Molecular biology of human gliomas

Glioblastoma multiforme: a glance at advanced therapies based on nanotechnology

Glioblastoma multiforme (GBM, grade IV) is the most common malignant and invasive central nervous system tumor with poor survival outcome. Various pathogenesis signatures such as genetic mutation, hypoxia, necrosis and neo-angiogenesis are involved in GBM. Standard treatment includes surgical resection along with radiation therapy and temozolomide (TMZ) chemotherapy that do not improve the overall survival of patients. In this review, we focused on the diagnosis, risk factors and novel therapies, using advanced therapies such as nanotechnology in drug delivery, gene therapy and hyperthermia that have promising roles in the treatment of aggressive brain tumors.

Aberrant expression of long non-coding RNAs (lncRNAs) is involved in brain glioma development

INTRODUCTION

Aberrant expression of long non-coding RNAs (lncRNAs) has been implicated in various diseases, including cancer. However, little is known about lncRNAs in human brain gliomas.

MATERIAL AND METHODS

We examined lncRNA profiles from three glioma specimens using lncRNA expression profiling microarrays. Quantitative real-time RT-PCR was used to analyze the differential expression of raw intensities of lncRNA expression in glioma and peritumoral tissues.

RESULTS

We found 4858 lncRNAs to be differentially expressed between tumor tissue and peritumoral tissue. Of these, 2845 lncRNAs were up-regulated (fold change > 3.0) and 2013 were down-regulated (fold change < 1/3). A total of 4084 messenger RNAs were also differentially expressed, including 2280 up-regulated transcripts (fold change > 3.0) and 1804 that were down-regulated (fold change < 1/3). Consistent with the microarray data, qPCR confirmed differential expression of these 6 lncRNAs (ak125809, ak098473, uc002ehu.1, bc043564, NR_027322, and uc003qmb.2) between tumor and peritumoral tissue. We next established co-expression networks of differentially expressed lncRNAs and mRNAs. Many mRNAs, such as LOC729991, NUDCD1, SHC3, PDGFA, and MDM2, and lncRNAs, such as ENST00000425922, ENST00000455568, uc002ukz.1, ENST00000502715, and NR_027873, have been shown to play important roles in glioma development. Consistent with this, pathway analysis revealed that "GLIOMA" (KEGG Pathway ID: hsa05214) was significantly enriched in tumor tissue.

CONCLUSIONS

Our data suggest that altered expression of lncRNAs may be a critical determinant of tumorigenesis in glioma patients.

Exogenous hydrogen sulfide exhibits anti-cancer effects though p38 MAPK signaling pathway in C6 glioma cells

It has been documented that H2S, in some types of cancer, promotes tumor proliferation, whereas, in the other types, it inhibits the tumor cell growth. In the present study, we investigated the anti-cancer effects and relevant mechanisms of NaHS in C6 glioma cells. C6 cells were subjected to different concentrations of NaHS, then cell viability and morphological changes were examined by MTT assay and Hoechst staining. The protein expression of Caspase-3, Bcl-2, Bax, p38 MAPK (mitogen-activated protein kinase), and p53 was measured by Western blotting. This work demonstrated that NaHS could reduce cell number and induce apoptosis of C6 gliomas cells. The protein expression of Caspase-3 and Bax was up-regulated, while the protein expression of Bcl-2 was down-regulated. Additionally, p38 MAPK and p53 were activated in response to NaHS. Moreover, p38 MAPK inhibitor, SB203580, counteracted the inhibitory effect of NaHS on C6 glioma cells. These data suggest that NaHS can effectively reduce cell number of C6 cells by triggering the apoptosis via Caspase-dependent pathway. p38 MAPK and p53 play an important role in NaHS-induced apoptosis in C6 cells. These findings imply that administration of NaHS may represent a new strategy for the treatment of glioma.

Epigenetic regulation of glial fibrillary acidic protein by DNA methylation in human malignant gliomas

Glial fibrillary acidic protein (GFAP) is an intermediate filament expressed in glial cells that stabilizes and maintains the cytoskeleton of normal astrocytes. In glial tumors, GFAP expression is frequently lost with increasing grade of malignancy, suggesting that GFAP is important for maintaining glial cell morphology or regulating astrocytoma cell growth. Most permanent human glioma cell lines are GFAP negative by immunocytochemistry. Given that the GFAP gene is not mutated in human glioma specimens or glioma cell lines, we considered epigenetic mechanisms, such as promoter methylation, as a cause of silencing of GFAP in these tumors. In this study, we treated known GFAP-negative glioma cell lines with 5-aza-2'-deoxycytidine to examine GFAP promoter hypermethylation. Additionally, we performed bisulfite sequencing on primary glioma samples and glioma cell lines and showed an inverse relationship between GFAP promoter methylation status and GFAP expression. Using a gene reporter assay with the GFAP promoter cloned upstream of a luciferase gene, we showed that methylation of the GFAP promoter downregulates the expression of the luciferase gene. Our results suggest that epigenetic silencing of the GFAP gene through DNA methylation of its promoter region may be one mechanism by which GFAP is downregulated in human gliomas and glioma cell lines.

PDCD4 gene silencing in gliomas is associated with 5'CpG island methylation and unfavourable prognosis

Programmed cell death 4 (PDCD4) is a newly described tumour suppressor that inhibits oncogenesis by suppressing gene transcription and translation. Loss of PDCD4 expression has been found in several types of human cancers including the most common cancer of the brain, the gliomas. However, the molecular mechanisms responsible for PDCD4 gene silencing in tumour cells remain unclear. Here we report the identification of 5′CpG island methylation as the predominant cause of PDCD4 mRNA silencing in gliomas. The methylation of the PDCD4 5′CpG island was found in 47% (14/30) of glioma tissues, which was significantly associated with the loss of PDCD4 mRNA expression (γ=−1.000, P < 0.0001). Blocking methylation in glioma cells using a DNA methyltransferase inhibitor, 5-aza-2′-deoxycytidine, restored the PDCD4 gene expression, inhibited their proliferation and reduced their colony formation capacity. Longitudinal studies of a cohort of 84 patients with gliomas revealed that poor prognosis of patients with high-grade tumours were significantly associated with loss of PDCD4 expression. Thus, our current study suggests, for the first time, that PDCD4 5′CpG island methylation blocks PDCD4 expression at mRNA levels in gliomas. These results also indicate that PDCD4 reactivation might be an effective new strategy for the treatment of gliomas.

The role of sphingosine kinase-1 in EGFRvIII-regulated growth and survival of glioblastoma cells

We have previously shown that high expression levels of the lipid kinase sphingosine kinase-1 (SphK1) correlate with poor survival of glioblastoma (GBM) patients. In this study we examined the regulation of SphK1 expression by epidermal growth factor receptor (EGFR) signaling in GBM cells. As the EGFR gene is often overexpressed and mutated in GBM, and EGFR has been shown to regulate SphK1 in some cell types, we examined the effect of EGF signaling and the constitutively active EGFRvIII mutant on SphK1 in GBM cells. Treatment of glioma cell lines with EGF led to increased expression and activity of SphK1. Expression of EGFRvIII in glioma cells also activated and induced SphK1. In addition, siRNA to SphK1 partially inhibited EGFRvIII-induced growth and survival of glioma cells as well as ERK MAP kinase activation. To further evaluate the connection between EGFR and SphK1 in GBM we examined primary neurosphere cells isolated from fresh human GBM tissue. The GBM-derived neurosphere cell line GBM9, which forms GBM-like tumors intracranially in nude mice, maintained expression of EGFRvIII in culture and had high levels of SphK1 activity. EGFR inhibitors modestly decreased SphK1 activity and proliferation of GBM9 cells. More extensive blockage of SphK1 activity by a SphK inhibitor, potently blocked cell proliferation and induced apoptotic cell death of GBM9 cells. Thus, SphK1 activity is necessary for survival of GBM-derived neurosphere cells, and EGFRvIII partially utilizes SphK1 to further enhance cell proliferation.

Rapid and robust transgenic high-grade glioma mouse models for therapy intervention studies

PURPOSE

To develop a transgenic mouse model of glioma that can be conveniently used for testing therapy intervention strategies. High-grade glioma is a devastating and uniformly fatal disease for which better therapy is urgently needed. Typical for high-grade glioma is that glioma cells infiltrate extensively into surrounding pivotal brain structures, thereby rendering current treatments largely ineffective. Evaluation of novel therapies requires the availability of appropriate glioma mouse models.

EXPERIMENTAL DESIGN

High-grade gliomas were induced by stereotactic intracranial injection of lentiviral GFAP-Cre or CMV-Cre vectors into compound LoxP-conditional mice, resulting in K-Ras(v12) expression and loss of p16(Ink4a)/p19(Arf) with or without concomitant loss of p53 or Pten.

RESULTS

Tumors reproduced many of the features that are characteristic for human high-grade gliomas, including invasiveness and blood-brain barrier functionality. Especially, CMV-Cre injection into p53;Ink4a/Arf;K-Ras(v12) mice resulted in high-grade glioma with a short tumor latency (2-3 weeks) and full penetrance. Early detection and follow-up was accomplished by noninvasive bioluminescence imaging, and the practical utility for therapy intervention was shown in a study with temozolomide.

CONCLUSION

We have developed a realistic high-grade glioma model that can be used with almost the same convenience as traditional xenograft models, thus allowing its implementation at the forefront of preclinical evaluation of new treatments.

Glioma angiogenesis: Towards novel RNA therapeutics

Brain tumors exhibit marked and aberrant blood vessel formation indicating angiogenic endothelial cells as a potential target for brain tumor treatment. The brain tumor blood vessels are used for nutrient delivery, and possibly for cancer cell migration. The process of angiogenesis is complex and involves multiple players. The current angiogenesis inhibitors used in clinical trials mostly target single angiogenic proteins and so far show limited effects on tumor growth. Besides the conventional angiogenesis inhibitors, RNA-based inhibitors such as small-interfering RNAs (siRNAs) are being analyzed for their capacity to silence the message of proteins involved in neovascularization. More recently, a new family of non-coding RNAs, named angiomirs [microRNAs (miRNAs) involved in angiogenesis] has emerged. These small RNAs have the advantage over siRNAs in that they have the potential of silencing multiple messages at the same time and therefore they might become therapeutically relevant in a "one-hit multiple-target" context against brain tumor angiogenesis. In this review we will discuss the emerging technologies in anti-angiogenesis emphasizing on RNA-based therapeutics.

Randomized Phase III controlled trials of therapy in malignant glioma: where are we after 40 years?

The objective of this study was to review the results of randomized Phase III controlled trials (RCTs) that involve initial treatments of malignant glioma and determine changes in median survival times (MST) over the last 40 years. An electronic database search identified RCTs for patients undergoing initial treatment for supratentorial high-grade malignant glioma. MSTs were analysed with respect to the date that patient accrual to the trial started, to identify the time course of changes in MST. Linear regression was used for statistical analysis. The review included 44 clinical trials that recruited patients between 1966 and 2004. Overall, there was a steady significant improvement in MST for the novel treatment cohorts over this period (r(2) = 0.43, p < 0.001), with MST increasing from around 8 to 15 months. There was also consistent improvement in the MST of the control cohorts, from around 7 months to 14 months, that reached statistical significance (r(2) = 0.41, p < 0.001). However, analysis including a quadratic term revealed a trend towards the rate of improvement in MST decreasing in the last two decades in the control, but not novel treatment, groups. The differences, either positive or negative, in MSTs between the control and novel treatment cohorts, and number of trials performed have all decreased with time. Subgroup analysis of the three most recent clinical trials report statistically significant better outcomes in MST after either >90% or 'complete' tumour resection. Despite tremendous advances in both the understanding of the biology of malignant gliomas and treatments in neuro-oncology, the prognosis for patients with malignant gliomas, although improved, remains very poor. The limitations of this type of analysis, including how trial design can bias outcomes and militate against comparison of trials are discussed.

Comparison between cells and cancer stem-like cells isolated from glioblastoma and astrocytoma on expression of anti-apoptotic and multidrug resistance-associated protein genes

This study is to explore and compare the features of the cells and cancer stem-like cells (CSCs) isolated from both glioblastoma and astrocytoma on expression of anti-apoptotic and multidrug resistance-associated protein (MRP) genes. As a result, the mRNA expression of livin, livinalpha and MRP1 was up-regulated in human CSCs from 2 times to 85 times, but the gene expression of MRP3 was down-regulated from 0.09 times to 0.5 times. After just differentiation the mRNA expression of livin, livinalpha and MRP3 was up-regulated from 9 times to 64 times, but the mRNA expression of MRP1 was down-regulated from 0.01 times to 0.03 times. It is a rare report that glioma stem-like cells can be induced successfully from a grade 2-3 astrocytoma tissue. The properties of glioblastoma and astrocytoma stem-like cells on anti-apoptotic and MRP genes are: anti-apoptotic gene livin and survivin are elevated in CSCs but are the most increased in just differentiated CSCs; MRP1 gene is significantly increased and MRP3 is decreased in CSCs, but when differentiating the MRP3 gene starts a remarkable increase in CSCs; the expression of anti-apoptotic and MRP genes shows no differences between the CSCs isolated from glioblastoma and astrocytoma tissues.