CD133 expression defines a tumor initiating cell population in primary human ovarian cancer

Noninvasive positron emission tomography and fluorescence imaging of CD133+ tumor stem cells

A technology that visualizes tumor stem cells with clinically relevant tracers could have a broad impact on cancer diagnosis and treatment. The AC133 epitope of CD133 currently is one of the best-characterized tumor stem cell markers for many intra- and extracranial tumor entities. Here we demonstrate the successful noninvasive detection of AC133(+) tumor stem cells by PET and near-infrared fluorescence molecular tomography in subcutaneous and orthotopic glioma xenografts using antibody-based tracers. Particularly, microPET with (64)Cu-NOTA-AC133 mAb yielded high-quality images with outstanding tumor-to-background contrast, clearly delineating subcutaneous tumor stem cell-derived xenografts from surrounding tissues. Intracerebral tumors as small as 2-3 mm also were clearly discernible, and the microPET images reflected the invasive growth pattern of orthotopic cancer stem cell-derived tumors with low density of AC133(+) cells. These data provide a basis for further preclinical and clinical use of the developed tracers for high-sensitivity and high-resolution monitoring of AC133(+) tumor stem cells.

Intestinal stem cell marker LGR5 expression during gastric carcinogenesis

AIM: To investigate the differential expression of leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5) in gastric cancer tissues and its significance related to tumor growth and spread.

METHODS: Formalin-fixed biopsy specimens of intestinal metaplasia (n = 90), dysplasia (n = 53), gastric adenocarcinoma (n = 180), metastases in lymph nodes and the liver (n = 15), and lesion-adjacent normal gastric mucosa (controls; n = 145) were obtained for analysis from the Peking University Cancer Hospital’s Department of Pathology and Gastrointestinal Surgery tissue archives (January 2003 to December 2011). The biopsied patients’ demographic and clinicopathologic data were retrieved from the hospital’s medical records database. Each specimen was subjected to histopathological typing to classify the tumor node metastasis (TNM) stage and to immunohistochemistry staining to detect the expression of the cancer stem cell marker LGR5. The intergroup differences in LGR5 expression were assessed by Spearman’s rank correlation analysis, and the relationship between LGR5 expression level and the patients’ clinicopathological characteristics was evaluated by the χ² test or Fisher’s exact test.

RESULTS: Significantly more gastric cancer tissues showed LGR5⁺ staining than normal control tissues (all P < 0.01), with immunoreactivity detected in 72.2% (65/90) and 50.9% (27/53) of intestinal metaplasia and dysplasia specimens, respectively, 52.8% (95/180) of gastric adenocarcinoma specimens, and 73.3%% (11/15) of metastasis specimens, but 26.9% (39/145) of lesion-adjacent normal gastric mucosa specimens. Comparison of the intensity of LGR5⁺ staining showed an increasing trend that generally followed increasing dedifferentiation and tumor spread (normal tissue < dysplasia, < gastric adenocarcinoma < metastasis; all P < 0.001), with the exception of expression level detected in intestinal metaplasia which was higher than that in normal gastric tissues (P < 0.001). Moreover, gastric cancer-associated enhanced expression of LGR5 was found to be significantly associated with age, tumor differentiation, Lauren type and TNM stage (I + II vs III + IV) (all P < 0.05), but not with sex, tumor site, location, size, histology, lymphovascular invasion, depth of invasion, lymph node metastasis or distant metastasis. Patients with LGR5⁺ gastric cancer specimens and without signs of metastasis from the original biopsy experienced more frequent rates of recurrence or metastasis during follow-up than patients with LGR5^- specimens (P < 0.05).

CONCLUSION: Enhanced LGR5 is related to progressive dedifferentiation and metastasis of gastric cancer, indicating the potential of this receptor as an early diagnostic and prognostic biomarker.

Ovarian cancer stem cells: are they real and why are they important?

The cancer stem cell hypothesis has been put forward as a paradigm to describe varying levels of aggressiveness in heterogeneous tumors. Specifically, many subpopulations have been clearly demonstrated to possess increased tumorigenicity in mice, broad differentiating capacity, and resistance to therapy. However, the extent to which these experimental findings are potentially clinically significant is still not clear. This review will describe the principles of this emerging hypothesis, ways in which it may be appropriate in ovarian cancer based on the clinical course of the disease, and how we might exploit it to improve outcomes in ovarian cancer patients.

Targeted cancer therapy--are the days of systemic chemotherapy numbered?

Targeted therapy or molecular targeted therapy has been defined as a type of treatment that blocks the growth of cancer cells by interfering with specific cell molecules required for carcinogenesis and tumor growth, rather than by simply interfering with all rapidly dividing cells as with traditional chemotherapy. There is a growing number of FDA approved monoclonal antibodies and small molecules targeting specific types of cancer suggestive of the growing relevance of this therapeutic approach. Targeted cancer therapies, also referred to as "Personalized Medicine", are being studied for use alone, in combination with other targeted therapies, and in combination with chemotherapy. The objective of personalized medicine is the identification of patients that would benefit from a specific treatment based on the expression of molecular markers. Examples of this approach include bevacizumab and olaparib, which have been designated as promising targeted therapies for ovarian cancer. Combinations of trastuzumab with pertuzumab, or T-DM1 and mTOR inhibitors added to an aromatase inhibitor are new therapeutic strategies for breast cancer. Although this approach has been seen as a major step in the expansion of personalized medicine, it has substantial limitations including its high cost and the presence of serious adverse effects. The Cancer Genome Atlas is a useful resource to identify novel and more effective targets, which may help to overcome the present limitations. In this review we will discuss the clinical outcome of some of these new therapies with a focus on ovarian and breast cancer. We will also discuss novel concepts in targeted therapy, the target of cancer stem cells.

Hypomethylation signature of tumor-initiating cells predicts poor prognosis of ovarian cancer patients

DNA methylation contributes to tumor formation, development and metastasis. Epigenetic dysregulation of stem cells is thought to predispose to malignant development. The clinical significance of DNA methylation in ovarian tumor-initiating cells (OTICs) remains unexplored. We analyzed the methylomic profiles of OTICs (CP70sps) and their derived progeny using a human methylation array. qRT-PCR, quantitative methylation-specific PCR (qMSP) and pyrosequencing were used to verify gene expression and DNA methylation in cancer cell lines. The methylation status of genes was validated quantitatively in cancer tissues and correlated with clinicopathological factors. ATG4A and HIST1H2BN were hypomethylated in OTICs. Methylation analysis of ATG4A and HIST1H2BN by qMSP in 168 tissue samples from patients with ovarian cancer showed that HIST1H2BN methylation was a significant and independent predictor of progression-free survival (PFS) and overall survival (OS). Multivariate Cox regression analysis showed that patients with a low level of HIST1H2BN methylation had poor PFS (hazard ratio (HR), 4.5; 95% confidence interval (CI), 1.4-14.8) and OS (HR, 4.3; 95% CI, 1.3-14.0). Hypomethylation of both ATG4A and HIST1H2BN predicted a poor PFS (HR, 1.8; 95% CI, 1.0-3.6; median, 21 months) and OS (HR, 1.7; 95% CI, 1.0-3.0; median, 40 months). In an independent cohort of ovarian tumors, hypomethylation predicted early disease recurrence (HR, 1.7; 95% CI, 1.1-2.5) and death (HR, 1.4; 95% CI, 1.0-1.9). The demonstration that expression of ATG4A in cells increased their stem properties provided an indication of its biological function. Hypomethylation of ATG4A and HIST1H2BN in OTICs predicts a poor prognosis for ovarian cancer patients.

Monoclonal antibody-based immunotherapy of ovarian cancer: targeting ovarian cancer cells with the B7-H3-specific mAb 376.96

OBJECTIVE

The high rate of relapse in patients with advanced ovarian cancer likely reflects the chemoresistance of cancer initiating cells (CICs). We evaluated the anti-tumor activity of monoclonal antibody (mAb) 376.96, which recognizes a B7-H3 epitope expressed on ovarian carcinoma cells (OCCs), in combination with the tyrosine kinase inhibitor Sunitinib and chemotherapy on chemosensitive and chemoresistant cells and CICs.

METHODS

Eight ovarian cancer cell lines including platinum- and taxane-resistant cell lines were analyzed by flow cytometry to establish expression of the mAb 376.96-defined-B7-H3-epitope on differentiated ovarian cancer cells and CICs. Samples from 10 ovarian cancer patients were analyzed via immunohistochemistry for mAb 376.96-defined-B7-H3-epitope expression. In vitro studies assessed mAb 376.96 alone and in combination with Sunitinib on the growth of chemosensitive and chemoresistant cell lines and on the content of CICs.

RESULTS

The mAb-376.96-defined-B7-H3 epitope is expressed on both differentiated cells and CICs in chemosensitive and chemoresistant ovarian cancer cell lines and 10 patient derived ovarian cancer tumors. In vitro treatment of chemoresistant cell lines with mAb 376.96 resulted in decreased cell viability. mAb 376.96 enhanced the cytotoxicity of Sunitinib and reduced the content of CICs.

CONCLUSION

The mAb-376.96-defined-B7-H3-epitope was found to be expressed on both differentiated ovarian cancer cells and CICs in chemosensitive and chemoresistant ovarian cancer cell lines. mAb 376.96 inhibited the in vitro growth of chemosensitive and chemoresistant OCCs and reduced the content of CICs when used with Sunitinib. Further studies examining B7-H3 as a potential target of mAb-based immunotherapy for this type of malignancy are warranted.

Tumour heterogeneity and cancer cell plasticity

Phenotypic and functional heterogeneity arise among cancer cells within the same tumour as a consequence of genetic change, environmental differences and reversible changes in cell properties. Some cancers also contain a hierarchy in which tumorigenic cancer stem cells differentiate into non-tumorigenic progeny. However, it remains unclear what fraction of cancers follow the stem-cell model and what clinical behaviours the model explains. Studies using lineage tracing and deep sequencing could have implications for the cancer stem-cell model and may help to determine the extent to which it accounts for therapy resistance and disease progression.

Unravelling cancer stem cell potential

The maintenance and repair of many adult tissues are ensured by stem cells (SCs), which reside at the top of the cellular hierarchy of these tissues. Functional assays, such as in vitro clonogenic assays, transplantation and in vivo lineage tracing, have been used to assess the renewing and differentiation potential of normal SCs. Similar strategies have suggested that solid tumours may also be hierarchically organized and contain cancer SCs (CSCs) that sustain tumour growth and relapse after therapy. In this Opinion article, we discuss the different parallels that can be drawn between adult SCs and CSCs in solid tumours.

Cytokine-induced killer (CIK) cells bound with anti-CD3/anti-CD133 bispecific antibodies target CD133(high) cancer stem cells in vitro and in vivo

CD133 is a common marker of cancer stem cells (CSCs). We generated an anti-CD3/anti-CD133 bispecific antibody (BsAb) and bound it to the cytokine-induced killer (CIK) cells as effector cells (BsAb-CIK) to target CD133(high) CSCs. The killing of CD133(high) pancreatic (SW1990) and hepatic (Hep3B) cancer cells by the BsAb-CIK cells was significantly (p<0.05) higher than the killing by the parental CIK or by CIK cells bound with anti-CD3 (CD3-CIK) without CD133 targeting. In nude mice, the BsAb-CIK cells inhibited CD133(high) tumor growth significantly (p<0.05) more than that by CIK or CD3-CIK cells, or by the BsAb alone. BsAb-CIK cells co-cultured with CD133(high) cells produced significantly (p<0.05) higher amount of IFN-γ. Treatment with the BsAb-CIK cells significantly downregulated the expression of S100P and IL-18bp, but upregulated STAT1. The findings may help with the development of novel immunotherapies for patients with cancer containing CD133(high) CSCs by selectively targeting this cell population.

Follicle-stimulating hormone inhibits apoptosis in ovarian cancer cells by regulating the OCT4 stem cell signaling pathway

OCT4, a stem cell marker, is overexpressed in several types of human cancer and can induce resistance to chemotherapy and inhibition of apoptosis. We previously demonstrated that human follicle stimulating hormone (FSH) can inhibit ovarian cancer cell apoptosis. However, the role of OCT4 in FSH-induced inhibition of apoptosis has not been reported in detail. Here, we profiled OCT4 protein expression in ovarian epithelial cancer (OEC) with benign cystadenoma, borderline tumor and carcinoma tissues as well as different ovarian cancer cell lines and normal ovarian epithelial cells. Furthermore, the effects of FSH on OCT4 expression and related signaling pathways were evaluated. The overexpression of OCT4 in ovarian carcinoma and OEC cell lines suggest that OCT4 plays a critical role in OEC carcinogenesis. Moreover, FSH-induced apoptosis inhibition was confirmed and FSH stimulation induced the expansion of CD44+CD117+ cells with a stem cell-like phenotype. Re-expression of OCT4 enhanced the expression of Notch, Sox2 and Nanog molecules that play critical roles in cancer stem cell proliferation and differentiation. FSH upregulated the expression of Notch, Sox2 and Nanog and these effects were abolished by knocking down OCT4, suggesting that several cancer stem cell pathways are involved in FSH regulation. We also examined OCT4 expression in surgical specimens of ovarian cancer. Immunohistostaining revealed that OCT4 expression was increased in ovarian carcinoma compared with benign cystadenomas and borderline tumors, and OCT4 expression was significantly correlated with histological grade. Staining for OCT4 was increased in serous cystadenocarcinoma, when compared with clear cell carcinoma. In summary, the OCT4 cancer stem cell signaling pathway may mediate FSH-induced inhibition of apoptosis and could provide a target for treatment of ovarian cancer.

Colorectal cancer defeating? Challenge accepted!

Colorectal tumours are actually considered as aberrant organs, within it is possible to notice a different stage of cell growth and differentiation. Their origin is reported to arise from a subpopulation of tumour cells endowed with, just like the healthy stem cells, self-renewal and aberrant multi-lineage differentiation capacity likely to be called colorectal cancer stem cells (CCSCs). Cancer stem cells (CSCs) fate, since their origin, reflects the influences from their microenvironment (or niche) both in the maintenance of stemness, in promoting their differentiation, and in inducing epithelial-mesenchymal transition, responsible of CSCs dissemination and subsequent formation of metastatic lesions. The tumour cells heterogeneity and their immuno-response resistance nowadays probably responsible of the failure of the conventional therapies, make this research field an open issue. Even more importantly, our increasing understanding of the cellular and molecular mechanisms that regulate CSC quiescence and cell cycle regulation, self-renewal, chemotaxis and resistance to cytotoxic agents, is expected to eventually result in tailor-made therapies with a significant impact on the morbidity and overall survival of colorectal cancer patients.

Colorectal micropapillary carcinomas are associated with poor prognosis and enriched in markers of stem cells

Colorectal micropapillary carcinoma has recently been reported as an aggressive variant of adenocarcinoma with a high incidence of lymph node metastasis, but has not been well investigated in terms of survival analysis. This study analyzed the clinicopathological characteristics, including survival data, of the patients with micropapillary carcinoma. We hypothesized that the aggressive features of micropapillary carcinoma might be related to the presence of more tumor cells with stem cell phenotype in colorectal cancer. Fifty-five (10%) micropapillary carcinoma cases were identified among 561 cases of colorectal cancer. We compared the clinicopathological characteristics, including survival data and immunohistochemical profiles of stem cell markers (SOX2, NOTCH3, CD44v6, CD166, ALDH1) of micropapillary carcinomas with those of randomly selected 112 conventional adenocarcinomas lacking micropapillary carcinoma components (non-micropapillary carcinoma) in the colorectum. To exclude the possibility of dilution of control group by patients with microsatellite instability-high carcinomas, we divided non-micropapillary carcinomas into microsatellite instability-high carcinoma and microsatellite stable tumors. Micropapillary carcinomas were characterized by more frequent lymphovascular invasion (P<0.0001) and lymph node metastasis (P<0.0001), higher pathological T and tumor node metastasis stages (P=0.047 and P=0.001), and more frequent SOX2 (P=0.038) and NOTCH3 expressions (P=0.005). Overall 5-year survival rate for patients with micropapillary carcinoma (37%) was significantly lower than for microsatellite instability-high carcinoma and microsatellite stable carcinoma patients (92 and 72%, P<0.0001). The presence of the micropapillary carcinoma component was shown to be associated with a significantly worse survival rate in univariate (P<0.0001) and multivariate (P=0.003, Cox hazard ratio 2.402) analyses. In conclusion, recognition of the micropapillary carcinoma component in colonic adenocarcinoma is very important, because the micropapillary carcinoma has been associated with a significantly worse prognosis. We also found a higher expression rate of cancer stem cell markers in micropapillary carcinomas, suggesting their potential contribution to the survival disadvantage of micropapillary carcinoma.

Emerging role of cancer stem cells in the biology and treatment of ovarian cancer: basic knowledge and therapeutic possibilities for an innovative approach

In 2013 there will be an estimated 22,240 new diagnoses and 14,030 deaths from ovarian cancer in the United States. Despite the improved surgical approach and the novel active drugs that are available today in clinical practice, about 80% of women presenting with late-stage disease have a 5-year survival rate of only 30%. In the last years a growing scientific knowledge about the molecular pathways involved in ovarian carcinogenesis has led to the discovery and evaluation of several novel molecular targeted agents, with the aim to test alternative models of treatment in order to overcome the clinical problem of resistance. Cancer stem cells tend to be more resistant to chemotherapeutic agents and radiation than more differentiated cellular subtypes from the same tissue. In this context the study of ovarian cancer stem cells is taking on an increasingly important strategic role, mostly for the potential therapeutic application in the next future. In our review, we focused our attention on the molecular characteristics of epithelial ovarian cancer stem cells, in particular on possible targets to hit with targeted therapies.

MicroRNA-21 promotes the ovarian teratocarcinoma PA1 cell line by sustaining cancer stem/progenitor populations in vitro

INTRODUCTION

Resistance of cancer stem/progenitor cells (CSPCs) to chemotherapy can lead to cancer relapse. Ovarian teratocarcinoma (OVTC) arises from germ cells and comprises pluripotent cells that can be used to study cancer cell stemness. In this study, we evaluated whether microRNA-21 (miR-21) promotes ovarian teratocarcinoma by maintaining cancer stem/progenitor populations.

METHODS

The lentiviral delivery system was used to upregulate or to suppress the expression of miR-21 in the human ovarian teratocarcinoma cell line PA1 and cell growth assays were used to monitor the expression of miR-21 at different time points. Antibodies directed toward CD133, a stem cell marker, were used to identify CSPCs in the PA1 cell population, and the level of miR-21 expression was determined in enriched CSPCs. Stem cell functional assays (sphere assay and assays for CD133 expression) were used to assess the effects of miR-21 on progression of the CD133+ population.

RESULTS

Knockdown of miR-21 in PA1 cells attenuated growth of PA1 cells whereas overexpression of miR-21 promoted cell growth. Moreover, knockdown of miR-21 resulted in a marked reduction in the CD133+ population and sphere formation of CSPCs. In contrast, overexpression of miR-21 resulted in a marked increase in the population of CD133+ cells as well as sphere formation of CSPCs.

CONCLUSIONS

MicroRNA-21 plays a significant role in cancer growth by regulating stemness in cancer cells.

SOX2 expression associates with stem cell state in human ovarian carcinoma

The SRY-related HMG-box family of transcription factors member SOX2 regulates stemness and pluripotency in embryonic stem cells and plays important roles during early embryogenesis. More recently, SOX2 expression was documented in several tumor types including ovarian carcinoma, suggesting an involvement of SOX2 in regulation of cancer stem cells (CSC). Intriguingly, however, studies exploring the predictive value of SOX2 protein expression with respect to histopathologic and clinical parameters report contradictory results in individual tumors, indicating that SOX2 may play tumor-specific roles. In this report, we analyze the functional relevance of SOX2 expression in human ovarian carcinoma. We report that in human serous ovarian carcinoma (SOC) cells, SOX2 expression increases the expression of CSC markers, the potential to form tumor spheres, and the in vivo tumor-initiating capacity, while leaving cellular proliferation unaltered. Moreover, SOX2-expressing cells display enhanced apoptosis resistance in response to conventional chemotherapies and TRAIL. Hence, our data show that SOX2 associates with stem cell state in ovarian carcinoma and induction of SOX2 imposes CSC properties on SOC cells. We propose the existence of SOX2-expressing ovarian CSCs as a mechanism of tumor aggressiveness and therapy resistance in human SOC.

Cancer stem cells, epithelial-mesenchymal transition, and drug resistance in high-grade ovarian serous carcinoma

Although epithelial ovarian cancer cells are eliminated by debulking surgery and chemotherapy during initial treatment, it is believed that only a subset of cancer cells, that is, cancer stem cells, may be an important source of tumor recurrence and drug resistance. This review highlights our current understanding of high-grade serous carcinoma, ovarian cancer stem cells, common methods for enrichment of ovarian cancer stem cells, mechanisms involved in drug resistance, and potential strategies for overcoming drug resistance, with associated potential controversies and pitfalls. We also review the potential relationship between epithelial-to-mesenchymal transition and cancer stem cells and how we can induce cancer cells to differentiate into benign stromal fibroblasts in response to certain chemotherapy drugs.

Surgical treatment for patients with Krukenberg tumor of stomach origin: clinical outcome and prognostic factors analysis

Krukenberg tumor originated from stomach in female patients is common in clinical practice, but it is still uncertain whether surgical resection of ovarian metastases could improve the outcome. Some studies suggested that a certain group of patients could benefit from the resection of ovarian metastases. However, conclusions were different between studies and there was no data to illustrate if certain molecular markers were associated with patients’ survival. In this study, we analyzed the effects of resection of ovarian metastases, and investigated prognostic factors in 133 patients with ovarian metastases originated from stomach. Furthermore, we examined the expression of some cancer stem cells (CSCs) markers or related molecules in 64 ovarian metastases specimens and analyzed the correlation between these molecules and patients’ survival. We found that the median overall survival (mOS) of all 133 patients was 16 months, and “gastrectomy” and “without ascites” were two independent prognostic factors associated with longer survival. The mOS of the patients with gastrectomy was longer than that of patients had not undergone gastrectomy (19 vs. 9 months, p = 0.048). Patients without ascites survived longer than those with ascites (mOS: 21 vs. 13 months, p = 0.008). We also found that Sox2, CD44 or CD133 positive expression in ovarian metastases were risk factors correlated with poor survival, and Sox2 expression was an independent prognostic indicator. These results suggested that ovarian metastasectomy might help to prolong the survivor of some patients with Krukenberg tumor originated from stomach. Patients without ascites, and with resected or resectable primary gastric cancer lesion could get benefit from and be potential candidate for surgical treatment. The expression of Sox2 might serve as a prognostic indicator for predicting patients’ survival and be helpful for selecting patients in future.

Characterization of disease progression in ovarian cancer by utilizing 'chemograms' of ovarian cancer stem cells

INTRODUCTION

Ovarian cancer is one of the leading causes of death in women with cancer. First-line chemotherapy with platinum compounds and taxane compounds has been effective, but most patients develop a relapse of the disease due to drug resistance. There is growing evidence that this resistance may be due to the presence of ovarian cancer stem cells.

DISCUSSION

Cells with properties of cancer stem cells have been isolated from the ascitic fluid of ovarian cancer patients. This subset of cells is highly tumourigenic compared to the rest of the cells in the ascitic fluid. They are known to exude harmful chemicals from their cytoplasm and have been found to be resistant to chemotherapeutic agents. This property has been utilized to purify them by fluorescence assisted cytometry to yield a subset of cells which are called 'side population'. These cells exhibit the properties of cancer stem cells and their role in disease progression is being currently investigated. The course of the disease can be potentially characterized at the cellular level by closely studying this cell population. They can also be cultured in different combinations of chemotherapeutic agents at varying concentrations to obtain 'chemograms' which are sensitivity charts. Chemotherapeutic agents which produce the most effective kill curves can then be rationally used as a second-line chemotherapy if the disease relapses. These sensitivity charts can provide insight into emerging patterns of chemoresistance and also help discover surface markers that accurately identify ovarian cancer stem cells.

CONCLUSION

The high rate of disease relapse in patients with ovarian cancer requires a new and different approach utilizing the sensitivity of cancer stem cells. Isolating and characterizing the resistance patterns of ovarian cancer stem cells may provide a rational approach towards an effective and individualized chemotherapeutic regimen.

Normal and cancer stem cells of the human female reproductive system

The female reproductive system (FRS) has a great capacity for regeneration. The existence of somatic stem cells (SSC) that are likely to reside in distinct tissue compartments of the FRS is anticipated. Normal SSC are capable of regenerating themselves, produce a progeny of cells that differentiate and maintain tissue architecture and functional characteristics, and respond to homeostatic controls. Among those SSC of the FRS that have been identified are: a) undifferentiated cells capable of differentiating into thecal cells and synthesizing hormones upon transplantation, b) ovarian surface epithelium stem cells, mitotically responsive to ovulation, c) uterine endometrial and myometrial cells, as clonogenic epithelial and stromal cells, and d) epithelial and mesenchymal cells with self-renewal capacity and multipotential from cervical tissues. Importantly, these cells are believed to significantly contribute to the development of different pathologies and tumors of the FRS.It is now widely accepted that cancer stem cells (CSC) are at the origin of many tumors. They are capable of regenerating themselves, produce a progeny that will differentiate aberrantly and do not respond adequately to homeostatic controls. Several cell surface antigens such as CD44, CD117, CD133 and MYD88 have been used to isolate ovarian cancer stem cells. Clonogenic epithelial and stromal endometrial and myometrial cells have been found in normal and cancer tissues, as side population, label-retaining cells, and CD146/PDGF-R beta-positive cells with stem-like features. In summary, here we describe a number of studies supporting the existence of somatic stem cells in the normal tissues and cancer stem cells in tumors of the human female reproductive system.

Ovarian tumor initiating cell populations persist following paclitaxel and carboplatin chemotherapy treatment in vivo

Development of recurrent platinum resistant disease following chemotherapy presents a challenge in managing ovarian cancer. Using tumors derived from genetically defined mouse ovarian cancer cells, we investigated the stem cell properties of residual cells post-chemotherapy. Utilizing CD133 and Sca-1 as markers of candidate tumor initiating cells (TIC), we determined that the relative levels of CD133+ and Sca-1+ cells were unaltered following chemotherapy. CD133+ and Sca-1+ cells exhibited increased stem cell-related gene expression, were enriched in G0/G1-early S phase and exhibited increased tumor initiating capacity, giving rise to heterogeneous tumors. Our findings suggest that residual TICs may contribute to recurrent disease.

ALDH1-high ovarian cancer stem-like cells can be isolated from serous and clear cell adenocarcinoma cells, and ALDH1 high expression is associated with poor prognosis

Cancer stem-like cells (CSCs)/cancer-initiating cells (CICs) are defined as a small population of cancer cells that have high tumorigenicity. Furthermore, CSCs/CICs are resistant to several cancer therapies, and CSCs/CICs are therefore thought to be responsible for cancer recurrence after treatment and distant metastasis. In epithelial ovarian cancer (EOC) cases, disease recurrence after chemotherapy is frequently observed, suggesting ovarian CSCs/CICs are involved. There are four major histological subtypes in EOC, and serous adenocarcinoma and clear cell adenocarcinoma are high-grade malignancies. We therefore analyzed ovarian CSCs/CICs from ovarian carcinoma cell lines (serous adenocarcinoma and clear cell adenocarcinoma) and primary ovarian cancer cells in this study. We isolated ovarian CSCs/CICs as an aldehyde dehydrogenase 1 high (ALDH1(high)) population from 6 EOC cell lines (3 serous adenocarcinomas and 3 clear cell adenocarcinomas) by the ALDEFLUOR assay. ALDH1(high) cells showed greater sphere-forming ability, higher tumorigenicity and greater invasive capability, indicating that ovarian CSCs/CICs are enriched in ALDH1(high) cells. ALDH1(high) cells could also be isolated from 8 of 11 primary ovarian carcinoma samples. Immunohistochemical staining revealed that higher ALDH1 expression levels in ovary cancer cases are related to poorer prognosis in both serous adenocarcinoma cases and clear cell adenocarcinoma cases. Taken together, the results indicate that ALDH1 is a marker for ovarian CSCs/CICs and that the expression level of ALDH1 might be a novel biomarker for prediction of poor prognosis.

Targeting CD133 in an in vivo ovarian cancer model reduces ovarian cancer progression

OBJECTIVES

While most women with ovarian cancer will achieve complete remission after treatment, the majority will relapse within two years, highlighting the need for novel therapies. Cancer stem cells (CSC) have been identified in ovarian cancer and most other carcinomas as a small population of cells that can self-renew. CSC are more chemoresistant and radio-resistant than the bulk tumor cells; it is likely that CSC are responsible for relapse, the major problem in cancer treatment. CD133 has emerged as one of the most promising markers for CSC in ovarian cancer. The hypothesis driving this study is that despite their low numbers in ovarian cancer tumors, CSC can be eradicated using CD133 targeted therapy and tumor growth can be inhibited.

METHODS

Ovarian cancer cell lines were evaluated using flow cytometry for expression of CD133. In vitro viability studies with an anti-CD133 targeted toxin were performed on one of the cell lines, NIH:OVCAR5. The drug was tested in vivo using a stably transfected luciferase-expressing NIH:OVCAR5 subline in nude mice, so that tumor growth could be monitored by digital imaging in real time.

RESULTS

Ovarian cancer cell lines showed 5.6% to 16.0% CD133 expression. dCD133KDEL inhibited the in vitro growth of NIH:OVCAR5 cells. Despite low numbers of CD133-expressing cells in the tumor population, intraperitoneal drug therapy caused a selective decrease in tumor progression in intraperitoneal NIH:OVCAR5-luc tumors.

CONCLUSIONS

Directly targeting CSC that are a major cause of drug resistant tumor relapse with an anti-CD133 targeted toxin shows promise for ovarian cancer therapy.

CD133+ subpopulation of the HT1080 human fibrosarcoma cell line exhibits cancer stem-like characteristics

The cancer stem cell (CSC) theory holds that a minority population within tumors possesses stem cell properties of self-renewal and multilineage differentiation capacity and provides the initiating cells from which tumors are derived and sustained. However, verifying the existence of these CSCs has been a significant challenge. The CD133 antigen is a pentaspan membrane glycoprotein proposed to be a CSC marker for cancer-initiating subpopulations in the brain, colon and various other tissues. Here, CD133+ cells were obtained and characterized from the HT1080 cell line to determine the utility of this marker for isolating CSCs from human fibrosarcoma cells. In this study, CD133+ cells were separated from HT1080 cells using magnetic beads and characterized for their proliferation rate and resistance to chemotherapeutic drugs, cisplatin and doxorubicin, by MTS assay. Relative expression of tumor-associated genes Sox2, Oct3/4, Nanog, c-Myc, Bmi-1 and ABCG2 was measured by real-time polymerase chain reaction (PCR). Clonal sphere formation and the ability of CD133+ cells to initiate tumors in BALB/c nude mice was also evaluated. We found that CD133+ cells showed a high proliferation rate, increased resistance to chemotherapy drugs and overexpression of tumor-associated genes compared with these features in CD133- cells. Additionally, CD133+ cells were able to form spherical clusters in serum-free medium with high clonogenic efficiency, indicating a significantly greater tumor-initiating potential when compared with CD133- cells. These findings indicate that CD133+ cells identified within the HT1080 human fibrosarcoma cell line possess many CSC properties and may facilitate the development of improved therapies for fibrosarcoma.

Strategies for isolating and enriching cancer stem cells: well begun is half done

Cancer stem cells (CSCs) constitute a subpopulation of cancer cells that have the potential for self-renewal, multipotent differentiation, and tumorigenicity. Studies on CSC biology and CSC-targeted therapies depend on CSC isolation and/or enrichment methodologies. Scientists have conducted extensive research in this field since John Dick's group successfully isolated CSCs based on the expression of the CD34 and CD38 surface markers. Progress in CSC research has been greatly facilitated by the enrichment and isolation of these cells. In this review, we summarize the current strategies used in our and other laboratories for CSC isolation and enrichment, including methods based on stem cell surface markers, intracellular enzyme activity, the concentration of reactive oxygen species, the mitochondrial membrane potential, promoter-driven fluorescent protein expression, autofluorescence, suspension/adherent culture, cell division, the identification of side population cells, resistance to cytotoxic compounds or hypoxia, invasiveness/adhesion, immunoselection, and physical property. Although many challenges remain to be overcome, it is reasonable to believe that more reliable, efficient, and convenient methods will be developed in the near future.

Growth kinetics of CD133-positive prostate cancer cells

BACKGROUND

In the adult human prostate CD133 expression is thought to mark rare prostate epithelial stem cells and malignant tumor stem/initiating cells. Such putative stem cell populations are thought to proliferate slowly, but possess unlimited proliferative potential. Based on this, we hypothesized that CD133(pos) prostate cancer cells proliferate slower than CD133(neg) cells.

METHODS

Human prostate cancer cell lines were analyzed for CD133 expression and DNA content using flow cytometry. Rates of cell division and DNA synthesis were determined using CFSE cell tracing and BrdU uptake, respectively. Changes in cell cycle distribution and the percentage of CD133(pos) cells were assayed under conditions of different cell density and AR-pathway modulation. Lastly, we over-expressed lentiviral CD133 to measure whether CD133 regulates the cell cycle.

RESULTS

The cell cycle distribution differs between CD133(pos) and CD133(neg) cells in all three human prostate cancer cell lines studied. CD133(pos) cells have a greater proportion of cells in G2 and proliferate faster than CD133(neg) cells. High cell density increases the percentage of CD133(pos) cells without changing CD133(pos) cell cycle progression. Treatment with the AR agonist R1881, or the anti-androgen MDV3100, significantly changed the percentage and proliferation of CD133(pos) cells. Finally, ectopic over-expression of CD133 had no effect on cell cycle progression.

CONCLUSIONS

Contrary to our hypothesis, we demonstrate that CD133(pos) cells proliferate faster than CD133(neg) cells. This association of CD133 expression with increased cell proliferation is not directly mediated by CD133, suggesting that surface CD133 is a downstream target gene of an undefined pathway controlling cell proliferation.

Clinicopathologic significance of putative stem cell marker, CD44 and CD133, in human gastric carcinoma

BACKGROUND AND OBJECTIVES

CD44 and CD133 have been reported as putative stem cell markers. However, the clinicopathologic significance of CD44 and CD133 expression in patients with gastric carcinoma (GC) has not been clearly elucidated.

METHODS

Immunohistochemistry (IHC) was performed to investigate the CD44 and CD133 expression in gastric carcinomas and normal mucosal tissues. Receiver operating characteristic (ROC) curve analysis, spearman's rank correlation, Kaplan-Meier plots, and Cox proportional hazards regression model were used to analyze the data.

RESULTS

The highly expressed CD44 and CD133 were observed in 27/152 (17.7%) and 64/152 (42.1%) of GCs and in 4/60 (6.7%) and 15/60 (25.0%) normal gastric mucosal tissues, respectively (P < 0.05, Fisher's exact test). High expression of CD44 was significantly correlated with tumor poorer differentiation, presence of distant metastasis, advanced TNM stage, and tumor relapse; and high expression of CD133 was positively associated with tumor invasion depth, presence of distant metastasis and advanced TNM stage. More importantly, high-expressed CD44 and CD133 were both associated with shorter survival as evidenced by univariate and multivariate analysis.

CONCLUSIONS

Our study introduces high expression of CD44 and CD133 as adverse independent prognostic factors in GC patients. The combined CD44 and CD133 expression may become a useful tool for identifying patients with different clinical outcomes.

Functional OCT4-specific CD4+ and CD8+ T cells in healthy controls and ovarian cancer patients

The identification of growth and differentiation pathways that are responsible for the proliferation and survival of cancer stem cells (CSCs) has opened avenues for the discovery of novel therapeutic targets. In the initial phase of an anticancer immune response, T cells specific for tumor-associated antigens develop in patients and, at least under selected circumstances, are able to eliminate malignant cells. However, it remains unknown whether CSC-specific T cells are also operational. We found naturally occurring multifunctional CD4⁺ and CD8⁺ T cells specific for the stem cell marker OCT4 among the peripheral blood mononuclear cells (PBMCs) of both healthy individuals and ovarian cancer patients. Moreover, lymphocytes isolated from the ascites of patients affected by ovarian malignancies also contained OCT4-specific T cells. OCT4-reactive CD4⁺ T cells did not produce interferon γ (IFNγ) and IFNγ-inducible protein 10 (IP-10) but were capable of proliferation upon stimulation with dendritic cells (DCs) loaded with an OCT4-derived peptide or OCT4 mRNA. OCT4-reactive CD8⁺ cells did not proliferate in response to a similar challenge, yet produced IP-10 as well as sufficient amounts of IFNγ to induce IP-10 . Furthermore, CD8⁺ cytotoxic T cells were able to release their lysosomal components, as indicated by the mobilization of CD107a. These results demonstrate the existence of anti-CSC specific T cells in ovarian cancer patients.

Regulation of ovarian cancer stem cells or tumor-initiating cells

Cancer stem cells or tumor-initiating cells (CSC/TICs), which can undergo self-renewal and differentiation, are thought to play critical roles in tumorigenesis, therapy resistance, tumor recurrence and metastasis. Tumor recurrence and chemoresistance are major causes of poor survival rates of ovarian cancer patients, which may be due in part to the existence of CSC/TICs. Therefore, elucidating the molecular mechanisms responsible for the ovarian CSC/TICs is required to develop a cure for this malignancy. Recent studies have indicated that the properties of CSC/TICs can be regulated by microRNAs, genes and signaling pathways which also function in normal stem cells. Moreover, emerging evidence suggests that the tumor microenvironments surrounding CSC/TICs are crucial for the maintenance of these cells. Similarly, efforts are now being made to unravel the mechanism involved in the regulation of ovarian CSC/TICs, although much work is still needed. This review considers recent advances in identifying the genes and pathways involved in the regulation of ovarian CSC/TICs. Furthermore, current approaches targeting ovarian CSC/TICs are described. Targeting both CSC/TICs and bulk tumor cells is suggested as a more effective approach to eliminating ovarian tumors. Better understanding of the regulation of ovarian CSC/TICs might facilitate the development of improved therapeutic strategies for recurrent ovarian cancer.

γ-Secretase Inhibitor, DAPT Inhibits Self-renewal and Stemness Maintenance of Ovarian Cancer Stem-like Cells In Vitro

OBJECTIVE

The Notch signaling pathway plays an important role in the stem cell signaling network and contributes to tumorigenesis. However, the functions of Notch signaling in ovarian cancer stem cells (OCSCs) are not well understood. We aimed to investigate the effects of Notch blockade on self-renewal and stemness maintenance of OCSCs.

METHODS

Ovarian cancer stem-like cells were enriched from ovarian cancer cell lines in serum-free medium. A γ-secretase inhibitor, (DAPT), was used to block Notch signaling. MTT assays were performed to assess self-renewal and proliferation inhibition, flow cytometry was performed to analyze cell surface marker and immunofluorescence, Western Blot and Real-time RT-PCR assays were performed to detect Oct4 and Sox2 protein and mRNA expression of the Ovarian cancer stem-like cells treated with DAPT.

RESULTS

Notch blockade markedly inhibits self-renewal and proliferation of ovarian cancer stem-like cells, significantly downregulates the expression of OCSCs-specific surface markers, and reduces protein and mRNA expression of Oct4 and Sox2 in OCSC-like cells.

CONCLUSION

Our results suggest that Notch signaling is not only critical for the self-renewal and proliferation of OCSCs, but also for the stemness maintenance of OCSCs. The γ-secretase inhibitor is a promising treatment targeting OCSCs.

Repopulation of ovarian cancer cells after chemotherapy

The high mortality rate caused by ovarian cancer has not changed for the past thirty years. Although most patients diagnosed with this disease respond to cytoreductive surgery and platinum-based chemotherapy and undergo remission, foci of cells almost always escape therapy, manage to survive, and acquire the capacity to repopulate the tumor. Repopulation of ovarian cancer cells that escape front-line chemotherapy, however, is a poorly understood phenomenon. Here I analyze cancer-initiating cells, transitory senescence, reverse ploidy, and cellular dormancy as putative players in ovarian cancer cell repopulation. As part of the standard of care, ovarian cancer patients do not receive treatment between primary cytotoxic therapy and clinical relapse. Understanding the mechanisms driving cellular escape from chemotherapy should lead to the development of low toxicity, chronic treatment approaches that can be initiated right after primary therapy to interrupt cell repopulation and disease relapse by keeping it dormant and, therefore, subclinical.

The CD133+ subpopulation of the SW982 human synovial sarcoma cell line exhibits cancer stem-like characteristics

Several soft tissues sarcomas have been reported to contain cancer stem-like cells (CSCs) or tumor-initiating cells, based on their ability to initiate and sustain tumor growth. However, these cells have not yet been identified in the human synovial sarcoma cell line SW982. CD133, a surface glycoprotein specific to stem and progenitor cells, has been described as a CSC marker in different tumor types. In the present study, we identified a CSC subpopulation in SW982 cells using the CD133 cell surface marker. CD133-positive (CD133(+)) cells were identified in SW982 cells (8.59%); these cells showed an increased ability to form spherical colonies and could self-renew in serum-starved culture conditions, compared to CD133-negative (CD133(-)) cells. Real-time PCR analysis of stemness genes revealed that the CD133+ subpopulation expresses higher levels of Bmi1, c-Myc, Nanog, Oct3/4 and Sox2. CD133(+) cells showed increased resistance to cisplatin (CDDP) and doxorubicin (DXR), possibly due to upregulation of the ABCG2 drug transporter gene. In vivo studies revealed that the CD133(+) subpopulation is highly tumorigenic. These findings indicate that CD133(+) SW982 cells have characteristics similar to CSCs. This discovery may lead to the development of novel therapies that specifically target CD133(+) synovial sarcoma CSCs.

CD24⁺ ovary cancer cells exhibit an invasive mesenchymal phenotype

We recently reported that the subset of CD24(+) cells in ovarian cancer possesses various cancer stem cell properties. In this study, we further show that this subpopulation of ovarian cancer cells exhibits an epithelial-mesenchymal transition (EMT) phenotype, high invasive capacity, and CXCR4/SDF-1-mediated chemotactic migration. We evaluated CD24 expression in various ovarian cancer cell lines by flow cytometric analysis. CAOV3 and a primary ovarian cancer cell line Clone 4 were sorted into CD24(+) and CD24(-) subpopulations by FACS and Western blot, cell invasion, adhesion, and in vitro chemotaxis assays were performed with these two subpopulations. We also assessed the effects of shRNA depletion of CD24 in CAOV3 and Clone 4 cells by Western blot and cell invasion assays. CD24 expression in ovarian cancer cell lines correlated with aggressive histologic subtypes of epithelial ovarian cancer. The CD24(+) subpopulation was also more invasive than the CD24(-) subpopulation and showed higher CXCR4/SDF-1-mediated chemotactic migration. CD24(+) cells exhibited an EMT phenotype as characterized by loss of E-cadherin expression and gain of vimentin, Twist, and Snail1 expression. In addition, CD24(+) cells stimulated cell attachment to fibronectin through the activation of β1 integrin. Depletion of CD24 expression by CD24 shRNA efficiently suppressed cell invasion and induced downregulation of CXCR4 as well as loss of the EMT phenotype. In conclusion, CD24 expression in ovarian cancer may be related to tumor aggressiveness, in particular cell invasion and chemotactic migration. Therefore, CD24 may be a good candidate for a therapeutic target for ovarian cancer.

LGR5 is a promising biomarker for patients with stage I and II gastric cancer

OBJECTIVE

To investigate Leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5) expressions in gastric cancer and to evaluate its clinical significance.

METHODS

LGR5 expression was assessed by immunohistochemistry in 257 gastric cancer patients after surgery. The relationships between LGR5 expression and clinicopathological features and patients prognosis were statistically analyzed.

RESULTS

The expression of LGR5 was significantly higher in gastric cancers as a cancer stem cell marker than in adjacent normal tissues (P<0.001), and more frequently in patients with intestinal type, well-moderate differentiation and stage I and II (P<0.05). Although we found gastric cancer patients with LGR5 positive expression had a poorer prognosis, it didn't meet statistical significance (P>0.05). LGR5 negative expression was significantly related to the favorable overall survival in stage I and II gastric cancer patients (P<0.05). Furthermore, patients with high LGR5 expression tended to be more likely to get progression and have poorer progress-free survival (P<0.05). Multivariate Cox regression analysis revealed that LGR5 expression was an independent factor of overall survival for the patients with stage I and II gastric cancer (P<0.05).

CONCLUSIONS

Our results show that LGR5 may play an important role in tumorigenesis and progression and would be a powerful marker to predict the prognosis of patients with stage I and II gastric cancer.

Cancer stem cells and their role in metastasis

Cancer stem cells (CSCs), which comprise a small fraction of cancer cells, are believed to constitute the origin of most human tumors. Considerable effort has been focused on identifying CSCs in multiple tumor types and identifying genetic signatures that distinguish CSCs from normal tissue stem cells. Many studies also suggest that CSCs serve as the basis of metastases. Yet, experimental evidence that CSCs are the basis of disseminated metastases has lagged behind the conceptual construct of CSCs. Recent work, however, has demonstrated that CSCs may directly or indirectly contribute to the generation of metastasis. Moreover, CSC heterogeneity may be largely responsible for the considerable complexity and organ specificity of metastases. In this review, we discuss the role of CSCs in metastasis and their potential as therapeutic targets.

Therapeutic strategies targeting cancer stem cells

Increasing studies have demonstrated a small proportion of cancer stem cells (CSCs) exist in the cancer cell population. CSCs have powerful self-renewal capacity and tumor-initiating ability and are resistant to chemotherapy and radiation. Conventional anticancer therapies kill the rapidly proliferating bulk cancer cells but spare the relatively quiescent CSCs, which cause cancer recurrence. So it is necessary to develop therapeutic strategies acting specifically on CSCs. In recent years, studies have shown that therapeutic agents such as metformin, salinomycin, DECA-14, rapamycin, oncostatin M (OSM), some natural compounds, oncolytic viruses, microRNAs, cell signaling pathway inhibitors, TNF-related apoptosis inducing ligand (TRAIL), interferon (IFN), telomerase inhibitors, all-trans retinoic acid (ATRA) and monoclonal antibodies can suppress the self-renewal of CSCs in vitro and in vivo. A combination of these agents and conventional chemotherapy drugs can significantly inhibit tumor growth, metastasis and recurrence. These strategies targeting CSCs may bring new hopes to cancer therapy.

TLR2 enhances ovarian cancer stem cell self-renewal and promotes tumor repair and recurrence

Primary ovarian cancer is responsive to treatment, but chemoresistant recurrent disease ensues in majority of patients. Recent compelling evidence demonstrates that a specific population of cancer cells, the cancer stem cells, initiates and sustains tumors. It is therefore possible that this cell population is also responsible for recurrence. We have shown previously that CD44+/MyD88+ epithelial ovarian cancer stem cells (CD44+/MyD88+ EOC stem cells) are responsible for tumor initiation. In this study, we demonstrate that this population drives tumor repair following surgery- and chemotherapy-induced tumor injury. Using in vivo and in vitro models, we also demonstrate that during the process of tumor repair, CD44+/MyD88+ EOC stem cells undergo self-renewal as evidenced by upregulation of stemness-associated genes. More importantly, we show that a pro-inflammatory microenvironment created by the TLR2-MyD88-NFκB pathway supports EOC stem cell-driven repair and self-renewal. Overall, our findings point to a specific cancer cell population, the CD44+/MyD88+ EOC stem cells and a specific pro-inflammatory pathway, the TLR2-MyD88-NFκB pathway, as two of the required players promoting tumor repair, which is associated with enhanced cancer stem cell load. Identification of these key players is the first step in elucidating the steps necessary to prevent recurrence in EOC patients.

The cancer stem cell marker CD133 interacts with plakoglobin and controls desmoglein-2 protein levels

The pentaspan membrane glycoprotein CD133 (also known as prominin-1) has been widely used as a marker for both cancer and normal stem cells. However, the function of CD133 has not been elucidated. Here we describe a cancer stem cell line established from clear cell carcinoma of the ovary (CCC) and show that CD133 interacts with plakoglobin (also known as γ-catenin), a desmosomal linker protein. We further demonstrate that knockdown of CD133 by RNA interference (RNAi) results in the downregulation of desmoglein-2, a desmosomal cadherin, and abrogates cell-cell adhesion and tumorigenicity of CCC stem cells. We speculate that CD133 may be a promising target for cancer chemotherapy.

The duplicitous origin of ovarian cancer

The past few decades have seen many advances in the treatment of a variety of cancers. Unfortunately, for ovarian cancer, which is the most lethal type of gynecologic malignancy, no new therapeutic approach has been successfully introduced since the 1990s. Ovarian cancer is usually detected in later stages, when remission rates are high and tumors are resistant to chemotherapy. Little is known about the primary lesion in ovarian cancer. Recently, it has been shown that the origin of ovarian cancer can be cells from adjacent tissue or cells from other primary tumors, which make their way to the ovaries due to the unique nature of their microenvironment during ovulation. The tumor in ovarian cancer is heterogeneous and hierarchically organized. In this review, we discuss the role of ovarian cancer stem cells in the process of tumor formation and recurrence. We propose the need to shift the paradigm away from the classification of ovarian cancer as a single disease with a single cellular origin. Understanding the complexity of the disease will facilitate devising new methods for fighting this cancer and improving the life of many women inflicted with the disease.

Human papillomavirus infections and cancer stem cells of tumors from the uterine cervix

Different rate of development of productive infections (as low grade cervical intraepithelial neoplasias), or high grade lesions and cervical malignant tumors associated with infections of the Transformation zone (TZ) by High-Risk Human Papillomavirus (HR-HPV), could suggest that different epithelial host target cells could exist. If there is more than one target cell, their differential infection by HR-HPV may play a central role in the development of cervical cancer. Recently, the concept that cancer might arise from a rare population of cells with stem cell-like properties has received support in several solid tumors, including cervical cancer (CC). According to the cancer stem cell (CSC) hypothesis, CC can now be considered a disease in which stem cells of the TZ are converted to cervical cancer stem cells by the interplay between HR-HPV viral oncogenes and cellular alterations that are thought to be finally responsible for tumor initiation and maintenance. Current studies of CSC could provide novel insights regarding tumor initiation and progression, their relation with viral proteins and interplay with the tumor micro-environment. This review will focus on the biology of cervical cancer stem cells, which might contribute to our understanding of the mechanisms responsible for cervical tumor development.

Role of the microenvironment in ovarian cancer stem cell maintenance

Despite recent progresses in cancer therapy and increased knowledge in cancer biology, ovarian cancer remains a challenging condition. Among the latest concepts developed in cancer biology, cancer stem cells and the role of microenvironment in tumor progression seem to be related. Indeed, cancer stem cells have been described in several solid tumors including ovarian cancers. These particular cells have the ability to self-renew and reconstitute a heterogeneous tumor. They are characterized by specific surface markers and display resistance to therapeutic regimens. During development, specific molecular cues from the tumor microenvironment can play a role in maintaining and expanding stemness of cancer cells. The tumor stroma contains several compartments: cellular component, cytokine network, and extracellular matrix. These different compartments interact to form a permissive niche for the cancer stem cells. Understanding the molecular cues underlying this crosstalk will allow the design of new therapeutic regimens targeting the niche. In this paper, we will discuss the mechanisms implicated in the interaction between ovarian cancer stem cells and their microenvironment.

CD44+ cancer stem-like cells in EBV-associated nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a unique EBV-associated epithelial malignancy, showing highly invasive and metastatic phenotype. Despite increasing evidence demonstrating the critical role of cancer stem-like cells (CSCs) in the maintenance and progression of tumors in a variety of malignancies, the existence and properties of CSC in EBV-associated NPC are largely unknown. Our study aims to elucidate the presence and role of CSCs in the pathogenesis of this malignant disease. Sphere-forming cells were isolated from an EBV-positive NPC cell line C666-1 and its tumor-initiating properties were confirmed by in vitro and in vivo assays. In these spheroids, up-regulation of multiple stem cell markers were found. By flow cytometry, we demonstrated that both CD44 and SOX2 were overexpressed in a majority of sphere-forming C666-1 cells. The CD44+SOX2+ cells was detected in a minor population in EBV-positive xenografts and primary tumors and considered as potential CSC in NPC. Notably, the isolated CD44+ NPC cells were resistant to chemotherapeutic agents and with higher spheroid formation efficiency, showing CSC properties. On the other hand, microarray analysis has revealed a number of differentially expressed genes involved in transcription regulation (e.g. FOXN4, GLI1), immune response (CCR7, IL8) and transmembrane transport (e.g. ABCC3, ABCC11) in the spheroids. Among these genes, increased expression of CCR7 in CD44+ CSCs was confirmed in NPC xenografts and primary tumors. Importantly, blocking of CCR7 abolished the sphere-forming ability of C666-1 in vitro. Expression of CCR7 was associated with recurrent disease and distant metastasis. The current study defined the specific properties of a CSC subpopulation in EBV-associated NPC. Our findings provided new insights into developing effective therapies targeting on CSCs, thereby potentiating treatment efficacy for NPC patients.

Overcoming challenges of ovarian cancer stem cells: novel therapeutic approaches

Understanding the genetic and molecular mechanisms of ovarian cancer has been the focus of research efforts working toward the greater goal of improving cancer therapy for patients with residual disease after initial treatment with conventional surgery and neoadjuvant chemotherapy. The focus of this review will be centered on new therapeutic strategies based on Cancer Stem Cells studies of chemoresistant subpopulations, the prevention of metastasis, and individualized therapy in order to find the most successful combination of treatments to effectively treat human ovarian cancer. We reviewed recent literature (1993-2011) of novel treatment approaches to ovarian cancer stem cells. As the focus of ovarian cancer investigation has centered on the cancer stem cell model and the complexities that it presents in the development of effective treatments, the future of treating ovarian cancer lies in utilizing individualized treatment systems that include enhancing existing treatments, aiming for novel therapy targets, managing the plasticity of stem cells to induce cellular differentiation, and regulating oncogenic signaling pathways.

Developmental signaling pathways in cancer stem cells of solid tumors

BACKGROUND

The intricate regulation of several signaling pathways is essential for embryonic development and adult tissue homeostasis. Cancers commonly display aberrant activity within these pathways. A population of cells identified in several cancers, termed cancer stem cells (CSCs) show similar properties to normal stem cells and evidence suggests that altered developmental signaling pathways play an important role in maintaining CSCs and thereby the tumor itself.

SCOPE OF REVIEW

This review will focus on the roles of the Notch, Wnt and Hedgehog pathways in the brain, breast and colon cancers. We describe the roles these pathways play in normal tissue homeostasis through the regulation of stem cell fate in these three tissues, and the experimental evidence indicating that the role of these pathways in cancers of these is directly linked to CSCs.

MAJOR CONCLUSIONS

A large body of evidence is accumulating to indicate that the deregulation of Notch, Wnt and Hedgehog pathways play important roles in both normal and cancer stem cells. We are only beginning to understand how these pathways interact, how they are coordinated during normal development and adult tissue homeostasis, and how they are deregulated during cancer. However, it is becoming increasingly clear that if we are to target CSCs therapeutically, it will likely be necessary to develop combination therapies.

GENERAL SIGNIFICANCE

If CSCs are the driving force behind tumor maintenance and growth then understanding the molecular mechanisms regulating CSCs is essential. Such knowledge will contribute to better targeted therapies that could significantly enhance cancer treatments and patient survival. This article is part of a Special Issue entitled Biochemistry of Stem Cells.