Glioblastoma stem cells

Rapid, label-free classification of glioblastoma differentiation status combining confocal Raman spectroscopy and machine learning

Label-free identification of tumor cells using spectroscopic assays has emerged as a technological innovation with a proven ability for rapid implementation in clinical care. Machine learning facilitates the optimization of processing and interpretation of extensive data, such as various spectroscopy data obtained from surgical samples. The here-described preclinical work investigates the potential of machine learning algorithms combining confocal Raman spectroscopy to distinguish non-differentiated glioblastoma cells and their respective isogenic differentiated phenotype by means of confocal ultra-rapid measurements. For this purpose, we measured and correlated modalities of 1146 intracellular single-point measurements and sustainingly clustered cell components to predict tumor stem cell existence. By further narrowing a few selected peaks, we found indicative evidence that using our computational imaging technology is a powerful approach to detect tumor stem cells in vitro with an accuracy of 91.7% in distinct cell compartments, mainly because of greater lipid content and putative different protein structures. We also demonstrate that the presented technology can overcome intra- and intertumoral cellular heterogeneity of our disease models, verifying the elevated physiological relevance of our applied disease modeling technology despite intracellular noise limitations for future translational evaluation.

Chemical Activation and Mechanical Sensitization of Piezo1 Enhance TRAIL-Mediated Apoptosis in Glioblastoma Cells

Glioblastoma multiforme (GBM), the most common and aggressive type of primary brain tumor, has a mean survival of less than 15 months after standard treatment. Treatment with the current standard of care, temozolomide (TMZ), may be ineffective if damaged tumor cells undergo DNA repair or acquire mutations that inactivate transcription factor p53. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) triggers apoptosis in multiple tumor types, while evading healthy cells, through a transcription-independent mechanism. GBM is particularly resistant to TRAIL, but studies have found that the mechanoreceptor Piezo1 can be activated under static conditions via Yoda1 agonist to induce TRAIL sensitization in other cancer cell lines. This study examines the effects and the mechanism of chemical and mechanical activation of Piezo1, via Yoda1 and fluid shear stress (FSS) stimulation, on TRAIL-mediated apoptosis in GBM cells. Here, we demonstrate that Yoda1 + TRAIL and FSS + TRAIL combination therapies significantly increase apoptosis in two GBM cell lines relative to controls. Further, cells known to be resistant to TMZ were found to have higher levels of Piezo1 expression and were more susceptible to TRAIL sensitization by Piezo1 activation. The combinatory Yoda1 + TRAIL treatment significantly decreased cell viability in TMZ-resistant GBM cells when compared to treatment with both low and high doses of TMZ. The results of this study suggest the potential of a highly specific and minimally invasive approach to overcome TMZ resistance in GBM by sensitizing cancer cells to TRAIL treatment via chemical or mechanical activation of Piezo1.

Expression analysis and regulation of GLI and its correlation with stemness and metabolic alteration in human brain tumor

GLI gene-mediated hedgehog (Hh) signaling pathway plays a substantial role in brain cancer development and growth including glioblastoma multiforme (GBM), lower-grade glioma (LGG), and medulloblastoma (MB). GLI2 and GLI3 gene expression levels are extremely enhanced in these cancers with poor patient survival. Moreover, GLI genes are correlated with stemness-related factors SOX2, SOX9, POU5F1, and NANOG that work as the driving factors for brain cancer stem cells (CSCs) progression. It's critical to find new ways to combat this deadly malignancy and CSCs. Using in silico approaches, our study explored the role of GLI genes (GLI1, GLI2, and GLI3), the primary transcription factors of the sonic hedgehog (SHH) signaling pathway, in GBM, LGG, MB, and glioblastoma stem-like cells (GSCs). Additionally, we found strong association of angiogenic-related gene VEGFA, metabolic genes ENO1, ENO2, and pluripotency-related genes SOX2, SOX9, NANOG, POU5F1 with GLI genes, suggesting their role in brain tumor initiation and progression. We also studied their transcriptional network and functional category enrichment analysis about brain tumor development to find a better therapeutic strategy against brain cancer and their stem cells.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03419-5.

Transcription factor YY1 mediates self-renewal of glioblastoma stem cells through regulation of the SENP1/METTL3/MYC axis

Glioma is a primary brain tumor with limited treatment approaches and glioblastoma stem cells (GSCs) are manifested with the self-renewal capability and high tumorigenic capacity. This study was performed to investigate the regulatory effect of the SUMO-specific protease 1 (SENP1)/methyltransferase-like 3 (METTL3)/MYC axis on the self-renewal of GSCs mediated by transcription factor Yin Yang 1 (YY1). Following bioinformatics analysis and clinical and cellular experiments, we found that YY1 was highly expressed in GBM tissues and cells, while silencing its expression reduced the self-renewal ability of GSCs. Functionally, YY1 promoted the transcriptional expression of SENP1 by binding to the promoter region of SENP1, while the deSUMOase SENP1 facilitated the methylase activity of m6A through deSUMOylation of the methylase METTL3, thereby promoting the m6A modification of MYC mRNA via METL3 and promoting the expression of MYC. A nude mouse xenograft model of GBM was also constructed to examine the tumorigenicity of GSCs. The obtained findings demonstrated that YY1 promoted tumorigenicity of GSCs by promoting the expression of MYC in vivo. Conclusively, YY1 can transcriptionally upregulate the SUMOylase SENP1 and enhance the methylase activity of METTL3, resulting in the increased m6A modification level of MYC mRNA, thereby promoting the self-renewal of GSCs.

Pathophysiological roles of integrins in gliomas from the perspective of glioma stem cells

Glioblastoma is the most common primary intracranial tumor and is also one of the most malignant central nervous system tumors. Its characteristics, such as high malignancy, abundant tumor vasculature, drug resistance, and recurrence-prone nature, cause great suffering to glioma patients. Furthermore, glioma stem cells are the primordial cells of the glioma and play a central role in the development of glioma. Integrins—heterodimers composed of noncovalently bound a and ß subunits—are highly expressed in glioma stem cells and play an essential role in the self-renewal, differentiation, high drug resistance, and chemo-radiotherapy resistance of glioma stem cells through cell adhesion and signaling. However, there are various types of integrins, and their mechanisms of function on glioma stem cells are complex. Therefore, this article reviews the feasibility of treating gliomas by targeting integrins on glioma stem cells.

A2B Adenosine Receptor Enhances Chemoresistance of Glioblastoma Stem-Like Cells under Hypoxia: New Insights into MRP3 Transporter Function

Glioblastoma is the most common and aggressive primary brain tumor, characterized by its high chemoresistance and the presence of a cell subpopulation that persists under hypoxic niches, called glioblastoma stem-like cells (GSCs). The chemoresistance of GSCs is mediated in part by adenosine signaling and ABC transporters, which extrude drugs outside the cell, such as the multidrug resistance-associated proteins (MRPs) subfamily. Adenosine promotes MRP1-dependent chemoresistance under normoxia. However, adenosine/MRPs-dependent chemoresistance under hypoxia has not been studied until now. Transcript and protein levels were determined by RT-qPCR and Western blot, respectively. MRP extrusion capacity was determined by intracellular 5 (6)-Carboxyfluorescein diacetate (CFDA) accumulation. Cell viability was measured by MTS assays. Cell cycle and apoptosis were determined by flow cytometry. Here, we show for the first time that MRP3 expression is induced under hypoxia through the A2B adenosine receptor. Hypoxia enhances MRP-dependent extrusion capacity and the chemoresistance of GSCs. Meanwhile, MRP3 knockdown decreases GSC viability under hypoxia. Downregulation of the A_2B receptor decreases MRP3 expression and chemosensibilizes GSCs treated with teniposide under hypoxia. These data suggest that hypoxia-dependent activation of A_2B adenosine receptor promotes survival of GSCs through MRP3 induction.

Microfluidic Lab-on-a-Chip Based on UHF-Dielectrophoresis for Stemness Phenotype Characterization and Discrimination among Glioblastoma Cells

Glioblastoma (GBM) is one of the most aggressive solid tumors, particularly due to the presence of cancer stem cells (CSCs). Nowadays, the characterization of this cell type with an efficient, fast and low-cost method remains an issue. Hence, we have developed a microfluidic lab-on-a-chip based on dielectrophoresis (DEP) single cell electro-manipulation to measure the two crossover frequencies: f_x01 in the low-frequency range (below 500 kHz) and f_x02 in the ultra-high-frequency range (UHF, above 50 MHz). First, in vitro conditions were investigated. An U87-MG cell line was cultured in different conditions in order to induce an undifferentiated phenotype. Then, ex vivo GBM cells from patients’ primary cell culture were passed through the developed microfluidic system and characterized in order to reflect clinical conditions. This article demonstrates that the usual exploitation of low-frequency range DEP does not allow the discrimination of the undifferentiated GBM cells from the differentiated one. However, the presented study highlights the use of UHF-DEP as a relevant discriminant parameter. The proposed microfluidic lab-on-a-chip is able to follow the kinetics of U87-MG phenotype transformation in a CSC enrichment medium and the cancer stem cells phenotype acquirement.

Dual-triggered biomimetic vehicles enable treatment of glioblastoma through a cancer stem cell therapeutic strategy

Glioma stem cells (GSCs) and their complex microenvironment play a crucial role in the high invasion of cancer and therapeutic resistance and are considered to be the most likely cause of cancer relapse. We constructed a biomimetic vehicle (LDL-SAL-Ang) based on a low density lipoprotein triggered by Angiopep-2 peptide and ApoB protein, to improve the transport of an anti-GSC therapeutic agent into the brain. The LDL-SAL-Ang showed significant inhabitation for GSC microsphere formation and induced the highest apoptotic rate in two types of GSCs. LDL-SAL-Ang reduced the number of GSC-derived endothelial tubules at a lower drug concentration and inhibited endothelial cell migration and angiogenesis. The pharmacokinetic analysis showed that the brain tissue uptake rate (% ID g^-1) for LDL-SAL-Ang was significantly enhanced at 0.45. For anti-glioblastoma activity in vivo, the median survival time of LDL-SAL-Ang plus temozolomide group was 47 days, which were significantly increased compared with the control or temozolomide only groups. The endogenous biomimetic nanomedicine that we designed provides a potential approach to improve treatments for intracranial tumors and reduced neurotoxicity of nanomedicine.

Adeno-associated virus (AAV)-based gene therapy for glioblastoma

Glioblastoma (GBM) is the most common and malignant Grade IV primary craniocerebral tumor caused by glial cell carcinogenesis with an extremely poor median survival of 12–18 months. The current standard treatments for GBM, including surgical resection followed by chemotherapy and radiotherapy, fail to substantially prolong survival outcomes. Adeno-associated virus (AAV)-mediated gene therapy has recently attracted considerable interest because of its relatively low cytotoxicity, poor immunogenicity, broad tissue tropism, and long-term stable transgene expression. Furthermore, a range of gene therapy trials using AAV as vehicles are being investigated to thwart deadly GBM in mice models. At present, AAV is delivered to the brain by local injection, intracerebroventricular (ICV) injection, or systematic injection to treat experimental GBM mice model. In this review, we summarized the experimental trials of AAV-based gene therapy as GBM treatment and compared the advantages and disadvantages of different AAV injection approaches. We systematically introduced the prospect of the systematic injection of AAV as an approach for AAV-based gene therapy for GBM.

Impact of the Tumor Microenvironment on Tumor Heterogeneity and Consequences for Cancer Cell Plasticity and Stemness

Tumor heterogeneity is considered the major cause of treatment failure in current cancer therapies. This feature of solid tumors is not only the result of clonal outgrowth of cells with genetic mutations, but also of epigenetic alterations induced by physical and chemical signals from the tumor microenvironment (TME). Besides fibroblasts, endothelial and immune cells, mesenchymal stroma/stem-like cells (MSCs) and tumor-associated macrophages (TAMs) intimately crosstalk with cancer cells and can exhibit both anti- and pro-tumorigenic effects. MSCs can alter cancer cellular phenotypes to increase cancer cell plasticity, eventually resulting in the generation of cancer stem cells (CSCs). The shift between different phenotypic states (phenotype switching) of CSCs is controlled via both genetic programs, such as epithelial-mesenchymal transdifferentiation or retrodifferentiation, and epigenetic alterations triggered by signals from the TME, like hypoxia, spatial heterogeneity or stromal cell-derived chemokines. Finally, we highlight the role of spontaneous cancer cell fusion with various types of stromal cells. i.e., MSCs in shaping CSC plasticity. A better understanding of cell plasticity and phenotype shifting in CSCs is a prerequisite for exploiting this phenomenon to reduce tumor heterogeneity, thereby improving the chance for therapy success.

Confocal investigation on colocalization between tubulin posttranslational modifications and associated proteins in rat C6 glioma cells

Glioblastoma multiforme is the most lethal brain tumor. In the study of mechanisms underlying its development attention has been paid to the microtubular network of its cells, mainly on βIII tubulin, considered as a marker of malignancy. In the present work, we chose to investigate the tubulin code in glioblastoma cells, analyzing the degree of interaction between tubulin post-translational modifications and different proteins associated with them. The pattern of diverse associated proteins such as EB-1, CLIP-170 and kinesin-1 and their degree of co-distribution with the most abundant post-translational tubulin modifications (tyrosination, acetylation and polyglutamylation) were evaluated. Through immunofluorescence we have shown that EB-1, CLIP-170 and kinesin-1 were well detectable in glioblastoma cells. The double fluorescence and colocalization index between the post-translational modifications of tubulin and associated proteins showed that tyrosinated α-tubulin has significantly high affinity with EB-1, CLIP-170 and kinesin-1, while for acetylated and polyglutamylated tubulin, the degree of interaction with the three associated proteins evaluated was less apparent. Data presented in this paper underline the importance of a thorough analysis of the microtubular mechanics in glioblastoma cells. This may suggest new experimental therapeutic approaches able to act more selectively on the microtubular network of cells in this type of cancer.

FRAT1 Enhances the Proliferation and Tumorigenesis of CD133+Nestin+ Glioma Stem Cells In Vitro and In Vivo

Glioma stem cells (GSCs) are considered the source for development, recurrence, and poor prognosis of glioma, so treatment targeted GSCs is of great interest. The frequently rearranged in advanced T cell lymphomas-1 (FRAT1) gene is an important member of the Wnt/β-catenin signaling transduction pathway, and aberrantly activation of Wnt signaling has been identified to contribute to the tumorigenesis, proliferation, invasion of a variety kinds of cancer stem cells. However, correlations between FRAT1 and GSCs and the specific mechanisms remain unclear. In this study, we aimed to investigate the effect of FRAT1 on GSCs proliferation, colony formation, sphere formation and tumorigenesity in vitro and in vivo and its underlying mechanism. Lentiviral transfection was used to construct GSCs with low FRAT1 expression. The expression of FRAT1 on GSCs proliferation in vitro was assessed by cell counting kit-8(CCK-8). Colony formation and sphere formation assays were conducted to assess the colony and sphere formation ability of GSCs. Then, an intracranial glioma nude mouse model was built to measure the effect of low FRAT1 expression on GSCs proliferation and tumorigenesity in vivo. Real-time PCR, Western blot, and Immunohistochemistry were processed to detect the mRNA and protein expressions of FRAT1, β-catenin in the glioma tissue of xenograft mice to study their correlations. The functional assays verifed that low FRAT1 expression inhibited CD133⁺Nestin⁺ GSCs proliferation, colony formation, sphere formation ability in vitro. In vivo GSCs xenograft mice model showed that low FRAT1 expression suppressed the proliferation and tumorigenesity of CD133⁺Nestin⁺ GSCs and reduced β-catenin mRNA and protein expression. Furthermore, the expression of FRAT1 and β-catenin were positively correlated. Altogether, results indicate that FRAT1 enhances the proliferation, colony formation, sphere formation and tumorigenesity of CD133⁺Nestin⁺ glioma stem cells in vitro and in vivo as well as the expression of β-catenin. Therefore, inhibiting proliferation of GSCs and FRAT1 may be a molecular target to GSCs in treating human glioma in the future.

Patient-Derived Glioma Models: From Patients to Dish to Animals

Glioblastoma (GBM) is the most common and malignant primary brain tumor in adults associated with a poor survival. Current standard of care consists of surgical resection followed by radiation and chemotherapy. GBMs are highly heterogeneous, having a complex interaction among different cells within the tumor as well as the tumor microenvironment. One of the main challenges in the neuro-oncology field in general, and GBM in particular, is to find an optimum culture condition that maintains the molecular genotype and phenotype as well as heterogeneity of the original tumor in vitro and in vivo. Established cell lines were shown to be a poor model of the disease, failing to recapitulate the phenotype and harboring non-parental genotypic mutations. Given the growing understanding of GBM biology, the discovery of glioma cancer stem-like cells (GSCs), and their role in tumor formation and therapeutic resistance, scientists are turning more towards patient-derived cells and xenografts as a more representative model. In this review, we will discuss the current state of patient-derived GSCs and their xenografts; and provide an overview of different established models to study GBM biology and to identify novel therapeutics in the pre-clinical phase.

CHD7 promotes glioblastoma cell motility and invasiveness through transcriptional modulation of an invasion signature

Chromatin remodeler proteins exert an important function in promoting dynamic modifications in the chromatin architecture, performing a central role in regulating gene transcription. Deregulation of these molecular machines may lead to striking perturbations in normal cell function. The CHD7 gene is a member of the chromodomain helicase DNA-binding family and, when mutated, has been shown to be the cause of the CHARGE syndrome, a severe developmental human disorder. Moreover, CHD7 has been described to be essential for neural stem cells and it is also highly expressed or mutated in a number of human cancers. However, its potential role in glioblastoma has not yet been tested. Here, we show that CHD7 is up-regulated in human glioma tissues and we demonstrate that CHD7 knockout (KO) in LN-229 glioblastoma cells suppresses anchorage-independent growth and spheroid invasion in vitro. Additionally, CHD7 KO impairs tumor growth and increases overall survival in an orthotopic mouse xenograft model. Conversely, ectopic overexpression of CHD7 in LN-428 and A172 glioblastoma cell lines increases cell motility and invasiveness in vitro and promotes LN-428 tumor growth in vivo. Finally, RNA-seq analysis revealed that CHD7 modulates a specific transcriptional signature of invasion-related target genes. Further studies should explore clinical-translational implications for glioblastoma treatment.

SWIM tool application to expression data of glioblastoma stem-like cell lines, corresponding primary tumors and conventional glioma cell lines

BACKGROUND

It is well-known that glioblastoma contains self-renewing, stem-like subpopulation with the ability to sustain tumor growth. These cells - called cancer stem-like cells - share certain phenotypic characteristics with untransformed stem cells and are resistant to many conventional cancer therapies, which might explain the limitations in curing human malignancies. Thus, the identification of genes controlling the differentiation of these stem-like cells is becoming a successful therapeutic strategy, owing to the promise of novel targets for treating malignancies.

METHODS

Recently, we developed SWIM, a software able to unveil a small pool of genes - called switch genes - critically associated with drastic changes in cell phenotype. Here, we applied SWIM to the expression profiling of glioblastoma stem-like cells and conventional glioma cell lines, in order to identify switch genes related to stem-like phenotype.

RESULTS

SWIM identifies 171 switch genes that are all down-regulated in glioblastoma stem-like cells. This list encompasses genes like CAV1, COL5A1, COL6A3, FLNB, HMMR, ITGA3, ITGA5, MET, SDC1, THBS1, and VEGFC, involved in "ECM-receptor interaction" and "focal adhesion" pathways. The inhibition of switch genes highly correlates with the activation of genes related to neural development and differentiation, such as the 4-core OLIG2, POU3F2, SALL2, SOX2, whose induction has been shown to be sufficient to reprogram differentiated glioblastoma into stem-like cells. Among switch genes, the transcription factor FOSL1 appears as the brightest star since: it is down-regulated in stem-like cells; it highly negatively correlates with the 4-core genes that are all up-regulated in stem-like cells; the promoter regions of the 4-core genes harbor a consensus binding motif for FOSL1.

CONCLUSIONS

We suggest that the inhibition of switch genes in stem-like cells could induce the deregulation of cell communication pathways, contributing to neoplastic progression and tumor invasiveness. Conversely, their activation could restore the physiological equilibrium between cell adhesion and migration, hampering the progression of cancer. Moreover, we posit FOSL1 as promising candidate to orchestrate the differentiation of cancer stem-like cells by repressing the 4-core genes' expression, which severely halts cancer growth and might affect the therapeutic outcome. We suggest FOSL1 as novel putative therapeutic and prognostic biomarker, worthy of further investigation.

Proscillaridin A exerts anti-tumor effects through GSK3β activation and alteration of microtubule dynamics in glioblastoma

Glioblastoma (GBM) is characterized by highly aggressive growth and invasive behavior. Due to the highly lethal nature of GBM, new therapies are urgently needed and repositioning of existing drugs is a promising approach. We have previously shown the activity of Proscillaridin A (ProA), a cardiac glycoside inhibitor of the Na(+)/K(+) ATPase (NKA) pump, against proliferation and migration of GBM cell lines. ProA inhibited tumor growth in vivo and increased mice survival after orthotopic grafting of GBM cells. This study aims to decipher the mechanism of action of ProA in GBM tumor and stem-like cells. ProA displayed cytotoxic activity on tumor and stem-like cells grown in 2D and 3D culture, but not on healthy cells as astrocytes or oligodendrocytes. Even at sub-cytotoxic concentration, ProA impaired cell migration and disturbed EB1 accumulation at microtubule (MT) plus-ends and MT dynamics instability. ProA activates GSK3β downstream of NKA inhibition, leading to EB1 phosphorylation on S155 and T166, EB1 comet length shortening and MT dynamics alteration, and finally inhibition of cell migration and cytotoxicity. Similar results were observed with digoxin. Therefore, we disclosed here a novel pathway by which ProA and digoxin modulate MT-governed functions in GBM tumor and stem-like cells. Altogether, our results support ProA and digoxin as potent candidates for drug repositioning in GBM.

Network-Based Approaches to Explore Complex Biological Systems towards Network Medicine

Network medicine relies on different types of networks: from the molecular level of protein–protein interactions to gene regulatory network and correlation studies of gene expression. Among network approaches based on the analysis of the topological properties of protein–protein interaction (PPI) networks, we discuss the widespread DIAMOnD (disease module detection) algorithm. Starting from the assumption that PPI networks can be viewed as maps where diseases can be identified with localized perturbation within a specific neighborhood (i.e., disease modules), DIAMOnD performs a systematic analysis of the human PPI network to uncover new disease-associated genes by exploiting the connectivity significance instead of connection density. The past few years have witnessed the increasing interest in understanding the molecular mechanism of post-transcriptional regulation with a special emphasis on non-coding RNAs since they are emerging as key regulators of many cellular processes in both physiological and pathological states. Recent findings show that coding genes are not the only targets that microRNAs interact with. In fact, there is a pool of different RNAs—including long non-coding RNAs (lncRNAs) —competing with each other to attract microRNAs for interactions, thus acting as competing endogenous RNAs (ceRNAs). The framework of regulatory networks provides a powerful tool to gather new insights into ceRNA regulatory mechanisms. Here, we describe a data-driven model recently developed to explore the lncRNA-associated ceRNA activity in breast invasive carcinoma. On the other hand, a very promising example of the co-expression network is the one implemented by the software SWIM (switch miner), which combines topological properties of correlation networks with gene expression data in order to identify a small pool of genes—called switch genes—critically associated with drastic changes in cell phenotype. Here, we describe SWIM tool along with its applications to cancer research and compare its predictions with DIAMOnD disease genes.

Computational identification of specific genes for glioblastoma stem-like cells identity

Glioblastoma, the most malignant brain cancer, contains self-renewing, stem-like cells that sustain tumor growth and therapeutic resistance. Identifying genes promoting stem-like cell differentiation might unveil targets for novel treatments. To detect them, here we apply SWIM - a software able to unveil genes (named switch genes) involved in drastic changes of cell phenotype - to public datasets of gene expression profiles from human glioblastoma cells. By analyzing matched pairs of stem-like and differentiated glioblastoma cells, SWIM identified 336 switch genes, potentially involved in the transition from stem-like to differentiated state. A subset of them was significantly related to focal adhesion and extracellular matrix and strongly down-regulated in stem-like cells, suggesting that they may promote differentiation and restrain tumor growth. Their expression in differentiated cells strongly correlated with the down-regulation of transcription factors like OLIG2, POU3F2, SALL2, SOX2, capable of reprogramming differentiated glioblastoma cells into stem-like cells. These findings were corroborated by the analysis of expression profiles from glioblastoma stem-like cell lines, the corresponding primary tumors, and conventional glioma cell lines. Switch genes represent a distinguishing feature of stem-like cells and we are persuaded that they may reveal novel potential therapeutic targets worthy of further investigation.

Biomimetic models to examine microenvironmental regulation of glioblastoma stem cells

Glioblastoma multiforme (GBM), a malignant brain tumor, is the deadliest form of human cancer with low survival rates because of its highly invasive nature. In recent years, there has been a growing appreciation for the role that glioblastoma stem cells (GSCs) play during tumorigenesis and tumor recurrence of GBM. GSCs are a specialized subset of GBM cells with stem cell-like features that contribute to tumor initiation and therapeutic resistance. Thus, to enhance therapeutic efficiency and improve survival, targeting GSCs and their microenvironmental niche appears to be a promising approach. To develop this approach, understanding GSC-microenvironment interactions is crucial. This review discusses various biomimetic model systems to understand the impact of biophysical, biochemical, and cellular microenvironmental cues on GSC behaviors. These models include two-dimensional or matrix-free environment models, engineered biomaterial-based three-dimensional models, co-culture models, and mouse and rat in vivo models. These systems have been used to study the effects of biophysical factors, modulation of signaling pathways, extracellular matrix components, and culture conditions on the GSC phenotype. The advantages and disadvantages of these model systems and their impact in the field of GSC research are discussed.

The versatile nature of miR-9/9* in human cancer

miR-9 and miR-9* (miR-9/9*) were first shown to be expressed in the nervous system and to function as versatile regulators of neurogenesis. The variable expression levels of miR-9/9* in human cancer prompted researchers to investigate whether these small RNAs may also have an important role in the deregulation of physiological and biochemical networks in human disease. In this review, we present a comprehensive overview of the involvement of miR-9/9* in various human malignancies focusing on their opposing roles in supporting or suppressing tumor development and metastasis. Importantly, it is shown that the capacity of miR-9/9* to impact tumor formation is independent from their influence on the metastatic potential of tumor cells. Moreover, data suggest that miR-9/9* may increase malignancy of one cancer cell population at the expense of another. The functional versatility of miR-9/9* emphasizes the complexity of studying miRNA function and the importance to perform functional studies of both miRNA strands in a relevant cellular context. The possible application of miR-9/9* as targets for miRNA-based therapies is discussed, emphasizing the need to obtain a better understanding of the functional properties of these miRNAs and to develop safe delivery methods to target specific cell populations.

How Nanotechnology and Biomedical Engineering Are Supporting the Identification of Predictive Biomarkers in Neuro-Oncology

The field of neuro-oncology is rapidly progressing and internalizing many of the recent discoveries coming from research conducted in basic science laboratories worldwide. This systematic review aims to summarize the impact of nanotechnology and biomedical engineering in defining clinically meaningful predictive biomarkers with a potential application in the management of patients with brain tumors. Data were collected through a review of the existing English literature performed on Scopus, MEDLINE, MEDLINE in Process, EMBASE, and/or Cochrane Central Register of Controlled Trials: all available basic science and clinical papers relevant to address the above-stated research question were included and analyzed in this study. Based on the results of this systematic review we can conclude that: (1) the advances in nanotechnology and bioengineering are supporting tremendous efforts in optimizing the methods for genomic, epigenomic and proteomic profiling; (2) a successful translational approach is attempting to identify a growing number of biomarkers, some of which appear to be promising candidates in many areas of neuro-oncology; (3) the designing of Randomized Controlled Trials will be warranted to better define the prognostic value of those biomarkers and biosignatures.

Cyclophilin A Maintains Glioma-Initiating Cell Stemness by Regulating Wnt/β-Catenin Signaling

Purpose: Glioma-initiating cells (GIC) are glioma stem-like cells that contribute to glioblastoma (GBM) development, recurrence, and resistance to chemotherapy and radiotherapy. They have recently become the focus of novel treatment strategies. Cyclophilin A (CypA) is a cytosolic protein that belongs to the peptidyl-prolyl isomerase (PPIase) family and the major intracellular target of the immunosuppressive drug cyclosporin A (CsA). In this study, we investigate the functions of CypA and its mechanism of action in GICs' development.Experimental Design: We analyzed differences in CypA expression between primary tumors and neurospheres from the GDS database, both before and after GIC differentiation. A series of experiments was conducted to investigate the role of CypA in GIC stemness, self-renewal, proliferation, radiotherapy resistance, and mechanism. We then designed glutathione S-transferase (GST) pulldown and coimmunoprecipitation assays to detect signaling activity.Results: In this study, we demonstrated that CypA promotes GIC stemness, self-renewal, proliferation, and radiotherapy resistance. Mechanistically, we found that CypA binds β-catenin and is recruited to Wnt target gene promoters. By increasing the interaction between β-catenin and TCF4, CypA enhances transcriptional activity.Conclusions: Our results demonstrate that CypA enhances GIC stemness, self-renewal, and radioresistance through Wnt/β-catenin signaling. Due to its promotive effects on GICs, CypA is a potential target for future glioma therapy. Clin Cancer Res; 23(21); 6640-9. ©2017 AACR.

Hematopoietic stem cells as a tool for the treatment of glioblastoma multiforme

Glioblastoma multiforme is an aggressive malignant brain tumor with terminal consequences. A primary reason for its resistance to treatment is associated with cancer stem cells (CSCs), of which there are currently no effective ways to destroy. It remains unclear what cancer cells become a target of stem cell migration, what the role of this process is in oncogenesis and what stem cell lines should be used in developing antitumor technologies. Using modern post‑genome technologies, the present study investigated the migration of human stem cells to cancer cells in vitro, the comparative study of cell proteomes of certain stem cells (including CSCs) was conducted and stem cell migration in vivo was examined. Of all glioblastoma cells, CSCs have the stability to attract normal stem cells. Critical differences in cell proteomes allow the consideration of hematopoietic stem cells (HSCs) as an instrument for interaction with glioblastoma CSCs. Following injection into the bloodstream of animals with glioblastoma, the majority of HSCs migrated to the tumor‑containing brain hemisphere and penetrated the tumor tissue. HSCs therefore are of potential use in the development of methods to target CSCs.

Multiscale Modeling of Glioblastoma Suggests that the Partial Disruption of Vessel/Cancer Stem Cell Crosstalk Can Promote Tumor Regression Without Increasing Invasiveness

OBJECTIVE

In glioblastoma, the crosstalk between vascular endothelial cells (VECs) and glioma stem cells (GSCs) has been shown to enhance tumor growth. We propose a multiscale mathematical model to study this mechanism, explore tumor growth under various initial and microenvironmental conditions, and investigate the effects of blocking this crosstalk.

METHODS

We develop a hybrid continuum-discrete model of highly organized vascularized tumors. VEC-GSC crosstalk is modeled via vascular endothelial growth factor (VEGF) production by tumor cells and by secretion of soluble factors by VECs that promote GSC self-renewal and proliferation.

RESULTS

VEC-GSC crosstalk increases both tumor size and GSC fraction by enhancing GSC activity and neovascular development. VEGF promotes vessel formation, and larger VEGF sources typically increase vessel numbers, which enhances tumor growth and stabilizes the tumor shape. Increasing the initial GSC fraction has a similar effect. Partially disrupting the crosstalk by blocking VEC secretion of GSC promoters reduces tumor size but does not increase invasiveness, which is in contrast to antiangiogenic therapies, which reduce tumor size but may significantly increase tumor invasiveness.

SIGNIFICANCE

Multiscale modeling supports the targeting of VEC-GSC crosstalk as a promising approach for cancer therapy.

The Novel Tubulin-Binding Checkpoint Activator BAL101553 Inhibits EB1-Dependent Migration and Invasion and Promotes Differentiation of Glioblastoma Stem-like Cells

Glioblastoma patients have limited treatment options. Cancer stem-like cells (CSLC) contribute to glioblastoma invasiveness and repopulation; hence, they represent promising targets for novel therapies. BAL101553 is a prodrug of BAL27862, a novel microtubule-destabilizing agent inhibiting tumor cell proliferation through activation of the spindle assembly checkpoint, which is currently in phase I/II clinical development. Broad anticancer activity has been demonstrated against human cancer models, including tumors refractory to conventional treatments. We have shown that overexpression of microtubule + end-binding 1-protein (EB1) correlates with glioblastoma progression and poor survival. Here, we show that BAL27862 inhibits the growth of two glioblastoma CSLCs. As EB1 is overexpressed in the CSLC line GBM6, which displays a high tumorigenicity and infiltrative pattern of migration in vivo, we investigated drug activity on GBM6 according to EB1 expression. BAL27862 inhibited migration and colony formation at subcytotoxic concentrations in EB1-expressing control cells (GBM6-sh0) but only at cytotoxic concentrations in EB1-downregulated (GBM-shE1) cells. Three administrations of BAL101553 were sufficient to provoke an EB1-dependent survival benefit in tumor-bearing mice. Patterns of invasion and quantification of tumor cells in brain demonstrated that GBM6-sh0 cells were more invasive than GBM6-shEB1 cells, and that the antiproliferative and anti-invasive effects of BAL101553 were more potent in mice bearing control tumors than in EB1-downregulated tumors. This was associated with inhibition of stem cell properties in the GBM6-sh0 model. Finally, BAL27862 triggered astrocytic differentiation of GBM6 in an EB1-dependent manner. These results support the potential of BAL101553 for glioblastoma treatment, with EB1 expression as a predictive biomarker of response. Mol Cancer Ther; 15(11); 2740-9. ©2016 AACR.

Spontaneously Arising Canine Glioma as a Potential Model for Human Glioma

Human gliomas are malignant brain tumours that carry a poor prognosis and are composed of a heterogeneous population of cells. There is a paucity of animal models available for study of these tumours and most have been created by genetic modification. Spontaneously arising canine gliomas may provide a model for the characterization of the human tumours. The present study shows that canine gliomas form a range of immunohistochemical patterns that are similar to those described for human gliomas. The in-vitro sphere assay was used to analyze the expansion and differentiation potential of glioma cells taken from the periphery and centre of canine tumours. Samples from the subventricular zone (SVZ) and contralateral parenchyma were used as positive and negative controls, respectively. The expansion potential for all of these samples was low and cells from only three cultures were expanded for six passages. These three cultures were derived from high-grade gliomas and the cells had been cryopreserved. Most of the cells obtained from the centre of the tumours formed spheres and were expanded, in contrast to samples taken from the periphery of the tumours. Spheres were also formed and expanded from two areas of apparently unaffected brain parenchyma. The neurogenic SVZ contralateral samples also contained progenitor proliferating cells, since all of them were expanded for three to five passages. Differentiation analysis showed that all cultured spheres were multipotential and able to differentiate towards both neurons and glial cells. Spontaneously arising canine gliomas might therefore constitute an animal model for further characterization of these tumours.

Interferon-β Modulates the Innate Immune Response against Glioblastoma Initiating Cells

Immunotherapy targeting glioblastoma initiating cells (GIC) is considered a promising strategy. However, GIC are prone to evade immune response and there is a need for potent adjuvants. IFN-β might enhance the immune response and here we define its net effect on the innate immunogenicity of GIC. The transcriptomes of GIC treated with IFN-β and controls were assessed by microarray-based expression profiling for altered expression of immune regulatory genes. Several genes involved in adaptive and innate immune responses were regulated by IFN-β. We validated these results using reverse transcription (RT)-PCR and flow cytometry for corresponding protein levels. The up-regulation of the NK cell inhibitory molecules HLA-E and MHC class I was balanced by immune stimulating effects including the up-regulation of nectin-2. In 3 out of 5 GIC lines tested we found a net immune stimulating effect of IFN-β in cytotoxicity assays using NKL cells as effectors. IFN-β therefore warrants further investigation as an adjuvant for immunotherapy targeting GIC.

The study of glioma by xenotransplantation in zebrafish early life stages

Zebrafish (Danio rerio) and their transparent embryos are becoming an increasingly popular tool for studying processes involved in tumor progression and in the search for novel tumor treatment approaches. The xenotransplantation of fluorescently labeled mammalian cancer cells into zebrafish embryos is an approach enabling relatively high-throughput in vivo analyses. The small size of the embryos as well as the relative simplicity of their manipulation and maintenance allow for large numbers of embryos to be processed efficiently in a short time and at low cost. Furthermore, the possibility of fluorescence microscopic imaging of tumor progression within zebrafish embryos and larvae holds unprecedented potential for the real-time visualization of these processes in vivo. This review presents the methodologies of xenotransplantation studies on zebrafish involving research on tumor invasion, proliferation, tumor-induced angiogenesis and screening for antitumor therapeutics. We further focus on the application of these zebrafish to the study of glioma; in particular, its most common and malignant form, glioblastoma.

Targeting the bHLH transcriptional networks by mutated E proteins in experimental glioma

Glioblastomas (GB) are aggressive primary brain tumors. Helix-loop-helix (HLH, ID proteins) and basic HLH (bHLH, e.g., Olig2) proteins are transcription factors that regulate stem cell proliferation and differentiation throughout development and into adulthood. Their convergence on many oncogenic signaling pathways combined with the observation that their overexpression in GB correlates with poor clinical outcome identifies these transcription factors as promising therapeutic targets. Important dimerization partners of HLH/bHLH proteins are E proteins that are necessary for nuclear translocation and DNA binding. Here, we overexpressed a wild type or a dominant negative form of E47 (dnE47) that lacks its nuclear localization signal thus preventing nuclear translocation of bHLH proteins in long-term glioma cell lines and in glioma-initiating cell lines and analyzed the effects in vitro and in vivo. While overexpression of E47 was sufficient to induce apoptosis in absence of bHLH proteins, dnE47 was necessary to prevent nuclear translocation of Olig2 and to achieve similar proapoptotic responses. Transcriptional analyses revealed downregulation of the antiapoptotic gene BCL2L1 and the proproliferative gene CDC25A as underlying mechanisms. Overexpression of dnE47 in glioma-initiating cell lines with high HLH and bHLH protein levels reduced sphere formation capacities and expression levels of Nestin, BCL2L1, and CDC25A. Finally, the in vivo induction of dnE47 expression in established xenografts prolonged survival. In conclusion, our data introduce a novel approach to jointly neutralize HLH and bHLH transcriptional networks activities, and identify these transcription factors as potential targets in glioma.

MicroRNA Regulation of Brain Tumour Initiating Cells in Central Nervous System Tumours

CNS tumours occur in both pediatric and adult patients and many of these tumours are associated with poor clinical outcome. Due to a paradigm shift in thinking for the last several years, these tumours are now considered to originate from a small population of stem-like cells within the bulk tumour tissue. These cells, termed as brain tumour initiating cells (BTICs), are perceived to be regulated by microRNAs at the posttranscriptional/translational levels. Proliferation, stemness, differentiation, invasion, angiogenesis, metastasis, apoptosis, and cell cycle constitute some of the significant processes modulated by microRNAs in cancer initiation and progression. Characterization and functional studies on oncogenic or tumour suppressive microRNAs are made possible because of developments in sequencing and microarray techniques. In the current review, we bring recent knowledge of the role of microRNAs in BTIC formation and therapy. Special attention is paid to two highly aggressive and well-characterized brain tumours: gliomas and medulloblastoma. As microRNA seems to be altered in the pathogenesis of many human diseases, “microRNA therapy” may now have potential to improve outcomes for brain tumour patients. In this rapidly evolving field, further understanding of miRNA biology and its contribution towards cancer can be mined for new therapeutic tools.

A major role for microRNAs in glioblastoma cancer stem-like cells

Studies have demonstrated that miRNAs contribute to the maintenance and phenotype of in several cancer types. This review will focus on the roles of a few well studied miRNAs in cancer stem-like cells of glioblastoma.

Directional migration of adult hematopoeitic progenitors to C6 glioma in vitro

Multiform glioblastoma is the most common primary, highly invasive, malignant tumor of the central nervous system, with an extremely poor prognosis. The median survival of patients following surgical resection, radiation therapy and chemotherapy does not exceed 12–15 months and thus, novel approaches for the treatment of the disease are required. The phenomenon of the directed migration of stem cells in tumor tissue presents a novel approach for the development of technologies that facilitate the targeted delivery of drugs and other therapeutic agents to the tumor foci. Hematopoietic cluster of differentiation (CD)34⁺/CD133⁺ stem cells possess significant reparative potential and are inert with respect to normal neural tissue. The aim of the present study was to investigate the substantiation ability of adult hematopoietic progenitors to the directed migration of glioma cells. A C6 glioma cell line, a culture of hematopoietic CD34⁺/CD133⁺ stem cells and primary cultures of rat astrocytes and fibroblasts were used. The cells were co-cultured for five days. The results revealed the formation of cell shaft hematopoietic stem cells on the perimeter of the culture inserts containing the glioma culture. However, this was not observed in the wells with fibroblast and astrocyte cultures. The results indicated that hematopoietic stem cells exhibit a high potential for the directional migration of C6 glioma cells, which allows them to be considered as a promising cell line for the development of novel anticancer biomedical technologies and increases our understanding with regard to previously unclear aspects of glial tumor carcinogenesis.

Anatomic features of glioblastoma and their potential impact on survival

BACKGROUND

Many reports on glioblastoma multiforme discuss the prognostic impact of anatomical features such as cysts, necrotic changes, extent of edema or subependymal spread of tumor cells. In the present study, we examined different growth patterns and their possible relations to patient survival.

METHODS

To analyze whether anatomical characteristics are related to prognosis, we reviewed the prospectively collected pre- and postoperative MRIs of 83 patients in the 5-ALA study, provided by the 5-ALA Glioma Study Group. Following a standardized analytic work flow, the tumor volume and site, presence of necrosis or cysts, and perifocal edema were assessed preoperatively. In the same way, postoperative MRI and the MRI at first recurrence were analyzed. In addition, survival time of the patients was documented.

RESULTS

Median survival time of all 83 patients was 15.1 months (range 1.5 to 70.1, mean 18). The site or volume of glioblastoma, as well as the presence of intratumoral necrosis or cysts, did not exert a significant effect on survival time; 96.4 % of recurrences occurred within the former resection margin. Tumors with initial contact with the subependymal zone had multifocal or ventricular recurrences significantly more often. In patients with residual tumor on early postoperative MRI, the follow-up images displayed enlargement of the remnants in 91.9 % of these cases.

CONCLUSIONS

A merely anatomical analysis of the glioblastoma growth pattern cannot reliably provide prognostic information. The occurrence of most recurrences next to the resection margin and the high percentage of growing residual tumors underline the importance of complete resections.

New advances of microRNAs in glioma stem cells, with special emphasis on aberrant methylation of microRNAs

Malignant brain tumors are thought to be originate from a small population of cells that display stem cell properties, including the capacity of self-renewal, multipotent differentiation, initiation of tumor tissues. Cancer stem cells (CSCs) have been identified in gliomas in which they are named as glioma stem cells (GSCs). GSCs, sharing some characteristics with normal neural stem cells (NSCs), contribute to the cellular origin for primary gliomas and the recurrence of malignant gliomas after current conventional therapy. Recently, increasing evidences have showed that miRNAs play a central role in GSCs. In this review we focus on the role of GSCs in gliomas and in the abnomal expression of miRNAs in GSCs. Furthermore, we also discuss epigenetic dysregulation of tumor-suppressor miRNAs by promoter DNA methylation is involved in the regulation of GSCs biology. Recent advances in understanding dysregulated expression of miRNAs and methylation of tumor-suppressor miRNAs in GSCs and their possible use as new therapeutic targets of gliomas.

Metabolic profiling of dividing cells in live rodent brain by proton magnetic resonance spectroscopy (1HMRS) and LCModel analysis

Rationale

Dividing cells can be detected in the live brain by positron emission tomography or optical imaging. Here we apply proton magnetic resonance spectroscopy (¹HMRS) and a widely used spectral fitting algorithm to characterize the effect of increased neurogenesis after electroconvulsive shock in the live rodent brain via spectral signatures representing mobile lipids resonating at ∼1.30 ppm. In addition, we also apply the same ¹HMRS methodology to metabolically profile glioblastomas with actively dividing cells growing in RCAS-PDGF mice.

Methods

¹HMRS metabolic profiles were acquired on a 9.4T MRI instrument in combination with LCModel spectral analysis of: 1) rat brains before and after ECS or sham treatments and 2) RCAS-PDGF mice with glioblastomas and wild-type controls. Quantified ¹HMRS data were compared to post-mortem histology.

Results

Dividing cells in the rat hippocampus increased ∼3-fold after ECS compared to sham treatment. Quantification of hippocampal metabolites revealed significant decreases in N-acetyl-aspartate but no evidence of an elevated signal at ∼1.3 ppm (Lip13a+Lip13b) in the ECS compared to the sham group. In RCAS-PDGF mice a high density (22%) of dividing cells characterized glioblastomas. Nile Red staining revealed a small fraction (3%) of dying cells with intracellular lipid droplets in the tumors of RCAS-PDGF mice. Concentrations of NAA were lower, whereas lactate and Lip13a+Lip13b were found to be significantly higher in glioblastomas of RCAS-PDGF mice, when compared to normal brain tissue in the control mice.

Conclusions

Metabolic profiling using ¹HMRS in combination with LCModel analysis did not reveal correlation between Lip13a+Lip13b spectral signatures and an increase in neurogenesis in adult rat hippocampus after ECS. However, increases in Lip13a+Lip13b were evident in glioblastomas suggesting that a higher density of actively dividing cells and/or the presence of lipid droplets is necessary for LCModel to reveal mobile lipids.

On the Genesis of Neuroblastoma and Glioma

As the emergence of cancer is most frequent in proliferating tissues, replication errors are considered to be at the base of this disease. This review concentrates mainly on two neural cancers, neuroblastoma and glioma, with completely different backgrounds that are well documented with respect to their ontogeny. Although clinical data on other cancers of the nervous system are available, usually little can be said about their origins. Neuroblastoma is initiated in the embryo at a moment when the nervous system (NS) is in full expansion and occasionally genomic damage can lead to neoplasia. Glioma, to the contrary, occurs in the adult brain supposed to be mostly in a postmitotic state. According to current consensus, neural stem cells located in the subventricular zone (SVZ) in the adult are thought to accumulate enough genomic mutations to diverge on a carcinogenic course leading to diverse forms of glioma. After weighing the pros and cons of this current hypothesis in this review, it will be argued that this may be improbable, yielding to the original old concept of glial origin of glioma.

A disintegrin and metalloproteinases 10 and 17 modulate the immunogenicity of glioblastoma-initiating cells

BACKGROUND

There are emerging reports that the family of a disintegrin and metalloproteinases (ADAM) are involved in the maintenance of the malignant phenotype of glioblastomas. Notably, ADAM proteases 10 and 17 might impair the immune recognition of glioma cells via the activating immunoreceptor NKG2D by cleavage of its ligands from the cell surface. Glioblastoma-initiating cells (GIC) with stem cell properties have been identified as an attractive target for immunotherapy. However, GIC immunogenicity seems to be low.

METHODS AND RESULTS

Here,we show that ADAM10 and ADAM17 are expressed on the cell surface of GIC and contribute to an immunosuppressive phenotype by cleavage of ULBP2. The cell surface expression of ULBP2 is enhanced upon blocking ADAM10 and ADAM17, and treatment with ADAM10 and ADAM17specific inhibitors leads to enhanced immunerecognition of GIC by natural killer cells.

CONCLUSIONS

Therefore, ADAM10 and ADAM17 constitute suitable targets to boost an immune response against GIC.

Diagnostic immunohistochemistry of canine and feline intracalvarial tumors in the age of brain biopsies

The focus of immunohistochemistry as applied to nervous system tumors is in identifying the neoplasm present and evaluating margins between normal and neoplastic tissue. Although not always utilized by specialists in neuropathology, immunohistochemistry remains useful to resolve concerns about the differentiation and rate of tumor growth. The aims of this review are to discuss the utility of immunohistochemical reagents currently used in diagnosis of canine and feline intracalvarial tumors, to indicate the applicability of some tests currently used in human nervous system tumors for domestic species, and to evaluate a few less commonly used reagents. A panel of biomarkers is usually needed to confirm a diagnosis, with groups of reagents for leptomeningeal, intraparenchymal, and ventricular neoplasms. In the future, signature genetic alterations found among feline and canine brain tumors--as correlated prospectively with diagnosis, rate of enlargement, or response to treatment--may result in new immunohistochemical reagents to simplify the task of diagnosis. Prospective studies determining the type and proportion of stem cell marker expression on patient longevity are likely to be fruitful and suggest new therapies. Due to increased frequency of biopsy or partial resection of tumors from the living patient, biomarkers are needed to serve as accurate prognostic indicators and assist in determining the efficacy of developing therapeutic options in nervous system tumors of dogs and cats.

Topoisomerase I inhibitors, shikonin and topotecan, inhibit growth and induce apoptosis of glioma cells and glioma stem cells

Gliomas, the most malignant form of brain tumors, contain a small subpopulation of glioma stem cells (GSCs) that are implicated in therapeutic resistance and tumor recurrence. Topoisomerase I inhibitors, shikonin and topotecan, play a crucial role in anti-cancer therapies. After isolated and identified the GSCs from glioma cells successfully, U251, U87, GSCs-U251 and GSCs-U87 cells were administrated with various concentrations of shikonin or topotecan at different time points to seek for the optimal administration concentration and time point. The cell viability, cell cycle and apoptosis were detected using cell counting kit-8 and flow cytometer to observe the inhibitory effects on glioma cells and GSCs. We demonstrated that shikonin and topotecan obviously inhibited proliferation of not only human glioma cells but also GSCs in a dose- and time-dependent manner. According to the IC50 values at 24 h, 2 μmol/L of shikonin and 3 μmol/L of topotecan were selected as the optimal administration concentration. In addition, shikonin and topotecan induced cell cycle arrest in G0/G1 and S phases and promoted apoptosis. The down-regulation of Bcl-2 expression with the activation of caspase 9/3-dependent pathway was involved in the apoptosis process. Therefore, the above results showed that topoisomerase I inhibitors, shikonin and topotecan, inhibited growth and induced apoptosis of GSCs as well as glioma cells, which suggested that they might be the potential anticancer agents targeting gliomas to provide a novel therapeutic strategy.

Pivotal role for ROS activation of p38 MAPK in the control of differentiation and tumor-initiating capacity of glioma-initiating cells

Reactive oxygen species (ROS) are involved in various aspects of cancer cell biology, yet their role in cancer stem cells (CSCs) has been poorly understood. In particular, it still remains unclear whether and how ROS control the self-renewal/differentiation process and the tumor-initiating capacity of CSCs. Here we show that ROS-mediated activation of p38 MAPK plays a pivotal role in the control of differentiation and tumor-initiating capacity of glioma-initiating cells (GICs) derived from human glioblastomas. Mechanistically, ROS triggered p38-dependent Bmi1 protein degradation and FoxO3 activation in GICs, which were shown to be responsible for the loss of their self-renewal capacity and differentiation, respectively. Thus, the results suggest that Bmi1 and FoxO3 govern distinct phases of transition from undifferentiated to fully differentiated cells. Furthermore, we also demonstrate in this study that oxidative stress deprives GICs of their tumor-initiating capacity through the activation of the ROS-p38 axis. As such, this is the first study to the best of our knowledge to delineate how ROS control self-renewal/differentiation and the tumor-initiating capacity of stem-like cancer cells. This study also suggests that targeting of the ROS-p38 axis could be a novel approach in the development of therapeutic strategies against gliomas, represented by glioblastoma.

ADAM17 promotes U87 glioblastoma stem cell migration and invasion

Glioblastoma stem cells (GSCs) are thought to contribute to the diffuse invasiveness of malignant gliomas. Emerging evidence supports a role for a disintegrin and metalloproteinase 17 (ADAM17) in proteolytic ectodomain shedding of several EGFR-binding ligands, which subsequently activate PI3K/AKT and MEK/ERK pathways through EGFR phosphorylation thus mediating glioma invasiveness. However, it is not clear if ADAM17 also plays important roles in promoting GSC invasion. In this study, we isolated CD133+ GSCs from the human glioblastoma cell line U87 using fluorescence-activated cell sorting and demonstrated their increased invasive potential compared with matched non-stem tumor cells. Furthermore, we showed that CD133+ GSCs expressed higher levels of ADAM17. Immunofluorescence staining revealed that high expression levels of ADAM17 at the invasive front were correlated with the presence of CD133+ GSCs in human glioblastoma specimens. Stimulation with the ADAM17 agonist chemokine phorbol myristate acetate increased migration and invasion of GSCs, which was counteracted by ADAM17 knockdown. In addition, ADAM17 also induced CD133+ GSC invasion via activation of the EGFR/PI3K/AKT signaling pathway. These findings suggest that ADAM17 is involved in U87 GSC invasive process and may provide a potential therapeutic target for glioma treatment.

Akt and c-Myc induce stem-cell markers in mature primary p53⁻/⁻ astrocytes and render these cells gliomagenic in the brain of immunocompetent mice

Astrocytomas and their most malignant variant glioblastoma multiforme (GBM) represent the vast majority of primary brain tumors. Despite the current progress in neurosurgery, radiation therapy and chemotherapy, most astrocytomas remain fatal disorders. Although brain tumor biology is a matter of intense research, the cell-of-origin and the complete astrocytoma-inducing signaling pathway remain unknown. To further identify the mechanisms leading to gliomagenesis, we transduced primary astrocytes on a p53^−/− background with c-Myc, constitutively active myr-Akt or both, myr-Akt and c-Myc. Transduced astrocytes showed oncogene-specific alterations of morphology, proliferation and differentiation. Following prolonged periods of cultivation, oncogene-transduced astrocytes expressed several stem-cell markers. Furthermore, astrocytes coexpressing c-Myc and Akt were tumorigenic when implanted into the brain of immunocompetent C57BL/6 mice. Our results reveal that the loss of p53 combined with oncogene overexpression in mature astrocytes simulates pivotal features of glioma pathogenesis, providing a good model for assessing the development of secondary glioblastomas.

ADAM17 regulates self-renewal and differentiation of U87 glioblastoma stem cells

Glioblastoma stem cells (GSCs) play an important role in the progression and recurrence of malignant glioblastoma because of their potential for self-renewal, multilineage differentiation and tumor initiation. A disintegrin and metalloproteinase 17 (ADAM17) is responsible for the proteolytic cleavage of Notch within its extracellular domain leading to the activation of Notch signaling, which is involved in the formation and maintenance of GSCs. Here, we show that glioma cells expressing the stem cell marker CD133 coexpress higher levels of ADAM17 than matched CD133-glioma cells. Knockdown of the ADAM17 gene in U87 GSCs down-regulated the expression of CD133, inhibited secondary neurosphere formation and induced multi-lineage differentiation. Furthermore, knockdown of ADAM17 inhibited Hes1 and Hes5 and activated Notch1 expression, which may explain the ADAM17 shRNA-induced suppression of self-renewal and differentiation of U87 GSCs. Our results suggest that ADAM17 may maintain the stemness of GSCs by promoting their self-renewal and inhibiting their differentiation via Notch signaling.

Glioma stem cell-targeted dendritic cells as a tumor vaccine against malignant glioma

PURPOSE

Cancer stem cells have recently been thought to be closely related to tumor development and reoccurrence. It may be a promising way to cure malignant glioma by using glioma stem cell-targeted dendritic cells as a tumor vaccine. In this study, we explored whether pulsing dendritic cells with antigens of glioma stem cells was a potent way to induce specific cytotoxic T lymphocytes and anti-tumor immunity.

MATERIALS AND METHODS

Cancer stem cells were cultured from glioma cell line U251. Lysate of glioma stem cells was obtained by the repeated freezing and thawing method. Dendritic cells (DCs) were induced and cultured from the murine bone marrow cells, the biological characteristics were detected by electron microscope and flow cytometry. The DC vaccine was obtained by mixing DCs with lysate of glioma stem cells. The DC vaccine was charactirizated through the mixed lymphocyte responses and cell killing experiment in vitro. Level of interferon-γ (IFN-γ) in the supernatant was checked by ELISA.

RESULTS

After stimulation of lysate of glioma stem cell, expression of surface molecules of DC was up-regulated, including CD80, CD86, CD11C and MHC-II. DCs pulsed with lysate of glioma stem cells were more effective than the control group in stimulating original glioma cells-specific cytotoxic T lymphocytes responses, killing glioma cells and boosting the secretion of IFN-γ in vitro.

CONCLUSION

The results demonstrated DCs loaded with antigens derived from glioma stem cells can effectively stimulate naive T cells to form specific cytotoxic T cells, kill glioma cells cultured in vitro.

A new approach to screening cancer stem cells from the U251 human glioma cell line based on cell growth state

Cancer stem cells (CSCs) play important roles in the biological behaviour of malignant tumours. To study their properties, they must be carefully identified and purified. Cancer cells can acquire three different morphological types during single cell cloning. A small subpopulation of clones acquires a regular and compact shape, and these clones are enriched for CSCs; however, the majority of clones have an irregular morphology with loose intercellular junctions, with fewer characteristics of CSCs. At present, the main method to isolate CSCs is to collect the regular clones in low-density culture conditions; therefore, an insufficient amount of CSCs is obtained for clonal expansion. To obtain a more sufficient amount of CSCs, the clones with an irregular and loose morphology were examined in our study. We found a small subpopulation of U251 glioma cells that arrested in the suspended state and that subsequently migrated to form new clones. The suspended cells were isolated from the irregular and loose clones. Clonogenic assays were performed in which 43.70% of the suspended cells and 32.91% of the adherent cells formed new clones. To determine the biological differences between the suspended and adherent cells, carboxyfluorescein succinimidyl ester (CFSE) labelling, MTT assays, and cell cycle assays were performed. The results demonstrated that the suspended cells had the characteristics of CSCs, including higher proliferation rates, as well as self-maintenance and self-renewal capabilities, and they stained positively for markers of brain CSCs and had multilineage potential. Thus, we established a new and efficient approach for screening CSCs from the U251 human glioma cell line based on the cell growth state.

Glioma-initiating cell elimination by metformin activation of FOXO3 via AMPK

Control of the cancer stem/initiating cell population is considered key to realizing the long-term survival of glioblastoma patients. Recently, we demonstrated that FOXO3 activation is sufficient to induce differentiation of glioma-initiating cells having stem-like properties and inhibit their tumor-initiating potential. Here we identified metformin, an antidiabetic agent, as a therapeutic activator of FOXO3. Metformin activated FOXO3 and promoted differentiation of such stem-like glioma-initiating cells into nontumorigenic cells. Furthermore, metformin promoted FOXO3 activation and differentiation via AMP-activated protein kinase (AMPK) activation, which was sensitive to extracellular glucose availability. Importantly, transient, systemic administration of metformin depleted the self-renewing and tumor-initiating cell population within established tumors, inhibited tumor formation by stem-like glioma-initiating cells in the brain, and provided a substantial survival benefit. Our findings demonstrate that targeting glioma-initiating cells via the AMPK-FOXO3 axis is a viable therapeutic strategy against glioblastoma, with metformin being the most clinically relevant drug ever reported for targeting of glioma-initiating cells. Our results also establish a novel, direct link between glucose metabolism and cancer stem/initiating cells.

Glioma-initiating cell elimination by metformin activation of FOXO3 via AMPK

Control of the cancer stem/initiating cell population is considered key to realizing the long-term survival of glioblastoma patients. Recently, we demonstrated that FOXO3 activation is sufficient to induce differentiation of glioma-initiating cells having stem-like properties and inhibit their tumor-initiating potential. Here we identified metformin, an antidiabetic agent, as a therapeutic activator of FOXO3. Metformin activated FOXO3 and promoted differentiation of such stem-like glioma-initiating cells into nontumorigenic cells. Furthermore, metformin promoted FOXO3 activation and differentiation via AMP-activated protein kinase (AMPK) activation, which was sensitive to extracellular glucose availability. Importantly, transient, systemic administration of metformin depleted the self-renewing and tumor-initiating cell population within established tumors, inhibited tumor formation by stem-like glioma-initiating cells in the brain, and provided a substantial survival benefit. Our findings demonstrate that targeting glioma-initiating cells via the AMPK-FOXO3 axis is a viable therapeutic strategy against glioblastoma, with metformin being the most clinically relevant drug ever reported for targeting of glioma-initiating cells. Our results also establish a novel, direct link between glucose metabolism and cancer stem/initiating cells.