Bmi1 marks intermediate precursors during differentiation of human brain tumor initiating cells. Stem Cell Res. 2012;8:141-153. [PMID: 22265735 DOI: 10.1016/j.scr.2011.09.008]

Diverse Roles of Protein Palmitoylation in Cancer Progression, Immunity, Stemness, and Beyond

Protein S-palmitoylation, a type of post-translational modification, refers to the reversible process of attachment of a fatty acyl chain-a 16-carbon palmitate acid-to the specific cysteine residues on target proteins. By adding the lipid chain to proteins, it increases the hydrophobicity of proteins and modulates protein stability, interaction with effector proteins, subcellular localization, and membrane trafficking. Palmitoylation is catalyzed by a group of zinc finger DHHC-containing proteins (ZDHHCs), whereas depalmitoylation is catalyzed by a family of acyl-protein thioesterases. Increasing numbers of oncoproteins and tumor suppressors have been identified to be palmitoylated, and palmitoylation is essential for their functions. Understanding how palmitoylation influences the function of individual proteins, the physiological roles of palmitoylation, and how dysregulated palmitoylation leads to pathological consequences are important drivers of current research in this research field. Further, due to the critical roles in modifying functions of oncoproteins and tumor suppressors, targeting palmitoylation has been used as a candidate therapeutic strategy for cancer treatment. Here, based on recent literatures, we discuss the progress of investigating roles of palmitoylation in regulating cancer progression, immune responses against cancer, and cancer stem cell properties.

Cobind: quantitative analysis of the genomic overlaps

Motivation

Analyzing the overlap between two sets of genomic intervals is a frequent task in the field of bioinformatics. Typically, this is accomplished by counting the number (or proportion) of overlapped regions, which applies an arbitrary threshold to determine if two genomic intervals are overlapped. By making binary calls but disregarding the magnitude of the overlap, such an approach often leads to biased, non-reproducible, and incomparable results.

Results

We developed the cobind package, which incorporates six statistical measures: the Jaccard coefficient, Sørensen-Dice coefficient, Szymkiewicz-Simpson coefficient, collocation coefficient, pointwise mutual information (PMI), and normalized PMI. These measures allow for a quantitative assessment of the collocation strength between two sets of genomic intervals. To demonstrate the effectiveness of these methods, we applied them to analyze CTCF's binding sites identified from ChIP-seq, cancer-specific open-chromatin regions (OCRs) identified from ATAC-seq of 17 cancer types, and oligodendrocytes-specific OCRs identified from scATAC-seq. Our results indicated that these new approaches effectively re-discover CTCF's cofactors, as well as cancer-specific and oligodendrocytes-specific master regulators implicated in disease and cell type development.

Availability and implementation

The cobind package is implemented in Python and freely available at https://cobind.readthedocs.io/en/latest/.

Derivation and culturing of neural stem cells from human embryonic brain tissue

Human neural stem cells (hNSCs) are a valuable tool in brain cancer research since they are used as a normal control for multiple assays, mainly pertaining to toxicity. Here, we present a protocol to safely and successfully derive and culture hNSCs in vitro from human embryonic brain tissue. We describe the steps to dissociate embryonic brain tissue and culture hNSCs, followed by the procedure to expand hNSCs. These cells can be used for downstream applications including RNA-seq and omics studies.

For complete details on the use and execution of this protocol, please refer to Venugopal et al. (2012b), Bakhshinyan et al. (2019), and Venugopal et al. (2012a).

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Derivation and cryopreservation of hNSCs from human embryonic tissue

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Long-term culture and expansion of primary hNSC cells

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Feasible to generate up to 200 million human neural stem cells in 1 to 2 months

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Can be used for downstream applications such as RNAseq and omics techniques

Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.

Discovery of HDAC6-Selective Inhibitor NN-390 with in Vitro Efficacy in Group 3 Medulloblastoma

Histone deacetylase 6 (HDAC6) has been targeted in clinical studies for anticancer effects due to its role in oncogenic transformation and metastasis. Through a second-generation structure-activity relationship (SAR) study, the design, and biological evaluation of the selective HDAC6 inhibitor NN-390 is reported. With nanomolar HDAC6 potency, >200-550-fold selectivity for HDAC6 in analogous HDAC isoform functional assays, potent intracellular target engagement, and robust cellular efficacy in cancer cell lines, NN-390 is the first HDAC6-selective inhibitor to show therapeutic potential in metastatic Group 3 medulloblastoma (MB), an aggressive pediatric brain tumor often associated with leptomeningeal metastases and therapy resistance. MB stem cells contribute to these patients' poor clinical outcomes. NN-390 selectively targets this cell population with a 44.3-fold therapeutic margin between patient-derived Group 3 MB cells in comparison to healthy neural stem cells. NN-390 demonstrated a 45-fold increased potency over HDAC6-selective clinical candidate citarinostat. In summary, HDAC6-selective molecules demonstrated in vitro therapeutic potential against Group 3 MB.

The Pivotal Immunomodulatory and Anti-Inflammatory Effect of Histone-Lysine N-Methyltransferase in the Glioma Microenvironment: Its Biomarker and Therapy Potentials

Enhancer of zeste homolog 2 (EZH2) is a histone-lysine N-methyltransferase that encrypts a member of the Polycomb group (PcG) family. EZH2 forms a repressive chromatin structure which eventually participates in regulating the development as well as lineage propagation of stem cells and glioma progression. Posttranslational modifications are distinct approaches for the adjusted modification of EZH2 in the development of cancer. The amino acid succession of EZH2 protein makes it appropriate for covalent modifications, like phosphorylation, acetylation, O-GlcNAcylation, methylation, ubiquitination, and sumoylation. The glioma microenvironment is a dynamic component that comprises, besides glioma cells and glioma stem cells, a complex network that comprises diverse cell types like endothelial cells, astrocytes, and microglia as well as stromal components, soluble factors, and the extracellular membrane. EZH2 is well recognized as an essential modulator of cell invasion as well as metastasis in glioma. EZH2 oversecretion was implicated in the malfunction of several fundamental signaling pathways like Wnt/β-catenin signaling, Ras and NF-κB signaling, PI3K/AKT signaling, β-adrenergic receptor signaling, and bone morphogenetic protein as well as NOTCH signaling pathways. EZH2 was more secreted in glioblastoma multiforme than in low-grade gliomas as well as extremely secreted in U251 and U87 human glioma cells. Thus, the blockade of EZH2 expression in glioma could be of therapeutic value for patients with glioma. The suppression of EZH2 gene secretion was capable of reversing temozolomide resistance in patients with glioma. EZH2 is a promising therapeutic as well as prognostic biomarker for the treatment of glioma.

Targeting BMI-1 with PLGA–PEG nanoparticle-containing PTC209 modulates the behavior of human glioblastoma stem cells and cancer cells

Despite advances in glioblastoma (GBM) treatments, current approaches have failed to improve the overall survival of patients. The oncogene BMI-1, a core member of the polycomb group proteins, is a potential novel therapeutic target for GBM. To enhance the efficacy and reduce the toxicity, PTC209, a BMI-1 inhibitor, was loaded into a PLGA–PEG nanoparticle conjugated with CD133 antibody (Nano-PTC209) and its effect on the behavior of human GBM stem-like cells (GSCs) and the human glioblastoma cell line (U87MG) was assessed. Nano-PTC209 has a diameter of ~ 75 nm with efficient drug loading and controlled release. The IC50 values of Nano-PTC209 for GSCs and U87MG cells were considerably lower than PTC209. Nano-PTC209 significantly decreased the viability of both GSCs and U87MG cells in a dose-dependent manner and caused a significant enhancement of apoptosis and p53 levels as well as inhibition of AKT and JNK signaling pathways. Furthermore, Nano-PTC209 significantly inhibited the migration ability, decreased the activity of metalloproteinase-2 and -9, and increased the generation of reactive oxygen species in both GSCs and U87MG cells. Our data indicate that PLGA–PEG nanoparticle conjugated with CD133 antibody could be an ideal nanocarrier to deliver PTC209 and effectively target BMI-1 for potential approaches in the treatment of GBM.

Advances in histone deacetylase inhibitors in targeting glioblastoma stem cells

Glioblastoma multiforme (GBM) is a lethal grade IV glioma (WHO classification) and widely prevalent primary brain tumor in adults. GBM tumors harbor cellular heterogeneity with the presence of a small subpopulation of tumor cells, described as GBM cancer stem cells (CSCs) that pose resistance to standard anticancer regimens and eventually mediate aggressive relapse or intractable progressive GBM. Existing conventional anticancer therapies for GBM do not target GBM stem cells and are mostly palliative; therefore, exploration of new strategies to target stem cells of GBM has to be prioritized for the development of effective GBM therapy. Recent developments in the understanding of GBM pathophysiology demonstrated dysregulation of epigenetic mechanisms along with the genetic changes in GBM CSCs. Altered expression/activity of key epigenetic regulators, especially histone deacetylases (HDACs) in GBM stem cells has been associated with poor prognosis; inhibiting the activity of HDACs using histone deacetylase inhibitors (HDACi) has been promising as mono-therapeutic in targeting GBM and in sensitizing GBM stem cells to an existing anticancer regimen. Here, we review the development of pan/selective HDACi as potential anticancer agents in targeting the stem cells of glioblastoma as a mono or combination therapy.

The Rational Development of CD133-Targeting Immunotherapies for Glioblastoma

CD133 marks self-renewing cancer stem cells (CSCs) in a variety of solid tumors, and CD133+ tumor-initiating cells are known markers of chemo- and radio-resistance in multiple aggressive cancers, including glioblastoma (GBM), that may drive intra-tumoral heterogeneity. Here, we report three immunotherapeutic modalities based on a human anti-CD133 antibody fragment that targets a unique epitope present in glycosylated and non-glycosylated CD133 and studied their effects on targeting CD133+ cells in patient-derived models of GBM. We generated an immunoglobulin G (IgG) (RW03-IgG), a dual-antigen T cell engager (DATE), and a CD133-specific chimeric antigen receptor T cell (CAR-T): CART133. All three showed activity against patient-derived CD133+ GBM cells, and CART133 cells demonstrated superior efficacy in patient-derived GBM xenograft models without causing adverse effects on normal CD133+ hematopoietic stem cells in humanized CD34+ mice. Thus, CART133 cells may be a therapeutically tractable strategy to target CD133+ CSCs in human GBM or other treatment-resistant primary cancers.

Evolution of Nucleic Acid Aptamers Capable of Specifically Targeting Glioma Stem Cells via Cell-SELEX

Glioma stem cells (GSCs), a particular group of cells from gliomas, are capable of infinite proliferation and differentiation. Recent studies have shown that GSCs may be the root of tumor recurrence, metastasis, and resistance. Early detection and targeted therapy of GSCs may significantly improve the survival rate of glioma patients. Therefore, molecular ligands capable of selectively recognizing GCSs are of great importance. The objective of this study is to generate DNA aptamers for selective identification of the molecular signature of GSCs using cell-based Systematic Evolution of Ligands by EXponential enrichment (cell-SELEX). GSCs were used as the positive selection target, while U87 cells were used in negative cycles for removal of DNA molecules binding to common glioma cell lines. Finally, we successfully identified one aptamer named W5-7 with a K_d value of 4.9 ± 1.4 nM. The sequence of the aptamer was further optimized, and its binding target was identified as a membrane protein. The aptamer W5-7 was stable in cerebral spinal fluid over 36 h and could also effectively detect glioma stem cells in cerebral spinal fluid samples. With its superb targeting properties and functional versatility, W5-7 holds great potential for use as a molecular probe for detecting and isolating GSCs.

DHHC protein family targets different subsets of glioma stem cells in specific niches

Background

Glioblastomas (GBM) comprise different subsets that exhibit marked heterogeneity and plasticity, leading to a lack of success of genomic profiling in guiding the development of precision medicine approaches against these tumors. Accordingly, there is an urgent need to investigate the regulatory mechanisms for different GBM subsets and identify novel biomarkers and therapeutic targets relevant in the context of GBM-specific niches. The DHHC family of proteins is associated tightly with the malignant development and progression of gliomas. However, the role of these proteins in the plasticity of GBM subsets remains unclear.

Methods

This study utilized human glioma proneural or mesenchymal stem cells as indicated. The effects of DHHC proteins on different GBM subsets were investigated through in vitro and in vivo assays (i.e., colony formation assay, flow cytometry assay, double immunofluorescence, western blot, and xenograft model). Western blot, co-immunoprecipitation, and liquid chromatograph mass spectrometer-mass spectrometry assays were used to detect the protein complexes of ZDHHC18 and ZDHHC23 in various GBM subtypes, and explore the mechanism of DHHC proteins in targeting different subsets of GSCs in specific niches.

Results

ZDHHC18 and ZDHHC23 could target the glioma stem cells of different GBM subsets in the context of their specific niches and regulate the cellular plasticity of these subtypes. Moreover, mechanistic investigations revealed that ZDHHC18 and ZDHHC23 competitively interact with a BMI1 E3 ligase, RNF144A, to regulate the polyubiquitination and accumulation of BMI1. These events contributed to the transition of glioma stem cells in GBM and cell survival under the stressful tumor microenvironment.

Conclusions

Our work highlights the role of DHHC proteins in the plasticity of GBM subsets and reveals that BMI1 represents a potential therapeutic target for human gliomas.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1033-2) contains supplementary material, which is available to authorized users.

Introduction to Brain Tumor Stem Cells

From stem cells, to the cancer stem cell hypothesis and intratumoral heterogeneity, the following introductory chapter on brain tumor stem cells explores the history of normal and cancerous stem cells, and their implication in the current model of brain tumor development. The origins of stem cells date back to the 1960s, when they were first described as cells capable of self-renewal, extensive proliferation, and differentiation. Since then, many advances have been made and adult stem cells are now known to be present in a very wide variety of tissues. Neural stem cells were subsequently discovered 30 years later, which was shortly followed by the discovery of cancer stem cells in leukemia and in brain tumors over the next decade, effectively enabling a new understanding of cancer. Since then, many markers including CD133, brain cancer stem cells have been implicated in a variety of phenomena including intratumoral heterogeneity on the genomic, cellular, and functional levels, tumor initiation, chemotherapy-resistance, radiation-resistance, and are believed to be ultimately responsible for tumor relapse. Understanding this small and rare population of cells could be the key to solving the great enigma that is cancer.

TAp73 Modifies Metabolism and Positively Regulates Growth of Cancer Stem-Like Cells in a Redox-Sensitive Manner

PURPOSE

Stem-like cancer cells, with characteristic self-renewal abilities, remain highly refractory to various clinical interventions. As such, stemness-inhibiting entities, such as tumor suppressor p53, are therapeutically pursued for their anticancer activities. Interestingly, similar implications for tumor suppressor TAp73 in regulating stemness features within stem-like cancer cells remain unknown.Experimental Design: This study utilizes various in vitro molecular biology techniques, including immunoblotting, qRT-PCR, and mass spectrometry-based proteomics, and metabolomics approaches to study the role of TAp73 in human and murine embryonal carcinoma stem-like cells (ECSLC) as well as human breast cancer stem-like cells (BCSLC). These findings were confirmed using patient-derived brain tumor-initiating cells (BTIC) and in vivo xenograft models.

RESULTS

TAp73 inhibition decreases the expression of stem cell transcription factors Oct4, Nanog, and Sox-2, as well as tumorsphere formation capacity in ECSLCs. In vivo, TAp73-deficient ECSLCs and BCSLCs demonstrate decreased tumorigenic potential when xenografted in mice. Mechanistically, TAp73 modifies the proline regulatory axis through regulation of enzymes GLS, OAT, and PYCR1 involved in the interconversion of proline-glutamine-ornithine. Further, TAp73 deficiency exacerbates glutamine dependency, enhances accumulation of reactive oxygen species through reduced superoxide dismutase 1 (SOD1) expression, and promotes differentiation by arresting cell cycle and elevating autophagy. Most importantly, the knockdown of TAp73 in CD133^HI BTICs, separated from three different glioblastoma patients, strongly decreases the expression of prosurvival factors Sox-2, BMI-1, and SOD1, and profoundly decreases their self-renewal capacity as evidenced through their reduced tumorsphere formation ability.

CONCLUSIONS

Collectively, we reveal a clinically relevant aspect of cancer cell growth and stemness regulation through TAp73-mediated redox-sensitive metabolic reprogramming.

Phosphoglycerate dehydrogenase inhibition induces p-mTOR-independent autophagy and promotes multilineage differentiation in embryonal carcinoma stem-like cells

Cancer cells with a less differentiated stem-like phenotype are more resistant to therapeutic manipulations than their differentiated counterparts, and are considered as one of the main causes of cancer persistence and relapse. As such, induction of differentiation in cancer stem-like cells (CSLCs) has emerged as an alternative strategy to enhance the efficacy of anticancer therapies. CSLCs are metabolically distinct from differentiated cells, and any aberration from the intrinsic metabolic state can induce differentiation of CSLCs. Therefore, metabolism-related molecular targets, with a capacity to promote differentiation within CSLCs, are of therapeutic importance. Here, we demonstrate that phosphoglycerate dehydrogenase (PHGDH), an essential enzyme catalyzing the synthesis of amino acid serine, is important for maintaining the poorly differentiated, stem-like state of CSLCs. Our data shows that PHGDH deficiency impairs the tumorsphere formation capacity in embryonal carcinoma stem-like cells (ECSLCs), breast cancer stem-like cells (BCSLCs) and patient-derived brain tumor-initiating cells (BTICs), which is accompanied by the reduced expression of characteristic stemness-promoting factors, such as Oct4, Nanog, Sox-2, and Bmi-1. Mechanistically, PHGDH deficiency in ECSLCs promotes differentiation to various lineages via degradation of Oct4 and by increasing the stability of differentiation marker β3-tubulin. Furthermore, PHGDH inhibition promotes p-mTOR independent but Beclin-1-dependent autophagy, independent of apoptosis. When studied in combination, the inhibition of both PHGDH and p-mTOR in ECSLCs causes further augmentation of autophagy, and additionally promotes apoptosis, demonstrating the clinical applicability of PHGDH-based manipulations in cancer therapies. Recapitulating these in vitro findings in CSLC models, the intratumoral PHGDH expression in patient-derived tumors is positively correlated with the mRNA levels of stemness factors, especially Oct4, and cancer patients co-expressing high levels of PHGDH and Oct4 display significantly lower survival than those with low PHGDH/Oct4 co-expression. Altogether, this study identifies a clinically-relevant role for PHGDH in the regulation of stemness-differentiation axis within CSLCs.

Ubiquitin-specific protease 22 acts as an oncoprotein to maintain glioma malignancy through deubiquitinating B cell-specific Moloney murine leukemia virus integration site 1 for stabilization

Ubiquitin‐specific protease 22 (USP22) is a member of the “death‐from‐cancer” signature, which plays a key role in cancer progression. Previous evidence has shown that USP22 is overexpressed and correlates with poor prognosis in glioma. The effect and mechanism of USP22 in glioma malignancy, especially cancer stemness, remain elusive. Herein, we find USP22 is more enriched in stem‐like tumorspheres than differentiated glioma cells. USP22 knockdown inhibits cancer stemness in glioma cell lines. With a cell‐penetrating TAT‐tag protein, B cell‐specific Moloney murine leukemia virus integration site 1 (BMI1), a robust glioma stem‐cell marker, is found to mediate the effect of USP22 on glioma stemness. By immunofluorescence, USP22 and BMI1 are found to share similar intranuclear expression in glioma cells. By analysis with immunohistochemistry and bioinformatics, USP22 is found to positively correlate with BMI1 at the post‐translational level only rather than at the transcriptional level. By immunoprecipitation and in vivo deubiquitination assay, USP22 is found to interact with and deubiquitinate BMI1 for protein stabilization. Microarray analysis shows that USP22 and BMI1 mutually regulate a series of genes involved in glioma stemness such as POSTN,HEY2,PDGFRA and ATF3. In vivo study with nude mice confirms the role of USP22 in promoting glioma tumorigenesis by regulating BMI1. All these findings indicate USP22 as a novel deubiquitinase of BMI1 in glioma. We propose a working model of the USP22‐BMI1 axis, which promotes glioma stemness and tumorigenesis through oncogenic activation. Thus, targeting USP22 might be an effective strategy to treat glioma especially in those with elevated BMI1 expression.

Targeting glioma stem cells through combined BMI1 and EZH2 inhibition

Glioblastomas are lethal cancers defined by angiogenesis and pseudopalisading necrosis. Here, we demonstrate that these histological features are associated with distinct transcriptional programs, with vascular regions showing a proneural profile, and hypoxic regions showing a mesenchymal pattern. As these regions harbor glioma stem cells (GSCs), we investigated the epigenetic regulation of these two niches. Proneural, perivascular GSCs activated EZH2, whereas mesenchymal GSCs in hypoxic regions expressed BMI1 protein, which promoted cellular survival under stress due to downregulation of the E3 ligase RNF144A. Using both genetic and pharmacologic inhibition, we found that proneural GSCs are preferentially sensitive to EZH2 disruption, whereas mesenchymal GSCs are more sensitive to BMI1 inhibition. Given that glioblastomas contain both proneural and mesenchymal GSCs, combined EZH2 and BMI1 targeting proved more effective than either agent alone both in culture and in vivo, suggesting that strategies that simultaneously target multiple epigenetic regulators within glioblastomas may be effective in overcoming therapy resistance caused by intratumoral heterogeneity.

Mathematical modelling of plasticity and phenotype switching in cancer cell populations

The cancer stem cell (CSC) hypothesis suggests that cancer stem cells proliferate via a hierarchical model of unidirectional differentiation. However, growing experimental evidence has advanced this hypothesis by introducing a bidirectional hierarchy, in which non-CSCs may dedifferentiate into CSCs. Various models have been developed enabling the incorporation of this plasticity within cancer cell populations, focusing on behaviour in the limit of a large number of cells. However, stochastic effects predominate in the limit of small numbers of cells, which correlates with biologically relevant assays such as the mammosphere formation assay (MFA). Here, we consider two mathematical models incorporating cellular plasticity, namely a two-compartment model and a hierarchical model, and by parameterizing these models with experimental data, we show this behavioural difference in the limits of large and small numbers of cells. Additionally, we analyse the effects of varying cellular plasticity on the survival of the cancer cell population, and show that interestingly, increased plasticity, in certain cases, may be advantageous in reducing the survival probability. Thus, this analysis highlights the necessity of experimentally studying both small and large populations of cancer cells concurrently to obtain valid model predictions, potentially aiding the design of novel therapeutics.

A Fraction of CD133+ CNE2 Cells Is Made of Giant Cancer Cells with Morphological Evidence of Asymmetric Mitosis

CD133 has been suggested as a broad-spectrum marker for cancer stem cells(CSCs). The present study investigated the expression of CD133 in biopsy tissues of nasopharyngeal carcinoma (NPC), NPC cell lines and the immortalized cell line NP69 by immunohistochemistry, flow cytometry and qRT-PCR. CD133+ cancer cells were isolated using magnetic-activated cell sorting technology. The study demonstrated that CD133+ cells are rare in NPC tissues and cell lines and that their self-renewal and proliferation abilities are stronger than those of CD133- cells and suggested that CD133+ NPC cells have characteristics of cancer stem cells. We further observed CD133+ cancer cells using a light microscope and scanning electron microscope. Generally, CD133+ cells are small, regular and round with small microvilli. On the other hand, CD133- cells are more polymorphic and larger with long micromicrovilli. Additionally, in some fields, several giant cancer cells (GCCs) in the CD133+ cell group were identified under the light microscope. Most of them were polynuclear cells. Under the scanning electron microscope, we found indefinite regular small bodies on the surface of or surrounding the giant cancer cells, some of which appeared to be creeping out the parental cells. This phenomenon was not observed in the CD133- cell groups. Through comparison with descriptions of apoptotic bodies in the literature and from the results of the acridine orange test, we propose that some of the small bodies are daughter cells of the GCCs. This phenomenon is a mode of division of cancer cells called neosis, or budding, which is a form of reproduction for simple organisms. Budding is satisfied with the rapid speed of tumor development. GCCs could be isolated by CD133 beads because the daughter cells have stem-cell characteristics and express stem-cell markers.

Establishment of a novel human medulloblastoma cell line characterized by highly aggressive stem-like cells

Medulloblastoma is a highly aggressive brain tumor and one of the leading causes of morbidity and mortality related to childhood cancer. These tumors display differential ability to metastasize and respond to treatment, which reflects their high degree of heterogeneity at the genetic and molecular levels. Such heterogeneity of medulloblastoma brings an additional challenge to the understanding of its physiopathology and impacts the development of new therapeutic strategies. This translational effort has been the focus of most pre-clinical studies which invariably employ experimental models using human tumor cell lines. Nonetheless, compared to other cancers, relatively few cell lines of human medulloblastoma are available in central repositories, partly due to the rarity of these tumors and to the intrinsic difficulties in establishing continuous cell lines from pediatric brain tumors. Here, we report the establishment of a new human medulloblastoma cell line which, in comparison with the commonly used and well-established cell line Daoy, is characterized by enhanced proliferation and invasion capabilities, stem cell properties, increased chemoresistance, tumorigenicity in an orthotopic metastatic model, replication of original medulloblastoma behavior in vivo, strong chromosome structural instability and deregulation of genes involved in neural development. These features are advantageous for designing biologically relevant experimental models in clinically oriented studies, making this novel cell line, named USP-13-Med, instrumental for the study of medulloblastoma biology and treatment.

miR-367 promotes proliferation and stem-like traits in medulloblastoma cells

In medulloblastoma, abnormal expression of pluripotency factors such as LIN28 and OCT4 has been correlated with poor patient survival. The miR-302/367 cluster has also been shown to control self-renewal and pluripotency in human embryonic stem cells and induced pluripotent stem cells, but there is limited, mostly correlational, information about these pluripotency-related miRNA in cancer. We evaluated whether aberrant expression of such miRNA could affect tumor cell behavior and stem-like traits, thereby contributing to the aggressiveness of medulloblastoma cells. Basal expression of primary and mature forms of miR-367 were detected in four human medulloblastoma cell lines and expression of the latter was found to be upregulated upon enforced expression of OCT4A. Transient overexpression of miR-367 significantly enhanced tumor features typically correlated with poor prognosis; namely, cell proliferation, 3-D tumor spheroid cell invasion and the ability to generate neurosphere-like structures enriched in CD133 expressing cells. A concurrent downregulation of the miR-367 cancer-related targets RYR3, ITGAV and RAB23, was also detected in miR-367-overexpressing cells. Overall, these findings support the pro-oncogenic activity of miR-367 in medulloblastoma and reveal a possible mechanism contributing to tumor aggressiveness, which could be further explored to improve patient stratification and treatment of this important type of pediatric brain cancer.

Targeting glioblastoma cancer stem cells: the next great hope?

Glioblastoma multiforme (GBM) is the most common primary brain tumor and is notorious for its poor prognosis. The highly invasive nature of GBM and its inherent resistance to therapy lead to very high rates of recurrence. Recently, a small cohort of tumor cells, called cancer stem cells (CSCs), has been recognized as a subset of tumor cells with self-renewal ability and multilineage capacity. These properties, along with the remarkable tumorigenicity of CSCs, are thought to account for the high rates of tumor recurrence after treatment. Recent research has been geared toward understanding the unique biological characteristics of CSCs to enable development of targeted therapy. Strategies include inhibition of CSC-specific pathways and receptors; agents that increase sensitivity of CSCs to chemotherapy and radiotherapy; CSC differentiation agents; and CSC-specific immunotherapy, virotherapy, and gene therapy. These approaches could inform the development of newer therapeutics for GBM.

Pyrvinium Targets CD133 in Human Glioblastoma Brain Tumor-Initiating Cells

PURPOSE

Clonal evolution of cancer may be regulated by determinants of stemness, specifically self-renewal, and current therapies have not considered how genetic perturbations or properties of stemness affect such functional processes. Glioblastoma-initiating cells (GICs), identified by expression of the cell surface marker CD133, are shown to be chemoradioresistant. In the current study, we sought to elucidate the functional role of CD133 in self-renewal and identify compounds that can specifically target this CD133(+) treatment-refractory population.

EXPERIMENTAL DESIGN

Using gain/loss-of-function studies for CD133 we assessed the in vitro self-renewal and in vivo tumor formation capabilities of patient-derived glioblastoma cells. We generated a CD133 signature combined with an in silico screen to find compounds that target GICs. Self-renewal and proliferation assays on CD133-sorted samples were performed to identify the preferential action of hit compounds. In vivo efficacy of the lead compound pyrvinium was assessed in intracranial GIC xenografts and survival studies. Lastly, microarray analysis was performed on pyrvinium-treated GICs to discover core signaling events involved.

RESULTS

We discovered pyrvinium, a small-molecule inhibitor of GIC self-renewal in vitro and in vivo, in part through inhibition of Wnt/β-catenin signaling and other essential stem cell regulatory pathways. We provide a therapeutically tractable strategy to target self-renewing, chemoradioresistant, and functionally important CD133(+) stem cells that drive glioblastoma relapse and mortality.

CONCLUSIONS

Our study provides an integrated approach for the eradication of clonal populations responsible for cancer progression, and may apply to other aggressive and heterogeneous cancers.

Understanding the colon cancer stem cells and perspectives on treatment

An area of research that has been recently gaining attention is the relationship between cancer stem cell (CSC) biology and chemo-resistance in colon cancer patients. It is well recognized that tumor initiation, growth, invasion and metastasis are promoted by CSCs. An important reason for the widespread interest in the CSC model is that it can comprehensibly explain essential and poorly understood clinical events, such as therapy resistance, minimal residual disease, and tumor recurrence. This review discusses the recent advances in colon cancer stem cell research, the genes responsible for CSC chemoresistance, and new therapies against CSCs.

Altered gene products involved in the malignant reprogramming of cancer stem/progenitor cells and multitargeted therapies

Recent studies in the field of cancer stem cells have revealed that the alterations in key gene products involved in the epithelial-mesenchymal transition (EMT) program, altered metabolic pathways such as enhanced glycolysis, lipogenesis and/or autophagy and treatment resistance may occur in cancer stem/progenitor cells and their progenies during cancer progression. Particularly, the sustained activation of diverse developmental cascades such as hedgehog, epidermal growth factor receptor (EGFR), Wnt/β-catenin, Notch, transforming growth factor-β (TGF-β)/TGF-βR receptors and/or stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor 4 (CXCR4) can play critical functions for high self-renewal potential, survival, invasion and metastases of cancer stem/progenitor cells and their progenies. It has also been observed that cancer cells may be reprogrammed to re-express different pluripotency-associated stem cell-like markers such as Myc, Oct-3/4, Nanog and Sox-2 along the EMT process and under stressful and hypoxic conditions. Moreover, the enhanced expression and/or activities of some drug resistance-associated molecules such as Bcl-2, Akt/molecular target of rapamycin (mTOR), nuclear factor-kappaB (NF-κB), hypoxia-inducible factors (HIFs), macrophage inhibitory cytokine-1 (MIC-1) and ATP-binding cassette (ABC) multidrug transporters frequently occur in cancer cells during cancer progression and metastases. These molecular events may cooperate for the survival and acquisition of a more aggressive and migratory behavior by cancer stem/progenitor cells and their progenies during cancer transition to metastatic and recurrent disease states. Of therapeutic interest, these altered gene products may also be exploited as molecular biomarkers and therapeutic targets to develop novel multitargeted strategies for improving current cancer therapies and preventing disease relapse.

FoxG1 interacts with Bmi1 to regulate self-renewal and tumorigenicity of medulloblastoma stem cells

Brain tumors represent the leading cause of childhood cancer mortality, of which medulloblastoma (MB) is the most frequent malignant tumor. Recent studies have demonstrated the presence of several MB molecular subgroups, each distinct in terms of prognosis and predicted therapeutic response. Groups 1 and 2 are characterized by relatively good clinical outcomes and activation of the Wnt and Shh pathways, respectively. In contrast, groups 3 and 4 ("non-Shh/Wnt MBs") are distinguished by metastatic disease, poor patient outcome, and lack a molecular pathway phenotype. Current gene expression platforms have not detected brain tumor-initiating cell (BTIC) self-renewal genes in groups 3 and 4 MBs as BTICs typically comprise a minority of tumor cells and may therefore go undetected on bulk tumor analyses. Since increasing BTIC frequency has been associated with increasing tumor aggressiveness and poor patient outcome, we investigated the subgroup-specific gene expression profile of candidate stem cell genes within 251 primary human MBs from four nonoverlapping MB transcriptional databases (Amsterdam, Memphis, Toronto, Boston) and 74 NanoString-subgrouped MBs (Vancouver). We assessed the functional relevance of two genes, FoxG1 and Bmi1, which were significantly enriched in non-Shh/Wnt MBs and showed these genes to mediate MB stem cell self-renewal and tumor initiation in mice. We also identified their transcriptional regulation through reciprocal promoter occupancy in CD15+ MB stem cells. Our work demonstrates the application of stem cell data gathered from genomic platforms to guide functional BTIC assays, which may then be used to develop novel BTIC self-renewal mechanisms amenable to therapeutic targeting.

Glioblastoma stem cells: Molecular characteristics and therapeutic implications

Glioblastoma Multiforme (GBM) is a grade IV astrocytoma, with a median survival of 14.6 mo. Within GBM, stem-like cells, namely glioblastoma stem cells (GSCs), have the ability to self-renew, differentiate into distinct lineages within the tumor and initiate tumor xenografts in immunocompromised animal models. More importantly, GSCs utilize cell-autonomous and tumor microenvironment-mediated mechanisms to overcome current therapeutic approaches. They are, therefore, very important therapeutic targets. Although the functional criteria defining GSCs are well defined, their molecular characteristics, the mechanisms whereby they establish the cellular hierarchy within tumors, and their contribution to tumor heterogeneity are not well understood. This review is aimed at summarizing current findings about GSCs and their therapeutic importance from a molecular and cellular point of view. A better characterization of GSCs is crucial for designing effective GSC-targeted therapies.

The cyclin-like protein Spy1 regulates growth and division characteristics of the CD133+ population in human glioma

The heterogeneity of brain cancers, as most solid tumors, complicates diagnosis and treatment. Identifying and targeting populations of cells driving tumorigenesis is a top priority for the cancer biology field. This is not a trivial task; considerable variance exists in the driving mutations, identifying markers, and evolutionary pressures influencing initiating cells in different individual tumors. Despite this, the ability to self-renew and differentiate must be conserved to reseed a heterogeneous tumor mass. Focusing on one example of a tumor-initiating cell population, we demonstrate that the atypical cyclin-like protein Spy1 plays a role in balancing the division properties of glioma cells with stemness properties. This mechanistic insight may provide new opportunities for therapeutic intervention of brain cancer.

Genetic and epigenetic analysis of putative breast cancer stem cell models

Background

Cancer stem cell model hypothesizes existence of a small proportion of tumor cells capable of sustaining tumor formation, self-renewal and differentiation. In breast cancer, these cells were found to be associated with CD44⁺CD24^-low and ALDH⁺ phenotype. Our study was performed to evaluate the suitability of current approaches for breast cancer stem cell analyses to evaluate heterogeneity of breast cancer cells through their extensive genetic and epigenetic characterization.

Methods

Breast cancer cell lines MCF7 and SUM159 were cultured in adherent conditions and as mammospheres. Flow cytometry sorting for CD44, CD24 and ALDH was performed. Sorted and unsorted populations, mammospheres and adherent cell cultures were subjected to DNA profiling by array CGH and methylation profiling by Epitect Methyl qPCR array. Methylation status of selected genes was further evaluated by pyrosequencing. Functional impact of methylation was evaluated by mRNA analysis for selected genes.

Results

Array CGH did not reveal any genomic differences. In contrast, putative breast cancer stem cells showed altered methylation levels of several genes compared to parental tumor cells.

Conclusions

Our results underpin the hypothesis that epigenetic mechanisms seem to play a major role in the regulation of CSCs. However, it is also clear that more efficient methods for CSC enrichment are needed. This work underscores requirement of additional approaches to reveal heterogeneity within breast cancer.

Investigating the link between molecular subtypes of glioblastoma, epithelial-mesenchymal transition, and CD133 cell surface protein

In this manuscript, we use genetic data to provide a three-faceted analysis on the links between molecular subclasses of glioblastoma, epithelial-to-mesenchymal transition (EMT) and CD133 cell surface protein. The contribution of this paper is three-fold: First, we use a newly identified signature for epithelial-to-mesenchymal transition in human mammary epithelial cells, and demonstrate that genes in this signature have significant overlap with genes differentially expressed in all known GBM subtypes. However, the overlap between genes up regulated in the mesenchymal subtype of GBM and in the EMT signature was more significant than other GBM subtypes. Second, we provide evidence that there is a negative correlation between the genetic signature of EMT and that of CD133 cell surface protein, a putative marker for neural stem cells. Third, we study the correlation between GBM molecular subtypes and the genetic signature of CD133 cell surface protein. We demonstrate that the mesenchymal and neural subtypes of GBM have the strongest correlations with the CD133 genetic signature. While the mesenchymal subtype of GBM displays similarity with the signatures of both EMT and CD133, it also exhibits some differences with each of these signatures that are partly due to the fact that the signatures of EMT and CD133 are inversely related to each other. Taken together these data shed light on the role of the mesenchymal transition and neural stem cells, and their mutual interaction, in molecular subtypes of glioblastoma multiforme.

The implications of cancer stem cells for cancer therapy

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

Processing of primary brain tumor tissue for stem cell assays and flow sorting

Brain tumors are typically comprised of morphologically diverse cells that express a variety of neural lineage markers. Only a relatively small fraction of cells in the tumor with stem cell properties, termed brain tumor initiating cells (BTICs), possess an ability to differentiate along multiple lineages, self-renew, and initiate tumors in vivo. We applied culture conditions originally used for normal neural stem cells (NSCs) to a variety of human brain tumors and found that this culture method specifically selects for stem-like populations. Serum-free medium (NSC) allows for the maintenance of an undifferentiated stem cell state, and the addition of bFGF and EGF allows for the proliferation of multi-potent, self-renewing, and expandable tumorspheres. To further characterize each tumor's BTIC population, we evaluate cell surface markers by flow cytometry. We may also sort populations of interest for more specific characterization. Self-renewal assays are performed on single BTICs sorted into 96 well plates; the formation of tumorspheres following incubation at 37 °C indicates the presence of a stem or progenitor cell. Multiple cell numbers of a particular population can also be sorted in different wells for limiting dilution analysis, to analyze self-renewal capacity. We can also study differential gene expression within a particular cell population by using single cell RT-PCR. The following protocols describe our procedures for the dissociation and culturing of primary human samples to enrich for BTIC populations, as well as the dissociation of tumorspheres. Also included are protocols for staining for flow cytometry analysis or sorting, self-renewal assays, and single cell RT-PCR.