CD133: molecule of the moment

Arsenic oxide targets stem cell marker CD133/prominin-1 in gallbladder carcinoma

CD133+ tumor cells are responsible for the initiation, propagation and recurrence of tumors, which raises the question of how to effectively target CD133+ tumor cells. Arsenic trioxide (As2O3) has considerable efficacy in treating solid tumors with induction of apoptosis. Here, we found that purified CD133+ gallbladder carcinoma cells are highly resistant to conventional chemotherapy. However, As2O3 effectively induces CD133+ gallbladder carcinoma cells apoptosis. Treatment with As2O3 reduces CD133 expression at transcriptional levels. Furthermore, the ectopic expression of CD133 attenuated the apoptotic effect of As2O3 on cells through activation of AKT signaling pathways. Collectively, As2O3 effectively targets CD133 in gallbladder carcinoma, providing a new mechanism of As2O3-induced cell apoptosis and a better understanding of drug resistance in gallbladder carcinoma.

Is CD133 a biomarker for cancer stem cells of colorectal cancer and brain tumors? A meta-analysis

BACKGROUND

CD133 has been used to identify normal and cancer stem cells from several different tissues. Nowadays some researchers have reported that CD133 expression was not restricted to cancer stem cells (CSCs) of colorectal cancer and brain tumors, and CD133-negative subsets could also initiate tumors. We therefore performed a meta-analysis to assess the value of CD133 as a biomarker of CSCs for colorectal cancer and brain tumors.

METHODS

A Medline search was performed to identify relevant studies for the analysis. The meta-analysis was done using RevMan 5.0 software. Outcome measures were colony formation rate and xenotransplanted tumor formation rate.

RESULTS

Fifteen identified studies were available for analysis. For in vitro tests, there were no significant differences in the colony formation rates between CD133-positive and CD133-negative cells for colorectal cancer and brain tumors. For in vivo tests, the xenotransplanted tumor formation rate showed a significant difference between CD133-positive cells and CD133-negative cells in colorectal cancer only, corresponding to a risk difference of 0.40 (95%CI: 0.07, 0.73). Samples (cell lines versus tissues), applied biomarkers (combined versus single), and injection site were included as factors in sensitivity analyses, but the results were very inconsistent.

CONCLUSIONS

CD133 may not be suitable as a universe biomarker in identifying CSCs of colorectal cancer and brain tumors. Additional studies are necessary to further delineate its role.

Immunohistochemical expression and cluster analysis of mesenchymal and neural stem cell-associated proteins in pediatric soft tissue sarcomas

Pediatric undifferentiated soft tissue sarcomas (USTSs) are a group of malignancies composed predominantly of primitive round cell sarcomas, the histogenesis of which is uncertain. Thus, diagnosis and therapy remain a challenge. The aims of the current study were to determine whether differential expression of stem cell-associated proteins could be used to aid in determining the histogenesis of pediatric USTSs and to determine whether pediatric USTSs expressed a unique panel of stem cell-associated proteins to aid diagnosis. Tumors included 28 Ewing sarcoma/primitive neuroectodermal tumors (ESs), 22 embryonal rhabdomyosarcomas (ERMSs), 8 alveolar rhabdomyosarcomas (ARMSs), 5 synovial sarcomas (SSs), 5 malignant peripheral nerve sheath tumors (MPNSTs), and 13 USTSs. Stem cell antibodies included 3 mesenchymal stem cell markers (CD44, CD105, and CD166) and 5 neural stem cell markers (CD15, CD29, CD56, CD133, and nestin). Sections were scored followed by statistical analysis, clustering analysis, and visualizations using Partek Genomic Suite Software. The Euclidean clustering divided the tumors into 2 major groups. ESs and USTSs formed the majority of the 1st group, whereas ERMSs, ARMSs, MPNSTs, and SSs formed the 2nd group. Reduced expression of CD56 was strongly associated with the ES/USTS cluster (P < 0.0001). ESs and USTSs were further separated by CD166 staining, wherein increased expression was associated with ES (P < 0.0001). The 2nd group included the majority of other sarcomas, with no consistent separation between subtypes. The current study demonstrates the usefulness of applying stem cell markers to pediatric sarcomas and indicates that USTSs and ESs are closely related and may share a common histogenesis.

Hypoxia promotes growth of stem cells in dental follicle cell populations

Adult stem cells (ASC) have been found in many tissues and are of great therapeutic potential due to their capability of differentiation. However, ASC comprise only a small fraction of the tissues. In order to use ASC for therapeutic purposes, it is important to obtain relatively pure stem cells in large quantities. Current methods for stem cell purification are mainly based on marker-dependent cell sorting techniques, which have various technical difficulties. In this study, we have attempted to develop novel conditions to favor the growth of the dental follicle stem cells (DFSC) such that the resultant cell populations are enriched in stem cells. Specifically, a heterogeneous dental follicle cell (H-DFC) population containing stem cells and homogenous non-stem cell dental follicle cell population were cultured at 1% or 5% hypoxic conditions. Only the heterogeneous population could increase proliferation in the hypoxic condition whereas the homogenous DFC did not change their proliferation rate. In addition, when the resultant cells from the heterogonous population were subjected to differentiation, they appeared to have a higher capacity of adipogenesis and osteogenesis as compared to the controls grown in the normal atmosphere (normoxic condition). These hypoxia-treated cells also express higher levels of some stem cell markers. Together, these data suggest that stem cells are enriched by culturing the heterogeneous cell populations in a reduced O(2) condition.

Inconsistent immunohistochemical expression patterns of four different CD133 antibody clones in glioblastoma

The putative tumor stem cell marker CD133 is the marker of choice for identifying brain tumor stem cells in gliomas, but the use of different CD133 antibody clones possibly recognizing different CD133 splice variants with epitopes of different glycosylation status confuses the field. The aim was to investigate if current inconsistent CD133 observations could be a result of using different CD133 antibodies for immunohistochemical identification of CD133. Ten glioblastomas were immunohistochemically stained with four different CD133 antibody clones (AC133, W6B3C1, C24B9, and ab19898) and analyzed by quantitative stereology. Moreover, the CD133 staining pattern of each antibody clone was investigated in kidney, pancreas, and placenta tissue as well as in glioblastoma and retinoblastoma cultures and cell lines. All antibody clones revealed CD133+ niches and single cells in glioblastomas, but when using different clones, their distribution rarely corresponded. Morphology of identified single cells varied, and staining of various tissues, cultures, and cells lines was also inconsistent among the clones. In conclusion, the authors report inconsistent CD133 detection when using different primary CD133 antibody clones. Thus, direct comparison of studies using different antibody clones and conclusions based on CD133 immunohistochemistry should be performed with caution.

Visualization of CD44 and CD133 in normal pancreas and pancreatic ductal adenocarcinomas: non-overlapping membrane expression in cell populations positive for both markers

Tumor-initiating cells of pancreatic ductal adenocarcinoma (PDAC) have been isolated based on expression of either CD133 or CD44. The authors aimed to visualize pancreatic cells simultaneously expressing both these cell surface markers by employing the same antibodies commonly used in cell-sorting studies. Normal and diseased pancreatic tissue, including 51 PDAC cases, were analyzed. CD44 and CD133 expression was determined by immunohistochemical double staining on formalin-fixed material and subcellular protein distribution evaluated by immunofluorescence/confocal microscopy. In the normal pancreas, CD44 and CD133 were coexpressed in the centroacinar regions but in non-overlapping subcellular compartments. As expected, CD44 was found mainly basolaterally, whereas CD133 was present on the apical/endoluminal membrane. This was also the case in chronically inflamed/atrophic pancreatic tissue and in PDAC. In some malignant ducts, CD44 was found at the apical cell membrane adjacent to but never overlapping with CD133 expression. CD44 level was significantly associated with the patient's lymph node status. In conclusion, a CD44+/CD133+ cell population does exist in the normal and neoplastic pancreas. The preferentially centroacinar localization of the doubly positive cells in the normal parenchyma suggests that this population could be of particular interest in attempts to identify tumor-initiating cells in PDAC.

Circulating bone-marrow-derived endothelial precursor cells contribute to neovascularization in diabetic epiretinal membranes

PURPOSE

The role of vasculogenesis, recruitment and differentiation of circulating bone-marrow-derived endothelial precursor cells into mature endothelium in proliferative diabetic retinopathy (PDR) remains undefined. We investigated the presence of bone-marrow-derived endothelial precursor cells and the expression of the chemotactic pathway SDF-1 ⁄CXCL12)CXCR4 in PDR epiretinal membranes.

METHODS

Membranes from eight patients with active PDR and nine patients with inactive PDR were studied by immunohistochemistry using antibodies against CD133, vascular endothelial growth factor receptor-2 (VEGFR-2), CD14, SDF-1 and CXCR4.

RESULTS

Blood vessels expressed CD133, VEGFR-2, CD14, SDF-1 and CXCR4 in 10, 10, 10, seven and seven out of 17 membranes, respectively. There were significant correlations between number of blood vessels expressing CD34 and number of blood vessels expressing CD133 (r(s) = 0.646; p = 0.005), VEGFR-2 (r(s) = 0.704; p = 0.002), CD14 (r(s) = 0.564; p = 0.018) and SDF-1 (r(s) = 0.577; p = 0.015). Stromal cells in close association with blood vessels expressed CD133, VEGFR-2, CD14 and CXCR4 in 10, 12, 13 and 14 membranes, respectively. The number of blood vessels expressing CD133 (p = 0.013), VEGFR-2 (p = 0.005), CD14 (p = 0.008) and SDF-1 (p = 0.005), and stromal cells expressing CD133 (p = 0.003), VEGFR-2 (p = 0.013) and CD14 (p = 0.002) was significantly higher in active membranes than in inactive membranes.

CONCLUSION

Bone-marrow-derived CD133(+) endothelial progenitor cells and CD14(+) monocytes may contribute to vasculogenesis in PDR.

Cancer stem cells: characteristics and their potential role for new therapeutic strategies

With the cancer stem cell (CSC) hypothesis many questions regarding cancer development and drug resistance can be answered more coherently than with the traditional model based on clonal evolution. CSCs are a small subset of cancer cells within the tumour that show stem cell characteristics like self-renewal, the capability to develop into multiple lineages and the potential to proliferate extensively, and are characterised by a typical profile of different markers like CD44 and CD133. In the CSC model, the role of embryonic pathways like Wnt, Hedgehog and Notch is of special interest. This review presents current scientific knowledge on this topic and discusses the potential role of CSC in the resistance against chemotherapy or radiation and presents challenging options for therapeutic interventions.

Cancer stem cells and side population cells in breast cancer and metastasis

In breast cancer it is never the primary tumour that is fatal; instead it is the development of metastatic disease which is the major cause of cancer related mortality. There is accumulating evidence that suggests that Cancer Stem Cells (CSC) may play a role in breast cancer development and progression. Breast cancer stem cell populations, including side population cells (SP), have been shown to be primitive stem cell-like populations, being long-lived, self-renewing and highly proliferative. SP cells are identified using dual wavelength flow cytometry combined with Hoechst 33342 dye efflux, this ability is due to expression of one or more members of the ABC transporter family. They have increased resistance to chemotherapeutic agents and apoptotic stimuli and have increased migratory potential above that of the bulk tumour cells making them strong candidates for the metastatic spread of breast cancer. Treatment of nearly all cancers usually involves one first-line agent known to be a substrate of an ABC transporter thereby increasing the risk of developing drug resistant tumours. At present there is no marker available to identify SP cells using immunohistochemistry on breast cancer patient samples. If SP cells do play a role in breast cancer progression/Metastatic Breast Cancer (MBC), combining chemotherapy with ABC inhibitors may be able to destroy both the cells making up the bulk tumour and the cancer stem cell population thus preventing the risk of drug resistant disease, recurrence or metastasis.

High levels of PROM1 (CD133) transcript are a potential predictor of poor prognosis in medulloblastoma

The surface marker PROM1 is considered one of the most important markers of tumor-initiating cells, and its expression is believed to be an adverse prognostic factor in gliomas and in other malignancies. To date, to our knowledge, no specific studies of its expression in medulloblastoma series have been performed. The aims of our study were to evaluate the expression profile of the PROM1 gene in medulloblastoma and to assess its possible role as a prognostic factor. The PROM1 gene expression was evaluated by quantitative- polymerase chain reaction on 45 medulloblastoma samples by using specific dye-labeled probe systems. A significantly higher expression of PROM1 was found both in patients with poorer prognosis (P= .007) and in those with metastasis (P= .03). Kaplan-Meier analysis showed that both overall survival (OS) and progression-free survival (PFS) were shorter in patients with higher PROM1 mRNA levels than in patients with lower expression, even when the desmoplastic cases were excluded (P= .0004 and P= .002, for OS and PFS for all cases, respectively; P= .002 and P= .008 for OS and PFS for nondesmoplastic cases, respectively). Cox regression model demonstrated that PROM1 expression is an independent prognostic factor (hazard ratio, 4.56; P= .008). The result was validated on an independent cohort of 42 cases by microarray-based analysis (P= .019). This work suggests that high mRNA levels of PROM1 are associated with poor outcome in pediatric medulloblastoma. Furthermore, high PROM1 expression levels seem to increase the likelihood of metastases. Such results need to be confirmed in larger prospective series to possibly incorporate PROM1 gene expression into risk classification systems to be used in the clinical setting.

Kidney regeneration and resident stem cells

Given its complexity, high metabolic activity and excretory functions, the kidney is particularly susceptible to acute ischemic and toxin-mediated injury. Current therapies do not facilitate kidney regeneration, and there is an increasing interest in newer therapies that are based on cellular sources of kidney regeneration, such as stem cell therapy. Our understanding of cellular sources for kidney regeneration and stem cells present in the adult kidney has dramatically evolved over the recent years. Herein, we discuss the current understanding of kidney stem cells present in the adult mammalian kidney and their role in kidney regeneration. We have also summarized the best available evidence supporting the role of stem cells in kidney regeneration.

Clinicopathological significance and prognostic value of EphA3 and CD133 expression in colorectal carcinoma

AIMS

To investigate clinicopathological significance and prognostic implications of EphA3, CD133 and Ki-67 expression in colorectal cancer.

METHODS

EphA3, CD133 and Ki-67 expression was assessed in 201 cases of paraffin-embedded colorectal carcinoma and 60 cases of distal normal mucosal tissue by immunohistochemistry. Medical records were reviewed and clinicopathological analysis was performed. The differential expression of EphA3 and CD133 protein was detected in 20 cases of fresh resected colorectal carcinoma and 20 cases of matched normal mucosal tissue adjacent to the carcinoma by western blot.

RESULTS

The expression of EphA3 and CD133 in carcinoma was significantly higher than that in normal mucosal tissue (p=0.008; p=0.004). EphA3 and CD133 were positively correlated with tumour size (p=0.029; p=0.017), histological grade (all p=0.001), infiltrative depth (all p=0.00), lymph node metastasis (all p=0.00), distant metastasis (p=0.017; p=0.030) and TNM stage (all p=0.001). Patients with high expression of EphA3 and CD133 had the lowest survival (all p=0.001) (median survival time of EphA3 positive and negative cases: 34.0 and 72.0 months; median survival time of CD133 positive and negative cases: 34.0 and 77.0 months). Multivariate survival analysis showed that EphA3 and CD133 expression was correlated significantly with shortened survival in patients with colorectal cancer (Cox regression: p=0.001, HR=4.722, 95% CI 2.667 to 8.361; p=0.001, HR=5.224, 95% CI 2.622 to 10.405). EphA3, CD133 and Ki-67 expression in colorectal cancer had positive correlations with each other (all p=0.001).

CONCLUSIONS

EphA3 and CD133 may play an important role in the development and progression of tumours, and thus become useful indicators for clinical assessment of tumour biological behaviour and prognosis in patients with colorectal carcinoma.

Cancer stem cells in breast cancer

The cancer stem cell (CSC) theory is generally acknowledged as an important field of cancer research, not only as an academic matter but also as a crucial aspect of clinical practice. CSCs share a variety of biological properties with normal somatic stem cells in self-renewal, the propagation of differentiated progeny, the expression of specific cell markers and stem cell genes, and the utilization of common signaling pathways and the stem cell niche. However, CSCs differ from normal stem cells in their chemoresistance and their tumorigenic and metastatic activities. In this review, we focus on recent reports regarding the identification of CSC markers and the molecular mechanism of CSC phenotypes to understand the basic properties and molecular target of CSCs. In addition, we especially focus on the CSCs of breast cancer since the use of neoadjuvant chemotherapy can lead to the enrichment of CSCs in patients with that disease. The identification of CSC markers and an improved understanding of the molecular mechanism of CSC phenotypes should lead to progress in cancer therapy and improved prognoses for patients with cancer.

Strong expression of CD133 is associated with increased cholangiocarcinoma progression

AIM: To determine the role of CD133 in cholangiocarcinoma progression.

METHODS: CD133 protein expression was evaluated by immunohistochemistry in 34 cholangiocarcinoma specimens. In addition, proliferation, chemoresistance and invasive properties of CD133-enriched (CD133⁺) and CD133-depleted (CD133^-) RMCCA1 cholangiocarcinoma cells were studied and compared.

RESULTS: Strong CD133 expression was observed in 67.6% (23/34) of the cholangiocarcinoma specimens. Strong expression of CD133 was significantly associated with nodal metastasis (P = 0.009) and positive surgical margin status (P = 0.011). In the in vitro study, both the CD133⁺ and CD133^- cells had similar proliferation abilities and resistance to chemotherapeutic drugs. However, the CD133⁺ cells had a higher invasive ability compared with CD133^- cells.

CONCLUSION: CD133+ cells play an important role in the invasiveness of cholangiocarcinoma. Targeting of the CD133+ cells may be a useful approach to improve treatment against cholangiocarcinoma.

Gene expression of growth signaling pathways is up-regulated in CD133-positive medulloblastoma cells

Medulloblastoma (MB) is the most common malignant brain tumor in children. Cancer initiating cells (CICs) have been proposed to be involved in the development of brain tumors including MB. Prominin-1 antigen (CD133) is a candidate surface molecular marker for CICs. In the present study, CD133-positive cells were isolated from human Daoy MB cells and their gene expression was compared with that of control Daoy cells. DNA microarray analysis revealed that there were 398 up-regulated genes (>2-fold increase) and 318 down-regulated genes (<50% decrease) in the CD133-positive cell-enriched fractions. Up-regulated genes included neuregulin-1, cyclin D1, cyclin-dependent kinase 6, vascular endothelial growth factor, inhibin β A, promyelocytic leukemia gene, MYC, and hairy enhancer of split-1, which are components of growth signaling pathways. Molecular studies suggest that developmentally regulated signals important for stem cell maintenance are also involved in MB tumorigenesis. Moreover, these molecules can serve as novel targets for MB treatment.

Endothelial progenitor cells: novel biomarker and promising cell therapy for cardiovascular disease

Bone-marrow-derived EPCs (endothelial progenitor cells) play an integral role in the regulation and protection of the endothelium, as well as new vessel formation. Peripheral circulating EPC number and function are robust biomarkers of vascular risk for a multitude of diseases, particularly CVD (cardiovascular disease). Importantly, using EPCs as a biomarker is independent of both traditional and non-traditional risk factors (e.g. hypertension, hypercholesterolaemia and C-reactive protein), with infused ex vivo-expanded EPCs showing potential for improved endothelial function and either reducing the risk of events or enhancing recovery from ischaemia. However, as the number of existing cardiovascular risk factors is variable between patients, simple EPC counts do not adequately describe vascular disease risk in all clinical conditions and, as such, the risk of CVD remains. It is likely that this limitation is attributable to variation in the definition of EPCs, as well as a difference in the interaction between EPCs and other cells involved in vascular control such as pericytes, smooth muscle cells and macrophages. For EPCs to be used regularly in clinical practice, agreement on definitions of EPC subtypes is needed, and recognition that function of EPCs (rather than number) may be a better marker of vascular risk in certain CVD risk states. The present review focuses on the identification of measures to improve individual risk stratification and, further, to potentially individualize patient care to address specific EPC functional abnormalities. Herein, we describe that future therapeutic use of EPCs will probably rely on a combination of strategies, including optimization of the function of adjunct cell types to prime tissues for the effect of EPCs.

Upregulated CD133 expression in tumorigenesis of colon cancer cells

AIM: To analyze the upregulated CD133 expression in tumorigenesis of primary colon cancer cells.

METHODS: Upregulated CD133 expression in tumorigenesis of colorectal cancer cell lines (Lovo, Colo205, Caco-2, HCT116 and SW620) was analyzed by flow cytometry. Human colon cancer tissue samples were stained with anti-human CD133. SW620 cells were sorted according to the CD133 expression level measured by fluorescence-activated cell sorting. Spheroids of colorectal cancer cells were cultured with the hanging drop. Expression of CD133 and Lgr5 in spheroids of colorectal cancer cells and monolayer culture was detected by RT-qPCR. Spheroids of colorectal cancer cells were analyzed using anti-human CD133 with immunohistochemical staining.

RESULTS: CD133 antigen was expressed in colorectal cancer cell lines (Lovo, Colo205, Caco-2, HCT116 and SW620) as well as in primary and metastatic human colon cancer tissues. However, the CD133 was differently expressed in these cell lines and tissues. The expression levels of CD133 and Lgr5 were significantly higher in spheroids of parental, CD133^hi and CD133^- cells than in their monolayer culture at the mRNA level (P < 0.05). Immunohistochemical staining of spheroids of CD133^- cells showed that CD133 was highly expressed in colorectal cancer cell lines.

CONCLUSION: Upregulated CD133 expression plays a role in tumorigenesis colorectal cancer cells, which may promote the expression of other critical genes that can drive tumorigenesis.

SOX2 expression levels distinguish between neural progenitor populations of the developing dorsal telencephalon

The HMG-Box transcription factor SOX2 is expressed in neural progenitor populations throughout the developing and adult central nervous system and is necessary to maintain their progenitor identity. However, it is unclear whether SOX2 levels are uniformly expressed across all neural progenitor populations. In the developing dorsal telencephalon, two distinct populations of neural progenitors, radial glia and intermediate progenitor cells, are responsible for generating a majority of excitatory neurons found in the adult neocortex. Here we demonstrate, using both cellular and molecular analyses, that SOX2 is differentially expressed between radial glial and intermediate progenitor populations. Moreover, utilizing a SOX2(EGFP) mouse line, we show that this differential expression can be used to prospectively isolate distinct, viable populations of radial glia and intermediate cells for in vitro analysis. Given the limited repertoire of cell-surface markers currently available for neural progenitor cells, this provides an invaluable tool for prospectively identifying and isolating distinct classes of neural progenitor cells from the central nervous system.

Phenotypic heterogeneity of breast cancer stem cells

Many types of tumors are organized in a hierarchy of heterogeneous cell populations, with only a small proportion of cancer stem cells (CSCs) capable of sustaining tumor formation and growth, giving rise to differentiated cells, which form the bulk of the tumor. Proof of the existence of CSC comes from clinical experience with germ-cell cancers, where the elimination of a subset of undifferentiated cells can cure patients (Horwich et al., 2006), and from the study of leukemic cells (Bonnet and Dick, 1997; Lapidot et al., 1994; and Yilmaz et al., 2006). The discovery of CSC in leukemias as well as in many solid malignancies, including breast carcinoma (Al-Hajj et al. 2003; Fang et al., 2005; Hemmati et al., 2003; Kim et al., 2005; Lawson et al., 2007; Li et al., 2007; Ricci-Vitiani et al., 2007; Singh et al., 2003; and Xin et al., 2005), has suggested a unifying CSC theory of cancer development. The reported general insensitivity of CSC to chemotherapy and radiation treatment (Bao et al., 2006) has suggested that current anticancer drugs, which inhibit bulk replicating cancer cells, may not effectively inhibit CSC. The clinical relevance of targeting CSC-associated genes is supported by several recent studies, including CD44 targeting for treatment of acute myeloid leukemia (Jin et al., 2006), CD24 targeting for treatment of colon and pancreatic cancer (Sagiv et al., 2008), and CD133 targeting for hepatocellular and gastric cancer (Smith et al., 2008). One promising approach is to target CSC survival signaling pathways, where leukemia stem cell research has already made some progress (Mikkola et al., 2010).

Stem cell marker prominin-1 regulates branching morphogenesis, but not regenerative capacity, in the mammary gland

Prominin-1 (Prom1) is recognized as a stem cell marker in several tissues, including blood, neuroepithelium, and gut, and in human and mouse embryos and many cancers. Although Prom1 is routinely used as a marker for isolating stem cells, its biological function remains unclear. Here we use a knockout model to investigate the role of Prom1 in the mammary gland. We demonstrate that complete loss of Prom1 does not affect the regenerative capacity of the mammary epithelium. Surprisingly, we also show that in the absence of Prom1, mammary glands have reduced ductal branching, and an increased ratio of luminal to basal cells. The effects of Prom1 loss in the mammary gland are associated with decreased expression of prolactin receptor and matrix metalloproteinase-3. These experiments reveal a novel, functional role for Prom1 that is not related to stem cell activity, and demonstrate the importance of tissue-specific characterization of putative stem cell markers.

Unicentric study of cell therapy in chronic obstructive pulmonary disease/pulmonary emphysema

Within the chronic obstructive pulmonary disease (COPD) spectrum, lung emphysema presents, as a primarily histopathologic feature, the destruction of pulmonary parenchyma and, accordingly, an increase in the airflow obstruction distal to the terminal bronchiole. Notwithstanding the significant advances in prevention and treatment of symptoms, no effective or curative therapy has been accomplished. In this context, cellular therapy with stem cells (SCs) arises as a new therapeutic approach, with a wide application potential. The purpose of this study is to evaluate the safety of SCs infusion procedure in patients with advanced COPD (stage IV dyspnea). After selection, patients underwent clinical examination and received granulocyte colony-stimulating factor, immediately prior to the bone marrow harvest. The bone marrow mononuclear cells (BMMC) were isolated and infused into a peripheral vein. The 12-month follow-up showed a significant improvement in the quality of life, as well as a clinical stable condition, which suggest a change in the natural process of the disease. Therefore, the proposed methodology in this study for BMMC cell therapy in sufferers of advanced COPD was demonstrated to be free of significant adverse effects. Although a larger sample and a greater follow-up period are needed, it is possible to infer that BMMC cell therapy introduces an unprecedented change in the course or in the natural history of emphysema, inhibiting or slowing the progression of disease. This clinical trial was registered with ClinicalTrials.gov (NCT01110252) and was approved by the Brazilian National Committee of Ethics in Research (registration no. 14764, CONEP report 233/2009).

Isolation and identification of cancer stem cells from a side population of a human hepatoblastoma cell line, HuH-6 clone-5

PURPOSE

It has been thought that the persistence of even a small number of tumor cells in the body may increase each tumor cell in a similar manner and may allow the disease to proceed. However, only a few percent of such tumor cells exist in cancerous tissue. They are called "cancer stem cells (CSCs)". If an alternative method of annihilating CSCs is found, it will greatly deter relapse and metastasis. We attempted to identify and separate CSCs in hepatoblastoma aiming to develop a new therapy for hepatoblastoma.

METHODS

The side population (SP) method was used as an indicator when extracting the CSC candidate group from the hepatoblastoma cells. The SP cells and non-SP cells were studied for tumourigenesis.

RESULTS

Although tumors were formed when SP fraction cells were inoculated into mice, tumor formation was not observed in non-SP cells. SP cells had higher tumor formation ability compared to non-SP cells.

CONCLUSION

Cancer stem-like cells were separated by the SP fraction method from hepatoblastoma cells. The in vivo experiment proved that SP fraction cells inoculated into mice were self-replicated, and the existence of cancer stem-like cells was identified.

In vivo gene delivery into hCD34+ cells in a humanized mouse model

In vivo targeted gene delivery to hematopoietic stem cells (HSCs) would mean a big step forward in the field of gene therapy. This would imply that the risk of cell differentiation and loss of homing/-engraftment is reduced, as there is no need for purification of the target cell. In vivo gene delivery also bypasses the issue that no precise markers that permit the isolation of a primitive hHSC exist up to now. Indeed, in vivo gene transfer could target all HSCs in their stem-cell niche, including those cells that are "missed" by the purification criteria. Moreover, for the majority of diseases, there is a requirement of a minimal number of gene-corrected cells to be reinfused to allow an efficient long-term engraftment. This requisite might become a limiting factor when treating children with inherited disorders, due to the low number of bone marrow (BM) CD34(+) HSCs that can actually be isolated. These problems could be overcome by using efficient in vivo HSC-specific lentiviral vectors (LVs). Additionally, vectors for in vivo HSC transduction must be specific for the target cell, to avoid vector spreading while enhancing transduction efficiency. Of importance, a major barrier in LV transduction of HSCs is that 75% of HSCs are residing in the G0 phase of the cell cycle and are not very permissive for classical VSV-G-LV transduction. Therefore, we engineered "early-activating-cytokine (SCF or/and TPO)" displaying LVs that allowed a slight and transient stimulation of hCD34(+) cells resulting in efficient lentiviral gene transfer while preserving the "stemness" of the targeted HSCs. The selective transduction of HSCs by these vectors was demonstrated by their capacity to promote selective transduction of CD34(+) cells in in vitro-derived, long-term culture-initiating cell colonies and long-term NOD/SCID repopulating cells. A second generation of these "early-acting-cytokine"-displaying lentiviral vectors has now been developed that is fit for targeted in vivo gene delivery to hCD34(+) cells. In the method presented here, we describe the in vivo gene delivery into hCD34(+) cells by intramarrow injection of these new vectors into humanized BALB/c Rag2( null )/IL2rgc ( null ) (BALB/c RAGA) mice.

Non-invasive in vivo imaging of tumor-associated CD133/prominin

Background

Cancer stem cells are thought to play a pivotal role in tumor maintenance, metastasis, tumor therapy resistance and relapse. Hence, the development of methods for non-invasive in vivo detection of cancer stem cells is of great importance.

Methodology/Principal Findings

Here, we describe successful in vivo detection of CD133/prominin, a cancer stem cell surface marker for a variety of tumor entities. The CD133-specific monoclonal antibody AC133.1 was used for quantitative fluorescence-based optical imaging of mouse xenograft models based on isogenic pairs of CD133 positive and negative cell lines. A first set consisted of wild-type U251 glioblastoma cells, which do not express CD133, and lentivirally transduced CD133-overexpressing U251 cells. A second set made use of HCT116 colon carcinoma cells, which uniformly express CD133 at levels comparable to primary glioblastoma stem cells, and a CD133-negative HCT116 derivative. Not surprisingly, visualization and quantification of CD133 in overexpressing U251 xenografts was successful; more importantly, however, significant differences were also found in matched HCT116 xenograft pairs, despite the lower CD133 expression levels. The binding of i.v.-injected AC133.1 antibodies to CD133 positive, but not negative, tumor cells isolated from xenografts was confirmed by flow cytometry.

Conclusions/Significance

Taken together, our results show that non-invasive antibody-based in vivo imaging of tumor-associated CD133 is feasible and that CD133 antibody-based tumor targeting is efficient. This should facilitate developing clinically applicable cancer stem cell imaging methods and CD133 antibody-based therapeutics.

Characterization of murine non-adherent bone marrow cells leading to recovery of endogenous hematopoiesis

Non-adherent bone marrow-derived cells (NA-BMCs) are a mixed cell population that can give rise to multiple mesenchymal phenotypes and that facilitates hematopoietic recovery. We characterized NA-BMCs by flow cytometry, fibroblast colony-forming units (CFU-f), real-time PCR, and in in vivo experiments. In comparison to adherent cells, NA-BMCs expressed high levels of CD11b(+) and CD90(+) within the CD45(+) cell fraction. CFU-f were significantly declining over the cultivation period, but NA-BMCs were still able to form CFU-f after 5 days. Gene expression analysis of allogeneic NA-BMCs compared to bone marrow (BM) indicates that NA-BMCs contain stromal, mesenchymal, endothelial cells and monocytes, but less osteoid, lymphoid, and erythroid cells, and hematopoietic stem cells. Histopathological data and analysis of weight showed an excellent recovery and organ repair of lethally irradiated mice after NA-BMC transplantation with a normal composition of the BM.

Stem cells in cancer: instigators and propagators?

There is growing realization that many - if not all - cancer-cell populations contain a subpopulation of self-renewing stem cells known as cancer stem cells (CSCs). Unlike normal adult stem cells that remain constant in number, CSCs can increase in number as tumours grow, and give rise to progeny that can be both locally invasive and colonise distant sites - the two hallmarks of malignancy. Immunodeficient mouse models in which human tumours can be xenografted provide persuasive evidence that CSCs are present in human leukaemias and many types of solid tumour. In addition, many studies have found similar subpopulations in mouse tumours that show enhanced tumorigenic properties when they are transplanted into histocompatible mice. In this Commentary, we refer to CSCs as tumour-propagating cells (TPCs), a term that reflects the assays that are currently employed to identify them. We first discuss evidence that cancer can originate from normal stem cells or closely related descendants. We then outline the attributes of TPCs and review studies in which they have been identified in various cancers. Finally, we discuss the implications of these findings for successful cancer therapies.

Autologous valve replacement-CD133+ stem cell-plus-fibrin composite-based sprayed cell seeding for intraoperative heart valve tissue engineering

OBJECTIVE

The development of biological valve prostheses with lifetime native-like performance and optimal host engraftment is an ultimate goal of heart valve tissue engineering. We describe a new concept for autologous graft coating based on a CD133(+)-stem-cells-plus-fibrin (SC+F) complex processed from bone marrow and peripheral blood of a single patient.

METHODS

CD133(+)-SC (1 × 10(6) cells/mL) from human bone marrow and autologous fibrin (20 mg/mL) were administered simultaneously via spray administration using the novel Vivostat Co-Delivery System. During static cultivation, SC+F performance was monitored for 20 days after delivery and compared with controls. For dynamic testing SC+F-composite was sprayed on a decellularized porcine pulmonary valve and transferred to a bioreactor under pulsatile flow conditions for 7 days.

RESULTS

Static cultivation of SC+F-composite induced significant improvements in stem cell proliferation as compared with controls. For dynamic testing, microscopic analyses on a smooth engineered heart valve surface detected homogenous distribution of stem cells. Ultrasonic analysis revealed native-like valve performance. Applied CD133(+) stem cells differentiated into endothelial-like cells positive for CD31 and vascular endothelial growth factor receptor 2 and engrafted the valve. However, occasional delamination was observed.

CONCLUSION

SC+F serves as an excellent autologous matrix for intraoperative tissue engineering of valve prostheses promising optimal in vivo integration. However, stability remains an issue.

Induction of apoptosis in glioma cells requires cell-to-cell contact with human umbilical cord blood stem cells

We have previously demonstrated the multipotent nature of human umbilical cord blood stem cells (hUCB). In this study, we have attempted to show the use of hUCB in glioma therapy. We used hUCB enriched in CD44 and CD133 cells for our studies and observed that glioma cells co-cultured with hUCB undergo apoptosis. To prove the role of cell-to-cell contact in the induction of apoptotic events, we used a modified 0.22 microm Boyden's chamber where the upper surface was used to culture glioma cells (SNB19 or U87) or xenografts (4910 or 5310) and the lower surface to culture hUCB. TUNEL assay was carried out to determine the degree of apoptotic induction and we observed that glioma or xenograft cells co-cultured with hUCB had a higher number of TUNEL-positive characteristics (63+/-6%) compared to the controls. Further, we co-cultured glioma cells labeled with lipophilic green fluorescent dye and hUCB labeled with lipophilic red fluorescent dye. FACS analysis of cells collected from the upper and lower surfaces revealed that glioma cells had taken up red fluorescent dye from the stem cells (70+/-3%) when compared to glioma cells co-cultured with fibroblast cells (15+/-4%). The apoptotic events in the glioma and xenograft cells co-cultured with hUCB were also confirmed by Western blot analysis for the cleavage of PARP and activation of caspase 8. In addition, elevated levels of CHK-2 levels and downregulation of MAP2K1 were observed in glioma cells co-cultured with hUCB indicating the DNA damage and decrease in cell survival. Nude mice, intracranially implanted with luciferase-expressing U87 cells followed by implantation of hUCB or human fibroblast cells showed retardation of intracranial tumors in hUCB-implanted mice. Taken together, these results demonstrate that hUCB have therapeutic potential with possible clinical implications.

FGF signaling gradient maintains symmetrical proliferative divisions of midbrain neuronal progenitors

For the correct development of the central nervous system, the balance between self-renewing and differentiating divisions of the neuronal progenitors must be tightly regulated. To maintain their self-renewing identity, the progenitors need to retain both apical and basal interfaces. However, the identities of fate-determining signals which cells receive via these connections, and the exact mechanism of their action, are poorly understood. The conditional inactivation of Fibroblast growth factor (FGF) receptors 1 and 2 in the embryonic mouse midbrain-hindbrain area results in premature neuronal differentiation. Here, we aim to elucidate the connection between FGF signaling and neuronal progenitor maintenance. Our results reveal that the loss of FGF signaling leads to downregulation of Hes1 and upregulation of Ngn2, Dll1, and p57 in the ventricular zone (VZ) cells, and that this increased neurogenesis occurs cell-autonomously. Yet the cell cycle progression, apico-basal-polarity, cell-cell connections, and the positioning of mitotic spindle in the mutant VZ appear unaltered. Interestingly, FGF8-protein is highly concentrated in the basal lamina. Thus, FGFs may act through basal processes of neuronal progenitors to maintain their progenitor status. Indeed, midbrain neuronal progenitors deprived in vitro of FGFs switched from symmetrical proliferative towards symmetrical neurogenic divisions. We suggest that FGF signaling in the midbrain VZ is cell-autonomously required for the maintenance of symmetrical proliferative divisions via Hes1-mediated repression of neurogenic genes.

Celecoxib and radioresistant glioblastoma-derived CD133+ cells: improvement in radiotherapeutic effects. Laboratory investigation

OBJECT

Glioblastoma, the most common primary brain tumor, has a poor prognosis, even with aggressive resection and chemoradiotherapy. Recent studies indicate that CD133(+) cells play a key role in radioresistance and recurrence of glioblastoma. Cyclooxygenase-2 (COX-2), which converts arachidonic acid to prostaglandins, is over-expressed in a variety of tumors, including CD133(+) glioblastomas. The COX-2-derived prostaglandins promote neovascularization during tumor development, and conventional radiotherapy increases the proportion of CD133(+) cells rather than eradicating them. The aim of the present study was to investigate the role of celecoxib, a selective COX-2 inhibitor, in enhancing the therapeutic effects of radiation on CD133(+) glioblastomas.

METHODS

Cells positive for CD133 were isolated from glioblastoma specimens and characterized by flow cytometry, then treated with celecoxib and/or ionizing radiation (IR). Clonogenic assay, cell irradiation, cell cycle analysis, Western blot, and xenotransplantation were used to assess the effects of celecoxib alone, IR alone, and IR with celecoxib on CD133(+) and CD133(-) glioblastoma cells. Three separate xenotransplantation experiments were carried out using 310 severe combined immunodeficient (SCID) mice: 1) an initial tumorigenicity evaluation in which 3 different quantities of untreated CD133(-) cells or untreated or pretreated CD133(+) cells (5 treatment conditions) from 7 different tumors were injected into the striatum of 2 mice (210 mice total); 2) a tumor growth study (50 mice); and 3) a survival study (50 mice). For these last 2 studies the same 5 categories of cells were used as in the tumorigenicity (untreated CD133(-) cells, untreated or pretreated CD133(+) cells, with pretreatment consisting of celecoxib alone, IR alone, or IR and celecoxib), but only 1 cell source (Case 2) and quantity (5 × 10(4) cells) were used.

RESULTS

High levels of COX-2 protein were detected in the CD133(+) but not the CD133(-) glioblastoma cells. The authors further demonstrated that 30 μM celecoxib was able to effectively enhance the IR effect in inhibiting colony formation and increasing IR-mediated apoptosis in celecoxib-treated CD133(+) glioblastoma cells. Furthermore, reduction in radioresistance was correlated with the induction of G2/M arrest, which was partially mediated through the increase in the level of phosphorylated-cdc2. In vivo xenotransplant analysis further confirmed that CD133(+)-associated tumorigenicity was significantly suppressed by celecoxib treatment. Importantly, pretreatment of CD133(+) glioblastoma cells with a combination of celecoxib and IR before injection into the striatum of SCID mice resulted in a statistically significant reduction in tumor growth and a statistically significant increase in the mean survival rate of the mice.

CONCLUSIONS

Celecoxib combined with radiation plays a critical role in the suppression of growth of CD133(+) glioblastoma stemlike cells. Celecoxib is therefore a radiosensitizing drug for clinical application in glioblastoma.

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.

Simultaneous color-coded imaging to distinguish cancer "stem-like" and non-stem cells in the same tumor

In this study, we demonstrate that the differential behavior, including malignancy and chemosensitivity, of cancer stem-like and non-stem cells can be simultaneously distinguished in the same tumor in real time by color-coded imaging. CD133(+) Huh-7 human hepatocellular carcinoma (HCC) cells were considered as cancer stem-like cells (CSCs), and CD133(-) Huh-7 cells were considered as non-stem cancer cells (NSCCs). CD133(+) cells were isolated by magnetic bead sorting after Huh-7 cells were genetically labeled with green fluorescent protein (GFP) or red fluorescent protein (RFP). In this scheme, CD133(+) cells were labeled with GFP and CD133(-) cells were labeled with RFP. CSCs had higher proliferative potential compared to NSCCs in vitro. The same number of GFP CSCs and the RFP NSCCs were mixed and injected subcutaneously or in the spleen of nude mice. CSCs were highly tumorigenic and metastatic as well as highly resistant to chemotherapy in vivo compared to NSCCs. The ability to specifically distinguish stem-like cancer cells in vivo in real time provides a visual target for prevention of metastasis and drug resistance.

Toponome imaging system: in situ protein network mapping in normal and cancerous colon from the same patient reveals more than five-thousand cancer specific protein clusters and their subcellular annotation by using a three symbol code

In a proof of principle study, we have applied an automated fluorescence toponome imaging system (TIS) to examine whether TIS can find protein network structures, distinguishing cancerous from normal colon tissue present in a surgical sample from the same patient. By using a three symbol code and a power of combinatorial molecular discrimination (PCMD) of 2(21) per subcellular data point in one single tissue section, we demonstrate an in situ protein network structure, visualized as a mosaic of 6813 protein clusters (combinatorial molecular phenotype or CMPs), in the cancerous part of the colon. By contrast, in the histologically normal colon, TIS identifies nearly 5 times the number of protein clusters as compared to the cancerous part (32 009). By subcellular visualization procedures, we found that many cell surface membrane molecules were closely associated with the cell cytoskeleton as unique CMPs in the normal part of the colon, while the same molecules were disassembled in the cancerous part, suggesting the presence of dysfunctional cytoskeleton-membrane complexes. As expected, glandular and stromal cell signatures were found, but interestingly also found were potentially TIS signatures identifying a very restricted subset of cells expressing several putative stem cell markers, all restricted to the cancerous tissue. The detection of these signatures is based on the extreme searching depth, high degree of dimensionality, and subcellular resolution capacity of TIS. These findings provide the technological rationale for the feasibility of a complete colon cancer toponome to be established by massive parallel high throughput/high content TIS mapping.

Mullerian inhibiting substance preferentially inhibits stem/progenitors in human ovarian cancer cell lines compared with chemotherapeutics

Cancer stem cells are proposed to be tumor-initiating cells capable of tumorigenesis, recurrence, metastasis, and drug resistance, and, like somatic stem cells, are thought to be capable of unlimited self-renewal and, when stimulated, proliferation and differentiation. Here we select cells by expression of a panel of markers to enrich for a population with stem cell-like characteristics. A panel of eight was initially selected from 95 human cell surface antigens as each was shared among human ovarian primary cancers, ovarian cancer cell lines, and normal fimbria. A total of 150 combinations of markers were reduced to a panel of three--CD44, CD24, and Epcam--which selected, in three ovarian cancer cell lines, those cells which best formed colonies. Cells expressing CD44, CD24, and Epcam exhibited stem cell characteristics of shorter tumor-free intervals in vivo after limiting dilution, and enhanced migration in invasion assays in vitro. Also, doxorubicin, cisplatin, and paclitaxel increased this enriched population which, conversely, was significantly inhibited by Müllerian inhibiting substance (MIS) or the MIS mimetic SP600125. These findings demonstrate that flow cytometry can be used to detect a population which shows differential drug sensitivity, and imply that treatment of patients can be individualized to target both stem/progenitor cell enriched and nonenriched subpopulations. The findings also suggest that this population, amenable to isolation by flow cytometry, can be used to screen for novel treatment paradigms, including biologic agents such as MIS, which will improve outcomes for patients with ovarian cancer.

Specific gene transfer to neurons, endothelial cells and hematopoietic progenitors with lentiviral vectors

We present a flexible and highly specific targeting method for lentiviral vectors based on single-chain antibodies recognizing cell-surface antigens. We generated lentiviral vectors specific for human CD105(+) endothelial cells, human CD133(+) hematopoietic progenitors and mouse GluA-expressing neurons. Lentiviral vectors specific for CD105 or for CD20 transduced their target cells as efficiently as VSV-G pseudotyped vectors but discriminated between endothelial cells and lymphocytes in mixed cultures. CD133-targeted vectors transduced CD133(+) cultured hematopoietic progenitor cells more efficiently than VSV-G pseudotyped vectors, resulting in stable long-term transduction. Lentiviral vectors targeted to the glutamate receptor subunits GluA2 and GluA4 exhibited more than 94% specificity for neurons in cerebellar cultures and when injected into the adult mouse brain. We observed neuron-specific gene modification upon transfer of the Cre recombinase gene into the hippocampus of reporter mice. This approach allowed targeted gene transfer to many cell types of interest with an unprecedented degree of specificity.

Expression of the zebrafish CD133/prominin1 genes in cellular proliferation zones in the embryonic central nervous system and sensory organs

The CD133/prominin1 gene encodes a pentamembrane glycoprotein cell surface marker that is expressed in stem cells from neuroepithelial, hematopoietic, and various organ tissues. Here we report the analysis of two zebrafish CD133/prominin1 orthologues, prominin1a and prominin1b. The expression patterns of the zebrafish prominin1a and b genes were analyzed during embryogenesis using whole mount in situ hybridization. prominin1a and b show novel complementary and overlapping patterns of expression in proliferating zones in the developing sensory organs and central nervous system. The expression patterns suggest functional conservation of the zebrafish prominin1 genes. Initial analyses of prominin1a and b in neoplastic tissue show increased expression of both genes in a subpopulation of cells in malignant peripheral nerve sheath tumors in tp53 mutants. Based on these analyses, the zebrafish prominin1 genes will be useful markers for examining proliferating cell populations in adult organs, tissues, and tumors.

Human endothelial stem/progenitor cells, angiogenic factors and vascular repair

Neovascularization or new blood vessel formation is of utmost importance not only for tissue and organ development and for tissue repair and regeneration, but also for pathological processes, such as tumour development. Despite this, the endothelial lineage, its origin, and the regulation of endothelial development and function either intrinsically from stem cells or extrinsically by proangiogenic supporting cells and other elements within local and specific microenvironmental niches are still not fully understood. There can be no doubt that for most tissues and organs, revascularization represents the holy grail for tissue repair, with autologous endothelial stem/progenitor cells, their proangiogenic counterparts and the products of these cells all being attractive targets for therapeutic intervention. Historically, a great deal of controversy has surrounded the identification and origin of cells and factors that contribute to revascularization, the use of such cells or their products as biomarkers to predict and monitor tissue damage and repair or tumour progression and therapeutic responses, and indeed their efficacy in revascularizing and repairing damaged tissues. Here, we will review the role of endothelial progenitor cells and of supporting proangiogenic cells and their products, principally in humans, as diagnostic and therapeutic agents for wound repair and tissue regeneration.

Tumor and host factors that may limit efficacy of chemotherapy in non-small cell and small cell lung cancer

While chemotherapy provides useful palliation, advanced lung cancer remains incurable since those tumors that are initially sensitive to therapy rapidly develop acquired resistance. Resistance may arise from impaired drug delivery, extracellular factors, decreased drug uptake into tumor cells, increased drug efflux, drug inactivation by detoxifying factors, decreased drug activation or binding to target, altered target, increased damage repair, tolerance of damage, decreased proapoptotic factors, increased antiapoptotic factors, or altered cell cycling or transcription factors. Factors for which there is now substantial clinical evidence of a link to small cell lung cancer (SCLC) resistance to chemotherapy include MRP (for platinum-based combination chemotherapy) and MDR1/P-gp (for non-platinum agents). SPECT MIBI and Tc-TF scanning appears to predict chemotherapy benefit in SCLC. In non-small cell lung cancer (NSCLC), the strongest clinical evidence is for taxane resistance with elevated expression or mutation of class III beta-tubulin (and possibly alpha tubulin), platinum resistance and expression of ERCC1 or BCRP, gemcitabine resistance and RRM1 expression, and resistance to several agents and COX-2 expression (although COX-2 inhibitors have had minimal impact on drug efficacy clinically). Tumors expressing high BRCA1 may have increased resistance to platinums but increased sensitivity to taxanes. Limited early clinical data suggest that chemotherapy resistance in NSCLC may also be increased with decreased expression of cyclin B1 or of Eg5, or with increased expression of ICAM, matrilysin, osteopontin, DDH, survivin, PCDGF, caveolin-1, p21WAF1/CIP1, or 14-3-3sigma, and that IGF-1R inhibitors may increase efficacy of chemotherapy, particularly in squamous cell carcinomas. Equivocal data (with some positive studies but other negative studies) suggest that NSCLC tumors with some EGFR mutations may have increased sensitivity to chemotherapy, while K-ras mutations and expression of GST-pi, RB or p27kip1 may possibly confer resistance. While limited clinical data suggest that p53 mutations are associated with resistance to platinum-based therapies in NSCLC, data on p53 IHC positivity are equivocal. To date, resistance-modulating strategies have generally not proven clinically useful in lung cancer, although small randomized trials suggest a modest benefit of verapamil and related agents in NSCLC.

The utility and limitations of neurosphere assay, CD133 immunophenotyping and side population assay in glioma stem cell research

The newly proposed glioma stem cell (GSC) hypothesis may re-model the way we diagnose and treat the tumor, which highlights the need for a complete knowledge on the genetic and epigenetic "blueprints" of GSCs. To identify the true "stemness" signatures, pure GSC populations are primarily needed. Reliable in vitro methods enriching for GSCs and thereby identifying the key stem-like characteristics constitute the preliminary step forward. We discuss in this review the current widely used methods for enriching and isolating GSCs, namely neurosphere assay, CD133 Immunophenotyping and side population assay, and detail their limitations and potential pitfalls that could complicate interpretation of corresponding results.

Toll-like receptor (TLR) 7 and TLR8 expression on CD133+ cells in colorectal cancer points to a specific role for inflammation-induced TLRs in tumourigenesis and tumour progression

Toll-like receptor (TLR) stimulation results in activation of NF-κB, a key modulator in driving inflammation to cancer and mitogen-activated protein kinases that have been shown to recruit mitotic and cyclooxygenase-2 (COX-2) induced pathways in carcinogenesis. Here we asked whether different TLR, COX-2 and stem cell marker expression profiles in colorectal cancer (CRC) provide further evidence for this hypothesis from a clinical perspective. We analysed gene and protein expression of TLR7-TLR10, COX-2 and CD133 as a marker for colon-initiating cells in CRC patients (n=65). Gene analysis demonstrated significantly upregulated TLR7-TLR10 and COX-2 expression in CRC tumour tissues. Analysis of isolated tumour cells from primary tumours showed co-expression of TLR7 and TLR8 with CD133 and gave evidence for a subpopulation of colon cancer-initiating cells. In multivariate analyses TLR8 expression was found to be an independent prognostic factor. Persistent TLR-specific activation of NF-κB in CRC and particularly in tumour-initiating cells may thus sustain further tumour growth and progression through perpetuated signalling known from inflammatory and tissue repair mechanisms with consecutive self-renewal in pluripotent tumour cells. Activation through self-ligands or viral RNA fragments may putatively maintain this inflammatory process, suggesting a key role in cancer progression.

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.

Photothermolysis of glioblastoma stem-like cells targeted by carbon nanotubes conjugated with CD133 monoclonal antibody

CD133(+) cells in glioblastoma (GBM) display cancer stem cell-like properties and have been considered as the culprit of tumor recurrence, justifying exploration of potential therapeutic modalities targeting CD133(+) cancer stem-like cells (CSCs). For photothermolysis studies, GBM-CD133(+) and GBM-CD133(-) cells mixed with various ratios were challenged with single-walled carbon nanotubes (SWNTs) conjugated with CD133 monoclonal antibody (anti-CD133) and then irradiated with near-infrared laser light. Results show that GBM-CD133(+) cells were selectively targeted and eradicated, whereas GBM-CD133(-) cells remained viable. In addition, in vitro tumorigenic and self-renewal capability of GBM-CD133(+) treated with localized hyperthermia was significantly blocked. Furthermore, GBM-CD133(+) cells pretreated with anti-CD133-SWNTs and irradiated by near-infrared laser 2 days after xenotransplantation in nude mice did not exhibit sustainability of CSC features for tumor growth. Taken altogether, our studies demonstrated that anti-CD133-SWNTs have the potential to be utilized as a thermal-coupling agent to effectively target and destroy GBM CSCs in vitro and in vivo.

FROM THE CLINICAL EDITOR

Glioblastoma remains one of the most notorious cancer from the standpoint of recurrence and overall resistance to therapy. CD133+ stem cells occur among GBM cells, and may be responsible for the huge recurrence risk. This paper discusses a targeted elimination method of these cells, which may enable more efficient therapy in an effort to minimize or prevent recurrence.

The role and therapeutic potential of endothelial progenitor cells in tumor neovascularization

Although the cellular and molecular mechanisms of tumor growth and metastasis are not completely understood, it is established that formation and growth of new blood vessels is a conditio sine qua non for tumor survival, growth, and expansion. Numerous studies over the past decades demonstrated that neovascularization associated with tumor growth occurs via angiogenic and vasculogenic mechanisms that involve sprouting angiogenesis, intussusceptive angiogenesis, vessel co-option, vasculogenic mimicry, lymphangiogenesis, and the recruitment of endothelial progenitor cells (EPCs). Due to their ability to self-renew, circulate, home to the ischemic sites, and differentiate into mature endothelial cells, EPCs hold enormous potential to be used as a diagnostic and/or therapeutic agent in antitumor therapies. Hence, this review focuses on EPCs and their role in tumor angiogenesis with the emphasis on EPC recruitment/migration, and the potential use of EPCs as a therapeutic tool and imaging probe.