Culture and Isolation of Brain Tumor Initiating Cells

ETS-Domain Transcription Factor Elk-1 Regulates Stemness Genes in Brain Tumors and CD133+ BrainTumor-Initiating Cells

Elk-1, a member of the ternary complex factors (TCFs) within the ETS (E26 transformation-specific) domain superfamily, is a transcription factor implicated in neuroprotection, neurodegeneration, and brain tumor proliferation. Except for known targets, c-fos and egr-1, few targets of Elk-1 have been identified. Interestingly, SMN, SOD1, and PSEN1 promoters were shown to be regulated by Elk-1. On the other hand, Elk-1 was shown to regulate the CD133 gene, which is highly expressed in brain-tumor-initiating cells (BTICs) and used as a marker for separating this cancer stem cell population. In this study, we have carried out microarray analysis in SH-SY5Y cells overexpressing Elk-1-VP16, which has revealed a large number of genes significantly regulated by Elk-1 that function in nervous system development, embryonic development, pluripotency, apoptosis, survival, and proliferation. Among these, we have shown that genes related to pluripotency, such as Sox2, Nanog, and Oct4, were indeed regulated by Elk-1, and in the context of brain tumors, we further showed that Elk-1 overexpression in CD133+ BTIC population results in the upregulation of these genes. When Elk-1 expression is silenced, the expression of these stemness genes is decreased. We propose that Elk-1 is a transcription factor upstream of these genes, regulating the self-renewal of CD133+ BTICs.

Inhibition of DHFR targets the self-renewing potential of brain tumor initiating cells

Brain tumors are a heterogeneous group of benign and malignant tumors arising from the brain parenchyma and its surrounding structures, with in general a poor clinical outcome due to high recurrence. One of the underlying causes for this somber prognostic is the presence of brain tumor initiating cells (BTIC) endowed with self-renewal potential, multi-lineage differentiation and resistance to treatment. One promising therapeutic avenue for brain tumors is targeting BTIC self-renewal potential and forcing their differentiation. A compelling candidate is one-carbon metabolism shown to play a key role in maintaining stem cell self-renewal in several lineages. Here, we focus on dihydrofolate reductase (DHFR), a key enzyme in one-carbon metabolism, and demonstrate this enzyme's overexpression in several human brain tumors and its expression in human BTIC. We show that DHFR inhibition, either by Methotrexate (MTX) or EphB activation with synthetic ligands, reduces the tumorigenic potential of 4 human BTIC lines, by reducing their self-renewal capacities both in vitro and in a cerebral organoid glioma (GLICO) model. Our data indicate that driving BTIC differentiation by inhibiting DHFR may provide a new therapeutic approach to treating highly refractory aggressive tumors.

Feasibility of Targeting Glioblastoma Stem Cells: From Concept to Clinical Trials

OBJECTIVE

Glioblastoma is a highly aggressive and invasive brain and Central Nervous System (CNS) tumor. Current treatment options do not prolong overall survival significantly because the disease is highly prone to relapse. Therefore, research to find new therapies is of paramount importance. It has been discovered that glioblastomas contain a population of cells with stem-like properties and that these cells are may be responsible for tumor recurrence.

METHODS

A review of relevant papers and clinical trials in the field was conducted. A PubMed search with related keywords was used to gather the data. For example, "glioblastoma stem cells AND WNT signaling" is an example used to find information on clinical trials using the database ClinicalTrials.gov.

RESULTS

Cancer stem cell research has several fundamental issues and uncertainties that should be taken into consideration. Theoretically, a number of treatment options that target glioblastoma stem cells are available for patients. However, only a few of them have obtained promising results in clinical trials. Several strategies are still under investigation.

CONCLUSION

The majority of treatments to target cancer stem cells have failed during clinical trials. Taking into account a number of biases in the field and the number of unsuccessful investigations, the application of the cancer stem cells concept is questionable in clinical settings, at least with respect to glioblastoma.

Genetic Abnormalities, Clonal Evolution, and Cancer Stem Cells of Brain Tumors

Brain tumors are highly heterogeneous and have been classified by the World Health Organization in various histological and molecular subtypes. Gliomas have been classified as ranging from low-grade astrocytomas and oligodendrogliomas to high-grade astrocytomas or glioblastomas. These tumors are characterized by a peculiar pattern of genetic alterations. Pediatric high-grade gliomas are histologically indistinguishable from adult glioblastomas, but they are considered distinct from adult glioblastomas because they possess a different spectrum of driver mutations (genes encoding histones H3.3 and H3.1). Medulloblastomas, the most frequent pediatric brain tumors, are considered to be of embryonic derivation and are currently subdivided into distinct subgroups depending on histological features and genetic profiling. There is emerging evidence that brain tumors are maintained by a special neural or glial stem cell-like population that self-renews and gives rise to differentiated progeny. In many instances, the prognosis of the majority of brain tumors remains negative and there is hope that the new acquisition of information on the molecular and cellular bases of these tumors will be translated in the development of new, more active treatments.

miR-497/Wnt3a/c-jun feedback loop regulates growth and epithelial-to-mesenchymal transition phenotype in glioma cells

Glioma is one of the most frequent intracranial malignant tumors. Abnormal expression of microRNAs usually contributes to the development and progression of glioma. In the current study, we explored the role and underlying mechanism of miR-497 in glioma. We revealed that miR-497 expression was significantly down-regulated in glioma tissues and cell lines. Reduced expression of miR-497 was associated with poor disease-free and over-all survival rate. Restoration of miR-497 decreased glioma cell growth and invasion both in vitro and in vivo. The oncogene Wnt3a was identified as a downstream target of miR-497 by using luciferase and western blot assays. Knockdown of Wnt3a mimicked the effect of miR-497 in glioma cells. In summary, our study demonstrated that miR-497 may function as a tumor suppressor in glioma and suggested that miR-497 is a potential therapeutic target for glioma patients.

Methylation-mediated silencing of microRNA-211 promotes cell growth and epithelial to mesenchymal transition through activation of the AKT/β-catenin pathway in GBM

Aberrant expression of miR-211 has frequently been reported in cancer studies; however, its role in glioblastoma multiforme (GBM) has not been examined in detail. We investigated the function and the underlying mechanism of miR-211 in GBM. We revealed that miR-211 was downregulated in GBM tissues and cell lines. Restoration of miR-211 inhibited GBM cell growth and invasion both in vitro and in vivo. The epithelial to mesenchymal transition (EMT) phenotype was reversed when miR-211 expression was restored. HMGA2 was identified as a down-stream target of miR-211. MiR-211 had an inhibitory effect on AKT/β-catenin signaling, which was reversed by HMGA2 overexpression or miR-211 restoration. In addition, miR-211 was transcriptionally repressed by EZH2-induced H3K27 trimethylation and promoter methylation. Overall, our findings revealed miR-211 as a tumor suppressor in GBM and mir-211 may be a potential therapeutic target for GBM patients.

Success of tumorsphere isolation from WHO grade IV gliomas does not correlate with the weight of fresh tumor specimens: an immunohistochemical characterization of tumorsphere differentiation

BACKGROUND

A trend of stage-by-stage increase in tumorsphere (TS) formation from glioma samples has been reported. Despite this trend, not all surgical specimens give rise to TSs, even World Health Organization (WHO) grade IV gliomas. Furthermore, it has been reported that differences in overall survival of primary glioblastoma patients depends on the propensity of their tumors to form TSs. However, the weights of fresh specimens vary from one surgical isolate to the next.

METHODS

Accordingly, we evaluated the relationship between the weights of surgical specimens in WHO grade IV gliomas with the capacity to isolate TSs. Thirty-five fresh WHO grade IV glioma specimens were separated into two groups, based on whether they were positive or negative for TS isolation, and the relationship between TS isolation and weight of surgical specimens was assessed.

RESULTS

We observed no significant difference in the weights of surgical samples in the two groups, and found that the optimal weight of specimens for TSs isolation was 500 mg.

CONCLUSION

Thus, contrary to our expectations, the ability to isolate TSs from WHO grade IV glioma specimens was not related to the weight of fresh specimens.

Relationship between microvessel density and cancer stem cells in tumor angiogenesis: a meta-analysis

Aim: Several studies have shown that cancer stem cells (CSCs) promote tumor angiogenesis and are involved in tumor growth. A meta-analysis was conducted to evaluate the association between cancer stem cell markers expression and microvessel density (MVD). Methods: Relevant literature was identified from diverse databases. The Stata 12.0 and Review Manager 5.3 software were used to performed meta-analysis. Results: Sixteen studies investigating the correlation between CSCs and tumor angiogenesis were included in a total of 1409 cases. The result showed that positive CSC markers expression were associated with increased MVD count in human tumors and CSC-transplanted mouse tumor models (p < 0.0001). Conclusion: CSCs may be associated with angiogenesis during the growth and development of tumors.