Identification and expansion of cancer stem cells in tumor tissues and peripheral blood derived from gastric adenocarcinoma patients

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.

Neurons generated from carcinoma stem cells support cancer progression

Recent evidences show that nervous system acts as a crucial part of cancer microenvironment. Infiltration of nerve fibers into cancer microenvironment has an important active role in cancer progression. The stimulations of both cancer growth and metastasis by members of nervous system such as neurons and glial cells have been demonstrated. However, how the nervous system is built in cancer is largely unknown. Here we show that a fraction of cancer stem cells (CSCs) derived from patients with gastric carcinoma and colorectal carcinoma are capable of producing neurons that are involved in tumor neurogenesis and tumor growth. Cancer stem cell monoclone derived from a single cancer stem cell was able to generate neurons including sympathetic and parasympathetic neurons to take part in the nervous system in cancer tissues. Knocking down the neural cell generating capability of the human CSCs inhibited the growth of xenograft tumors in mouse model. Our data demonstrate that human CSCs are able to produce one of most important components in the cancer microenvironment that are required for cancer development and progression.

Identification of stem-like cells and clinical significance of candidate stem cell markers in gastric cancer

The existence of gastric cancer stem cells (CSCs) has not been definitively proven and specific cell surface markers for identifying gastric CSCs have largely not been identified. Our research aimed to isolate potential gastric CSCs and clarify their clinical significance, while defining markers for GCSC identification and verification. Here, we report that spheroid cells possess stem cell-like properties, and overexpress certain stem cell markers. CD133 or CD44-positive cells also exhibit properties of CSCs. The expression of Oct4, Sox2, Gli1, CD44, CD133, p-AKT, and p-ERK was significantly higher in metastatic lesions compared to that in primary lesions. Elevated expression of some of these proteins was correlated with a more aggressive phenotype and poorer prognosis, including Oct4, Sox2, Gli1, CD44, and p-ERK. Multivariate Cox proportional hazards model analysis showed that only CD44 is an independent factor. Knockdown of CD44 down-regulated the stem cell-like properties, which was accompanied by the down-regulation of p-ERK and Oct4. Oct4 overexpression could reverse the decreased CSCs properties induced by CD44 knockdown. Taken together, our research revealed that spheroid cell culture, and CD133 or CD44-labeled FACS methods can be used to isolate gastric CSCs. Some CSC markers have clinical significance in predicting the prognosis. CD44 is an independent prognostic factor and maintains the properties of CSCs in CD44-p-ERK-Oct4 positive feedback loop.

LGR5 Is a Gastric Cancer Stem Cell Marker Associated with Stemness and the EMT Signature Genes NANOG, NANOGP8, PRRX1, TWIST1, and BMI1

Background

Accumulating evidence supports the hypothesis that cancer stem cells (CSCs) are essential for cancer initiation, metastasis and drug resistance. However, the functional association of gastric CSC markers with stemness and epithelial-mesenchymal transition (EMT) signature genes is unclear.

Methods

qPCR was performed to measure the expression profiles of stemness and EMT signature genes and their association with putative CSC markers in gastric cancer tissues, cancer cell lines and sphere cells. Western blot analysis was used to confirm the results of the transcript analysis. Cell proliferation, cell migration, drug resistance and sphere cell growth assays were conducted to measure the expansion and invasion abilities of the cells. Tumor xenograft experiments were performed in NOD/SCID mice to test cell stemness in vivo. Flow cytometry and immunofluorescence staining were used to analyze cell subpopulations.

Results

The expression of LGR5 was strikingly up-regulated in sphere cells but not in cancer tissues or parental adherent cells. The up-regulation of LGR5 was also positively associated with stemness regulators (NANOG, OCT4, SOX2, and AICDA) and EMT inducers (PRRX1, TWIST1, and BMI1). In addition, sphere cells exhibited up-regulated vimentin and down-regulated E-cadherin expression. Using gene-specific primers, we found that the NANOG expression primarily originates from the retrogene NANOGP8. Western blot analysis showed that the expression of both LGR5 and NANOG is significantly higher in sphere cells. LGR5 over-expression significantly enhanced sphere cell growth, cell proliferation, cell migration and drug resistance in MGC803 cells. Tumor xenografts in nude mice showed that sphere cells are at least 10 times more efficient at tumor initiation than adherent cells. Flow cytometry analysis showed that ~20% of sphere cells are LGR5+/CD54+, but only ~3% of adherent cells are Lgr5+/CD54+. Immunofluorescence staining supports the above results.

Conclusion

The LGR5-expressing fraction of CD54+ cells represents gastric cancer CSCs, in which LGR5 is closely associated with stemness and EMT core genes, and NANOG expression is mainly contributed by the retrogene NANOGP8. Sphere cells are the best starting materials for the characterization of CSCs.

Surface Antigen Profiling of Helicobacter pylori-Infected and -Uninfected Gastric Cancer Cells Using Antibody Microarray

BACKGROUND

Comprehensive immunophenotyping cluster of differentiation (CD) antigens in gastric adenocarcinoma, specifically between Helicobacter pylori-infected and -uninfected gastric cancer patients by using DotScan(™) antibody microarray has not been conducted. Current immunophenotyping techniques include flow cytometry and immunohistochemistry are limited to the use of few antibodies for parallel examination. We used DotScan(™) antibody microarray consisting 144 CD antibodies to determine the distribution of CD antigens in gastric adenocarcinoma cells and to elucidate the effect of H. pylori infection toward CD antigen expression in gastric cancer.

METHODS

Mixed leukocytes population derived from gastric adenocarcinoma patients were immunophenotyped using DotScan(™) antibody microarray. AGS cells were infected with H. pylori strains and cells were captured on DotScan(™) slides.

RESULTS

Cluster of differentiation antigens involved in perpetuating the tolerance of immune cells to tumor cells was upregulated in gastric adenocarcinoma cells compared to normal cells. CD279 which is essential in T cells apoptosis was found to be upregulated in normal cells. Remarkably, H. pylori-infected gastric cancer patients exhibited upregulated expression of CD27 that important in maintenance of T cells. Infection of cagA+ H. pylori with AGS cells increased CD antigens expression which involved in cancer stem cell while cagA- H. pylori polarized AGS cells to express immune-regulatory CD antigens. Increased CD antigens expression in AGS cells infected with cagA+ H. pylori were also detected in H. pylori-infected gastric cancer patients.

CONCLUSION

This study suggests the tolerance of immune system toward tumor cells in gastric cancer and distinct mechanisms of immune responses exploited by different H. pylori strains.

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.

Current evidence for cancer stem cells in gastrointestinal tumors and future research perspectives

Cancer stem cells (CSCs) are a very heterogeneous subpopulation of "stem-like" cancer cells that have been identified in many cancers, including leukemias and solid tumors. It is believed that CSCs drive tumor growth, malignant behavior and are responsible for the initiation of metastatic spread. In addition, CSCs have been implicated in chemotherapy and radiotherapy resistance. Current evidence supports the theory that CSCs share at least two main features of normal stem cells: self-renewal and differentiation, properties that contribute to tumor survival even in the presence of aggressive chemotherapy; however, the mechanism(s) governing the unique biology of CSCs remain unclear. In the field of gastrointestinal cancer, where we face very low survival rates across different tumor types, unraveling the role of CSCs in gastrointestinal tumors should improve our knowledge of cancer biology and chemoresistance, ultimately benefiting patient survival. Towards this end, much effort is being invested in the characterization of CSCs as a means of overcoming drug resistance and controlling metastatic spread. In this review we will cover the concept of CSCs, the current evidence for CSCs in gastrointestinal tumors and future research directions.

Genomic landscape of gastric cancer: molecular classification and potential targets

Gastric cancer imposes a considerable health burden worldwide, and its mortality ranks as the second highest for all types of cancers. The limited knowledge of the molecular mechanisms underlying gastric cancer tumorigenesis hinders the development of therapeutic strategies. However, ongoing collaborative sequencing efforts facilitate molecular classification and unveil the genomic landscape of gastric cancer. Several new drivers and tumorigenic pathways in gastric cancer, including chromatin remodeling genes, RhoA-related pathways, TP53 dysregulation, activation of receptor tyrosine kinases, stem cell pathways and abnormal DNA methylation, have been revealed. These newly identified genomic alterations await translation into clinical diagnosis and targeted therapies. Considering that loss-of-function mutations are intractable, synthetic lethality could be employed when discussing feasible therapeutic strategies. Although many challenges remain to be tackled, we are optimistic regarding improvements in the prognosis and treatment of gastric cancer in the near future.

Spheres from cervical cancer cells display stemness and cancer drug resistance

Cervical cancer is one of the most common gynecological malignant tumors and is the cause of a serious health problem worldwide. An increasing amount of evidence has shown that cancer stem cells (CSCs) are present in tumors, and that these CSCs may be responsible for tumor metastasis and relapse. The present study aimed to identify and characterize a CSC population from the CaSki cell line. First, a stem cell culture medium was used to selectively expand the cancer stem-like cell spheres, and the putative stemness markers, Oct4 and Sox2, were identified. These markers were all highly expressed in the CaSki sphere-forming cells. Next, target region amplified polymorphism-polymerase chain reaction was performed and the CaSki sphere-forming cells were found to exhibit higher telomerase activity than the CaSki control cells cultured in non-stem cell medium. Using the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay, it was found that the CaSki sphere-forming cells were more resistant to chemotherapeutic drugs than the control CaSki cells. Using the tumor invasive assay, it was shown that the CaSki sphere-forming cells were more invasive than the control CaSki cells. These characteristics all suggested that the tumor sphere-forming cells mirrored the acknowledged CSC phenotypes. Overall, the use of a suspended sphere culture of CaSki cells may be an easy and feasible approach for enriching cancer stem-like cells in cervical cancer research.

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.

Prognostic value of Sox2 expression in digestive tract cancers: A meta-analysis

The aim of the present study was to accurately evaluate the association of Sox2 expression with the survival of patients with digestive tract cancers. Relevant literatures were identified by comprehensively searching databases including the Pubmed, Embase, CBMdisc, and Wanfang (up to October 2014). A meta-analysis was performed to clarify the association between Sox2 expression and overall survival or clinicopathological parameters of patients with digestive tract cancers (esophageal, gastric, and colorectal cancers). The results showed a significant association between high Sox2 expression and poor overall survival in patients with digestive tract carcinomas (HR=1.55, 95% CI=1.04-2.31), especially for patients with esophageal cancer (HR=2.04, 95%CI=1.30-3.22), colorectal cancer (HR=1.40, 95% CI=1.04-1.89), and digestive tract adenocarcinoma (HR=1.80, 95% CI=1.12-2.89), for Europeans (HR=1.98, 95% CI=1.44-2.71) or patients who did not receive neoadjuvant treatment (HR=1.73, 95% CI=1.10-2.72). Furthermore, Sox2 over-expression was highly correlated with vascular invasion (OR=1.86, 95% CI=1.25-2.77) and poor differentiation (OR=1.88, 95% CI=1.14-3.08), especially in esophageal and colorectal cancers. In conclusion, Sox2 expression may serve as a novel prognostic factor for patients with digestive tract cancers. Over-expression of Sox2 that is correlated with vascular invasion and poor differentiation suggests poor outcomes of patients with digestive tract cancers.

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.

Acquisition of resistance to trastuzumab in gastric cancer cells is associated with activation of IL-6/STAT3/Jagged-1/Notch positive feedback loop

In the present study, we demonstrate that prolonged treatment by trastuzumab induced resistance of NCI-N87 gastric cancer cells to trastuzumab. The resistant cells possessed typical characteristics of epithelial to mesenchymal transition (EMT)/cancer stem cells and acquired more invasive and metastatic potentials both in vitro and in vivo. Long term treatment with trastuzumab dramatically inhibited the phosphorylation of Akt, but triggered the activation of STAT3. The level of IL-6 was remarkably increased, implicating that the release of IL-6 that drives the STAT3 activation initiates the survival signaling transition. Furthermore, the Notch activities were significantly enhanced in the resistant cells, companied by upregulation of the Notch ligand Jagged-1 and the Notch responsive genes Hey1 and Hey2. Inhibiting the endogenous Notch pathway reduced the IL-6 expression and restored the sensitivities of the resistant cells to trastuzumab. Blocking of the STAT3 signaling abrogated IL-6-induced Jagged-1 expression, effectively inhibited the growth of the trastuzumab resistant cells, and enhanced the anti-tumor activities of trastuzumab in the resistant cells. These findings implicate that the IL-6/STAT3/Jagged-1/Notch axis may be a useful target and that combination of the Notch or STAT3 inhibitors with trastuzumab may prevent or delay clinical resistance and improve the efficacy of trastuzumab in gastric cancer.

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.

Clinicopathological characterisation of duodenal adenocarcinoma with high CD44 variant 9 expression

CD44 has been identified as a cancer stem cell (CSC) biomarker in various malignancies. The aim of this study was to elucidate the clinicopathological features of CD44v9 positive cells in duodenal adenocarcinoma (DA).Twenty-nine DA patients were selected from medical archives at our hospital. CD44v9 expression was analysed together with that of MUC2, MUC5AC, and MUC6 by immunohistochemistry. High levels of CD44v9 expression weakly correlated with inflammatory cell infiltration (r = 0.431, p = 0.020) and MUC6 expression (r = 0.425, p = 0.022). Furthermore, double immunofluorescence staining of CD44v9 and Ki-67 or cleaved caspase 3 (CC3) was performed. High- and low-density areas of CD44v9 positive cells were designated as CD44v9 positive and negative areas, respectively. Within CD44v9 positive areas, the level of Ki-67 positivity among CD44v9 positive cells was significantly lower than that of CD44v9 negative cells (p = 0.002). Meanwhile, the level of CC3 positivity among CD44v9 positive cells was significantly lower than that of CD44v9 negative cells (p < 0.001).CD44v9 expression may be affected by mononuclear cell infiltration and MUC6 expression in DA. CD44v9 positive cells also have a low mitotic activity and resist apoptosis. These characteristics suggest that CD44v9 positive cells possess CSC-like properties in DA.

Peripheral trafficking of bone-marrow-derived stem cells in patients with different types of gastric neoplasms

Recently, there has been a growing interest in the importance of stem cells (SCs) in the development/progression of gastric neoplasms. In this study, we performed a comprehensive analysis of different populations of bone-marrow-derived stem cells (BMSCs) in patients with various types of gastric malignancies, including gastric cancer, gastrointestinal stromal tumors (GISTs), neuroendocrine neoplasms (NENs), and lymphomas. We found significantly lower numbers of circulating Lin-/CD45 +/ CD133 + hematopoietic stem/progenitor cells (HSPCs), and intensified peripheral trafficking of both Lin-/CD45-/CXCR4+/CD34+/CD133+ very small embryonic/epiblast-like stem cells (VSELs) and CD105 + /STRO-1 +/ CD45- mesenchymal SCs (MSCs) in patients with gastric cancer, but not in those with other types of gastric neoplasms. No significant differences in the absolute numbers of circulating CD34 +/ KDR +/ CD31 +/ CD45- endothelial progenitor cells (EPCs) were observed between the groups. This abnormal balance in the peripheral trafficking of BMSCs in patients with gastric cancer was neither associated with clinical stage of the disease nor with systemic levels of stromal-derived factor-1 (SDF-1), as these were comparable to the values observed in control individuals. Interestingly, the absolute numbers of circulating BMSCs correlated with the concentrations of complement cascade-derived anaphylatoxins/molecules (mainly C5b-9/membrane attack complex-MAC) and sphingosine-1-phosphate (S1P). In summary, our translational study revealed that abnormal peripheral trafficking of BMSCs occurs in patients with gastric cancer, but not in those with other types of gastric neoplasms. Further, our findings indicate that highlighted complement cascade-derived molecules and S1P, but not SDF-1, are significant players associated with this phenomenon.

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.

Increased Oxidative Stress as a Selective Anticancer Therapy

Reactive oxygen species (ROS) are closely related to tumorgenesis. Under hypoxic environment, increased levels of ROS induce the expression of hypoxia inducible factors (HIFs) in cancer stem cells (CSCs), resulting in the promotion of the upregulation of CSC markers, and the reduction of intracellular ROS level, thus facilitating CSCs survival and proliferation. Although the ROS level is regulated by powerful antioxidant defense mechanisms in cancer cells, it is observed to remain higher than that in normal cells. Cancer cells may be more sensitive than normal cells to the accumulation of ROS; consequently, it is supposed that increased oxidative stress by exogenous ROS generation therapy has an effect on selectively killing cancer cells without affecting normal cells. This paper reviews the mechanisms of redox regulation in CSCs and the pivotal role of ROS in anticancer treatment.

CD44v6 Monoclonal Antibody-Conjugated Gold Nanostars for Targeted Photoacoustic Imaging and Plasmonic Photothermal Therapy of Gastric Cancer Stem-like Cells

Developing safe and effective nanoprobes for targeted imaging and selective therapy of gastric cancer stem cells (GCSCs) has become one of the most promising anticancer strategies. Herein, gold nanostars-based PEGylated multifunctional nanoprobes were prepared with conjugated CD44v6 monoclonal antibodies (CD44v6-GNS) as the targeting ligands. It was observed that the prepared nanoprobes had high affinity towards GCSC spheroid colonies and destroyed them completely with a low power density upon near-infrared (NIR) laser treatment (790 nm, 1.5 W/cm(2), 5 min) in vitro experiment. Orthotopic and subcutaneous xenografted nude mice models of human gastric cancer were established. Subsequently, biodistribution and photothermal therapeutic effects after being intravenously injected with the prepared nanoprobes were assessed. Photoacoustic imaging revealed that CD44v6-GNS nanoprobes could target the gastric cancer vascular system actively at 4 h post-injection, while the probes inhibited tumor growth remarkably upon NIR laser irradiation, and even extended survivability of the gastric cancer-bearing mice. The CD44v6-GNS nanoprobes exhibited great potential for applications of gastric cancer targeted imaging and photothermal therapy in the near future.

Analysis of circulating tumor cells derived from advanced gastric cancer

Studies in circulating tumor cells (CTCs) have proceeded to be accepted as prognostic markers in several types of cancers. But they are still limited because many are mainly from enumeration of CTCs. Here, we tried to evaluate the tumorigenicity of CTCs from advanced gastric cancer patients (n = 42). Peripheral blood mononuclear cells (PBMC) from the patients were separated into CD45 negative and positive fractions and both were subcutaneously injected into immunodeficient mice. Within 5 months nine tumor-like-structures from six patients but not from healthy volunteers were established. They were durable for passages and all had been confirmed human origin. Eight of the nine tumor-like-structures were from nonauthorized CTC containing cells expressing CD45 and B-cell markers. On the contrary, one of them was developed from CD45(-) PBMC fraction of a patient with bone marrow metastasis reflecting authorized CTCs. Histopathology showed common features with that of original gastric tumor. The cells isolated from the tumor-like-structure expressed EpCAM and CEA further supporting they were from the original tumor. Moreover the cells were CD44 positive to varying degree and a limiting dilution study showed that the CD44(+/high) fraction had tumorigenicity. The CD44 was dominantly in the form of CD44 variant 8-10. The CD44(+/high) cells had higher expression of the glutamate/cysteine transporter xCT compared with the CD44(-/low) cells. Our results showed the existence of tumor-initiating cells in blood of advanced gastric cancer patients and they could be a therapeutic target and prospective tool for further investigations.

Combined epithelial-mesenchymal transition with cancer stem cell-like marker as predictors of recurrence after radical resection for gastric cancer

Background

The aim of the study was to identify the incidence and the predictors of recurrence after curative resection and the clinical significance of epithelial-mesenchymal transition (EMT) and stem cell-like phenotypes in gastric cancer.

Methods

In a total of 1,463 patients that underwent curative resection for gastric cancer between January 2001 and January 2008 at Drum Tower Hospital, 402 (27.5%) experienced recurrence. They were divided into early recurrence (within two years) and late recurrence (more than two years). The clinicopathological characteristics, including five EMT-related proteins (Snail-1, ZEB-1, E-cadherin, vimentin, and β-catenin) and the gastric cancer stem cell markers CD44 and CD54, therapeutic modalities, survival time after recurrence, and recurrence patterns were compared between the two groups.

Results

Loss of E-cadherin expression and aberrant expression of vimentin and the known gastric cancer stem cell maker CD44 were significantly associated with aggressive clinicopathologic features. Multivariate analysis showed that stage III gastric cancer patients with early recurrence had larger tumors and more lymph node metastasis, coupled with aberrant expression EMT and cancer stem cell marker, than patients with late recurrence. Early recurrence was associated with more distant metastasis than late recurrence and patients tended to die within two years of recurrence.

Conclusions

Combined EMT with cancer stem cell-like marker is a predictor of recurrence after radical resection for gastric cancer. Advanced TNM stage was associated with early cancer death after recurrence.

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.

The effect of hyaluronic acid functionalized carbon nanotubes loaded with salinomycin on gastric cancer stem cells

Gastric cancer stem cells (CSCs) play a crucial role in the initiation, development, relapse and metastasis of gastric cancer because they are resistant to a standard chemotherapy and the residual CSCs are able to proliferate indefinitely. Therefore, eradication of this cell population is a primary objective in gastric cancer therapy. Here, we report a gastric CSCs-specifically targeting drug delivery system (SAL-SWNT-CHI-HA complexes) based on chitosan(CHI) coated single wall carbon nanotubes (SWNTs) loaded with salinomycin (SAL) functionalized with hyaluronic acid (HA) can selectively eliminate gastric CSCs. Gastric CSCs were identified as CD44+ cells and cultured in serum-free medium. SAL-SWNT-CHI-HA complexes were capable of inhibiting the self-renewal capacity of CD44+ population, and decrease mammosphere- and colon-formation of CSCs. In addition, the migration and invasion of gastric CSCs were significantly blocked by SAL-SWNT-CHI-HA complexes. Quantitative and qualitative analysis of cellular uptake demonstrated that HA functionalization facilitated the uptake of SWNTs in gastric CSCs while free HA competitively inhibited cellular uptake of SAL-SWNT-CHI-HA delivery system, revealing the mechanism of CD44 receptor-mediated endocytosis. The SAL-SWNT-CHI-HA complexes showed the strongest antitumor efficacy in gastric CSCs by inducing apoptosis, and in CSCs mammospheres by penetrating deeply into the core. Taken altogether, our studies demonstrated that this gastric CSCs-targeted SAL-SWNT-CHI-HA complexes would provide a potential strategy to selectively target and efficiently eradicate gastric CSCs, which is promising to overcome the recurrence and metastasis of gastric cancer and improve gastric cancer treatment.

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.

OCT3/4 expression is correlated with the invasion of gastric carcinoma

The present study aimed to evaluate the effect of OCT3/4 on the invasion and metastasis ability of gastric cancer. First, the expression level of OCT3/4 was detected in gastric cancer tissues of different tumor-node-metastasis stages. Furthermore, the correlation between the expression of OCT3/4 and the invasion ability of gastric cancer cells, and the probable regulatory mechanism were observed by RNA interference of OCT3/4 in gastric cancer cell strain MKN28, so as to provide the molecular mechanism for the occurrence and development of gastric cancer. The present study found the expression of OCT3/4 in gastric carcinoma tissues (22.56±8.72%) was markedly higher compared with that in para-cancer tissue (1.12±0.18%) (P<0.01). The expression of OCT3/4 was associated with the infiltration degree, and demonstrated an increasing tendency from Tis-T4 stages or from N0-N3. The expression of OCT3/4 in M0 tissues was markedly lower than that in M1 tissues (P<0.01). The level of OCT3/4 was markedly decreased following transfection with OCT3/4 small interfering (si)RNA (P<0.01). The number of cell clones was reduced in a dose-dependent manner following transfection with increasing levels of siRNA, and the number of cells that permeated through the filter membrane was also decreased. It may be concluded that the expression of OCT3/4 increases along with the degree of the infiltration and metastasis of gastric carcinoma, and that OCT3/4 siRNA inhibits the invasion of gastric carcinoma cells.

CD44v8-10 is a cancer-specific marker for gastric cancer stem cells

The surface marker CD44 has been identified as one of several markers associated with cancer stem cells (CSC) in solid tumors, but its ubiquitous expression in many cell types, including hematopoietic cells, has hindered its use in targeting CSCs. In this study, 28 paired primary tumor and adjacent nontumor gastric tissue samples were analyzed for cell surface protein expression. Cells that expressed pan-CD44 were found to occur at significantly higher frequency in gastric tumor tissues. We identified CD44v8-10 as the predominant CD44 variant expressed in gastric cancer cells and verified its role as a gastric CSC marker by limiting dilution and serial transplantation assays. Parallel experiments using CD133 failed to enrich for gastric CSCs. Analyses of another 26 primary samples showed significant CD44v8-10 upregulation in gastric tumor sites. Exogenous expression of CD44v8-10 but not CD44 standard (CD44s) increased the frequency of tumor initiation in immunocompromised mice. Reciprocal silencing of total CD44 resulted in reduced tumor-initiating potential of gastric cancer cells that could be rescued by CD44v8-10 but not CD44s expression. Our findings provide important functional evidence that CD44v8-10 marks human gastric CSCs and contributes to tumor initiation, possibly through enhancing oxidative stress defense. In addition, we showed that CD44v8-10 expression is low in normal tissues. Because CD44 also marks CSCs of numerous human cancers, many of which may also overexpress CD44v8-10, CD44v8-10 may provide an avenue to target CSCs in other human cancers.

Genistein-inhibited cancer stem cell-like properties and reduced chemoresistance of gastric cancer

Genistein, the predominant isoflavone found in soy products, has exerted its anticarcinogenic effect in many different tumor types in vitro and in vivo. Accumulating evidence in recent years has strongly indicated the existence of cancer stem cells in gastric cancer. Here, we showed that low doses of genistein (15 µM), extracted from Millettia nitida Benth var hirsutissima Z Wei, inhibit tumor cell self-renewal in two types of gastric cancer cells by colony formation assay and tumor sphere formation assay. Treatment of gastric cancer cells with genistein reduced its chemoresistance to 5-Fu (fluorouracil) and ciplatin. Further results indicated that the reduced chemoresistance may be associated with the inhibition of ABCG2 expression and ERK 1/2 activity. Furthermore, genistein reduced tumor mass in the xenograft model. Together, genistein inhibited gastric cancer stem cell-like properties and reduced its chemoresistance. Our results provide a further rationale and experimental basis for using the genistein to improve treatment of patients with gastric cancer.

Plasma miR-122 and miR-192 as potential novel biomarkers for the early detection of distant metastasis of gastric cancer

The aim of the present study was to ascertain whether plasma levels of specific microRNAs (miRNAs) are associated with distant metastasis (DM) in gastric cancer (GC). miRNA profiling was performed on 12 pairs of samples of gastric cancer with distant metastasis (GC/DM) and gastric cancer with no distant metastasis (GC/NDM); 14 differentially expressed miRNAs were identified for further inspection. Validation of these 14 miRNAs using quantitative reverse transcription PCR (qRT-PCR) on an independent validation set identified 2 differentially expressed miRNAs (miR-122 and miR-192). further validation of these two candidate miRNAs was conducted in a disease control set, a self-paired plasma set and finally in gastric cell lines in vitro. The results revealed that when compared with GC/NDM and healthy controls (HCs), plasma levels of miR-122 were significantly lower and plasma levels of miR-192 were significantly higher in GC/DM samples (both P<0.01). The plasma miR-122 level was again lower and the plasma miR-192-level was again higher in patients with GC/DM than in patients with benign gastric ulcer (BGC) and chronic gastritis (CG) (P<0.01). Compared to the level in patients with pre-distant metastases, miR-122 was significantly decreased while miR-192 was markedly elevated in patients with post-distant metastases (P<0.01). In CTC105 and CTC141 cells, miR-122 levels were moderately lower and miR-192 levels were markedly higher when compared to the levels in the GES-1 cells. ROC analyses showed that the AUC for plasma miR-122 was 0.808 (95% CI, 0.712-0.905; P<0.01), and the AUC for plasma miR-192 was 0.732 (95% CI, 0.623-0.841; P<0.01) for distinguishing GC/DM from GC/NDM. High expression of miR-122 in plasma independently contributed to a more favorable prognosis for GC (hazard ratio, 0.262; 95% CI, 0.164-0.816; P=0.038; Cox regression analysis), whereas the miR-192 level was not associated with the overall survival time. Our results demonstrated that assessment of decreased circulating miR-122 and elevated circulating miR-192 levels has the potential to improve early detection of DM in GC. Higher plasma levels of miR-122 in GC may indicate a favorable prognosis.

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.

Evaluating stem and cancerous biomarkers in CD15+CD44+ KYSE30 cells

Digestive system cancers are listed among the ten top causes of cancer-related death worldwide. Cancer stem cells (CSCs) are malignant cells that share some of their characteristics with normal stem cells, including self-renewal and multipotency, and also cancer cells, such as drug resistance and metastasis. Despite many reports on CSCs with digestive system origin, identification and characterization of esophageal CSCs have remained elusive. To examine the validity of routine SC, cancer cell and CSC markers in KYSE30 cells, derived from esophageal carcinoma, cells were first characterized by immunofluorescence and RT-PCR techniques, and then the significance of candidate biomarkers was evaluated in retinoic acid-treated cells by flow cytometry and/or real-time RT-PCR. Meanwhile, to study CD15 (a newly introduced CSC marker) expression in digestive tract cancers, human normal and tumoral tissues of esophagus, stomach, and colon were analyzed by immunohistochemistry. Using several experimental approaches, we show that CD44, but not CD15, could serve as a reliable marker for undifferentiated malignant squamous cells of esophagus. In conclusion, our study confirms the role of CD44 as a CSC marker in KYSE30 cells, an esophageal squamous cell carcinoma cell line, and for the first time indicates the expression of CD15 in non-neural stem-like cancer cells. Although the importance of CD15 was not indicated in diagnosis of digestive cancers, further studies are needed to better understand the biological identity and function of this molecule in non-neural malignancies.

Cancer-initiating cells derived from human rectal adenocarcinoma tissues carry mesenchymal phenotypes and resist drug therapies

Accumulating evidence indicates that cancer-initiating cells (CICs) are responsible for cancer initiation, relapse, and metastasis. Colorectal carcinoma (CRC) is typically classified into proximal colon, distal colon, and rectal cancer. The gradual changes in CRC molecular features within the bowel may have considerable implications in colon and rectal CICs. Unfortunately, limited information is available on CICs derived from rectal cancer, although colon CICs have been described. Here we identified rectal CICs (R-CICs) that possess differentiation potential in tumors derived from patients with rectal adenocarcinoma. The R-CICs carried both CD44 and CD54 surface markers, while R-CICs and their immediate progenies carried potential epithelial–mesenchymal transition characteristics. These R-CICs generated tumors similar to their tumor of origin when injected into immunodeficient mice, differentiated into rectal epithelial cells in vitro, and were capable of self-renewal both in vitro and in vivo. More importantly, subpopulations of R-CICs resisted both 5-fluorouracil/calcium folinate/oxaliplatin (FolFox) and cetuximab treatment, which are the most common therapeutic regimens used for patients with advanced or metastatic rectal cancer. Thus, the identification, expansion, and properties of R-CICs provide an ideal cellular model to further investigate tumor progression and determine therapeutic resistance in these patients.

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.

CD49f(high) cells retain sphere-forming and tumor-initiating activities in human gastric tumors

Identification of gastric tumor-initiating cells (TICs) is essential to explore new therapies for gastric cancer patients. There are reports that gastric TICs can be identified using the cell surface marker CD44 and that they form floating spheres in culture, but we could not obtain consistent results with our patient-derived tumor xenograft (PDTX) cells. We thus searched for another marker for gastric TICs, and found that CD49f(high) cells from newly-dissected gastric cancers formed tumors with histological features of parental ones while CD49f(low) cells did not when subcutaneously injected into immunodeficient mice. These results indicate that CD49f, a subunit of laminin receptors, is a promising marker for human gastric TICs. We established a primary culture system for PDTX cells where only CD49f(high) cells could grow on extracellular matrix (ECM) to form ECM-attaching spheres. When injected into immunodeficient mice, these CD49f(high) sphere cells formed tumors with histological features of parental ones, indicating that only TICs could grow in the culture system. Using this system, we found that some sphere-forming TICs were more resistant than gastric tumor cell lines to chemotherapeutic agents, including doxorubicin, 5-fluorouracil and doxifluridine. There was a patient-dependent difference in the tumorigenicity of sphere-forming TICs and their response to anti-tumor drugs. These results suggest that ECM plays an essential role for the growth of TICs, and that this culture system will be useful to find new drugs targeting gastric TICs.

Downregulation of tumor suppressor MBP-1 by microRNA-363 in gastric carcinogenesis

Gastric carcinoma is one of the most common malignancies and the second most lethal cancer worldwide. The mechanisms underlying aggressiveness of gastric cancer still remain obscure. c-Myc promoter binding protein 1 (MBP-1) is a negative regulator of c-myc expression and ubiquitously expressed in normal human tissues. It is produced by alternative translation initiation of α-enolase gene. Both MBP-1 and α-enolase are involved in the control of tumorigenesis including gastric cancer. MicroRNAs (miRNAs) are involved in tumorigenesis and could have diagnostic, prognostic and therapeutic potential. In this study, whether miRNAs modulate tumorigenesis of gastric cancer cells through targeting MBP-1 was evaluated. We found that miR-363 targets 3'-untranslated region of human MBP-1/α-enolase messenger RNA. The exogenous miR-363 promotes growth, viability, progression, epithelial-mesenchymal transition and tumorsphere formation of SC-M1 gastric cancer cells through downregulation of MBP-1, whereas the knockdown of endogenous miR-363 suppresses tumorigenesis and progression of SC-M1 cells via upregulation of MBP-1. The miR-363/MBP-1 axis is also involved in the control of carcinogenesis in KATO III and SNU-16 gastric cancer cells. Furthermore, miR-363 induces the xenografted tumor growth and lung metastasis of SC-M1 cells through MBP-1 in vivo. Taken together, these results suggest that miR-363 plays an important role in the increment of gastric carcinogenesis via targeting MBP-1.

Prognostic value of CD166 expression in cancers of the digestive system: a systematic review and meta-analysis

Objective

Many studies have reported the prognostic predictive value of CD166 as a cancer stem cell marker in cancers of the digestive system; however, its predictive value remains controversial. Here, we investigate the correlation between CD166 positivity in digestive system cancers and clinicopathological features using meta-analysis.

Methods

A comprehensive search in PubMed and ISI Web of Science through March of 2013 was performed. Only articles containing CD166 antigen immunohistochemical staining in cancers of the digestive system were included,including pancreatic cancer, esophageal cancer, gastric cancer and colorectal cancer. Data comparing 3- and 5-year overall survival along with other clinicopathological features were collected.

Results

Nine studies with 2553 patients who met the inclusion criteria were included for the analysis. The median rate of CD166 immunohistochemical staining expression was 56% (25.4%–76.3%). In colorectal cancer specifically, the results of a fixed-effects model indicated that CD166-positive expression was an independent marker associated with a smaller tumor burden (T category; RR = 0.93, 95%, CI: 0.88–0.98) but worse spread to nearby lymph nodes (N category; RR = 1.17, 95% CI: 1.05–1.30). The 5-year overall survival rate was showed relationship with cytoplasmic positive staining of CD166 (RR = 1.47 95% 1.21–1.79), but no significant association was found in the pool or any other stratified analysis with 3- or 5- year overall survival rate.

Conclusion

Based on the published studies, different cellular location of CD166 has distinct prognostic value and cytoplasmic positive expression is associated with worse prognosis outcome. Besides, our results also find CD166 expression indicate advanced T category and N-positive status in colorectal cancer specifically.

Cancer stem cells: the 'heartbeat' of gastric cancer

Gastric cancer (GC) remains one of the most common cancers worldwide. Its prevalence is still on the rise in the developing countries due to the ageing population. The cancer stem cell (CSC) theory provides a new insight into the interpretation of tumor initiation, aggressive growth, recurrence, and metastasis of cancer, as well as the development of new strategies for cancer treatment. This review will focus on the progress of biomarkers and signaling pathways of CSCs, the complex crosstalk networks between the microenvironment and CSCs, and the development of therapeutic approaches against CSCs, predominantly focusing on GC.

Patient-derived tumor xenografts: transforming clinical samples into mouse models

Tumor graft models (also known as patient-derived xenografts or PDX) are based on the transfer of primary tumors directly from the patient into an immunodeficient mouse. Because PDX mice are derived from human tumors, they offer a tool for developing anticancer therapies and personalized medicine for patients with cancer. In addition, these models can be used to study metastasis and tumor genetic evolution. This review examines the development, challenges, and broad use of these attractive preclinical models.

Gastric cancer stem cells: a novel therapeutic target

Gastric cancer remains one of the leading causes of global cancer mortality. Multipotent gastric stem cells have been identified in both mouse and human stomachs, and they play an essential role in the self-renewal and homeostasis of gastric mucosa. There are several environmental and genetic factors known to promote gastric cancer. In recent years, numerous in vitro and in vivo studies suggest that gastric cancer may originate from normal stem cells or bone marrow-derived mesenchymal cells, and that gastric tumors contain cancer stem cells. Cancer stem cells are believed to share a common microenvironment with normal niche, which play an important role in gastric cancer and tumor growth. This mini-review presents a brief overview of the recent developments in gastric cancer stem cell research. The knowledge gained by studying cancer stem cells in gastric mucosa will support the development of novel therapeutic strategies for gastric cancer.

CD44+ gastric cancer cells with stemness properties are chemoradioresistant and highly invasive

CD44 has been confirmed as a cancer stem cell marker in a variety of human cancer cell lines and primary tumours, but whether this marker is applicable to gastric cancer (GC) remains unknown. The responses of CD44⁺ GC stem-like cells to chemoradiation and the roles they play in cancer invasion are not well understood. In the present study, cell sorting was applied to the poorly differentiated human GC cells to isolate a pure concentration of the CD44⁺ cell populations (<1% CD44⁻ cells). The stemness properties of the CD44⁺ cell population were confirmed by two ‘gold standard’ methods; an in vivo tumourigenicity assay and an in vitro spheroid colony formation assay. In addition, the treatment response was evaluated in CD44⁺ and CD44⁻ cell fractions that underwent chemoradiation. In general, CD44⁺ stem-like cells tended to respond more poorly to chemoradiation than their non-stem-like counterparts. Further experimentation revealed that the CD44⁺ stem-like cells that recorded positive scores in the migration and invasion assay in vitro formed invasive tumours in vivo. Therefore, we hypothesized that CD44⁺ stem-like cells may significantly express invasion-associated genes. Consistent with this prediction, increased expression of the cancer invasion-related genes matrix metalloproteinase (MMP)-1, MMP-2, epidermal growth factor receptor (EGFR) and cyclooxygenase 2 (COX-2) were detected in the CD44⁺ stem-like cells. To the best of our knowledge, this is the first study that reveals the correlation between CD44⁺ GC cells and cancer invasion. By selectively eliminating CD44⁺ stem-like cells, it may be possible to treat patients with aggressive, non-resectable GCs, as well as preventing the tumours from metastasizing.

Gastric stem cells and gastric cancer stem cells

The gastric epithelium is continuously regenerated by gastric stem cells, which give rise to various kinds of daughter cells, including parietal cells, chief cells, surface mucous cells, mucous neck cells, and enteroendocrine cells. The self-renewal and differentiation of gastric stem cells need delicate regulation to maintain the normal physiology of the stomach. Recently, it was hypothesized that cancer stem cells drive the cancer growth and metastasis. In contrast to conventional clonal evolution hypothesis, only cancer stem cells can initiate tumor formation, self-renew, and differentiate into various kinds of daughter cells. Because gastric cancer can originate from gastric stem cells and their self-renewal mechanism can be used by gastric cancer stem cells, we review here how critical signaling pathways, including hedgehog, Wnt, Notch, epidermal growth factor, and bone morphogenetic protein signaling, may regulate the self-renewal and differentiation of gastric stem cells and gastric cancer stem cells. In addition, the precancerous change of the gastric epithelium and the status of isolating gastric cancer stem cells from patients are reviewed.

Prognostic value of cancer stem cell marker CD133 expression in gastric cancer: a systematic review

Objective

To investigate the correlation between CD133-positive gastric cancer and clinicopathological features and its impact on survival.

Methods

A search in the Medline and Chinese CNKI (up to 1 Dec 2011) was performed using the following keywords gastric cancer, CD133, AC133, prominin-1 etc. Electronic searches were supplemented by hand searching reference lists, abstracts and proceedings from meetings. Outcomes included overall survival and various clinicopathological features.

Results

A total of 773 gastric cancer patients from 7 studies were included. The median rate of CD133 expression by immunohistochemistry (IHC) was 44.8% (15.2%–57.4%) from 5 studies, and that by reverse transcription polymerase chain reaction (RT-PCR) was 91.3% (66.7%–100%) from 4 studies. The accumulative 5-year overall survival rates of CD133-positive and CD133-negative patients were 21.4% and 55.7%, respectively. Meta-analysis showed that CD133-positive patients had a significant worse 5-year overall survival compared to the negative ones (OR = 0.20, 95% CI 0.14–0.29, P<0.00001). With respect to clinicopathological features, CD133 overexpression by IHC method was closely correlated with tumor size, N stage, lymphatic/vascular infiltration, as well as TNM stage.

Conclusion

CD133-positive gastric cancer patients had worse prognosis, and was associated with common clinicopathological poor prognostic factors.

Aldehyde dehydrogenase high gastric cancer stem cells are resistant to chemotherapy

Cancer stem cells (CSCs) are known to influence chemoresistance, survival, relapse and metastasis. Aldehyde dehydrogenase (ALDH) functions as an epithelial CSC marker. In the present study, we investigated the involvement of ALDH in gastric CSC maintenance, chemoresistance and survival. Following screening for eight candidate markers (CD13, CD26, CD44, CD90, CD117, CD133, EpCAM and ALDH), five gastric cancer cell lines were found to contain small subpopulations of high ALDH activity (ALDH(high) cells). We also examined the involvement of ALDH(high) cell populations in human primary tumor samples. Immunodeficient NOD/SCID mice were inoculated with tumor tissues obtained from surgical specimens. ALDH(high) cells were found to persist in the xenotransplanted primary tumor samples. in the immunodeficient mice, ALDH(high) cells exhibited a greater sphere‑forming ability in vitro and tumorigenic potential in vivo, compared with subpopulations of low ALDH activity (ALDH(low) cells). Cell cultures treated with 5-fluoro-uracil and cisplatin exhibited higher numbers of ALDH(high) cells. Notch1 and Sonic hedgehog (Shh) expression was also found to increase in ALDH(high) cells compared with ALDH(low) cells. Therefore, it can be concluded that ALDH generates chemoresistance in gastric cancer cells through Notch1 and Shh signaling, suggesting novel treatment targets.

Suppression of myeloid cell leukemia-1 (Mcl-1) enhances chemotherapy-associated apoptosis in gastric cancer cells

BACKGROUND

Myeloid cell leukemia-1 (Mcl-1) is an anti-apoptotic protein that regulates apoptosis sensitivity in a variety of cell types. Here we evaluate the roles of Mcl-1 in chemotherapy-associated apoptosis in gastric cancer cells. In addition, our study examined whether Mcl-1 contributed to apoptosis resistance in so-called cancer stem cell (CSC)-like populations in gastric cancer.

METHODS

Seven gastric cancer cell lines were used. The expression of Mcl-1 was assessed by either real-time polymerase chain reaction or Western blot analysis. Apoptosis was quantitated by morphological observation and caspase activity measurement. Adenovirus-mediated RNA interference (RNAi) technology was used to knockdown the expression of Mcl-1. The release of cytochrome c was evaluated by subcellular fractionation and immunoblot analysis. To identify and isolate the CSC-like populations, we used the CSC-associated cell surface marker CD44 and flow cytometry.

RESULTS

Six out of the 7 gastric cancer cell lines overexpressed Mcl-1 protein. These Mcl-1-expressing cell lines were relatively resistant to chemotherapeutic agents such as 5-fluorouracil (5-FU) and cisplatin (CDDP). Depletion of Mcl-1 protein by RNAi technology effectively sensitized the cells to anticancer drug-induced mitochondrial cytochrome c release, caspase activation, and apoptosis. In addition, vast amounts of Mcl-1 mRNA were expressed in CD44-positive CSC-like cells. Mcl-1 suppression enhanced the apoptosis in CD44-positive cells to a level equivalent to that in CD44-negative cells, suggesting that Mcl-1 mediates chemotherapy resistance in CSC-like populations.

CONCLUSION

These results suggest that Mcl-1 mediates the resistance to apoptosis in gastric cancer cells by blocking the mitochondrial pathway of cell death. Mcl-1 depletion appears to be an attractive strategy to overcome chemotherapy resistance in gastric cancer cells.

Sox2 enhances the tumorigenicity and chemoresistance of cancer stem-like cells derived from gastric cancer

Gastric cancer stem-like cells (GCSCs) have been identified to possess the ability of self-renewal and tumor initiation. However, the mechanisms involved remain largely unknown. Here, we isolated and characterized the GCSCs by side population (SP) sorting procedure and cultured sphere cells (SC) from human gastric cancer cell lines SGC-7901, BGC-823, MGC-803, HGC-27 and MKN-28. The sorting and culture assay revealed that SP cells proliferated in an asymmetric division manner. In addition, SP cells exhibited a higher potential of spheroid colony formation and greater drug resistance than non-SP cells (NSP). Moreover, the SC were found with enhanced capabilities of drug resistance in vitro and tumorigenicity in vivo. Sox2 mRNA and protein was highly and significantly overexpressed in the SP cells and SC. Importantly, downregulation of Sox2 with siRNA obviously reduced spheroid colony formation and doxorubicin efflux, as well as increased apoptosis rate in sphere cells in vitro and suppressed tumorigenicity in vivo. These results suggest that both SP cells and cultured SC enrich with GCSCs and that Sox2 plays a pivotal role in sustaining stem cell properties and might be a potential target for gastric cancer therapy.