Is CD133 a marker of metastatic colon cancer stem cells?

Cancer stem cells: advances in knowledge and implications for cancer therapy

Cancer stem cells (CSCs), a small subset of cells in tumors that are characterized by self-renewal and continuous proliferation, lead to tumorigenesis, metastasis, and maintain tumor heterogeneity. Cancer continues to be a significant global disease burden. In the past, surgery, radiotherapy, and chemotherapy were the main cancer treatments. The technology of cancer treatments continues to develop and advance, and the emergence of targeted therapy, and immunotherapy provides more options for patients to a certain extent. However, the limitations of efficacy and treatment resistance are still inevitable. Our review begins with a brief introduction of the historical discoveries, original hypotheses, and pathways that regulate CSCs, such as WNT/β-Catenin, hedgehog, Notch, NF-κB, JAK/STAT, TGF-β, PI3K/AKT, PPAR pathway, and their crosstalk. We focus on the role of CSCs in various therapeutic outcomes and resistance, including how the treatments affect the content of CSCs and the alteration of related molecules, CSCs-mediated therapeutic resistance, and the clinical value of targeting CSCs in patients with refractory, progressed or advanced tumors. In summary, CSCs affect therapeutic efficacy, and the treatment method of targeting CSCs is still difficult to determine. Clarifying regulatory mechanisms and targeting biomarkers of CSCs is currently the mainstream idea.

Mattertronics for programmable manipulation and multiplex storage of pseudo-diamagnetic holes and label-free cells

Manipulating and separating single label-free cells without biomarker conjugation have attracted significant interest in the field of single-cell research, but digital circuitry control and multiplexed individual storage of single label-free cells remain a challenge. Herein, by analogy with the electrical circuitry elements and electronical holes, we develop a pseudo-diamagnetophoresis (PsD) mattertronic approach in the presence of biocompatible ferrofluids for programmable manipulation and local storage of single PsD holes and label-free cells. The PsD holes conduct along linear negative micro-magnetic patterns. Further, eclipse diode patterns similar to the electrical diode can implement directional and selective switching of different PsD holes and label-free cells based on the diode geometry. Different eclipse heights and junction gaps influence the switching efficiency of PsD holes for mattertronic circuitry manipulation and separation. Moreover, single PsD holes are stored at each potential well as in an electrical storage capacitor, preventing multiple occupancies of PsD holes in the array of individual compartments due to magnetic Coulomb-like interaction. This approach may enable the development of large programmable arrays of label-free matters with high throughput, efficiency, and reliability as multiplex cell research platforms.

Molecular pathology underlying the robustness of cancer stem cells

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

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Intratumoral heterogeneity driven by CSCs is responsible for therapeutic resistance.

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

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

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

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

A method to culture human alveolar rhabdomyosarcoma cell lines as rhabdospheres demonstrates an enrichment in stemness and Notch signaling

The development of three-dimensional cell culture techniques has allowed cancer researchers to study the stemness properties of cancer cells in in vitro culture. However, a method to grow PAX3-FOXO1 fusion-positive rhabdomyosarcoma (FP-RMS), an aggressive soft tissue sarcoma of childhood, has to date not been reported, hampering efforts to identify the dysregulated signaling pathways that underlie FP-RMS stemness. Here, we first examine the expression of canonical stem cell markers in human RMS tumors and cell lines. We then describe a method to grow FP-RMS cell lines as rhabdospheres and demonstrate that these spheres are enriched in expression of canonical stemness factors as well as Notch signaling components. Specifically, FP-RMS rhabdospheres have increased expression of SOX2, POU5F1 (OCT4), and NANOG, and several receptors and transcriptional regulators in the Notch signaling pathway. FP-RMS rhabdospheres also exhibit functional stemness characteristics including multipotency, increased tumorigenicity in vivo, and chemoresistance. This method provides a novel practical tool to support research into FP-RMS stemness and chemoresistance signaling mechanisms.

Summary: Here we report on a method to culture human PAX3-FOXO1 fusion-positive rhabdomyosarcoma cells in three dimensions, and use these rhabdospheres as a novel tool to study their stemness and chemoresistance signaling mechanisms.

Surface expression marker profile in colon cancer cell lines and sphere-derived cells suggests complexity in CD26+ cancer stem cells subsets

Taking advantage of eight established cell lines from colorectal cancer patients at different stages of the disease and the fact that all of them could form spheres, cell surface biomarkers of cancer stem cells and epithelial-mesenchymal transition were tested. The aim was to investigate cancer stem cells and metastatic stem cells in order to provide functional characterization of circulating tumor cells and promote the development of new anti-metastatic therapies. Our model showed an important heterogeneity in EpCAM, CD133, CD44, LGR5, CD26 and E-cadherin expression. We showed the presence of a subset of E-cadherin⁺ (some cells being E-cadherin^high) expressing CD26⁺ (or CD26^high) together with the well-known CSC markers LGR5 and EpCAM^high, sometimes in the absence of CD44 or CD133. The already described CD26⁺/E-cadherin^low or ^negative and CD26⁺/EpCAM⁻/CD133⁻ subsets were also present. Cell division drastically affected the expression of all markers, in particular E-cadherin, so new-born cells resembled mesenchymal cells in surface staining. CD26 and/or dipeptidyl peptidase 4 inhibitors have already shown anti-metastatic effects in pre-clinical models, and the existence of these CD26⁺ subsets may help further research against cancer metastasis.

Summary: In our model of eight established cell lines from colorectal cancer patients we show the presence of different putative cancer stem cell (CSC) subsets with expression of CD26/DPP4.

Replication Study: Wnt activity defines colon cancer stem cells and is regulated by the microenvironment

As part of the Reproducibility Project: Cancer Biology we published a Registered Report (Evans et al., 2015), that described how we intended to replicate selected experiments from the paper 'Wnt activity defines colon cancer stem cells and is regulated by the microenvironment' (Vermeulen et al., 2010). Here, we report the results. Using three independent primary spheroidal colon cancer cultures that expressed a Wnt reporter construct we observed high Wnt activity was associated with the cell surface markers CD133, CD166, and CD29, but not CD24 and CD44, while the original study found all five markers were correlated with high Wnt activity (Figure 2F; Vermeulen et al., 2010). Clonogenicity was highest in cells with high Wnt activity and clonogenic potential of cells with low Wnt activity were increased by myofibroblast-secreted factors, including HGF. While the effects were in the same direction as the original study (Figure 6D; Vermeulen et al., 2010) whether statistical significance was reached among the different conditions varied. When tested in vivo, we did not find a difference in tumorigenicity between high and low Wnt activity, while the original study found cells with high Wnt activity were more effective in inducing tumors (Figure 7E; Vermeulen et al., 2010). Tumorigenicity, however, was increased with myofibroblast-secreted factors, which was in the same direction as the original study (Figure 7E; Vermeulen et al., 2010), but not statistically significant. Finally, we report meta-analyses for each results where possible.

Soft Tissue Sarcoma Cancer Stem Cells: An Overview

Soft tissue sarcomas (STSs) are an uncommon group of solid tumors that can arise throughout the human lifespan. Despite their commonality as non-bony cancers that develop from mesenchymal cell precursors, they are heterogeneous in their genetic profiles, histology, and clinical features. This has made it difficult to identify a single target or therapy specific to STSs. And while there is no one cell of origin ascribed to all STSs, the cancer stem cell (CSC) principle—that a subpopulation of tumor cells possesses stem cell-like properties underlying tumor initiation, therapeutic resistance, disease recurrence, and metastasis—predicts that ultimately it should be possible to identify a feature common to all STSs that could function as a therapeutic Achilles' heel. Here we review the published evidence for CSCs in each of the most common STSs, then focus on the methods used to study CSCs, the developmental signaling pathways usurped by CSCs, and the epigenetic alterations critical for CSC identity that may be useful for further study of STS biology. We conclude with discussion of some challenges to the field and future directions.

Characterisation of mesenchymal colon tumour-derived cells in tumourspheres as a model for colorectal cancer progression

Cellular plasticity, the ability of cells to switch from an epitheial phenotype to a mesenchymal one and vice versa, plays a crucial role in tumour progression and metastases development. In 20-25% of patients with colon cancer and in 18% of patients with rectal cancer, metastases are present at the time of the first diagnosis. They are the first cause of colorectal cancer (CRC)-related mortality, defining stage IV CRC, which is characterized by a relatively short overall survival. We previously isolated two primary colon adenocarcinoma cell cultures that had undergone epithelial-mesenchymal transition (EMT), one with a high microsatellite instability phenotype (T88) and one with a chromosomal instability phenotype (T93). The aim of this study was to establish a model with which to study EMT, stemness features and cell plasticity in cancer progression and to examine the effects of incubation with lithium chloride (LiCl), a specific glycogen synthase kinase 3 β (GSK-3β) inhibitor, on these cellular processes. Indeed, GSK3β is an important regulator of cell survival, which promotes tumourigenesis in colon cells by facilitating the crosstalk between colorectal cancer pathways. Thus, we further characterized our system of adherent primary mesenchymal colon cancer cells and their paired tumourspheres by examining the expression and localisation of a panel of markers, including E- and N‑cadherin, CD133, CD44v6, aldehyde dehydrogenase 1 (ALDH1) and leucine-rich repeat‑containing G-protein coupled receptor 5 (LGR5). We also characterised the molecular features of these tumourspheres and examined their response to LiCl. Furthermore, we explored the effects of LiCl on cell motility and plasticity. We demonstrated that LiCl reduced cell migration, stemness features and cell plasticity. We also observed the atypical nuclear localisation of membrane proteins, including N‑cadherin, CD133 and CD44v6 in mesenchymal tumour cells. Of note, CD133 and CD44v6 appeared to localise at the plasma membrane in cells with a more epithelial phenotype, suggesting that the cytoplasmic/nuclear localisation of these proteins could favour and characterize cell plasticity in colorectal cancer progression.

Roles of microRNAs and RNA-Binding Proteins in the Regulation of Colorectal Cancer Stem Cells

Colorectal cancer stem cells (CSCs) are responsible for the initiation, progression and metastasis of human colorectal cancers, and have been characterized by the expression of cell surface markers, such as CD44, CD133, CD166 and LGR5. MicroRNAs (miRNAs) are differentially expressed between CSCs and non-tumorigenic cancer cells, and play important roles in the maintenance and regulation of stem cell properties of CSCs. RNA binding proteins (RBPs) are emerging epigenetic regulators of various RNA processing events, such as splicing, localization, stabilization and translation, and can regulate various types of stem cells. In this review, we summarize current evidences on the roles of miRNA and RBPs in the regulation of colorectal CSCs. Understanding the epigenetic regulation of human colorectal CSCs will help to develop biomarkers for colorectal cancers and to identify targets for CSC-targeting therapies.

The metastasis suppressor, NDRG1, inhibits "stemness" of colorectal cancer via down-regulation of nuclear β-catenin and CD44

N-myc downstream-regulated gene 1 (NDRG1), has been identified as an important metastasis suppressor for colorectal cancer (CRC). In this study, we investigated: (1) the effects of NDRG1 on CRC stemness and tumorigenesis; (2) the molecular mechanisms involved; and (3) the relationship between NDRG1 expression and colorectal cancer prognosis. Our investigation demonstrated that CRC cells with silenced NDRG1 showed more tumorigenic ability and stem cell-like properties, such as: colony and sphere formation, chemoresistance, cell invasion, high expression of CD44, and tumorigenicity in vivo. Moreover, NDRG1 silencing reduced β-catenin expression on the cell membrane, while increasing its nuclear expression. The anti-tumor activity of NDRG1 was demonstrated to be mediated by preventing β-catenin nuclear translocation, as silencing of this latter molecule could reverse the effects of silencing NDRG1 expression. NDRG1 expression was also demonstrated to be negatively correlated to CRC prognosis. In addition, there was a negative correlation between NDRG1 and nuclear β-catenin and also NDRG1 and CD44 expression in clinical CRC specimens. Taken together, our investigation demonstrates that the anti-metastatic activity of NDRG1 in CRC occurs through the down-regulation of nuclear β-catenin and suggests that NDRG1 is a significant therapeutic target.

Inhibition of c-Yes induces differentiation of HT-29 human colon cancer stem cells through midbody elongation

Recent research suggests that a small group of cells, named cancer stem cells (CSCs), is responsible for initiating tumor formation, recurrence, and metastasis. c-Yes, a proto-oncogene that is a subfamily of Src family kinase, is often activated in human colon cancer; this implicates c-Yes in the onset and progression of the disease. The objective of this study was to investigate the correlation between c-Yes and CSCs. We performed a sphere formation assay and reverse transcription-polymerase chain reaction for studying the differentiation of HT-29 human colon CSCs. To demonstrate the specific role of c-Yes in CSCs, we performed live cell microscopy and a cell cycle assay. These study shows, for the first time, that c-Yes is enriched in CD133⁺ CSCs, compared to their CD133^- counterparts, and that c-Yes depletion in CD133⁺ cells induces cell differentiation. Moreover, c-Yes depletion was found to elongate the midbody and increase the proliferation doubling time. This also suggested that the misregulation of microtubules during chromosomal separation causes aneuploidy. Our results suggest that c-Yes may play a crucial role in initiating, maintaining, and driving the tumorigenic property of colon cancer.

Cancer stem cells CD133 and CD24 in colorectal cancers in Northern Iran

AIM

We aimed to study the expression of CD24 and CD133 in colorectal cancer and normal adjacent tissues to assess a relationship between these markers and clinic-pathological characteristics and patient's survival.

BACKGROUND

Cancer stem cells are a group of tumor cells that have regeneration and multi-order differentiation capabilities.

PATIENTS AND METHODS

Expression of CD24 and CD133 was studied in a paraffin block of colorectal cancer and normal tissues near tumors with the immuneohistochemical method in patients who were referred to Imam Khomeini Hospital in Sari.

RESULTS

A total of 50 samples (25 males and 25 females) with a mean age of 67.57±13.9 years old with range 28-93 years, included 3 mucinous carcinoma and 47 adenocarcinoma. Expression of CD133 marker was negative in 29 cases and positive in 21 cases. Expression of CD24 in tissue near tumor cells was found in 30% of available samples. The relationship between expressing CD24 with treatment (surgery and chemotherapy) was significant and its relationship with patient's survival was insignificant statistically. However, there was a clear difference as mean survival age of patients based on CD24 expression was 26.64±18.15 for negative cases and 41.75±28.76 months for positive cases. CD24 and CD133 expressions and their co-expression with other clinic-pathological factors were not significant.

CONCLUSION

During this study, the relationship between CD24 and treatment type was significant. To confirm this result, various studies with high sample numbers and other stem cell markers are recommended.

Therapeutic strategies targeting cancer stem cells

Cancer stem cells (CSCs) are undifferentiated cancer cells with a high tumorigenic activity, the ability to undergo self-renewal, and a multilineage differentiation potential. Cancer stem cells are responsible for the development of tumor cell heterogeneity, a key feature for resistance to anticancer treatments including conventional chemotherapy, radiation therapy, and molecularly targeted therapy. Furthermore, minimal residual disease, the major cause of cancer recurrence and metastasis, is enriched in CSCs. Cancer stem cells also possess the property of "robustness", which encompasses several characteristics including a slow cell cycle, the ability to detoxify or mediate the efflux of cytotoxic agents, resistance to oxidative stress, and a rapid response to DNA damage, all of which contribute to the development of therapeutic resistance. The identification of mechanisms underlying such characteristics and the development of novel approaches to target them will be required for the therapeutic elimination of CSCs and the complete eradication of tumors. In this review, we focus on two prospective therapeutic approaches that target CSCs with the aim of disrupting their quiescence or redox defense capability.

B7H1 Expression and Epithelial-To-Mesenchymal Transition Phenotypes on Colorectal Cancer Stem-Like Cells

Cancer stem cells (CSCs) can invade and metastasize by epithelial-to-mesenchymal transition (EMT). However, how they escape immune surveillance is unclear. B7H1 is crucial negative co-stimulatory molecule but little information about whether it works in CSCs. Therefore, we determined the expression of B7H1 and EMT-associated markers in colorectal cancer stem-like cells to investigate a possible immunoevasion way of CSCs. We enriched CD133+ colorectal cancer cells which manifested the CSCs-like properties such as higher levels of other stem cell markers Oct-4 and Sox-2, tumor sphere forming ability and more tumorigenic in NOD/SCID mice. These CD133+ cells possess EMT gene expression profile including higher level of Snail, Twist, vimentin, fibronectin and lower level of E-cadherin. Moreover, CD133+ cells in both cell line and colorectal cancer tissues expressed high level of negative co-stimulate molecule B7H1. Furthermore, some B7H1+ cancer cells also showed the characteristic of EMT, indicating EMT cells could escape immune attack during metastasis. B7H1 expression and EMT phenotypes on CSCs indicates a possible immunoevasion way.

Metastatic colon cancer cell populations contain more cancer stem-like cells with a higher susceptibility to natural killer cell-mediated lysis compared with primary colon cancer cells

In the present study, the soft agar clonogenicity and the susceptibility of clonogenic cancer cells to natural killer (NK) cells were compared between primary colon cancer cells (KM12C) and metastatic colon cancer cells (KM12L4a and KM12SM) to determine whether the metastatic cancer cells consisted of more cancer stem-like cells and were resistant to NK cell-mediated lysis. The majority of colon cancer cells were positive for putative cancer stem cell markers, including CD44, CD133 and EpCAM, with the exception of KM12C cells, of which only ~55% were positive for CD133. In addition, the expression levels of sex determining region Y-box 2, Nanog and octamer-binding transcription factor 4, which are essential for maintaining self-renewal, were higher in KM12L4a and KM12SM compared with that in KM12C cells. Consistently, an increased clonogenicity of KM12L4a and KM12SM compared with KM12C cells in soft agar was observed. The expression levels of NKG2D ligands, including major histocompatibility complex class I polypeptide-related sequence A/B and UL16 binding protein 2, and of death receptor 5 were significantly higher in KM12L4a and KM12SM than in KM12C cells. Furthermore, the results indicated an increased susceptibility of KM12L4a and KM12SM to NK cell-mediated cytotoxicity in comparison with KM12C cells. These results indicated that metastatic colon cancer cell populations may consist of more cancer stem-like cells, and have greater susceptibility to NK cell-mediated lysis compared with that of primary colon cancers.

Prominin-1 (CD133, AC133) and dipeptidyl-peptidase IV (CD26) are indicators of infinitive growth in colon cancer cells

Advanced colorectal cancer is characterized by uncontrolled growth and resistance against anti-cancer agents, including ErbB inhibitors. Recent data suggest that cancer stem cells (CSC) are particularly resistant. These cells may reside within a CD133+ fraction of the malignant cells. Using HCT116 cells we explored the role of CD133 and other CSC markers in drug resistance in colon cancer cells. CD133+ cells outnumbered CD133- cells over time in long-term culture. Both populations displayed the KRAS mutation 38G > A and an almost identical target profile, including EGFR/ErbB1, ErbB2, and ErbB4. Microarray analyses and flow cytometry identified CD26 as additional CSC marker co-expressed on CD133+ cells. However, knock-down of CD133 or CD26 did not affect short-term growth of HCT116 cells, and both cell-populations were equally resistant to various targeted drugs except irreversible ErbB inhibitors, which blocked growth and ERK1/2 phosphorylation in CD133- cells more efficiently than in CD133+ cells. Moreover, the MEK inhibitor AS703026 was found to overcome resistance against ErbB blockers in CD133+ cells. Together, CD133 and CD26 are markers of long-term growth and resistance to ErbB blockers in HCT116 cells, which may be mediated by constitutive ERK activity.

CD58, a novel surface marker, promotes self-renewal of tumor-initiating cells in colorectal cancer

Colorectal tumor-initiating cells (CT-ICs) have self-renewal capabilities and have an important role in tumorigenesis, metastasis, recurrence and treatment resistance in colorectal cancer. Multiple cell-surface molecules targeting CT-ICs, possibly representing different CT-IC subpopulations, have been reported. However, whether new surface markers exist, as well as the mechanisms by which the markers regulate self-renewal, remain unclear. In this study, we enriched a CT-IC population through a serum-free low-adhesion system in vitro. Within this population, we found that CD58 and CD44 were upregulated using a cDNA GeneChip, and CD44(high)CD58(high) cancer cells, the common existence of which was demonstrated by flow cytometry in multiple colon cancer cell lines and primary specimens, exhibited enhanced self-renewal ability, epithelial-mesenchymal transition ability and tumorigenicity, both in vitro and in vivo. Furthermore, activated CD58 upregulated the Wnt/β-catenin pathway and thus promoted self-renewal of CT-ICs; conversely, knockdown of CD58 significantly impaired sphere formation and tumor growth. With immunoprecipitation and western blotting approaches, CD58 was found to upregulate the Wnt pathway by degradation of Dickkopf 3. These results indicate that CD58 is a novel cell-surface marker that functionally regulates self-renewal of CT-ICs, which may provide an intriguing therapeutic target for the efficient killing and elimination of CT-ICs.

Cancer Stem Cell Markers CD44, CD133 in Primary Gastric Adenocarcinoma

Cancer stem cells (CSCs) are unique subpopulations that have the capacity to drive malignant progression with renewal abilities. Recently the role of some of CSCs in gastric adenocarcinoma has been studied. This study was performed in order to evaluate CD44 and CD133 expressions by immunohistochemistry in 95 primary gastric adenocarcinoma and their relation to clinical and pathological parameters of these tumors. There was a significant correlation between CD44 expression and cancer subtype (intestinal), tumor size (4-8 cm), depth of invasion, no lymphatic/vascular invasion and moderate differentiation. There was a significant correlation between CD133 expression and patient's age (> 65 years), cancer subtype (intestinal), tumor size (4-8 cm), depth of invasion and moderate differentiation. CSC markers like CD 44 and CD133 had high expression in primary gastric adenocarcinoma and had some relations to clinical and pathological parameters of tumors.

A comprehensive promoter landscape identifies a novel promoter for CD133 in restricted tissues, cancers, and stem cells

PROM1 is the gene encoding prominin-1 or CD133, an important cell surface marker for the isolation of both normal and cancer stem cells. PROM1 transcripts initiate at a range of transcription start sites (TSS) associated with distinct tissue and cancer expression profiles. Using high resolution Cap Analysis of Gene Expression (CAGE) sequencing we characterize TSS utilization across a broad range of normal and developmental tissues. We identify a novel proximal promoter (P6) within CD133⁺ melanoma cell lines and stem cells. Additional exon array sampling finds P6 to be active in populations enriched for mesenchyme, neural stem cells and within CD133⁺ enriched Ewing sarcomas. The P6 promoter is enriched with respect to previously characterized PROM1 promoters for a HMGI/Y (HMGA1) family transcription factor binding site motif and exhibits different epigenetic modifications relative to the canonical promoter region of PROM1.

Drug-resistant colon cancer cells produce high carcinoembryonic antigen and might not be cancer-initiating cells

Purpose

We evaluated the higher levels of carcinoembryonic antigen (CEA) secreted by the LoVo human colon carcinoma cells in a medium containing anticancer drugs. Drug-resistant LoVo cells were analyzed by subcutaneously xenotransplanting them into mice. The aim of this study was to evaluate whether the drug-resistant cells isolated in this study were cancer-initiating cells, known also as cancer stem cells (CSCs).

Methods

The production of CEA was investigated in LoVo cells that were cultured with 0–10 mM of anticancer drugs, and we evaluated the increase in CEA production by the LoVo cells that were stimulated by anticancer drug treatment. The expression of several CSC markers in LoVo cells treated with anticancer drugs was also evaluated. Following anticancer drug treatment, LoVo cells were injected subcutaneously into the flanks of severe combined immunodeficiency mice in order to evaluate the CSC fraction.

Results

Production of CEA by LoVo cells was stimulated by the addition of anticancer drugs. Drug-resistant LoVo cells expressed lower levels of CSC markers, and LoVo cells treated with any of the anticancer drugs tested did not generate tumors within 8 weeks from when the cells were injected subcutaneously into severe combined immunodeficiency mice. These results suggest that the drug-resistant LoVo cells have a smaller population of CSCs than the untreated LoVo cells.

Conclusion

Production of CEA by LoVo cells can be stimulated by the addition of anticancer drugs. The drug-resistant subpopulation of LoVo colon cancer cells could stimulate the production of CEA, but these cells did not act as CSCs in in vivo tumor generation experiments.

In vitro and in vivo properties of CD133 expressing cells from human lung cancer cell lines

Background

Tumor development is recently hypothesized to depend on a rare cell population with stem cell properties, such cells are called cancer stem cells (CSCs) or tumor-initiating cells (TICs). From various cancer tissues or cancer cell lines, CD133 expressing cells were found to define a unique CSC/TIC phenotype. To study whether that also could be the case in lung cancer, we examined different lung cancer cell lines for CD133 expression.

Results

Among the 4 cell lines studied, only the cell line LC-42 expressed CD133. Therefore, LC-42 was further characterized and studied with special emphasis on identifying the presence of CD133⁺ CSCs/TICs. FACS sorted CD133^high and CD133^dim subpopulations from LC-42 showed no differences in soft agar colony-forming capacity and spheres-forming capacity in serum-free cultures. LC-42 cells contained Side Population (SP), and only SP cells were able to form spheres. Furthermore, Nanog expression was significantly higher in SP than in non-SP. However, no difference was observed of CD133 expression in SP and non-SP. When CD133^high and CD133^dim cells were serially xeno-transplanted in NOD/SCID mice, both formed tumours similar to their parental LC-42 cells. There were no expression differences for NANOG, OCT4 and SOX2 examined immunohistochemically in the xenografts from both cell fractions.

Conclusion

Our data do not show a difference in tumorigenic potential of CD133^high and CD133^dim cells with respect to any of the parameters analyzed in vitro and in vivo, suggesting that CD133 expression is not restricted to cancer-initiating cells in the human lung cancer cell line LC-42.

CD133: A cancer stem cells marker, is used in colorectal cancers

Colorectal cancer is one of the most common malignant tumors worldwide. A model of cancer development involving cancer stem cells has been put forward because it provides a possible explanation of tumor hierarchy. Cancer stem cells are characterized by their proliferation, tumorigenesis, differentiation, and self-renewal capacities, and chemoradiotherapy resistance. Due to the role of cancer stem cells in tumor initiation and treatment failure, studies of cancer stem cell markers, such as CD133, have been of great interest. CD133, a five-transmembrane glycoprotein, is widely used as a marker to identify and isolate colorectal cancer stem cells. This marker has been investigated to better understand the characteristics and functions of cancer stem cells. Moreover, it can also be used to predict tumor progression, patient survival, chemoradiotherapy resistance and other clinical parameters. In this review, we discuss the use of CD133 in the identification of colorectal cancer stem cell, which is currently controversial. Although the function of CD133 is as yet unclear, we have discussed several possible functions and associated mechanisms that may partially explain the role of CD133 in colorectal cancers. In addition, we focus on the prognostic value of CD133 in colorectal cancers. Finally, we predict that CD133 may be used as a possible target for colorectal cancer treatment.

Cancer stem cell markers in head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is one of the world's top ten most common cancers. Current survival rates are poor with only 50% of patients expected to survive five years after diagnosis. The poor survival rate of HNSCC is partly attributable to the tendency for diagnosis at the late stage of the disease. One of the reasons for treatment failure is thought to be related to the presence of a subpopulation of cells within the tumour called cancer stem cells (CSCs). CSCs display stem cell-like characteristics that impart resistance to conventional treatment modalities and promote tumour initiation, progression, and metastasis. Specific markers for this population have been investigated in the hope of developing a deeper understanding of their role in the pathogenesis of HNSCC and elucidating novel therapeutic strategies.

Rapid re-expression of CD133 protein in colorectal cancer cell lines in vitro and in vivo

Studies related to the cancer stem cell hypothesis are challenging because of the imperfect tools to identify cell populations of interest and controversy on the usefulness of established cancer cell lines. We previously found CD133 to not be selective for a tumor-propagating or radioresistant population in a near-diploid, microsatellite-instable colorectal carcinoma (CRC) cell line. Because of discrepant literature data, we herein systematically analyzed the behavior of microsatellite-stable cell line subpopulations reflecting the more frequent carcinogenesis pathway in spontaneous CRC. CD133⁺ and CD133(-/low) populations were isolated by fluorescence-activated cell sorting and further processed. HT29 and SW620 cells were studied in detail in monolayer and/or spheroid culture assays and upon subcutaneous injection in NMRI (nu/nu) mice using a limiting dilution approach. CD133(-/low) HT29 cells showed a significantly lower clonogenic survival and reduced spheroid formation capacity than their CD133⁺ counterparts. However, the cell populations neither differed in growth kinetics and response to treatment in vitro nor in tumor formation capacity when injecting as low as 10 cells. CD133(-/low) HT29 cells rapidly re-expressed CD133 protein in vitro and in vivo as shown by flow cytometry and/or western blot analyses, and they also showed a particular survival benefit under tissue normoxic conditions. In contrast, CD133 protein in the CD133⁺ population was quite stable throughout culturing. The observation of CD133 re-expression and lack of difference in tumor take rate of subpopulations was confirmed in SW620 cells. Here, we found cell density to affect CD133 re-expression in the CD133(-)-sorted population. And even SW480 cells, classified as a CD133⁻ cell line, presented some CD133 protein on their surface upon in vivo engraftment. We conclude that (i) CD133 protein expression shows high plasticity in CRC cell lines, and (ii) in vitro CD133 status on the cell surface neither determines tumorigenic potential nor CD133 profile in vivo.

A tumor hypoxic niche protects human colon cancer stem cells from chemotherapy

PURPOSE

Hypoxia has been found to play an important role in regulating the biological characteristics of cancer stem cells (cCSCs). In this study, we tested whether a tumor hypoxic niche serves to the chemotherapeutic resistance of colon cCSCs.

METHODS

Each of 23 fresh samples of human colon adenocarcinoma was transplanted into nude mice. The tumor-bearing mice randomly and equally received (A) saline, (B) 5-fluorouracil (15 mg/kg), (C) oxaliplatin (10 mg/kg), and (D) oxaliplatin plus 5-fluorouracil when xenografts reached 250 mm(3) (n = 10). After 2-week treatment, tumor cells were quantified by flow cytometry for expression of CD133 and the hypoxic proportion of CD133(+) and CD133(-) cells which were also sorted and detected for ki67 and pimonidazole via immunofluorescence.

RESULTS

The hypoxic subpopulation of CD133(+) and CD133(-) cells was 66.5 and 26.4 %, respectively. Although there was no marked change for the hypoxic subpopulation of CD133(+) cells after treatment, the hypoxic fraction of proliferative CD133(+) cells was increased by 14.62, 16.45, and 20.46 % in groups B, C, and D, respectively. Furthermore, proliferative cells in CD133(+) and CD133(-) cells were reduced by 29.93 and 62.5 % in group C, and by 25.26 and 68.22 % in group D; in group B, however, the proliferative CD133(+) cells were increased by 37.09 %; the CD133(-) cells were unchanged.

CONCLUSIONS

Most CD133(+) cCSCs are located in a hypoxic niche, where cCSCs are better at retaining proliferating property under chemotherapy. Oxaliplatin, rather than 5-FU, inhibits proliferation of cCSCs, which may be the mechanism underlying a better outcome by oxaliplatin in colon cancer patients.

CD133(+)CXCR4(+) colon cancer cells exhibit metastatic potential and predict poor prognosis of patients

BACKGROUND

Colorectal cancer (CRC), which frequently metastasizes to the liver, is one of the three leading causes of cancer-related deaths worldwide. Growing evidence suggests that a subset of cells exists among cancer stem cells. This distinct subpopulation is thought to contribute to liver metastasis; however, it has not been fully explored in CRC yet.

METHODS

Flow cytometry analysis was performed to detect distinct subsets with CD133 and CXCR4 markers in human primary and metastatic CRC tissues. The 'stemness' and metastatic capacities of different subpopulations derived from the colon cancer cell line HCT116 were compared in vitro and in vivo. The roles of epithelial-mesenchymal transition (EMT) and stromal-cell derived factor-1 (SDF-1) in the metastatic process were also investigated. A survival curve was used to explore the correlation between the content of CD133(+)CXCR4(+) cancer cells and patient survival.

RESULTS

In human specimens, the content of CD133(+)CXCR4(+) cells was higher in liver metastases than in primary colorectal tumors. Clonogenic and tumorigenic cells were restricted to CD133(+) cells in the HCT116 cell line, with CXCR4 expression having no impact on the 'stemness' properties. We found that CD133(+)CXCR4(+)cancer cells had a high metastatic capacity in vitro and in vivo. Compared with CD133(+)CXCR4(-) cells, CD133(+)CXCR4(+)cancer cells experienced EMT, which contributed partly to their metastatic phenotype. We then determined that SDF-1/CXCL12 treatment could further induce EMT in CD133(+)CXCR4(+)cancer cells and enhance their invasive behavior, while this could not be observed in CD133(+)CXCR4- cancer cells. Blocking SDF-1/CXCR4 interaction with a CXCR4 antagonist, AMD3100 (1,10-[1,4-phenylenebis(methylene)]bis-1,4,8,11 -tetraazacyclotetradecane octahydrochloride), inhibited metastatic tumor growth in a mouse hepatic metastasis model. Finally, a high percentage of CD133(+)CXCR4(+)cells in human primary CRC was associated with a reduced two-year survival rate.

CONCLUSIONS

Strategies targeting the SDF-1/CXCR4 interaction may have important clinical applications in the suppression of colon cancer metastasis. Further investigations on how high expression of CXCR4 and EMT occur in this identified cancer stem cell subset are warranted to provide insights into our understanding of tumor biology.

Correlation of aberrant expression of CD133 with FHIT and malignant phenotype of colorectal adenocarcinoma

BACKGROUND

The relationship between the expression of CD133 and fragile histidine triad (FHIT) or prognosis in Chinese colorectal adenocarcinoma is unknown and needs to be explored.

MATERIAL AND METHODS

The samples of colorectal adenocarcinoma from 200 Chinese patients with follow-up were analyzed for the expression of CD133 and FHIT proteins by immunohistochemical method.

RESULTS

CD133 was highly expressed in up to 42.0%(84/200) of this group of colorectal adenocarcinomas. The expression of CD133 was significantly higher in carcinoma than in normal (P=0.0001) and in adenomatous mucosas (P=0.004). CD133 positively corresponds to histological grade, clinical stage, regional lymphatic metastasis, and distant metastasis (all P<0.05). The mean overall survival time was shorter in patients with CD133 high expression than in those with CD133 low expression (P00.0001). The expression of CD133 was inversely correlative with that of FHIT (r=-0.464, P=0.0001) in colorectal adenocarcinoma. CD133 was an independent prognostic factor (P=0.0001).

CONCLUSIONS

The expression of CD133 may be inversely correlated with the expression of FHIT. It is suggested that CD133 may play an important role in the evolution of colorectal adenocarcinoma and be considered as a potential marker for the prognosis.

Cornering metastases: therapeutic targeting of circulating tumor cells and stem cells

The last decade has witnessed an evolution of our understanding of the biology of the metastatic cascade. Recent insights into the metastatic process show that it is complex, dynamic, and multi-directional. This process starts at a very early stage in the natural history of solid tumor growth leading to early development of metastases that grow in parallel with the primary tumor. The role of stem cells in perpetuating cancer metastases is increasingly becoming more evident. At the same time, there is a growing recognition of the crucial role circulating tumor cells (CTCs) play in the development of metastases. These insights have laid the biological foundations for therapeutic targeting of CTCs, a promising area of research that aims to reduce cancer morbidity and mortality by preventing the development of metastases at a very early stage. The hematogenous transport phase of the metastatic cascade provides critical access to CTCs for therapeutic targeting aiming to interrupt the metastatic process. Recent advances in the fields of nanotechnology and microfluidics have led to the development of several devices for in vivo targeting of CTC during transit in the circulation. Selectin-coated tubes that target cell adhesion molecules, immuno-magnetic separators, and in vivo photo-acoustic flow cytometers are currently being developed for this purpose. On the pharmacological front, several pharmacological and immunological agents targeting cancer stem cells are currently being developed. Such agents may ultimately prove to be effective against circulating tumor stem cells (CTSCs). Although still in its infancy, therapeutic targeting of CTCs and CTSCs offers an unprecedented opportunity to prevent the development of metastasis and potentially alter the natural history of cancer. By rendering cancer a "local" disease, these approaches could lead to major reductions in metastasis-related morbidity and mortality.

Sarcoma stem cells: do we know what we are looking for?

Sarcomas represent a heterogeneous group of cancers thought to originate from malignant transformation of mesenchymal cells. There is increasing evidence that many, if not all, sarcomas contain within them tumor-initiating, or "cancer stem," cells responsible for the initiation, maintenance, and potentially relapse and metastasis of the tumor. Various techniques have been adopted in recent years to identify putative sarcoma stem cell populations. The goal of this paper is to summarize the criteria used to identify a stem cell population, describe the more prominent markers and techniques used to isolate cancer stem cells in sarcomas, and review the evidence for the existence of cancer stem cells in sarcomas.

CD133 and CD44 are universally overexpressed in GIST and do not represent cancer stem cell markers

Although imatinib mesylate has been a major breakthrough in the treatment of advanced gastrointestinal stromal tumors (GIST), complete responses are rare and most patients eventually develop resistance to the drug. Thus, the possibility of an imatinib-insensitive cell subpopulation within GIST tumors, harboring stem cell characteristics, may be responsible for the clinical failures. However, the existence of a cancer stem cell component in GIST has not been yet established. This study was aimed to determine whether expression of commonly used stem cell markers in other malignancies, that is, CD133 and CD44, might identify cells with characteristics of cancer stem/progenitor cells in human GIST. CD133 and CD44 expression in GIST explants was analyzed by flow cytometry, immunofluorescence, and gene expression. Their transcription levels were correlated with clinical and molecular factors in a large, well-annotated cohort of GIST patients. FACS sorted GIST cells based on CD133 and CD44 expression were isolated and used to assess phenotypic characteristics, ability to maintain their surface expression, sensitivity to imatinib, and expression signature. The enrichment in CD133/CD44 cells in the side population (SP) assay was also investigated. CD133 expression was consistently found in GIST. CD133(-) cells formed more colonies, were more invasive in a matrigel assay, and showed enrichment in the SP cells, compared to CD133(+) cells. CD133 expression was also detected in the two imatinib-sensitive GIST cell lines, while was absent in the imatinib-resistant lines. Our results show that CD133 and CD44 are universally expressed in GIST, and may represent a lineage rather than a cancer stem cell marker.

APOBEC3G promotes liver metastasis in an orthotopic mouse model of colorectal cancer and predicts human hepatic metastasis

Colorectal cancer is the second leading cause of death from cancer in the United States. Metastases in the liver, the most common metastatic site for colorectal cancer, are found in one-third of the patients who die of colorectal cancer. Currently, the genes and molecular mechanisms that are functionally critical in modulating colorectal cancer hepatic metastasis remain unclear. Here, we report our studies using functional selection in an orthotopic mouse model of colorectal cancer to identify a set of genes that play an important role in mediating colorectal cancer liver metastasis. These genes included APOBEC3G, CD133, LIPC, and S100P. Clinically, we found these genes to be highly expressed in a cohort of human hepatic metastasis and their primary colorectal tumors, suggesting that it might be possible to use these genes to predict the likelihood of hepatic metastasis. We have further revealed what we believe to be a novel mechanism in which APOBEC3G promotes colorectal cancer hepatic metastasis through inhibition of miR-29-mediated suppression of MMP2. Together, our data elucidate key factors and mechanisms involved in colorectal cancer liver metastasis, which could be potential targets for diagnosis and treatment.

Genome and transcriptome profiles of CD133-positive colorectal cancer cells

Colorectal carcinomas (CRC) might be organized hierarchically and contain a subpopulation of tumorigenic, putative cancer stem cells that are CD133 positive. We studied the biological and genetic characteristics of such cells in CRC cell lines and primary tumors. Three CRC cell lines were sorted in CD133 positive and negative fractions. The respective genetic aberration profiles were studied using array comparative genomic hybridization (aCGH) and expression profiling. Tumorigenicity for each cellular population was tested by injection into nude mice. Additionally, we compared CD133+ and CD133- cells of 12 primary colorectal tumors using laser capture microdissection and aCGH. Three of five CRC cell lines displayed both CD133+ and CD133- cells, but tumorigenicity of these subfractions did not differ significantly and aCGH revealed essentially identical genomic imbalances. However, 96 genes were differentially expressed between the two populations. Array comparative genomic hybridization analysis after laser capture microdissection of CD133+ and CD133- areas in primary colorectal tumors revealed genetic differences in 7 of 12 cases. The use of cell lines for studying genomic alterations that define cancer stem cell characteristics, therefore, seems questionable. In contrast, CD133+ cells in primary cancer samples showed a unique genomic aberration profile. In conclusion, our data suggest that CD133 positivity defines a genetically distinct cellular compartment in primary CRC, which potentially includes tumor initiating cells.

Cancer stem cell subsets and their relationships

Emerging evidence suggests that cancer stem cells account for the initiation and progression of cancer. While many types of cancer stem cells with specific markers have been isolated and identified, a variety of differences among them began to be appreciated. Cancer stem cells are hierarchical populations that consist of precancerous stem cells, primary cancer stem cells, migrating cancer stem cells and chemoradioresistant cancer stem cells, playing different roles in cancer initiation and progression. Here we propose a new concept "horizontal hierarchy of cancer stem cells" to distinguish them from vertical hierarchy cancer stem cells, cancer transient-amplifying cells and cancer differentiated cells, and summarize our current understanding of these subsets of cancer stem cells with the aim to open up novel therapeutic strategies for cancer based on this understanding.

The Notch ligand Jagged2 promotes lung adenocarcinoma metastasis through a miR-200-dependent pathway in mice

Epithelial tumor cells transit to a mesenchymal state in response to extracellular cues, in a process known as epithelial-to-mesenchymal transition (EMT). The precise nature of these cues has not been fully defined, an important issue given that EMT is an early event in tumor metastasis. Here, we have found that a population of metastasis-prone mouse lung adenocarcinoma cells expresses Notch and Notch ligands and that the Notch ligand Jagged2 promotes metastasis. Mechanistically, Jagged2 was found to promote metastasis by increasing the expression of GATA-binding (Gata) factors, which suppressed expression of the microRNA-200 (miR-200) family of microRNAs that target the transcriptional repressors that drive EMT and thereby induced EMT. Reciprocally, miR-200 inhibited expression of Gata3, which reversed EMT and abrogated metastasis, suggesting that Gata3 and miR-200 are mutually inhibitory and have opposing effects on EMT and metastasis. Consistent with this, high levels of Gata3 expression correlated with EMT in primary tumors from 2 cohorts of lung adenocarcinoma patients. These findings reveal what we believe to be a novel Jagged2/miR-200-dependent pathway that mediates lung adenocarcinoma EMT and metastasis in mice and may have implications for the treatment of human epithelial tumors.

Tumour-initiating stem-like cells in human prostate cancer exhibit increased NF-κB signalling

Androgen depletion is a key strategy for treating human prostate cancer, but the presence of hormone-independent cells escaping treatment remains a major therapeutic challenge. Here, we identify a minor subset of stem-like human prostate tumour-initiating cells (TICs) that do not express prostate cancer markers, such as androgen receptor or prostate specific antigen. These TICs possess stem cell characteristics and multipotency as demonstrated by in vitro sphere-formation and in vivo tumour-initiation, respectively. The cells represent an undifferentiated subtype of basal cells and can be purified from prostate tumours based on coexpression of the human pluripotent stem cell marker TRA-1-60 with CD151 and CD166. Such triple-marker-positive TICs recapitulate the original parent tumour heterogeneity in serial xeno-transplantations indicating a tumour cell hierarchy in human prostate cancer development. These TICs exhibit increased nuclear factor-κB activity. These findings are important in understanding the molecular basis of human prostate cancer.

Tumours consist of heterogeneous cell types that respond differently to treatment. Here, on the basis of the expression of three different proteins, the authors describe a subset of prostate cancer cells that have stem cell-like properties that are able to initiate tumour formation in vivo.

Proliferation characteristics of CD133+ cell population in colorectal cancer

In this study, CD133+ subpopulations were isolated from 41 primary colorectal cancer tissues, the proliferation and cell cycle distribution of the cells were examined without in vitro expansion, and then compared to those of cell lines. The detection of CD133 in colorectal cancer tissues, isolation of CD133+ and CD133- epithelial subpopulations, Ki-67/DNA multiparameter assay and cell volume analysis were flow cytometrically conducted. The results showed that Ki-67 expression was correlated with CD133 level in primary cancer tissues, while cell cycle G2/M phase distribution or clinicopathological characteristics was not. In addition, the CD133+ cells showed larger cell volume and higher Ki-67 expression as compared with CD133- cells. But there was no statistically significant difference in G(2)/M phase distribution between the two subpopulations. Our results demonstrated that the CD133+ subpopulation in colorectal cancer tissue contained more actively cycling and proliferating cells, which was not correlated to clinicopathological factors but might contribute to tumor progression and poor clinical outcome.

A single intravenous injection of oncolytic picornavirus SVV-001 eliminates medulloblastomas in primary tumor-based orthotopic xenograft mouse models

Difficulties of drug delivery across the blood-brain barrier (BBB) and failure to eliminate cancer stem cells (CSCs) are believed to be the major causes of tumor recurrences in children with medulloblastoma (MB). Seneca Valley virus-001 (SVV-001) is a naturally occurring oncolytic picornavirus that can be systemically administered. Here, we report its antitumor activities against MB cells in a panel of 10 primary tumor-based orthotopic xenograft mouse models. We found that SVV-001 killed the primary cultured xenograft cells, infected and replicated in tumor cells expressing CSC surface marker CD133, and eliminated tumor cells capable of forming neurospheres in vitro in 5 of the 10 xenograft models. We confirmed that SVV-001 could pass through BBB in vivo. A single i.v. injection of SVV-001 in 2 anaplastic MB models led to widespread infection of the preformed intracerebellar (ICb) xenografts, resulting in significant increase in survival (2.2-5.9-fold) in both models and complete elimination of ICb xenografts in 8 of the 10 long-term survivors. Mechanistically, we showed that the intracellular replication of SVV-001 is mediated through a subverted autophagy that is different from the bona fide autophagic process induced by rapamycin. Our data suggest that SVV-001 is well suited for MB treatment. This work expands the current views in the oncolytic therapy field regarding the utility of oncolytic viruses in simultaneous targeting of stem and nonstem tumor cells.

Overexpression of CD133 promotes drug resistance in C6 glioma cells

Glioblastoma multiforme is an extremely aggressive and clinically unresponsive form of cancer. Transformed neoplastic neural stem cells, resistant to chemotherapy and radiation therapy, are thought to be responsible for the initial tumor formation and the recurrence of disease following surgical resection. These stem cells express multidrug resistance markers along with CD133. We show that ectopic overexpression of CD133 in rat C6 glioma cells leads to significant reluctance to undergo apoptosis from camptothecin and doxorubicin. Although p53 was upregulated in CD133-overexpressing glioma cells treated with DNA-damaging agents, apoptosis seems to be p53 independent. At least one ABC transporter, rat P-glycoprotein/ABCB1, was upregulated by 62% in CD133(+) cells with a corresponding increase in activity. Thus, the combination of higher P-glycoprotein mRNA transcription and elevated transporter activity seems to contribute to the protection from cytotoxic reagents. In conclusion, previous investigators have reported that resilient cancer stem cells coexpress CD133 and ABC transporters with increased reluctance toward apoptosis. Our data suggest that CD133 may contribute to the observed resistance to apoptosis of CD133(+) cancer stem cells.

CD133(+) single cell-derived progenies of colorectal cancer cell line SW480 with different invasive and metastatic potential

Single cell progenies (SCPs) inherit biological properties from their isogenetic mother cells. If a single cancer cell can give rise to progenies, which can be passaged sustainably in vitro and produce tumor in xenotransplantation, the cell should be cancer initiating cell. CD133 (Prominin-1, Prom1) is the marker of human colorectal cancer (CRC) stem cells and probably a marker of metastatic cancer stem cells (CSCs). Thirty-three SCPs of CRC cell line SW480 were isolated by limited dilution methods, thirty of which are CD133 positive and three negative. All of the CD133(+) SCPs are tumorigenic, and the subcutaneous tumors expanded rapidly, while only 1 of 3 CD133(-) SCPs developed a minimal tumor in nude mice. Orthotopic transplantation experiments showed that CD133(+) SCPs possessed heterogeneity in intestinal wall invasion, lymph node and liver metastases. CD133(+) SCPs varied in cell growth, invasive ability, epithelial-mesenchymal-transition and expression of CSCs markers (CD133, CD44, and CXCR4) associated with metastatic potential. CD133(-) SCPs did not produce secondary transplanted tumor, intestinal invasion and metastasis. The results indicated CD133(+) subpopulation of SW480 SCPs bear heterogeneous invasive and metastatic ability, and CRC-CSCs might be a heterogeous subpopulation.

The difficulty of targeting cancer stem cell niches

Normal stem cell niches typically are identified by their distinctive anatomical features and by association with tissue-specific stem cells. Identifying cancer stem cell (CSC) niches presents a special problem because there are few if any common anatomical features among tumors, and the physical phenotypes that reportedly describe the CSCs as entities may be subject to the host's microenvironment, sex, and tumor stage. Irrespective of a niche's location, the occupant's phenotype, or the precise molecular composition, all niches must do basically the same thing: maintain the activities in a stem cell that define it as such. Therefore, a potentially successful strategy, both for elaborating a molecular and cellular portrait of a CSC niche, and for therapeutically targeting them, is to identify components in the tumor microenvironment that are required for maintaining the functions of self-renewal, differentiation, and quiescence in the face of cytotoxic therapeutic regimens.

Aberrant expression of CD133 protein correlates with Ki-67 expression and is a prognostic marker in gastric adenocarcinoma

Background

The relationships between the expression of CD133, Ki-67 and prognosis in gastric adenocarcinoma are unknown and needs exploring.

Methods

The samples of gastric adenocarcinoma from 336 Chinese patients with follow-up were analyzed for CD133 and Ki-67 protein expressions by immunohistochemical method.

Results

CD133 was expressed in up to 57.4% (193/336) of this group of gastric carcinoma. The expression of CD133 was significantly higher in carcinoma than in normal (P = 0.0001) and dysplastic mucosas (P = 0.004). CD133 was positive corresponded with the tumour size, grade, infiltrative depth and clinical stage (all P < 0.05). The overall mean survival time of the patients with CD133 positive expression was shorter than that of patients with negative expression (P = 0.0001). The expression of CD133 has a positive correlation with that of Ki-67 (r = 0.188, P = 0.001) in gastric adenocarcinoma. CD133 was an independent prognostic indicator. (P = 0.0001).

Conclusions

It is suggested that CD133 may play an important role in the evolution of gastric adenocarcinoma and should be considered as a potential marker for the prognosis.

Role of oxidative stress in stem, cancer, and cancer stem cells

The term ‘‘oxidative stress” refers to a cell’s state characterized by excessive production of reactive oxygen species (ROS) and oxidative stress is one of the most important regulatory mechanisms for stem, cancer, and cancer stem cells. The concept of cancer stem cells arose from observations of similarities between the self-renewal mechanism of stem cells and that of cancer stem cells, but compared to normal stem cells, they are believed to have no control over the cell number. ROS have been implicated in diverse processes in various cancers, and generally the increase of ROS in cancer cells is known to play an important role in the initiation and progression of cancer. Additionally, ROS have been considered as the most significant mutagens in stem cells; when elevated, blocking self-renewal and at the same time, serving as a signal stimulating stem cell differentiation. Several signaling pathways enhanced by oxidative stress are suggested to have important roles in tumorigenesis of cancer or cancer stem cells and the self-renewal ability of stem or cancer stem cells. It is now well established that mitochondria play a prominent role in apoptosis and increasing evidence supports that apoptosis and autophagy are physiological phenomena closely linked with oxidative stress. This review elucidates the effect and the mechanism of the oxidative stress on the regulation of stem, cancer, and cancer stem cells and focuses on the cell signaling cascades stimulated by oxidative stress and their mechanism in cancer stem cell formation, as very little is known about the redox status in cancer stem cells. Moreover, we explain the link between ROS and both of apoptosis and autophagy and the impact on cancer development and treatment. Better understanding of this intricate link may shed light on mechanisms that lead to better modes of cancer treatment.

Emerging strategies for the identification and targeting of cancer stem cells

The hypothesis of cancer stem cells (CSCs) is receiving increasing interest and has become the subject of considerable debate among cancer researchers. Recent rapid progress in CSC research has encountered increasing difficulties and challenges. Understanding the biologic characteristic of CSCs is crucial to start with better identification and diagnosis based on CSC markers and eventually targeting to CSCs will undoubtedly result in improved prevention and treatment of many types of CSCs. We discuss here some of the approaching strategies that include establishing special methods of identifying CSCs and targeting therapies of CSCs.

In situ protein expression in tumour spheres: development of an immunostaining protocol for confocal microscopy

Background

Multicellular tumour sphere models have been shown to closely mimic phenotype characteristics of in vivo solid tumours, or to allow in vitro propagation of cancer stem cells (CSCs). CSCs are usually characterized by the expression of specific membrane markers using flow cytometry (FC) after enzymatic dissociation. Consequently, the spatial location of positive cells within spheres is not documented. Confocal microscopy is the best technique for the imaging of thick biological specimens after multi-labelling but suffers from poor antibody penetration. Thus, we describe here a new protocol for in situ confocal imaging of protein expression in intact spheroids.

Methods

Protein expression in whole spheroids (150 μm in diameter) from two human colon cancer cell lines, HT29 and CT320X6, has been investigated with confocal immunostaining, then compared with profiles obtained through paraffin immunohistochemistry (pIHC) and FC. Target antigens, relevant for colon cancer and with different expression patterns, have been studied.

Results

We first demonstrate that our procedure overcomes the well-known problem of antibody penetration in compact structures by performing immunostaining of EpCAM, a membrane protein expressed by all cells within our spheroids. EpCAM expression is detected in all cells, even the deepest ones. Likewise, antibody access is confirmed with CK20 and CD44 immunostaining. Confocal imaging shows that 100% of cells express β-catenin, mainly present in the plasma membrane with also cytoplasmic and nuclear staining, in agreement with FC and pIHC data. pIHC and confocal imaging show similar CA 19-9 cytoplasmic and membranar expression profile in a cell subpopulation. CA 19-9⁺ cell count confirms confocal imaging as a highly sensitive method (75%, 62% and 51%, for FC, confocal imaging and pIHC, respectively). Finally, confocal imaging reveals that the weak expression of CD133, a putative colon CSC marker, is restricted to the luminal cell surface of colorectal cancer acini, with CD133⁺ cellular debris into glandular lumina.

Conclusion

The present protocol enables in situ visualization of protein expression in compact three-dimensional models by whole mount confocal imaging, allowing the accurate localization and quantification of cells expressing specific markers. It should prove useful to study rare events like CSCs within tumour spheres.

CD133, Trop-2 and alpha2beta1 integrin surface receptors as markers of putative human prostate cancer stem cells

Cancer stem cells (CSCs) play a key role in initiation and development of cancer and are attractive targets for therapy. The identification of CSC surface receptors to be used as therapeutic targets in vivo remains a difficult task. In this study, we assessed the expression pattern of three surface receptors: CD133, Trop-2 and alpha2beta1 integrin in human prostate cancer in order to identify CSC-niches. CD133 was found to be expressed in small clusters of cells localized in focal areas of benign as well as malignant lesions, suggesting that this protein is a bona fide marker of the prostate stem/progenitor compartment. Trop-2 was localized in both basal and luminal layers of benign glands and was highly expressed in malignant lesions. Moreover, isolated cells in benign and malignant areas were found to co-express both CD133 and Trop-2. alpha2beta1 integrin was expressed in the prostatic epithelium as well as in the surrounding stroma, limiting its utility as a marker of CSCs. In summary, we demonstrate that the combination of CD133 and Trop-2 is useful to mark putative CSC-containing compartments in human prostate.

CD133 expression is not selective for tumor-initiating or radioresistant cell populations in the CRC cell line HCT-116

BACKGROUND AND PURPOSE

CD133 is controversially discussed as putative (surrogate) marker for cancer stem/tumor-initiating cell populations (CSC/TIC) in epithelial tumors including colorectal carcinomas (CRCs). We studied CD133 expression in established CRC cell lines and examined in vitro behavior, radioresponse and in vivo tumor formation of CD133+/- subpopulations of one cell line of interest.

MATERIALS AND METHODS

Ten CRC cell lines were analyzed for CD133 expression using flow cytometry and Western blotting. CD133+ and CD133- HCT-116 subpopulations were separated by FACS and studied in 2-D and 3-D culture and colony formation assays after irradiation. Subcutaneous xenograft formation was monitored in NMRI (nu/nu) mice.

RESULTS AND CONCLUSIONS

CRC cell lines could be classified into three groups: (i) CD133-, (ii) CD133+ and (iii) those with two distinct CD133+ and CD133- subpopulations. Isolated CD133+/- HCT-116 subpopulations were studied relative to the original fraction. No difference was found in 2-D growth, spheroid formation or radioresponse in vitro. Also, tumor formation and growth rate did not differ for the sorted subpopulations. However, a subset of xenografts originated from CD133- HCT-116 showed a striking enrichment in the CD133+ fraction. Our data show that CD133 expression is not selective for sphere forming, tumor-initiating or radioresistant subpopulations in the HCT-116 CRC cell line. This implies that CD133 cannot be regarded as a CSC/TIC marker in all CRC cell lines and that functional measurements of tumor formation have to generally accompany CSC/TIC-directed mechanistic or therapeutic studies.

Inhibition of Functional Hyaluronan-CD44 Interactions in CD133-positive Primary Human Ovarian Carcinoma Cells by Small Hyaluronan Oligosaccharides

PURPOSE: CD44 is one of the most common markers used for identification of highly tumorigenic subpopulations of human carcinoma cells, but little is known about the function of CD44 or its major ligand, hyaluronan, in these cells. The purpose of this study was to investigate the involvement of hyaluronan and its interaction with CD44 in the properties of a tumorigenic subpopulation of primary ovarian carcinoma cells. EXPERIMENTAL DESIGN: A tumorigenic subpopulation was identified in ascites fluids from ovarian carcinoma patients by expression of high CD133 levels. Treatment with small hyaluronan oligosaccharides, which dissociate constitutive hyaluronan polymer-CD44 interactions, was used to test the importance of hyaluronan-CD44 interaction in assembly of multidrug and monocarboxylate transporters and receptor tyrosine kinases in the plasma membrane of cells with high CD133 levels, and in the tumorigenic capacity of the CD133-high subpopulation. RESULTS: Although total CD44 levels were similar in cells with high or low CD133 expression, CD44 was present in close association with transporters, receptor tyrosine kinases, and emmprin (CD147) in the plasma membrane of cells with high CD133 levels. Treatment with small hyaluronan oligosaccharides reduced association of the transporters and receptor tyrosine kinases with CD44 in the plasma membrane, diminished drug transporter activity, and inhibited i.p. tumorigenesis in these cells. CONCLUSIONS: We conclude that hyaluronan-CD44 interaction plays an important role in the properties of highly tumorigenic cells by stabilizing oncogenic complexes in their plasma membrane, and that treatment with hyaluronan-CD44 antagonists provides a logical therapeutic approach for abrogating the properties of these cells. (Clin Cancer Res 2009;15(24):7593-601).

Newly characterised ex vivo colospheres as a three-dimensional colon cancer cell model of tumour aggressiveness

Background:

New models continue to be required to improve our understanding of colorectal cancer progression. To this aim, we characterised in this study a three-dimensional multicellular tumour model that we named colospheres, directly obtained from mechanically dissociated colonic primary tumours and correlated with metastatic potential.

Methods:

Colorectal primary tumours (n=203) and 120 paired non-tumoral colon mucosa were mechanically disaggregated into small fragments for short-term cultures. Features of tumours producing colospheres were analysed. Further characterisation was performed using colospheres, generated from a human colon cancer xenograft, and spheroids, formed on agarose by the paired cancer cell lines.

Results:

Colospheres, exclusively formed by viable cancer cells, were obtained in only 1 day from 98 tumours (47%). Inversely, non-tumoral colonic mucosa never generated colospheres. Colosphere-forming capacity was statistically significantly associated with tumour aggressiveness, according to AJCC stage analysis. Despite a close morphology, colospheres displayed higher invasivity than did spheroids. Spheroids and colospheres migrated into Matrigel but matrix metalloproteinase (MMP)-2 and MMP-9 activity was detected only in colospheres. Mouse subrenal capsule assay revealed the unique tumorigenic and metastatic phenotype of colospheres. Moreover, colospheres and parental xenograft reproduced similar CD44 and CD133 expressions in which CD44⁺ cells represented a minority subset of the CD133⁺ population.

Conclusion:

The present colospheres provide an ex vivo three-dimensional model, potentially useful for studying metastatic process.

Cells with characteristics of cancer stem/progenitor cells express the CD133 antigen in human endometrial tumors

PURPOSE

Cancer stem cells represent an attractive therapeutic target for tumor eradication. The present study aimed to determine whether CD133 expression may identify cells with characteristics of cancer stem/progenitor cells in human endometrial tumors.

EXPERIMENTAL DESIGN

We analyzed 113 tumor samples for CD133/1 expression by flow cytometry, immunohistochemistry, and semiquantitative reverse transcription-PCR. CD133(+) cells were isolated and used to assess phenotypic characteristics, self-renewal capacity, ability to maintain CD133 expression and form sphere-like structures in long-term cultures, sensitivity to chemotherapeutic agents, gene expression profile, and ability to initiate tumors in NOD/SCID mice.

RESULTS

Primary tumor samples exhibited a variable degree of immunoreactivity for CD133/1, ranging from 1.3% to 62.6%, but stained negatively for other endothelial and stem cell-associated markers. Isolated CD133(+) cells expanded up to 4.6-fold in serum-replenished cultures and coexpressed the GalNAcalpha1-O-Ser/Thr MUC-1 glycoform, a well-characterized tumor-associated antigen. Dissociated bulk tumors formed sphere-like structures; cells grown as tumor spheres maintained CD133 expression and could be propagated for up to 12 weeks. CD133(+) cells purified from endometrioid adenocarcinomas were resistant to cisplatin-induced and paclitaxel-induced cytotoxicity and expressed a peculiar gene signature consisting of high levels of matrix metalloproteases, interleukin-8, CD44, and CXCR4. When serially transplanted into NOD/SCID mice, CD133(+) cells were capable of initiating tumor formation and recapitulating the phenotype of the original tumor.

CONCLUSIONS

CD133 is expressed by human endometrial cancers and might represent a valuable tool to identify cells with cancer stem cell characteristics.