Persistence of a small subpopulation of cancer stem-like cells in the C6 glioma cell line

Berberine diminishes side population and down-regulates stem cell-associated genes in the pancreatic cancer cell lines PANC-1 and MIA PaCa-2

Cancer stem cells play an important role in metastasis and the relapse of drug resistant cancers. Side-population (SP) cells are capable of effluxing Hoechst 33342 dye and are referred to as cancer stem cells. We investigated the effect of berberine on pancreatic cancer stem cells of PANC-1 and MIA PaCa-2. For both cell lines, the proportions of SP cells in the presence of berberine were investigated and compared to the proportions in the presence of gemcitabine, a standard pancreatic anti-cancer drug. The proportions of SP cells in the PANC-1 and MIA PaCa-2 cell lines were about 9 and <0.1%, respectively. After berberine and gemcitabine treatments, the SP cell proportion of PANC-1 decreased to 5.7 ± 2.0 and 6.8 ± 0.8%, respectively, which compares to the control proportion of (9.7 ± 1.7). After berberine and gemcitabine treatment of PANC-1, of the four stem cell-associated genes (SOX2, POU5F1, NANOG, and NOTCH1), all but NOTCH1 were down-regulated. Unfortunately, the effect of berberine and gemcitabine treatments on MIA PaCa-2 SP cells could not be clearly observed because SP cells represented only a very small proportion of MIA PaCa-2 cells. However, SOX2, POU5F1, and NANOG genes were shown to be effectively down-regulated in the MIA PaCa-2 cell line as a whole. Taken together, these results indicate that berberine is as effective at targeting pancreatic cancer cell lines as gemcitabine. Therefore, we believe that POU5F1, SOX2, and NANOG can serve as potential markers, and berberine may be an effective anti-cancer agent when targeting human pancreatic cancer cells and/or their cancer stem cells.

Glioma spheroids obtained via ultrasonic aspiration are viable and express stem cell markers: a new tissue resource for glioma research

BACKGROUND

Ultrasonic aspirators allow safe, rapid, and accurate removal of brain tumors. However, the tissue fragments removed are used surprisingly little in research.

OBJECTIVE

To investigate whether such tissue fragments could be cultured as organotypic multicellular spheroids because access to biopsy tissue is often limited.

METHODS

Tissue fragments obtained by ultrasonic aspiration from 10 glioblastomas and tumor biopsy tissue from 7 of these tumors were cultured in serum-containing and serum-free medium. On culturing, the fragments formed spheroids, which were prepared for histology. Two glioblastoma cell lines from ultrasonic fragments and biopsy tissue were established as well.

RESULTS

Hematoxylin and eosin staining showed viable glioma spheroids obtained from both ultrasonic and biopsy tissue in both types of medium. Endothelial growth factor receptor and PTEN/chromosome 10 status was found to be preserved in most spheroids (7-8 of 10 tumors), together with the level of glial fibrillary acidic protein, von Willebrand factor, and Ki-67. The levels of stem cell markers CD133, Bmi-1, nestin, and Sox2 also were preserved. The ultrasonic spheroids had higher levels of glial fibrillary acidic protein and von Willebrand factor and lower levels of Bmi-1, nestin, Sox2, and Olig2 compared with conventional biopsy spheroids. For both types of spheroids, the stem cell medium seemed to favor expression of stem cell markers. The established cell lines were capable of both spheroid formation at clonal density and tumor formation in vivo.

CONCLUSION

Viable organotypic and proliferating spheroids were easily obtained from ultrasonic tissue fragments. The preservation of markers and the establishment of cell lines with tumor-initiating cell properties suggest ultrasonic spheroids as a new tissue resource for glioma research.

MAGE-A3 is highly expressed in a cancer stem cell-like side population of bladder cancer cells

Cancer stem cells (CSCs), which have the abilities of tumor-initiating, self-renewal and differentiation, are thought to cause post-therapeutic recurrence and the progression of cancer. However, CSCs are commonly resistant to current cancer therapies including chemotherapy and radiotherapy. In this study, we isolated cancer stem celllike side population (SP) cells from human bladder cancer cell line SW780 by a flow cytometry-based SP technique. SP cells were only about 3.6% of SW780 cells and showed higher expression of ATP-binding cassette sub-family G member 2 (ABCG2) and CD133. In vitro assay of tumor sphere growth as well as in vivo assay of xenograft transplantation confirmed the higher tumorigenicity of isolated SP cells. These data indicated that SP cells were enriched with CSCs of bladder cancer. Furthermore, we determined the expression of melanoma antigen family A, 3 (MAGEA3), one of the most studied cancer testis (CT) antigens, in these SP and main population (MP) cells derived from SW780 cells. SW780 SP cells representing CSCs of bladder cancer showed an up-regulated expression of MAGE-A3 and a positive coexpression of MAGE-A3 and CD133, indicating that MAGE-A3 was a novel CT antigen preferentially expressed in the CSCs of bladder cancer. In summary, our findings confirmed the existence of cancer stem cell-like SP cells in bladder cancer cells, and further indicated that MAGE-A3 is a novel CSC antigen and therefore may serve as an immunotherapeutic target for CSCs of bladder cancer.

Cancer stem cells: biological functions and therapeutically targeting

Almost all tumors are composed of a heterogeneous cell population, making them difficult to treat. A small cancer stem cell population with a low proliferation rate and a high tumorigenic potential is thought to be responsible for cancer development, metastasis and resistance to therapy. Stem cells were reported to be involved in both normal development and carcinogenesis, some molecular mechanisms being common in both processes. No less controversial, stem cells are considered to be important in treatment of malignant diseases both as targets and drug carriers. The efforts to understand the role of different signalling in cancer stem cells requires in depth knowledge about the mechanisms that control their self-renewal, differentiation and malignant potential. The aim of this paper is to discuss insights into cancer stem cells historical background and to provide a brief review of the new therapeutic strategies for targeting cancer stem cells.

Cells isolated from human glioblastoma multiforme express progesterone-induced blocking factor (PIBF)

Glioblastoma multiforme (GBM) is the most common and malignant tumor in the central nervous system. One of the contemporary hypotheses postulates that its pathogenesis is associated with the cancer stem cells (CSCs) which originate from mutations in the normal neural stem cells residing in their specific "niches." Simultaneously with its aggressive development the tumor suppresses the local immune system by different secreted and/or cell expressed factors. Progesterone-induced blocking factor (PIBF) is an immunomodulatory protein with known role in the regulation of the immune response in the reproductive system. Expression of PIBF has been described in some tumors as one of the factors suppressing the anti-tumor immunity. The aim of the present study was to check for the expression of PIBF from cells isolated from six GBMs. To characterize the cultured cells and to study the PIBF expression confocal microscopy, flow cytometry, ELISA, and real-time PCR were used. The results obtained showed expression of markers typical for cancer CSCs and secretion of interleukin 6 by the GBM-derived cultured cells. The results convincingly prove that PIBF is intracellularly expressed by the cultured cells from the all six GBM samples, and this fact is confirmed by three different methods-flow cytometry, confocal microscopy, and real-time PCR. This paper reports for the first time the expression of PIBF by GBM-derived cells cultured in vitro and reveals a new aspect of the immunosuppressive mechanism used by GBM in escaping the immune control.

Side population cell fractions from hepatocellular carcinoma cell lines increased with tumor dedifferentiation, but lack characteristic features of cancer stem cells

BACKGROUND AND AIM

Cancer stem cells (CSCs), a minority population with stem cell-like characteristics, play important roles in cancer development and progression. Putative CSC markers, such as CD13, CD90, CD133, and epithelial cell adhesion molecule (EpCAM), and side population (SP) technique are generally used in an attempt to isolate CSCs. We aimed to clarify the relationship between CSCs and clonal dedifferentiation in hepatocellular carcinoma (HCC).

METHODS

We used a well-differentiated HCC cell line (HAK-1A) and a poorly differentiated HCC cell line (HAK-1B) established from a single nodule with histological heterogeneity. HAK-1B arose because of clonal dedifferentiation of HAK-1A. The SP cells and non-SP (NSP) cells were isolated from the two cell lines with a FACSAria II and used for the analyses.

RESULTS

The SP cell fractions in HAK-1A and HAK-1B were 0.2% and 0.9%, respectively. CD90 or EpCAM was not expressed in either HAK-1A or HAK-1B, while CD13 and CD133 were expressed in HAK-1B alone. Although sphere forming ability, tumorigenicity, growth rate, and CD13 expression were higher in HAK-1B SP cells than HAK-1B NSP cells, there were no differences in drug resistance, colony forming ability, or cell cycle rates between HAK-1B SP and NSP cells, suggesting HAK-1B SP cells do not fulfill CSC criteria.

CONCLUSIONS

Our findings suggested a possible relationship between the expression of CSC markers and clonal dedifferentiation. However, the complete features of CSC could not be identified in SP cells, and the concept of SP cells as a universal marker for CSC may not apply to HAK-1A and HAK-1B.

Expressions of ABCG2, CD133, and podoplanin in salivary adenoid cystic carcinoma

Adenoid cystic carcinoma (ACC) is one of the most common salivary gland malignant tumors with a high risk of recurrence and metastasis. Current studies on cancer stem cells (CSCs) have verified that CSCs are the driving force behind tumor initiation and progression, suggesting that new cancer therapies may be established by effectively targeting and killing the CSCs. The primary goal of this study is to investigate the expression patterns of ABCG2, CD133, and podoplanin in ACC of minor salivary glands by immunohistochemistry analysis. We found that ABCG2 was weakly expressed in normal looking salivary gland tissues. A significant upregulation of ABCG2 expression in ACC was observed with a similar expression pattern of Ki-67. CD133 was detected in apical membrane of epithelial cells and podoplanin was expressed positively in myoepithelial cells of both normal looking tissue and ACC. However, no significant difference was found of the expression pattern of CD133 and podoplanin between normal looking tissues and ACC. Our observations suggest that CSCs may exist in quiescent cells with ABCG2 positive staining, which are surrounded by cells with positive expression of ABCG2 and Ki-67 in ACC, and costaining with ABCG2 and Ki-67 may help predict the location of CSCs.

Type 1 collagen as a potential niche component for CD133-positive glioblastoma cells

Cancer stem cells are thought to be closely related to tumor progression and recurrence, making them attractive therapeutic targets. Stem cells of various tissues exist within niches maintaining their stemness. Glioblastoma stem cells (GSCs) are located at tumor capillaries and the perivascular niche, which are considered to have an important role in maintaining GSCs. There were some extracellular matrices (ECM) on the perivascular connective tissue, including type 1 collagen. We here evaluated whether type 1 collagen has a potential niche for GSCs. Imunohistochemical staining of type 1 collagen and CD133, one of the GSCs markers, on glioblastoma (GBM) tissues showed CD133-positive cells were located in immediate proximity to type 1 collagen around tumor vessels. We cultured human GBM cell lines, U87MG and GBM cells obtained from fresh surgical tissues, T472 and T555, with serum-containing medium (SCM) or serum-free medium with some growth factors (SFM) and in non-coated (Non-coat) or type 1 collagen-coated plates (Col). The RNA expression levels of CD133 and Nestin as stem cell markers in each condition were examined. The Col condition not only with SFM but SCM made GBM cells more enhanced in RNA expression of CD133, compared to Non-coat/SCM. Semi-quantitative measurement of CD133-positive cells by immunocytochemistry showed a statistically significant increase of CD133-positive cells in Col/SFM. In addition, T472 cell line cultured in the Col/SFM had capabilities of sphere formation and tumorigenesis. Type 1 collagen was found in the perivascular area and showed a possibility to maintain GSCs. These findings suggest that type 1 collagen could be one important niche component for CD133-positive GSCs and maintain GSCs in adherent culture.

Nicotine promotes apoptosis resistance of breast cancer cells and enrichment of side population cells with cancer stem cell-like properties via a signaling cascade involving galectin-3, α9 nicotinic acetylcholine receptor and STAT3

Nicotine, a main addictive compound in tobacco smoke, has been linked to promotion and progression of lung, head and neck, pancreatic, and breast cancers, but the detailed mechanisms of cancer progression remain elusive. Here, we show that nicotine induces the expression of galectin-3 (an anti-apoptotic β-galactoside-binding lectin) in breast cancer cell line and in primary tumors from breast cancer patients. Nicotine-induced up regulation of galectin-3 is due to an increased expression of α9 isoform of nicotinic acetylcholine receptor (α9nAChR), which activates transcription factor STAT3 that in turn, physically binds to galectin-3 (LGALS3) promoter and induces transcription of galectin-3. Intracellular galectin-3 increased mitochondrial integrity and suppressed chemotherapeutic-induced apoptosis of breast cancer cell. Moreover, nicotine-induced enrichment of side population cells with cancer stem cell-like properties was modulated by galectin-3 expression and could be significantly reduced by transient knock down of LGALS3 and its upstream signaling molecules STAT3 and α9nAChR. Thus, galectin-3 or its upstream signaling molecule STAT3 or α9nAChR could be a potential target to prevent nicotine-induced chemoresistance in breast cancer.

Enhanced myeloid differentiation factor 88 promotes tumor metastasis via induction of epithelial-mesenchymal transition in human hepatocellular carcinoma

Metastasis is the leading cause of death in patients with hepatocellular carcinoma (HCC) after curative resection. Therefore, it is critical to understand the mechanisms underlying tumor metastasis in HCC. We have previously shown that elevated expression of myeloid differentiation factor 88 (MyD88) may promote tumor growth and metastasis in HCC. In this study, we reported that enhanced expression of MyD88 promoted epithelial–mesenchymal transition (EMT) properties and tumor-initiating capabilities in HCC cells. MyD88 was found to be able to interact with p85, a regulatory subunit of phosphoinositide 3-kinase (PI3-K), independent of TLR/IL-1R-mediated response and caused PI3-K/v-akt murine thymoma viral oncogene homolog (Akt) activation, which resulted in subsequent phosphorylation of glycogen synthase kinase-3β and stabilization of Snail, a critical EMT mediator. Consistently, we observed a significant correlation between MyD88 expression and p-Akt levels in a cohort of HCC patients, and found that the combination of these two parameters have better prognostic value for HCC patients. Taken together, these results suggest that elevated MyD88 may facilitate HCC metastasis by promoting EMT properties and tumor-initiating capabilities via PI3–K/Akt pathway.

Kinase-independent mechanisms of resistance of leukemia stem cells to tyrosine kinase inhibitors

Tyrosine kinase inhibitors such as imatinib mesylate have changed the clinical course of chronic myeloid leukemia; however, the observation that these inhibitors do not target the leukemia stem cell implies that patients need to maintain lifelong therapy. The mechanism of this phenomenon is unclear: the question of whether tyrosine kinase inhibitors are inactive inside leukemia stem cells or whether leukemia stem cells do not require breakpoint cluster region (Bcr)-Abl signaling is currently under debate. Herein, I propose an alternative model: perhaps the leukemia stem cell requires Bcr-Abl, but is dependent on its kinase-independent functions. Kinases such as epidermal growth factor receptor and Janus kinase 2 possess kinase-independent roles in regulation of gene expression; it is worth investigating whether Bcr-Abl has similar functions. Mechanistically, Bcr-Abl is able to activate the Ras, phosphatidylinositol 3-kinase/Akt, and/or the Src-kinase Hck/Stat5 pathways in a scaffolding-dependent manner. Whereas the scaffolding activity of Bcr-Abl with Grb2 is dependent on autophosphorylation, kinases such as Hck can use Bcr-Abl as substrate, inducing phosphorylation of Y177 to enable scaffolding ability in the absence of Bcr-Abl catalytic activity. It is worth investigating whether leukemia stem cells exclusively express kinases that are able to use Bcr-Abl as substrate. A kinase-independent role for Bcr-Abl in leukemia stem cells would imply that drugs that target Bcr-Abl's scaffolding ability or its DNA-binding ability should be used in conjunction with current therapeutic regimens to increase their efficacy and eradicate the stem cells of chronic myeloid leukemia.

An endogenous inhibitor of angiogenesis inversely correlates with side population phenotype and function in human lung cancer cells

The side population (SP) in human lung cancer cell lines and tumors is enriched with cancer stem cells. An endogenous inhibitor of angiogenesis known as tissue inhibitor of matrix metalloproteinase-2 (TIMP-2), characterized for its ability to inhibit matrix metalloproteinases (MMPs), has been shown by several laboratories to impede tumor progression through MMP-dependent or -independent mechanisms. We recently reported that forced expression of TIMP-2, as well as the modified form Ala+TIMP-2 (that lacks MMP inhibitory activity) significantly blocks growth of A549 human lung cancer cells in vivo. However, the mechanisms underlying TIMP-2 antitumor effects are not fully characterized. Here, we examine the hypothesis that the TIMP-2 antitumor activity may involve regulation of the SP in human lung cancer cells. Indeed, using Hoechst dye efflux assay and flow cytometry, as well as quantitative reverse transcriptase-PCR analysis, we found that endogenous TIMP-2 mRNA levels showed a significant inverse correlation with SP fraction size in six non-small cell lung cancer cell lines. In A549 cells expressing increased levels of TIMP-2, a significant decrease in SP was observed, and this decrease was associated with lowered gene expression of ABCG2, ABCB1 and AKR1C1. Functional analysis of A549 cells showed that TIMP-2 overexpression increased chemosensitivity to cytotoxic drugs. The SP isolated from TIMP-2-overexpressing A549 cells also demonstrated impaired migratory capacity compared with the SP from empty vector control. More importantly, our data provide strong evidence that these TIMP-2 functions occur independent of MMP inhibition, as A549 cells overexpressing Ala+TIMP-2 exhibited identical behavior to those overexpressing TIMP-2 alone. Our findings provide the first indication that TIMP-2 modulates SP phenotype and function, and suggests that TIMP-2 may act as an endogenous suppressor of the SP in human lung cancer cells.

Determination of telomerase activity in stem cells and non-stem cells of breast cancer

Although all normal tissue cells, including stem cells, are genetically homologous, variation in gene expression patterns has already determined the distinct roles for individual cells in the physiological process due to the occurrence of epigenetic modification. This is of special importance for the existence of tissue stem cells because they are exclusively immortal within the body, capable of self-replicating and differentiating by which tissues renew and repair itself and the total tissue cell population maintains a steady-state. Impairment of tissue stem cells is usually accompanied by a reduction in cell number, slows down the repair process and causes hypofunction. For instance, chemotherapy usually leads to depression of bone marrow and hair loss. Cellular aging is closely associated with the continuous erosion of the telomere while activation of telomerase repairs and maintains telomeres, thus slowing the aging process and prolonging cell life. In normal adults, telomerase activation mainly presents in tissue stem cells and progenitor cells giving them unlimited growth potential. Despite the extensive demonstration of telomerase activation in malignancy (> 80%), scientists found that heterogeneity also exists among the tumor cells and only minorities of cells, designated as cancer stem cells, undergo processes analogous to the self-renewal and differentiation of normal stem cells while the rest have limited lifespans. In this study, telomerase activity was measured and compared in breast cancer stem cells and non-stem cells that were phenotypically sorted by examining surface marker expression. The results indicated that cancer stem cells show a higher level of enzyme activity than non-stem cells. In addition, associated with the repair of cancer tissue (or relapse) after chemotherapy, telomerase activity in stem cells was markedly increased.

MC3 Mucoepidermoid carcinoma cell line enriched cancer stem-like cells following chemotherapy

Mucoepidermoid carcinoma (MEC) is common in human salivary glands. Surgery is the preferred treatment method for MEC and chemotherapy is often administered following surgery as an adjuvant cancer treatment; however, chemotherapy does not completely prevent tumor recurrence. Emerging evidence has indicated the existence of cancer stem-like (CSL)-cells in tumors. CSL-cells are important in the development, invasion and drug resistance of carcinomas. The present study aimed to investigate whether chemotherapy enriched the CSL-cells in the MEC cell line of MC3 using 5-fluorouracil (5-Fu). The MC3 cells were treated with 5-Fu, which enhanced the spherogenesis and vitality of the cells and upregulated the pluripotency gene, octamer-binding transcription factor 4. Side population analysis demonstrated that the proportion of CSL-cells also increased. These findings showed that compared with other types of cancer cells, chemotherapy was unable to effectively kill the CSL-cells resulting in an enriched CSL-cell subpopulation with a higher resistance to chemotherapy, which may have been key the recurrence of MEC.

Loss of TRPV2 Homeostatic Control of Cell Proliferation Drives Tumor Progression

Herein we evaluate the involvement of the TRPV2 channel, belonging to the Transient Receptor Potential Vanilloid channel family (TRPVs), in development and progression of different tumor types. In normal cells, the activation of TRPV2 channels by growth factors, hormones, and endocannabinoids induces a translocation of the receptor from the endosomal compartment to the plasma membrane, which results in abrogation of cell proliferation and induction of cell death. Consequently, loss or inactivation of TRPV2 signaling (e.g., glioblastomas), induces unchecked proliferation, resistance to apoptotic signals and increased resistance to CD95-induced apoptotic cell death. On the other hand, in prostate cancer cells, Ca2+-dependent activation of TRPV2 induced by lysophospholipids increases the invasion of tumor cells. In addition, the progression of prostate cancer to the castration-resistant phenotype is characterized by de novo TRPV2 expression, with higher TRPV2 transcript levels in patients with metastatic cancer. Finally, TRPV2 functional expression in tumor cells can also depend on the presence of alternative splice variants of TRPV2 mRNA that act as dominant-negative mutant of wild-type TRPV2 channels, by inhibiting its trafficking and translocation to the plasma membrane. In conclusion, as TRP channels are altered in human cancers, and their blockage impair tumor progression, they appear to be a very promising targets for early diagnosis and chemotherapy.

Integrin inhibition promotes atypical anoikis in glioma cells

Integrins regulate cellular adhesion and transmit signals important for cell survival, proliferation and motility. They are expressed by glioma cells and may contribute to their malignant phenotype. Integrin inhibition may therefore represent a promising therapeutic strategy. GL-261 and SMA-560 glioma cells grown under standard conditions uniformly detached and formed large cell clusters after integrin gene silencing or pharmacological inhibition using EMD-121974, a synthetic Arg-Gly-Asp-motif peptide, or GLPG0187, a nonpeptidic integrin inhibitor. After 120 h, the clusters induced by integrin inhibition decayed and cells died. In contrast, when cells were cultured under stem cell (sphere) conditions, no disaggregation became apparent upon integrin inhibition, and cell death was not observed. As poly-HEMA-mediated detachment had similar effects on cell viability as integrin inhibition, we postulated that cell death may result from detachment alone, which was confirmed using various permissive and nonpermissive substrates. No surrogate markers of apoptosis were detected and electron microscopy confirmed that necrosis represents the dominant morphology of detachment-induced cell death. In addition, integrin inhibition resulted in the induction of autophagy that represents a survival signal. When integrins were inhibited in nonsphere glioma cells, the TGF-β pathway was strongly impaired, whereas no such effect was observed in glioma cells cultured under sphere conditions. Cell death induced by integrin inhibition was rescued by the addition of recombinant transforming growth factor-β (TGF-β) and accelerated by exposure to the TGF-β receptor inhibitor, SD-208. In summary, cell death following integrin inhibition is detachment mediated, represents an atypical form of anoikis involving necrosis as well as autophagy, and is modulated by TGF-β pathway activity.

Side populations from cervical-cancer-derived cell lines have stem-cell-like properties

The target cells for the transforming mutations caused by high-risk human papillomavirus (HPV) infection could be the stem cells of the uterine cervical epithelium, generating particular cancer stem cells (CSCs). The aim of this study was to identify and characterize the CSCs from cervical-cancer-derived cell lines. The ability of SiHa, CaLo, and C-33A cell lines to efflux Hoechst 33342 was evaluated by flow cytometry and cells from the corresponding side populations (SPs) and nonside populations (NSPs) were analyzed for their cell-cycle status (pyronin Y) and their mRNA levels of ABC transporter family members (with qPCR). Specific markers (α6-integrin(bri)/CD71(dim), CK17) of normal epithelial stem cells were evaluated by flow cytometry. The biological properties of these cells were analyzed, including their colony heterogeneity, repopulation, and anchorage-independent colony formation. We identified SPs (around 3 %) in the SiHa and CaLo cell lines, more than 70 % of which were in G0 phase and strongly expressed ABC transporters (predominantly ABCG2 and ABCB1). The SP from CaLo cells showed an α6-integrin(bri)/CD(dim) pattern, whereas the SP from the SiHa cells showed an α6-integrin(-)/CD(dim) pattern. Recultured cells from the SPs of both cell lines generated both SPs and NSPs, and had higher clonogenic potential to form mainly holoclones and greater colony-forming efficiency under anchorage-independent growth conditions than the cells from the NSPs or total cell populations. Interestingly, we identified no SP in the HPV-uninfected C-33A cell line, and it did not express ABCG2 or other members of the ABC transporters (ABCB1, ABCC1, or ABCA3).

Sorting and identification of side population cells in the human cervical cancer cell line HeLa

BACKGROUND

Several reports have revealed that cancer stem cells (CSCs) exist in many types of solid tumors. Some studies have demonstrated that side population (SP) cells isolated from diverse cancer lines harbor cancer stem-like properties, but there are few reports examining the characteristic of SP cells in human cervical cancer. The aim of this study is 1) to find out a feasible way to detect the tumor stem-like cells in cervical cancer, and 2) to analyze the properties of the SP cells being sorted.

METHODS

Isolated SP and non-SP cells from human cervical cancer cell line Hela by Hoechst 33342 dying method and flow cytometry analysis. Observing morphology of SP and non-SP cells. The expression of various biomarkers putatively related to cancer stem cells were investigated by immucytochemistry of SP and non-SP cells. We also analyzed cell cycle and cell apoptosis for sorted cells. The oncogenicity of the SP and non-SP cells were analyzed by tumor formation in nonobesediabeti- c/severe combined immune- deficient (NOD/SCID) mice. The drug-resistant and radiation-resistant index between SP, non-SP and Hela cells was estimated by MTS assay.

RESULTS

The fraction of SP cells in Hela was approximately 1.07 ± 0.32%. SP cells were smaller and rounder in shape than non-SP cells, and mostly showed colony-like growth. Immunocytochemistry showed that stem cell makers (Oct3/4, CD133, BCRP) were highly expressed in SP cells. Moreover, the number of apoptotic cells among non-SP cells (17.6 ± 3.7%) was significantly higher compared with that among SP cells (4.4 ± 1.2%). The HE staining of in vivo grown tumors result from SP cells showed more poor differentiation, though no significant differences were shown between SP and non-SP cells in NOD/SCID mice tumorigenicity. Furthermore, SP cells demonstrated a higher degree of drug resistance against trichostatin A (TSA) compared with that of non-SP and Hela cells. SP cells were also found to be more resistant against radiotherapy.

CONCLUSIONS

SP cells possess some characteristics of CSCs, namely high proliferation ability, chemoresistance and radioresistance, which may be helpful to elucidate novel targets for effective clinical treatments of cervical cancer in the future.

Characterization of subpopulation lacking both B-cell and plasma cell markers in Waldenstrom macroglobulinemia cell line

Cancer cells with tumorigenic potential are limited to a small population known as cancer-initiating cells (CICs). To date, CICs have not been identified in non-Hodgkin's lymphomas. Here, we investigated a candidate of CICs of an indolent non-Hodgkin's lymphoma, Waldenstrom macroglobulinemia (WM), using WM cell line MWCL-1. WM tumor expresses both B-cell and plasma cell markers, CD20 and CD138. When stained with anti-CD20 and anti-CD138 antibodies, MWCL-1 cells were classified into three subpopulations: CD20⁻ CD138⁻, CD20⁺ CD138⁻, and CD20⁺ CD138⁺. When cultured, CD20⁻ CD138⁻ cells yielded all three subpopulations, but CD20⁺ cells did not yield CD20⁻ CD138⁻ cells. Higher reactive oxygen species (ROS) expelling and in vitro colony formation activities were detected in CD20⁻ CD138⁻ cells than in CD20⁺ CD138⁻ and CD20⁺ CD138⁺ cells. When cultured in the absence of serum or with anti-cancer drug, CD20⁻ CD138⁻ cells were resistant to apoptosis. In contrast, CD20⁺ CD138⁺ cells were vulnerable to apoptosis in the same condition. In fact, the immunohistochemical analysis with clinical samples revealed that tumor cells in apoptosis were CD138-positive. The production of all three subpopulations, the efficient ROS expelling and in vitro colony-forming activities, and the resistance to apoptosis suggested that the CD20⁻ CD138⁻ cell might be a candidate of CICs in WM.

A concise review on the current understanding of pancreatic cancer stem cells

Several evidences suggest that a small population of cells known as cancer stem cells (CSCs) or tumor initiating stemlike cells within a tumor is capable of tumor initiation, maintenance and propagation. Recent publications have supported the existence of CSCs in pancreatic tumors. The pancreatic stem/progenitor cells, which express self-renewal markers, are identified to be present in the peribiliary gland. Based on the CSC hypothesis, mutations can lead to the transformation of stem/progenitor cells or differentiated cells into CSCs. The pancreatic CSCs express a wide array of markers such as CD44, CD24, ESA, CD133, c-MET, CXCR4, PD2/Paf1 and ALDH1. The CSCs are isolated based on surface markers or by other methods such as ALDEFLOUR assay or Hoechst 33342 dye exclusion assay. The isolated cells are further characterized by in vitro and in vivo tumorigenic assays. The most important characteristics of CSCs are its ability to self-renew and impart drug resistance towards chemotherapy. Moreover, these distinct cells display alteration of signaling pathways pertaining to CSCs such as Notch, Wnt and Shh to maintain the self-renewal process. Failure of cancer treatment could be attributed to the therapy resistance exhibited by the CSCs. Metastasis and drug resistance in pancreatic cancer is associated with epithelial to mesenchymal transition (EMT). Furthermore, mucins, the high molecular weight proteins are found to be associated with pancreatic CSCs and EMT. Understanding the underlying molecular pathways that aid in the metastatic and drug resistant nature of these distinct cells will aid in targeting these cells. Overall, this review focuses on the various aspects of pancreatic adult/stem progenitors, CSC hypothesis, its markers, pathways, niche, EMT and novel therapeutic drugs used for the elimination of pancreatic CSCs.

Differential Nrf2 expression between glioma stem cells and non-stem-like cells in glioblastoma

Glioblastoma multiforme (GBM), the most commonly occurring primary intracranial tumor, is associated with a negative outcome, regardless of the availability of multimodal therapies. However, the identification of glioma stem cells (GSCs), which are small groups of cells within the GBM, has resulted in novel avenues for research. GSCs are resistant to numerous types of environmental stress, such as irradiation, antitumor drugs and hypoxia. Nuclear factor erythroid 2-related factor 2 (Nrf2) has a significant role the cellular response to oxidative stress and previous studies have supported the significance of Nrf2 in GBM; however, the role of Nrf2 in GSCs remains unclear. In the present study, Nrf2 in CD133^- GBM cells and CD133⁺ GSCs from GBM were compared. GSCs from GBM, which express the surface marker CD133, were separated by magnetic cell sorting and analyzed by immunofluorescence in 24-well clusters and cell counting using flow cytometry. The expression of Nrf2 was detected at the transcriptional and translational levels in CD133⁺ and CD133^- cells, and the result indicated that GSCs were successfully isolated from the GBM. The percentage of tumor stem cells in total cells was between 0.49 and 0.91%. Nrf2 was overexpressed in CD133⁺ GSCs when compared with CD133^- GBM cells, which indicated that the expression of Nrf2 in GSCs was closely correlated with malignant proliferation and differentiation of the GBM. Therefore, it was concluded that Nrf2 may be a potential biomarker and rational therapeutic target in GBM.

Circadian properties of cancer stem cells in glioma cell cultures and tumorspheres

Increased cancer risk is linked to disruption of circadian rhythms. Cancer stem cells (CSCs) are a known cause of cancer aggressiveness, but their circadian properties have not been described. We discovered circadian rhythms in gene expression within C6 glioma tumorspheres enriched in CSCs and found that the circadian clock is particularly robust in medium lacking any growth factors. A method is introduced for identifying individual CSCs in culture for single-cell analysis. CSCs in monolayer cell culture failed to show a circadian rhythm in nuclear localization of mPER2 protein, suggesting that cell interactions or the tumor-like microenvironment within tumorspheres enable circadian timing.

Expression of dedifferentiation markers and multilineage markers in U251 glioblastoma cells with silenced EGFR and FGFR genes

Epithelial growth factor (EGF) and basic fibroblast growth factor (bFGF), and their receptors, epithelial growth factor receptor (EGFR) and bFGF receptor (bFGFR), are frequently overexpressed in high-grade gliomas. In the present study, the EGF and bFGF levels in U251 glioblastoma cell culture supernatants were determined by ELISA, and enhanced green fluorescent protein (EGFP)-labeled recombinant lentiviral expression vectors with small interfering RNA targeting the EGFR and bFGFR genes were constructed. The mRNA expression levels of EGFR, bFGFR, cluster of differentiation (CD)133, glial fibrillary acidic protein (GFAP), tubulin-β3 (TUBB3) and myelin basic protein (MBP) were determined using quantitative polymerase chain reactions in U251 cells prior to and following silencing of the EGFR and/or bFGFR genes. Prior to silencing, the U251 cells secreted EGF and bFGF, and expressed EGFR, bFGFR, CD133, GFAP, TUBB3 and MBP mRNA. Subsequent to silencing the EGFR and/or bFGFR gene, CD133 mRNA expression decreased and GFAP and TUBB3 mRNA expression increased. Silencing the EGFR and FGFR genes acted synergistically to downregulate CD133 expression. The downregulation of CD133 mRNA expression and the upregulation of GFAP and TUBB3 mRNA expression were not significantly different when blocking the EGFR and FGFR pathways. These results indicate that autocrine or paracrine EGF and/or FGF mechanisms exist in U251 cells. Knocking down the EGFR and/or FGFR genes downregulates CD133 mRNA expression and facilitates glial and neuronal differentiation in U251 cells.

Ectopically expressed variant form of sperm mitochondria-associated cysteine-rich protein augments tumorigenicity of the stem cell population of lung adenocarcinoma cells

Cancer stem-like cells (CSCs)/cancer-initiating cells (CICs) are defined as a small population of cancer cells that have self-renewal ability, differentiation ability and high tumor-initiating ability. CSCs/CICs are resistant to cancer therapies including chemotherapy and radiotherapy. Therefore, CSCs/CICs are thought to be responsible for cancer recurrence and distant metastasis after treatment. However, the molecular mechanisms of CSCs/CICs are still elusive. In this study, we isolated CSCs/CICs as side population (SP) cells from lung carcinoma, colon carcinoma and breast carcinoma cells and analyzed the molecular mechanisms of CSCs/CICs. cDNA micro-array screening and RT-PCR analysis revealed that sperm mitochondria-associated cysteine-rich protein (SMCP) is ectopically expressed in SP cells. 5′-Rapid amplification of cDNA end (RACE) analysis revealed that the SMCP transcript in SP cells was a variant form (termed vt2) which is composed from only one exon. SMCP vt2 was detected in only cancer cells, whereas the wild-type (vt1) form of SMCP was expressed in the testis. SMCP was shown to have a role in tumor initiation by SMCP overexpression and SMCP knockdown using siRNAs in lung cancer cells. Taken together, the initiation results indicate that an ectopically expressed variant form of SMCP has a role in tumor initiation of CSCs/CICs and that the variant form of SMCP might be a novel CSC/CIC marker and a potential and promising target of CSC/CIC-targeting therapy.

New treatment strategies to eradicate cancer stem cells and niches in glioblastoma

Glioblastoma multiforme (GBM) harbors are not only rapidly dividing cells but also small populations of slowly dividing and dormant cells with tumorigenesity, self-renewal, and multi-lineage differentiation capabilities. Known as glioblastoma stem cells (GSCs), they are resistant to conventional chemo- and radiotherapy and may be a causative factor in recurrence. The treatment outcome in patients with GBM remains unsatisfactory and their mean survival time has not improved sufficiently. We studied clinical evidence and basic research findings to assess the possibility of new treatment strategies that target GSCs and their specific microenvironments (GBM niches) and raise the possibility of adding new treatments to eradicate GSCs and GBM niches.

A c-Met inhibitor increases the chemosensitivity of cancer stem cells to the irinotecan in gastric carcinoma

Background:

Cancer stem cells (CSCs) may be postulated mediators of the chemoresistance. This study aimed to determine an effective signal inhibitor with effects on the proliferation of CSCs in combination with anticancer drugs.

Methods:

We used three gastric cancer cell lines and three side population (SP)-enriched CSC cell lines. We examined the combined effects of inhibitors against stemness signals, including c-Met inhibitor SU11274, and five anticancer drugs on the CSC proliferation and mRNA expression of chemoresistance-associated genes.

Results:

The IC₅₀ of irinotecan in SP-enriched CSC was 10.5 times higher than parent OCUM-2M cells, whereas that of oxaliplatin, taxol, gemcitabine, and 5-fluorouracil was 2.0, 2.8, 2.0, and 1.2, respectively. The SP cell lines had higher expression levels of UGT1A1, ABCG2, and ABCB1 than their parent cell lines. There was a synergistic antiproliferative effect with a combination of SU11274 and SN38 in SP cells, but not other inhibitors. The SU11274 significantly decreased the expression of UGT1A1, but not ABCG2 and ABCB1. The SN38 plus SU11274 group more effectively suppressed in vivo tumour growth by OCUM-2M/SP cells than either group alone.

Conclusion:

Cancer stem cells have chemoresistance to irinotecan. The c-Met inhibitor may be a promising target molecule for irinotecan-based chemotherapy of gastric cancer.

Aldehyde dehydrogenase 1 identifies cells with cancer stem cell-like properties in a human renal cell carcinoma cell line

Cancer stem cells (CSC) or cancer stem cell-like cells (CSC-LCs) have been identified in many malignant tumors. CSCs are proposed to be related with drug resistance, tumor recurrence, and metastasis and are considered as a new target for cancer treatment; however, there are only a few reports on CSCs or CSC-LCs in renal cell carcinoma (RCC). Different approaches have been reported for CSC identification, but there are no universal markers for CSC. We used two different approaches, the traditional side population (SP) approach, and the enzymatic (aldehyde dehydrogenase 1 (ALDH1)) approach to identify CSC-LC population in two RCC cell lines, ACHN and KRC/Y. We found that ACHN and KRC/Y contain 1.4% and 1.7% SP cells, respectively. ACHN SP cells showed a higher sphere forming ability, drug resistance, and a slightly higher tumorigenic ability in NOD/SCID mice than Non-SP (NSP) cells, suggesting that cells with CSC-LC properties are included in ACHN SP cells. KRC/Y SP and NSP cells showed no difference in such properties. ALDH1 activity analysis revealed that ACHN SP cells expressed a higher level of activity than NSP cells (SP vs. NSP: 32.7% vs 14.6%). Analysis of ALDH1-positive ACHN cells revealed that they have a higher sphere forming ability, self-renewal ability, tumorigenicity and express higher mRNA levels of CSC-LC property-related genes (e.g., ABC transporter genes, self-replication genes, anti-apoptosis genes, and so forth) than ALDH1-negative cells. Drug treatment or exposure to hypoxic condition induced a 2- to 3-fold increase in number of ALDH1-positive cells. In conclusion, the results suggest that the ALDH1-positive cell population rather than SP cells show CSC-LC properties in a RCC cell line, ACHN.

Vitamin D analog EB1089 induces apoptosis in a subpopulation of SGC-7901 gastric cancer cells through a mitochondrial-dependent apoptotic pathway

Gastric cancer is the second leading cause of cancer death worldwide. Cancer stem-like side population (SP) cells may be important factors that hinder efficacy of chemopreventative and chemotherapeutic approaches in gastric cancer. EB1089 is an antitumor agent that has been used in many cancers; however, no reports to date have determined the effects of EB1089 in gastric cancer. In our study, SP and main population (MP) cells were isolated from 4 gastric cancer cell lines in different stages of differentiation by flow cytometry (FCM) and confirmed by reverse transcription polymerase chain reaction (RT-PCR) and Western blot. EB1089 decreased the proliferation, increased apoptosis, and induced mitochondrial damage in the SP cells isolated from 1 cell type (SGC-7901), but not MP cells, through increased Bax and decreased Bcl-2 and Bcl-xL protein expression. This protein expression pattern induced the activation of caspase-3 and caspase-9. The effects of EB1089 on SGC-7901 SP cells were blocked by treating cells with vitamin D receceptor (VDR) siRNA or butin (an inhibitor of the mitochondrial apoptosis pathway). Our results suggest that EB1089 targets SGC-7901 SP cells through a mitochondrial apoptosis pathway. However, further studies are needed to elucidate the signal transduction between VDR and the mitochondrial apoptosis pathway.

Identification of a cancer stem cell-like side population in the HeLa human cervical carcinoma cell line

The present study aimed to identify the stem cell characteristics of side population (SP) cells sorted from the widely-used HeLa human cervical carcinoma cell line. The SP cells were sorted from the HeLa cell line using fluorescence-activating cell sorting (FACS). Stem cell characteristics of the SP cells, including proliferation, self-renewal, differentiation and the ability to form xenografts, were investigated in vitro and in vivo. The SP cells demonstrated strong tumorigenesis following in vivo transplantation into five to six-week-old female Balb/c mice. The SP cells were observed to be more resistant to chemotherapy and radiotherapy compared with non-side population (NSP) cells. A higher expression of CD133 was observed in the SP cells compared with the NSP cells following FACS. The results demonstrated that the SP cells from the HeLa human cervical carcinoma cell line exhibit stem cell characteristics in vitro and also have a strong ability to form tumors in vivo. The cell surface marker CD133 may serve as a potential molecular marker for the identification of cervical cancer stem cells (CSCs).

Isolation of side population cells from endometrial cancer cells using a violet laser diode

Cancer stem cells (CSCs) possess the ability for self-renewal, differentiation, and tumorigenesis and play a role in cancer recurrence and metastasis. CSCs are usually sorted in analysis into side population (SP) cells using ultraviolet (UV) laser (350 nm) excitation; they cannot be stained with Hoechst 33342 because of their efflux ability. However, it is difficult to avoid cell damage using a UV laser. Therefore, we attempted to isolate CSCs using a violet laser (407 nm) excitation to avoid cellular DNA damage. We sorted SP cells and main population (MP) cells from a human endometrial cancer cell line using the FACSAria system equipped with a violet laser and analyzed the biological properties of these cells. SP cells exhibited drug efflux, self-renewal, differentiation abilities, and tumorigenicity. It was found that v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS) expression was significantly higher in SP cells than in MP cells. Our results suggest that CSCs exist in the SP fraction sorted using the FACSAria system equipped with a violet laser, which presents a useful tool to isolate small populations of viable putative CSCs from solid tumors and can be used to identify and characterize CSCs.

Drug screening identifies niclosamide as an inhibitor of breast cancer stem-like cells

The primary cause of death from breast cancer is the progressive growth of tumors and resistance to conventional therapies. It is currently believed that recurrent cancer is repopulated according to a recently proposed cancer stem cell hypothesis. New therapeutic strategies that specifically target cancer stem-like cells may represent a new avenue of cancer therapy. We aimed to discover novel compounds that target breast cancer stem-like cells. We used a dye-exclusion method to isolate side population (SP) cancer cells and, subsequently, subjected these SP cells to a sphere formation assay to generate SP spheres (SPS) from breast cancer cell lines. Surface markers, stemness genes, and tumorigenicity were used to test stem properties. We performed a high-throughput drug screening using these SPS. The effects of candidate compounds were assessed in vitro and in vivo. We successfully generated breast cancer SPS with stem-like properties. These SPS were enriched for CD44^high (2.8-fold) and CD24^low (4-fold) cells. OCT4 and ABCG2 were overexpressed in SPS. Moreover, SPS grew tumors at a density of 10³, whereas an equivalent number of parental cells did not initiate tumor formation. A clinically approved drug, niclosamide, was identified from the LOPAC chemical library of 1,258 compounds. Niclosamide downregulated stem pathways, inhibited the formation of spheroids, and induced apoptosis in breast cancer SPS. Animal studies also confirmed this therapeutic effect. The results of this proof-of-principle study may facilitate the development of new breast cancer therapies in the near future. The extension of niclosamide clinical trials is warranted.

Complete regression of glioblastoma by mesenchymal stem cells mediated prodrug gene therapy simulating clinical therapeutic scenario

Suicide gene therapy mediated by mesenchymal stem cells with their ability to engraft into tumors makes these therapeutic stem cells an attractive tool to activate prodrugs directly within the tumor mass. In this study, we evaluated the therapeutic efficacy of human mesenchymal stem cells derived from bone marrow and from adipose tissue, engineered to express the suicide gene cytosine deaminase::uracil phosphoribosyltransferase to treat intracerebral rat C6 glioblastoma in a simulated clinical therapeutic scenario. Intracerebrally grown glioblastoma was treated by resection and subsequently with single or repeated intracerebral inoculations of therapeutic stem cells followed by a continuous intracerebroventricular delivery of 5-fluorocytosine using an osmotic pump. Kaplan-Meier survival curves revealed that surgical resection of the tumor increased the survival time of the resected animals depending on the extent of surgical intervention. However, direct injections of therapeutic stem cells into the brain tissue surrounding the postoperative resection cavity led to a curative outcome in a significant number of treated animals. Moreover, the continuous supply of therapeutic stem cells into the brain with growing glioblastoma by osmotic pumps together with continuous prodrug delivery also proved to be therapeutically efficient. We assume that observed curative therapy of glioblastoma by stem cell-mediated prodrug gene therapy might be caused by the destruction of both tumor cells and the niche where glioblastoma initiating cells reside.

In vitro enrichment of tumor-initiating cells from human established cell lines

This unit describes protocols for culturing and subsequently enriching cancer stem cells (CSCs), also referred to as tumor-initiating cells (TICs), from human established cell lines. TICs are thought to display the major cell population in the tumor with the proliferative capacity to seed tumors, implying that they( )are critical in initiating and driving tumorigenesis. The protocols show the methods for enriching and subsequently characterizing TIC populations from a series of human tumors including glioblastoma, breast, and pancreatic tumors. Protocols evaluating the morphology, phenotypic, and functional properties of TICs are described. Long-term cultures grown either as monolayers ("TIC-low") or as non-adherent tumor spheres ("TIC-high") are generated. As a result, cells from the TIC-high culture exhibit increased expression of stem cell surface markers, such as CD133, CD44, and CD24, high aldehyde dehydrogenase (ALDH) activity, and elevated expression levels of p21, in comparison to cells from the TIC-low culture. Studying TICs by using such protocols is cost effective and is considered as a suitable and simple way for studying them.

Enrichment of putative prostate cancer stem cells after androgen deprivation: upregulation of pluripotency transactivators concurs with resistance to androgen deprivation in LNCaP cell lines

BACKGROUND

Prostate cancer stem cells (PCSC) offer theoretical explanations to many clinical and biological behaviors of the disease in human. In contrast to approaches of using side populations and cell-surface markers to isolate and characterize the putative PCSC, we hypothesize that androgen deprivation leads to functional enrichment of putative PCSC.

METHODS AND RESULTS

Human prostate cancer lines LNCaP, LAPC4 and LAPC9 were depleted of androgen in cell cultures and in castrated SCID mice. The resultant androgen deprivation-resistant or castration-resistant populations, in particular in LNCaP and its derivative cell lines, displayed increased expression of pluripotency transactivators and significantly higher tumorigenicity. Individual tumor cell clones were isolated from castration-resistant bulk cultures of LNCaP (CR-LNCaP) and tested for tumorigenicity in male SCID mice under limiting dilution conditions. As few as 200 cells were able to form spheres in vitro, and generate tumors with similar growth kinetics as 10(6) LNCaP or 10(4) CR-LNCaP cells in vivo. These putative PCSC were CD44(+) /CD24(-) and lack the expression of prostate lineage proteins. When transplanted into the prostate of an intact male SCID mouse, these putative PCSC seemed to show limited differentiation into Ck5(+) , Ck8(+) , Ck5(+) /Ck8(+) , and AR(+) cells. On the other hand, stable transduction of LNCaP with retrovirus encoding Sox2 led to androgen-deprivation resistant growth and down-regulation of major prostate lineage gene products in vitro.

CONCLUSION

Concurrence of overexpression of pluripotency transactivators and resistance to androgen deprivation supported the role of putative PCSC in the emergence of prostate cancer resistant to androgen deprivation.

GRP78 mediates radiation resistance of a stem cell-like subpopulation within the MCF-7 breast cancer cell line

Emerging evidence indicates that breast cancer-initiating cells (CICs) are relatively resistant to radiotherapy; however, the critical mechanisms determining breast CIC resistance to radiation remain elusive. In the present study, a subpopulation of cells displaying characteristics generally attributed to stem cells was identified within the breast cancer cell line MCF-7. This subpopulation displays cancer stem cell features characterized by overexpression of embryonic stem cell markers, high tumorigenic potential following transplantation into BALB/c-nu mice, self-renewal capacity and resistance to ionizing radiation (IR). Moreover, glucose‑regulated protein 78KD (GRP78), which was found to play a crucial role in stem cell oncogenesis, was also shown to be overexpressed in this subpopulation. GRP78 is required for the cancer stem-like subpopulation cell resistance to IR, as knockdown of this gene augments the effects of IR, while overexpression of GRP78 increases the radiation resistance of the subpopulation to IR. These findings indicate that GRP78 acts as a potential therapeutic target aimed at tumor-generating subsets of breast cancer cells.

Expression of FoxO3a in clinical cases of malignant lymphoma

Cancer-initiating cells (CICs) are a limited number of cells with tumorigenic activity. Few studies have been performed on CICs in malignant lymphoma. We recently demonstrated that a small number of FoxO3a-expressing cells possessed CIC-like potential in Hodgkin's lymphoma (HL) cell lines. In the present study, FoxO3a expression was examined immunohistochemically in 137 patients with malignant lymphoma. Among patients with HL, FoxO3a-positive tumor cells were detected in 11 of 11 with nodular sclerosis classical HL, 8 of 15 with mixed cellularity classical HL, 0 of 1 with lymphocyte-rich classical HL, and 2 of 3 with nodular lymphocyte-predominant HL. Only limited numbers of patients with non-HL expressed FoxO3a: 4 of 66 with diffuse large B-cell lymphoma, 1 of 20 with follicular lymphoma, and 1 of 5 with peripheral T-cell lymphoma, not otherwise specified. No FoxO3a expression was detected in patients with mantle cell lymphoma (n=3), extranodal marginal zone B-cell lymphoma (n=3), mediastinal large B-cell lymphoma (n=1), NK/T cell lymphoma (n=5), anaplastic large cell lymphoma (n=2), or T-lymphoblastic lymphoma/leukemia (n=2). These results suggest that FoxO3a is expressed mostly in patients with HL, but not in patients with non-HL. FoxO3a expression was limited to a small number of Hodgkin cells in a quiescent state. FoxO3a may be a CIC marker of HL, but not of non-HL.

A new method for identifying stem-like cells in esophageal cancer cell lines

Cancer stem cells (CSCs) appear to resist chemo-radiotherapy and initiate tumor recurrence in patients. Isolation and further characterization of this subpopulation is important for targeting CSCs. Flow cytometry using Aldefluor, a fluorescent substrate of aldehyde dehydrogenase, has been used to isolate CSCs from various cancer cell lines. However, new techniques are needed to locate and identify CSCs in culture for live-cell analyses such as fluorescence microscopy without introducing artifacts during cell sorting and to observe CSC and non-CSC interactions. Previously, we characterized a distinct CSC subpopulation within human esophageal cancer cell lines (ESCC). In this study we introduce the attached-cell Aldefluor method (ACAM) to detect CSCs in ESCC cell lines (KY-5, KY-10, TE-1, TE-8, YES-1, YES-2). To validate this technique, we isolated CSCs from the YES-2 parental line using standard Aldefluor flow cytometry to create a cell line enriched in CSCs (YES-2CSC). This line showed significantly greater ACAM staining and higher CD44 levels than YES-2. ACAM also showed significantly higher ALDH activity in YES-2CSC than in YES-2S, a cell line that has a diminished CSC subpopulation after having survived treatment with curcumin. ACAM stained cells within tumorspheres made from the CSC-enriched line but not differentiating cells from the tumorspheres. This study also demonstrates a new method for generating and growing tumorspheres without the growth factor supplements normally used in medium to form tumorspheres. ACAM should be evaluated using other cancer cell lines to further substantiate its effectiveness and to characterize CSCs in culture through various imaging techniques.

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

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

Gene therapy for high-grade glioma

High-grade glioma is the most frequently occurring primary brain tumor and is associated with a poor prognosis. Current treatment regimens have had only a modest effect on the progressive course despite recent advances in surgery, radiotherapy, and chemotherapy. Gene therapy for brain tumors represents a novel and promising therapeutic approach and has been investigated clinically for the last two decades. The strategies of gene therapy include suicide gene therapy, immune gene therapy, oncolytic viral therapy, tumor suppressor gene therapy, and antisense therapy. Here, we review gene therapy approaches considering the clinical results, limitations, and future directions.

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

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

Activation of the phosphorylation of ATM contributes to radioresistance of glioma stem cells

Ionizing radiation (IR) is currently the most efficient therapy available for malignant glioma. Unfortunately, this strategy is palliative due to the characteristics of radioresistance of malignant glioma. The aim of our study was to compare glioma stem cells (GSCs) with glioma cells (GCs) to determine whether GSCs are responsible for the radioresistance phenotype and to elucidate whether cell cycle checkpoint proteins are responsible for the radioresistance of GSCs. In this study, CD133 (a marker of brain cancer stem cells) and nestin were co-expressed in GSCs isolated from GCs. The percent of CD133+ cells in GSCs and GCs were >80 and <2%, respectively. Significantly more GSCs survived following 2, 4, 6 and 8 Gy IR than GCs. IR kills cancer cells primarily through DNA double-strand breaks (DSBs). The neutral comet assay is often used to intuitively show the level of DSBs. Significantly fewer GSCs showed DNA damage than GCs following 2 Gy IR. This demonstrated that GSCs are more resistant to in vitro radiation than GCs. Furthermore, activated ataxia telangiectasia mutated (ATM) is essential for the activation of downstream effector kinases, such as checkpoint kinase 2 (Chk2) and p53 which mainly contribute to the proper regulation of IR-induced arrest in the G1 phase. DNA damage induced by IR potently initiated activation of phosphorylation of the ATM, p53 and Chk2 checkpoint proteins. Activation of the phosphorylation of these checkpoint proteins was significantly higher in the GSCs compared to GCs. We found that inhibition of ATM activation induced cell cycle checkpoint defects and increased the rate of apoptosis of GSCs following IR. Our results suggest that GSCs were more resistant to radiation compared to GCs due to high expression of phosphorylated cell cycle checkpoint proteins, and inhibition of ATM could significantly reduce the radioresistance of GSCs and GCs. ATM may represent a source of radioresistance in GSCs and a target of improved radiosensitivity of GSCs.

Targeting cancer stem cells expressing an embryonic signature with anti-proteases to decrease their tumor potential

Cancer stem cells (CSCs) are a specific subset of cancer cells that sustain tumor growth and dissemination. They might represent a significant treatment target to reduce malignant progression and prevent tumor recurrence. In solid tumors, several hierarchically organized CSC clones coexist, even within a single tumor. Among them, CSCs displaying an embryonic stem cell ‘stemness' signature, based on the expression of Oct-4, Nanog and Sox2, are present in distinct high-grade tumor types associated with poor prognosis. We previously designed a model to isolate pure populations of these CSCs from distinct solid tumors and used it to screen for molecules showing selective toxicity for this type of CSC. Here we show that human immunodeficiency virus (HIV)-protease inhibitors (HIV-PIs) specifically target CSCs expressing an embryonic signature derived from tumors with distinct origins. They reduced proliferation in a dose-dependent manner with a higher specificity as compared with the total population of cancer cells and/or healthy stem cells, and they were efficient in inducing cell death. Lopinavir was the most effective HIV-PI among those tested. It reduced self-renewal and induced apoptosis of CSCs, subsequently impairing in vivo CSC-induced allograft formation. Two key pharmacophores in the LPV structure were also identified. They are responsible for the specificity of CSC targeting and also for the overall antitumoral activity. These results contribute to the identification of molecules presenting selective toxicity for CSCs expressing an embryonic stemness signature. This paves the way to promising therapeutic opportunities for patients suffering from solid cancer tumors of poor prognosis.

Combined gemcitabine and CHK1 inhibitor treatment induces apoptosis resistance in cancer stem cell-like cells enriched with tumor spheroids from a non-small cell lung cancer cell line

Evaluating the effects of novel drugs on appropriate tumor models has become crucial for developing more effective therapies that target highly tumorigenic and drug-resistant cancer stem cell (CSC) populations. In this study, we demonstrate that a subset of cancer cells with CSC properties may be enriched into tumor spheroids under stem cell conditions from a non-small cell lung cancer cell line. Treating these CSC-like cells with gemcitabine alone and a combination of gemcitabine and the novel CHK1 inhibitor PF-00477736 revealed that PF-00477736 enhances the anti-proliferative effect of gemcitabine against both the parental and the CSC-like cell populations. However, the CSC-like cells exhibited resistance to gemcitabine-induced apoptosis. Collectively, the spheroid-forming CSC-like cells may serve as a model system for understanding the mechanism underlying the drug resistance of CSCs and for guiding the development of better therapies that can inhibit tumor growth and eradicate CSCs.

Analysis of the genome-wide DNA methylation profile of side population cells in hepatocellular carcinoma

BACKGROUND

DNA methylation plays an important role in maintaining pluripotency and regulating the differentiation of stem cells, but the DNA methylation profile of stem cells in hepatocellular carcinoma (HCC) remains unclear.

AIMS

To investigate the genome-wide DNA methylation profile of side population (SP) cells of HCC, a special subpopulation of cells enriched with cancer stem cells, by DNA methylation microarray analysis and to analyze the functions and signal pathways of the aberrantly methylated genes in SP cells.

METHODS

Side population cells were isolated from HCC cell lines Huh7 and PLC/PRF/5 using flow cytometry, and the tumorigenicity of these SP cells was assessed in NOD/SCID mice. The genome-wide DNA methylation status of SP cells and non-SP (NSP) cells was detected and compared by DNA methylation microarray analysis. Genes with differential methylation between SP and NSP cells were further analyzed for their functions and roles in related signaling pathways.

RESULTS

Subcutaneous inoculation of 1 × 10(3) SP cells yielded tumors in 60 % NOD/SCID mice, whereas no tumor was developed after the inoculation of 1 × 10(6) NSP cells. Genome-wide DNA methylation microarray analysis showed that 72 and 181 genes were hypermethylated and hypomethylated, respectively, in both Huh7 and PLC/PRF/5 SP cells as compared with their corresponding NSP cells. Analyses of signaling pathways revealed that hypermethylated and hypomethylated genes were related to four and eight pathways, respectively.

CONCLUSIONS

Hepatocellular carcinoma SP cells possessed a differential DNA methylation status compared with NSP cells, and the differentially methylated genes in SP cells were involved in 12 signaling pathways. Our results provide valuable clues for further investigations in elucidating the importance of epigenetic regulation in sustaining HCC SP cells and tumorigenesis.