Stem-like cancer cells are inducible by increasing genomic instability in cancer cells

Meta-analysis of the global gene expression profile of triple-negative breast cancer identifies genes for the prognostication and treatment of aggressive breast cancer

Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype lacking expression of estrogen and progesterone receptors (ER/PR) and HER2, thus limiting therapy options. We hypothesized that meta-analysis of TNBC gene expression profiles would illuminate mechanisms underlying the aggressive nature of this disease and identify therapeutic targets. Meta-analysis in the Oncomine database identified 206 genes that were recurrently deregulated in TNBC compared with non-TNBC and in tumors that metastasized or led to death within 5 years. This ‘aggressiveness gene list' was enriched for two core functions/metagenes: chromosomal instability (CIN) and ER signaling metagenes. We calculated an ‘aggressiveness score' as the ratio of the CIN metagene to the ER metagene, which identified aggressive tumors in breast cancer data sets regardless of subtype or other clinico-pathological indicators. A score calculated from six genes from the CIN metagene and two genes from the ER metagene recapitulated the aggressiveness score. By multivariate survival analysis, we show that our aggressiveness scores (from 206 genes or the 8 representative genes) outperformed several published prognostic signatures. Small interfering RNA screen revealed that the CIN metagene holds therapeutic targets against TNBC. Particularly, the inhibition of TTK significantly reduced the survival of TNBC cells and synergized with docetaxel in vitro. Importantly, mitosis-independent expression of TTK protein was associated with aggressive subgroups, poor survival and further stratified outcome within grade 3, lymph node-positive, HER2-positive and TNBC patients. In conclusion, we identified the core components of CIN and ER metagenes that identify aggressive breast tumors and have therapeutic potential in TNBC and aggressive breast tumors. Prognostication from these metagenes at the mRNA level was limited to ER-positive tumors. However, we provide evidence that mitosis-independent expression of TTK protein was prognostic in TNBC and other aggressive breast cancer subgroups, suggesting that protection of CIN/aneuploidy drives aggressiveness and treatment resistance.

Dynamics between cancer cell subpopulations reveals a model coordinating with both hierarchical and stochastic concepts

Tumors are often heterogeneous in which tumor cells of different phenotypes have distinct properties. For scientific and clinical interests, it is of fundamental importance to understand their properties and the dynamic variations among different phenotypes, specifically under radio- and/or chemo-therapy. Currently there are two controversial models describing tumor heterogeneity, the cancer stem cell (CSC) model and the stochastic model. To clarify the controversy, we measured probabilities of different division types and transitions of cells via in situ immunofluorescence. Based on the experiment data, we constructed a model that combines the CSC with the stochastic concepts, showing the existence of both distinctive CSC subpopulations and the stochastic transitions from NSCCs to CSCs. The results showed that the dynamic variations between CSCs and non-stem cancer cells (NSCCs) can be simulated with the model. Further studies also showed that the model can be used to describe the dynamics of the two subpopulations after radiation treatment. More importantly, analysis demonstrated that the experimental detectable equilibrium CSC proportion can be achieved only when the stochastic transitions from NSCCs to CSCs occur, indicating that tumor heterogeneity may exist in a model coordinating with both the CSC and the stochastic concepts. The mathematic model based on experimental parameters may contribute to a better understanding of the tumor heterogeneity, and provide references on the dynamics of CSC subpopulation during radiotherapy.

XAV939, a tankyrase 1 inhibitior, promotes cell apoptosis in neuroblastoma cell lines by inhibiting Wnt/β-catenin signaling pathway

Background

Neuroblastoma (NB) is the most common extracranial solid tumor in childhood. The present treatment including surgery, chemotherapy and radiation, which have only 40% long-term cure rates, and usually cause tumor recurrence. Thus, looking for new effective and less toxic therapies has important significance. XAV939 is a small molecule inhibitor of tankyrase 1(TNKS1). The objective of this study is to investigate the effect of XAV939 on the proliferation and apoptosis of NB cell lines, and the related mechanism.

Methods

In the present study, we used both XAV939 treatment and RNAi method to demonstrate that TNKS1 inhibition may be a potential mechanism to cure NB. MTT method was used for determining the cell viability and the appropriate concerntration for follow-up assays. The colony formation assay, Annexin V staining and cell cycle analysis were used for detecting colony forming ability, cell apoptosis and the percentage of different cell cycle. The Western blot was used for detecting the expression of key proteins of Wnt/ beta-catenin (Wnt/β-catenin) signaling pathway.

Results

The results showed that TNKS1 inhibition decreased the viability of SH-SY5Y, SK-N-SH and IMR-32 cells, induced apoptosis in SH-SY5Y as well as SK-N-SH cells, and led to the accumulation of NB cells in the S and G2/M phase of the cell cycle. Moreover, we demonstrated TNKS1 inhibition may in part blocked Wnt/β-catenin signaling and reduced the expression of anti-apoptosis protein. Finally, we also demonstrated that TNKS1 inhibition decreased colony formation in vitro.

Conclusions

These findings suggested that TNKS1 may be a potential molecule target for the treatment of NB.

Aberrant expression of plastin-3 via copy number gain induces the epithelial-mesenchymal transition in circulating colorectal cancer cells

PURPOSE

Plastin-3 (PLS3) is a novel marker for circulating tumor cells (CTCs) in colorectal cancer (CRC). We sought to investigate the mechanisms mediating the aberrant expression of PLS3, the role of PLS3 in the epithelial-mesenchymal transition (EMT), and its association with the acquisition of invasive and metastatic abilities in human CRC.

METHODS

The expression levels of PLS3 messenger RNA in the tumor drainage venous blood (TDB) were examined in 177 CRC cases, and the associations between PLS3 expression and Xq23 copy numbers were analyzed in 132 CRC samples. We then established a stable PLS3-expressing CRC cell line and assessed the role of PLS3 in the EMT.

RESULTS

In clinical CRC cases, high expression of PLS3 in CTCs of TDB as well as peripheral blood was established as an independent prognostic factor of overall survival (p < 0.001), and the copy number gain of Xq23, which is the locus of the PLS3 gene, was significantly related to PLS3 overexpression. PLS3 induced the EMT via transforming growth factor (TGF)-β signaling and resulted in the acquisition of invasive ability in CRC cells.

CONCLUSIONS

The aberrant expression of PLS3 was associated with copy number gain in CTCs from primary tumors and was involved in the regulation of the EMT, contributing to a poor prognosis in CRC patients.

Side population cells as prototype of chemoresistant, tumor-initiating cells

Classically, isolation of CSCs from tumors exploits the detection of cell surface markers associated with normal stem cells. Invariable expression of these cell surface markers in almost all proliferating tumor cells that albeit impart specific functionality, the universality, and clinical credibility of CSC phenotype based on markers is still dubious. Side Population (SP) cells, as defined by Hoechst dye exclusion in flow cytometry, have been identified in many solid tumors and cell lines and the SP phenotype can be considered as an enriched source of stem cells as well as an alternative source for the isolation of cancer stem cells especially when molecular markers for stem cells are unknown. SP cells may be responsible for the maintenance and propagation of tumors and the proportion of SP cells may be a predictor of patient outcome. Several of these markers used in cell sorting have emerged as prognostic markers of disease progression though it is seen that the development of new CSC-targeted strategies is often hindered by poor understanding of their regulatory networks and functions. This review intends to appraise the experimental progress towards enhanced isolation and drug screening based on property of acquired chemoresistance of cancer stem cells.

Expression of betapapillomavirus oncogenes increases the number of keratinocytes with stem cell-like properties

Human papillomaviruses (HPV) of genus Betapapillomavirus (betaPV) are associated with nonmelanoma skin cancer development in epidermodysplasia verruciformis (EV) and immunosuppressed patients. Epidemiological and molecular studies suggest a carcinogenic activity of betaPV during early stages of cancer development. Since viral oncoproteins delay and perturb keratinocyte differentiation, they may have the capacity to either retain or confer a "stem cell-like" state on oncogene-expressing cells. The aim of this study was to determine (i) whether betaPV alters the expression of cell surface markers, such as CD44 and epithelial cell adhesion molecule (EpCAM), that have been associated with epithelial stemness, and (ii) whether this confers functional stem cell-like properties to human cutaneous keratinocytes. Fluorescence-activated cell sorter (FACS) analysis revealed an increase in the number of cells with high CD44 and EpCAM expression in keratinocyte cultures expressing HPV type 8 (HPV8) oncogenes E2, E6, and E7. Particularly through E7 expression, a distinct increase in clonogenicity and in the formation and size of tumor spheres was observed, accompanied by reduction of the epithelial differentiation marker Calgranulin B. These stem cell-like properties could be attributed to the pool of CD44(high) EpCAM(high) cells, which was increased within the E7 cultures of HPV5, -8, and -20. Enhanced EpCAM levels were present in organotypic skin cultures of primary keratinocytes expressing E7 of the oncogenic HPV types HPV5, -8, and -16 and in clinical samples from EV patients. In conclusion, our data show that betaPV may increase the number of stem cell-like cells present during early carcinogenesis and thus enable the persistence and accumulation of DNA damage necessary to generate malignant stem cells.

Downregulation of MCT1 inhibits tumor growth, metastasis and enhances chemotherapeutic efficacy in osteosarcoma through regulation of the NF-κB pathway

Monocarboxylate transporter isoform 1 (MCT1) is an important member of the proton-linked MCT family and has been reported in an array of human cancer cell lines and primary human tumors. MCT1 expression is associated with developing a new therapeutic approach for cancer. In this study, we initially showed that MCT1 is expressed in a variety of human osteosarcoma cell lines. Moreover, we evaluated the therapeutic response of targeting MCT1 using shRNA or MCT1 inhibitor. Inhibiting MCT1 delayed tumor growth in vitro and in vivo, including in an orthotopic model of osteosarcoma. Targeting MCT1 greatly enhanced the sensitivity of human osteosarcoma cells to the chemotherapeutic drugs adriamycin (ADM). In addition, we observed that MCT1 knockdown significantly suppressed the metastatic activity of osteosarcoma, including wound healing, invasion and migration. Further mechanistic studies revealed that the antitumor effects of targeting MCT1 might be related to the NF-κB pathway. Immunochemistry assay showed that MCT1 was an independent positive prognostic marker in osteosarcoma patients. In conclusion, our data, for the first time, demonstrate that MCT1 inhibition has antitumor potential which is associated with the NF-κB pathway, and high MCT1 expression predicates poor overall survival in patients with osteosarcoma.

Differential effect of long-term drug selection with doxorubicin and vorinostat on neuroblastoma cells with cancer stem cell characteristics

Numerous studies have confirmed that cancer stem cells (CSCs) are more resistant to chemotherapy; however, there is a paucity of data exploring the effect of long-term drug treatment on the CSC sub-population. The purpose of this study was to investigate whether long-term doxorubicin treatment could expand the neuroblastoma cells with CSC characteristics and histone acetylation could affect stemness gene expression during the development of drug resistance. Using n-myc amplified SK-N-Be(2)C and non-n-myc amplified SK-N-SH human neuroblastoma cells, our laboratory generated doxorubicin-resistant cell lines in parallel over 1 year; one cell line intermittently treated with the histone deacetylase inhibitor (HDACi) vorinostat and the other without exposure to HDACi. Cells' sensitivity to chemotherapeutic drugs, the ability to form tumorspheres, and capacity for in vitro invasion were examined. Cell-surface markers and side populations (SPs) were analyzed using flow cytometry. Differentially expressed stemness genes were identified through whole genome analysis and confirmed with real-time PCR. Our results indicated that vorinostat increased the sensitivity of only SK-N-Be(2)C-resistant cells to chemotherapy, made cells lose the ability to form tumorspheres, and reduced in vitro invasion and the SP percentage. CD133 was not enriched in doxorubicin-resistant or vorinostat-treated doxorubicin-resistant cells. Nine stemness-linked genes (ABCB1, ABCC4, LMO2, SOX2, ERCC5, S100A10, IGFBP3, TCF3, and VIM) were downregulated in vorinostat-treated doxorubicin-resistant SK-N-Be(2)C cells relative to doxorubicin-resistant cells. A sub-population of cells with CSC characteristics is enriched during prolonged drug selection of n-myc amplified SK-N-Be(2)C neuroblastoma cells. Vorinostat treatment affects the reversal of drug resistance in SK-N-Be(2)C cells and may be associated with downregulation of stemness gene expression. This work may be valuable for clinicians to design treatment protocols specific for different neuroblastoma patients.

Telomerase at the intersection of cancer and aging

Although cancer and aging have been studied as independent diseases, mounting evidence suggests that cancer is an aging-associated disease and that cancer and aging share many molecular pathways. In particular, recent studies validated telomerase activation as a potential therapeutic target for age-related diseases; in addition, abnormal telomerase expression and telomerase mutations have been associated with many different types of human tumor. Here, we revisit the connection between telomerase and cancer and aging in light of recent findings supporting a role for telomerase not only in telomere elongation, but also in metabolic fitness and Wnt activation. Understanding the physiological impact of telomerase regulation is fundamental given the therapeutic strategies that are being developed that involve telomerase modulation.

Cancer stem cell-like side population cells in clear cell renal cell carcinoma cell line 769P

Although cancers are widely considered to be maintained by stem cells, the existence of stem cells in renal cell carcinoma (RCC) has seldom been reported, in part due to the lack of unique surface markers. We here identified cancer stem cell-like cells with side population (SP) phenotype in five human RCC cell lines. Flow cytometry analysis revealed that 769P, a human clear cell RCC cell line, contained the largest amount of SP cells as compared with other four cell lines. These 769P SP cells possessed characteristics of proliferation, self-renewal, and differentiation, as well as strong resistance to chemotherapy and radiotherapy that were possibly related to the ABCB1 transporter. In vivo experiments with serial tumor transplantation in mice also showed that 769P SP cells formed tumors in NOD/SCID mice. Taken together, these results indicate that 769P SP cells have the properties of cancer stem cells, which may play important roles in tumorigenesis and therapy-resistance of RCC.

Nigericin selectively targets cancer stem cells in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is prevalent in southern China, northern Africa, and Alaska. The prognosis for NPC patients at early stage is good, while it is poor for patients at late stages. Cancer stem cells (CSCs) have been proposed to be associated with tumor initiation, relapse and metastasis, and the poor prognosis of NPC likely results from residual CSCs after therapy. Study on the therapy targeting CSCs in NPC remains poor, though it received intensive attentions in other cancers. Here, we used NPC cell lines with high and low proportion of CSCs as models to explore the effect of nigericin, an antibiotic, on CSCs. We found that nigericin could selectively target CSCs and sensitize CSCs in NPC to the widely used clinical drug cisplatin both in vitro and in vivo. Moreover, downregulation of the polycomb group protein Bmi-1 may contribute to the inhibitory effect of nigericin on CSCs. Furthermore, by using the in vitro NPC cell models, we found that nigericin could significantly decrease the migration and invasion abilities, which are known to be associated with CSCs. Taken together, our results suggest that nigericin can selectively target CSCs in NPC, which could be a candidate CSCs targeting drug for clinical evaluation.

Breast cancer stem cells, pathways and therapeutic perspectives 2011

The evidence for the existence of a heterogeneous population of cancer stem cells (CSCs) responsible for the initiation and maintenance of cancer has been characterized for several tumors recently. Purification and molecular characterization of normal human mammary stem cells from cultured mammospheres has been achieved, providing evidence supporting a model in which breast tumor heterogeneity is a reflection of a number of CSC-like cells in the tumor. A number of experimental methodologies have been developed to characterize epithelial stem cells, including the expression of cell surface or intracellular markers, mammosphere formation, exclusion of fluorescent dye by a side population, retention of the radionucleotide label, etc. Methodologies have also been successfully employed to identify tumorigenic cells within breast cancers. The most important characteristics of stem cells are the capacity for self-renewal and the regulation of the balance between self-renewal and differentiation. In the mammary gland, signaling pathways, such as Hedgehog (Hh), Wnt/β-catenin, and Notch, play a role in embryogenesis and organogenesis and maintenance of tissues in the adult through regulation of the balance between self-renewal and differentiation of stem cells. Breast TAAs include epitopes from proteins, such as carcinoembryonic antigen and NYBR-1, which are involved in tissue differentiation. Targeting BCSCs may be achieved by a number of approaches such as chemotherapy sensitization of BCSCs, differentiating therapy, targeting stem cell elimination, targeting signaling pathways and drug transporters, and inhibition of regulatory pathways involved in self-renewal. Targeting cells which have the potential to metastasize will be an important aspect of the BCSC field as these are the cells that cause the majority of morbidity and mortality from breast cancer.

Cancer stem-like cell properties are regulated by EGFR/AKT/β-catenin signaling and preferentially inhibited by gefitinib in nasopharyngeal carcinoma

We report that the epidermal growth factor receptor (EGFR) pathway plays a critical role in regulating cancer stem-like cells (CSCs) in nasopharyngeal carcinoma (NPC), one of the most common malignant tumors in Southeast Asia. Effects of EGFR on maintaining CSCs are mainly mediated by AKT signaling, and β-catenin is responsible for governing CSC properties in response to EGFR/AKT activation. Significantly, CSCs are enriched by cisplatin and decreased by gefitinib in NPC xenograft models. Upon reimplantation in secondary mice, tumor cells derived from cisplatin-treated mice grew rapidly, whereas regrowth of tumor cells from gefitinib-treated mice was severely diminished. We further demonstrate that expression of EGFR correlates with expression of β-catenin and Nanog in primary tumor specimens from NPC patients. These findings provide mechanistic and preclinical evidence supporting the use of gefitinib alone or in combination with a chemotherapeutic agent in first-line therapy for patients with NPC. In addition, our results suggest that targeting β-catenin represents a rational clinical modality for patients whose tumors harbor activated EGFR or AKT.

The implications of cancer stem cells for cancer therapy

Surgery, radiotherapy and chemotherapy are universally recognized as the most effective anti-cancer therapies. Despite significant advances directed towards elucidating molecular mechanisms and developing clinical trials, cancer still remains a major public health issue. Recent studies have showed that cancer stem cells (CSCs), a small subpopulation of tumor cells, can generate bulk populations of nontumorigenic cancer cell progeny through the self-renewal and differentiation processes. As CSCs are proposed to persist in tumors as a distinct population and cause relapse and metastasis by giving rise to new tumors, development of CSC-targeted therapeutic strategies holds new hope for improving survival and quality of life in patients with cancer. Therapeutic innovations will emerge from a better understanding of the biology and environment of CSCs, which, however, are largely unexplored. This review summarizes the characteristics, evidences and development of CSCs, as well as implications and challenges for cancer treatment.

Chromosome instability modulated by BMI1-AURKA signaling drives progression in head and neck cancer

Chromosomal instability (CIN) is widely considered a hallmark of cancer, but its precise roles in cancer stem cells (CSC) and malignant progression remain uncertain. BMI1 is a member of the Polycomb group of chromatin-modifier proteins that is essential for stem cell self-renewal. In human cancers, BMI1 overexpression drives stem-like properties associated with induction of epithelial-mesenchymal transition (EMT) that promotes invasion, metastasis, and poor prognosis. Here, we report that BMI1 mediates its diverse effects through upregulation of the mitotic kinase Aurora A, which is encoded by the AURKA gene. Two mechanisms were found to be responsible for BMI1-induced AURKA expression. First, BMI1 activated the Akt pathway, thereby upregulating AURKA expression through activation of the β-catenin/TCF4 transcription factor complex. Second, BMI1 repressed miRNA let-7i through a Polycomb complex-dependent mechanism, thereby relieving AURKA expression from let-7i suppression. AURKA upregulation by BMI1 exerts several effects, including centrosomal amplification and aneuploidy, antiapoptosis, and cell-cycle progression through p53 degradation and EMT through stabilization of Snail. Inhibiting Aurora A kinase activity attenuated BMI1-induced tumor growth in vivo. In clinical specimens of head and neck cancer, we found that coamplification of BMI1 and AURKA correlated with poorer prognosis. Together, our results link CSCs, EMT, and CIN through the BMI1-AURKA axis and suggest therapeutic use from inhibiting Aurora A in head and neck cancers, which overexpress BMI1.

Stem cell expansion during carcinogenesis in stem cell-depleted conditional telomeric repeat factor 2 null mutant mice

To examine the role of TRF2 in epithelial tumorigenesis, we characterized conditional loss of TRF2 expression in the basal layer of mouse epidermis. These mice exhibit some characteristics of dyskeratosis congenita, a human stem cell depletion syndrome caused by telomere dysfunction. The epidermis in conditional TRF2 null mice exhibited DNA damage response and apoptosis which correlated with stem cell depletion. The stem cell population in conditional TRF2 null epidermis exhibited shorter telomeres than those in control mice. Squamous cell carcinomas induced in conditional TRF2 null mice developed with increased latency and slower growth due to reduced numbers of proliferating cells as the result of increased apoptosis. TRF2 null epidermal stem cells were found in both primary and metastatic tumors. Despite the low grade phenotype of the conditional TRF2 null primary tumors, the number of metastatic lesions was similar to control cancers. Basal cells from TRF2 null tumors demonstrated extreme telomere shortening and dramatically increased numbers of telomeric signals by fluorescence in situ hybridization due to increased genomic instability and aneuploidy in these cancers. DNA damage response signals were detected at telomeres in TRF2 null tumor cells from these mice. The increased genomic instability in these tumors correlated with 8 fold expansion of the transformed stem cell population compared to that in control cancers. We concluded that genomic instability resulting from loss of TRF2 expression provides biological advantages to the cancer stem cell population.

Cisplatin selects for multidrug-resistant CD133+ cells in lung adenocarcinoma by activating Notch signaling

Platinum-based chemotherapy is the first-line treatment for non-small cell lung cancer, but recurrence occurs in most patients. Recent evidence suggests that CD133(+) cells are the cause of drug resistance and tumor recurrence. However, the correlation between chemotherapy and regulation of CD133(+) cells has not been investigated methodically. In this study, we revealed that CD133(+) lung cancer cells labeled by a human CD133 promoter-driven GFP reporter exhibited drug resistance and stem cell characteristics. Treatment of H460 and H661 cell lines with low-dose cisplatin (IC(20)) was sufficient to enrich CD133(+) cells, to induce DNA damage responses, and to upregulate ABCG2 and ABCB1 expression, which therefore increased the cross-resistance to doxorubicin and paclitaxel. This cisplatin-induced enrichment of CD133(+) cells was mediated through Notch signaling as judged by increased levels of cleaved Notch1 (NICD1). Pretreatment with the γ-secretase inhibitor, N-[N-(3,5-difluorophenacetyl)-1-alanyl]-S-phenylglycine t-butyl ester (DAPT), or Notch1 short hairpin RNAs (shRNA) remarkably reduced the cisplatin-induced enrichment of CD133(+) cells and increased the sensitivity to doxorubicin and paclitaxel. Ectopic expression of NICD1 reversed the action of DAPT on drug sensitivity. Immunohistochemistry showed that CD133(+) cells were significantly increased in the relapsed tumors in three of six patients with lung cancer who have received cisplatin treatment. A similar effect was observed in animal experiments as cisplatin treatment increased Notch1 cleavage and the ratio of CD133(+) cells in engrafted tumors. Intratumoral injection of DAPT with cisplatin treatment significantly reduced CD133(+) cell number. Together, our results showed that cisplatin induces the enrichment of CD133(+) cells, leading to multidrug resistance by the activation of Notch signaling.

Sorafenib modulates the radio sensitivity of hepatocellular carcinoma cells in vitro in a schedule-dependent manner

BACKGROUND

Hepatocellular carcinoma (HCC) has a high incidence and mortality. Radiotherapy and sorafenib have proven effective for HCC. Here, we investigated whether sorafenib modulated the response of HCC cells to irradiation in vitro, effect of timing of sorafenib, and the underlying mechanisms.

METHODS

Cell viability of the HCC cell lines, SMMC-7721 and Bel-7402, was examined by the 3-(4,5-dimethylthiazol-2-yl)-5(3-carboxymethoxyphenyl)-2(4-sulfophenyl)-2 H-terazolium (MTT) assays. Clonogenic growth assays of SMMC-7721 and Bel-7402 were determined by colony formation assays. DNA damage was assessed by monitoring γ-HAX foci in irradiated cells with immunofluorescence microscopy, and cell cycle distribution changes were examined by flow cytometry. Effects of sorafenib (15 μM) added 30 min prior to radiation (pre-irradiation sorafenib) of SMMC-7721 and BEL-7402 or 24 h post-irradiation (post-irradiation sorafenib) on irradiated SMMC-7721 and BEL-7402 cells were compared to those of radiation alone or no treatment.

RESULTS

The effect of sorafenib was dependent on its time of addition in relationship to irradiation of cells. Pre-irradiation sorafenib did not significantly affect the viability of SMMC-7221 and BEL-7402 cells compared with irradiation treatment alone. In contrast, post-irradiation sorafenib increased the sensitivity of irradiated SMMC-7221 and BEL-7402 cells significantly in a time-dependent manner. Pre-irradiation sorafenib significantly increased the surviving fraction of SMMC-7221 and BEL-7402 cells in clonogenic assays whereas post-irradiation sorafenib significantly reduced the surviving fractions of SMMC-7221 and BEL-7402 cells. SMMC-7721 cells treated with sorafenib 30 min before irradiation had significantly fewer cells with γ-H2AX foci (23.8 ± 2.9%) than SMMC-7721 cells receiving radiation alone (59.9 ± 2.4; P < 0.001). Similarly, BEL-7402 cells receiving sorafenib prior to irradiation had significantly fewer cells with γ-H2AX foci (46.4 ± 3.8%) than those receiving radiation alone (25.0 ± 3.0%; P < 0.001). In addition, irradiation (6 Gy) caused a significant increase in the percentage of both SMMC-7721 and BEL-7402 cells in G2/M at 12 to 16 h post irradiation, which was markedly delayed by pre-irradiation sorafenib.

CONCLUSIONS

Sorafenib combined with irradiation exerted a schedule-dependent effect in HCC cells in vitro, which has significant implications for the combined use of sorafenib and radiotherapy for HCC patients.

Enrichment of osteosarcoma stem cells by chemotherapy

Osteosarcoma is the most common primary malignant bone cancer in children and adolescents. Emerging evidence has suggested that the capability of a tumor to grow is driven by a small subset of cells within a tumor, termed cancer stem cells (CSCs). Although several methods have been explored to identify or enrich CSCs in osteosarcoma, these methods sometimes seem impractical, and chemotherapy enrichment for CSCs in osteosarcoma is rarely investigated. In the present study, we found that short exposure to chemotherapy could change the morphology of osteosarcoma cells and increase sarcosphere formation in vitro, as well as increase tumor formation in vivo. Furthermore, methotrexate (MTX)-resistant U2OS/MTX300 osteosarcoma cells were larger in size and grew much more tightly than parental U2OS cells. More importantly, U2OS/MTX300 cells possessed a higher potential to generate sarcospheres in serum-free conditions compared to parental U2OS cells. Also, U2OS/MTX300 cells exhibited the side population (SP) phenotype and expressed CSC surface markers CD117 and Stro-1. Notably, U2OS/MTX300 cells showed a substantially higher tumorigenicity in nude mice relative to U2OS cells. Therefore, we conclude that chemotherapy enrichment is a feasible and practical way to enrich osteosarcoma stem cells.

Correlation of Skp2 overexpression to prognosis of patients with nasopharyngeal carcinoma from South China

S-phase kinase-associated protein 2 (Skp2), which plays a role in cell cycle regulation, is commonly overexpressed in a variety of human cancers and associated with poor prognosis. However, its role in nasopharyngeal carcinoma (NPC) is not well understood. In this study, we examined the clinical significance of Skp2, with a particular emphasis on overall survival (OS) and disease-free survival (DFS), in NPC cases in South China, where NPC is an epidemic. Additionally, we explored the function of Skp2 in maintaining a cancer stem cell-like phenotype in NPC cell lines. Skp2 expression was assessed for 127 NPC patients using tissue microarrays and immunohistochemistry and analyzed together with clinicopathologic features, OS, and DFS. Skp2 expression was detectable, or positive, in 75.6% of patients. Although there was no correlation between Skp2 and any clinicopathologic factor, Skp2 expression significantly portended inferior OS (P = 0.013) and DFS (P = 0.012). In the multivariate model, Skp2 expression remained significantly predictive of poor OS [P = 0.009, risk ratio (RR) = 4.06] and DFS (P = 0.008, RR = 3.56), and this was also true for clinical stage (P = 0.012 and RR=3.201 for OS; P = 0.002 and RR=1.94 for DFS) and sex (P = 0.016 and RR=0.31 for OS; P = 0.006 and RR = 0.27 for DFS). After Skp2 knockdown, a colony formation assay was used to evaluate the self-renewal property of stem-like cells in the NPC cell lines CNE-1 and CNE-2. The colony formation efficiency in CNE-1 and CNE-2 cells was decreased. In Skp2-transfected CNE-1 and CNE-2 cells, side population (SP) proportion was increased as detected by flow cytometry. Skp2 is an independent prognostic marker for OS and DFS in NPC. Skp2 may play a role in maintaining the cancer stem cell-like phenotype of NPC cell lines.

Epithelial mesenchymal transition and lung cancer

Despite the therapeutic advances, lung cancer remains the leading cause of cancer-related death in the United States and worldwide. Metastasis and recurrence are considered to be responsible for the failure of treatment. Recent studies indicate Epithelial mesenchymal transition, an evolutionarily conserved process, plays an important role in the embryonic development and cancer progression and is involved in the metastasis, drug resistance and correlated with progression of many tumors. Of importance, EMT is also involved in the acquisition of stemness phenotype of tumor cells. Although a growing body of evidence supports the role of EMT in the progression of many cancers, and a number of signal pathways, transcriptional factors and microRNAs involved in EMT process have been identified. However, the role of EMT in lung cancer is elusive. In this review, we present the recent findings in EMT including the molecular mechanisms of EMT, and the involvement of EMT in cancer progression, cancer stem cells and drug resistance, especially focusing on the correlation of EMT and lung cancer.

Centrosome loss or amplification does not dramatically perturb global gene expression in Drosophila

Centrosome defects are a common feature of many cancers, and they can predispose fly brain cells to form tumours. In flies, centrosome defects perturb the asymmetric division of the neural stem cells, but it is unclear how this might lead to malignant transformation. One possibility is that centrosome defects might also perturb cellular homeostasis: for example, stress pathways are often activated in response to centrosome defects in cultured cells, and stress contributes to tumourigenesis in some fly models. Here we attempt to assess whether centrosome loss or centrosome amplification perturbs cell physiology in vivo by profiling the global transcriptome of Drosophila larval brains and imaginal discs that either lack centrosomes or have too many centrosomes. Surprisingly, we find that centrosome loss or amplification leads to few changes in the transcriptional profile of these cells, indicating that centrosome defects are surprisingly well tolerated by these cells. These observations indicate that centrosome defects can predispose fly brain cells to form tumours without, at least initially, dramatically altering their physiology.

Wnt pathway activity confers chemoresistance to cancer stem-like cells in a neuroblastoma cell line

Neuroblastoma is the most common solid tumor in infancy. We have shown that the neuroblastoma cell line SK-N-SH contains CD133+ cells that are more resistant than 133- cells to Doxorubicin (DOX), a common chemotherapeutic agent. We hypothesize that activation of wnt signaling pathway in CD133+ cells contributes to their chemoresistance. To test this hypothesis, CD133+ cells were positively selected using magnetic micro-beads. Subsequently, CD133+ and negatively selected CD133- cells were treated with 100 ng/ml of DOX for up to 72 h. Then, cells were either lysed for total RNA extraction or fixed for immunostaining. Wnt "SIGNATURE" PCR Array was used to determine if changes in wnt related gene expression levels occurred and to estimate a pathway activity score. Expression of wnt pathway proteins β-Catenin and p-GSK3β (S-9) was determined by immunocytochemistry. Two wnt pathway inhibitors were used to determine the changes in cell viability, using the MTT assay. Results showed that wnt related genes were differentially expressed in CD133+ cells as compared to CD133- cells, both with and without DOX treatment. Pathway activity scores showed that DOX treatment significantly suppressed the wnt pathway activity in CD133- cells. Expression of β-catenin and p-GSK3β (S-9) was significantly greater in DOX treated and untreated CD133+ cells. The presence of wnt inhibitors with DOX decreased the number of live cells in CD133+ group and the percentage of live cells in both groups were equal. These data suggest that higher wnt pathway activity could be responsible for the chemoresistance of CD133+ cells in neuroblastoma cell lines.

Sp1 and Sp3 are involved in the full transcriptional activity of centromere protein H in human nasopharyngeal carcinoma cells

The overexpression of centromere protein H (CENPH), one of the fundamental components of the human active kinetochore, has been shown to be closely associated with human cancers. However, the mechanism of its transcriptional regulation has not been reported. The aim of the present study was to investigate the regulatory elements for the transcriptional regulation of CENPH in nasopharyngeal carcinoma cells. To characterize the CENPH promoter and identify regulatory elements, we cloned 1015 bp (-975/+40 bp) of the 5'-flanking region of the CENPH gene from immortalized normal nasopharyngeal epithelial cells (Bmi-1/NPEC). Functional analysis established a minimal region (-140/-87 bp) involved in the regulation of human CENPH promoter activity. Through site-directed mutagenesis, a transactivation assay, chromatin immunoprecipitation, and electrophoretic mobility shift assay, we found that the Sp1/Sp3 transcription factors could bind to the CENPH promoter in vitro and in vivo, and that they regulated CENPH promoter activation in human nasopharyngeal carcinoma cells. Furthermore, Sp1 and Sp3 were highly expressed in nasopharyngeal carcinoma cells. Knockdown of Sp1 and Sp3 by small interfering RNA or inhibition of Sp1 and Sp3 activity by mithramycin A decreased CENPH mRNA expression, whereas the exogenous expression of Sp1 and Sp3 upregulated CENPH mRNA expression. Taken together, our results indicate that Sp1 and Sp3 bind to the CENPH minimal promoter and function as a regulator of the transcription of CENPH in human nasopharyngeal carcinomas.

Dynamic equilibrium between cancer stem cells and non-stem cancer cells in human SW620 and MCF-7 cancer cell populations

Background:

Cancer stem cells (CSCs) paradigm suggests that CSCs might have important clinical implications in cancer therapy. Previously, we reported that accumulation efficiency of CSCs is different post low- and high-LET irradiation in 48 h.

Methods:

Cancer stem cells and non-stem cancer cells (NSCCs) were sorted and functionally identified through a variety of assays such as antigen profiles and sphere formation. Inter-conversion between CSCs and NSCCs were in situ visualised. Cancer stem cells proportions were assayed over multiple generations under normal and irradiation surroundings. Supplement and inhibition of TGF-β1, as well as immunofluorescence assay of E-cadherin and Vimentin, were performed.

Results:

Surface antigen markers of CSCs and NSCCs exist in an intrinsic homoeostasis state with spontaneous and in situ visualisable inter-conversions, irrespective of prior radiations. Supplement with TGF-β1 accelerates the equilibrium, whereas inhibition of TGF-β signalling disturbs the equilibrium and significantly decreases CSC proportion. Epithelial mesenchymal transition (EMT) might be activated during the process.

Conclusion:

Our results indicate that the intrinsic inter-conversion and dynamic equilibrium between CSCs and NSCCs exist under normal and irradiation surroundings, and TGF-β might have important roles in the equilibrium through activating EMT.

The propensity for tumorigenesis in human induced pluripotent stem cells is related with genomic instability

The discovery of induced pluripotent stem cells (iPSCs) is a promising advancement in the field of regenerative medicine. Previous studies have indicated that the teratoma-forming propensity of iPSCs is variable; however, the relationship between tumorigenic potential and genomic instability in human iPSCs (HiPSCs) remains to be fully elucidated. Here, we evaluated the malignant potential of HiPSCs by using both colony formation assays and tumorigenicity tests. We demonstrated that HiPSCs formed tumorigenic colonies when grown in cancer cell culture medium and produced malignancies in immunodeficient mice. Furthermore, we analyzed genomic instability in HiPSCs using whole-genome copy number variation analysis and determined that the extent of genomic instability was related with both the cells' propensity to form colonies and their potential for tumorigenesis. These findings indicate a risk for potential malignancy of HiPSCs derived from genomic instability and suggest that quality control tests, including comprehensive tumorigenicity assays and genomic integrity validation, should be rigorously executed before the clinical application of HiPSCs. In addition, HiPSCs should be generated through the use of combined factors or other approaches that decrease the likelihood of genomic instability.

CHK1 targets spleen tyrosine kinase (L) for proteolysis in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most prevalent malignancies resistant to current chemotherapies or radiotherapies, which makes it urgent to identify new therapeutic targets for HCC. In this study, we found that checkpoint kinase 1 (CHK1) was frequently overexpressed and correlated with poor clinical outcome in patients with HCC. We further showed that the CHK1 inhibitor GÖ6976 was capable of sensitizing HCC cells to cisplatin, indicating that CHK1 may have oncogenic function in HCC. We found that CHK1 phosphorylated the tumor suppressor spleen tyrosine kinase (L) (SYK[L]) and identified the phosphorylation site at Ser295. Furthermore, CHK1 phosphorylation of SYK(L) promoted its subsequent proteasomal degradation. Expression of a nonphosphorylated mutant of SYK(L) was more efficient at suppressing proliferation, colony formation, mobility, and tumor growth in HCC lines. Importantly, a strong inverse correlation between the expression levels of CHK1 and SYK(L) was observed in patients with HCC. Collectively, our data demonstrate that SYK(L) is a substrate of CHK1 in tumor cells and suggest that targeting the CHK1/SYK(L) pathway may be a promising strategy for treating HCC.

MicroRNA expression profiling identifies miR-328 regulates cancer stem cell-like SP cells in colorectal cancer

Background:

Side population (SP) cells and their relationship to stem cell-like properties have been insufficiently studied in colorectal cancer (CRC). MicroRNAs (miRNAs) have attracted much attention but their roles in the maintenance of SP phenotype remain unclear.

Methods:

The SPs from CRC cell lines and primary cell cultures were analysed for stem cell-like properties. MiRNA microarray analysis identified miR-328 as a potential stemness miRNA of SP phenotype. The level of miR-328 expression in clinical samples and its correlation with SP fraction were determined. Gain-of-function and loss-of-function studies were performed to examine its roles in cancer stem-like SP cells. Furthermore, bioinformatics prediction and experimental validation were used to identify miR-328 target genes.

Results:

The SP cells sorted from CRC possess cancer stem cell (CSC)-like properties, including self-renewal, differentiation, resistance to chemotherapy, invasive and strong tumour formation ability. MiR-328 expression was significantly reduced in SP cells compared with Non-SP cells (P<0.05). Moreover, miR-328 expression was downregulated in CRC (n=33, P<0.05) and low miR-328 expression tend to correlate with high SP fraction (n=15, r=0.6559, P<0.05, Pearson's correlation). Functional studies indicated that miR-328 expression affects the number of SP cells. In addition, miR-328 overexpression reversed drug resistance and inhibited cell invasion of SP cells. Furthermore, luciferase reporter assay demonstrated that miR-328 directly targets ABCG2 and MMP16 and affects the levels of mRNA and protein expression in SP cells.

Conclusion:

These findings indicate that CRC contain cancer stem-like SP cells. MiR-328 has an important role in maintaining cancer stem-like SP phenotype that may be a potential target for effective CRC therapy.

Glycogen synthase kinase-3β, NF-κB signaling, and tumorigenesis of human osteosarcoma

Background

Glycogen synthase kinase-3β (GSK-3β), a serine/threonine protein kinase, may function as a tumor suppressor or an oncogene, depending on the tumor type. We sought to determine the biological function of GSK-3β in osteosarcoma, a rare pediatric cancer for which the identification of new therapeutic targets is urgent.

Methods

We used cell viability assays, colony formation assays, and apoptosis assays to analyze the effects of altered GSK-3β expression in U2OS, MG63, SAOS2, U2OS/MTX300, and ZOS osteosarcoma cell lines. Nude mice (n = 5–8 mice per group) were injected with U2OS/MTX300, and ZOS cells to assess the role of GSK-3β in osteosarcoma growth in vivo and to evaluate the effects of inhibitors and/or anticancer drugs on tumor growth. We used an antibody array, polymerase chain reaction, western blotting, and a luciferase reporter assay to establish the effect of GSK-3β inhibition on the nuclear factor-κB (NF-κB) pathway. Immunochemistry was performed on primary tumor specimens from osteosarcoma patients (n = 74) to determine the relationship of GSK-3β activity with overall survival.

Results

Osteosarcoma cells with low levels of inactive p-Ser9-GSK-3β formed colonies in vitro and tumors in vivo more readily than cells with higher levels and cells in which GSK-3β had been silenced formed fewer colonies and smaller tumors than parental cells. Silencing or pharmacological inhibition of GSK-3β resulted in apoptosis of osteosarcoma cells. Inhibition of GSK-3β resulted in inhibition of the NF-κB pathway and reduction of NF-κB-mediated transcription. Combination treatments with GSK-3β inhibitors, NF-κB inhibitors, and chemotherapy drugs increased the effectiveness of chemotherapy drugs in vitro and in vivo. Patients whose osteosarcoma specimens had hyperactive GSK-3β, and nuclear NF-κB had a shorter median overall survival time (49.2 months) compared with patients whose tumors had inactive GSK-3β and NF-κB (109.2 months).

Conclusion

GSK-3β activity may promote osteosarcoma tumor growth, and therapeutic targeting of the GSK-3β and/or NF-κB pathways may be an effective way to enhance the therapeutic activity of anticancer drugs against osteosarcoma.

Recombinant human endostatin normalizes tumor vasculature and enhances radiation response in xenografted human nasopharyngeal carcinoma models

BACKGROUND

Hypoxic tumor cells can reduce the efficacy of radiation. Antiangiogenic therapy may transiently "normalize" the tumor vasculature to make it more efficient for oxygen delivery. The aim of this study is to investigate whether the recombinant human endostatin (endostar) can create a "vascular normalization window" to alleviate hypoxia and enhance the inhibitory effects of radiation therapy in human nasopharyngeal carcinoma (NPC) in mice.

METHODOLOGY/PRINCIPAL FINDINGS

Transient changes in morphology of tumor vasculature and hypoxic tumor cell fraction in response to endostar were detected in mice bearing CNE-2 and 5-8F human NPC xenografts. Various treatment schedules were tested to assess the influence of endostar on the effect of radiation therapy. Several important factors relevant to the angiogenesis were identified through immunohistochemical staining. During endostar treatment, tumor vascularity decreased, while the basement membrane and pericyte coverage associated with endothelial cells increased, which supported the idea of vessel normalization. Hypoxic tumor cell fraction also decreased after the treatment. The transient modulation of tumor physiology caused by endostar improved the effect of radiation treatment compared with other treatment schedules. The expressions of vascular endothelial growth factor (VEGF), matrix metalloproteinase-2 (MMP-2), MMP-9, and MMP-14 decreased, while the level of pigment epithelium-derived factor (PEDF) increased.

CONCLUSIONS

Endostar normalized tumor vasculature, which alleviated hypoxia and significantly sensitized the function of radiation in anti-tumor in human NPC. The results provide an important experimental basis for combining endostar with radiation therapy in human NPC.

Clinical aspect and molecular mechanism of DNA aneuploidy in gastric cancers

The biological characteristics of cancers depend mostly on genetic alterations in the cancer cells of individuals. Gastric cancers show a high frequency of DNA aneuploidy, a phenotype of chromosomal instability. Compared to diploid tumors, gastric carcinomas with aneuploidy have been shown to have high proliferative activity and high metastatic or invasive potential; these characteristics lead to a poor prognosis. It has been suggested that an abnormal spindle assembly checkpoint is involved in DNA aneuploidy, but the underlying mechanism is still unclear. This review, in order to determine whether gastric carcinomas that display aneuploidy are associated with a poorer prognosis than diploid tumors, and to discuss the biological mechanisms that induce aneuploidy, summarizes the results of studies on DNA ploidy in gastric cancer published in the English literature. Analysis of DNA ploidy in gastric cancer may provide clinically useful information from diagnostic, therapeutic, and prognostic standpoints. Further investigations may be needed to clarify the relationship between chromosome instability and DNA ploidy.

CD133, Stem Cells, and Cancer Stem Cells: Myth or Reality?

CD133, a member of the prominin family, is found in a variety of tissues with at least three variants. The function of CD133 is not well understood, but its expression is subject to changes in the microenvironment cues including bioenergetic stress. Knockout of CD133 does not affect renewal, but mammary gland branching. A point mutation of CD133 (R733C) leads to retinal disorder. CD133 is found in embryonic stem cells, normal tissue stem cells, stem cell niches, and circulating endothelial progenitors as well as cancer stem cells. Maintenance of stemness in cancer may be attributable to asymmetric cell division in association with a set of embryonic expression signatures in CD133+ tumor cells. CD133 could enrich cancer stem cells, which are associated with chemo- and radiation resistance phenotype. High CD133 is associated with poor survival in a variety of solid tumors, including lung, colon, prostate, etc. Monitoring CD133+ cells in peripheral blood, and targeting CD133 in cancer, may further predict and improve the clinical outcomes.

Drug-induced senescence generates chemoresistant stemlike cells with low reactive oxygen species

Tumor recurrence after chemotherapy or radiation remains a major obstacle to successful cancer treatment. A subset of cancer cells, termed cancer stem cells, can elude conventional treatments and eventually regenerate a tumor that is more aggressive. Despite the large number of studies, molecular events that govern the emergence of aggressive therapy-resistant cells with stem cell properties after chemotherapy are poorly defined. The present study provides evidence for the rare escape of tumor cells from drug-induced cell death, after an intermediate stay in a non-cycling senescent stage followed by unstable multiplication characterized by spontaneous cell death. However, some cells appear to escape and generate stable colonies with an aggressive tumor stem cell-like phenotype. These cells displayed higher CD133 and Oct-4 expression. Notably, the drug-selected cells that contained low levels of reactive oxygen species (ROS) also showed an increase in antioxidant enzymes. Consistent with this in vitro experimental data, we observed lower levels of ROS in breast tumors obtained after neoadjuvant chemotherapy compared with samples that did not receive preoperative chemotherapy. These latter tissues also expressed enhanced levels of ROS defenses with enhanced expression of superoxide dismutase. Higher levels of Oct-4 and CD133 were also observed in tumors obtained after neoadjuvant chemotherapy. Further studies provided evidence for the stabilization of Nrf2 due to reduced 26 S proteasome activity and increased p21 association as the driving signaling event that contributes to the transition from a high ROS quiescent state to a low ROS proliferating stage in drug-induced tumor stem cell enrichment.

Side population is not necessary or sufficient for a cancer stem cell phenotype in glioblastoma multiforme

There is strong evidence for the existence of cancer stem cells (CSCs) in the aggressive brain tumor glioblastoma multiforme (GBM). These cells have stem-like self-renewal activity and increased tumor initiation capacity and are believed to be responsible for recurrence due to their resistance to therapy. Several techniques have been used to enrich for CSC, including growth in serum-free defined media to induce sphere formation, and isolation of a stem-like cell using exclusion of the fluorescent dye Hoechst 33342, the side population (SP). We show that sphere formation in GBM cell lines and primary GBM cells enriches for a CSC-like phenotype of increased self-renewal gene expression in vitro and increased tumor initiation in vivo. However, the SP was absent from all sphere cultures. Direct isolation of the SP from the GBM lines did not enrich for stem-like activity in vitro, and tumor-initiating activity was lower in sorted SP compared with non-SP and parental cells. Transient exposure to doxorubicin enhanced both CSC and SP frequency. However, doxorubicin treatment altered the cytometric profile and obscured the SP demonstrating the difficulty of identifying SP in cells under stress. Doxorubicin-exposed cells showed a transient increase in SP, but the doxorubicin-SP cells were still not enriched for a stem-like self-renewal phenotype. These data demonstrate that the GBM SP does not necessarily contribute to self-renewal or tumor initiation, key properties of a CSC, and we advise against using SP to enumerate or isolate CSC.

Combination of salinomycin and gemcitabine eliminates pancreatic cancer cells

Previous research has documented that a subpopulation of pancreatic cancer cells, named cancer stem cells (CSCs), harbor stem cell-like properties. Here, we examined the efficacy of combined treatments of salinomycin and gemcitabine in human pancreatic cancer cells. Salinomycin inhibited the growth of CSCs, while gemcitabine suppressed the viability of non-CSCs. Consistently, in vivo studies showed that salinomycin combined with gemcitabine could eliminate the engraftment of human pancreatic cancer more effectively than the individual agents. These data indicated that administration of salinomycin, which targets CSCs, may constitute a potential therapeutic strategy for improving the efficacy of gemcitabine to eradicate pancreatic cancer.

Cancer cells cyclically lose and regain drug-resistant highly tumorigenic features characteristic of a cancer stem-like phenotype

Drug resistance and brisk tumor initiation have traditionally been viewed as preexisting phenotypes present in small subpopulations of neoplastic cells sometimes termed cancer stem cells. However, recent work in cancer cell lines has shown that drug-resistant tumor-initiating features can emerge de novo within fractionated subpopulations of cells initially lacking these phenotypes. In the present study, we asked whether such phenotypic plasticity exists broadly in unperturbed cancer cell lines and tumor xenografts growing spontaneously without interventions such as drug selection or fractionation into subpopulations used in prior studies. To address this question, we used side population (SP) analysis combined with fluorescence labeling to identify a drug-resistant highly tumorigenic subpopulation and to track and analyze its interaction with the larger phenotypically negative population over time. Remarkably, we observed that SP size fluctuated in a cyclical manner: first contracting via differentiation into the non-SP (NSP) and then reexpanding via simultaneous direct conversion of numerous NSP cells back to the SP phenotype both in culture and in tumor xenografts. These findings show for the first time that adaptive, cancer-promoting traits such as drug resistance and brisk tumor initiation arise not only as solitary events under selective pressures but also as highly orchestrated transitions occurring concurrently in large numbers of cells even without specifically induced drug selection, ectopic gene expression, or fractionation into subpopulations. This high level of coordinated phenotypic plasticity bears consideration when using cancer cell lines as experimental models and may have significant implications for therapeutic efforts targeting cancer stem cells, which are marked by a drug-resistant tumor-initiating phenotype.

Relationship of cellular drug resistance to proportion of side population cells and expression of Mdr1 and ERCC1 in human gastric cell line SGC7901/OXA

AIM: To investigate the mechanism of acquired drug resistance in human gastric cancer cell line SGC7901/OXA.

METHODS: SGC7901/OXA cell line was obtained by exposure of SGC7901 cells to increasing doses of oxaliplatin (OXA). The parental cell line SGC7901 was used as a control. The reduced rate of cell growth, half maximal inhibitory concentration (IC50), and resistance index (RI) were measured by MTT assay and compared between the two groups of cells. The expression of multidrug resistance 1 (Mdr1) mRNA and excision repair cross-complementing group 1 (ERCC1) protein was detected by RT-PCR and Western blot, respectively. The proportion of side population (SP) cells was determined by flow cytometry.

RESULTS: The reduced rate of cell growth significantly decreased and IC50 increased (38.23 μmol/L vs 7.12 μmol/L) in SGC7901/OXA cells compared to parental SGC7901 cells. The RI was 5.37 in SGC7901/OXA cells. There was no significant difference in the relative expression level of Mdr1 mRNA (0.468 ± 0.147 vs 0.427 ± 0.136, P = 0.079) between the two groups. ERCC1 protein level was significantly higher in SGC7901/OXA cells than in SGC7901 cells. The proportion of SP cells was also significantly higher in SGC7901/OXA cells than in SGC7901 cells (6.1% vs 1.8%, P < 0.05).

CONCLUSION: SGC7901/OXA cells were more significantly resistant to OXA than SGC7901. The mechanism of acquired resistance of SGC7901/OXA cells may be associated with changes in ERCC1 protein expression and proportion of SP cells.

Combination therapy targeting both tumor-initiating and differentiated cell populations in prostate carcinoma

PURPOSE

The cancer stem cell hypothesis predicts that standard prostate cancer monotherapy eliminates bulk tumor cells but not a tumor-initiating cell population, eventually leading to relapse. Many studies have sought to determine the underlying differences between bulk tumor and cancer stem cells.

EXPERIMENTAL DESIGN

Our previous data suggest that the PTEN/PI3K/AKT pathway is critical for the in vitro maintenance of CD133(+)/CD44(+) prostate cancer progenitors and, consequently, that targeting PI3K signaling may be beneficial in treatment of prostate cancer.

RESULTS

Here, we show that inhibition of PI3K activity by the dual PI3K/mTOR inhibitor NVP-BEZ235 leads to a decrease in the population of CD133(+)/CD44(+) prostate cancer progenitor cells in vivo. Moreover, the combination of the PI3K/mTOR modulator NVP-BEZ235, which eliminates prostate cancer progenitor populations, and the chemotherapeutic drug Taxotere, which targets the bulk tumor, is significantly more effective in eradicating tumors in a prostate cancer xenograft model than monotherapy.

CONCLUSION

This combination treatment ultimately leads to the expansion of cancer progenitors with a PTEN E91D mutation, suggesting that the analysis of PTEN mutations could predict therapeutic response to the dual therapy.

Cancer stem cells of differentiated B-cell malignancies: models and consequences

The concept of cancer stem cells has revolutionized our current vision of cancer development and was validated in solid tumors and cancers of the primitive hematopoietic compartment. Proof of the principle is still lacking, however, in malignancies of differentiated B-cells. We review here the current literature, which nevertheless suggests hierarchical organizations of the tumor clone for mostly incurable B-cell cancers such as multiple myeloma, lymphomas and B-chronic lymphocytic leukemia. We propose two models accounting for cancer stem cells in these contexts: a “top-to-bottom” clonal hierarchy from memory B-cells and a “bottom-to-top” model of clonal reprogramming. Selection pressure on the growing tumor can drive such reprogramming and increase its genetic diversity.

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.

Epithelial mesenchymal transition and lung cancer

Despite the therapeutic advances, lung cancer remains the leading cause of cancer-related death in the United States and worldwide. Metastasis and recurrence are considered to be responsible for the failure of treatment. Recent studies indicate Epithelial mesenchymal transition, an evolutionarily conserved process, plays an important role in the embryonic development and cancer progression and is involved in the metastasis, drug resistance and correlated with progression of many tumors. Of importance, EMT is also involved in the acquisition of stemness phenotype of tumor cells. Although a growing body of evidence supports the role of EMT in the progression of many cancers, and a number of signal pathways, transcriptional factors and microRNAs involved in EMT process have been identified. However, the role of EMT in lung cancer is elusive. In this review, we present the recent findings in EMT including the molecular mechanisms of EMT, and the involvement of EMT in cancer progression, cancer stem cells and drug resistance, especially focusing on the correlation of EMT and lung cancer.

Chk1 inhibitor Gö6976 enhances the sensitivity of nasopharyngeal carcinoma cells to radiotherapy and chemotherapy in vitro and in vivo

Nasopharyngeal carcinoma (NPC) is a malignant tumor. This type of carcinoma has a low 5-year patient survival rate. Thus, there is a need for improved therapeutics. We determined that the Chk1 inhibitor Gö6976 enhanced the sensitivity of CNE1 and CNE2 cells to ionizing radiation (IR) or cisplatin by abrogating S and G(2)/M arrest and subsequently promoting apoptosis. Furthermore, Gö6976 appeared to sensitize NPC xenografts in nude mice to IR or cisplatin treatment. This is the first report to show that the Chk1 inhibitor Gö6976 sensitizes NPC cells to treatment using in vitro and in vivo models.