Retention of intrinsic stem cell hierarchies in carcinoma-derived cell lines

Cancer stem-like cells enriched with CD29 and CD44 markers exhibit molecular characteristics with epithelial-mesenchymal transition in squamous cell carcinoma

Increasing evidences have indicated that only a phenotypic subset of cancer cells, termed as the cancer stem cells (CSCs), is capable of initiating tumor growth and provide a reservoir of cells that cause tumor recurrence after therapy. Epithelial-mesenchymal transition (EMT), a cell type change from an epithelial cobblestone phenotype to an elongated fibroblastic phenotype, plays a critical role not only in tumor metastasis but also in tumor recurrence and contributes to drug resistance. Accumulating evidence has shown that cells with an EMT phenotype are rich sources for CSCs, suggesting a biological link between EMT and CSCs; thus study on the link will help understand the cellular and molecular mechanisms of tumor metastasis and drug resistance. CD29 is involved in EMT through cross-talk with cadherins and CD44 has been reported as a successful used marker for CSCs. Here, we try to address whether combination of CD29 and CD44 could be used to identify cancer stem-like cells undergoing EMT in squamous cell carcinoma (SCC) and compare the molecular differences between CD29high/CD44high and CD29low/CD44low cells in SCC. Expression pattern of CD29 and CD44 was analyzed in tissues of skin SCC and cultured A431 cells by immunostaining. Subtype cells of CD29high/CD44high and CD29low/CD44low A431 were sorted by fluorescence-activated cell sorting and proliferating abilities were assayed by cell counting, colony forming and tumorigenicity in NOD/SCID mice. Finally, to probe more deeply into the molecular differences between CD29high/CD44high and CD29low/CD44low A431 cells, gene microarray analysis was applied to compare gene expression profiling. Staining of CD29 and CD44 showed similar heterogeneous expression pattern with positive cells located in the invasion front of SCC tissue as well as in cultured A431 cells. Sorted CD29high/CD44high A431 cells had higher proliferating ability in vitro and in NOD/SCID mice as compared with CD29low/CD44low cells. Gene profiling identified differentiated gene expressions between CD29high/CD44high and CD29low/CD44low A431 cells. These genes are involved in cell cycle, cell malignant transformation, metastasis, drug resistance and EMT, implying that CD29high/CD44high cells have properties of CSCs and EMT. Our present results demonstrated heterogeneous gene expression patterns and different biological behavior in SCC. Combination of CD29 and CD44 can be used as markers to enrich CSCs in human SCC. Moreover, CD29high/CD44high cells exhibit molecular characteristics of EMT, suggesting that CSC-associated pathways were involved in EMT. Studies on correlation of CSCs and the cells undergoing EMT may explain some aspects of tumor progression and drug resistance.

FRMD4A upregulation in human squamous cell carcinoma promotes tumor growth and metastasis and is associated with poor prognosis

New therapeutic strategies are needed to improve treatment of head and neck squamous cell carcinoma (HNSCC), an aggressive tumor with poor survival rates. FRMD4A is a human epidermal stem cell marker implicated previously in epithelial polarity that is upregulated in SCC cells. Here, we report that FRMD4A upregulation occurs in primary human HNSCCs where high expression levels correlate with increased risks of relapse. FRMD4A silencing decreased growth and metastasis of human SCC xenografts in skin and tongue, reduced SCC proliferation and intercellular adhesion, and stimulated caspase-3 activity and expression of terminal differentiation markers. Notably, FRMD4A attenuation caused nuclear accumulation of YAP, suggesting a potential role for FRMD4A in Hippo signaling. Treatment with the HSP90 inhibitor 17-DMAG or ligation of CD44 with hyaluronan caused nuclear depletion of FRMD4A, nuclear accumulation of YAP and reduced SCC growth and metastasis. Together, our findings suggest FRMD4A as a novel candidate therapeutic target in HNSCC based on the key role in metastatic growth we have identified.

Head and neck cancer stem cells

Most cancers contain a small sub-population of cells that are endowed with self-renewal, multipotency, and a unique potential for tumor initiation. These properties are considered hallmarks of cancer stem cells. Here, we provide an overview of the field of cancer stem cells with a focus on head and neck cancers. Cancer stem cells are located in the invasive fronts of head and neck squamous cell carcinomas (HNSCC) close to blood vessels (perivascular niche). Endothelial cell-initiated signaling events are critical for the survival and self-renewal of these stem cells. Markers such as aldehyde dehydrogenase (ALDH), CD133, and CD44 have been successfully used to identify highly tumorigenic cancer stem cells in HNSCC. This review briefly describes the orosphere assay, a method for in vitro culture of undifferentiated head and neck cancer stem cells under low attachment conditions. Notably, recent evidence suggests that cancer stem cells are exquisitely resistant to conventional therapy and are the "drivers" of local recurrence and metastatic spread. The emerging understanding of the role of cancer stem cells in the pathobiology of head and neck squamous cell carcinomas might have a profound impact on the treatment paradigms for this malignancy.

FOXM1 induces a global methylation signature that mimics the cancer epigenome in head and neck squamous cell carcinoma

The oncogene FOXM1 has been implicated in all major types of human cancer. We recently showed that aberrant FOXM1 expression causes stem cell compartment expansion resulting in the initiation of hyperplasia. We have previously shown that FOXM1 regulates HELLS, a SNF2/helicase involved in DNA methylation, implicating FOXM1 in epigenetic regulation. Here, we have demonstrated using primary normal human oral keratinocytes (NOK) that upregulation of FOXM1 suppressed the tumour suppressor gene p16(INK4A) (CDKN2A) through promoter hypermethylation. Knockdown of HELLS using siRNA re-activated the mRNA expression of p16(INK4A) and concomitant downregulation of two DNA methyltransferases DNMT1 and DNMT3B. The dose-dependent upregulation of endogenous FOXM1 (isoform B) expression during tumour progression across a panel of normal primary NOK strains (n = 8), dysplasias (n = 5) and head and neck squamous cell carcinoma (HNSCC) cell lines (n = 11) correlated positively with endogenous expressions of HELLS, BMI1, DNMT1 and DNMT3B and negatively with p16(INK4A) and involucrin. Bisulfite modification and methylation-specific promoter analysis using absolute quantitative PCR (MS-qPCR) showed that upregulation of FOXM1 significantly induced p16(INK4A) promoter hypermethylation (10-fold, P<0.05) in primary NOK cells. Using a non-bias genome-wide promoter methylation microarray profiling method, we revealed that aberrant FOXM1 expression in primary NOK induced a global hypomethylation pattern similar to that found in an HNSCC (SCC15) cell line. Following validation experiments using absolute qPCR, we have identified a set of differentially methylated genes, found to be inversely correlated with in vivo mRNA expression levels of clinical HNSCC tumour biopsy samples. This study provided the first evidence, using primary normal human cells and tumour tissues, that aberrant upregulation of FOXM1 orchestrated a DNA methylation signature that mimics the cancer methylome landscape, from which we have identified a unique FOXM1-induced epigenetic signature which may have clinical translational potentials as biomarkers for early cancer screening, diagnostic and/or therapeutic interventions.

Nonadhesive culture system as a model of rapid sphere formation with cancer stem cell properties

Background

Cancer stem cells (CSCs) play an important role in tumor initiation, progression, and metastasis and are responsible for high therapeutic failure rates. Identification and characterization of CSC are crucial for facilitating the monitoring, therapy, or prevention of cancer. Great efforts have been paid to develop a more effective methodology. Nevertheless, the ideal model for CSC research is still evolving. In this study, we created a nonadhesive culture system to enrich CSCs from human oral squamous cell carcinoma cell lines with sphere formation and to characterize their CSC properties further.

Methods

A nonadhesive culture system was designed to generate spheres from the SAS and OECM-1 cell lines. A subsequent investigation of their CSC properties, including stemness, self-renewal, and chemo- and radioresistance in vitro, as well as tumor initiation capacity in vivo, was also performed.

Results

Spheres were formed cost-effectively and time-efficiently within 5 to 7 days. Moreover, we proved that these spheres expressed putative stem cell markers and exhibited chemoradiotherapeutic resistance, in addition to tumor-initiating and self-renewal capabilities.

Conclusions

Using this nonadhesive culture system, we successfully established a rapid and cost-effective model that exhibits the characteristics of CSCs and can be used in cancer research.

[Translational approaches in cancer stem cell research]

There has been a growing body of evidence in recent years to indicate that the presence of cancer stem cells may be responsible for tumour development and early recurrence after conventional therapy strategies such as surgery, radiation, or chemotherapy. Although this concept of a small subpopulation of cancer cells with stem cell properties is not new as such and was already discussed by Virchow decades ago, the identification of cells of this kind in human malignancies was first successful in 1997 in acute myeloid leukemia. The recent identification of cancer stem cells and the detection of their fundamental signalling pathways (e.g. Hedgehog, Notch) may offer new therapeutic options in the future and become part of a therapeutic concept. In this article, we introduce the cancer stem cell model, provide an overview of current cancer stem cell markers in different human malignancies as well as head and neck squamous cell carcinoma, and discuss studies on the first targeted therapies against cancer stem cells and their signalling pathways.

Cancer stem cells and EMT in carcinoma

The majority of deaths from carcinoma are caused by secondary growths that result from tumour invasion and metastasis. The importance of epithelial-to-mesenchymal transition (EMT) as a driver of invasion and metastasis is increasingly recognised, and recent evidence has highlighted a link between EMT and the cancer stem cells that initiate and maintain tumours and have also been implicated in invasion and metastasis. Here, we review cancer stem cells and their link with EMT, and explore the importance of this link in metastasis and therapeutic resistance of tumours. We also discuss new evidence from our laboratory demonstrating that cancer stem cells display a remarkable phenotypic plasticity that enables them to switch between an epithelial phenotype that drives tumour growth and an EMT phenotype that drives metastasis. As successful therapies must eradicate cancer stem cells in all their guises, the identification of sub-types of cancer stem cells that display therapeutic resistance and phenotypic plasticity has important implications for the future design of therapeutic strategies. The ability to assay the responses of different cancer stem cell phenotypes in vitro holds promise for the rapid development of a new generation of targeted therapies that fulfil this objective.

Detection of putative cancer stem cells of the side population phenotype in human tumor cell cultures

Human solid tumors and clonal tumor cell lines comprise phenotypically and functionally diverse subsets of cancer cells and also contain stem cell-like cancer cells. Side population (SP) cells, which pump out the fluorescent dye Hoechst 33342 (H33342) via the ABCG2 transporter, define a fraction of adult tissue stem cells in a wide variety of organs. Rare cancer cells with similar H33342 efflux capacity and delimited expression of ABCG2 are present in various types of human tumors, such as breast cancer, lung cancer, and hepatocellular carcinoma. These cancer SP cells display several properties attributable to stem cell-like cancer cells and have been implicated in tumor growth, progression, and metastasis. Here we provide a detailed protocol for the detection of putative cancer stem cells of the SP phenotype in human adherent breast cancer cell cultures.

Cancer stem cells hypothesis and stem cells in head and neck cancers

There is increasing evidence that the growth and spread of cancer is driven by a small subpopulation of cancer cells, defined as cancer stem cells (CSCs). Recent data indicate that the initiation, growth, recurrence and metastasis of cancers are related to the behavior of a small population of malignant cells with properties of stem cells, and information about them are potentially helpful in identifying the target for the tumor's therapeutic elimination. The presence of subpopulation cells with phenotypic and behavioral characteristics corresponding to both normal epithelial stem cells and to cells capable of initiating tumors has been also reported in head and neck squamous cell carcinomas (HNSCCs).

Endothelial derived factors inhibit anoikis of head and neck cancer stem cells

Recent evidence demonstrated that cancer stem cells reside in close proximity to blood vessels in human head and neck squamous cell carcinomas (HNSCC). These findings suggest the existence of a supporting perivascular niche for cancer stem cells. The purpose of this study was to evaluate the effect of endothelial cell-secreted factors on the behavior of head and neck cancer stem-like cells (HNCSC). HNCSC were identified by sorting UM-SCC-22A (cell line derived from a primary squamous cell carcinoma of the oropharynx) and UM-SCC-22B (derived from the metastatic lymph node of the same patient) for CD44 expression and ALDH (aldehyde dehydrogenase) activity. HNCSC (ALDH+CD44+) and control (ALDH-CD44-) cells were cultured in ultra-low attachment plates in presence of conditioned medium from primary human endothelial cells. ALDH+CD44+ generated more orospheres than control cells when cultured in suspension. The growth factor milieu secreted by endothelial cells protected HNCSC against anoikis. Mechanistic studies revealed that endothelial cell-secreted vascular endothelial growth factor (VEGF) induces proliferation of HNCSC derived from primary UM-SCC-22A, but not from the metastatic UM-SCC-22B. Likewise, blockade of VEGF abrogated endothelial cell-induced Akt phosphorylation in HNCSC derived from UM-SCC-22A while it had a modest effect in Akt phosphorylation in HNCSC from UM-SCC-22B. This study revealed that endothelial cells initiate a crosstalk that protect head and neck cancer stem cells against anoikis, and suggest that therapeutic interference with this crosstalk might be beneficial for patients with head and neck cancer.

Holoclone forming cells from pancreatic cancer cells enrich tumor initiating cells and represent a novel model for study of cancer stem cells

Background

Pancreatic cancer is one of the direct causes of cancer-related death. High level of chemoresistance is one of the major obstacles of clinical treatment. In recent years, cancer stem cells have been widely identified and indicated as the origin of chemoresistance in multi-types of solid tumors. Increasing evidences suggest that cancer stem cells reside in the cells capable of forming holoclones continuously. However, in pancreatic cancer, holoclone-forming cells have not been characterized yet. Therefore, the goal of our present study was to indentify the holoclone-forming pancreatic cancer stem cells and develop an in vitro continuous colony formation system, which will greatly facilitate the study of pancreatic cancer stem cells.

Methodology/Principal Findings

Pancreatic cancer cell line BxPC3 was submitted to monoclonal cultivation to generate colonies. Based on the morphologies, colonies were classified and analyzed for their capacities of secondary colony formation, long-term survival in vitro, tumor formation in vivo, and drug resistance. Flowcytometry and quantitative RT-PCR were performed to detect the expression level of cancer stem cells associated cell surface markers, regulatory genes and microRNAs in distinct types of colonies. Three types of colonies with distinct morphologies were identified and termed as holo-, mero-, and paraclones, in which only holoclones generated descendant colonies of all three types in further passages. Compared to mero- and paraclones, holoclones possessed higher capacities of long-term survival, tumor initiation, and chemoresistance. The preferential expression of cancer stem cells related marker (CXCR4), regulatory genes (BMI1, GLI1, and GLI2) and microRNAs (miR-214, miR-21, miR-221, miR-222 and miR-155) in holoclones were also highlighted.

Conclusions/Significance

Our results indicate that the pancreatic tumor-initiating cells with high level of chemoresistance were enriched in holoclones derived from BxPC3 cell line. Generation of holoclones can serve as a novel model for studying cancer stem cells, and attribute to developing new anti-cancer drugs.

Calcineurin signaling as a negative determinant of keratinocyte cancer stem cell potential and carcinogenesis

Calcineurin is the only known serine-threonine phosphatase under calcium-calmodulin control and key regulator of the immune system. Treatment of patients with calcineurin-inhibitory drugs like cyclosporin A and FK506 to prevent graft rejection dramatically increases the risk of cutaneous squamous cell carcinoma, which is a major cause of death after organ transplants. Recent evidence indicates that suppression of calcineurin signaling, together with its impact on the immune system, exerts direct tumor-promoting effects in keratinocytes, enhancing cancer stem cell potential. The underlying mechanism involves interruption of a double negative regulatory axis, whereby calcineurin and nuclear factors of activated T-cell signaling inhibits expression of ATF3, a negative regulator of p53. The resulting suppression of keratinocyte cancer cell senescence is of likely clinical significance for the many patients under treatment with calcineurin inhibitors and may be of relevance for other cancer types in which altered calcium-calcineurin signaling plays a role.

Epithelial to mesenchymal transition by TGFβ-1 induction increases stemness characteristics in primary non small cell lung cancer cell line

Background

Cancer Stem Cells (CSCs) hypothesis asserts that only a small subset of cells within a tumour is capable of both tumour initiation and sustainment. The Epithelial-Mesenchymal Transition (EMT) is an embryonic developmental program that is often activated during cancer invasion and metastasis. The aim of this study is to shed light on the relationship between EMT and CSCs by using LC31 lung cancer primary cell line.

Materials and Methods

A549 and LC31 cell lines were treated with 2 ng/ml TGFβ-1 for 30 days, and 80 days, respectively. To evaluate EMT, morphological changes were assessed by light microscopy, immunofluorescence and cytometry for following markers: cytokeratins, e-cadherin, CD326 (epithelial markers) and CD90, and vimentin (mesenchymal markers). Moreover, RT-PCR for Slug, Twist and β-catenin genes were performed. On TGFβ-1 treated and untreated LC31 cell lines, we performed stemness tests such as pneumospheres growth and stem markers expression such as Oct4, Nanog, Sox2, c-kit and CD133. Western Blot for CD133 and tumorigenicity assays using NOD/SCID mice were performed.

Results

TGFβ-1 treated LC31 cell line lost its epithelial morphology assuming a fibroblast-like appearance. The same results were obtained for the A549 cell line (as control). Immunofluorescence and cytometry showed up-regulation of vimentin and CD90 and down-regulation of cytocheratin, e-cadherin and CD326 in TGFβ-1 treated LC31 and A549 cell lines. Slug, Twist and β-catenin m-RNA transcripts were up-regulated in TGFβ-1 treated LC31 cell line confirming EMT. This cell line showed also over-expression of Oct4, Nanog, Sox2 and CD133, all genes of stemness. In addition, in TGFβ-1 treated LC31 cell line, an increased pneumosphere-forming capacity and tumours-forming ability in NOD/SCID mice were detectable.

Conclusions

The induction of EMT by TGFβ-1 exposure, in primary lung cancer cell line results in the acquisition of mesenchymal profile and in the expression of stem cell markers.

Cancer stem cells in squamous cell carcinoma switch between two distinct phenotypes that are preferentially migratory or proliferative

Epithelial-to-mesenchymal transition (EMT) is an important driver of tumor invasion and metastasis, which causes many cancer deaths. Cancer stem cells (CSC) that maintain and initiate tumors have also been implicated in invasion and metastasis, but whether EMT is an important contributor to CSC function is unclear. In this study, we investigated whether a population of CSCs that have undergone EMT (EMT CSCs) exists in squamous cell carcinoma (SCC). We also determined whether a separate population of CSCs that retain epithelial characteristics (non-EMT CSCs) is also present. Our studies revealed that self-renewing CSCs in SCC include two biologically-distinct phenotypes. One phenotype, termed CD44(high)ESA(high), was proliferative and retained epithelial characteristics (non-EMT CSCs), whereas the other phenotype, termed CD44(high)ESA(low), was migratory and had mesenchymal traits characteristic of EMT CSCs. We found that non-EMT and EMT CSCs could switch their epithelial or mesenchymal traits to reconstitute the cellular heterogeneity which was characteristic of CSCs. However, the ability of EMT CSCs to switch to non-EMT character was restricted to cells that were also ALDH1(+), implying that only ALDH1(+) EMT cells had the ability to seed a new epithelial tumor. Taken together, our findings highlight the identification of two distinct CSC phenotypes and suggest a need to define therapeutic targets that can eradicate both of these variants to achieve effective SCC treatment.

Implications of understanding cancer stem cell (CSC) biology in head and neck squamous cell cancer

Head and neck squamous cell cancer (HNSCC) is the sixth most common cancer in the world. Effective therapeutic modalities such as surgery, radiation, chemotherapy and combinations of each are used in the management of this disease. Efforts are ongoing throughout the world to improve early detection and prevention of HNSCCs. Often, treatment fails to obtain total cancer cure and this is more likely with advanced stage disease. In recent years it appears that one of the key determinants of treatment failure may be the presence of cancer stem cells (CSC) that 'escape' currently available therapies. CSCs form a minute portion of the total tumour burden but may play a disproportionately important role in determining outcomes. Molecular mechanisms which underlie the genesis of CSCs are yet not fully understood and their detection within the total tumour bulk remains a challenge. Specific markers like Aldehyde dehydrogenase 1 (ALDH1), CD44 and Bmi-1 have shown early promising results both in CSC detection and in guiding treatment protocols. CSCs have been shown to be relatively resistant to standard treatment modalities. It is hoped that developing robust in vitro and in vivo experimental models of CSCs might provide a means of devising more effective therapeutic strategies.

Canine Mammary Cancer Stem Cells are Radio- and Chemo- Resistant and Exhibit an Epithelial-Mesenchymal Transition Phenotype

Canine mammary carcinoma is the most common cancer among female dogs and is often fatal due to the development of distant metastases. In humans, solid tumors are made up of heterogeneous cell populations, which perform different roles in the tumor economy. A small subset of tumor cells can hold or acquire stem cell characteristics, enabling them to drive tumor growth, recurrence and metastasis. In veterinary medicine, the molecular drivers of canine mammary carcinoma are as yet undefined. Here we report that putative cancer stem cells (CSCs) can be isolated form a canine mammary carcinoma cell line, REM134. We show that these cells have an increased ability to form tumorspheres, a characteristic of stem cells, and that they express embryonic stem cell markers associated with pluripotency. Moreover, canine CSCs are relatively resistant to the cytotoxic effects of common chemotherapeutic drugs and ionizing radiation, indicating that failure of clinical therapy to eradicate canine mammary cancer may be due to the survival of CSCs. The epithelial to mesenchymal transition (EMT) has been associated with cancer invasion, metastasis, and the acquisition of stem cell characteristics. Our results show that canine CSCs predominantly express mesenchymal markers and are more invasive than parental cells, indicating that these cells have a mesenchymal phenotype. Furthermore, we show that canine mammary cancer cells can be induced to undergo EMT by TGFβ and that these cells have an increased ability to form tumorspheres. Our findings indicate that EMT induction can enrich for cells with CSC properties, and provide further insight into canine CSC biology.

Frequency of cells expressing CD44, a head and neck cancer stem cell marker: correlation with tumor aggressiveness

BACKGROUND

We previously identified by flow cytometry a Lineage-CD44+ (Lin-CD44+) subpopulation of cells with cancer stem cell properties in head and neck squamous cell carcinoma (HNSCC). We now correlate clinical and histologic factors with Lin-CD44+ cell frequency.

METHODS

The study included 31 patients with HNSCC, of whom 87% had stage IV disease. The frequency of Lin-CD44+ cells and the success of xenografting patient tumors in mice were correlated with clinical and pathologic data.

RESULTS

The mean frequency of Lin-CD44+ cells was 25% (0.4%-81%). It was 36% in patients who had recurrence versus 15% for those without recurrence (p = .04). Successful xenograft implantation occurred in 53%. Seventy-five percent of patients with successful xenografts had recurrence versus 21% of patients with unsuccessful xenografts (p = .003).

CONCLUSIONS

Successful xenograft implantation and a high frequency of Lin-CD44+ cells correlate with known poor prognostic factors such as advanced T classification and recurrence. These findings may support the stem cell concept in HNSCC.

Cancer stem cells and epithelial ovarian cancer

The cancer stem cell hypothesis is becoming more widely accepted as a model for carcinogenesis. Tumours are heterogeneous both at the molecular and cellular level, containing a small population of cells that possess highly tumourigenic “stem-cell” properties. Cancer stem cells (CSCs), or tumour-initiating cells, have the ability to self-renew, generate xenografts reminiscent of the primary tumour that they were derived from, and are chemoresistant. The characterisation of the CSC population within a tumour that drives its growth could provide novel target therapeutics against these cells specifically, eradicating the cancer completely. There have been several reports describing the isolation of putative cancer stem cell populations in several cancers; however, no defined set of markers has been identified that conclusively characterises “stem-like” cancer cells. This paper highlights the current experimental approaches that have been used in the field and discusses their limitations, with specific emphasis on the identification and characterisation of the CSC population in epithelial ovarian cancer.

Targeted inhibition of CD133+ cells in oral cancer cell lines

Resistance to treatment and the appearance of secondary tumors in head and neck squamous cell carcinomas (HNSCC) have been attributed to the presence of cells with stem-cell-like properties in the basal layer of the epithelium at the site of the lesion. In this study, we tested the hypothesis that these putative cancer stem cells (CSC) in HNSCC could be specifically targeted and inhibited. We found that 9 of 10 head and neck tumor biopsies contained a subpopulation of cells that expressed CD133, an unusual surface-exposed membrane-spanning glycoprotein associated with CSC. A genetically modified cytolethal distending toxin (Cdt), from the periodontal pathogen Aggregatibacter actinomycetemcomitans, was conjugated to an anti-human CD133 monoclonal antibody (MAb). The Cdt-MAb complex preferentially inhibited the proliferation of CD133(+) cells in cultures of established cell lines derived from HNSCC. Inhibition of the CD133(+) cells was rate- and dose-dependent. Saturation kinetics indicated that the response to the Cdt-MAb complex was specific. Healthy primary gingival epithelial cells that are native targets of the wild-type Cdt were not affected. Analysis of these data provides a foundation for the future development of new therapies to target CSC in the early treatment of HNSCC.

ABBREVIATIONS

Cdt, cytolethal distending toxin; CSC, cancer stem cells; HNSCC, head and neck squamous cell carcinoma; MAb, monoclonal antibody.

PC3 prostate tumor-initiating cells with molecular profile FAM65Bhigh/MFI2low/LEF1low increase tumor angiogenesis

BACKGROUND

Cancer stem-like cells are proposed to sustain solid tumors by virtue of their capacity for self-renewal and differentiation to cells that comprise the bulk of the tumor, and have been identified for a variety of cancers based on characteristic clonal morphologies and patterns of marker gene expression.

METHODS

Single cell cloning and spheroid culture studies were used to identify a population of cancer stem-like cells in the androgen-independent human prostate cancer cell line PC3.

RESULTS

We demonstrate that, under standard culture conditions, ~10% of PC3 cells form holoclones with cancer stem cell characteristics. These holoclones display high self-renewal capability in spheroid formation assays under low attachment and serum-free culture conditions, retain their holoclone morphology when passaged at high cell density, exhibit moderate drug resistance, and show high tumorigenicity in scid immunodeficient mice. PC3 holoclones readily form spheres, and PC3-derived spheres yield a high percentage of holoclones, further supporting their cancer stem cell-like nature. We identified one gene, FAM65B, whose expression is consistently up regulated in PC3 holoclones compared to paraclones, the major cell morphology in the parental PC3 cell population, and two genes, MFI2 and LEF1, that are consistently down regulated. This molecular profile, FAM65Bhigh/MFI2low/LEF1low, also characterizes spheres generated from parental PC3 cells. The PC3 holoclones did not show significant enriched expression of the putative prostate cancer stem cell markers CD44 and integrin α2β1. PC3 tumors seeded with holoclones showed dramatic down regulation of FAM65B and dramatic up regulation of MFI2 and LEF1, and unexpectedly, a marked increase in tumor vascularity compared to parental PC3 tumors, suggesting a role of cancer stem cells in tumor angiogenesis.

CONCLUSIONS

These findings support the proposal that PC3 tumors are sustained by a small number of tumor-initiating cells with stem-like characteristics, including strong self-renewal and pro-angiogenic capability and marked by the expression pattern FAM65Bhigh/MFI2low/LEF1low. These markers may serve as targets for therapies designed to eliminate cancer stem cell populations associated with aggressive, androgen-independent prostate tumors such as PC3.

Stem cell characteristics of cell sub-populations in cell lines derived from head and neck cancers of Fanconi anemia patients

Increasing evidence indicates that cancer growth is driven by a sub-population of self-renewing cancer stem cells (CSCs) and that clinical problems of tumor recurrence after therapy may be related to differential resistance of CSCs to therapeutic elimination. Fanconi anemia (FA) is an autosomal recessive disorder associated with deficiencies of DNA repair and a greatly enhanced risk of hematopoietic malignancies and of head and neck squamous cell carcinoma (HNSCC). In FA patients, lack of DNA repair complicates therapies acting through DNA damage and alternative approaches, such as targeting signaling pathways associated with stem cell maintenance, might be of particular benefit. To assess effects of FA gene defects on the expression of stem cell properties, CSC patterns in cell lines derived from FA-related and sporadic HNSCC were compared. As for sporadic cell lines, FA cell lines showed colony morphologies associated with stem cell patterns. In all cell lines, cells with strong staining for CD44 (CD44(high) ) showed lower rates of apoptosis and a greater DNA damage induced block in the G2 phase of the cell cycle than CD44(low) cells. Mitomycin C, and UVB increased overall rates of apoptosis for both sporadic and FA cell lines, although FA cells tended to be more sensitive to apoptotic induction. Fluorescence activated cell sorting, immunohistochemistry, and QPCR indicated distinctly different patterns of gene expression of CD44(high) and CD44(low) cells in both sporadic and FA cell lines.

Identification of cancer stem cell-like cells from human epithelial ovarian carcinoma cell line

Cancer stem cells (CSCs) play an important role in the development, invasion, and drug resistance of carcinoma, but the exact phenotype and characteristics of ovarian CSCs are still disputable. In this study, we identified cancer stem cell-like cells (CSC-LCs) and investigated their characteristics from the ovarian adenocarcinoma cell line 3AO. Our results showed that CSC-LCs were enriched in sphere-forming test and highly expressed CD44(+)CD24⁻. The spheres and CD24⁻ cells possessed strong tumorigenic ability by transplantation into nonobese diabetic/severe combined immunodeficient mice. CD44(+)CD24⁻ cells expressed stem cell markers and differentiated to CD44(+)CD24(+) cells by immunofluorescence assay and fluorescence-activated cell-sorting analysis. In vitro experiments verified that CD44(+)CD24⁻ cells were markedly resistant to carboplatin and paclitaxol. In conclusion, our study identifies the CD44(+)CD24⁻ phenotype, self-renewal, high tumorigenicity, differentiation potential, and drug resistance of ovarian CSC-LCs. Our findings may provide the evidence needed to explore a new strategy in the treatment of ovarian cancer.

Octamer 4 (Oct4) mediates chemotherapeutic drug resistance in liver cancer cells through a potential Oct4-AKT-ATP-binding cassette G2 pathway

Chemoresistance presents a major obstacle to the efficacy of chemotherapeutic treatment of cancers. Using chemotherapeutic drugs to select drug-resistant cancer cells in hepatocellular carcinoma (HCC) and several other cancer cell lines, we demonstrate that chemoresistant cells displayed cancer stem cell features, such as increased self-renewal ability, cell motility, multiple drug resistance, and tumorigenicity. Octamer 4 (Oct4) messenger RNA (mRNA) levels were dramatically increased in chemoresistant cancer cells due to DNA demethylation regulation of Oct4. By functional study, Oct4 overexpression enhanced whereas Oct4 knockdown reduced liver cancer cell resistance to chemotherapeutic drugs in vitro and in xenograft tumors. It is known that the Oct4-TCL1-AKT pathway acts on embryonic stem cells and cancer stem cells in cell proliferation through inhibition of apoptosis. We further demonstrate that Oct4 overexpression induced activation of TCL1, AKT, and ABCG2 to mediate chemoresistance, which can be overcome by addition of the PI3K/AKT inhibitor; therefore, a direct pathway of Oct4-TCL1-AKT-ABCG2 or a combination of Oct4-TCL1-AKT with the AKT-ABCG2 pathway could be a potential new mechanism involved in liver cancer cell chemoresistance. Moreover, the clinical significance of the Oct4-AKT-ABCG2 pathway can be demonstrated in HCC patients, with a strong correlation of expression patterns in human HCC tumors. The role of the Oct4-AKT-ABCG2 axis in cancer cell chemoresistant machinery suggests that AKT pathway inhibition (PI3K inhibitors) not only inhibits cancer cell proliferation, but may also enhance chemosensitivity by target potential chemoresistant cells.

CONCLUSION

Oct4, a transcriptional factor of pluripotent cells, can mediate chemoresistance through a potential Oct4-AKT-ABCG2 pathway.

Mouse sarcoma L1 cell line holoclones have a stemness signature

Accumulating data suggest that cancers contain a fraction of cells called cancer stem cells (CSCs), that may be responsible for upkeep and relapses of disease. In experimental settings, CSCs are regarded as most effective at tumour initiation in in vivo assays. Since the first isolation of cancer stem cells from acute myeloid leukaemia in 1994, cancer stem cells have been identified in human solid tumours and they have also been found in the established cell lines, based on ability of CSCs to form in vitro colonies of a specific morphology, called holoclones. Our study examined the ability of a mouse sarcoma cell line, derived from a lung metastasis of a BALB/c mouse and established as a stably growing line (L1), to produce holoclones in vitro. We aimed to verify a stemness signature of the holoclone cells. The L1 cell line was found to form holoclone colonies in vitro, which were shown to contain a percentage of CSC-like cells. A fraction of the L1 cells was able to repopulate the original cell line, and presented an increased clonogenic and metastatic potential (18th passage). In addition, MTT assay and flow cytometry of the side population fraction revealed that these cells were more resistant to chemotherapeutic drugs than the original cell line, and over-expressed the anti-apoptotic genes, GRP78 and GADD153. We conclude that mouse L1 sarcoma cell line contains CSC-like cells.

Opposing roles for calcineurin and ATF3 in squamous skin cancer

Calcineurin inhibitors such as cyclosporin A (CsA) are the mainstay of immunosuppressive treatment for organ transplant recipients. Squamous cell carcinoma (SCC) of the skin is a major complication of treatment with these drugs, with a 65–100 fold higher risk than in the normal population1. By contrast, the incidence of basal cell carcinoma (BCC), the other major keratinocyte-derived tumour of the skin, of melanoma and of internal malignancies increases to a significantly lesser extent 1. Here we report that genetic and pharmacological suppression of calcineurin/NFAT function promotes tumour formation in mouse skin and in xenografts, in immune compromised mice, of H-ras^V12 expressing primary human keratinocytes or keratinocyte-derived SCC cells. Calcineurin/NFAT inhibition counteracts p53-dependent cancer cell senescence thereby increasing tumourigenic potential. ATF3, a member of the “enlarged” AP-1 family, is selectively induced by calcineurin/NFAT inhibition, both under experimental conditions and in clinically occurring tumours, and increased ATF3 expression accounts for suppression of p53-dependent senescence and enhanced tumourigenic potential. Thus, intact calcineurin/NFAT signalling is critically required for p53 and senescence-associated mechanisms that protect against skin squamous cancer development.

The effects of telomerase inhibition on prostate tumor-initiating cells

Prostate cancer is the most common malignancy in men, and patients with metastatic disease have poor outcome even with the most advanced therapeutic approaches. Most cancer therapies target the bulk tumor cells, but may leave intact a small population of tumor-initiating cells (TICs), which are believed to be responsible for the subsequent relapse and metastasis. Using specific surface markers (CD44, integrin alpha(2)beta(1) and CD133), Hoechst 33342 dye exclusion, and holoclone formation, we isolated TICs from a panel of prostate cancer cell lines (DU145, C4-2 and LNCaP). We have found that prostate TICs have significant telomerase activity which is inhibited by imetelstat sodium (GRN163L), a new telomerase antagonist that is currently in Phase I/II clinical trials for several hematological and solid tumor malignancies. Prostate TICs telomeres were of similar average length to the telomeres of the main population of cells and significant telomere shortening was detected in prostate TICs as a result of imetelstat treatment. These findings suggest that telomerase inhibition therapy may be able to efficiently target the prostate TICs in addition to the bulk tumor cells, providing new opportunities for combination therapies.

Telomeres and telomerase in normal and cancer stem cells

Differences between normal adult tissue stem cells and cancer stem/initiating cells remain poorly defined. For example, it is controversial if cancer stem cells can become fully quiescent, require a stem cell niche, are better at repairing DNA damage than the bulk of the cancer cells, and if and how they regulate symmetric versus asymmetric cell divisions. This minireview will not only provide our personal views to address some of these outstanding questions, but also present evidence that an understanding of telomere dynamics and telomerase activity in normal and cancer stem cells may provide additional insights into how tumors are initiated, and how they should be monitored and treated.

Normal and malignant epithelial cells with stem-like properties have an extended G2 cell cycle phase that is associated with apoptotic resistance

Background

Subsets of cells with stem-like properties have been previously isolated from human epithelial cancers and their resistance to apoptosis-inducing stimuli has been related to carcinoma recurrence and treatment failure. The aim of this study was to investigate the mechanisms of resistance to apoptosis-inducing agents of cells with stem-like properties in both normal and malignant human epithelia.

Methods

Cells isolated from fresh human head and neck carcinomas (n = 11), cell lines derived from head and neck, prostate and breast human carcinomas (n = 7), and from normal human oral mucosa (n = 5), were exposed to various apoptosis-inducing stimuli (UV, Tumour Necrosis Factor, Cisplatin, Etoposide, and Neocarzinostatin). Flow cytometry for CD44 and epithelial-specific antigen (ESA) expression, colony morphology, tumour sphere formation and rapid adherence assays were used to identify the subset of cells with stem-like properties. Apoptosis, cell cycle and expression of various cell cycle checkpoint proteins were assessed (Western Blot, qPCR). The role of G2-checkpoint regulators Chk1 and Chk2 was investigated by use of debromohymenialdisine (DBH) and siRNA.

Results

In both cancer biopsies and carcinoma cell lines a subset of CD44^high cells showed increased clonogenicity, a significantly lower rate of apoptosis, and a significantly higher proportion of cells in the G2-phase of the cell cycle. An inverse correlation between the percentage of cells in G2-phase and the rate of apoptosis was found. Pulse-chase with iododeoxyuridine (IdU) demonstrated that CD44^high carcinoma cells spent longer time in G2, even in un-treated controls. These cells expressed higher levels of G2 checkpoint proteins, and their release from G2 with BDH or Chk1 siRNA increased their rate of apoptosis. Low passage cultures of normal keratinocytes were also found to contain a subset of CD44^high cells showing increased clonogenicity, and a similar pattern of G2-block associated with apoptotic resistance.

Conclusions

These data indicate that both normal and malignant human epithelial cells with stem-like properties show greater resistance to apoptosis associated with extended G2 cell cycle phase, and that this property is not a consequence of neoplastic transformation. Targeting G2 checkpoint proteins releases these cells from the G2-block and makes them more prone to apoptosis, implying an opportunity for improved therapeutic approaches.

Downstream targets of FOXM1: CEP55 and HELLS are cancer progression markers of head and neck squamous cell carcinoma

We recently showed that upregulation of a key oncogene FOXM1 precedes head and neck squamous cell carcinoma (HNSCC) malignancy. Furthermore, we also identified a centrosomal protein CEP55 and a DNA helicase/putative stem cell marker HELLS, which are both downstream targets of FOXM1. In this study, we have investigated the expression profiles of CEP55 and HELLS using immunohistochemistry and quantified by digital densitometry in a tissue panel (20 samples) consisting of normal oral mucosa, dysplasias, HNSCC and lymph node metastasis (LnMet) samples. Furthermore, we corroborated our findings using absolute real-time PCR (qPCR) on a panel of 12 primary normal human oral keratinocytes, five dysplasia and 10 HNSCC cell lines. Finally, we validated our study using bioinformatics microarray analysis on an independent HNSCC patient cohort (four normal and 16 tumours). In normal oral mucosa, CEP55 protein was detected at very low level within the upper differentiated layers. In contrast, CEP55 was highly expressed in oral dysplasia whereas only moderate expression was detected in HNSCC and LnMet. Low level of HELLS expression was detected in the basal cell layer of the normal oral mucosa, moderate level was seen in dysplasia and high levels in both HNSCC and LnMet. These expression patterns were consistent with both qPCR data from the cell line panel and microarray data analysis of TNM-stage defined HNSCC samples confirming the progressive expression pattern of CEP55 and HELLS. To our knowledge, this is the first pilot study demonstrating that both CEP55 and HELLS mRNA and protein expression positively correlate with pre-malignancy and HNSCC progression. This study provides strong evidence that CEP55 and HELLS may be used in conjunction with FOXM1 as a biomarker set for early cancer detection and indicators of malignant conversion and progression.

Expression of pluripotent stem cell reprogramming factors by prostate tumor initiating cells

PURPOSE

We identified a discrete population of stem cell-like tumor cells expressing 5 essential transcription factors required to reprogram pluripotency in prostate tumor cell lines and primary prostate cancer tissue.

MATERIALS AND METHODS

DU145 and PC3 human prostate cancer cell lines (ATCC), tumor tissue from patients with prostate cancer and normal prostate tissue were evaluated for the reprogramming factors OCT3/4 (Cell Signaling Technology), SOX2, Klf4 (Santa Cruz Biotechnology, Santa Cruz, California), Nanog (BioLegend) and c-Myc (Cell Signaling) by semiquantitative reverse transcriptase-polymerase chain reaction, histological and immunohistochemical analysis. Stem cell-like tumor cells were enriched by flow cytometric cell sorting using E-cadherin (R&D Systems) as a surface marker, and soft agar, spheroid and tumorigenicity assays to confirm cancer stem cell-like characteristics.

RESULTS

mRNA expression of transcription factors OCT3/4 and SOX2 highly correlated in primary prostate tumor tissue samples. The number of OCT3/4 or SOX2 expressing cells was significantly increased in prostate cancer tissue compared to that in normal prostate or benign prostate hyperplasia tissue (p <0.05). When isolated from the DU145 and PC3 prostate cancer cell lines by flow cytometry, stem cell-like tumor cells expressing high OCT3/4 and SOX2 levels showed high tumorigenicity in immunodeficient mice. In vivo growth of the parental DU145 and PC3 prostate cancer cell lines was inhibited by short hairpin RNA knockdown of OCT3/4 or SOX2.

CONCLUSIONS

Data suggest that prostate tumor cells expressing pluripotent stem cell transcription factors are highly tumorigenic. Identifying such cells and their importance in prostate cancer growth could provide opportunities for novel targeting strategies for prostate cancer therapy.

Investigations of prostate epithelial stem cells and prostate cancer stem cells

Although both prostate epithelial stem cells and prostate cancer stem cells are implicated in the differentiation of the normal prostate gland and carcinogenesis of prostate cancer, there has, until recently, been little information regarding their biology. This review summarizes the recent advancements in cell biological research including various in vitro culture systems that have offered the characterization and isolation of prostate epithelial stem cells and prostate cancer stem cells. In addition, the stromal niche or microenvironment of stem cells plays an essential role in proliferation and differentiation of normal stem cells. Stroma surrounding cancer cells, which also provide another unique niche, may involve the initiation and development of cancer stem cells. Investigation of stem cells and their microenvironments in the prostate should lead to the elucidation of biological features and the development of novel treatments for prostate cancer.

Maintenance of HCT116 colon cancer cell line conforms to a stochastic model but not a cancer stem cell model

The cancer stem cell (CSC) model, in which a small population of cells within a tumor possesses the ability to self-renew and reconstitute the phenotype of primary tumor, has gained wide acceptance based on evidence over the past decade. It has also been reported that cancer cell lines contain a CSC subpopulation. However, phenotypic differences between CSCs and non-CSCs in cancer cell lines are not better defined than in primary tumors. Furthermore, some cell lines do not have a CSC population, revealed as a side population and expression of CD133. Thus, the identification of CSCs in cancer cell lines remains elusive. Here, we investigated the CSC hierarchy within HCT116 colon cancer cells, which do not have a CD133-positive subpopulation. We examined the expression of alternative CSC markers epithelial specific antigen (ESA) and CD44 in floating-sphere-derived cells, which are known to be the cells of enriching CSCs. Sphere-derived HCT116 cells exhibited heterogeneous expression of ESA and CD44. The two major subpopulations of HCT116 sphere cells (ESA(low)CD44(-/low) and ESA(high)CD44(high)) exhibited a biological/proliferative hierarchy of sphere-forming and soft agar colony-forming activity. However, there was no difference between the two subpopulations in the incidence of xenograft tumors. When ESA(low)CD44(-/low) cells were allowed to aggregate and re-form floating-spheres, the biological/proliferative hierarchy of parental HCT116 spheres was reconstituted, in terms of ESA and CD44 expression. Thus, HCT116 cells have plasticity when they are set in floating-spheres, suggesting that maintenance of the HCT116 cell line conforms to a stochastic model, not a CSC model.

Distinct population of highly malignant cells in a head and neck squamous cell carcinoma cell line established by xenograft model

The progression and metastasis of solid tumors, including head and neck squamous cell carcinoma (HNSCC), have been related to the behavior of a small subpopulation of cancer stem cells. Here, we have established a highly malignant HNSCC cell line, SASVO3, from primary tumors using three sequential rounds of xenotransplantation. SASVO3 possesses enhanced tumorigenic ability both in vitro and in vivo. Moreover, SASVO3 exhibits properties of cancer stem cells, including that increased the abilities of sphere-forming, the number of side population cells, the potential of transplanted tumor growth and elevated expression of the stem cell marker Bmi1. Injection of SASVO3 into the tail vein of nude mice resulted in lung metastases. These results are consistent with the postulate that the malignant and/or metastasis potential of HNSCC cells may reside in a stem-like subpopulation.

In vitro propagation and characterization of neoplastic stem/progenitor-like cells from human prostate cancer tissue

BACKGROUND

According to the cancer stem cell hypothesis, tumor growth is sustained by a subpopulation of cancer stem/progenitor-like cells. Self-renewal and high clonogenic potential are characteristics shared by normal stem and neoplastic stem/progenitor-like cells. We investigated whether human prostate cancer specimens contain cells with these properties.

METHODS

Self-renewal and clonogenic potential were assessed by serial passaging of spheres and colony formation, respectively. Gene expression was analyzed by real time PCR. Protein expression was detected by immunocytochemistry. The neoplastic nature of the cells was verified by detection of the TMPRSS2/ERG gene fusion expression.

RESULTS

The epithelial fraction isolated from surgical specimens generated colonies in 68% (19/28) of the patients. Laminin adhesion selected for cells with high clonogenic potential. The epithelial fraction from 85% (42/49) of the patients generated primary prostaspheres. Serial passaging of prostaspheres demonstrated their self-renewal capacity, which is also supported by their expression of the stem cell markers Oct-4, Nanog, Bmi-1, and Jagged-1 mRNA. Cells derived from prostaspheres were more clonogenic than the parental epithelial fraction. The pattern of mRNA expression in prostaspheres resembled that of the basal compartment of the prostate (CK5(+)/CK14(+)/CK19(high)/CK18(-/low)/c-met(+)/AR(-/low)/PSA(-/low)), but also included stem cell markers (CD49b(+)/CD49f(+)/CD44(+)/DeltaNp63(+)/Nestin(+)/CD133(+)). The distribution of marker expression in prostaspheres suggests their heterogeneous cell composition. Prostaspheres expressed significantly higher PSCA mRNA levels than the epithelial fraction.

CONCLUSION

Human prostate cancer specimens contain neoplastic cells with self-renewal and clonogenic potential, which can be enriched and perpetuated in prostaspheres. Prostaspheres should prove valuable for the identification of prostate cancer stem/progenitor-like cells.

Colorectal cancer stem cells

PURPOSE

The cancer stem cell hypothesis predicts that only a subpopulation of cells within a tumor is responsible for driving growth. If this hypothesis were true, it would have a significant impact on our current treatment of cancer because conventional chemotherapy and radiotherapy target rapidly proliferating cells making up the bulk of the tumor, not specifically cancer stem cells. The aims of this review are to highlight the current evidence supporting the existence of cancer stem cells in colorectal cancer, to consider the relative merits of current cancer stem cell markers, and to discuss the implications of this on our current treatment of cancer.

METHODS

Published scientific articles were selected by searching the PubMed database by use of the terms "colorectal," "cancer," and "stem cells," and by use of the bibliographies of extracted articles.

RESULTS AND CONCLUSION

CD133, a glycosylated cell surface protein, has been demonstrated to isolate for a subpopulation of colorectal tumor cells enriched in cancer stem cells. However, only 1 in 262 CD133+ cells are able to initiate tumors. Other cancer stem cell markers have been investigated, but an overall need exists to identify more specific markers to allow further characterization of these cancer stem cells. We discuss how increased understanding of the distribution and behavior of cancer stem cells within tumors could have significant implications for the management of colorectal cancer, including screening, resection margins, sentinel node biopsy, determination of prognosis, and the development of novel therapeutic targets.

A subpopulation of CD133(+) cancer stem-like cells characterized in human oral squamous cell carcinoma confer resistance to chemotherapy

The potential role of cancer stem-like cells (CSCs) in chemoresistance of human oral squamous cell carcinoma (OSCC) was examined. A small subpopulation (1-2%) of CD133(+) CSCs was identified in OSCC cell lines and tissues. These CD133(+) CSCs possess higher clonogenicity, invasiveness, and increased in vivo tumorigenicity as compared to CD133(-) counterparts. Meanwhile, CD133(+) CSCs were substantially resistant to standard chemotherapy, wherein both in vitro and in vivo treatment with paclitaxel resulted in a marked enrichment for CD133(+) CSCs. Our data suggest that CD133(+) cells represent a small subpopulation of CSCs that may contribute to chemoresistance in human OSCC.

A novel organotypic model mimics the tumor microenvironment

Carcinoma cell invasion is traditionally studied in three-dimensional organotypic models composed of type I collagen and fibroblasts. However, carcinoma cell behavior is affected by the various cell types and the extracellular matrix (ECM) in the tumor microenvironment. In this study, a novel organotypic model based on human uterine leiomyoma tissue was established and characterized to create a more authentic environment for carcinoma cells. Human tongue squamous cell carcinoma cells (HSC-3) were cultured on top of either collagen or myoma. Organotypic sections were examined by immunohistochemistry and in situ hybridization. The maximal invasion depth of HSC-3 cells was markedly increased in myomas compared with collagen. In myomas, various cell types and ECM components were present, and the HSC-3 cells only expressed ECM molecules in the myoma model. Organotypic media were analyzed by radioimmunoassay, zymography, or Western blotting. During carcinoma cell invasion, matrix metalloprotease-9 production and collagen degradation were enhanced particularly in the myoma model. To evaluate the general applicability of the myoma model, several oral carcinoma, breast carcinoma, and melanoma cell lines were cultured on myomas and found to invade in highly distinct patterns. We conclude that myoma tissue mimics the native tumor microenvironment better than previous organotypic models and possibly enhances epithelial-to-mesenchymal transition. Thus, the myoma model provides a promising tool for analyzing the behavior of carcinoma cells.

A novel approach to the identification and enrichment of cancer stem cells from a cultured human glioma cell line

Enrichment of cancer stem cells for studies of carcinogenesis remains a difficult issue. We hypothesized that the unique features of cancer stem cells (CSCs) may allow formation of their colonies in vitro with distinct morphology. We therefore investigated the possibility to use morphological diversity of colonies to identify and enrich CSCs from cultured malignant human glioma cells. We found that a small proportion of the cells from a human glioma cell line U251 formed tight and round-shaped colonies in culture. Most cells in such colonies were capable of self-renewal, generating tumor spheres and differentiating into lineages with markers for neurons, astrocytes and oligodendrocytes. In addition, several neural stem cell-related genes were highly expressed by tumor cells in those tight colonies. Our results thus demonstrate a novel approach to the identification and enrichment of CSCs based on unique morphology of their colonies formed in vitro.

FOXM1 upregulation is an early event in human squamous cell carcinoma and it is enhanced by nicotine during malignant transformation

BACKGROUND

Cancer associated with smoking and drinking remains a serious health problem worldwide. The survival of patients is very poor due to the lack of effective early biomarkers. FOXM1 overexpression is linked to the majority of human cancers but its mechanism remains unclear in head and neck squamous cell carcinoma (HNSCC).

METHODOLOGY/PRINCIPAL FINDINGS

FOXM1 mRNA and protein expressions were investigated in four independent cohorts (total 75 patients) consisting of normal, premalignant and HNSCC tissues and cells using quantitative PCR (qPCR), expression microarray, immunohistochemistry and immunocytochemistry. Effect of putative oral carcinogens on FOXM1 transcriptional activity was dose-dependently assayed and confirmed using a FOXM1-specific luciferase reporter system, qPCR, immunoblotting and short-hairpin RNA interference. Genome-wide single nucleotide polymorphism (SNP) array was used to 'trace' the genomic instability signature pattern in 8 clonal lines of FOXM1-induced malignant human oral keratinocytes. Furthermore, acute FOXM1 upregulation in primary oral keratinocytes directly induced genomic instability. We have shown for the first time that overexpression of FOXM1 precedes HNSCC malignancy. Screening putative carcinogens in human oral keratinocytes surprisingly showed that nicotine, which is not perceived to be a human carcinogen, directly induced FOXM1 mRNA, protein stabilisation and transcriptional activity at concentrations relevant to tobacco chewers. Importantly, nicotine also augmented FOXM1-induced transformation of human oral keratinocytes. A centrosomal protein CEP55 and a DNA helicase/putative stem cell marker HELLS, both located within a consensus loci (10q23), were found to be novel targets of FOXM1 and their expression correlated tightly with HNSCC progression.

CONCLUSIONS/SIGNIFICANCE

This study cautions the potential co-carcinogenic effect of nicotine in tobacco replacement therapies. We hypothesise that aberrant upregulation of FOXM1 may be inducing genomic instability through a program of malignant transformation involving the activation of CEP55 and HELLS which may facilitate aberrant mitosis and epigenetic modifications. Our finding that FOXM1 is upregulated early during oral cancer progression renders FOXM1 an attractive diagnostic biomarker for early cancer detection and its candidate mechanistic targets, CEP55 and HELLS, as indicators of malignant conversion and progression.