Biology of glioma cancer stem cells

Ion channel expression and function in glioblastoma multiforme (GBM): pathophysiological mechanisms and therapeutic potential

Glioblastoma Multiforme (GBM) is a highly malignant and diffusely invasive WHO Grade IV brain tumor arising from glial and neural stem cells. GBM is characterized by rapid proliferation and migration, aggressive invasion of local brain parenchyma, a hypoxic microenvironment, resistance to apoptosis and high vascular remodeling and angiogenesis. These hallmarks contribute to a near universal tumor recurrence after treatment or resection and poor patient prognosis. Ion channels, a superfamily of proteins responsible for permitting ion flux across otherwise impermeant membranes, show extensive remodeling in GBM with aberrant function mechanistically linked to manipulation of each of these hallmarks. In this review, we will discuss the known links between ion channel expression and activity and cellular processes that are enhanced or perturbed during GBM formation or progression. We will also discuss the extent to which basic or translational findings on ion channels in GBM samples or cell lines have shown preclinical promise towards the development of improved therapeutics against GBMs.

Increased oxygen stimulation promotes chemoresistance and phenotype shifting through PLCB1 in gliomas

Gliomas, the most common CNS (central nerve system) tumors, face poor survival due to severe chemoresistance exacerbated by hypoxia. However, studies on whether altered hypoxic conditions benefit for chemo-sensitivity and how gliomas react to increased oxygen stimulation are limited. In this study, we demonstrated that increased oxygen stimulation promotes glioma growth and chemoresistance. Mechanically, increased oxygen stimulation upregulates miR-1290 levels. miR-1290, in turn, downregulates PLCB1, while PLCB1 facilitates the proteasomal degradation of β-catenin and active-β-catenin by increasing the proportion of ubiquitinated β-catenin in a destruction complex-independent mechanism. This process inhibits PLCB1 expression, leads to the accumulation of active-β-catenin, boosting Wnt signaling through an independent mechanism and ultimately promoting chemoresistance in glioma cells. Pharmacological inhibition of Wnt by WNT974 could partially inhibit glioma volume growth and prolong the shortened survival caused by increased oxygen stimulation in a glioma-bearing mouse model. Moreover, PLCB1, a key molecule regulated by increased oxygen stimulation, shows promising predictive power in survival analysis and has great potential to be a biomarker for grading and prognosis in glioma patients. These results provide preliminary insights into clinical scenarios associated with altered hypoxic conditions in gliomas, and introduce a novel perspective on the role of the hypoxic microenvironment in glioma progression. Furthermore, the outcomes reveal the potential risks of utilizing hyperbaric oxygen treatment (HBOT) in glioma patients, particularly when considering HBOT as a standalone option to ameliorate neuro-dysfunctions or when combining HBOT with a single chemotherapy agent without radiotherapy.

CD57 defines a novel cancer stem cell that drive invasion of diffuse pediatric-type high grade gliomas

BACKGROUND

Diffuse invasion remains a primary cause of treatment failure in pediatric high-grade glioma (pHGG). Identifying cellular driver(s) of pHGG invasion is needed for anti-invasion therapies.

METHODS

Ten highly invasive patient-derived orthotopic xenograft (PDOX) models of pHGG were subjected to isolation of matching pairs of invasive (HGGINV) and tumor core (HGGTC) cells.

RESULTS

pHGGINV cells were intrinsically more invasive than their matching pHGGTC cells. CSC profiling revealed co-positivity of CD133 and CD57 and identified CD57+CD133- cells as the most abundant CSCs in the invasive front. In addition to discovering a new order of self-renewal capacities, i.e., CD57+CD133- > CD57+CD133+ > CD57-CD133+ > CD57-CD133- cells, we showed that CSC hierarchy was impacted by their spatial locations, and the highest self-renewal capacities were found in CD57+CD133- cells in the HGGINV front (HGGINV/CD57+CD133- cells) mediated by NANOG and SHH over-expression. Direct implantation of CD57+ (CD57+/CD133- and CD57+/CD133+) cells into mouse brains reconstituted diffusely invasion, while depleting CD57+ cells (i.e., CD57-CD133+) abrogated pHGG invasion.

CONCLUSION

We revealed significantly increased invasive capacities in HGGINV cells, confirmed CD57 as a novel glioma stem cell marker, identified CD57+CD133- and CD57+CD133+ cells as a new cellular driver of pHGG invasion and suggested a new dual-mode hierarchy of HGG stem cells.

Gliomagenesis is orchestrated by the Oct3/4 regulatory network

BACKGROUND

Glioblastoma multiforme (GBM) is a lethal brain tumor characterized by developmental hierarchical phenotypic heterogeneity, therapy resistance and recurrent growth. Neural stem cells (NSCs) from human central nervous system (CNS), and glioblastoma stem cells from patient-derived GBM (pdGSC) samples were cultured in both 2D well-plate and 3D monoclonal neurosphere culture system (pdMNCS). The pdMNCS model shows promise to establish a relevant 3D-tumor environment that maintains GBM cells in the stem cell phase within suspended neurospheres.

METHODS

Utilizing the pdMNCS, we examined GBM cell-lines for a wide spectrum of developmental cancer stem cell markers, including the early blastocyst inner-cell mass (ICM)-specific Nanog, Oct3/4,B, and CD133.

RESULTS

We observed that MNCS epigenotype is recapitulated using gliomasphere-derived cells. CD133, the marker of GSC is robustly expressed in 3D-gliomaspheres and localized within the plasma membrane compartment. Conversely, gliomasphere cultures grown in conventional 2D culture quickly lost CD133 expression, indicating its variable expression is dependent on cell-culture conditions. Incomplete differentiation of cytoskeleton microtubules and intermediate filaments (IFs) of patient derived cells, similar to commercially available GBM cell lines, was seen. Subsequently, in order to determine whether Oct3/4 it was necessary for CD133 expression and cancer stemness, we transfected 2D and 3D culture with siRNA against Oct3/4 and found a significant reduction in gliomasphere formation.

CONCLUSIONS

These results suggest that expression of Oct3/4,A- and CD133 suppress differentiation of GSCs.

The impact of MEIS1 TALE homeodomain transcription factor knockdown on glioma stem cell growth

Myeloid ecotropic virus insertion site 1 (MEIS1) is a HOX co-factor necessary for organ development and normal hematopoiesis. Recently, MEIS1 has been linked to the development and progression of various cancers. However, its role in gliomagenesis particularly on glioma stem cells (GSCs) remains unclear. Here, we demonstrate that MEIS1 is highly upregulated in GSCs compared to normal, and glioma cells and to its differentiated counterparts. Inhibition of MEIS1 expression by shRNA significantly reduced GSC growth in both in vitro and in vivo experiments. On the other hand, integrated transcriptomics analyses of glioma datasets revealed that MEIS1 expression is correlated to cell cycle-related genes. Clinical data analysis revealed that MEIS1 expression is elevated in high-grade gliomas, and patients with high MEIS1 levels have poorer overall survival outcomes. The findings suggest that MEIS1 is a prognostic biomarker for glioma patients and a possible target for developing novel therapeutic strategies against GBM.

Establishing Brain Tumor Stem Cell Culture from Patient Brain Tumors and Imaging Analysis of Patient-Derived Xenografts

Brain tumor stem cells (BTSCs) have been isolated from different types of brain tumors including glioblastoma. Although BTSCs share common characteristics with neural stem cells (NSCs), such as capacity to self-renew and undergo long-term proliferation, they have tumor-propagating capabilities. A small population of BTSC can give rise to secondary tumor when transplanted into severe immunodeficient (SCID) mice. The histological and cytological features, as well as genetic heterogeneity of the xenografted tumors in mice, closely resemble those of primary tumors in patients. Patient-derived xenografts (PDX), therefore, provide a clinically relevant model to study brain tumors. Here, we describe our protocol for establishing BTSC cultures following surgical excision of human brain tumors and the procedures to conduct PDX studies in SCID mice. We also provide our detailed step-by-step protocol on in vivo imaging system (IVIS) of the PDX tumors as a noninvasive method to trace the cells and tumor volume.

Isolation of Cells from Glioblastoma Multiforme Grade 4 Tumors for Infection with Zika Virus prME and ME Pseudotyped HIV-1

This study aimed to isolate cells from grade 4 glioblastoma multiforme tumors for infection experiments with Zika virus (ZIKV) prME or ME enveloped HIV-1 pseudotypes. The cells obtained from tumor tissue were successfully cultured in human cerebrospinal fluid (hCSF) or a mixture of hCSF/DMEM in cell culture flasks with polar and hydrophilic surfaces. The isolated tumor cells as well as the U87, U138, and U343 cells tested positive for ZIKV receptors Axl and Integrin αvβ5. Pseudotype entry was detected by the expression of firefly luciferase or green fluorescent protein (gfp). In prME and ME pseudotype infections, luciferase expression in U-cell lines was 2.5 to 3.5 logarithms above the background, but still two logarithms lower than in the VSV-G pseudotype control. Infection of single cells was successfully detected in U-cell lines and isolated tumor cells by gfp detection. Even though prME and ME pseudotypes had low infection rates, pseudotypes with ZIKV envelopes are promising candidates for the treatment of glioblastoma.

Molecular mechanism(s) of regulations of cancer stem cell in brain cancer propagation

Brain tumors are most often diagnosed with solid neoplasms and are the primary reason for cancer-related deaths in both children and adults worldwide. With recent developments in the progression of novel targeted chemotherapies, the prognosis of malignant glioma remains dismal. However, the high recurrence rate and high mortality rate remain unresolved and are closely linked to the biological features of cancer stem cells (CSCs). Research on tumor biology has reached a new age with more understanding of CSC features. CSCs, a subpopulation of whole tumor cells, are now regarded as candidate therapeutic targets. Therefore, in the diagnosis and treatment of tumors, recognizing the biological properties of CSCs is of considerable significance. Here, we have discussed the concept of CSCs and their significant role in brain cancer growth and propagation. We have also discussed personalized therapeutic development and immunotherapies for brain cancer by specifically targeting CSCs.

A Quality Control Mechanism of Splice Site Selection Abrogated under Stress and in Cancer

Simple Summary

Splicing and alternative splicing play a major role in regulating gene expression, and mis-regulation of splicing can lead to several diseases, including cancer. The aim of this review is to summarize the current knowledge of a quality control mechanism of splice site selection termed Suppression of Splicing (SOS), proposed to protect cells from splicing at the numerous intronic unused 5′ splice sites, and emphasize its relevance to cancer. This relevance stems from the finding that SOS is abrogated under stress and in cancer resulting in the expression of thousands of aberrant nonsense mRNAs that may be toxic to cells. These findings highlight the unexplored potential of such aberrant isoforms as novel targets for cancer diagnosis and therapies.

Abstract

Latent 5’ splice sites, highly abundant in human introns, are not normally used. This led to the proposal of a quality control mechanism, Suppression of Splicing (SOS), which protects cells from splicing at the numerous intronic latent sites, and whose activation can generate nonsense mRNAs. SOS was shown to be independent of Nonsense-Mediated mRNA Decay (NMD). Efforts to decipher the SOS mechanism revealed a pivotal role for initiator-tRNA, independent of protein translation. Recently, nucleolin (a multifunctional protein) was found to directly and specifically bind the initiator-tRNA in the nucleus and was shown to be a protein component of SOS, enabling an updated model of the SOS mechanism. Importantly, SOS is abrogated under stress and in cancer (e.g., in breast cancer cells and gliomas), generating thousands of nonsense mRNAs due to activation of latent splicing. The resulting affected human genes cover a variety of functional groups, including genes involved in cell proliferation and differentiation. Furthermore, in oligodendroglioma, the extent of activation of latent splicing increases with the severity of the cancer. Interesting examples are genes expressing aberrant nonsense mRNAs in both breast cancer and glioma, due to latent splicing activation. These findings highlight the unexplored potential of such aberrant isoforms as novel targets for cancer diagnosis and therapies.

PIM1 Inhibition Affects Glioblastoma Stem Cell Behavior and Kills Glioblastoma Stem-like Cells

Despite comprehensive therapy and extensive research, glioblastoma (GBM) still represents the most aggressive brain tumor in adults. Glioma stem cells (GSCs) are thought to play a major role in tumor progression and resistance of GBM cells to radiochemotherapy. The PIM1 kinase has become a focus in cancer research. We have previously demonstrated that PIM1 is involved in survival of GBM cells and in GBM growth in a mouse model. However, little is known about the importance of PIM1 in cancer stem cells. Here, we report on the role of PIM1 in GBM stem cell behavior and killing. PIM1 inhibition negatively regulates the protein expression of the stem cell markers CD133 and Nestin in GBM cells (LN-18, U-87 MG). In contrast, CD44 and the astrocytic differentiation marker GFAP were up-regulated. Furthermore, PIM1 expression was increased in neurospheres as a model of GBM stem-like cells. Treatment of neurospheres with PIM1 inhibitors (TCS PIM1-1, Quercetagetin, and LY294002) diminished the cell viability associated with reduced DNA synthesis rate, increased caspase 3 activity, decreased PCNA protein expression, and reduced neurosphere formation. Our results indicate that PIM1 affects the glioblastoma stem cell behavior, and its inhibition kills glioblastoma stem-like cells, pointing to PIM1 targeting as a potential anti-glioblastoma therapy.

Radiotherapy versus combination radiotherapy-bevacizumab for the treatment of recurrent high-grade glioma: a systematic review

Background

High-grade gliomas (HGG) comprise the most common primary adult brain cancers and universally recur. Combination of re-irradiation therapy (reRT) and bevacizumab (BVZ) therapy for recurrent HGG is common, but its reported efficacy is mixed.

Objective

To assess clinical outcomes after reRT ± BVZ in recurrent HGG patients receiving stereotactic radiosurgery (SRS), hypofractionated radiosurgery (HFSRT), or fully fractionated radiotherapy (FFRT).

Methods

We performed a systematic review of PubMed, Web of Science, Scopus, Embase, and Cochrane databases, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We identified studies reporting outcomes for patients with recurrent HGG treated via reRT ± BVZ. Cohorts were stratified by BVZ treatment status and re-irradiation modality (SRS, HFSRT, and FFRT). Outcome variables were overall survival (OS), progression-free survival (PFS), and radiation necrosis (RN).

Results

Data on 1399 patients was analyzed, with 954 patients receiving reRT alone and 445 patients receiving reRT + BVZ. All patients initially underwent standard-of-care therapy for their primary HGG. In a multivariate analysis that adjusted for median patient age, WHO grade, RT dosing, reRT fractionation regimen, time between primary and re-irradiation, and re-irradiation target volume, BVZ therapy was associated with significantly improved OS (2.51, 95% CI [0.11, 4.92] months, P = .041) but no significant improvement in PFS (1.40, 95% CI [− 0.36, 3.18] months, P = .099). Patients receiving BVZ also had significantly lower rates of RN (2.2% vs 6.5%, P < .001).

Conclusions

Combination of reRT + BVZ may improve OS and reduce RN rates in recurrent HGG, but further controlled studies are needed to confirm these effects.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00701-021-04794-3.

Photocrosslinked Bioreducible Polymeric Nanoparticles for Enhanced Systemic siRNA Delivery as Cancer Therapy

Clinical translation of polymer-based nanocarriers for systemic delivery of RNA has been limited due to poor colloidal stability in the blood stream and intracellular delivery of the RNA to the cytosol. To address these limitations, this study reports a new strategy incorporating photocrosslinking of bioreducible nanoparticles for improved stability extracellularly and rapid release of RNA intracellularly. In this design, the polymeric nanocarriers contain ester bonds for hydrolytic degradation and disulfide bonds for environmentally triggered small interfering RNA (siRNA) release in the cytosol. These photocrosslinked bioreducible nanoparticles (XbNPs) have a shielded surface charge, reduced adsorption of serum proteins, and enable superior siRNA-mediated knockdown in both glioma and melanoma cells in high-serum conditions compared to non-crosslinked formulations. Mechanistically, XbNPs promote cellular uptake and the presence of secondary and tertiary amines enables efficient endosomal escape. Following systemic administration, XbNPs facilitate targeting of cancer cells and tissue-mediated siRNA delivery beyond the liver, unlike conventional nanoparticle-based delivery. These attributes of XbNPs facilitate robust siRNA-mediated knockdown in vivo in melanoma tumors colonized in the lungs following systemic administration. Thus, biodegradable polymeric nanoparticles, via photocrosslinking, demonstrate extended colloidal stability and efficient delivery of RNA therapeutics under physiological conditions, and thereby potentially advance systemic delivery technologies for nucleic acid-based therapeutics.

The Development and Applications of a Dual Optical Imaging System for Studying Glioma Stem Cells

Glioblastoma multiforme represents one of the deadliest brain tumor types, manifested by a high rate of recurrence and poor prognosis. The presence of glioma stem cells (GSCs) can repopulate the tumor posttreatment and resist therapeutics. A better understanding of GSC biology is essential for developing more effective interventions. We established a CD133 promoter-driven dual reporter, expressing green fluorescent protein (GFP) and firefly luciferase (CD133-LG), capable for in vitro and in vivo imaging of CD133+ GSCs. We first demonstrated the reporter enabled in vitro analyses of GSCs. DBTRG-05MG (Denver Brain Tumor Research Group 05) carrying CD133-LG (DBTRG-05MG-CD133-LG) system reported increased GFP/luciferase activities in neurospheres. Additionally, we identified and isolated CD133+/GFP+ cells with increased tumorigenic properties, stemness markers, Notch1, β-catenin, and Bruton’s tyrosine kinase (Btk). Furthermore, prolonged temozolomide (TMZ) treatment enriched GSCs (reflected by increased percentage of CD133+ cells). Subsequently, Btk inhibitor, ibrutinib, suppressed GSC generation and stemness markers. Finally, we demonstrated real-time evaluation of anti-GSC function of ibrutinib in vivo with TMZ-enriched GSCs. Tumorigenesis was noninvasively monitored by bioluminescence imaging and mice that received ibrutinib showed a significantly lower tumor burden, indicating ibrutinib as a potential GSC inhibitor. In conclusion, we established a dual optical imaging system which enables the identification of CD133+ GSCs and screening for anti-GSC drugs.

Elucidating the pathogenic and biomarker potentials of FOXG1 in glioblastoma

Glioblastoma (GB) is an extremely pugnacious brain cancer originating from neural stem (NS) cell-like cells. Forkhead box G1 (FOXG1; previously recognized as BF-1, qin, Chicken Brain Factor 1, or XBF-1 and renamed FOXG1 for mouse and human, and FoxG1 for other chordates) is an evolutionary preserved transcription factor driven from the forkhead box group of proteins FOXG1 modulates the speed of neurogenesis by maintaining progenitor cells in a proliferative mode as well as obstructing their differentiation into neurons during the initial periods of cortical formation. FOXG1 has been implicated in the formation of central nervous system (CNS) tumors and precisely GBs. Pathophysiologically, joint actions of FOXG1 and phosphatidylinositol- 3-kinases (PI3K) intermediate in intrinsic resistance of human GB cells to transforming growth factor-beta (TGF-β) stimulation of cyclin-dependent kinase inhibitor 1(p21Cip1) as well as growth inhibition. FOXG1 and NOTCH signaling pathways may functionally interrelate at different stages to facilitate gliomagenesis. Furthermore, FoxG1 actively contributed to the formation of transcription suppression complexes with corepressors of the Groucho/transducin-like Enhancer of split (Gro/TLEs). Also, FOXG1 was stimulated by Gro/TLE1 and abridged by Grg6. FOXG1 silencing in brain tumor-initiating cells (BTICs) also resulted in diminished secretion of markers characteristic undifferentiated natural neural stem/progenitor cells (NSPC) states, such as Oligodendrocyte transcription factor (OLIG2), (sex determining region Y)-box 2. (SOX2) and B lymphoma Mo-MLV insertion region 1 homolog (BMI1). This review therefore focuses on the pathogenic and biomarker potentials of FOXG1 in GB.

Retinoid receptor turnover mediated by sumoylation, ubiquitination and the valosin-containing protein is disrupted in glioblastoma

Resistance to therapeutic use of retinoids in glioma has been observed for over 20 years; however, the exact mechanism of resistance remains unknown. To understand retinoic acid resistance in glioma, we studied the turnover mechanism of retinoid receptor proteins in neural stem cells and glioma stem-like cells. Here, we show that in normal neural stem cells, proteasomal degradation of retinoid receptors involves sumoylation, ubiquitination and recognition by the valosin-containing protein (VCP/p97/Cdc48). We find that Sumo1 modification has a dual role to stabilize the retinoid receptor from unwanted degradation and signal additional modification via ubiquitination. Subsequently, the modified receptor binds to the VCP chaperone and both proteins are degraded by the proteasome. Additionally, we reveal that all trans retinoic acid (ATRA) induces VCP expression, creating a positive feedback loop that enhances degradation. In contrast, the pathway is impaired in the glioma stem-like cells resulting in the accumulation of sumoylated and high molecular weight forms of retinoid receptors that lack transcriptional activity and fail to be recognized by the proteasome. Moreover, modified receptor accumulation occurs before ATRA treatment; therefore, the transcritptional defect in glioma is due to a block in the proteasomal degradation pathway that occurs after the sumo modification step.

Dexamethasone in Glioblastoma Multiforme Therapy: Mechanisms and Controversies

Glioblastoma multiforme (GBM) is the most common and malignant of the glial tumors. The world-wide estimates of new cases and deaths annually are remarkable, making GBM a crucial public health issue. Despite the combination of radical surgery, radio and chemotherapy prognosis is extremely poor (median survival is approximately 1 year). Thus, current therapeutic interventions are highly unsatisfactory. For many years, GBM-induced brain oedema and inflammation have been widely treated with dexamethasone (DEX), a synthetic glucocorticoid (GC). A number of studies have reported that DEX also inhibits GBM cell proliferation and migration. Nevertheless, recent controversial results provided by different laboratories have challenged the widely accepted dogma concerning DEX therapy for GBM. Here, we have reviewed the main clinical features and genetic and epigenetic abnormalities underlying GBM. Finally, we analyzed current notions and concerns related to DEX effects on cerebral oedema, cancer cell proliferation and migration and clinical outcome.

MMP-2 expression and correlation with pathology and MRI of glioma

The expression of matrix metalloproteinase-2 (MMP-2) in brain glioma and its correlation with patients' clinicopathological characteristics and magnetic resonance imaging (MRI) features were investigated. A total of 104 patients with brain glioma admitted and treated in the First Affiliated Hospital of Anhui Medical University from June 2010 to September 2014 were randomly enrolled. MRI examination was performed before operation. Immunohistochemistry (IHC) was used to detect the expression levels of MMP-2 in brain glioma tissues and paired normal brain tissues after operation and to analyze the associations of MMP-2 expression with the clinicopathological characteristics of brain glioma and survival time of patients. The relationship between MMP-2 expression and preoperative MRI features of glioma was analyzed. The positive rate of MMP-2 expression in brain glioma was 73.08% (76/104), while that in paired normal brain tissues was only 12.5% (13/104), obviously lower than that in brain glioma tissues (P<0.05). The MMP-2 expression in the body of glioma was not related to the patients' sex, age, tumor location and pathological type (P>0.05), but there was a significant correlation with the tumor diameter and pathological grade of the patients (P<0.05). Analysis by Cox model suggested that tumor diameter, pathological grade and MMP-2 were independent prognostic factors for glioma (P<0.05). The overall survival (OS) of patients in the positive MMP-2 expression group was 16.4 months, while the OS in the negative MMP-2 expression group was 20.16 months, and the difference between the two groups was statistically significant (P<0.05). The positive expression of MMP-2 in glioma was closely related to the uniformity of MRI signal for tumor, tumor diameter, severity of peritumoral edema, degree of enhancement and pathological grade of tumor (P<0.05). MMP-2 is highly expressed in brain glioma, and it is a negative factor for prognosis. Therefore, the MRI manifestations of glioma can reflect to some extent the intensity of MMP-2 expression.

Targetome Analysis Revealed Involvement of MiR-126 in Neurotrophin Signaling Pathway: A Possible Role in Prevention of Glioma Development

OBJECTIVES

For the first time, we used molecular signaling pathway enrichment analysis to determine possible involvement of miR-126 and IRS-1 in neurotrophin pathway.

MATERIALS AND METHODS

In this prospective study, Validated and predicted targets (targetome) of miR-126 were collected following searching miRtarbase (http://mirtarbase.mbc.nctu.edu.tw/) and miRWalk 2.0 databases, respectively. Then, approximate expression of miR-126 targeting in Glioma tissue was examined using UniGene database (http://www.ncbi. nlm.nih.gov/unigene). In silico molecular pathway enrichment analysis was carried out by DAVID 6.7 database (http://david. abcc.ncifcrf.gov/) to explore which signaling pathway is related to miR-126 targeting and how miR-126 attributes to glioma development.

RESULTS

MiR-126 exerts a variety of functions in cancer pathogenesis via suppression of expression of target gene including PI3K, KRAS, EGFL7, IRS-1 and VEGF. Our bioinformatic studies implementing DAVID database, showed the involvement of miR-126 target genes in several signaling pathways including cancer pathogenesis, neurotrophin functions, Glioma formation, insulin function, focal adhesion production, chemokine synthesis and secretion and regulation of the actin cytoskeleton.

CONCLUSIONS

Taken together, we concluded that miR-126 enhances the formation of glioma cancer stem cell probably via down regulation of IRS-1 in neurotrophin signaling pathway.

The p38 signaling pathway mediates quiescence of glioma stem cells by regulating epidermal growth factor receptor trafficking

EGFR pathway is upregulated in malignant gliomas, and its downstream signaling is important for self-renewal of glioma cancer stem-like cells (GSC). p38 mitogen-activated protein kinase (MAPK) signaling, a stress-activated signaling cascade with suppressive and permissive effects on tumorigenesis, can promote internalization and ubiquitin ligase mediated degradation of EGFR. In this study, we investigated the role of p38 MAPK signaling on the self-renewal of GSCs with the hypothesis that inhibition may lead to enhanced self-renewal capacity by retention of EGFR. Inhibition of p38 MAPK pathway led to increase in EGFR expression but surprisingly, reduced proliferation. Additional functional evaluation revealed that p38 inhibition was associated with decrease in cell death and maintenance of undifferentiated state. Further probing the effect of p38 inhibition demonstrated attenuation of EGFR downstream signaling activity in spite of prolonged surface expression of the receptor. In vitro observations were confirmed in xenograft in vivo experiments. These data suggest that p38 MAPK control of EGFR signaling activity may alter GSC cell cycle state by regulating quiescence and passage into transit amplifying state.

Activation of PPARγ mediates icaritin-induced cell cycle arrest and apoptosis in glioblastoma multiforme

BACKGROUND

Glioblastoma multiforme (GBM) is the most prevalent primary malignancy of the brain. This study was designed to investigate whether icaritin exerts anti-neoplastic activity against GBM in vitro.

MATERIALS AND METHODS

Cell Counting Kit-8 (CCK-8) assay was utilized to examine the viability of GBM cells. The apoptotic cell population was measured by flow cytometry analysis. Cell cycle distribution was detected by flow cytometry as well. Western blot analysis was performed to examine the level of biomarker proteins in GBM cells. Levels of PPARγ mRNA and protein were detected by qPCR and western blot analysis, respectively. To examine the role of PPARγ in the anti-neoplastic activity of icaritin, PPARγ antagonist GW9662 or PPARγ siRNA was used. The activity of PPARγ was determined by DNA binding and luciferase assays.

RESULTS

Our findings revealed that icaritin markedly suppresses cell growth in a dose-dependent and time-dependent fashion. The cell population at the G0/G1 phase of the cell cycle was significantly increased following icaritin treatment. Meanwhile, icaritin promoted apoptotic cell death in T98G and U87MG cells. Further investigation showed upregulation of PPARγ played a key role in the anti-neoplastic activities of icaritin. Moreover, our result demonstrated activation of AMPK signaling by icaritin mediated the modulatory effect of icaritin on PPARγ.

CONCLUSION

Our results suggest the PPARγ may mediate anti-neoplastic activities against GBM.

Therapeutic targeting of chemoresistant and recurrent glioblastoma stem cells with a proapoptotic variant of oncolytic herpes simplex virus

Temozolomide (TMZ) chemotherapy, in combination with maximal safe resection and radiotherapy, is the current standard of care for patients with glioblastoma (GBM). Despite this multimodal approach, GBM inevitably relapses primarily due to resistance to chemo-radiotherapy, and effective treatment is not available for recurrent disease. In this study we identified TMZ resistant patient-derived primary and previously treated recurrent GBM stem cells (GSC), and investigated the therapeutic activity of a pro-apoptotic variant of oHSV (oHSV-TRAIL) in vitro and in vivo. We show that oHSV-TRAIL modulates cell survival and MAP Kinase proliferation signaling pathways as well as DNA damage response pathways in both primary and recurrent TMZ-resistant GSC. Utilizing real time in vivo imaging and correlative immunohistochemistry, we show that oHSV-TRAIL potently inhibits tumor growth and extends survival of mice bearing TMZ-insensitive recurrent intracerebral GSC tumors via robust and selective induction of apoptosis-mediated death in tumor cells, resulting in cures in 40% of the treated mice. In comparison, the anti-tumor effects in a primary chemoresistant GSC GBM model exhibiting a highly invasive phenotype were significant but less prominent. This work thus demonstrates the ability of oHSV-TRAIL to overcome the therapeutic resistance and recurrence of GBM, and provides a basis for its testing in a GBM clinical trial.

Hypoxia in the glioblastoma microenvironment: shaping the phenotype of cancer stem-like cells

Glioblastoma is the most common and aggressive malignant primary brain tumor. Cellular heterogeneity is a characteristic feature of the disease and contributes to the difficulty in formulating effective therapies. Glioma stem-like cells (GSCs) have been identified as a subpopulation of tumor cells that are thought to be largely responsible for resistance to treatment. Intratumoral hypoxia contributes to maintenance of the GSCs by supporting the critical stem cell traits of multipotency, self-renewal, and tumorigenicity. This review highlights the interaction of GSCs with the hypoxic tumor microenvironment, exploring the mechanisms underlying the contribution of GSCs to tumor vessel dynamics, immune modulation, and metabolic alteration.

Notch3 signaling-mediated melanoma-endothelial crosstalk regulates melanoma stem-like cell homeostasis and niche morphogenesis

Melanoma is among the most virulent cancers, owing to its propensity to metastasize and its resistance to current therapies. The treatment failure is largely attributed to tumor heterogeneity, particularly subpopulations possessing stem cell-like properties, ie, melanoma stem-like cells (MSLCs). Evidence indicates that the MSLC phenotype is malleable and may be acquired by non-MSLCs through phenotypic switching upon appropriate stimuli, the so-called 'dynamic stemness'. Since the phenotypic characteristics and functional integrity of MSLCs depend on their vascular niche, using a two-dimensional (2D) melanoma-endothelium co-culture model, where the MSLC niche is recapitulated in vitro, we identified Notch3 signaling pathway as a micro-environmental cue governing MSLC phenotypic plasticity via pathway-specific gene expression arrays. Accordingly, lentiviral shRNA-mediated Notch3 knockdown (KD) in melanoma cell lines exhibiting high levels of endogenous Notch3 led to retarded/abolished tumorigenicity in vivo through both depleting MSLC fractions, evinced by MSLC marker downregulation (eg, CD133 and CD271); and impeding the MSLC niche, corroborated by the attenuated tumor angiogenesis as well as vasculogenic mimicry. In contrast, Notch3 KD affected neither tumor growth nor MSLC subsets in a melanoma cell line with relatively low endogenous Notch3 expression. Thus, Notch3 signaling may facilitate MSLC plasticity and niche morphogenesis in a cell context-dependent manner. Our findings illustrate Notch3 as a molecular switch driving melanoma heterogeneity, and provide the biological rationale for Notch inhibition as a promising therapeutic option.

TRIM8 regulates stemness in glioblastoma through PIAS3-STAT3

Glioblastoma (GBM) is the most malignant form of primary brain tumor, and GBM stem-like cells (GSCs) contribute to the rapid growth, therapeutic resistance, and clinical recurrence of these fatal tumors. STAT3 signaling supports the maintenance and proliferation of GSCs, yet regulatory mechanisms are not completely understood. Here, we report that tri-partite motif-containing protein 8 (TRIM8) activates STAT3 signaling to maintain stemness and self-renewing capabilities of GSCs. TRIM8 (also known as 'glioblastoma-expressed ring finger protein') is expressed equally in GBM and normal brain tissues, despite its hemizygous deletion in the large majority of GBMs, and its expression is highly correlated with stem cell markers. Experimental knockdown of TRIM8 reduced GSC self-renewal and expression of SOX2, NESTIN, and p-STAT3, and promoted glial differentiation. Overexpression of TRIM8 led to higher expression of p-STAT3, c-MYC, SOX2, NESTIN, and CD133, and enhanced GSC self-renewal. We found that TRIM8 activates STAT3 by suppressing the expression of PIAS3, an inhibitor of STAT3, most likely through E3-mediated ubiquitination and proteasomal degradation. Interestingly, we also found that STAT3 activation upregulates TRIM8, providing a mechanism for normalized TRIM8 expression in the setting of hemizygous gene deletion. These data demonstrate that bidirectional TRIM8-STAT3 signaling regulates stemness in GSC.

Icaritin Sensitizes Human Glioblastoma Cells to TRAIL-Induced Apoptosis

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been considered to be one of the most promising candidates in research on treatments for cancer, because it induces apoptosis in a wide variety of cancer cells but not in most normal human cell types. However, many cells including glioblastoma (GBM) cells are resistant to TRAIL-induced apoptosis, which limits the potential application of TRAIL in cancer therapy. Icaritin, a hydrolytic product of icariin from Epimedium Genus, has been identified as a potential therapeutic and preventive agent in renal cell carcinoma and breast cancer. In this study, we investigated whether Icaritin treatment could modulate TRAIL-induced apoptosis in GBM. The effect of icaritin on TRAIL sensitivity was assessed in human GBM U87 and U373 cells. The underlying regulatory cascades were approached by biochemical and pharmacological strategies. We found that nontoxic concentration of icaritin alone had no significant effect on the level of apoptosis, but a combination treatment of TRAIL and icaritin caused a significantly more profound apoptosis. The sensitization was accompanied by c-FLIP down-regulation and inhibition of NF-κB activity. Studies have further demonstrated that silencing NF-κB alone was sufficient to down-regulate c-FLIP expression and sensitized both tested cells to TRAIL-induced apoptosis. These data suggest that icaritin sensitizes TRAIL-induced tumor cell apoptosis via suppression of NF-κB-dependent c-FLIP expression, providing in vitro evidence supporting the notion that icaritin is a potential sensitizer of TRAIL in anticancer therapy against human GBM.

An update on the epigenetics of glioblastomas

Glioblastomas, also known as glioblastoma multiforme (GBM), are the most aggressive and malignant type of primary brain tumor in adults, exhibiting notable variability at the histopathological, genetic and epigenetic levels. Recently, epigenetic alterations have emerged as a common hallmark of many tumors, including GBM. Considering that a deeper understanding of the epigenetic modifications that occur in GBM may increase the knowledge regarding the tumorigenesis, progression and recurrence of this disease, in this review we discuss the recent major advances in GBM epigenetics research involving histone modification, glioblastoma stem cells, DNA methylation, noncoding RNAs expression, including their main alterations and the use of epigenetic therapy as a valid option for GBM treatment.

Translational potential of astrocytes in brain disorders

Fundamentally, all brain disorders can be broadly defined as the homeostatic failure of this organ. As the brain is composed of many different cells types, including but not limited to neurons and glia, it is only logical that all the cell types/constituents could play a role in health and disease. Yet, for a long time the sole conceptualization of brain pathology was focused on the well-being of neurons. Here, we challenge this neuron-centric view and present neuroglia as a key element in neuropathology, a process that has a toll on astrocytes, which undergo complex morpho-functional changes that can in turn affect the course of the disorder. Such changes can be grossly identified as reactivity, atrophy with loss of function and pathological remodeling. We outline the pathogenic potential of astrocytes in variety of disorders, ranging from neurotrauma, infection, toxic damage, stroke, epilepsy, neurodevelopmental, neurodegenerative and psychiatric disorders, Alexander disease to neoplastic changes seen in gliomas. We hope that in near future we would witness glial-based translational medicine with generation of deliverables for the containment and cure of disorders. We point out that such as a task will require a holistic and multi-disciplinary approach that will take in consideration the concerted operation of all the cell types in the brain.

Mesenchymal stem cell-like properties of CD133+ glioblastoma initiating cells

Glioblastoma is composed of dividing tumor cells, stromal cells and tumor initiating CD133+ cells. Recent reports have discussed the origin of the glioblastoma CD133+ cells and their function in the tumor microenvironment. The present work sought to investigate the multipotent and mesenchymal properties of primary highly purified human CD133+ glioblastoma-initiating cells. To accomplish this aim, we used the following approaches: i) generation of tumor subspheres of CD133+ selected cells from primary cell cultures of glioblastoma; ii) analysis of the expression of pluripotency stem cell markers and mesenchymal stem cell (MSC) markers in the CD133+ glioblastoma-initiating cells; iii) side-by-side ultrastructural characterization of the CD133+ glioblastoma cells, MSC and CD133+ hematopoietic stem cells isolated from human umbilical cord blood (UCB); iv) assessment of adipogenic differentiation of CD133+ glioblastoma cells to test their MSC-like in vitro differentiation ability; and v) use of an orthotopic glioblastoma xenograft model in the absence of immune suppression. We found that the CD133+ glioblastoma cells expressed both the pluripotency stem cell markers (Nanog, Mush-1 and SSEA-3) and MSC markers. In addition, the CD133+ cells were able to differentiate into adipocyte-like cells. Transmission electron microscopy (TEM) demonstrated that the CD133+ glioblastoma-initiating cells had ultrastructural features similar to those of undifferentiated MSCs. In addition, when administered in vivo to non-immunocompromised animals, the CD133+ cells were also able to mimic the phenotype of the original patient's tumor. In summary, we showed that the CD133+ glioblastoma cells express molecular signatures of MSCs, neural stem cells and pluripotent stem cells, thus possibly enabling differentiation into both neural and mesodermal cell types.

Concise review: bullseye: targeting cancer stem cells to improve the treatment of gliomas by repurposing disulfiram

Cancer stem cells (CSCs) are thought to be at the root of cancer recurrence because they resist conventional therapies and subsequently reinitiate tumor cell growth. Thus, targeting CSCs could be the bullseye to successful cancer therapeutics in the future. Brain tumors are some of the most challenging types of cancer to treat and the median survival following the initial diagnosis is 12-18 months. Among the different types of brain tumors, glioblastoma (GBM) is considered the most aggressive and remains extremely difficult to treat. Despite surgery, radiation, and chemotherapy, most patients develop refractory disease. Temozolomide (TMZ) is a chemotherapy used to treat GBM however resistance develops in most patients. The underlying mechanisms for TMZ resistance (TMZ-resistant) involve the expression of DNA repair gene O(6)-methylguanine-DNA methyltransferase. CSC genes such as Sox-2, BMI-1, and more recently Y-box binding protein-1 also play a role in resistance. In order to develop novel therapies for GBM, libraries of small interfering RNAs and off-patent drugs have been screened. Over the past few years, several independent laboratories identified disulfiram (DSF) as an off-patent drug that kills GBM CSCs. Reportedly DSF has several modes of action including its ability to inhibit aldehyde dehydrogenases, E3 ligase, polo-like kinase 1, and NFkB. Due to the fact that GBM is a disease of heterogeneity, chemotherapy with multitargeting properties may be the way of the future. In broader terms, DSF kills CSCs from a range of different cancer types further supporting the idea of repurposing it for "target practice."

Paramagnetic albumin decorated CuInS2/ZnS QDs for CD133+ glioma bimodal MR/fluorescence targeted imaging

A sensitive, specific, accurate and biocompatible molecular nanoprobe is constructed, by rational design of the structure and an advanced surface engineering strategy, with MR/fluorescence imaging modalities for CD133⁺ glioma bimodal targeted imaging.

Expression of ZFX gene correlated with the central features of the neoplastic phenotype in human brain tumors with distinct phenotypes

Background:

The zinc finger transcription factor zinc finger protein, X-linked (ZFX) acts as an important director of self-renewal in several stem cell types. Moreover, ZFX expression abnormally increases in various cancers and relates to tumor grade. We performed this study, to examine its role in the pathogenesis of astrocytoma and meningioma.

Materials and Methods:

We used real-time reverse transcription polymerase chain reaction method for evaluation of ZFX expression in 25 astrocytoma tumoral tissue and 25 meningioma tumoral tissues with different WHO grades. Furthermore, the association of gene expression with various clinic-pathological characteristics was examined.

Results:

We found that there is a significant association between gene expression and different tumor grades, the presence or absence of invasion, forming and nonforming of glomeruloid vessels, the age over or under 50 and the presence or absence of calcification in astrocytomas. This is the first report that shows that ZFX was directly correlated with the central features of the neoplastic phenotype, including the growth of cancer cells, angiogenesis, and invasion.

Conclusion:

Regarding all the above-mentioned studies, it is highly plausible that silencing the expression of ZFX gene in gliomas has a major role in the therapeutic interventions of the disease in future.

The role of glioma stem cells in chemotherapy resistance and glioblastoma multiforme recurrence

Glioma stem cells (GSCs) constitute a slow-dividing, small population within a heterogeneous glioblastoma. They are able to self-renew, recapitulate a whole tumor, and differentiate into other specific glioblastoma multiforme (GBM) subpopulations. Therefore, they have been held responsible for malignant relapse after primary standard therapy and the poor prognosis of recurrent GBM. The failure of current therapies to eliminate specific GSC subpopulations has been considered a major factor contributing to the inevitable recurrence in GBM patients after treatment. Here, we discuss the molecular mechanisms of chemoresistance of GSCs and the reasons why complete eradication of GSCs is so difficult to achieve. We will also describe the targeted therapies currently available for GSCs and possible mechanisms to overcome such chemoresistance and avoid therapeutic relapse.

Isolation, cultivation and identification of brain glioma stem cells by magnetic bead sorting

This study describes a detailed process for obtaining brain glioma stem cells from freshly dissected human brain glioma samples using an immunomagnetic bead technique combined with serum-free media pressure screening. Furthermore, the proliferation, differentiation and self-renewal biological features of brain glioma stem cells were identified. Results showed that a small number of CD133 positive tumor cells isolated from brain glioma samples survived as a cell suspension in serum-free media and proliferated. Subcultured CD133 positive cells maintained a potent self-renewal and proliferative ability, and expressed the stem cell-specific markers CD133 and nestin. After incubation with fetal bovine serum, the number of glial fibrillary acidic protein and microtubule associated protein 2 positive cells increased significantly, indicating that the cultured brain glioma stem cells can differentiate into astrocytes and neurons. Western blot analysis showed that tumor suppressor phosphatase and tensin homolog was highly expressed in tumor spheres compared with the differentiated tumor cells. These experimental findings indicate that the immunomagnetic beads technique is a useful method to obtain brain glioma stem cells from human brain tumors.

The LIM-only transcription factor LMO2 determines tumorigenic and angiogenic traits in glioma stem cells

Glioblastomas (GBMs) maintain their cellular heterogeneity with glioma stem cells (GSCs) producing a variety of tumor cell types. Here we interrogated the oncogenic roles of Lim domain only 2 (LMO2) in GBM and GSCs in mice and human. High expression of LMO2 was found in human patient-derived GSCs compared with the differentiated progeny cells. LMO2 is required for GSC proliferation both in vitro and in vivo, as shRNA-mediated LMO2 silencing attenuated tumor growth derived from human GSCs. Further, LMO2 is sufficient to induce stem cell characteristics (stemness) in mouse premalignant astrocytes, as forced LMO2 expression facilitated in vitro and in vivo growth of astrocytes derived from Ink4a/Arf null mice and acquisition of GSC phenotypes. A subset of mouse and human GSCs converted into vascular endothelial-like tumor cells both in vitro and in vivo, which phenotype was attenuated by LMO2 silencing and promoted by LMO2 overexpression. Mechanistically, the action of LMO2 for induction of glioma stemness is mediated by transcriptional regulation of Jagged1 resulting in activation of the Notch pathway, whereas LMO2 directly occupies the promoter regions of the VE-cadherin gene for a gain of endothelial cellular phenotype. Subsequently, selective ablation of human GSC-derived VE-cadherin-expressing cells attenuated vascular formation in mouse intracranial tumors, thereby significantly prolonging mouse survival. Clinically, LMO2 expression was elevated in GBM tissues and inversely correlated with prognosis of GBM patients. Taken together, our findings describe novel dual roles of LMO2 to induce tumorigenesis and angiogenesis, and provide potential therapeutic targets in GBMs.

Expression of a-disintegrin and metalloproteinase 10 correlates with grade of malignancy in human glioma

The aim of the present study was to determine the expression of a-disintegrin and metalloproteinase 10 (ADAM10) in human glioma tissues from surgical specimens and discuss its possible significance in glioma biology. A total of 43 glioma specimens obtained from patients between 2007 and 2010 were collected and a series of assays were performed. Of these, 22 cases were low-grade gliomas, while 21 cases were high-grade gliomas. In addition, 20 cases of meningioma were used as the control group. Reverse transcription-polymerase chain reaction (RT-PCR), western blot analysis and immunohistochemistry were used to determine the mRNA and protein expression levels of ADAM10. Besides the quantitative analysis, histological observations were also performed to localize ADAM10 expression in glioma cells. The RT-PCR and western blot analysis results demonstrated increased ADAM10 expression in the low-grade glioma samples compared with the control (P<0.05), while ADAM10 expression was further increased in the high-grade glioma samples (P<0.01 vs. control; P<0.05 vs. low-grade glioma), indicating that the mRNA and protein expression levels of ADAM10 were malignancy-dependent. The immunohistochemical analysis revealed that the ADAM10 protein was located on both the tumor cell membrane and blood vessel walls within tumor tissues. In conclusion, these results indicated that ADAM10 expression correlates with the grade of malignancy in human glioma from surgical specimens. In addition, the fact that ADAM10 protein was expressed on cell membranes and blood vessel walls within tumor tissues, indicates that its expression may be associated with invasive tumor growth and peritumoral edema formation.

CD38 is a putative functional marker for side population cells in human nasopharyngeal carcinoma cell lines

Cancer stem cells (CSCs) are thought to be responsible for cancer progression and therapeutic resistance but identification of this subpopulation requires selective markers. Fortunately, side population (SP) cells analysis brings a novel method to CSCs study. In this study, we identified SP cells, which are demonstrated rich in CSCs, in four nasopharyngeal carcinoma (NPC) cell lines. We investigated SP cells from HK-1 NPC cell line and showed CSCs characteristics in this subpopulation. SP cells displayed greater proliferation and invasion and expressed high levels of CSCs markers than NSP cells. Furthermore, our microRNA microarray analysis of SP versus NSP cells revealed that CD38-related miRNAs were down-regulated in SP cell, but the mRNA and protein level of CD38 were highly expressed in SP cells. We further searched for molecules interacting with CD38 and identified ZAP70, which was also well expressed in SP cells at both mRNA and protein levels. Our results uncover a CD38 pathway that may regulate the proliferation and migration of SP cells from HK-1 NPC cell line.

The evidence of glioblastoma heterogeneity

Cancers are composed of heterogeneous combinations of cells that exhibit distinct phenotypic characteristics and proliferative potentials. Because most cancers have a clonal origin, cancer stem cells (CSCs) must generate phenotypically diverse progenies including mature CSCs that can self-renew indefinitely and differentiated cancer cells that possess limited proliferative potential. However, no convincing evidence exists to suggest that only single CSCs are representative of patients' tumors. To investigate the CSCs' diversity, we established 4 subclones from a glioblastoma patient. These subclones were subsequently propagated and analyzed. The morphology, the self-renewal and proliferative capacities of the subclones differed. Fluorescence-activated cell sorting and cDNA-microarray analyses revealed that each subclone was composed of distinct populations of cells. Moreover, the sensitivities of the subclones to an inhibitor of epidermal growth factor receptor were dissimilar. In a mouse model featuring xenografts of the subclones, the progression and invasion of tumors and animal survival were also different. Here, we present clear evidence that a brain tumor contains heterogeneous subclones that exhibit dissimilar morphologies and self-renewal and proliferative capacities. Our results suggest that single cell-derived subclones from a patient can produce phenotypically heterogeneous self-renewing progenies in both in vitro and in vivo settings.

Selective calcium sensitivity in immature glioma cancer stem cells

Tumor-initiating cells are a subpopulation in aggressive cancers that exhibit traits shared with stem cells, including the ability to self-renew and differentiate, commonly referred to as stemness. In addition, such cells are resistant to chemo- and radiation therapy posing a therapeutic challenge. To uncover stemness-associated functions in glioma-initiating cells (GICs), transcriptome profiles were compared to neural stem cells (NSCs) and gene ontology analysis identified an enrichment of Ca²⁺ signaling genes in NSCs and the more stem-like (NSC-proximal) GICs. Functional analysis in a set of different GIC lines regarding sensitivity to disturbed homeostasis using A23187 and Thapsigargin, revealed that NSC-proximal GICs were more sensitive, corroborating the transcriptome data. Furthermore, Ca²⁺ drug sensitivity was reduced in GICs after differentiation, with most potent effect in the NSC-proximal GIC, supporting a stemness-associated Ca²⁺ sensitivity. NSCs and the NSC-proximal GIC line expressed a larger number of ion channels permeable to potassium, sodium and Ca²⁺. Conversely, a higher number of and higher expression levels of Ca²⁺ binding genes that may buffer Ca²⁺, were expressed in NSC-distal GICs. In particular, expression of the AMPA glutamate receptor subunit GRIA1, was found to associate with Ca²⁺ sensitive NSC-proximal GICs, and decreased as GICs differentiated along with reduced Ca²⁺ drug sensitivity. The correlation between high expression of Ca²⁺ channels (such as GRIA1) and sensitivity to Ca²⁺ drugs was confirmed in an additional nine novel GIC lines. Calcium drug sensitivity also correlated with expression of the NSC markers nestin (NES) and FABP7 (BLBP, brain lipid-binding protein) in this extended analysis. In summary, NSC-associated NES⁺/FABP7⁺/GRIA1⁺ GICs were selectively sensitive to disturbances in Ca²⁺ homeostasis, providing a potential target mechanism for eradication of an immature population of malignant cells.

Silencing BMI1 eliminates tumor formation of pediatric glioma CD133+ cells not by affecting known targets but by down-regulating a novel set of core genes

Clinical outcome of children with malignant glioma remains dismal. Here, we examined the role of over-expressed BMI1, a regulator of stem cell self-renewal, in sustaining tumor formation in pediatric glioma stem cells. Our investigation revealed BMI1 over-expression in 29 of 54 (53.7%) pediatric gliomas, 8 of 8 (100%) patient derived orthotopic xenograft (PDOX) mouse models, and in both CD133⁺ and CD133⁻ glioma cells. We demonstrated that lentiviral-shRNA mediated silencing of suppressed cell proliferation in vitro in cells derived from 3 independent PDOX models and eliminated tumor-forming capacity of CD133⁺ and CD133⁻ cells derived from 2 PDOX models in mouse brains. Gene expression profiling showed that most of the molecular targets of BMI1 ablation in CD133⁺ cells were different from that in CD133- cells. Importantly, we found that silencing BMI1 in CD133⁺ cells derived from 3 PDOX models did not affect most of the known genes previously associated with the activated BMI1, but modulated a novel set of core genes, including RPS6KA2, ALDH3A2, FMFB, DTL, API5, EIF4G2, KIF5c, LOC650152, C20ORF121, LOC203547, LOC653308, and LOC642489, to mediate the elimination of tumor formation. In summary, we identified the over-expressed BMI1 as a promising therapeutic target for glioma stem cells, and suggest that the signaling pathways associated with activated BMI1 in promoting tumor growth may be different from those induced by silencing BMI1 in blocking tumor formation. These findings highlighted the importance of careful re-analysis of the affected genes following the inhibition of abnormally activated oncogenic pathways to identify determinants that can potentially predict therapeutic efficacy.

Sevoflurane promotes the expansion of glioma stem cells through activation of hypoxia-inducible factors in vitro

BACKGROUND

Growing evidences indicate that inhalational anaesthetics can enhance the growth and malignant potential of tumour cells and may affect tumour recurrence after surgery. Tumour stem cells play a vital role in tumour recurrence. This study investigates the effect of sevoflurane on glioma stem cells (GSCs) in vitro and the underlying molecular mechanisms in this process.

METHODS

Cultured GSCs were exposed to clinically relevant concentrations and durations of sevoflurane exposure. Cell proliferation and self-renewal capacity were determined. Expression of the stem cell marker CD133, vascular endothelial growth factor (VEGF), hypoxia-inducible factors (HIFs), and phosphorylated Akt, which is a protein kinase invoved in multiple cellular processes, were measured using western blotting. Small interfering RNAs and an Akt inhibitor were used to investigate specific pathways.

RESULTS

Compared with controls, cells exposed to 2% sevoflurane for 6 h induced a larger number of proliferated cells (31.2±7.6% vs 19.0±5.8%; P<0.01). Levels of CD133, VEGF, HIF-1α, HIF-2α, and p-Akt were up-regulated by sevoflurane in a time- and concentration-dependent manner. Small interfering RNA against HIFs decreased the percentage of proliferating GSCs after sevoflurane exposure and pre-treatment of cells with an Akt inhibitor abrogated the expression of HIFs induced by sevoflurane.

CONCLUSIONS

Sevoflurane can promote the expansion of human GSCs through HIFs in vitro. Inhaled anaesthetics may enhance tumour growth through tumour stem cells.

Knockdown of nuclear factor erythroid 2-related factor 2 by lentivirus induces differentiation of glioma stem-like cells

Glioma stem cells (GSCs) are key in the progression and recurrence of glioblastoma. Inducing the differentiation of GSCs is an important therapeutic target for glioblastoma. Nuclear factor erythroid 2-related factor 2 (Nrf2) has been reported to be important in maintaining the stem cell status of GSCs; however, its association with differentiation has not been studied. Herein, we knocked down Nrf2 from GSCs to investigate the role of Nrf2 in the differentiation of GSCs. First, Nrf2 expression was observed at different stages of differentiation; then, Nrf2 was knocked down and the association of Nrf2 with differentiation degree was observed in vitro. Finally, GSCs were planted in nude mice to study the association of Nrf2 with differentiation in vivo. The expression of Nrf2 decreased with the differentiation process. Following Nrf2 knockdown, the proportion of sphere-like colonies decreased and the dendritic cells in spheres increased; the expression of Nrf2 significantly decreased while the expression of differentiation marker glial fibrillary acidic protein (GFAP) and βIII-tubulin increased both at the protein and the gene level. In the xenografts of nude mice, the differentiation of tumor cells was improved. These results suggest that Nrf2 is a key factor inhibiting the differentiation of GSCs, and knockdown of Nrf2 may promote the differentiation process, providing a therapy target for GSCs.

Transcription factors FOXG1 and Groucho/TLE promote glioblastoma growth

Glioblastoma (GBM) is the most common and deadly malignant brain cancer, with a median survival of less than two years. GBM displays a cellular complexity that includes brain tumour-initiating cells (BTICs), which are considered as potential key targets for GBM therapies. Here we show that the transcription factors FOXG1 and Groucho/TLE are expressed in poorly differentiated astroglial cells in human GBM specimens and in primary cultures of GBM-derived BTICs, where they form a complex. FOXG1 knockdown in BTICs causes downregulation of neural stem/progenitor and proliferation markers, increased replicative senescence, upregulation of astroglial differentiation genes, and decreased BTIC-initiated tumour growth upon intracranial transplantation into host mice. These effects are phenocopied by Groucho/TLE knockdown or dominant-inhibition of the FOXG1:Groucho/TLE complex. These results provide evidence that transcriptional programs regulated by FOXG1 and Groucho/TLE are important for BTIC-initiated brain tumour growth, implicating FOXG1 and Groucho/TLE in GBM tumorigenesis.

Brain barriers and a subpopulation of astroglial progenitors of developing human forebrain are immunostained for the glycoprotein YKL-40

YKL-40, a glycoprotein involved in cell differentiation, has been associated with neurodevelopmental disorders, angiogenesis, neuroinflammation and glioblastomas. We evaluated YKL-40 protein distribution in the early human forebrain using double-labeling immunofluorescence and immunohistochemistry. Immunoreactivity was detected in neuroepithelial cells, radial glial end feet, leptomeningeal cells and choroid plexus epithelial cells. The subpial marginal zone was YKL-40-positive, particularly in the hippocampus, from an early beginning stage in its development. Blood vessels in the intermediate and subventricular zones showed specific YKL-40 reactivity confined to pericytes. Furthermore, a population of YKL-40-positive, small, rounded cells was identified in the ventricular and subventricular zones. Real-time quantitative RT-PCR analysis showed strong YKL-40 mRNA expression in the leptomeninges and the choroid plexuses, and weaker expression in the telencephalic wall. Immunohistochemistry revealed a differential distribution of YKL-40 across the zones of the developing telencephalic wall. We show that YKL-40 is associated with sites of the brain barrier systems and propose that it is involved in controlling local angiogenesis and access of peripheral cells to the forebrain via secretion from leptomeningeal cells, choroid plexus epithelium and pericytes. Furthermore, we suggest that the small, rounded, YKL-40-positive cells represent a subpopulation of astroglial progenitors, and that YKL-40 could be involved in the differentiation of a particular astrocytic lineage.

CD133-targeted niche-dependent therapy in cancer: a multipronged approach

Cancer treatment continues to be challenged by the development of therapeutic resistances and relapses in the clinical setting, which are largely attributed to tumor heterogeneity, particularly the existence of cancer stem cells (CSCs). Thus, targeting the CSC subpopulation may represent an effective therapeutic strategy. However, despite advances in identifying and characterizing CD133(+) CSCs in various human cancers, efforts to translate these experimental findings to clinical modalities have been slow in the making, especially in light of the growing awareness of CSC plasticity and the foreseeable pitfall of therapeutically targeting CSC base sorely on a surface marker. We, and others, have demonstrated that the CD133(+) CSCs reside in complex vascular niches, where reciprocal signaling between the CD133(+) CSCs and their microenvironment may govern niche morphogenesis and homeostasis. Herein, we discuss the multifaceted functional role of the CD133(+) cells in the context of their niche, and the potential of targeting CD133 as a niche-dependent approach in effective therapy.

The ID proteins: master regulators of cancer stem cells and tumour aggressiveness

Inhibitor of DNA binding (ID) proteins are transcriptional regulators that control the timing of cell fate determination and differentiation in stem and progenitor cells during normal development and adult life. ID genes are frequently deregulated in many types of human neoplasms, and they endow cancer cells with biological features that are hijacked from normal stem cells. The ability of ID proteins to function as central 'hubs' for the coordination of multiple cancer hallmarks has established these transcriptional regulators as therapeutic targets and biomarkers in specific types of human tumours.

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.