Cancer spheres from gastric cancer patients provide an ideal model system for cancer stem cell research

Epigenetic silencing of miR-1271 enhances MEK1 and TEAD4 expression in gastric cancer

Epigenetic dysregulation is a major driver of tumorigenesis. To identify tumor-suppressive microRNAs repressed by DNA methylation in gastric cancer (GC), we analyzed the genome-wide DNA methylation and microRNA expression profiles of EpCAM+/CD44+ GC cells. Among the set of microRNAs screened, miR-1271 was identified as a microRNA repressed by DNA methylation in GC. Forced miR-1271 expression substantially suppressed the growth, migration, and invasion of GC cells. To identify candidate target genes and signaling pathways regulated by miR-1271, we performed RNA sequencing. Among the genes down-regulated by miR-1271, MAP2K1 (MEK1) was significantly repressed by miR-1271, and the associated ERK/MAPK signaling pathway was also inhibited. TEAD4 was also repressed by miR-1271, and the associated YAP1 signatures within genes regulated by miR-1271 were significantly enriched. These findings uncovered MEK1 and TEAD4 as novel miR-1271 targets and suggest that the epigenetic silencing of miR-1271 is crucial for GC development.

The viable circulating tumor cells with cancer stem cells feature, where is the way out?

With cancer stem cells (CSCs) became the research hotspot, emerging studies attempt to reveal the functions of these special subsets in tumorigenesis. Although various approaches have been used in CSCs researches, only a few could really reflect or simulate the microenvironment in vivo. At present, CSCs theories are still difficult to apply for clinical remedy because CSCs subpopulations are always hard to identify and trace. Thus an ideal approach for clinicians and researchers is urgently needed. Circulating tumor cells (CTCs), as the method of noninvasive-liquid biopsy, could be detected in the peripheral blood (PB) from many tumors and even could be treated as procurators for CSCs deeper researches from patient-derived sample. However, CTCs, as a diagnostic marker, also raise much controversy over theirs clinical value. Mechanisms causing CTCs to shed from the tumor have not been fully characterized, thus it is unclear whether CTCs represent the entire makeup of cancer cells in the tumor or only a subset. The heterogeneity of CTCs also caused different clinical outcomes. To overcome these unsolved problems, recently, CTC researches are not just depend on enumerations, whereas those CTC subsets that could expand in vitro may play a pivotal role in the metastatic cascade. Here, we retrospect the CTC developmental history and discourse upon the enrichment of viable CTCs in functional assays, probe the further avenue at the crossroad.

HIF-1α induces the epithelial-mesenchymal transition in gastric cancer stem cells through the Snail pathway

Substantial evidence suggests that the epithelial-mesenchymal transition (EMT) phenotype is associated with the invasive characteristics of cancer stem cells (CSCs),which possess an EMT phenotype that may predominate in tumor invasion and metastasis. However, the mechanisms for the generation and regulation of these CSCs have not been clearly defined. As hypoxia and EMT-related factors may have important functions in EMT-like CSCs, the aim of this study was to investigate the effects of hypoxia on these cells. CSCs were established from the gastric cancer cell lines MGC-803 and SGC7901, and the relationship between hypoxia and EMT-like CSCs was investigated in gastric cancer. After hypoxia treatment, some gastric CSCs exhibited a marked increase in hypoxia-inducible factor-1α (HIF-1α)expression and increased migration and invasion capabilities compared with the normoxic control. These CSCs were defined by activation of the mesenchymal cell marker Vimentin and by inhibition of the epithelial cell marker E-cadherin. Our analyses also show that HIF-1α was responsible for activating EMT via increased expression of the transcription factor Snail in gastric CSCs. Moreover, inhibition of Snail by shRNA reduced HIF-1α-induced EMT in gastric CSCs. The results demonstrated that hypoxia-induced EMT-like CSCs rely on HIF-1αto activate Snail, which may result in recurrence and metastasis of gastric cancer.

CBX7 regulates stem cell-like properties of gastric cancer cells via p16 and AKT-NF-κB-miR-21 pathways

Background

Chromobox protein homolog 7 (CBX7), a member of the polycomb group (PcG) family of proteins, is involved in the regulation of cell proliferation and cancer progression. PcG family members, such as BMI, Mel-18, and EZH2, are integral constituents of the polycomb repressive complexes (PRCs) and have been known to regulate cancer stem cell (CSC) phenotype. However, the role of other PRCs’ constituents such as CBX7 in the regulation of CSC phenotype remains largely elusive. This study was to investigate the role of CBX7 in regulating stem cell-like properties of gastric cancer and the underlying mechanisms.

Methods

Firstly, the role of CBX7 in regulating stem cell-like properties of gastric cancer was investigated using sphere formation, Western blot, and xenograft tumor assays. Next, RNA interference and ectopic CBX7 expression were employed to determine the impact of CBX7 on the expression of CSC marker proteins and CSC characteristics. The expression of CBX7, its downstream targets, and stem cell markers were analyzed in gastric stem cell spheres, common cancer cells, and gastric cancer tissues. Finally, the pathways by which CBX7 regulates stem cell-like properties of gastric cancer were explored.

Results

We found that CBX7, a constituent of the polycomb repressive complex 1 (PRC1), plays an important role in maintaining stem cell-like characteristics of gastric cancer cells via the activation of AKT pathway and the downregulation of p16. Spearman rank correlation analysis showed positive correlations among the expression of CBX7 and phospho-AKT (pAKT), stem cell markers OCT-4, and CD133 in gastric cancer tissues. In addition, CBX7 was found to upregulate microRNA-21 (miR-21) via the activation of AKT-NF-κB pathway, and miR-21 contributes to CBX7-mediated CSC characteristics.

Conclusions

CBX7 positively regulates stem cell-like characteristics of gastric cancer cells by inhibiting p16 and activating AKT-NF-κB-miR-21 pathway.

Electronic supplementary material

The online version of this article (10.1186/s13045-018-0562-z) contains supplementary material, which is available to authorized users.

Targeting cancer stem cells in the clinic: Current status and perspectives

Resistance to chemotherapy and cancer relapse are major clinical challenges attributed to a sub population of cancer stem cells (CSCs). The concept of CSCs has been the subject of intense research by the oncology community since evidence for their existence was first published over twenty years ago. Emerging data indicates that they are also able to evade novel therapies such as targeted agents, immunotherapies and anti-angiogenics. The inability to appropriately identify and isolate CSCs is a major hindrance to the field and novel technologies are now being utilized. Agents that target CSC-associated cell surface receptors and signaling pathways have generated promising pre-clinical results and are now entering clinical trial. Here we discuss and evaluate current therapeutic strategies to target CSCs.

In vitro and in vivo effects of miRNA-19b/20a/92a on gastric cancer stem cells and the related mechanism

We aimed to analyze the in vitro and in vivo effects of miRNA-19b/20a/92a on gastric cancer stem cells (GCSCs) and the related mechanism. GCSCs were cultured until adherence and differentiation, and subjected to miRNA microarray analysis to find and to verify miRNA deletion. Cells stably expressing lentivirus carrying miRNA-19b/20a/92a were constructed by transfection. The relationship between miRNA-19b/20a/92a and renewal of GCSCs was studied by the tumor sphere assay, and that between miRNA-19b/20a/92a and their proliferation was explored with MTT and colony formation assays. Target genes of miRNA for promoting the proliferation and self-renewal of GCSCs were found by using bioinformatics database, and verified by the reporter gene assay and Western blot. The expressions of miRNA-19b/20a/92a gradually decreased during the adherence and differentiation of GCSCs. The expressions of lentivirus carrying miRNA-17-19 gene in MKN28 and CD44^-/EpCAM^- cells were increased significantly. Transient transfection with pre-miRNA-19b/20a/92a elevated miRNA expressions in CD44^-/EpCAM^- and MKN28 cells, whereas transfection with pre-miRNA-19b/20a/92a antagonists reduced the expressions in SGC7901 and CD44⁺/EpCAM⁺ cells. Overexpression of lenti-miRNA-19b/20a/92a significantly enhanced the capability of GCSCs to form tumor spheres. In the presence of chemotherapeutic agent, the survival of lenti-miRNA-19b/20a/92a-infected cells was prolonged. Transient transfection with pre-miRNA-19b/20a/92a significantly increased the number of CD44⁺/EpCAM⁺ cells, but transfection with antagonists had the opposite outcomes. The stable miRNA-19b/20a/92a expression groups proliferated faster than the control group did. The proliferation of cells transfected with pre-miRNA-19b/20a/92a was accelerated, whereas that of cells transfected with the antagonists was decelerated. Compared with the control group, the number of colonies in the former group was higher, but that in the latter group was lower. miRNA-19b and miRNA-92a could bind the 3' untranslated region of HIPK1, while miRNA-20a was able to bind that of E2F1. Expressions of miRNA-20a and miRNA-92a in gastric cancer samples were negatively correlated with the prognosis of patients. miRNA-19b/20a/92a facilitated the self-renewal of GCSCs by targeting E2F1 and HIPK1 on the post-transcriptional level and activating the β-catenin signal transduction pathway. miRNA-92a was an independent factor and index predicting the prognosis of gastric cancer.

New Opportunities and Challenges to Defeat Cancer Stem Cells

Cancer stem cells (CSCs) are a subpopulation of cancer cells that are capable of self-renewal, proliferation, differentiation, plastic adaptation, and immune regulation, thereby mediating tumorigenesis, metastasis, and therapy resistance. CSCs are associated with cancer progression and clinical outcome in cancer patients. Successful targeting of CSCs will therefore be necessary to eradicate and cure cancer. Functional regulators of stem cell (stemness) signaling pathways in human cancers have brought new opportunities to target CSCs and reframe cancer-targeting strategies in clinical settings. However, challenges remain due to a lack of complete understanding of CSC plasticity/heterogeneity and the limited efficacy of individual stemness inhibitors in cancer treatment. In this article we review CSC signaling pathways and the current state of CSC-targeting therapeutics in combinatory treatments in clinical trials.

CD24, CD44 and EpCAM enrich for tumour-initiating cells in a newly established patient-derived xenograft of nasopharyngeal carcinoma

Subpopulations of nasopharyngeal carcinoma (NPC) contain cells with differential tumourigenic properties. Our study evaluates the tumourigenic potential of CD24, CD44, EpCAM and combination of EpCAM/CD44 cells in NPC. CD44br and EpCAMbr cells enriched for higher S-phase cell content, faster-growing tumourigenic cells leading to tumours with larger volume and higher mitotic figures. Although CD44br and EpCAMbr cells significantly enriched for tumour-initiating cells (TICs), all cells could retain self-renewal property for at least four generations. Compared to CD44 marker alone, EpCAM/CD44dbr marker did not enhance for cells with faster-growing ability or higher TIC frequency. Cells expressing high CD44 or EpCAM had lower KLF4 and p21 in NPC subpopulations. KLF4-overexpressed EpCAMbr cells had slower growth while Kenpaullone inhibition of KLF4 transcription increased in vitro cell proliferation. Compared to non-NPC, NPC specimens had increased expression of EPCAM, of which tumours from advanced stage of NPC had higher expression. Together, our study provides evidence that EpCAM is a potentially important marker in NPC.

A modified method by differential adhesion for enrichment of bladder cancer stem cells

Purpose:

In a previous study the vaccine was effective against bladder cancer in a mouse model. However, a small portion of tumors regrew because the vaccine could not eliminate bladder cancer stem cells (CSCs). In this study, we showed a modified method for the isolation of bladder CSCs using a combination of differential adhesion method and serum-free culture medium (SFM) method.

Materials and Methods:

Trypsin-resistant cells and trypsin-sensitive cells were isolated from MB49, EJ and 5637 cells by a combination of differential adhesion method and SFM method. The CSCs characterizations of trypsin-resistant cells were verified by the flow cytometry, the western blotting, the quantitative polymerase chain reaction, the resistance to chemotherapy assay, the transwell assay, and the tumor xenograft formation assay.

Results:

Trypsin-resistant cells were isolated and identified in CSCs characters, with high expression of CSCs markers, higher resistance to chemotherapy, greater migration in vitro, and stronger tumorigenicity in vivo.

Conclusion:

Trypsin-resistant cells displayed specific CSCs properties. Our study showed trypsin-resistant cells were isolated successfully with a modified method using a combination of differential adhesion method and SFM method.

MicroRNA-34 dysregulation in gastric cancer and gastric cancer stem cell

Gastric cancer is a major cause of cancer mortality worldwide, with a low survival rate for patients with advanced forms of the disease. Over the recent decades, the investigation of the pathophysiological mechanisms of tumourigenesis has opened promising avenues to understand some of the complexities of cancer treatment. However, tumour regeneration and metastasis impose great difficulty for gastric cancer cure. In recent years, cancer stem cells - a small subset of tumour cells in many cancers - have become a major focus of cancer research. Cancer stem cells are capable of self-renewal and are known to be responsible for tumour initiation, metastasis, therapy resistance and cancer recurrence. Recent studies have revealed the key role of microRNAs - small noncoding RNAs regulating gene expression - in these processes. MicroRNAs play crucial roles in the regulation of a wide range of biological processes in a post-transcriptional manner, though their expression is dysregulated in most malignancies, including gastric cancer. In this article, we review the consequences of aberrant expression of microRNA-34 in cancer and cancer stem cells, with a specific focus on the miR-34 dysregulation in gastric cancer and gastric cancer stem cells. We address the critical effects of the aberrant expression of miR-34 and its target genes in maintaining cancer stem cell properties. Information collection and discussion about the advancements in gastric cancer stem cells and microRNAs can be useful for providing novel insights into patient treatment.

Involvement of Polo-like kinase 1 (Plk1) in quiescence regulation of cancer stem-like cells of the gastric cancer cell lines

Cancer stem cells (CSCs) have been hypothesized to initiate tumor growth and be resistant to chemoradiotherapy, and these processes appear to be closely related to CSC quiescence. Here, a CSC-like cell population with a high level of CD44 expression was obtained from the human gastric cancer cell lines MKN45 and MKN74. Using a PKH26-labeling retention assay, quiescent CSC-like cells with low levels of Ki67 and PCNA expression were found in spheres formed in serum-free medium, and exhibited resistance to drug and radiation treatments. Polo-like kinase 1 (Plk1) and ribosomal S6 kinase 1 (RSK1) were silenced in the quiescent CSC-like cells. The Plk1-specific inhibitors inhibited the activation of RSK1 and induced quiescence in the CSC-like cells, but increased RSK1 activity and resulted in apoptosis in non-CSCs. Furthermore, RSK1 silencing by inhibitors activated Plk1 and had no effect on the growth of spheres in the CSC-like cells, but did not affect phosphorylation of Plk1 and led to decreased proliferation in non-CSCs. Our results showed that Plk1 and RSK1 play important roles in the conversion of CSCs between active and quiescent states.

PMP22 Regulates Self-Renewal and Chemoresistance of Gastric Cancer Cells

Cancer stem cells possess self-renewal and chemoresistance activities. However, the manner in which these features are maintained remains obscure. We sought to identify cell surface protein(s) that mark self-renewing and chemoresistant gastric cancer cells using the explorer antibody microarray. We identified PMP22, a target gene of the Wnt/β-catenin pathway, as the most upregulated cell surface protein in gastric cancer xenografts exposed to cisplatin (DDP). PMP22 expression was markedly upregulated in tumorspheric cells and declined with differentiation. Infecting gastric cancer cells with lentivirus expressing PMP22 shRNAs reduced proliferation, tumorsphere formation, and chemoresistance to cisplatin in vitro and in NOD/SCID mice. When combined with bortezomib, a PMP22 inhibitor, the chemotherapeutic sensitivity to cisplatin treatment was dramatically increased by inducing cell apoptosis in cultured cells and xenograft mouse models. Finally, mRNA expression levels of PMP22 were detected in 38 tumor specimens from patients who received six cycles of perioperative chemotherapy. A strong correlation between PMP22 level and tumor recurrence was revealed, thus showing a pivotal role of PMP22 in the clinical chemoresistance of gastric cancer. Our study is the first to show the role of PMP22 in gastric cancer stemness and chemoresistance and reveals a potential new target for the diagnosis and treatment of recurrent gastric cancer. Mol Cancer Ther; 16(6); 1187-98. ©2017 AACR.

Sorafenib inhibits 5-fluorouracil-resistant gastric cancer cell growth

BACKGROUND

Sorafenib is a multi-kinase inhibitor used in the treatment of various cancers. This study investigated the inhibitory effect of sorafenib on xenograft models of gastric cancer cells and 5-fluorouracil (5-FU)-resistant cells.

METHODS

The half-maximal inhibitory concentration (IC₅₀) of sorafenib in NCI-N87 cells was determined. Xenograft models were established using BALB/c nude mice and were divided into four groups treated with vehicle, sorafenib (20 mg kg^-1 day^-1), 5-FU (50 mg kg^-1 week^-1), or a combination of sorafenib (20 mg kg^-1 day^-1) plus 5-FU (50 mg kg^-1 week^-1). 5-FU-resistant NCI-N87 cells were established by repeated exposure to 5-FU.

RESULTS

Sorafenib inhibited NCI-N87 cell growth in a concentration-dependent manner with a mean IC₅₀ of 16.345 ± 5.391 μM. Phosphorylation levels of mitogen-activated protein kinase kinase and extracellular signal-regulated kinase in these cells decreased in a dose-dependent manner after exposure to sorafenib. Sorafenib induced the activation of caspase-3, and its combination with 5-FU more effectively inhibited the growth of xenograft tumors than either sorafenib or 5-FU alone (p < 0.05). Sorafenib markedly inhibited 5-FU-resistant NCI-N87 cell growth as well as sphere formation in both parental and 5-FU-resistant NCI-N87 cells.

CONCLUSIONS

The sorafenib and 5-FU combination exhibited enhanced antitumor effects in a gastric cancer xenograft model and inhibited 5-FU-resistant cell proliferation and sphere formation. These findings suggest that sorafenib is useful in overcoming gastric cancer resistance to conventional chemotherapy.

A unified model of the hierarchical and stochastic theories of gastric cancer

Gastric cancer (GC) is a life-threatening disease worldwide. Despite remarkable advances in treatments for GC, it is still fatal to many patients due to cancer progression, recurrence and metastasis. Regarding the development of novel therapeutic techniques, many studies have focused on the biological mechanisms that initiate tumours and cause treatment resistance. Tumours have traditionally been considered to result from somatic mutations, either via clonal evolution or through a stochastic model. However, emerging evidence has characterised tumours using a hierarchical organisational structure, with cancer stem cells (CSCs) at the apex. Both stochastic and hierarchical models are reasonable systems that have been hypothesised to describe tumour heterogeneity. Although each model alone inadequately explains tumour diversity, the two models can be integrated to provide a more comprehensive explanation. In this review, we discuss existing evidence supporting a unified model of gastric CSCs, including the regulatory mechanisms of this unified model in addition to the current status of stemness-related targeted therapy in GC patients.

MicroRNA-320a and microRNA-4496 attenuate Helicobacter pylori cytotoxin-associated gene A (CagA)-induced cancer-initiating potential and chemoresistance by targeting β-catenin and ATP-binding cassette, subfamily G, member 2

Infection with Helicobacter pylori is closely linked to an increased risk of gastric cancer. Although cytotoxin-associated gene A (CagA), a major virulence factor of H. pylori, is known to be a causal factor for gastric carcinogenesis, the molecular link between CagA and gastric cancer-initiating cell (CIC)-like properties remains elusive. Here, we demonstrate that CagA is required for increased expression of β-catenin and its target CIC markers via downregulation of microRNA (miR)-320a and miR-4496. CagA promoted gastric CIC properties and was responsible for chemoresistance. miR-320a and miR-4496 attenuated the in vitro self-renewal and tumour-initiating capacity of CagA-expressing CICs by targeting β-catenin. Moreover, miR-320a and miR-4496 decreased CagA-induced chemoresistance by targeting ATP-binding cassette, subfamily G, member 2 (ABCG2) at the transcriptional and post-transcriptional levels, respectively. Combination therapy with 5-fluorouracil and miR-320a/miR-4496 suppressed gastric tumourigenesis and metastatic potential in an orthotopic mouse model, probably via suppression of CagA-induced CIC properties and chemoresistance. Our results provide novel evidence that CIC properties, chemoresistance and tumourigenesis associated with H. pylori are linked to CagA-induced upregulation of β-catenin and ABCG2. These data provide novel insights into the molecular mechanisms of CagA-induced carcinogenisis and the therapeutic potential of of miR-320a and miR-4496. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Identifying and targeting cancer stem cells in the treatment of gastric cancer

Current treatment regimens for gastric cancer are not adequate. Cancer stem cells (CSCs) may be a key driving factor for growth and metastasis of this tumor type. In contrast to the conventional clonal evolution hypothesis, CSCs can initiate tumor formation, self‐renew, and differentiate into tumor‐propagating cells. Because gastric cancer can originate from CSCs, it is necessary to review current targets of signaling pathways for CSCs in gastric cancer that are being studied in clinical trials. These pathways are known to regulate the self‐renewal and differentiation process in gastric CSCs. A better understanding of the clinical results of trials that target gastric CSCs will lead to better outcomes for patients with gastric cancer. Cancer 2017;123:1303–1312. © 2017 The Authors. Cancer published by Wiley Periodicals, Inc. on behalf of American Cancer Society. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Cancer stem cells may be a key driving factor in the growth and metastasis of gastric cancer. Because gastric cancer can originate from cancer stem cells, it is necessary to review current targets of signaling pathways for cancer stem cells in gastric cancer that are being studied in clinical trials.

Sulforaphane improves chemotherapy efficacy by targeting cancer stem cell-like properties via the miR-124/IL-6R/STAT3 axis

Gastric carcinoma (GC) is the second leading cause of cancer-related mortality worldwide. The efficacy of standard chemotherapy for GC, such as cisplatin (CDDP), is dissatisfactory partly due to the toxic/side-effects. Sulforaphane (SFN), which exhibits effective anti-cancer functions, is a phytochemical converted from cruciferous plants. Our present study aimed to identify whether SFN could enhance the anti-cancer effects of low-dose CDDP and to determine the underlying mechanisms. Herein, co-exposure of SFN and CDDP significantly inhibited the viabilities of gastric cancer cells. For the molecular mechanisms, CDDP alone increased the cancer stem cell (CSC)-like properties in gastric cancer cells via activating the interleukin-6 (IL-6)/IL-6 receptor (IL-6R)/signal transducer and activator of transcription 3 (STAT3) signaling. However, SFN could activate the microRNA-124 (miR-124), which directly targets the 3'-untranslated regions (UTR) of the IL-6R and STAT3. Moreover, knockdown of miR-124 eliminated the effects of SFN on CSC-like properties in GC cells, and in turn enhanced the anti-cancer effects of low-dose CDDP. These findings not only suggested a mechanism whereby SFN enhanced the anti-cancer functions of CDDP, but also helped to regard SFN as a potential chemotherapeutic factor in gastric cancer.

Identification of a cancer stem cell-specific function for the histone deacetylases, HDAC1 and HDAC7, in breast and ovarian cancer

Tumours are comprised of a highly heterogeneous population of cells, of which only a small subset of stem-like cells possess the ability to regenerate tumours in vivo. These cancer stem cells (CSCs) represent a significant clinical challenge as they are resistant to conventional cancer therapies and play essential roles in metastasis and tumour relapse. Despite this realization and great interest in CSCs, it has been difficult to develop CSC-targeted treatments due to our limited understanding of CSC biology. Here, we present evidence that specific histone deacetylases (HDACs) play essential roles in the CSC phenotype. Utilizing a novel CSC model, we discovered that the HDACs, HDAC1 and HDAC7, are specifically over-expressed in CSCs when compared to non-stem-tumour-cells (nsTCs). Furthermore, we determine that HDAC1 and HDAC7 are necessary to maintain CSCs, and that over-expression of HDAC7 is sufficient to augment the CSC phenotype. We also demonstrate that clinically available HDAC inhibitors (HDACi) targeting HDAC1 and HDAC7 can be used to preferentially target CSCs. These results provide actionable insights that can be rapidly translated into CSC-specific therapies.

Bmi-1 regulates stem cell-like properties of gastric cancer cells via modulating miRNAs

Background

B cell-specific Moloney murine leukemia virus integration site 1 (Bmi-1) plays an important role in regulating stemness in some kinds of cancer. However, the mechanisms remain unclear. This study was to investigate whether and how Bmi-1 regulates stemness of gastric cancer.

Methods

We firstly explored the role of Bmi-1 in regulating stem cell-like features in gastric cancer. Secondly, we screened out its downstream miRNAs and clarified whether these miRNAs are involved in the regulation of stemness. Finally, we investigated the mechanisms how Bmi-1 regulates miRNAs.

Results

Bmi-1 positively regulates stem cell-like properties of gastric cancer and upregulates miR-21 and miR-34a. There was a positive correlation between Bmi-1 and miR-21 expression in gastric cancer tissues. MiR-21 mediated the function of Bmi-1 in regulating stem cell-like properties, while miR-34a negatively regulates stem cell-like characteristics via downregulating Bmi-1. Bmi-1 binds to PTEN promoter and directly inhibits PTEN and thereafter activates AKT. Bmi-1 also regulates p53 and PTEN via miR-21. Bmi-1 activated NF-kB via AKT and enhanced the binding of NF-kB to the promoter of miR-21 and miR-34a and increased their expression.

Conclusions

Bmi-1 positively regulates stem cell-like properties via upregulating miR-21, and miR-34a negatively regulates stem cell-like characteristics by negative feedback regulation of Bmi-1 in gastric cancer. Bmi-1 upregulates miR-21 and miR-34a by activating AKT-NF-kB pathway.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-016-0323-9) contains supplementary material, which is available to authorized users.

Lapatinib-resistant cancer cells possessing epithelial cancer stem cell properties develop sensitivity during sphere formation by activation of the ErbB/AKT/cyclin D2 pathway

Lapatinib, a dual inhibitor of epidermal growth factor receptor (EGFR)/ErbB2, has antiproliferative effects and is used to treat patients with ErbB2-positive metastatic breast cancer. In the present study, we examined the effects of lapatinib on growth of oral and prostate cancer cells. Oral squamous cell carcinoma (OSCC) cell lines HSC3, HSC4 and Ca9-22 were sensitive to the antiproliferative effects of lapatinib in anchorage-dependent culture, but the OSCC cell lines KB and SAS and the prostate cancer cell line DU145 were resistant to lapatinib. Phosphorylation levels of EGFR in all cell lines decreased during lapatinib treatment in anchorage‑dependent culture. Furthermore, the phosphorylation levels of ErbB2, ErbB3 and Akt and the protein levels of cyclin D1 were decreased by lapatinib treatment of HSC3, HSC4 and Ca9-22 cells. ErbB3 was not expressed and cyclin D1 protein levels were not altered by lapatinib treatment in KB, DU145 and SAS cells. The phosphorylation of ErbB2 and AKT was not affected by lapatinib in SAS cells and was not detected in KB and DU145 cells. Lapatinib-resistant cell lines exhibited sphere-forming ability, and SAS cells developed sensitivity to lapatinib during sphere formation. The phosphorylation levels of ErbB2 and AKT and protein levels of cyclin D2 increased during sphere formation of SAS cells and decreased with lapatinib treatment. In addition, sphere formation of SAS cells was inhibited by the AKT inhibitor MK2206. AKT phosphorylation and cyclin D2 levels in SAS spheres were decreased by MK2206 treatment. SAS cells expressed E-cadherin, but not vimentin and KB cells expressed vimentin, but not E-cadherin. DU145 cells expressed vimentin and E-cadherin. These results suggested that phosphorylation of EGFR and ErbB2 by cell detachment from the substratum induces the AKT pathway/cyclin D2-dependent sphere growth in SAS epithelial cancer stem-like cells, thereby rendering SAS spheres sensitive to lapatinib treatment.

Molecular classification of gastric cancer: Towards a pathway-driven targeted therapy

Gastric cancer (GC) is the third leading cause of cancer mortality worldwide. Although surgical resection is a potentially curative approach for localized cases of GC, most cases of GC are diagnosed in an advanced, non-curable stage and the response to traditional chemotherapy is limited. Fortunately, recent advances in our understanding of the molecular mechanisms that mediate GC hold great promise for the development of more effective treatment strategies. In this review, an overview of the morphological classification, current treatment approaches, and molecular alterations that have been characterized for GC are provided. In particular, the most recent molecular classification of GC and alterations identified in relevant signaling pathways, including ErbB, VEGF, PI3K/AKT/mTOR, and HGF/MET signaling pathways, are described, as well as inhibitors of these pathways. An overview of the completed and active clinical trials related to these signaling pathways are also summarized. Finally, insights regarding emerging stem cell pathways are described, and may provide additional novel markers for the development of therapeutic agents against GC. The development of more effective agents and the identification of biomarkers that can be used for the diagnosis, prognosis, and individualized therapy for GC patients, have the potential to improve the efficacy, safety, and cost-effectiveness for GC treatments.

Role of Helicobacter pylori infection in generation of gastric cancer stem cells

Helicobacter pylori (H. pylori) is a key cause of gastric cancer, and gastric cancer stem cells play an important role in the development of gastric cancer. Therefore in this paper, we try to explore the relationship between H. pylori infection and stem cells in gastric cancer. H. pylori infection promotes the generation of gastric cancer stem cells through the epithelial-mesenchymal transition (EMT). In addition, H. pylori participates in the processes of the formation and progression of gastric cancer stem cells by affecting related signal pathways, such as Wnt/β-catenin, Hh/SHH, Notch, FGF/BMP. On this basis, we disscuss the challenges and future directions in the research of H. pylori infection and gastric cancer stem cells.

Rebamipide attenuates Helicobacter pylori CagA-induced self-renewal capacity via modulation of β-catenin signaling axis in gastric cancer-initiating cells

Rebamipide, a mucosal-protective agent, is used clinically for treatment of gastritis and peptic ulcers induced by Helicobacter pylori (H. pylori) which is associated with increased risk of gastric cancer. Although rebamipide is known to inhibit the growth of gastric cancer cells, the action mechanisms of rebamipide in gastric carcinogenesis remains elusive. Here, we show that rebamipide suppresses H. pylori CagA-induced β-catenin and its target cancer-initiating cells (C-IC) marker gene expression via upregulation of miRNA-320a and -4496. Rebamipide attenuated in vitro self-renewal capacity of H. pylori CagA-infected gastric C-IC via modulation of miRNA-320a/-4496-β-catenin signaling axis. Moreover, rebamipide enhanced sensitivity to chemotherapeutic drugs in CagA-expressed gastric C-IC. Furthermore, rebamipide suppressed tumor-initiating capacity of gastric C-IC, probably via suppression of CagA-induced C-IC properties. These data provide novel insights for the efficacy of rebamipide as a chemoprotective drug against H. pylori CagA-induced carcinogenic potential.

Interaction between Wnt/β-catenin pathway and microRNAs regulates epithelial-mesenchymal transition in gastric cancer (Review)

Gastric cancer (GC) is the third primary cause of cancer-related mortality and one of the most common type of malignant diseases worldwide. Despite remarkable progress in multimodality therapy, advanced GC with high aggressiveness always ends in treatment failure. Epithelial-mesenchymal transition (EMT) has been widely recognized to be a key process associating with GC evolution, during which cancer cells go through phenotypic variations and acquire the capability of migration and invasion. Wnt/β-catenin pathway has established itself as an EMT regulative signaling due to its maintenance of epithelial integrity as well as tight adherens junctions while mutations of its components will lead to GC initiation and diffusion. The E-cadherin/β-catenin complex plays an important role in stabilizing β-catenin at cell membrane while disruption of this compound gives rise to nuclear translocation of β-catenin, which accounts for upregulation of EMT biomarkers and unfavorable prognosis. Additionally, several microRNAs positively or negatively modify EMT by reciprocally acting with certain target genes of Wnt/β-catenin pathway in GC. Thus, this review centers on the strong associations between Wnt/β-catenin pathway and microRNAs during alteration of EMT in GC, which may induce advantageous therapeutic strategies for human gastric cancer.

Gastric cancer stem cells: evidence, potential markers, and clinical implications

Gastric cancer is a significant global health problem. It is the fifth most common cancer and third leading cause of cancer-related death worldwide (Torre et al. in CA Cancer J Clin 65(2):87-108, 2015). Despite advances in treatment, overall prognosis remains poor, due to tumour relapse and metastasis. There is an urgent need for novel therapeutic approaches to improve clinical outcomes in gastric cancer. The cancer stem cell (CSC) model has been proposed to explain the high rate of relapse and subsequent resistance of cancer to current systemic treatments (Vermeulen et al. in Lancet Oncol 13(2):e83-e89, 2012). CSCs have been identified in many solid malignancies, including gastric cancer, and have significant clinical implications, as targeting the CSC population may be essential in preventing the recurrence and spread of a tumour (Dewi et al. in J Gastroenterol 46(10):1145-1157, 2011). This review seeks to summarise the current evidence for CSC in gastric cancer, with an emphasis on candidate CSC markers, clinical implications, and potential therapeutic approaches.

STAT3 is Overactivated in Gastric Cancer Stem-Like Cells

Objective

Gastric cancer (GC) is widely associated with chronic inflammation. The pro inflammatory microenvironment provides conditions that disrupt stem/progenitor cell proliferation and differentiation. The signal transducer and activator of transcrip- tion-3 (STAT3) signaling pathway is involved in inflammation and also contributes to the maintenance of embryonic stem cell (ESCs) pluripotency. Here, we have investi- gated the activation status of STAT3 in GC stem-like cells (GCSLCs).

Materials and Methods

In this experimental research, CSLCs derived from the human GC cell line MKN-45 and patient specimens, through spheroid body formation, character- ized and then assayed for the STAT3 transcription factor expression in mRNA and protein level further to its activation.

Results

Spheroid cells showed higher potential for spheroid formation than the pa- rental cells. Furthemore, stemness genes NANOG, c-MYC and SOX-2 were over expressed in spheroids of MKN-45 and in patient samples. In MKN-45 spheroid cells, epithelial mesenchymal transition (EMT) related markers CDH2, SNAIL2, TWIST and VIMENTIN were upregulated (P<0.05), but we observed no change in expression of the E-cadherin epithelial marker. These cells exhibited more resistance to docetaxel (DTX) when compared with parental cells (P<0.05) according to the MTS assay. Al- though immunostaining and Western blotting showed expression of the STAT3 pro- tein in both spheroids and parents, the mRNA level of STAT3 in spheroids was higher than the parents. Nuclear translocation of STAT3 was accompanied by more intensive phospho-STAT3 (p-STAT3) in spheroid structures relative to the parent cells accord- ing to flow cytometry analysis (P<0.05).

Conclusion

The present findings point to STAT3 over activation in GCSLCs. Com- plementary experiments are required to extend the role of STAT3 in stemness fea- tures and invasion properties of GCSCs and to consider the STAT3 pathway for CSC targeted therapy.

Cancer Gastric Chemoprevention: Isolation of Gastric Tumor-Initiating Cells

Gastric cancer is an important healthcare problem and represents the second leading cause of death for malignant disease worldwide. In the Western world, the diagnosis is done at late stage when treatments can be only palliative. Searches for new therapeutic regimens as well as for new biomarkers are in progress. To reduce cancer mortality is crucial the prevention of the lesion at earlier stages. Therefore, new bullets to prevention are needed. Nowadays, studies relating to different kinds of tumor are unanimous in considering cancer stem cells (CSCs) as "the core" of the tumor and the responsible of tumor chemoresistance and relapse. This chapter aims to provide the instructions to (1) isolate, (2) grow, and (3) validate, both in vivo and in vitro, the gastric CSC subpopulation.

Development of a therapy against metastatic bladder cancer using an interleukin-2 surface-modified MB49 bladder cancer stem cells vaccine

Introduction

In previous study the streptavidin interleukin-2 (SA-IL-2)-modified MB49 vaccine was effective against bladder cancer in a mouse model. However, a small portion of tumors regrew because the vaccine could not eliminate MB49 bladder cancer stem cells (MCSCs). Accordingly, we developed a SA-IL-2-modified MCSCs vaccine and evaluated its antitumor effects.

Methods

MCSCs were isolated and identified in cancer stem cells (CSCs) characters, with high expression of CSCs markers, higher resistance to chemotherapy, greater migration in vitro, and stronger tumorigenicity in vivo. The SA-IL-2 MCSCs vaccine was prepared and its bioactivity was evaluated. The protective, therapeutic, specific and memory immune response in animal experiments were designed to identify whether the vaccine elicited antitumor immunity and acted against metastatic bladder cancer.

Results

MCSCs had higher level of CD133 and CD44, less susceptibility to chemotherapy, more pronounced migration and greater tumorigenic ability. The successfully prepared SA-IL-2 MCSCs vaccine inhibited the tumor volume and prolonged mice survival in animal experiments. The expression of IgG, the population of dendritic cells, CD8⁺ and CD4⁺ T cells were highest in the experimental group than in the four control groups.

Conclusions

The SA-IL-2 MCSCs vaccine induced an antitumor immune response and was used to eliminate MCSCs to prevent tumor regrowth.

Gastric tumor-initiating CD44+ cells and epithelial-mesenchymal transition are inhibited by γ-secretase inhibitor DAPT

It has been proposed that the Notch signaling pathway may serve a pivotal role in cellular differentiation, proliferation and apoptosis. However, the function of Notch signaling in gastric cancer stem cells (GCSCs) is largely unknown. The present study aimed to delineate the role of the Notch1 pathway in GCSCs and during epithelial-mesenchymal transition (EMT). Flow cytometry was used to isolate CD44⁺ cells from the human gastric cancer cell line, MKN45. CD44⁺ cells displayed the characteristics of CSCs and exhibited higher Notch1 expression compared with CD44^- cells. To investigate the role of the Notch1 pathway in GCSCs, CD44⁺ cells were treated with the γ-secretase inhibitor DAPT. DAPT treatment inhibited the expression of the Notch1 downstream target Hes1 and EMT markers, suppressed the properties of CSCs and impaired the invasion and proliferation capabilities of CD44⁺ cells. In addition, intraperitoneal treatment with DAPT effectively inhibited the growth of CD44⁺ cell xenograft tumors. The present study indicated that CD44⁺ GCSCs possess the characteristics of CSCs and that the Notch1 pathway serves a critical role in the maintenance of CSCs and EMT.

Overexpression of NRG1 promotes progression of gastric cancer by regulating the self-renewal of cancer stem cells

BACKGROUND

Gastric cancer stem cells (GCSCs) have been successfully isolated from patients. However, the molecular mechanisms underlying the self-renewal of GCSCs and their relationship with the microenvironment are poorly characterized.

METHODS

GCSCs and cancer-associated fibroblasts (CAFs) were cultured directly from gastric cancer patients. The self-renewal of GCSCs was assayed by sphere formation assay and in vivo tumorigenicity. Expression of neuregulin1 (NRG1) was examined by immunohistochemistry, real-time PCR and western blotting.

RESULTS

CAFs increased the self-renewal of GCSCs by secreting NRG1. NRG1 activated NF-κB signaling and this activation regulated GCSC self-renewal. Moreover, NF-κB-active GCSCs were tumorigenic, however NF-κB-inactive GCSCs were not. The overexpression of NRG1 in stromal cells and cancer cells was observed in the tumor tissues of gastric cancer patients and was associated with clinical stage lymph node metastasis and survival in gastric cancer patients. In addition, we also found that NRG1 can regulate the proliferation and invasion of gastric cancer cells.

CONCLUSIONS

These results indicate that NRG1, which can be secreted by CAFs or cancer cells, promotes progression of gastric cancer by regulating the self-renewal of GCSCs and its overexpression is associated with a prognosis of gastric cancer.

Dysregulation of the PI3K/Akt signaling pathway affects cell cycle and apoptosis of side population cells in nasopharyngeal carcinoma

Increasing evidence has suggested that certain types of cancer possess their own stem-like cells, and that one subset of these cells, termed the side population (SP), may have an important role in tumorigenesis and cancer therapy. However, the molecular mechanisms underlying the modulation of SP cells in nasopharyngeal carcinoma (NPC) have remained elusive. In the present study, it was hypothesized that dysregulation of the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/Akt signaling pathway may influence SP and non-SP (NSP) phenotype. SP cells from the HK-1 NPC cell line were identified, and cancer stem cell markers were found to be highly expressed in SP cells compared with that of NSP cells. Freshly sorted SP cells demonstrated a significant increase in the proportion of cells in G0/G1 phase, while the majority of NSP cells were in the proliferative phase. Following 48 h of culture subsequent to cell sorting, the differences in cell cycle distribution between the SP and NSP cells converged. In addition, the apoptotic ratio of NSP cells was higher than that of SP cells at 24 h following sorting, but had no significant differences 48 h following sorting. To elucidate the potential mechanism mediating the cell cycle and apoptosis in SP cells, the expression levels of key molecules in the PI3K/Akt signaling pathway were evaluated. PI3K and Akt were upregulated, while 14-3-3σ protein was downregulated in SP cells when freshly sorted (0 h). However, there was no significant difference in the expression of these molecules between SP and NSP cells following 48 h of culture. These results suggested that dysregulation of the PI3K/Akt signaling pathway may be associated with the cell cycle and apoptosis of SP cells in NPC. However, further investigation is required to elucidate the detailed mechanisms underlying these effects.

ATOH1 Can Regulate the Tumorigenicity of Gastric Cancer Cells by Inducing the Differentiation of Cancer Stem Cells

Cancer stem cells (CSCs) have been shown to mediate tumorigenicity, chemo-resistance, radio-resistance and metastasis, which suggest they be considered therapeutic targets. Because their differentiated daughter cells are no longer tumorigenic, to induce the differentiation of CSCs can be one of strategies which can eradicate CSCs. Here we show that ATOH1 can induce the differentiation of gastric cancer stem cells (GCSCs). Real time PCR and western blot analysis showed that ATOH1 was induced during the differentiation of GCSCs. Furthermore, the lentivirus-induced overexpression of ATOH1 in GCSCs and in gastric cancer cell lines significantly induced differentiation, reduced proliferation and sphere formation, and reduced in vivo tumor formation in the subcutaneous injection and liver metastasis xenograft models. These results suggest ATOH1 be considered for the development of a differentiation therapy for gastric cancer.

Surgically resected human tumors reveal the biological significance of the gastric cancer stem cell markers CD44 and CD26

Cancer tissue is maintained by relatively small populations of cancer stem cells (CSCs), which are involved in chemotherapy resistance, recurrence and metastasis. As tumor tissues are comprised of various cells, studies of human clinical samples are important for the characterization of CSCs. In the present study, an expression profiling study was performed in which an anti-cell surface marker antibody-based array platform, a flow cytometry-based cell separation technique and a tumorigenicity analysis in immunodeficient animals were utilized. These approaches revealed that the markers cluster of differentiation (CD)44 and CD26 facilitated the fractionation of surgically resected human gastric cancer (GC) cells into the following subset populations with distinct tumorigenic potentials: Highly tumorigenic CD26⁺CD44⁺ cells (6/6 mice formed tumors), moderately tumorigenic CD26⁺CD44^- cells (5/6 mice formed tumors), and weakly or non-tumorigenic CD26^-CD44^- cells (2/6 mice formed tumors). Furthermore, exposure to 5-fluorouracil significantly increased the proportion of CD26⁺ cells in vitro. The present study demonstrated that the combined expression of CD26 and CD44 presents a potential marker of human GC stem cells.

Cancer stem cells in basic science and in translational oncology: can we translate into clinical application?

Since their description and identification in leukemias and solid tumors, cancer stem cells (CSC) have been the subject of intensive research in translational oncology. Indeed, recent advances have led to the identification of CSC markers, CSC targets, and the preclinical and clinical evaluation of the CSC-eradicating (curative) potential of various drugs. However, although diverse CSC markers and targets have been identified, several questions remain, such as the origin and evolution of CSC, mechanisms underlying resistance of CSC against various targeted drugs, and the biochemical basis and function of stroma cell-CSC interactions in the so-called ‘stem cell niche.’ Additional aspects that have to be taken into account when considering CSC elimination as primary treatment-goal are the genomic plasticity and extensive subclone formation of CSC. Notably, various cell fractions with different combinations of molecular aberrations and varying proliferative potential may display CSC function in a given neoplasm, and the related molecular complexity of the genome in CSC subsets is considered to contribute essentially to disease evolution and acquired drug resistance. In the current article, we discuss new developments in the field of CSC research and whether these new concepts can be exploited in clinical practice in the future.

Characterization of sphere‑forming cells with stem‑like properties from the gastric cancer cell lines MKN45 and SGC7901

Traditionally, it was presumed that gastric cancer was derived from tumor cells with stem‑like properties. In the present study, stem‑like cells from the gastric cancer cell lines MKN45 and SGC7901 were enriched by growing them as spheres in a defined serum‑free medium. Following enrichment for stem‑like cells, cluster of differentiation (CD)24 and CD44 were applied as candidate stem cell markers to examine the expression profile. It was revealed that the sphere‑derived cells contained a higher proportion of cells expressing the stem cell surface markers CD24 and CD44 when compared with the parental cells. It was also identified that the expression of cytokeratin 18 in sphere‑derived cells was decreased and the expression of vimentin and aldehyde dehydrogenase 1 (ALDH1) was increased compared with the parental cells. This finding supports the existence of a population of tumor sphere‑forming cells with stem cell properties in the MKN45 and SGC7901 cell lines. Furthermore, the stem cell population was enriched in cells expressing CD24, CD44, vimentin and ALDH1 cell surface markers. These results support the existence of gastric cancer stem cells and provide an alternative approach to the diagnosis and treatment of gastric cancer.

Clinical significance of POU5F1P1 rs10505477 polymorphism in Chinese gastric cancer patients receving cisplatin-based chemotherapy after surgical resection

This study aimed to investigate the association between POU class5 homeobox 1 pseudogene 1 gene (POU5F1P1) rs10505477 polymorphism and the prognosis of Chinese gastric cancer patients, who received cisplatin-based chemotherapy after surgical resection. POU5F1P1 rs10505477 was genotyped using the SNaPshot method in 944 gastric cancer patients who received gastrectomy. The association of rs10505477 G > A polymorphism with the progression and prognosis in gastric cancer patients was statistically analyzed using the SPSS version 18.0 for Windows. The results reveal that rs10505477 polymorphism has a negatively effect on the overall survival of gastric cancer patients in cisplatin-based chemotherapy subgroup (HR = 1.764, 95% CI = 1.069–2.911, p = 0.023). Our preliminary study indicates for the first time that POU5F1P1 rs10505477 is correlated with survival of gastric cancer patients who receving cisplatin-based chemotherapy after gastrectomy. Further studies are warranted to investigate the mechanism and to verify our results in different populations.

Interaction between gastric cancer stem cells and the tumor microenvironment

Gastric cancer (GC) remains a leading cause of cancer-related deaths worldwide. Cancer stem cells (CSCs) are selectively capable of tumor initiation and are implicated in tumor relapse and metastasis, thus, governing the prognosis of GC patients. Stromal cells and extracellular matrix adjacent to cancer cells are known to form a supportive environment for cancer progression. CSC properties are also regulated by their microenvironment through cell signaling and related factors. This review presents the current findings regarding the influence of the tumor microenvironment on GC stem cells, which will support the development of novel therapeutic strategies for patients with GC.

Gastric cancer stem cells in gastric carcinogenesis, progression, prevention and treatment

In recent decades, the study of the mechanism of tumorigenesis has brought much progress to cancer treatment. However, cancer stem cell (CSC) theory has changed previous views of tumors, and has provided a new method for treatment of cancer. The discovery of CSCs and their characteristics have contributed to understanding the molecular mechanism of tumor genesis and development, resulting in a new effective strategy for cancer treatment. Gastric CSCs (GCSCs) are the basis for the onset of gastric cancer. They may be derived from gastric stem cells in gastric tissues, or bone marrow mesenchymal stem cells. As with other stem cells, GCSCs highly express drug-resistance genes such as aldehyde dehydrogenase and multidrug resistance, which are resistant to chemotherapy and thus form the basis of drug resistance. Many specific molecular markers such as CD44 and CD133 have been used for identification and isolation of GCSCs, diagnosis and grading of gastric cancer, and research on GCSC-targeted therapy for gastric cancer. Therefore, discussion of the recent development and advancements in GCSCs will be helpful for providing novel insight into gastric cancer treatment.

Protein kinase C-δ inactivation inhibits the proliferation and survival of cancer stem cells in culture and in vivo

Background

A subpopulation of tumor cells with distinct stem-like properties (cancer stem-like cells, CSCs) may be responsible for tumor initiation, invasive growth, and possibly dissemination to distant organ sites. CSCs exhibit a spectrum of biological, biochemical, and molecular features that are consistent with a stem-like phenotype, including growth as non-adherent spheres (clonogenic potential), ability to form a new tumor in xenograft assays, unlimited self-renewal, and the capacity for multipotency and lineage-specific differentiation. PKCδ is a novel class serine/threonine kinase of the PKC family, and functions in a number of cellular activities including cell proliferation, survival or apoptosis. PKCδ has previously been validated as a synthetic lethal target in cancer cells of multiple types with aberrant activation of Ras signaling, using both genetic (shRNA and dominant-negative PKCδ mutants) and small molecule inhibitors. In contrast, PKCδ is not required for the proliferation or survival of normal cells, suggesting the potential tumor-specificity of a PKCδ-targeted approach.

Methods

shRNA knockdown was used validate PKCδ as a target in primary cancer stem cell lines and stem-like cells derived from human tumor cell lines, including breast, pancreatic, prostate and melanoma tumor cells. Novel and potent small molecule PKCδ inhibitors were employed in assays monitoring apoptosis, proliferation and clonogenic capacity of these cancer stem-like populations. Significant differences among data sets were determined using two-tailed Student’s t tests or ANOVA.

Results

We demonstrate that CSC-like populations derived from multiple types of human primary tumors, from human cancer cell lines, and from transformed human cells, require PKCδ activity and are susceptible to agents which deplete PKCδ protein or activity. Inhibition of PKCδ by specific genetic strategies (shRNA) or by novel small molecule inhibitors is growth inhibitory and cytotoxic to multiple types of human CSCs in culture. PKCδ inhibition efficiently prevents tumor sphere outgrowth from tumor cell cultures, with exposure times as short as six hours. Small-molecule PKCδ inhibitors also inhibit human CSC growth in vivo in a mouse xenograft model.

Conclusions

These findings suggest that the novel PKC isozyme PKCδ may represent a new molecular target for cancer stem cell populations.

Analysis of multiple markers for cancer stem-like cells in human thyroid carcinoma cell lines

Cancer stem-like cells (CSCs) play important roles in cancer initiation and progression. CSCs have been isolated using several markers, but those for thyroid CSCs remain to be confirmed. We therefore conducted a comprehensive search for thyroid CSC markers. Expression of nine cell surface markers (CD13, CD15, CD24, CD44, CD90, CD117, CD133, CD166, and CD326) and aldehyde dehydrogenase (ALDH) activity, which are CSC markers in various solid cancers, and the ability to form spheres in vitro and tumors in vivo were investigated using eight thyroid cancer cell lines (FRO, KTC1/2/3, TPC1, WRO, ACT1, and 8505C). Among these, four cell lines (FRO, KTC3, ACT1, and 8505C) possessed the both abilities; however, common markers indicative of CSCs were not observed. The pattern of ability to form spheres was completely matched to that of tumor formation, suggesting that our sphere assay is valuable for assessment of tumor-forming ability. Next, the cells were sorted using these markers and subjected to the sphere assay. In three cell lines (FRO, KTC3, and ACT1), ALDH(pos) cells showed higher sphere forming ability than ALDH(neg) cells but not in other cells. CD326(hi) also appeared to be a candidate marker only in FRO cells. However, these subpopulations did not follow a classical hierarchical model because ALDH(neg) and CD326(low) fractions also generated ALDH(pos) and CD326(hi) cells, respectively. These data suggest that ALDH activity is probably a major candidate marker to enrich thyroid CSCs but not universal; other markers such as CD326 that regulate different CSC properties may exist.

Gastric cancer stem cells: therapeutic targets

During the past decade, a growing body of evidence has implied that cancer stem cells (CSCs) play an important role in the development of gastric cancer (GC). The notion that CSCs give rise to GC and may be responsible for invasion, metastasis, and resistance to treatment has profound implications for anti-cancer therapy. Recent major advances in the rapidly evolving field of CSCs have opened novel exciting opportunities for developing CSC-targeted therapies. Discovery of specific markers and signaling pathways in gastric CSCs (GCSCs), with the perfecting of technologies for identification, isolation, and validation of CSCs, may provide the basis for a revolutionary cancer treatment approach based on the eradication of GCSCs. Emerging therapeutic tools based on specific properties and functions of CSCs, including activation of self-renewal signaling pathways, differences in gene expression profiles, and increased activity of telomerase or chemoresistance mechanisms, are developing in parallel with advances in nanotechnology and bioengineering. The addition of GCSC-targeted therapies to current oncological protocols and their complementary application may be the key to successfully fighting GC.

A modified method for isolation of bladder cancer stem cells from a MB49 murine cell line

BACKGROUND

The vaccine was efficiently effective against bladder cancer in earlier studies. However, a part of the mouse bladder tumour regrew due to regression after a period of time as the cancer stem cells could not be eliminated. In this study, we showed a modified method for the isolation of MB49 bladder cancer stem cells (MCSCs).

METHODS

Through a comparison of different serum-free culture mediums (SFM), MCSCs were isolated by a combination of the limited dilution method and the optimal SFM method. The characterizations of MCSCs were verified by the fluorescence activated cell sorting, the quantitative polymerase chain reaction, the western blotting, the cell proliferation assay, the soft agar assay, the transwell assay, the resistance to chemotherapy assay and the tumor xenograft formation assay.

RESULTS

The optimal SFM contained a RPMI1640+ epidermal growth factor (20 ng/ml), a basic fibroblast growth factor (20 ng/ml), a leukemia inhibitory factor (20 ng/ml), a B-27 serum-free supplement (20 μl/ml), and a bovine serum albumin (4 μg/ml). MCSCs possessed the high expression of cancer stem cell markers (CD133, CD44, OCT4, NANOG, and ABCG2) and the ability of differentiation. In functional comparisons, MCSCs had higher proliferative abilities, lower susceptibility to chemotherapy, greater migration in vitro, and stronger tumorigenic abilities in vivo.

CONCLUSION

MCSCs displayed specific cancer stem cells properties. Our study showed MCSCs were isolated successfully with a modified method using a combination of limited dilution and SFM methods.

Biomarkers for predicting future metastasis of human gastrointestinal tumors

The recent advances in surgery and radiation therapy have significantly improved the prognosis of patients with primary cancer, and the major challenge of cancer treatment now is metastatic disease development. The 5-year survival rate of cancer patients who have distant metastasis at diagnosis is extremely low, suggesting that prediction and early detection of metastasis would definitely improve their prognosis because suitable patient therapeutic management and treatment strategy can be provided. Cancer cells from a primary site give rise to a metastatic tumor via a number of steps which require the involvement and altered expression of many regulators. These regulators may serve as biomarkers for predicting metastasis. Over the past few years, numerous regulators have been found correlating with metastasis. In this review, we summarize the findings of a number of potential biomarkers that are involved in cadherin-catenin interaction, integrin signaling, PI3K/Akt/mTOR signaling and cancer stem cell identification in gastrointestinal cancers. We will also discuss how certain biomarkers are associated with the tumor microenvironment that favors cancer metastasis.

Epithelial cell adhesion molecule (EpCAM) is associated with prostate cancer metastasis and chemo/radioresistance via the PI3K/Akt/mTOR signaling pathway

Prostate cancer (CaP) is the second leading malignancy in men. The role of epithelial cell adhesion molecule (EpCAM), also known as CD326, in CaP progression and therapeutic resistance is still uncertain. Here, we aimed to investigate the roles of EpCAM in CaP metastasis and chemo/radioresistance. Expression of EpCAM in CaP cell lines and human CaP tissues was assessed using immunofluorescence and immunohistochemistry, respectively. EpCAM was knocked down (KD) in PC-3, DU145 and LNCaP-C4-2B cells using small interfering RNA (siRNA), and KD results were confirmed by confocal microscope, Western blotting and quantitative real time polymerase chain reaction (qRT-PCR). Cell growth was evaluated by proliferation and colony formation assays. The invasive potential was assessed using a matrigel chamber assay. Tumorigenesis potential was measured by a sphere formation assay. Chemo-/radiosensitivity were measured using a colony formation assay. Over-expression of EpCAM was found in primary CaP tissues and lymph node metastases including cancer cells and surrounding stromal cells. KD of EpCAM suppressed CaP proliferation and invasive ability, reduced sphere formation, enhanced chemo-/radiosensitivity, and down-regulated E-cadherin, p-Akt, p-mTOR, p-4EBP1 and p-S6K expression in CaP cells. Our findings suggest that EpCAM plays an important role in CaP proliferation, invasion, metastasis and chemo-/radioresistance associated with the activation of the PI3K/Akt/mTOR signaling pathway and is a novel therapeutic target to sensitize CaP cells to chemo-/radiotherapy.