Cancer stem cells: a new framework for the design of tumor therapies

The Natural Product Secoemestrin C Inhibits Colorectal Cancer Stem Cells via p38-S100A8 Feed-Forward Regulatory Loop

Cancer stem cells (CSCs) are closely associated with tumor initiation, metastasis, chemoresistance, and recurrence, which represent some of the primary obstacles to cancer treatment. Targeting CSCs has become an important therapeutic approach to cancer care. Secoemestrin C (Sec C) is a natural compound with strong anti-tumor activity and low toxicity. Here, we report that Sec C effectively inhibited colorectal CSCs and non-CSCs concurrently, mainly by inhibiting proliferation, self-renewal, metastasis, and drug resistance. Mechanistically, RNA-seq analysis showed that the pro-inflammation pathway of the IL17 axis was enriched, and its effector S100A8 was dramatically decreased in Sec C-treated cells, whose roles in the stemness of CSCs have not been fully clarified. We found that the overexpression of S100A8 hindered the anti-CSCs effect of Sec C, and S100A8 deficiency attenuated the stemness traits of CSCs to enhance the Sec C killing activity on them. Meanwhile, the p38 signal pathway, belonging to the IL17 downstream axis, can also mediate CSCs and counter with Sec C. Notably, we found that S100A8 upregulation increased the p38 protein level, and p38, in turn, promoted S100A8 expression. This indicated that p38 may have a mutual feedback loop with S100A8. Our study discovered that Sec C was a powerful anti-colorectal CSC agent, and that the positive feedback loop of p38-S100A8 mediated Sec C activity. This showed that Sec C could act as a promising clinical candidate in colorectal cancer treatment, and S100A8 could be a prospective drug target.

Identification of prognostic stemness biomarkers in colon adenocarcinoma drug resistance

BACKGROUND

Colon adenocarcinoma (COAD) is one of the leading causes of death worldwide. Cancer stem cells (CSCs) are vital for COAD chemoresistance and recurrence, however little is known about stem cell-related biomarkers in drug resistance and COAD prognosis prediction.

METHODS

To uncover the roles of CSC in COAD tumorigenesis, chemoresistance, and prognosis, we retrieved COAD patients' RNAseq data from TCGA (The Cancer Genome Atlas). We further performed analysis of differentially expressed genes (DEGs) and mRNA expression-based stemness index (mRNAsi) to identify stemness-related COAD biomarkers. We then evaluated the roles of mRNAsi in tumorigenesis, clinical-stage, overall survival (OS), and chemoresistance. Afterward, we used identified prognostic stemness-related genes (PSRGs) to construct a prediction model. After constructing the prediction model, we used elastic Net regression and area under the curve (AUC) to explore the prediction value of PSRGs based on risk scores and the receiver operator characteristic (ROC) curve. To elucidate the underlying interconnected systems, we examined relationships between the levels of TFs, PSRGs, and 50 cancer hallmarks by a Pearson correlation analysis.

RESULTS

Twelve thousand one hundred eight DEGs were identified by comparing 456 primary COADs and 41 normal solid tissue samples. Furthermore, we identified 4351 clinical stage-related DEGs, 16,516 stemness-associated DEGs, and 54 chemoresistance-related DEGs from cancer stages: mRNAsi, and COAD chemoresistance. Compared to normal tissue samples, mRNAsi in COAD patients were marked on an elevation and involved in prognosis (p = 0.027), stemness-related DEGs based on chemoresistance (OR = 3.28, p ≤ 0.001) and AJCC clinical stage relating (OR = 4.02, p ≤ 0.001) to COAD patients. The prediction model of prognosis were constructed using the 6 PSRGs with high accuracy (AUC: 0.659). The model identified universal correlation between NRIP2 and FDFT1 (key PRSGs), and some cancer related transcription factors (TFs) and trademarks of cancer gene were in the regulatory network.

CONCLUSION

We found that mRNAsi is a reliable predictive biomarker of tumorigenesis and COAD prognosis. Our established prediction model of COAD chemoresistance, which includes the six PSRGs, is effective, as the model provides promising therapeutic targets in the COAD.

DNA binding ability and cytotoxicity, cell cycle arrest and apoptosis inducing properties of a benzochromene derivative against K562 human leukemia cells

Chromene and its derivatives are generally spread in nature. Heterocylic-based compounds like chromenes have displayed pharmacological activities. Chromene derivatives are critical due to some biological features such as anticancer activity. CML, chronic myelogenous leukemia, is a fatal malignancy determined by resistance to apoptosis and contains the Philadelphia chromosome. Induction of apoptosis is one of the main approaches in cancer therapy. In this research, benzochromene derivative, 2-amino-4-(4-methoxy phenyl)-4H-benzochromene-3-carbonitrile (4-MC) was tested for cytotoxic and apoptotic induction activities in the human leukemic K562 cell line. The MTT growth inhibition assay was used to determine the cellular growth and survival. Moreover, the binding attribute of 4-MC with double helix DNA was assessed by some spectroscopic and viscosity measurement, and also for docking analysis. 4-MC exhibited good cytotoxicity on K562 cell line and the IC₅₀ value was calculated to be 30 µM. Furthermore, the mechanisms of apoptosis induction were determined morphologically by fluorescence dual staining with acridine orange and ethidium bromide and cell cycle analysis was based on DNA content, as well as the presence of phosphatidyl serine on the outside of the cells by the flow cytometric method. The results showed that 4-MC had potent cytotoxic activity via sub-G1 cell cycle arrest and induction of apoptosis. The experimental and simulation studies reported that 4-MC binds to ctDNA through groove binding mode with the binding constant (K_b) of 2.5 × 10³ M^-1. These data represent a considerable anticancer potential of 4-MC and could be suggested for further pharmacological studies.

Targeting Tumorigenicity of Breast Cancer Stem Cells Using SAHA/Wnt-b Catenin Antagonist Loaded Onto Protein Corona of Gold Nanoparticles

BACKGROUND

Among various theories for the origin of cancer, the "stemness phenotype model" suggests a dynamic feature for tumor cells in which non-cancer stem cells (non-CSCs) can inter-convert to CSCs. Differentiation with histone-deacetylase inhibitor, vorinostat (SAHA), can induce stem cells to differentiate as well as enforces non-CSCs to reprogram to CSCs. To avoid this undesirable effect, one can block the Wnt-βcatenin pathway. Thus, a dual delivery system of SAHA and a Wnt-βcatenin blocker will be beneficial in the induction of differentiation of CSCs. Protein corona (PC) formation in nanoparticle has a biologic milieu, and despite all problematic properties, it can be employed as a medium for dual loading of the drugs.

MATERIALS AND METHODS

We prepared sphere gold nanoparticles (GNPs) with human plasma protein corona loaded with SAHA as differentiating agent and PKF118-310 (PKF) as a Wnt-βcatenin antagonist. The MCF7 breast cancer stem cells were treated with NPs and the viability and differentiation were evaluated by Western blotting and sphere formation assay.

RESULTS

We found that both drugs loaded onto corona-capped GNPs had significant cytotoxicity in comparison to bare GNP-corona. Data demonstrated an increase in stem cell population and upregulation of mesenchymal marker, Snail by SAHA-loaded GNPs treatment; however, the combination of PKF loaded GNPs along with SAHA-loaded GNPs resulted in a reduction of stem cell populations and Snail marker. We have shown that in MCF7 and its CSCs simultaneous treatment with SAHA and PKF118-310 induced differentiation and inhibition of Snail induction.

CONCLUSION

Our study reveals the PC-coated GNPs as a biocompatible career for both hydrophilic (PKF) and hydrophobic (SAHA) agents which can decrease breast cancer stem cell populations along with reduced stemness state regression.

Differential mechanisms of autophagy in cancer stem cells: Emphasizing gastrointestinal cancers

Gastrointestinal (GI) cancers are one of the most common forms of malignancies and still are the most important cause of cancer-related mortality worldwide. Autophagy is a conserved catabolic pathway involving lysosomal degradation and recycling of whole cellular components, which is essential for cellular homeostasis. For instance, it acts as a pivotal intracellular quality control and repair mechanism but also implicated in cell reformation during cell differentiation and development. Indeed, GI cancer stem cells (CSCs) are thought to be responsible for tumour initiation, traditional therapies resistance, metastasis and tumour recurrence. Molecular mechanisms of autophagy in normal vs CSCs gain great interest worldwide. Here, we shed light on the role of autophagy in normal stem cells differentiation for embryonic progression and its role in maintaining the activity and self-renewal capacity of CSCs which offer novel viewpoints on promising cancer therapeutic strategies based on the differential roles of autophagy in CSCs.

Gene silencing of HIF-2α disrupts glioblastoma stem cell phenotype

Aim: Improved treatment strategies are desperately needed for eradicating cancer stem cells (CSCs), which drive malignancy and recurrence in glioblastoma multiforme. Hypoxic regions within the tumor microenvironment help maintain and promote the proliferation of CSCs. Here, we explored the effects of silencing hypoxia inducible factor-2α (HIF-2α) because of its specificity for CSCs within the hypoxic environment.

Methods: Cancer stem cell neurospheres were formed by enriching from both the glioblastoma cell line U87 and from brain tumor stem cells isolated directly from human brain tumors. Silencing of human HIF-2α was performed using both commercial and in-house transfection of a validated short interfering RNA, with all results compared to an established non-silencing control short interfering RNA. Silencing of HIF-2α was established by Western blotting, and phenotypic effects were assayed by cell migration assays, cell viability measurements, and immunofluorescence staining of differentiation markers.

Results: Transfection with either our previously reported pH-sensitive, cationic amphiphilic macromolecule-based delivery system or Lipofectamine was similarly effective in silencing HIF-2α. The chemotherapeutic resistance and neurosphere formation were reduced when HIF-2α was silenced. Migratory capacities in the presence of macrophage conditioned media were modulated. HIF-2α silencing was complementary to temozolomide treatment in producing phenotypic rather than cytotoxic effects.

Conclusion: HIF-2α silencing under hypoxia inhibited CSC phenotypes while promoting differentiated cell phenotypes and is complementary to existing DNA alkylating treatments in inhibiting glioma CSC activity.

Expression of ALDH1A1 and CD133 is associated with the prognosis and effect of different chemotherapeutic regimens in gastric cancer

Gastric cancer (GC) is one of the most common malignant tumors worldwide. Previous studies have reported that aldehyde dehydrogenase-1A1 (ALDH1A1) and cluster of differentiation (CD)-133 are considered to be cancer stem cell markers in GCs. The present study immunohistochemically examined the distribution and expression of two tumor stem cell markers, CD133 and ALDH1A1, in both primary tumors and para-tumor tissues. In 91 cases with stage III, 57 (62%) were positive for ALDH1A1 and 60 (66%) were positive for CD133. ALDH1A1 was detected in para-tumors and cancerous tissues of the stomach, and the immunoreactivity of the tumors was stronger than that in para-tumor tissues. CD133 was only detected in tumors. The expression of ALDH1A1 was significantly associated with advanced T/N stage (T stage, P=0.012; N stage, P=0.023) and poor differentiation (P=0.020), while CD133 was associated with advanced T stage (P=0.007). Univariate and multivariate Cox proportional hazards analysis revealed that tumor stage, CD133 expression, vascular invasion and sex were independent predictors of disease-free survival (DFS) time, and tumor size, vascular invasion and sex were independent predictors of overall survival (OS) time in patients with GC. Patients with CD133⁺ GC had poorer DFS (P=0.042), while ALDH1A1⁺ GC was not associated with poorer DFS. In regard to chemotherapy, improvements in survival were not observed after the addition of taxane compared with two-drug therapy. However, the subgroup analysis indicated that in the ALDH1A1⁻ subgroup, and CD133⁺ and ALDH1A1⁻ subgroups, an increased OS was observed in two-drug therapy (P=0.043). The results of the present study indicate that ALDH1A1 and CD133 may play an important role in tumor invasion, metastasis and prognosis, and ALDH1A1⁻ expression does not benefit the taxane-based triple chemotherapeutic regimen in patients with GC.

The molecular markers of cancer stem cells in head and neck tumors

Head and neck cancer (HNC) is the six most common malignancy worldwide leading to more than 350,000 deaths annually. Despite recent advances in treatment modalities for these patients, there has been only a slight improvement of prognosis. As cancer stem cells (CSCs) have been implicated in tumor cell survival, progression, and response to therapy, the identification of this tumor subpopulation would have important therapeutic and prognostic implications. In this structured appraisal of the literature, Embase, PubMed, and Ovid were searched for publications that investigated CSC markers of HNC in humans. The search was conducted under the PRISMA guidelines with clear inclusion and exclusion criteria for articles published in the last two decades. The review process resulted in the identification of some key CSC-associated molecules such as CD44, ALDH1, CD133, Oct3/4, Nanog, and Sox2, although a single common CSC sorting marker could not be found. These biomarkers were identified in a range of HNCs but the most common one was squamous cell carcinoma (SCC), predominantly oral SCC. Patient cohorts were of variable size (3-195 individuals) and the most common technique used for detection was immunohistochemistry. Some of the molecules were associated with poor prognosis and may be able to inform the choice of appropriate treatment for these patients.

The Evolving Landscape of Cancer Stem Cells and Ways to Overcome Cancer Heterogeneity

Cancer stem cells (CSCs) with therapeutic resistance and plasticity can be found in various types of tumors and are recognized as attractive targets for treatments. As CSCs are derived from tissue stem or progenitor cells, and/or dedifferentiated mature cells, their signal transduction pathways are critical in the regulation of CSCs; chronic inflammation causes the accumulation of genetic mutations and aberrant epigenetic changes in these cells, potentially leading to the production of CSCs. However, the nature of CSCs appears to be stronger than the treatments of the past. To improve the treatments targeting CSCs, it is important to inhibit several molecules on the signaling cascades in CSCs simultaneously, and to overcome cancer heterogeneity caused by the plasticity. To select suitable target molecules for CSCs, we have to explore the landscape of CSCs from the perspective of cancer stemness and signaling systems, based on the curated databases of cancer-related genes. We have been studying the integration of a broad range of knowledge and experiences from cancer biology, and also from other interdisciplinary basic sciences. In this review, we have introduced the concept of developing novel strategies targeting CSCs.

Stroma-derived IL-6, G-CSF and Activin-A mediated dedifferentiation of lung carcinoma cells into cancer stem cells

Cancer stem cells (CSCs) are a small population of resistant cells inhabiting the tumors. Although comprising only nearly 3% of the tumor mass, these cells were demonstrated to orchestrate tumorigenesis and differentiation, underlie tumors’ heterogeneity and mediate therapy resistance and tumor relapse. Here we show that CSCs may be formed by dedifferentiation of terminally differentiated tumor cells under stress conditions. Using a elegant co-culture cellular system, we were able to prove that nutrients and oxygen deprivation activated non-malignant stromal fibroblasts, which in turn established with tumor cells a paracrine loop mediated by Interleukine-6 (IL-6), Activin-A and Granulocyte colony-stimulating factor (G-CSF), that drove subsequent tumor formation and cellular dedifferentiation. However, by scavenging these cytokines from the media and/or blocking exosomes’ mediated communication it was possible to abrogate dedifferentiation thus turning these mechanisms into potential therapeutic targets against cancer progression.

Cancer Stem Cell Metabolism and Potential Therapeutic Targets

Malignant tumors contain heterogeneous populations of cells in various states of proliferation and differentiation. The presence of cancer stem or initiating cells is a well-established concept wherein quiescent and poorly differentiated cells within a tumor mass contribute to drug resistance, and under permissive conditions, are responsible for tumor recurrence and metastasis. A number of studies have identified molecular markers that are characteristic of tissue-specific cancer stem cells (CSCs). Isolation of CSCs has enabled studies on the metabolic status of CSCs. As metabolic plasticity is a hallmark of cancer cell adaptation, the intricacies of CSC metabolism and their phenotypic behavior are critical areas of research. Unlike normal stem cells, which rely heavily on oxidative phosphorylation (OXPHOS) as their primary source of energy, or cancer cells, which are primarily glycolytic, CSCs demonstrate a unique metabolic flexibility. CSCs can switch between OXPHOS and glycolysis in the presence of oxygen to maintain homeostasis and, thereby, promote tumor growth. Here, we review key factors that impact CSC metabolic phenotype including heterogeneity of CSCs across different histologic tumor types, tissue-specific variations, tumor microenvironment, and CSC niche. Furthermore, we discuss how targeting key players of glycolytic and mitochondrial pathways has shown promising results in cancer eradication and attenuation of disease recurrence in preclinical models. In addition, we highlight studies on other potential therapeutic targets including complex interactions within the microenvironment and cellular communications in the CSC niche to interfere with CSC growth, resistance, and metastasis.

Antipsychotic dopamine receptor antagonists, cancer, and cancer stem cells

Cancer is one of the deadliest diseases in the world. Despite extensive studies, treating metastatic cancers remains challenging. Years of research have linked a rare set of cells known as cancer stem cells (CSCs) to drug resistance, leading to the suggestion that eradication of CSCs might be an effective therapeutic strategy. However, few drug candidates are active against CSCs. New drug discovery is often a lengthy process. Drug screening has been advantageous in identifying drug candidates. Current understanding of cancer biology has revealed various clues to target cancer from different points of view. Many studies have found dopamine receptors (DRs) in various cancers. Therefore, DR antagonists have attracted a lot of attention in cancer research. Recently, a group of antipsychotic DR antagonists has been demonstrated to possess remarkable abilities to restrain and sensitize CSCs to existing chemotherapeutics by a process called differentiation approach. In this review, we will describe current aspects of CSC-targeting therapeutics, antipsychotic DR antagonists, and their extraordinary abilities to fight cancer.

MicroRNA-142-5p induces cancer stem cell-like properties of cutaneous squamous cell carcinoma via inhibiting PTEN

Cutaneous squamous cell carcinoma (cSCC) is a malignancy of keratinocyte-derived skin tumor, which is regarded as the second most common skin cancer worldwide. Accumulating evidence has established that microRNAs (miRNAs) can play a critical role in tumor initiation, progression, and metastasis including cSCC. Abnormal expression of hsa-miR-142-5p has been elaborated in various tumors. Nevertheless, its expression and function in the development of cSCC remain unclear. In our study, we found that the expression of hsa-miR-142-5p in cSCC cells were greatly overexpressed compared to human benign epidermal keratinocyte cells. Moreover, inhibited hsa-miR-142-5p can repress cSCC cell growth and induce apoptosis while upregulated hsa-miR-142-5p exhibited a reverse phenomenon. Recently, cancer stem cells (CSCs) which possess the ability of self-renewal and proliferation and are able to produce cancer cells have been widely reported. However, the correlation between hsa-miR-142-5p and CSCs in cSCC is still unknown. Interestingly, we observed that overexpressing hsa-miR-142-5p can induce CSC-like properties in cSCC via activating Wnt signaling. In addition, the luciferase reporter assay data and bioinformatics analysis demonstrated that hsa-miR-142-5p can target the 3'UTR of PTEN mRNA. Taken these together, we draw a conclusion that hsa-miR-142-5p can trigger cancer stem cell-like properties of cSCC through inhibition of PTEN. Our findings may provide hsa-miR-142-5p as a new therapeutic target for cSCC.

Induced-Decay of Glycine Decarboxylase Transcripts as an Anticancer Therapeutic Strategy for Non-Small-Cell Lung Carcinoma

Self-renewing tumor-initiating cells (TICs) are thought to be responsible for tumor recurrence and chemo-resistance. Glycine decarboxylase, encoded by the GLDC gene, is reported to be overexpressed in TIC-enriched primary non-small-cell lung carcinoma (NSCLC). GLDC is a component of the mitochondrial glycine cleavage system, and its high expression is required for growth and tumorigenic capacity. Currently, there are no therapeutic agents against GLDC. As a therapeutic strategy, we have designed and tested splicing-modulating steric hindrance antisense oligonucleotides (shAONs) that efficiently induce exon skipping (half maximal inhibitory concentration [IC₅₀] at 3.5–7 nM), disrupt the open reading frame (ORF) of GLDC transcript (predisposing it for nonsense-mediated decay), halt cell proliferation, and prevent colony formation in both A549 cells and TIC-enriched NSCLC tumor sphere cells (TS32). One candidate shAON causes 60% inhibition of tumor growth in mice transplanted with TS32. Thus, our shAONs candidates can effectively inhibit the expression of NSCLC-associated metabolic enzyme GLDC and may have promising therapeutic implications.

Noncanonical GLI1 signaling promotes stemness features and in vivo growth in lung adenocarcinoma

Aberrant Hedgehog/GLI signaling has been implicated in a diverse spectrum of human cancers, but its role in lung adenocarcinoma (LAC) is still under debate. We show that the downstream effector of the Hedgehog pathway, GLI1, is expressed in 76% of LACs, but in roughly half of these tumors, the canonical pathway activator, Smoothened, is expressed at low levels, possibly owing to epigenetic silencing. In LAC cells including the cancer stem cell compartment, we show that GLI1 is activated noncanonically by MAPK/ERK signaling. Different mechanisms can trigger the MAPK/ERK/GLI1 cascade including KRAS mutation and stimulation of NRP2 by VEGF produced by the cancer cells themselves in an autocrine loop or by stromal cells as paracrine cross talk. Suppression of GLI1, by silencing or drug-mediated, inhibits LAC cells proliferation, attenuates their stemness and increases their susceptibility to apoptosis in vitro and in vivo. These findings provide insight into the growth of LACs and point to GLI1 as a downstream effector for oncogenic pathways. Thus, strategies involving direct inhibition of GLI1 may be useful in the treatment of LACs.

Cancer stem cells in human gastrointestinal cancer

Cancer stem cells (CSCs) are thought to be responsible for tumor initiation, drug and radiation resistance, invasive growth, metastasis, and tumor relapse, which are the main causes of cancer-related deaths. Gastrointestinal cancers are the most common malignancies and still the most frequent cause of cancer-related mortality worldwide. Because gastrointestinal CSCs are also thought to be resistant to conventional therapies, an effective and novel cancer treatment is imperative. The first reported CSCs in a gastrointestinal tumor were found in colorectal cancer in 2007. Subsequently, CSCs were reported in other gastrointestinal cancers, such as esophagus, stomach, liver, and pancreas. Specific phenotypes could be used to distinguish CSCs from non-CSCs. For example, gastrointestinal CSCs express unique surface markers, exist in a side-population fraction, show high aldehyde dehydrogenase-1 activity, form tumorspheres when cultured in non-adherent conditions, and demonstrate high tumorigenic potential in immunocompromised mice. The signal transduction pathways in gastrointestinal CSCs are similar to those involved in normal embryonic development. Moreover, CSCs are modified by the aberrant expression of several microRNAs. Thus, it is very difficult to target gastrointestinal CSCs. This review focuses on the current research on gastrointestinal CSCs and future strategies to abolish the gastrointestinal CSC phenotype.

[Expressions of OCT4, Notch1 and DLL4 and their clinical implications in epithelial ovarian cancer]

OBJECTIVE

To investigate the correlations among OCT4, Notch1 and DLL4 and their association with the clinicopathological features of patients with epithelial ovarian cancer (EOC).

METHODS

A total of 207 specimens of EOC and 65 specimens of benign ovarian epithelial tumor tissues were examined for expressions of OCT4, Notch1 and DLL4 proteins using immunohistochemistry.

RESULTS

The positivity rates of OCT4, Notch1 and DLL4 in EOC tissues were 60.0%, 61.8% and 60.9%, respectively, significantly higher than the rates in benign epithelial tumor tissues (9.2%, 6.2%, and 0, respectively; P<0.05). The expressions of OCT4, Notch1 and DLL4 in EOC were significantly correlated with tumor differentiation, FIGO stage, and lymph node metastasis (P<0.05). DLL4 was positively correlated with OCT4 and Notch1 expressions (r=0.758 and 0.704, respectively, P<0.001), and the latter two were also positively correlated (r=0.645, P<0.001). Overexpressions of OCT4, Notch1 and DLL4 were associated with a poor prognosis, and the survival rate was significantly lower in patients positive for OCT4, Notch1, and DLL4 than in the negative patients (P<0.05). FIGO stage and expressions of OCT4 and DLL4 were independent prognostic factors of EOC (P<0.05).

CONCLUSION

The expressions of OCT4, Notch1 and DLL4 are correlated with the differentiation, lymph node metastasis, clinical stage and prognosis of EOC. Combined detection of the 3 proteins has an important value in predicting the progression and prognosis of EOC.

Blockade of Hedgehog Signaling Synergistically Increases Sensitivity to Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitors in Non-Small-Cell Lung Cancer Cell Lines

Aberrant activation of the hedgehog (Hh) signaling pathway has been implicated in the epithelial-to-mesenchymal transition (EMT) and cancer stem-like cell (CSC) maintenance; both processes can result in tumor progression and treatment resistance in several types of human cancer. Hh cooperates with the epidermal growth factor receptor (EGFR) signaling pathway in embryogenesis. We found that the Hh signaling pathway was silenced in EGFR-TKI-sensitive non-small-cell lung cancer (NSCLC) cells, while it was inappropriately activated in EGFR-TKI-resistant NSCLC cells, accompanied by EMT induction and ABCG2 overexpression. Upregulation of Hh signaling through extrinsic SHH exposure downregulated E-cadherin expression and elevated Snail and ABCG2 expression, resulting in gefitinib tolerance (P < 0.001) in EGFR-TKI-sensitive cells. Blockade of the Hh signaling pathway using the SMO antagonist SANT-1 restored E-cadherin expression and downregulate Snail and ABCG2 in EGFR-TKI-resistant cells. A combination of SANT-1 and gefitinib markedly inhibited tumorigenesis and proliferation in EGFR-TKI-resistant cells (P < 0.001). These findings indicate that hyperactivity of Hh signaling resulted in EGFR-TKI resistance, by EMT introduction and ABCG2 upregulation, and blockade of Hh signaling synergistically increased sensitivity to EGFR-TKIs in primary and secondary resistant NSCLC cells. E-cadherin expression may be a potential biomarker of the suitability of the combined application of an Hh inhibitor and EGFR-TKIs in EGFR-TKI-resistant NSCLCs.

[Cancer stem cell markers and their prognostic value]

Based on an analysis of a large number of sources of literature, the paper gives general information on the markers for cancer stem cells (CSCs), which allow the detection of this rare cell subpopulation, on the possibilities of estimating their immunohistochemical or immunofluorescent expression in tumors, and on the prognostic and predictive values of these molecules. For their detection, investigators generally use definite molecules, the so-called markers of CSCs, among which there are CD44, CD133, CD24, aldehyde dehydrogenase, and others. The expression of these molecules in the tumor tissue obtained from patients affects survival rates and permits the prediction of a response to therapy. A better insight into the immunophenotype of CSCs, the role of CSC markers in retaining the special properties of this call population, and the clinical significance of the expression of CSC markers will be able to elaborate new approaches to therapy for malignancies.

MB3W1 is an orthotopic xenograft model for anaplastic medulloblastoma displaying cancer stem cell- and Group 3-properties

Background

Medulloblastoma is the most common malignant brain tumor in children and can be divided in different molecular subgroups. Patients whose tumor is classified as a Group 3 tumor have a dismal prognosis. However only very few tumor models are available for this subgroup.

Methods

We established a robust orthotopic xenograft model with a cell line derived from the malignant pleural effusions of a child suffering from a Group 3 medulloblastoma.

Results

Besides classical characteristics of this tumor subgroup, the cells display cancer stem cell characteristics including neurosphere formation, multilineage differentiation, CD133/CD15 expression, high ALDH-activity and high tumorigenicity in immunocompromised mice with xenografts exactly recapitulating the original tumor architecture.

Conclusions

This model using unmanipulated, human medulloblastoma cells will enable translational research, specifically focused on Group 3 medulloblastoma.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2170-z) contains supplementary material, which is available to authorized users.

Design, synthesis and evaluation of cytotoxic properties of bisamino glucosylated antitumor ether lipids against cancer cells and cancer stem cells

Glycosylated antitumor ether lipids (GAELs) are a class of amphiphilic antitumor agents that kill cancer cells by a non-apoptotic pathway.

Implications of Oxygen Homeostasis for Tumor Biology and Treatment

Tumors serve as a prototype system to study the role of the hypoxic microenvironment and gain insight in the regulation oxygen homeostasis. A series of biochemical and cell biological studies have significantly extended our knowledge of how tumor cells activate key regulatory mechanisms of oxygen homeostasis not only to adapt to the hostile tumor microenvironment but also to acquire a more aggressive tumor phenotype. Reduced oxygen levels and tumor-specific genetic alterations synergistically drive tumor progression by activating a key transcriptional system, the hypoxia inducible factors (HIFs). HIFs trigger a set of adaptive responses commonly associated with tumor malignancy including tumor angiogenesis, a shift in metabolism, proliferation, invasion, and metastasis. We and others could demonstrate that cancer stem cells are controlled by HIFs within a hypoxic niche, establishing an intriguing link between the well known function of hypoxia in tumor growth and stem cell biology. Additionally, HIF activation potentially conveys resistance to current tumor therapies including the evasive resistance phenotype observed after anti-angiogenic treatment. Together, these findings provide strong evidence that activation of the HIF system is a decisive step in cancer progression that critically shapes therapy response and clinical outcome. Recent insight into the precise mechanisms of oxygen sensing and signalling has offered new promising and potentially selective strategies to counteract this crucial pathway.

STAT3 signaling is activated preferentially in tumor-initiating cells in claudin-low models of human breast cancer

In breast cancer, a subset of tumor-initiating cells (TIC) or "cancer stem cells" are thought to be responsible for tumor maintenance, treatment resistance, and disease recurrence. While current breast cancer stem cell markers (e.g., CD44(high) /CD24(low/neg) , ALDH positive) have allowed enrichment for such cells, they are not universally expressed and may actually identify distinct TIC subpopulations in the same tumor. Thus, additional markers of functional stem cells are needed. The STAT3 pathway is a critical regulator of the function of normal stem cells, and evidence is accumulating for its important role in breast cancer stem cells. However, due to the lack of a method for separating live cells based on their level of STAT3 activity, it remains unknown whether STAT3 functions in the cancer stem cells themselves, or in surrounding niche cells, or in both. To approach this question, we constructed a series of lentiviral fluorescent (enhanced green fluorescent protein, EGFP) reporters that enabled flow cytometric enrichment of cells differing in STAT3-mediated transcriptional activity, as well as in vivo/in situ localization of STAT3 responsive cells. Using in vivo claudin-low cell line xenograft models of human breast cancer, we found that STAT3 signaling reporter activity (EGFP(+) ) is associated with a subpopulation of cancer cells enriched for mammosphere-forming efficiency, as well as TIC function in limiting dilution transplantation assays compared to negative or unsorted populations. Our results support STAT3 signaling activity as another functional marker for human breast cancer stem cells thus making it an attractive therapeutic target for stem-cell-directed therapy in some breast cancer subtypes.

Translational potential of cancer stem cells: A review of the detection of cancer stem cells and their roles in cancer recurrence and cancer treatment

Cancer stem cells (CSCs) are a subpopulation of cancer cells with many clinical implications in most cancer types. One important clinical implication of CSCs is their role in cancer metastases, as reflected by their ability to initiate and drive micro and macro-metastases. The other important contributing factor for CSCs in cancer management is their function in causing treatment resistance and recurrence in cancer via their activation of different signalling pathways such as Notch, Wnt/β-catenin, TGF-β, Hedgehog, PI3K/Akt/mTOR and JAK/STAT pathways. Thus, many different therapeutic approaches are being tested for prevention and treatment of cancer recurrence. These may include treatment strategies targeting altered genetic signalling pathways by blocking specific cell surface molecules, altering the cancer microenvironments that nurture cancer stem cells, inducing differentiation of CSCs, immunotherapy based on CSCs associated antigens, exploiting metabolites to kill CSCs, and designing small interfering RNA/DNA molecules that especially target CSCs. Because of the huge potential of these approaches to improve cancer management, it is important to identify and isolate cancer stem cells for precise study and application of prior the research on their role in cancer. Commonly used methodologies for detection and isolation of CSCs include functional, image-based, molecular, cytological sorting and filtration approaches, the use of different surface markers and xenotransplantation. Overall, given their significance in cancer biology, refining the isolation and targeting of CSCs will play an important role in future management of cancer.

Cell surface markers of cancer stem cells: diagnostic macromolecules and targets for drug delivery

The recognition that the persistence of cancer stem cells (CSCs) in patients following chemotherapy can result in disease relapse underscores the necessity to develop therapeutics against those cells. CSCs display a unique repertoire of cell surface macromolecules, which have proven essential for their characterization and isolation. Additionally, CSC-specific cell surface macromolecules or markers provide targets for the development of specific agents to destroy them. In this review, we compiled those cell surface molecules that have been validated as CSC markers for many common blood and solid tumors. We describe the unique chemical and structural features of the most common cell surface markers, as well as recent efforts to deliver chemotherapeutic agents into CSCs by targeting those macromolecules.

Synthetic Glycosylated Ether Glycerolipids as Anticancer Agents

Glycosylated antitumor ether lipids (GAELs) are a class of synthetic antitumor ether lipids (AELs) with a sugar moiety in place of the phosphocholine found in the prototypical AEL, edelfosine. This chapter reviews the development of GAELs as antitumor agents. Studies on structure–activity relationships, mechanism of induction of cell death, metabolism, selectivity against cancer cells, toxicity, hemolysis and thrombogenic effects are discussed. The requirements for significant cytotoxic activity include a glycerol moiety, a cationic sugar other than mannose and an O- or C-glycosidic bond with either α- or β-configuration. Compounds with S- and N-glycosidic linkages are not very active. The most active GAEL to date, 1-O-hexadecyl-2-O-methyl-3-O-(2′-amino-2′-deoxy-α-d-galactopyranosyl)-sn-glycerol, displays greater in vitro activity than edelfosine, the AEL “gold standard”. The unique properties of GAELs as antitumor agents include their apoptotic-independent mechanism of inducing cell death and the ability to kill cancer stem cells. These characteristics of GAELs offer the potential for their development into chemotherapeutic agents to prevent the recurrence of tumors as well as for treatment against drug-resistant cancers.

Redox biology in normal cells and cancer: restoring function of the redox/Fyn/c-Cbl pathway in cancer cells offers new approaches to cancer treatment

This review discusses a unique discovery path starting with novel findings on redox regulation of precursor cell and signaling pathway function and identification of a new mechanism by which relatively small changes in redox status can control entire signaling networks that regulate self-renewal, differentiation, and survival. The pathway central to this work, the redox/Fyn/c-Cbl (RFC) pathway, converts small increases in oxidative status to pan-activation of the c-Cbl ubiquitin ligase, which controls multiple receptors and other proteins of central importance in precursor cell and cancer cell function. Integration of work on the RFC pathway with attempts to understand how treatment with systemic chemotherapy causes neurological problems led to the discovery that glioblastomas (GBMs) and basal-like breast cancers (BLBCs) inhibit c-Cbl function through altered utilization of the cytoskeletal regulators Cool-1/βpix and Cdc42, respectively. Inhibition of these proteins to restore normal c-Cbl function suppresses cancer cell division, increases sensitivity to chemotherapy, disrupts tumor-initiating cell (TIC) activity in GBMs and BLBCs, controls multiple critical TIC regulators, and also allows targeting of non-TICs. Moreover, these manipulations do not increase chemosensitivity or suppress division of nontransformed cells. Restoration of normal c-Cbl function also allows more effective harnessing of estrogen receptor-α (ERα)-independent activities of tamoxifen to activate the RFC pathway and target ERα-negative cancer cells. Our work thus provides a discovery strategy that reveals mechanisms and therapeutic targets that cannot be deduced by standard genetics analyses, which fail to reveal the metabolic information, isoform shifts, protein activation, protein complexes, and protein degradation critical to our discoveries.

Isolation and assessment of the in vitro anti-tumor activity of smenothiazole A and B, chlorinated thiazole-containing peptide/polyketides from the Caribbean sponge, Smenospongia aurea

The study of the secondary metabolites contained in the organic extract of Caribbean sponge Smenospongia aurea led to the isolation of smenothiazole A (3) and B (4), hybrid peptide/polyketide compounds. Assays performed using four solid tumor cell lines showed that smenothiazoles exert a potent cytotoxic activity at nanomolar levels, with selectivity over ovarian cancer cells and a pro-apoptotic mechanism.

Isolation and culture of primary glioblastoma cells from human tumor specimens

Cultured tumor cells are a central tool in cancer research and have provided fundamental insights in tumor biology. Recent evidence, however, indicates that classically established cell lines from different tumors, including glioblastoma, do not fully reflect the genotypes and phenotypes of the respective primary tumors. By contrast, primary cells, isolated from human tumor samples and maintained in serum-free spheroid cultures at low passage under defined growth factor conditions, reproduce key aspects of tumor cell physiology much more faithfully. Among the tumor cell characteristics that are better represented in primary glioblastoma cell cultures is the self-renewal and differentiation potential of the tumor cells. Indeed, a large body of evidence from the past decade indicates that glioblastomas and other tumors are composed of a hierarchy of heterogeneous types of cells, which are generated and maintained by cells that share characteristics of stem cells. This cancer stem cell/tumor initiating cell population is optimally preserved and maintained in primary glioblastoma cultures. Here, we describe a method for the isolation and culture of primary tumor cells from human glioblastomas in serum-free conditions, which allows the routine generation and proper maintenance of tumor cells as spheroid cultures. Such primary tumor cultures can serve as a model of choice for the study of the mechanisms behind key aspects of glioblastoma biology, including tumorigenicity, stem cell hierarchy, invasion, and therapeutic resistance.

The cancer stem cell hypothesis: a guide to potential molecular targets

Common cancer theories hold that tumor is an uncontrolled somatic cell proliferation caused by the progressive addition of random mutations in critical genes that control cell growth. Nevertheless, various contradictions related to the mutation theory have been reported previously. These events may be elucidated by the persistence of residual tumor cells, called Cancer Stem Cells (CSCs) responsible for tumorigenesis, tumor maintenance, tumor spread, and tumor relapse. Herein, we summarize the current understanding of CSCs, with a focus on the possibility to identify specific markers of CSCs, and discuss the clinical application of targeting CSCs for cancer treatment.

Cancer stem-like cells in Epstein-Barr virus-associated nasopharyngeal carcinoma

Although the Epstein-Barr virus (EBV) has spread to all populations in the world, EBV-associated nasopharyngeal carcinoma (NPC) is prevalent only in South China and Southeast Asia. The role of EBV in the malignant transformation of nasopharyngeal epithelium is the main focus of current researches. Radiotherapy and chemoradiotherapy have been successful in treating early stage NPC, but the recurrence rates remain high. Unfortunately, local relapse and metastasis are commonly unresponsive to conventional treatments. These recurrent and metastatic lesions are believed to arise from residual or surviving cells that have the properties of cancer stem cells. These cancer stem-like cells (CSCs) have the ability to self-renew, differentiate, and sustain propagation. They are also chemo-resistant and can form spheres in anchorage-independent environments. This review summarizes recent researches on the CSCs in EBV-associated NPC, including the findings regarding cell surface markers, stem cell-related transcription factors, and various signaling pathways. In particular, the review focuses on the roles of EBV latent genes [latent membrane protein 1 (LMP1) and latent membrane protein 2A (LMP2A)], cellular microRNAs, and adenosine triphosphate (ATP)-binding cassette chemodrug transporters in contributing to the properties of CSCs, including the epithelial-mesenchymal transition, stem-like transition, and chemo-resistance. Novel therapeutics that enhance the efficacy of radiotherapy and chemoradiotherapy and inhibitors that suppress the properties of CSCs are also discussed.

Cytotoxic properties of D-gluco-, D-galacto- and D-manno-configured 2-amino-2-deoxy-glycerolipids against epithelial cancer cell lines and BT-474 breast cancer stem cells

Glycosylated antitumor ether lipids (GAELs) 6 and 7 containing a α- or β-D-gluco-configured 2-amino-2-deoxy (2-NH2-Glc) sugar moiety linked to a glycerolipid aglycone kill cancer cell lines via a non-apoptotic mechanism that could be exploited to kill cancer stem cells. To test this hypothesis and develop novel potent GAEL analogs, we synthesized GAELS which contain D-galacto- and D-manno-configured 2-amino-2-deoxy sugar moieties (2-NH2-Gal or 2-NH2-Man) and investigated their cytotoxicity against human epithelial cancer cell lines and cancer stem cells derived from BT-474 breast cancer cells. Within the class of D-galacto-configured GAELs, we prepared both O- and S-glycosidic linkages as well as their corresponding α- and β-anomers and screened against breast (BT-474, JIMT-1 and BT-549), pancreas (MiaPaCa2) and prostate cancer (DU145, PC3) cancer cell lines. The α-anomeric 2-NH2-Gal-based lipid 1 was the most active of all the compounds tested with CC50 values of 4.4-8 μM and is the most active GAEL synthesized to date. The β-anomer 2 was 4->5-fold less active than 1. Replacement of the α-O-glycosidic by an α-S-glycosidic linkage resulted in a 2-4-fold reduction in activity, while the β-S-glycolipid 4 was inactive. In comparison, α-configured 2-NH2-Man-based glycerolipid 5 displayed very little activity with CC50 > 30 μM. The effect of the most active GAELs, 1, 6, or 7, on cancer stem cell viability revealed that all three inhibited the formation of tumorspheres from BT-474 cancer stem cell lines, caused the disintegration of preformed tumorspheres and resulted in total loss of cell viability of the cancer stem cells at concentrations of 20 μM. In contrast, the related antitumor ether lipid gold standard, edelfosine that is in clinical development was much less effective in preventing tumorsphere formation and affecting the viability of the cancer stem cells. Taken together our study demonstrates that α-GAEL anomers are more potent than their corresponding β-anomers and that the nature of the CHO moiety as well as the glycosidic bond significantly affects activity. The study also showed that GAELs are effective in killing CSCs while the apoptosis-inducing edelfosine is not.

Stemness in human thyroid cancers and derived cell lines: the role of asymmetrically dividing cancer stem cells resistant to chemotherapy

CONTEXT

Cancer stem cells (CSCs) have the ability to self-renew through symmetric and asymmetric cell division. CSCs may arise from mutations within an embryonic stem cell/progenitor cell population or via epithelial-mesenchymal transition (EMT), and recent advances in the study of thyroid stem cells have led to a growing recognition of the likely central importance of CSCs in thyroid tumorigenesis.

OBJECTIVE

The objectives of this study were to establish the presence of a stem cell population in human thyroid tumors and to identify, isolate, and characterize CSCs in thyroid cancer cell lines.

RESULTS

1) Human thyroid cancers (n = 10) and thyroid cancer cell lines (n = 6) contained a stem cell population as evidenced by pluripotent stem cell gene expression. 2) Pulse-chase experiments with thyroid cancer cells identified a label-retaining cell population, a primary characteristic of CSCs, which at mitosis divided their DNA both symmetrically and asymmetrically and included a population of cells expressing the progenitor marker, stage-specific embryonic antigen 1 (SSEA-1). 3) Cells positive for SSEA-1 expressed additional stem cell markers including Oct4, Sox2, and Nanog were confirmed as CSCs by their tumor-initiating properties in vivo, their resistance to chemotherapy, and their multipotent capability. 4) SSEA-1-positive cells showed enhanced vimentin expression and decreased E-cadherin expression, indicating their likely derivation via EMT.

CONCLUSIONS

Cellular diversity in thyroid cancer occurs through both symmetric and asymmetric cell division, and SSEA-1-positive cells are one form of CSCs that appear to have arisen via EMT and may be the source of malignant thyroid tumor formation. This would suggest that thyroid cancer CSCs were the result of thyroid cancer transformation rather than the source.

Therapy-induced enrichment of putative lung cancer stem-like cells

Tumour drug resistance is a major issue in the management of lung cancer patients as almost all lung tumours are either intrinsically resistant or quickly develop acquired resistance to chemotherapeutic drugs. Cancer drug resistance has recently been linked, at least in part, to the existence of cancer stem-like cells (CSLCs), a small sub-population of cells within the tumour that possess stem-like properties. CSLCs are often isolated by fluorescence activated cell sorting (FACS) according to the expression of certain stem-like cell membrane markers. Conflicting results regarding the specificity of particular stem cell surface markers for isolating CSLCs have, however, been recently reported. Therefore, alternative strategies enabling the identification and study of CSLCs should be considered, particularly in tumour types where appropriate stem cell markers are not well established and validated, like in lung cancer. In this article, we review data indicating therapy-selection as a valid approach for putative lung CSLCs enrichment. We believe that this strategy would be determinant for correctly assessing and characterising the sub-populations of CSLCs that are able to survive chemo or radiotherapy regimens and, at the same time, also have the ability to recapitulate and sustain tumour growth. Using therapy-induced enrichment of CSLCs may, therefore, prove to be an extremely useful method for studying CSLCs and provide new clues regarding potential therapeutic targets for their efficient elimination, which will undoubtedly play a decisive role in improving lung cancer patients' survival.

Sequential transformation of mesenchymal stem cells is associated with increased radiosensitivity and reduced DNA repair capacity

We used sequentially transformed mesenchymal stem cells to investigate how the events that lead to tumorigenicity influence the cellular response to radiation. Bone marrow derived SH2(+), SH4(+), Stro-1(+) mesenchymal stem cells (MSC) were transformed stepwise by retroviral transfection of hTERT, HPV-16 E6 and E7, SV40 small T antigen and oncogenic H-ras. Cells at three different stages of transformation were irradiated and compared using assays for cytotoxicity, apoptosis, DNA double-strand break (DSB) repair and checkpoint signaling. The effects of inhibition of cell cycle checkpoint signaling on radiosensitivity were investigated using RNA interference. During stepwise transformation, specifically after HPV-16 E6 and E7 transduction, MSCs became more sensitive to radiation. This was associated with increased residual DNA DSB at 24 h and increased apoptosis. Enhanced checkpoint signaling occurred during transformation and there was a differential effect of checkpoint targeting in cells at different stages; Chk1 knockdown enhanced radiosensitivity in all cells while Chk2 knockdown only affected non-transformed cells. These data show that transformation of MSC is associated with a reduction in DNA DSB repair capacity and increased radiosensitivity. Up-regulation of checkpoint signaling does not overcome this and the effect of checkpoint inhibition may change with transformation status.

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.

CD44+ cancer stem-like cells in EBV-associated nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a unique EBV-associated epithelial malignancy, showing highly invasive and metastatic phenotype. Despite increasing evidence demonstrating the critical role of cancer stem-like cells (CSCs) in the maintenance and progression of tumors in a variety of malignancies, the existence and properties of CSC in EBV-associated NPC are largely unknown. Our study aims to elucidate the presence and role of CSCs in the pathogenesis of this malignant disease. Sphere-forming cells were isolated from an EBV-positive NPC cell line C666-1 and its tumor-initiating properties were confirmed by in vitro and in vivo assays. In these spheroids, up-regulation of multiple stem cell markers were found. By flow cytometry, we demonstrated that both CD44 and SOX2 were overexpressed in a majority of sphere-forming C666-1 cells. The CD44+SOX2+ cells was detected in a minor population in EBV-positive xenografts and primary tumors and considered as potential CSC in NPC. Notably, the isolated CD44+ NPC cells were resistant to chemotherapeutic agents and with higher spheroid formation efficiency, showing CSC properties. On the other hand, microarray analysis has revealed a number of differentially expressed genes involved in transcription regulation (e.g. FOXN4, GLI1), immune response (CCR7, IL8) and transmembrane transport (e.g. ABCC3, ABCC11) in the spheroids. Among these genes, increased expression of CCR7 in CD44+ CSCs was confirmed in NPC xenografts and primary tumors. Importantly, blocking of CCR7 abolished the sphere-forming ability of C666-1 in vitro. Expression of CCR7 was associated with recurrent disease and distant metastasis. The current study defined the specific properties of a CSC subpopulation in EBV-associated NPC. Our findings provided new insights into developing effective therapies targeting on CSCs, thereby potentiating treatment efficacy for NPC patients.

Cancer stem cells, microRNAs, and therapeutic strategies including natural products

Embryonic stem cells divide continuously and differentiate into organs through the expression of specific transcription factors at specific time periods. Differentiated adult stem cells on the other hand remain in quiescent state and divide by receiving cues from the environment (extracellular matrix or niche), as in the case of wound healing from tissue injury or inflammation. Similarly, it is believed that cancer stem cells (CSCs), forming a smaller fraction of the tumor bulk, also remain in a quiescent state. These cells are capable of initiating and propagating neoplastic growth upon receiving environmental cues, such as overexpression of growth factors, cytokines, and chemokines. Candidate CSCs express distinct biomarkers that can be utilized for their identification and isolation. This review focuses on the known and candidate cancer stem cell markers identified in various solid tumors and the promising future of disease management and therapy targeted at these markers. The review also provides details on the differential expression of microRNAs (miRNAs), and the miRNA- and natural product-based therapies that could be applied for the treatment of cancer stem cells.

High frequency of putative ovarian cancer stem cells with CD44/CK19 coexpression is associated with decreased progression-free intervals in patients with recurrent epithelial ovarian cancer

OBJECTIVE

Epithelial ovarian cancer (EOC) cells with CD44 and CK19 coexpression may represent a subset of ovarian cancer stem cells (OCSCs). This study was conducted to evaluate the correlation of the frequency of putative OCSCs (CD44 + CK19 + OCSCs) with the clinicopathologic features and the prognostic value in patients with recurrent advanced stage EOC.

METHODS

A retrospective study was carried out on 33 patients with EOC and a uniformly treated tissue microarray was constructed. A multiplexed, immunofluorescence-based method of automated in situ quantitative measurement of protein analysis was used for evaluation of the frequency or density of CD44 + CK19 + OCSCs in EOC.

RESULTS

The mean follow-up time was 42.8 ± 27.1 months. High frequency of EOC cells with CD44+ or CD44+/CK19+ was associated with chemoresistance (P = .033 and P = .02, respectively). Using K-M analysis with log-rank test, a high frequency of putative OCSCs was associated with short disease-free interval (7.9 months vs 20.9 months, P = .019). In univariable analysis, the frequency of OCSCs, International Federation of Gynecology and Obstetrics stage and residual tumor volume were significant predictor variables and were entered into multivariable analysis (P = .019, .037, and .005, respectively). Although no independent significant predictor was found, the frequency of putative OCSCs was the most promising predictor variable compared with the other 2 variables (hazard ratio = 2.344, P = .052).

CONCLUSION

Our findings suggest that high frequency of OCSCs (CD44+ and CK19+) in epithelial ovarian tumors correlates with short progression-free intervals.