Identifying cancer stem cells in solid tumors: case not proven

Signaling pathways in the regulation of cancer stem cells and associated targeted therapy

Cancer stem cells (CSCs) are defined as a subpopulation of malignant tumor cells with selective capacities for tumor initiation, self-renewal, metastasis, and unlimited growth into bulks, which are believed as a major cause of progressive tumor phenotypes, including recurrence, metastasis, and treatment failure. A number of signaling pathways are involved in the maintenance of stem cell properties and survival of CSCs, including well-established intrinsic pathways, such as the Notch, Wnt, and Hedgehog signaling, and extrinsic pathways, such as the vascular microenvironment and tumor-associated immune cells. There is also intricate crosstalk between these signal cascades and other oncogenic pathways. Thus, targeting pathway molecules that regulate CSCs provides a new option for the treatment of therapy-resistant or -refractory tumors. These treatments include small molecule inhibitors, monoclonal antibodies that target key signaling in CSCs, as well as CSC-directed immunotherapies that harness the immune systems to target CSCs. This review aims to provide an overview of the regulating networks and their immune interactions involved in CSC development. We also address the update on the development of CSC-directed therapeutics, with a special focus on those with application approval or under clinical evaluation.

Cytoskeletal and Cytoskeleton-Associated Proteins: Key Regulators of Cancer Stem Cell Properties

Cancer stem cells (CSCs) are a subpopulation of cancer cells possessing stemness characteristics that are closely associated with tumor proliferation, recurrence and resistance to therapy. Recent studies have shown that different cytoskeletal components and remodeling processes have a profound impact on the behavior of CSCs. In this review, we outline the different cytoskeletal components regulating the properties of CSCs and discuss current and ongoing therapeutic strategies targeting the cytoskeleton. Given the many challenges currently faced in targeted cancer therapy, a deeper comprehension of the molecular events involved in the interaction of the cytoskeleton and CSCs will help us identify more effective therapeutic strategies to eliminate CSCs and ultimately improve patient survival.

Molecular subtypes of osteosarcoma classified by cancer stem cell related genes define immunological cell infiltration and patient survival

Recent studies have shown that tumor stemness has biological significance in tumorigenicity and tumor progression. However, the characteristics of TME immune infiltration in osteosarcoma mediated by the combined effects of multiple cancer stem cell-related genes remain unknown.

Methods

In this study, we identified different cancer stem cell-associated subtypes in osteosarcoma based on 25 cancer stem cell-associated genes by consensus clustering analysis, and we comprehensively evaluated the association between these subtypes and immunocytes infiltration in the TME. The cancer stem cell (CSC) score was constructed to quantify the stemness of individual tumors.

Results

We performed a comprehensive evaluation of 218 osteosarcoma patients based on 25 cancer stem cell-related genes. Three different cancer stem cells related subtypes were identified, which were related to different biological processes and clinical outcomes. The three subtypes have different TME cells infiltrating characteristics, and CSC Cluster A had a higher level of immunocyte infiltration compared to CSC Cluster B and C. We constructed a scoring system, called the CSC score, to assess the stemness of individual patients. Then we found that the prognosis of patients was predicted by CSC score, and patients with low CSC score had prolonged survival. Further analyses showed that low CSC score was correlated with enhanced immune infiltration. CSC score may predict the effect of immunotherapy, and patients with low CSC score may have better immune response and clinical prognosis.

Conclusions

This study demonstrates that there could be three cancer stem cell-associated subtypes in osteosarcoma and that they were associated with different patient prognosis and TME immune infiltration characteristics. CSC score could be used to assess the stemness of individual patients, improve our comprehension of TME characteristics, and direct more effective immune therapy.

Breast Cancer Stem Cell Membrane Biomarkers: Therapy Targeting and Clinical Implications

Breast cancer is the most common malignancy affecting women worldwide. Importantly, there have been significant improvements in prevention, early diagnosis, and treatment options, which resulted in a significant decrease in breast cancer mortality rates. Nevertheless, the high rates of incidence combined with therapy resistance result in cancer relapse and metastasis, which still contributes to unacceptably high mortality of breast cancer patients. In this context, a small subpopulation of highly tumourigenic cancer cells within the tumour bulk, commonly designated as breast cancer stem cells (BCSCs), have been suggested as key elements in therapy resistance, which are responsible for breast cancer relapses and distant metastasis. Thus, improvements in BCSC-targeting therapies are crucial to tackling the metastatic progression and might allow therapy resistance to be overcome. However, the design of effective and specific BCSC-targeting therapies has been challenging since there is a lack of specific biomarkers for BCSCs, and the most common clinical approaches are designed for commonly altered BCSCs signalling pathways. Therefore, the search for a new class of BCSC biomarkers, such as the expression of membrane proteins with cancer stem cell potential, is an area of clinical relevance, once membrane proteins are accessible on the cell surface and easily recognized by specific antibodies. Here, we discuss the significance of BCSC membrane biomarkers as potential prognostic and therapeutic targets, reviewing the CSC-targeting therapies under clinical trials for breast cancer.

Cancer Stem Cells and their Management in Cancer Therapy

BACKGROUND

In the last decade, the proposed Cancer Stem Cell (CSC) hypothesis has steadily changed the way cancer treatment is approached. CSCs may be the source of the heterogeneous non-tumorigenic cell population included in a neoplasm. Intratumor and intertumoral heterogeneity is a well-known phenomenon that massively entangles the diagnosis and treatment of cancer. The literature seems to suggest that heterogeneity develops progressively within tumor-initiating stem cells. CSCs harbor genetic and/or epigenetic alterations that allow them to differentiate into multiple tumor cell types sequentially.

OBJECTIVE

The CSC hypothesis, cellular therapy, and the most recent patents on CSCs were reviewed.

METHODS

PubMed, Scopus, and Google Scholar were screened for this information. Also, an analysis of the most recent data targeting CSCs in pediatric cancer developed at two Canadian institutions is provided. The genes involved with the activation of CSCs and the drugs used to antagonize them are also highlighted.

RESULTS

It is underlined that (1) CSCs possess stem cell-like properties, including the ability for self-renewal; (2) CSCs can start carcinogenesis and are responsible for tumor recurrence after treatment; (3) Although some limitations have been raised, which may oppose the CSC hypothesis, cancer progression and metastasis have been recognized to be caused by CSCs.

CONCLUSION

The significant roles of cell therapy may include an auto-transplant with high-dose treatment, an improvement of the immune function, creation of chimeric antigen receptor T cells, and the recruitment of NK cell-based immunotherapy.

Identification of key genes controlling cancer stem cell characteristics in gastric cancer

BACKGROUND

Self-renewal of gastric cancer stem cells (GCSCs) is considered to be the underlying cause of the metastasis, drug resistance, and recurrence of gastric cancer (GC).

AIM

To characterize the expression of stem cell-related genes in GC.

METHODS

RNA sequencing results and clinical data for gastric adenoma and adenocarcinoma samples were obtained from The Cancer Genome Atlas database, and the results of the GC mRNA expression-based stemness index (mRNAsi) were analyzed. Weighted gene coexpression network analysis was then used to find modules of interest and their key genes. Survival analysis of key genes was performed using the online tool Kaplan-Meier Plotter, and the online database Oncomine was used to assess the expression of key genes in GC.

RESULTS

mRNAsi was significantly upregulated in GC tissues compared to normal gastric tissues (P < 0.0001). A total of 16 modules were obtained from the gene coexpression network; the brown module was most positively correlated with mRNAsi. Sixteen key genes (BUB1, BUB1B, NCAPH, KIF14, RACGAP1, RAD54L, TPX2, KIF15, KIF18B, CENPF, TTK, KIF4A, SGOL2, PLK4, XRCC2, and C1orf112) were identified in the brown module. The functional and pathway enrichment analyses showed that the key genes were significantly enriched in the spindle cellular component, the sister chromatid segregation biological process, the motor activity molecular function, and the cell cycle and homologous recombination pathways. Survival analysis and Oncomine analysis revealed that the prognosis of patients with GC and the expression of three genes (RAD54L, TPX2, and XRCC2) were consistently related.

CONCLUSION

Sixteen key genes are primarily associated with stem cell self-renewal and cell proliferation characteristics. RAD54L, TPX2, and XRCC2 are the most likely therapeutic targets for inhibiting the stemness characteristics of GC cells.

Exploiting the Complexities of Glioblastoma Stem Cells: Insights for Cancer Initiation and Therapeutic Targeting

The discovery of glioblastoma stem cells (GSCs) in the 2000s revolutionized the cancer research field, raising new questions regarding the putative cell(s) of origin of this tumor type, and partly explaining the highly heterogeneous nature of glioblastoma (GBM). Increasing evidence has suggested that GSCs play critical roles in tumor initiation, progression, and resistance to conventional therapies. The remarkable oncogenic features of GSCs have generated significant interest in better defining and characterizing these cells and determining novel pathways driving GBM that could constitute attractive key therapeutic targets. While exciting breakthroughs have been achieved in the field, the characterization of GSCs is a challenge and the cell of origin of GBM remains controversial. For example, the use of several cell-surface molecular markers to identify and isolate GSCs has been a challenge. It is now widely accepted that none of these markers is, per se, sufficiently robust to distinguish GSCs from normal stem cells. Finding new strategies that are able to more efficiently and specifically target these niches could also prove invaluable against this devastating and therapy-insensitive tumor. In this review paper, we summarize the most relevant findings and discuss emerging concepts and open questions in the field of GSCs, some of which are, to some extent, pertinent to other cancer stem cells.

Targeting cancer stem cell pathways for cancer therapy

Since cancer stem cells (CSCs) were first identified in leukemia in 1994, they have been considered promising therapeutic targets for cancer therapy. These cells have self-renewal capacity and differentiation potential and contribute to multiple tumor malignancies, such as recurrence, metastasis, heterogeneity, multidrug resistance, and radiation resistance. The biological activities of CSCs are regulated by several pluripotent transcription factors, such as OCT4, Sox2, Nanog, KLF4, and MYC. In addition, many intracellular signaling pathways, such as Wnt, NF-κB (nuclear factor-κB), Notch, Hedgehog, JAK-STAT (Janus kinase/signal transducers and activators of transcription), PI3K/AKT/mTOR (phosphoinositide 3-kinase/AKT/mammalian target of rapamycin), TGF (transforming growth factor)/SMAD, and PPAR (peroxisome proliferator-activated receptor), as well as extracellular factors, such as vascular niches, hypoxia, tumor-associated macrophages, cancer-associated fibroblasts, cancer-associated mesenchymal stem cells, extracellular matrix, and exosomes, have been shown to be very important regulators of CSCs. Molecules, vaccines, antibodies, and CAR-T (chimeric antigen receptor T cell) cells have been developed to specifically target CSCs, and some of these factors are already undergoing clinical trials. This review summarizes the characterization and identification of CSCs, depicts major factors and pathways that regulate CSC development, and discusses potential targeted therapy for CSCs.

Lipid droplets: platforms with multiple functions in cancer hallmarks

Lipid droplets (also known as lipid bodies) are lipid-rich, cytoplasmic organelles that play important roles in cell signaling, lipid metabolism, membrane trafficking, and the production of inflammatory mediators. Lipid droplet biogenesis is a regulated process, and accumulation of these organelles within leukocytes, epithelial cells, hepatocytes, and other nonadipocyte cells is a frequently observed phenotype in several physiologic or pathogenic situations and is thoroughly described during inflammatory conditions. Moreover, in recent years, several studies have described an increase in intracellular lipid accumulation in different neoplastic processes, although it is not clear whether lipid droplet accumulation is directly involved in the establishment of these different types of malignancies. This review discusses current evidence related to the biogenesis, composition and functions of lipid droplets related to the hallmarks of cancer: inflammation, cell metabolism, increased proliferation, escape from cell death, and hypoxia. Moreover, the potential of lipid droplets as markers of disease and targets for novel anti-inflammatory and antineoplastic therapies will be discussed.

Correlation of TERT and Stem Cell Markers in the Context of Human Breast Cancer

BACKGROUND

Telomerase reverse transcriptase (TERT) has a well-known role in carcinogenesis due to its functions in inducing cell immortality and preventing senescence. In this study, the relationships between TERT and a panel of known stem cell markers was examined in order to direct future enquiries into the role of 'stem-ness' in human breast cancer.

MATERIALS AND METHODS

Breast cancer tissues (n=124) and adjacent normal tissues (n=30) underwent reverse transcription and quantitative polymerase chain reaction. Transcript levels were analyzed for the correlation with that of TERT.

RESULTS

A significant direct correlation was found in cancerous tissue between TERT and BMI1 proto-oncogene polycomb ring finger 4 (BMI1; n=88, p<0.001), nestin (NES; n=88, p<0.001), POU domain, class 5, transcription factor 1 (POU5F1; n=88, p<0.001), aldehyde dehydrogenase 1 family member A2 (ALDH1A2; n=87, p=0.0298), cyclin-dependent kinase inhibitor 1A (CDKN1A; n=88, p<0.001), integrin subunit beta 1 (ITGNB1; n=88, p<0.001), integrin subunit alpha 6 (ITGA6; n=88, p<0.001), cluster of differentiation antigen 24 (CD24; n=88, p=0.0114), MET proto-oncogene (MET; n=78, p<0.001) and noggin (NOG; n=88, p<0.001).

CONCLUSION

The evidence presented in this article of possible interactions between TERT and a discrete subset of known stem cell markers would significantly contribute to further enquiries regarding clonal dynamics in the context of human breast cancer.

ALDH as a Stem Cell Marker in Solid Tumors

Aldehyde dehydrogenase (ALDH) is an enzyme that participates in important cellular mechanisms as aldehyde detoxification and retinoic acid synthesis; moreover, ALDH activity is involved in drug resistance, a characteristic of cancer stem cells (CSCs). Even though ALDH is found in stem cells, CSCs and progenitor cells, this enzyme has been successfully used to identify and isolate cell populations with CSC properties from several tumor origins. ALDH is allegedly involved in cell differentiation through its product, retinoic acid. However, direct or indirect ALDH inhibition, using specific inhibitors or retinoic acid, has shown a reduction in ALDH activity, along with the loss of stem cell traits, reduction of cell proliferation, invasion, and drug sensitization. For these reasons, ALDH and retinoic acid are promising therapeutic targets. This review summarizes the current evidence for ALDH as a CSCs marker in solid tumors, as well as current knowledge about the functional roles of ALDH in CSCs. We discuss the controversy of ALDH activity to maintain CSC stemness, or conversely, to promote cell differentiation. Finally, we review the advances in using ALDH inhibitors as anti-cancer drugs.

Microenvironment-Driven Dynamic Heterogeneity and Phenotypic Plasticity as a Mechanism of Melanoma Therapy Resistance

Drug resistance constitutes a major challenge in designing melanoma therapies. Microenvironment-driven tumor heterogeneity and plasticity play a key role in this phenomenon. Melanoma is highly heterogeneous with diverse genomic alterations and expression of different biological markers. In addition, melanoma cells are highly plastic and capable of adapting quickly to changing microenvironmental conditions. These contribute to variations in therapy response and durability between individual melanoma patients. In response to changing microenvironmental conditions, like hypoxia and nutrient starvation, proliferative melanoma cells can switch to an invasive slow-cycling state. Cells in this state are more aggressive and metastatic, and show increased intrinsic drug resistance. During continuous treatment, slow-cycling cells are enriched within the tumor and give rise to a new proliferative subpopulation with increased drug resistance, by exerting their stem cell-like behavior and phenotypic plasticity. In melanoma, the proliferative and invasive states are defined by high and low microphthalmia-associated transcription factor (MITF) expression, respectively. It has been observed that in MITFhigh melanomas, inhibition of MITF increases the efficacy of targeted therapies and delays the acquisition of drug resistance. Contrarily, MITF is downregulated in melanomas with acquired drug resistance. According to the phenotype switching theory, the gene expression profile of the MITFlow state is predominantly regulated by WNT5A, AXL, and NF-κB signaling. Thus, different combinations of therapies should be effective in treating different phases of melanoma, such as the combination of targeted therapies with inhibitors of MITF expression during the initial treatment phase, but with inhibitors of WNT5A/AXL/NF-κB signaling during relapse.

Functional Isolation of Tumor-Initiating Cells using Microfluidic-Based Migration Identifies Phosphatidylserine Decarboxylase as a Key Regulator

Isolation of tumor-initiating cells currently relies on markers that do not reflect essential biologic functions of these cells. We proposed to overcome this limitation by isolating tumor-initiating cells based on enhanced migration, a function tightly linked to tumor-initiating potential through epithelial-to-mesenchymal transition (EMT). We developed a high-throughput microfluidic migration platform with automated cell tracking software and facile recovery of cells for downstream functional and genetic analyses. Using this device, we isolated a small subpopulation of migratory cells with significantly greater tumor formation and metastasis in mouse models. Whole transcriptome sequencing of migratory versus non-migratory cells from two metastatic breast cancer cell lines revealed a unique set of genes as key regulators of tumor-initiating cells. We focused on phosphatidylserine decarboxylase (PISD), a gene downregulated by 8-fold in migratory cells. Breast cancer cells overexpressing PISD exhibited reduced tumor-initiating potential in a high-throughput microfluidic mammosphere device and mouse xenograft model. PISD regulated multiple aspects of mitochondria, highlighting mitochondrial functions as therapeutic targets against cancer stem cells. This research establishes not only a novel microfluidic technology for functional isolation of tumor-initiating cells regardless of cancer type, but also a new approach to identify essential regulators of these cells as targets for drug development.

Biomarker discovery for renal cancer stem cells

Characterised by high intra- and inter-tumor heterogeneity, metastatic renal cell carcinoma (RCC) is resistant to chemo- and radiotherapy. Therefore, the development of new prognostic and diagnostic markers for RCC patients is needed. Cancer stem cells (CSCs) are a small population of neoplastic cells within a tumor which present characteristics reminiscent of normal stem cells. CSCs are characterised by unlimited cell division, maintenance of the stem cell pool (self-renewal), and capability to give rise to all cell types within a tumor; and contribute to metastasis in vivo (tumourigenicity), treatment resistance and recurrence. So far, many studies have tried to establish unique biomarkers to identify CSC populations in RCC. At the same time, different approaches have been developed with the aim to isolate CSCs. Consequently, several markers were found to be specifically expressed in CSCs and cancer stem-like cells derived from RCC such as CD105, ALDH1, OCT4, CD133, and CXCR4. However, the contribution of genetic and epigenetic mechanisms, and tumor microenvironment, to cellular plasticity have made the discovery of unique biomarkers a very difficult task. In fact, contrasting results regarding the applicability of such markers to the isolation of renal CSCs have been reported in the literature. Therefore, a better understanding of the mechanism underlying CSC may help dissecting tumor heterogeneity and drug treatment efficiency.

Cancer cell-soluble factors reprogram mesenchymal stromal cells to slow cycling, chemoresistant cells with a more stem-like state

BACKGROUND

Mesenchymal stem cells (MSCs) play different roles in modulating tumor progression, growth, and metastasis. MSCs are recruited to the tumor site in large numbers and subsequently have an important microenvironmental role in modulating tumor progression and drug sensitivity. However, the effect of the tumor microenvironment on MSC plasticity remains poorly understood. Herein, we report a paracrine effect of cancer cells, in which they secrete soluble factors that promote a more stem-like state in bone marrow mesenchymal stem cells (BM-MSCs).

METHODS

The effect of soluble factors secreted from MCF7, Hela, and HepG2 cancer cell lines on BM-MSCs was assessed using a Transwell indirect coculture system. After 5 days of coculture, BM-MSCs were characterized by flow cytometry for surface marker expression, by qPCR for gene expression profile, and by confocal immunofluorescence for marker expression. We then measured the sensitivity of cocultured BM-MSCs to chemotherapeutic agents, their cell cycle profile, and their response to DNA damage. The sphere formation, invasive properties, and in-vivo performance of BM-MSCs after coculture with cancer cells were also measured.

RESULTS

Indirect coculture of cancer cells and BM-MSCs, without direct cell contact, generated slow cycling, chemoresistant spheroid stem cells that highly expressed markers of pluripotency, cancer cells, and cancer stem cells (CSCs). They also displayed properties of a side population and enhanced sphere formation in culture. Accordingly, these cells were termed cancer-induced stem cells (CiSCs). CiSCs showed a more mesenchymal phenotype that was further augmented upon TGF-β stimulation and demonstrated a high expression of the β-catenin pathway and ALDH1A1.

CONCLUSIONS

These findings demonstrate that MSCs, recruited to the tumor microenvironment in large numbers, may display cellular plasticity, acquire a more stem-like state, and acquire some properties of CSCs upon exposure to cancer cell-secreted factors. These acquired characteristics may contribute to tumor progression, survival, and metastasis. Our findings provide new insights into the interactions between MSCs and cancer cells, with the potential to identify novel molecular targets for cancer therapy.

Mathematical models of tissue stem and transit target cell divisions and the risk of radiation- or smoking-associated cancer

There is compelling biological data to suggest that cancer arises from a series of mutations in single target cells, resulting in defects in cell renewal and differentiation processes which lead to malignancy. Because much mutagenic damage is expressed following cell division, more-rapidly renewing tissues could be at higher risk because of the larger number of cell replications. Cairns suggested that renewing tissues may reduce cancer risk by partitioning the dividing cell populations into lineages comprising infrequently-dividing long-lived stem cells and frequently-dividing short-lived daughter transit cells. We develop generalizations of three recent cancer-induction models that account for the joint maintenance and renewal of stem and transit cells, also competing processes of partially transformed cell proliferation and differentiation/apoptosis. We are particularly interested in using these models to separately assess the probabilities of mutation and development of cancer associated with "spontaneous" processes and with those linked to a specific environmental mutagen, specifically ionizing radiation or cigarette smoking. All three models demonstrate substantial variation in cancer risks, by at least 20 orders of magnitude, depending on the assumed number of critical mutations required for cancer, and the stem-cell and transition-cell mutation rates. However, in most cases the conditional probabilities of cancer being mutagen-induced range between 7-96%. The relative risks associated with mutagen exposure compared to background rates are also stable, ranging from 1.0-16.0. Very few cancers, generally <0.5%, arise from mutations occurring solely in stem cells rather than in a combination of stem and transit cells. However, for cancers with 2 or 3 critical mutations, a substantial proportion of cancers, in some cases 100%, have at least one mutation derived from a mutated stem cell. Little difference is made to relative risks if competing processes of proliferation and differentiation in the partially transformed stem and transit cell population are allowed for, nor is any difference made if one assumes that transit cells require an extra mutation to confer malignancy from the number required by stem cells. The probability of a cancer being mutagen-induced correlates across cancer sites with the estimated cumulative number of stem cell divisions in the associated tissue (p<0.05), although in some cases there is sensitivity of findings to removal of high-leverage outliers and in some cases only modest variation in probability, but these issues do not affect the validity of the findings. There are no significant correlations (p>0.3) between lifetime cancer-site specific radiation risk and the probability of that cancer being mutagen-induced. These results do not depend on the assumed critical number of mutations leading to cancer, or on the assumed mutagen-associated mutation rate, within the generally-accepted ranges tested. However, there are borderline significant negative correlations (p = 0.08) between the smoking-associated mortality rate difference (current vs former smokers) and the probability of cancer being mutagen-induced. This is only the case where values of the critical number of mutations leading to cancer, k, is 3 or 4 and not for smaller values (1 or 2), but does not strongly depend on the assumed mutagen-associated mutation rate.

Oncolytic herpes simplex virus kills stem-like tumor-initiating colon cancer cells

Stem-like tumor-initiating cells (TICs) are implicated in cancer progression and recurrence, and can be identified by sphere-formation and tumorigenicity assays. Oncolytic viruses infect, replicate in, and kill a variety of cancer cells. In this study, we seek proof of principle that TICs are susceptible to viral infection. HCT8 human colon cancer cells were subjected to serum-free culture to generate TIC tumorspheres. Parent cells and TICs were infected with HSV-1 subtype NV1066. Cytotoxicity, viral replication, and Akt1 expression were assessed. TIC tumorigenicity was confirmed and NV1066 efficacy was assessed in vivo. NV1066 infection was highly cytotoxic to both parent HCT8 cells and TICs. In both populations, cell-kill of >80% was achieved within 3 days of infection at a multiplicity of infection (MOI) of 1.0. However, the parent cells required 2-log greater viral replication to achieve the same cytotoxicity. TICs overexpressed Akt1 in vitro and formed flank tumors from as little as 100 cells, growing earlier, faster, larger, and with greater histologic atypia than tumors from parent cells. Treatment of TIC-induced tumors with NV1066 yielded tumor regression and slowed tumor growth. We conclude that colon TICs are selected for by serum-free culture, overexpress Akt1, and are susceptible to oncolytic viral infection.

Calmidazolium chloride inhibits growth of murine embryonal carcinoma cells, a model of cancer stem-like cells

Calmidazolium chloride (CMZ) is widely used as a calmodulin (CaM) antagonist, but is also known to induce apoptosis in certain cancer cell lines. However, in spite of the importance of cancer stem cells (CSCs) in cancer therapy, the effects of CMZ on CSCs are not yet well understood. We investigated the effects of CMZ on the F9 embryonal carcinoma cell (ECC) line as a surrogate model of CSCs. To avoid bias due to culture conditions, F9 ECCs and E14 embryonic stem cells (ESCs) were grown in the same culture medium. Results obtained using a cell-counting kit showed that CMZ significantly inhibited growth in F9 ECCs compared with growth in E14 ESCs. CMZ also induced apoptosis of F9 ECCs, but not of E14 ESCs, which was associated with caspase-3 activation and an increased fraction of the sub-G1 cell population. In addition, our data revealed that the expression of stemness-related genes including c-Myc was selectively down regulated in CMZ-treated F9 ECCs. Our results suggest that CMZ can inhibit the growth of ECCs by inducing apoptosis and down regulating stemness-related genes, without causing any harm to normal stem cells. These findings indicate a potential application of CMZ in the development of anti-CSC therapeutics.

Cancer stem cells are underestimated by standard experimental methods in clear cell renal cell carcinoma

Rare cancer stem cells (CSC) are proposed to be responsible for tumour propagation and re-initiation and are functionally defined by identifying tumour-initiating cells (TICs) using the xenotransplantation limiting dilution assay (LDA). While TICs in clear cell renal cell carcinoma (ccRCC) appeared rare in NOD/SCID/IL2Rγ(-/-) (NSG) mice, xenografts formed more efficiently from small tumour fragments, indicating the LDA underestimated ccRCC TIC frequency. Mechanistic interrogation of the LDA identified multiple steps that influence ccRCC TIC quantitation. For example, tissue disaggregation destroys most ccRCC cells, common assays significantly overestimate tumour cell viability, and microenvironmental supplementation with human extracellular factors or pharmacological inhibition of anoikis increase clonogenicity and tumourigenicity of ccRCC cell lines and primary tumour cells. Identification of these previously uncharacterized concerns that cumulatively lead to substantial underestimation of TICs in ccRCC provides a framework for development of more accurate TIC assays in the future, both for this disease and for other cancers.

Cancer Stem Cell and Gastrointestinal Cancer: Current Status, Targeted Therapy and Future Implications

The cancer stem cells (CSCs) are biologically distinct subset of rare cancer cells with inherent ability of self-renewal, de-differentiation, and capacity to initiate and maintain malignant tumor growth. Studies have further reported that CSCs prime cancer recurrence and therapy resistance. Therefore, targeting CSCs to inhibit cancer progression has become an attractive anti-cancer therapeutical strategy. Recent technical advances have provided a greater appreciation of the multistep nature of the oncogenesis and also clarified that CSC concept is not universally applicable. Irrespective, the role of the CSCs in gastrointestinal (GI) cancers, responsible for the most cancer-associated death, has been widely accepted and appreciated. However, despite the tremendous progress made in the last decade in developing markers to identify CSCs, and assays to assess tumorigenic function of CSCs, it remains an area of active investigation. In current article, we review findings related to the role and identification of CSCs in GI-cancers and discuss the crucial pathways involved in regulating CSCs populations’ development and drug resistance, and use of the tumoroid culture to test novel CSCs-targeted cancer therapies.

Imaging metabolic heterogeneity in cancer

As our knowledge of cancer metabolism has increased, it has become apparent that cancer metabolic processes are extremely heterogeneous. The reasons behind this heterogeneity include genetic diversity, the existence of multiple and redundant metabolic pathways, altered microenvironmental conditions, and so on. As a result, methods in the clinic and beyond have been developed in order to image and study tumor metabolism in the in vivo and in vitro regimes. Both regimes provide unique advantages and challenges, and may be used to provide a picture of tumor metabolic heterogeneity that is spatially and temporally comprehensive. Taken together, these methods may hold the key to appropriate cancer diagnoses and treatments in the future.

Cancer Stem and Progenitor-Like Cells as Pharmacological Targets in Breast Cancer Treatment

The present review is focused on the current role of neoplastic stem and progenitor-like cells as primary targets in the pharmacotherapy of cancer as well as in the development of new anticancer drugs. We begin by summarizing the main characteristics of these tumor-initiating cells and key concepts that support their participation in therapeutic failure. In particular, we discuss the differences between the major carcinogenesis models (ie, clonal evolution vs cancer stem cell (CSC) model) with emphasis on breast cancer (given its importance to the study of CSCs) and their implications for the development of new treatment strategies. In addition, we describe the main ways to target these cells, including the main signaling pathways that are more activated or altered in CSCs. Finally, we provide a comprehensive compilation of the most recently tested drugs.

Is sphere assay useful for the identification of cancer initiating cells of the ovary?

OBJECTIVE

Current evidence suggests that the presence of tumor-initiating cells (TICs) in epithelial ovarian cancer (EOC) has a role in chemoresistance and relapse. Surface markers such as CD44(+)/CD24(-), CD117(+), and CD133(+) expression have been reported as potential markers for TICs related to ovarian cancer and tumorigenic cell lines. In this study, we have investigated if spheroid forms are TIC specific or whether they can also be produced by somatic stem cells from healthy tissue in vitro. In addition, we also investigated the specificity of surface markers to identify TICs from papillary serous EOC patients.

METHODS

Cells were obtained from fresh tumors from 10 chemotherapy-naive patients with EOC, and cells from ovarian and tubal epithelium were obtained from 5 healthy menopausal women undergoing surgery for benign pathology and cultured in standard and in selective medium. Cells forming nonadherent spheroids were considered TICs, and the adherent cells were considered as non-TIC-like. Percentages of CD24(+), CD44(+), CD117(+), CD133(+), and vascular endothelial growth factor receptor (VEGF-R)(+) cell surface markers were analyzed by flow cytometry.

RESULTS

Four of 10 EOC cell tissues were excluded from the study. Tumor cells cultured in selective medium developed spheroid forms after 1 to 7 weeks in 5 of 6 EOC patients. No spheroid forms were observed in cultures of cells from healthy women. Unlike previously published data, low levels of CD24(+), CD44(+), CD117(+), and VEGF-R(+) expression were observed in spheroid cells, whereas expression of CD133(+) was moderate but higher in adherent cells from papillary serous EOC cells in comparison with adherent cells from controls.

CONCLUSIONS

Papillary serous EOC contains TICs that form spheroids with low expression of CD44(+), CD24(+), CD117(+) and VEGF-R(+). Further research is required to find specific surface markers to identify papillary serous TICs.

Significance of ATP-binding cassette transporter proteins in multidrug resistance of head and neck squamous cell carcinoma

According to the cancer stem cell theory, a small subpopulation of cancer cells, known as cancer stem cells (CSCs), exist that are self-renewing and are involved in tumor invasion, metastasis and recurrence. A number of studies have reported that certain cancer cells are able to efflux the Hoechst 33342 dye. These cells are termed side population (SP) cells and share characteristic features of CSCs. The results of the present study revealed that 2.7% of primary head and neck squamous cell carcinoma (HNSCC) cells were SP cells. This was reduced to 0.7% following treatment with verapamil. The immunofluorescence and reverse transcription polymerase chain reaction analysis revealed that SP cells have an enhanced expression of the ATP-binding cassette (ABC) transporter protein ABC subfamily G, member 2 (ABCG2), which has been identified to be actively involved in drug exclusion. Similarly, the mRNA level of the oncogene B lymphoma Mo-MLV insertion region-1 and the stem cell surface proteins nestin and octamer-binding transcription factor-4 were highly expressed in the SP cells compared with the non-SP cells. In addition, it was demonstrated that HNSCC SP cells exhibited increased proliferation and were highly resistant to multiple drugs. These findings suggest that the presence of CSCs, such as SP cells, may be responsible for chemotherapy failure and tumor relapse in patients with HNSCC. Therefore, the identification of a novel therapeutic drug that could effectively target CSCs may help to eradicate refractory tumors.

Improved Methods to Generate Spheroid Cultures from Tumor Cells, Tumor Cells & Fibroblasts or Tumor-Fragments: Microenvironment, Microvesicles and MiRNA

Diagnostic and prognostic indicators are key components to achieve the goal of personalized cancer therapy. Two distinct approaches to this goal include predicting response by genetic analysis and direct testing of possible therapies using cultures derived from biopsy specimens. Optimally, the latter method requires a rapid assessment, but growing xenograft tumors or developing patient-derived cell lines can involve a great deal of time and expense. Furthermore, tumor cells have much different responses when grown in 2D versus 3D tissue environments. Using a modification of existing methods, we show that it is possible to make tumor-fragment (TF) spheroids in only 2–3 days. TF spheroids appear to closely model characteristics of the original tumor and may be used to assess critical therapy-modulating features of the microenvironment such as hypoxia. A similar method allows the reproducible development of spheroids from mixed tumor cells and fibroblasts (mixed-cell spheroids). Prior literature reports have shown highly variable development and properties of mixed-cell spheroids and this has hampered the detailed study of how individual tumor-cell components interact. In this study, we illustrate this approach and describe similarities and differences using two tumor models (U87 glioma and SQ20B squamous-cell carcinoma) with supporting data from additional cell lines. We show that U87 and SQ20B spheroids predict a key microenvironmental factor in tumors (hypoxia) and that SQ20B cells and spheroids generate similar numbers of microvesicles. We also present pilot data for miRNA expression under conditions of cells, tumors, and TF spheroids.

Cancer stem cells: a systems biology view of their role in prognosis and therapy

Evidence has accumulated that characterizes highly tumorigenic cancer cells residing in heterogeneous populations. The accepted term for such a subpopulation is cancer stem cells (CSCs). While many questions still remain about their precise role in the origin, progression, and drug resistance of tumors, it is clear they exist. In this review, a current understanding of the nature of CSC, their potential usefulness in prognosis, and the need to target them will be discussed. In particular, separate studies now suggest that the CSC is plastic in its phenotype, toggling between tumorigenic and nontumorigenic states depending on both intrinsic and extrinsic conditions. Because of this, a static view of gene and protein levels defined by correlations may not be sufficient to either predict disease progression or aid in the discovery and development of drugs to molecular targets leading to cures. Quantitative dynamic modeling, a bottom up systems biology approach whereby signal transduction pathways are described by differential equations, may offer a novel means to overcome the challenges of oncology today. In conclusion, the complexity of CSCs can be captured in mathematical models that may be useful for selecting molecular targets, defining drug action, and predicting sensitivity or resistance pathways for improved patient outcomes.

Intratumor heterogeneity: nature and biological significance

Intratumor heterogeneity inherent in the majority of human cancers is a major obstacle for a highly efficient diagnosis and successful prognosis and treatment of these diseases. Being a result of clonal diversity within the same tumor, intratumor heterogeneity can be manifested in variability of genetic and epigenetic status, gene and protein expression, morphological structure, and other features of the tumor. It is most likely that the appearance of this diversity is a source for the adaptation of the tumor to changes in microenvironmental conditions and/or a tool for changing its malignant potential. In any case, both processes result in the appearance of cell clones with different undetermined sets of hallmarks. In this review, we describe the heterogeneity of molecular disorders in various human tumors and consider modern viewpoints of its development including genetic and non-genetic factors of heterogeneity origin and the role of cancer stem cells and clonal evolution. We also systematize data on the contribution of tumor diversity to progression of various tumors and the efficiency of their treatment. The main problems are indicated in the diagnosis and therapy of malignant tumors caused by intratumor heterogeneity and possible pathways for their solution. Moreover, we also suggest the key goals whose achievement promises to minimize the problem of intratumor heterogeneity and to identify new prognostic, predictive, and target markers for adequate and effective treatment of cancer.

Essential role of the cancer stem/progenitor cell marker nucleostemin for indole-3-carbinol anti-proliferative responsiveness in human breast cancer cells

BACKGROUND

Nucleostemin is a nucleolus residing GTPase that is considered to be an important cancer stem/progenitor cell marker protein due to its high expression levels in breast cancer stem cells and its role in tumor-initiation of human mammary tumor cells. It has been proposed that nucleostemin may represent a valuable therapeutic target for breast cancer; however, to date evidence supporting the cellular mechanism has not been elucidated.

RESULTS

Expression of exogenous HER2, a member of the EGF receptor gene family, in the human MCF-10AT preneoplastic mammary epithelial cell line formed a new breast cancer cell line, 10AT-Her2, which is highly enriched in cells with stem/progenitor cell-like character. 10AT-Her2 cells display a CD44+/CD24-/low phenotype with high levels of the cancer stem/progenitor cell marker proteins nucleostemin, and active aldehyde dehydrogenase-1. The overall expression pattern of HER2 protein and the stem/progenitor cell marker proteins in the 10AT-Her2 cell population is similar to that of the luminal HER2+ SKBR3 human breast cancer cell line, whereas, both MCF-7 and MDA-MB-231 cells display reduced levels of nucleostemin and no detectable expression of ALDH-1. Importantly, in contrast to the other well-established human breast cancer cell lines, 10AT-Her2 cells efficiently form tumorspheres in suspension cultures and initiate tumor xenograft formation in athymic mice at low cell numbers. Furthermore, 10AT-Her2 cells are highly sensitive to the anti-proliferative apoptotic effects of indole-3-carbinol (I3C), a natural anti-cancer indolecarbinol from cruciferous vegetables of the Brassica genus such as broccoli and cabbage. I3C promotes the interaction of nucleostemin with MDM2 (Murine Double Mutant 2), an inhibitor of the p53 tumor suppressor, and disrupts the MDM2 interaction with p53. I3C also induced nucleostemin to sequester MDM2 in a nucleolus compartment, thereby freeing p53 to mediate its apoptotic activity. siRNA knockdown of nucleostemin functionally documented that nucleostemin is required for I3C to trigger its cellular anti-proliferative responses, inhibit tumorsphere formation, and disrupt MDM2-p53 protein-protein interactions. Furthermore, expression of an I3C-resistant form of elastase, the only known target protein for I3C, prevented I3C anti-proliferative responses in cells and in tumor xenografts in vivo, as well as disrupt the I3C stimulated nucleostemin-MDM2 interactions.

CONCLUSIONS

Our results provide the first evidence that a natural anti-cancer compound mediates its cellular and in vivo tumor anti-proliferative responses by selectively stimulating cellular interactions of the stem/progenitor cell marker nucleostemin with MDM2, which frees p53 to trigger its apoptotic response. Furthermore, our study provides a new mechanistic template that can be potentially exploited for the development of cancer stem/progenitor cell targeted therapeutic strategies.

PTEN expression and function in adult cancer stem cells and prospects for therapeutic targeting

Phosphatase and tensin homolog deleted on chromosome ten (PTEN) is a non-redundant lipid phosphatase that restrains and fine tunes the phosphatidylinositol-3-kinase (PI3K) signaling pathway. PTEN is involved in inherited syndromes, which predispose to different types of cancers and is among the most frequently inactivated tumor suppressor genes in sporadic cancers. Indeed, loss of PTEN function occurs in a wide spectrum of human cancers through a variety of mechanisms, including mutations, deletions, transcriptional silencing, or protein instability. PTEN prevents tumorigenesis through multiple mechanisms and regulates a plethora of cellular processes, including survival, proliferation, energy metabolism and cellular architecture. Moreover, recent studies have demonstrated that PTEN is able to exit, exist, and function outside the cell, allowing for inhibition of the PI3K pathway in neighboring cells in a paracrine fashion. Most recently, studies have shown that PTEN is also critical for stem cell maintenance and that PTEN loss can lead to the emergence and proliferation of cancer stem cell (CSC) clones. Depending on the cellular and tissue context of origin, PTEN deletion may result in increased self-renewal capacity or normal stem cell exhaustion and PTEN-defìcient stem and progenitor cells have been reported in prostate, lung, intestinal, and pancreatic tissues before tumor formation; moreover, reversible or irreversible PTEN loss is frequently observed in CSC from a variety of solid and hematologic malignancies, where it may contribute to the functional phenotype of CSC. In this review, we will focus on the role of PTEN expression and function and downstream pathway activation in cancer stem cell biology and regulation of the tumorigenic potential; the emerging role of PTEN in mediating the crosstalk between the PI3K and MAPK pathways will also be discussed, together with prospects for the therapeutic targeting of tumors lacking PTEN expression.

Cancer stem cell detection and isolation

Only 10 % of cancer-related deaths result from primary tumors; most are caused by metastatic tumors. It is believed that the metastatic power of tumor cells is attributed to features of a stem cell-like subpopulation of tumor cells known as cancer stem cells (CSCs). Cancer stem cells are resistant to chemotherapeutic treatments and can induce dormancy in tumor cells for long periods. Detection, isolation, and characterization of CSCs in solid tumors are hallmarks of cancer-targeted therapies in recent years. There are inevitable similarities between normal and cancer stem cells; therefore, finding specific methods or markers to differentiate them is critical to cancer therapies. Considering CSCs involvement in tumor relapse and chemotherapeutic resistance, identification of such cells in tumors is imperative for effective targeted therapy. The present review introduces practical and specific protocols used to isolate CSCs from solid tumors from colon, esophagus, liver, breast, brain, and cervix.

Vitamin A/retinol and maintenance of pluripotency of stem cells

Retinol, the alcohol form of vitamin A is a key dietary component that plays a critical role in vertebrate development, cell differentiation, reproduction, vision and immune system. Natural and synthetic analogs of retinol, called retinoids, have generally been associated with the cell differentiation via retinoic acid which is the most potent metabolite of retinol. However, a direct function of retinol has not been fully investigated. New evidence has now emerged that retinol supports the self-renewal of stem cells including embryonic stem cells (ESCs), germ line stem cells (GSCs) and cancer stem cells (CSCs) by activating the endogenous machinery for self-renewal by a retinoic acid independent mechanism. The studies have also revealed that stem cells do not contain enzymes that are responsible for metabolizing retinol into retinoic acid. This new function of retinol may have important implications for stem cell biology which can be exploited for quantitative production of pure population of pluripotent stem cells for regenerative medicine as well as clinical applications for cancer therapeutics.

Investigating molecular profiles of ovarian cancer: an update on cancer stem cells

Currently we are more and more improving our knowledge about the characteristics and the role of cancer stem cells in human cancer. Particularly we have realized that self-renewing ovarian cancer stem cells (CSCs) or ovarian cancer-initiating cells, and mesenchymal stem cells (SCs) too, are probably implicated in the etiopathogenesis of epithelial ovarian cancer (EOC). There is clear evidence that these cells are also involved in its intra- and extra-peritoneal diffusion and in the occurrence of chemo-resistance. In assessing the molecular characteristics of ovarian CSCs, we have to take note that these cellular populations are rare and the absence of specific cell surface markers represents a challenge to isolate and identify pure SC populations. In our review, we focused our attention on the molecular characteristics of epithelial ovarian CSCs and on the methods to detect them starting from their biological features. The study of ovarian CSCs is taking on an increasingly important strategic role, mostly for the potential therapeutic application in the next future.

Glioblastoma multiforme: a look inside its heterogeneous nature

Heterogeneity is a hallmark of tumors and has a crucial role in the outcome of the malignancy, because it not only confounds diagnosis, but also challenges the design of effective therapies. There are two types of heterogeneity: inter-tumor and intra-tumor heterogeneity. While inter-tumor heterogeneity has been studied widely, intra-tumor heterogeneity has been neglected even though numerous studies support this aspect of tumor pathobiology. The main reason has been the technical difficulties, but with new advances in single-cell technology, intra-tumor heterogeneity is becoming a key area in the study of cancer. Several models try to explain the origin and maintenance of intra-tumor heterogeneity, however, one prominent model compares cancer with a tree where the ubiquitous mutations compose the trunk and mutations present in subpopulations of cells are represented by the branches. In this review we will focus on the intra-tumor heterogeneity of glioblastoma multiforme (GBM), the most common brain tumor in adults that is characterized by a marked heterogeneity at the cellular and molecular levels. Better understanding of this heterogeneity will be essential to design effective therapies against this devastating disease to avoid tumor escape.

CD44 and CD24 cannot act as cancer stem cell markers in human lung adenocarcinoma cell line A549

Cancer stem cells (CSCs) are subpopulations of tumor cells that are responsible for tumor initiation, maintenance and metastasis. Recent studies suggested that lung cancer arises from CSCs. In this study, the expression of potential CSC markers in cell line A549 was evaluated. We applied flow cytometry to assess the expression of putative stem cell markers, including aldehyde dehydrogenase 1 (ALDH1), CD24, CD44, CD133 and ABCG2. Cells were then sorted according to the expression of CD44 and CD24 markers by fluorescence-activated cell sorting (FACS) Aria II and characterized using their clonogenic and sphere-forming capacity. A549 cells expressed the CSC markers CD44 and CD24 at 68.16% and 54.46%, respectively. The expression of the putative CSC marker ALDH1 was 4.20%, whereas the expression of ABCG2 and CD133 was 0.93%. Double-positive CD44/133 populations were rare. CD44⁺/24⁺ and CD44⁺/CD24^−/low subpopulations respectively exhibited 64% and 27.92% expression. The colony-forming potentials in the CD44⁺/CD24⁺ and CD44⁺/CD24^−/low subpopulations were 84.37 ± 2.86% and 90 ± 3.06%, respectively, while the parental A549 cells yielded 56.65 ± 2.33% using the colony-formation assay. Both isolated subpopulations formed spheres in serumfree medium supplemented with basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF). CD44 and CD24 cannot be considered potential markers for isolating lung CSCs in cell line A549, but further investigation using in vivo assays is required.

Host-microbiota interaction and intestinal stem cells in chronic inflammation and colorectal cancer

Inflammatory bowel disease (IBD) and colorectal cancer (CRC) are the major diseases of the lower gastrointestinal tract. The intestinal epithelium plays a critical role in the host's interactions with the large communities of resident luminal bacteria. Epithelial cells recognize the bacterial components via pattern-recognition receptors. Toll-like receptors (TLRs) are a major class of pattern-recognition receptors that are present on intestinal epithelial cells, including putative stem cells. Stem cells are responsible for tissue homeostasis and regeneration after injury including IBD. Stem cells are also implicated in the pathogenesis of CRC. In susceptible individuals, disruption of normal homeostatic balance between the host's mucosal cells and enteric microflora is believed to result in aberrant immune responses against the resident commensal bacteria, leading to IBD. Microbiological analyses have revealed that the composition and localization of microbiota is altered in CRC and IBD. It is plausible that stem cells directly sense and respond to microbiota. This review aims to summarize the current knowledge on the effect of microbiota and TLR signaling on intestinal stem cells. It also describes how TLR signaling could affect the stem cell regulatory pathways.

New cancer diagnostics and therapeutics from a ninth 'hallmark of cancer': symmetric self-renewal by mutated distributed stem cells

A total of eight cellular alterations associated with human carcinogenesis have been framed as the 'hallmarks of cancer'. This representation overlooks a ninth hallmark of cancer: the requirement for tumor-originating distributed stem cells to shift sufficiently from asymmetric to symmetric self-renewal kinetics for attainment of the high cell production rate necessary to form clinically significant tumors within a human lifespan. Overlooking this ninth hallmark costs opportunities for discovery of more selective molecular targets for development of improved cancer therapeutics and missing cancer stem cell biomarkers of greater specificity. Here, the biological basis for the ninth hallmark of cancer is considered toward highlighting its importance in human carcinogenesis and, as such, its potential for revealing unique molecules for targeting cancer diagnostics and therapeutics.

A possible explanation for the variable frequencies of cancer stem cells in tumors

A controversy surrounds the frequency of cancer stem cells (CSCs) in solid tumors. Initial studies indicated that these cells had a frequency ranging from 0.0001 to 0.1% of the total cells. Recent studies have shown that this does not always seem to be the case. Some of these studies have indicated a frequency of [Formula: see text]. In this paper we propose a stochastic model that is able to capture this potential variability in the frequency of CSCs among the various type of tumors. Considerations regarding the heterogeneity of the tumor cells and its consequences are included. Possible effects on conventional treatments in clinical practice are also described. The model results suggest that traditional attempts to combat cancer cells with rapid cycling can be very stimulating for the cancer stem cell populations.

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

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

Histological and prognostic importance of CD44(+) /CD24(+) /EpCAM(+) expression in clinical pancreatic cancer

CD44(+) /CD24(+) /EpCAM(+) cells have been reported to be cancer stem cells in pancreatic cancer; however, the histological and clinical importance of these cells has not yet been investigated. Here we clarified the characteristics of CD44(+) /CD24(+) /EpCAM(+) cells in clinical specimens of pancreatic cancer using immunohistochemical assay. We used surgical specimens of pancreatic ductal adenocarcinoma from 101 patients. In view of tumor heterogeneity, we randomly selected 10 high-power fields per case, and triple-positive CD44(+) /CD24(+) /EpCAM(+) expression was identified using our scoring system. The distribution, histological characteristics, and prognostic importance of CD44(+) /CD24(+) /EpCAM(+) cells were then analyzed. As a result, the distribution of CD44(+) /CD24(+) /EpCAM(+) cells varied widely among the 101 cases examined, and CD44(+) /CD24(+) /EpCAM(+) expression was correlated with poor glandular differentiation and high proliferation. Survival analysis showed that CD44(+) /CD24(+) /EpCAM(+) expression was not correlated with patient outcome; however, CD44(+) /CD24(+) expression appeared to be correlated with poor prognosis. In conclusion, CD44(+) /CD24(+) /EpCAM(+) expression overlapped with poorly differentiated cells and possessed high proliferative potential in clinical pancreatic cancer. In particular, the presence of double-positive CD44(+) /CD24(+) expression seemed to have clinical relevance, associating with poor prognosis.

Amplification of tumor inducing putative cancer stem cells (CSCs) by vitamin A/retinol from mammary tumors

Solid tumors contain a rare population of cancer stem cells (CSCs) that are responsible for relapse and metastasis. The existence of CSC however, remains highly controversial issue. Here we present the evidence for putative CSCs from mammary tumors amplified by vitamin A/retinol signaling. The cells exhibit mammary stem cell specific CD29(hi)/CD49f(hi)/CD24(hi) markers, resistance to radiation and chemo therapeutic agents and form highly metastatic tumors in NOD/SCID mice. The cells exhibit indefinite self renewal as cell lines. Furthermore, the cells exhibit impaired retinol metabolism and do not express enzymes that metabolize retinol into retinoic acid. Vitamin A/retinol also amplified putative CSCs from breast cancer cell lines that form highly aggressive tumors in NOD SCID mice. The studies suggest that high purity putative CSCs can be isolated from solid tumors to establish patient specific cell lines for personalized therapeutics for pre-clinical translational applications. Characterization of CSCs will allow understanding of basic cellular and molecular pathways that are deregulated, mechanisms of tumor metastasis and evasion of therapies that has direct clinical relevance.

Expression of stem cell markers, CD133 and CD44, in pediatric solid tumors: a study using tissue microarray

Based on the cancer stem cell (CSC) concept model, a small population of cells with unique self-renewal properties and malignant potential exists in tumors. Immunohistochemistry was performed to detect the expression of CSC markers, CD133 and CD44, in a series of pediatric tumors. The association between expression of these markers and tumor characteristics was then analyzed. In Wilms tumors (WT), a significant positive correlation was found between expression of CD133 and the National Wilms Tumor Stage (NWTS) (p = 0.047). In neuroblastomas (NB), expression of CD133 was positively correlated with the International Neuroblastoma Staging System (INSS) (p-value = 0.012), indicating that the rate of CD133 positivity increased with the stage of these tumors. CD133, as a putative stem cell marker, is associated with more advanced stages of Wilms and NB tumors; therefore, this molecule can be a potential clinical prognostic marker in children suffering from NB or Wilms tumor.

Cancer stem cells: the challenges ahead

Cancer stem cells (CSCs) have been proposed as the driving force of tumorigenesis and the seeds of metastases. However, their existence and role remain a topic of intense debate. Recently, the identification of CSCs in endogenously developing mouse tumours has provided further support for this concept. Here I discuss the challenges in identifying CSCs, their dependency on a supportive niche and their role in metastasis, and propose that stemness is a flexible — rather than fixed — quality of tumour cells that can be lost and gained.

Cancerous ovarian stem cells: obscure targets for therapy but relevant to chemoresistance

Chemotherapy with platinum and taxanes is the first line of treatment for all epithelial ovarian cancer (EOC) patients after debulking surgery. Even though the treatment is initially effective in 80% of patients, recurrent cancer is inevitable in the vast majority of cases. Emerging evidence suggests that some tumor cells can survive chemotherapy by activating the self-renewal pathways resulting in tumor progression and clinical recurrence. These defined population of cells commonly termed as "cancer stem cells" (CSC) may generate the bulk of the tumor by using differentiating pathways. These cells have been shown to be resistant to chemotherapy and, to have enhanced tumor initiating abilities, suggesting CSCs as potential targets for treatment. Recent studies have introduced a new paradigm in ovarian carcinogenesis which proposes in situ carcinoma at the fimbrial end of the fallopian tube to generate high-grade serous ovarian carcinomas, in contrast to ovarian cortical inclusion cysts (CIC) which produce borderline and low grade serous, mucinous, endometrioid, and clear cell carcinomas. This review summarizes recent advances in our understanding of the cellular origin of EOC and the molecular mechanisms defining the basis of CSC in EOC progression and chemoresistance. Using a model ovarian cancer cell line, we highlight the role of CSC in response to chemotherapy, and relate how CSCs may impact on chemoresistance and ultimately recurrence. We also propose the molecular targeting of CSCs and suggest ways that may improve the efficacy of current chemotherapeutic regimens needed for the management of this disease.

Isolation of glioma cancer stem cells in relation to histological grades in glioma specimens

PURPOSE

The existence of cancer stem cells (CSCs) in glioblastoma has been proposed. However, the unknown knowledge that is yet to be revealed is the presence of glioma CSCs (gCSCs) in correlation to each WHO grades of glioma. We approached this study with a hypothesis that specimens from high-grade gliomas would have higher isolation rate of gCSCs in comparison to those of lower-grade gliomas.

METHODS

The glioma specimens were obtained from patients and underwent gliomasphere assay. The gliomaspheres were chosen to be analyzed with immunocytochemisty for surface markers. Then the selected gliomaspheres were exposed to neural differentiation conditions. Lastly, we made mouse orthotopic glioma models to examine the capacity of gliomagenesis.

RESULTS

The gliomaspheres were formed in WHO grade IV (13 of 21) and III (two of nine) gliomas. Among them, WHO grade IV (11 of 13) and III (two of two) gliomaspheres showed similar surface markers to gCSCs and were capable of neural differentiation. Lastly, among the chosen cells, 10 of 11 WHO grade IV and two of two WHO grade III gliomaspheres were capable of gliomagenesis. Thus, overall, the rates of existence of gCSCs were more prominent in high-grade gliomas: 47.6% (10 of 21) in WHO grade IV gliomas and 22.2% (two of nine) in WHO grade III gliomas, whereas WHO grade II and I gliomas showed virtually no gCSCs.

CONCLUSIONS

This trend of stage-by-stage increase of gCSCs in gliomas showed statistical significance by chi-square test linear-by-linear association. We prove that the rates of existence of gCSCs increase proportionally as the WHO grades of gliomas rise.