicity of ATL‐derived cells and may be involved in malignant development of lymphoma‐type ATL.

p53 and its mutants on the slippery road from stemness to carcinogenesis

Normal development, tissue homeostasis and regeneration following injury rely on the proper functions of wide repertoire of stem cells (SCs) persisting during embryonic period and throughout the adult life. Therefore, SCs employ robust mechanisms to preserve their genomic integrity and avoid heritage of mutations to their daughter cells. Importantly, propagation of SCs with faulty DNA as well as dedifferentiation of genomically altered somatic cells may result in derivation of cancer SCs, which are considered to be the driving force of the tumorigenic process. Multiple experimental evidence suggest that p53, the central tumor suppressor gene, plays a critical regulatory role in determination of SCs destiny, thereby eliminating damaged SCs from the general SC population. Notably, mutant p53 proteins do not only lose the tumor suppressive function, but rather gain new oncogenic function that markedly promotes various aspects of carcinogenesis. In this review, we elaborate on the role of wild type and mutant p53 proteins in the various SCs types that appear under homeostatic conditions as well as in cancer. It is plausible that the growing understanding of the mechanisms underlying cancer SC phenotype and p53 malfunction will allow future optimization of cancer therapeutics in the context of precision medicine.

Single cell time-lapse analysis reveals that podoplanin enhances cell survival and colony formation capacity of squamous cell carcinoma cells

Tumor initiating cells (TICs) are characterized by high clonal expansion capacity. We previously reported that podoplanin is a TIC-specific marker for the human squamous cell carcinoma cell line A431. The aim of this study is to explore the molecular mechanism underlying the high clonal expansion potential of podoplanin-positive A431cells using Fucci imaging. Single podoplanin-positive cells created large colonies at a significantly higher frequency than single podoplanin-negative cells, whereas no difference was observed between the two types of cells with respect to cell cycle status. Conversely, the cell death ratio of progenies derived from podoplanin-positive single cell was significantly lower than that of cells derived from podoplanin-negative cells. Single A431 cells, whose podoplanin expression was suppressed by RNA interference, exhibited increased cell death ratios and decreased frequency of large colony forming. Moreover, the frequency of large colony forming decreased significantly when podoplanin-positive single cells was treated with a ROCK (Rho-associated coiled-coil kinase) inhibitor, whereas no difference was observed in single podoplanin-negative cells. Our current study cleared that high clonal expansion capacity of podoplanin-positive TICs populations was the result of reduced cell death by podoplanin-mediated signaling. Therefore, podoplanin activity may be a therapeutic target in the treatment of squamous cell carcinomas.

p53 on the crossroad between regeneration and cancer

Regeneration and tumorigenesis share common molecular pathways, nevertheless the outcome of regeneration is life, whereas tumorigenesis leads to death. Although the process of regeneration is strictly controlled, malignant transformation is unrestrained. In this review, we discuss the involvement of TP53, the major tumor-suppressor gene, in the regeneration process. We point to the role of p53 as coordinator assuring that regeneration will not shift to carcinogenesis. The fluctuation in p53 activity during the regeneration process permits a tight control. On one hand, its inhibition at the initial stages allows massive proliferation, on the other its induction at advanced steps of regeneration is essential for preservation of robustness and fidelity of the regeneration process. A better understanding of the role of p53 in regulation of regeneration may open new opportunities for implementation of TP53-based therapies, currently available for cancer patients, in regenerative medicine.

Oncogenic Mutant p53 Gain of Function Nourishes the Vicious Cycle of Tumor Development and Cancer Stem-Cell Formation

More than half of human tumors harbor an inactivated p53 tumor-suppressor gene. It is well accepted that mutant p53 shows an oncogenic gain-of-function (GOF) activity that facilitates the transformed phenotype of cancer cells. In addition, a growing body of evidence supports the notion that cancer stem cells comprise a seminal constituent in the initiation and progression of cancer development. Here, we elaborate on the mutant p53 oncogenic GOF leading toward the acquisition of a transformed phenotype, as well as placing mutant p53 as a major component in the establishment of cancer stem cell entity. Therefore, therapy targeted toward cancer stem cells harboring mutant p53 is expected to pave the way to eradicate tumor growth and recurrence.

Heterogeneity of tumor cells in terms of cancer-initiating cells

Tumors derive from a single cell clone but consist of heterogeneous cell subpopulations with diverse features and functions. A limited number of subclones with a selective advantage can initiate tumors when inoculated into immunocompromised mice, and are called cancer-initiating cells (CICs). CICs can be isolated from the bulk of tumors on the basis of their characteristics, such as high reagent efflux, degradation of reactive oxygen species, and aldehyde dehydrogenase (ALDH) activity. Under normal conditions, new CICs are produced by existing CICs rather than non-CICs. However, under stress conditions, non-CICs can occasionally produce CICs, a phenomenon known as plasticity. The dynamic exchange between CICs and non-CICs may enable tumors to survive under unfavorable conditions. CICs are located in a small portion of tumors. This suggests that microenvironmental factors induce or inhibit the CIC phenotype, which might be regulated by intercellular signaling between tumor cells. This review describes isolation of CICs from tumor cell populations and the microenvironmental factors that regulate CIC phenotypes in uterine cancer and lymphoma.

Cancer stem cells: understanding tumor hierarchy and heterogeneity

Heterogeneity within and between tumors is a well-known phenomenon that greatly complicates the diagnosis and treatment of cancer. A large body of research indicates that heterogeneity develops through time as tumor-initiating stem cells, also known as cancer stem cells (CSCs), evolve genetic or epigenetic alterations that allow them to differentiate into multiple tumor cell types. Similar to normal stem cells, CSCs can self-renew and possess long-term repopulation potential. However, unlike normal stem cells, CSCs are not subject to the usual controls that limit growth. Different models have been postulated to explain the heterogeneity of tumors, but it is widely agreed that interactions between tumor cells and their microenvironment create niches that promote CSC properties and enable their survival. Within the microenvironment, CSC self-renewal, replication, and differentiation are postulated to produce a hierarchy of cells constituting the tumor mass. Increased understanding of the factors that create and contribute to tumor heterogeneity may support the design of therapies that affect CSC function and their microenvironments.

Cancer stem cells as a potential therapeutic target in thyroid carcinoma

A number of studies have indicated that tumor growth and proliferation is dependent on a small subset of cells, defined as cancer stem cells (CSCs). CSCs have the capability to self-renew, and are involved with cancer propagation, relapse and metastatic dissemination. CSCs have been isolated from numerous tissues, including normal and cancerous thyroid tissue. A regulatory network of signaling pathways and microRNAs (miRNAs) control the properties of CSCs. Differentiated thyroid carcinoma is the most common type of endocrine cancer, with an increasing incidence. Anaplastic thyroid carcinoma is the most rare type of endocrine cancer; however, it also exhibits the highest mortality rate among thyroid malignancies, with an extremely short survival time. Thyroid CSCs are invasive and highly resistant to conventional therapies, including radiotherapy and chemotherapy, which results in disease relapse even when the primary lesion has been eradicated. Therefore, targeting thyroid CSCs may represent an effective treatment strategy against aggressive neoplasms, including recurrent and radioresistant tumors. The present review summarizes the current literature regarding thyroid CSCs and discusses therapeutic strategies that target these cells, with a focus on the function of self-renewal pathways and miRNAs. Elucidation of the mechanisms that regulate CSC growth and survival may improve novel therapeutic approaches for treatment-resistant thyroid cancers.

Concise Review: Stem Cells and Epithelial-Mesenchymal Transition in Cancer: Biological Implications and Therapeutic Targets

Cancer stem cells (CSCs) constitute a small subpopulation of cancer cells with stem-like properties that are able to self-renew, generate differentiated daughter cells, and give rise to heterogeneous tumor tissue. Tumor heterogeneity is a hallmark of cancer and underlies resistance to anticancer therapies and disease progression. The epithelial-mesenchymal transition (EMT) is a reversible phenomenon that is mediated by EMT-inducing transcription factors (EMT-TFs) and plays an important role in normal organ development, wound healing, and the invasiveness of cancer cells. Recent evidence showing that overexpression of several EMT-TFs is associated with stemness in cancer cells has suggested the existence of a link between EMT and CSCs. In this review, we focus on the roles of CSCs and EMT signaling in driving tumor heterogeneity. A better understanding of the dynamics of both CSCs and EMT-TFs in the generation of tumor heterogeneity may provide a basis for the development of new treatment options for cancer patients. Stem Cells 2016;34:1997-2007.

CD44 variant-dependent redox status regulation in liver fluke-associated cholangiocarcinoma: A target for cholangiocarcinoma treatment

Expression of CD44, especially the variant isoforms (CD44v) of this major cancer stem cell marker, contributes to reactive oxygen species (ROS) defense through stabilizing xCT (a cystine–glutamate transporter) and promoting glutathione synthesis. This enhances cancer development and increases chemotherapy resistance. We investigate the role of CD44v in the regulation of the ROS defense system in cholangiocarcinoma (CCA). Immunohistochemical staining of CD44v and p38^MAPK (a major ROS target) expression in Opisthorchis viverrini‐induced hamster CCA tissues (at 60, 90, 120, and 180 days) reveals a decreased phospho‐p38^MAPK signal, whereas the CD44v signal was increased during bile duct transformation. Patients with CCA showed CD44v overexpression and negative‐phospho‐p38^MAPK patients a significantly shorter survival rate than the low CD44v signal and positive‐phospho‐p38^MAPK patients (P = 0.030). Knockdown of CD44 showed that xCT and glutathione levels were decreased, leading to a high level of ROS. We examined xCT‐targeted CD44v cancer stem cell therapy using sulfasalazine. Glutathione decreased and ROS increased after the treatment, leading to inhibition of cell proliferation and induction of cell death. Thus, the accumulation of CD44v leads to the suppression of p38^MAPK in transforming bile duct cells. The redox status regulation of CCA cells depends on the expression of CD44v to contribute the xCT function and is a link to the poor prognosis of patients. Thus, an xCT inhibitor could inhibit cell growth and activate cell death. This suggests that an xCT‐targeting drug may improve CCA therapy by sensitization to the available drug (e.g. gemcitabine) by blocking the mechanism of the cell's ROS defensive system.