Molecular Advances of Brain Tumors in Radiation Oncology

Steroid receptor coactivator-1 enhances the stemness of glioblastoma by activating long noncoding RNA XIST/miR-152/KLF4 pathway

Glioblastoma (GBM) recurrence is attributed to the presence of therapy-resistant glioblastoma stem cells. Steroid receptor coactivator-1 (SRC-1) acts as an oncogenic regulator in many human tumors. The relationship between SRC-1 and GBM has not yet been studied. Herein, we investigate the role of SRC-1 in GBM. In this study, we found that SRC-1 expression is positively correlated with grades of glioma and inversely correlated with glioma patient's prognosis. Steroid receptor coactivator-1 promotes the proliferation, migration, and tumor growth of GBM cells. Notably, SRC-1 knockdown suppresses the stemness of GBM cells. Mechanistically, long noncoding RNA X-inactive specific transcript (XIST) is regulated by SRC-1 at the posttranscriptional level and mediates the function of SRC-1 in promoting stemness-like properties of GBM. Steroid receptor coactivator-1 can promote the expression of Kruppel-like factor 4 (KLF4) through the XIST/microRNA (miR)-152 axis. Additionally, arenobufagin and bufalin, SRC small molecule inhibitors, can reduce the proliferation and stemness of GBM cells. This study reveals SRC-1 promotes the stemness of GBM by activating the long noncoding RNA XIST/miR-152/KLF4 pathway and provides novel markers for diagnosis and therapy of GBM.

Apoptosis related microRNAs and MGMT in glioblastoma cell lines submitted to treatments with ionizing radiation and temozolomide

Aim

To evaluate the effect of radiotherapy and temozolomide on the expression of miRNAs apoptotic (miRNAs-21, -221, -222 (anti-apoptotic) and miRNAs-15a, -16 (pro-apoptotic)) and the gene MGMT in glioblastoma cell lines.

Background

The limited knowledge of the molecular biology of malignant gliomas may hinder the development of therapeutic modalities. In this scenario, one of the greatest advances of recent years was the identification of microRNAs. These molecules have an important role in biological processes involving cancer, including glioblastoma.

Materials and methods

Trypan blue was used to verify the cell viability, and real time PCR to quantify the expression of microRNAs and gene 24, 48 and 120 h after exposure to treatments.

Results

There was a statistically significant decrease of expression of miR-15a between 48 and 120 h in line T98 G treated with radiation, increased expression of miR-15a between 24 and 120 h in line U251 treated with radiation and temozolomide, and increased expression of miR-16 between 24 and 120 h in line U251 treated with radiation alone and when combined with temozolomide. There was a decrease in MGMT gene expression, between 24 and 48 h in U343 cells treated with temozolomide.

Conclusions

Ionizing radiation and temozolomide modified the expression of miRNAs studied and MGMT.

The radiobiological effects of He, C and Ne ions as a function of LET on various glioblastoma cell lines

The effects of the charged ion species 4He, 12C and 20Ne on glioblastoma multiforme (GBM) T98G, U87 and LN18 cell lines were compared with the effects of 200 kVp X-rays (1.7 keV/μm). These cell lines have different genetic profiles. Individual GBM relative biological effectiveness (RBE) was estimated in two ways: the RBE10 at 10% survival fraction and the RBE2Gy after 2 Gy doses. The linear quadratic model radiosensitivity parameters α and β and the α/β ratio of each ion type were determined as a function of LET. Mono-energetic 4He, 12C and 20Ne ions were generated by the Heavy Ion Medical Accelerator at the National Institute of Radiological Sciences in Chiba, Japan. Colony-formation assays were used to evaluate the survival fractions. The LET of the various ions used ranged from 2.3 to 100 keV/μm (covering the depth-dose plateau region to clinically relevant LET at the Bragg peak). For U87 and LN18, the RBE10 increased with LET and peaked at 85 keV/μm, whereas T98G peaked at 100 keV/μm. All three GBM α parameters peaked at 100 keV/μm. There is a statistically significant difference between the three GBM RBE10 values, except at 100 keV/μm (P < 0.01), and a statistically significant difference between the α values of the GBM cell lines, except at 85 and 100 keV/μm. The biological response varied depending on the GBM cell lines and on the ions used.

Potential lethal damage repair in glioblastoma cells irradiated with ion beams of various types and levels of linear energy transfer

Glioblastoma (GBM), a Grade IV brain tumour, is a well-known radioresistant cancer. To investigate one of the causes of radioresistance, we studied the capacity for potential lethal damage repair (PLDR) of three altered strains of GBM: T98G, U87 and LN18, irradiated with various ions and various levels of linear energy transfer (LET). The GBM cells were exposed to 12C and 28Si ion beams with LETs of 55, 100 and 200 keV/μm, and with X-ray beams of 1.7 keV/μm. Mono-energetic 12C ions and 28Si ions were generated by the Heavy Ion Medical Accelerator at the National Institute of Radiological Science, Chiba, Japan. Clonogenic assays were used to determine cell inactivation. The ability of the cells to repair potential lethal damage was demonstrated by allowing one identical set of irradiated cells to repair for 24 h before subplating. The results show there is definite PLDR with X-rays, some evidence of PLDR at 55 keV/μm, and minimal PLDR at 100 keV/μm. There is no observable PLDR at 200 keV/μm. This is the first study, to the authors' knowledge, demonstrating the capability of GBM cells to repair potential lethal damage following charged ion irradiations. It is concluded that a GBM's PLDR is dependent on LET, dose and GBM strain; and the more radioresistant the cell strain, the greater the PLDR.

The FOXM1/BUB1B signaling pathway is essential for the tumorigenicity and radioresistance of glioblastoma

Accumulating evidence indicates that mitotic checkpoint serine/threonine kinase B (BUB1B) plays a critical role in multiple types of cancer. However, the biological function and molecular regulatory mechanism of BUB1B in glioblastoma (GBM) remain unclear. In the present study, we identified that BUB1B expression was enriched in GBM tumors and was functionally required for tumor proliferation both in vitro and in vivo. Clinically, BUB1B expression was associated with poor prognosis in GBM patients and BUB1B-dependent radioresistance in GBM was decreased by targeting BUB1B via shRNAs. Mechanistically, forkhead box protein M1 (FOXM1) transcriptionally regulated BUB1B expression by binding to and then activating the BUB1B promoter. Therapeutically, we found that FOXM1 inhibitor attenuated tumorigenesis and radioresistance of GBM both in vitro and in vivo. Altogether, BUB1B promotes tumor proliferation and induces radioresistance in GBM, indicating that BUB1B could be a potential therapeutic target for GBM.

Identification of a gene signature associated with radiotherapy and prognosis in gliomas

Glioma is one of the most common primary brain tumors with poor prognosis. Although radiotherapy is an important treatment method for gliomas, the efficacy is still limited by the high occurrence of radioresistance and the underlying molecular mechanism is unclear. Here, we performed a data mining work based on four glioma expression datasets. These datasets were classified into training set and validation set. Radiotherapy-induced differential expressed genes and prognosis-associated genes were screened using different classifiers. The Kaplan-Meier curves along with the two-sided Log Rank (Mantel-Cox) test were used to evaluate overall survival. We found the gene expression profiles of gliomas between those patients received radiotherapy and those patients without received radiotherapy were quite different. A 20-gene signature was identified, which was associated with radiotherapy.Furthermore, a novel 5-gene signature (HOXC10, LOC101928747, CYB561D2, RPL36A and RPS4XP2) as an independent predictor of glioma patients’ prognosis was further derived from the 20-gene signature. These findings provided a new insight into the molecular mechanism of radioresistance in gliomas. The 5-gene signature might represent therapeutic target for gliomas.

RETRACTED: Physcion 8-O-β-glucopyranosideregulates cell cycle, apoptosis, and invasion in glioblastoma cells through modulating Skp2

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief, following the initial request of the corresponding author. The journal has further requested the author to provide explanations for the figure similarities with papers previously published by different authors. However, the author was not able to fulfil the request. The panels U251/PG+Skp2 cDNA from Figure 4E and U251/Vehicle from Figure 6D appear similar to the panels SOX2 shRNA from Figure 3D and CoCl2 from Figure 6B of the article previously published by Yan-tao Han, Xue-hong Chen, Hui Gao, Jun-li Ye and Chun-bo Wang in Acta Pharmacologica Sinica 37(2) (2016) 264–275 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4753366/. The panel U251/PG from Figure 6B appears similar to the panel KYSE30/miR-370 mimic + PIM1 vector from Figure 5D of the article previously published by Yantao Han, Xiuwei Yang, Ning Zhao, Jianjun Peng, Hui Gao and Xia Qiu in the American Journal of Cancer Research 6(12) (2016) 2755–2771 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5199752/.

MiR-429 suppresses glioblastoma multiforme by targeting SOX2

Accumulating evidence has shown that miR-429 plays an important role in the development and progression of tumour. However, the role of miR-429 in glioblastoma multiforme (GBM) remains largely unknown. The present study is designed to investigate the function of miR-429 in GBM and to explore the molecular mechanism underlying its function. The expression level of miR-429 was detected in GBM tissues and cell lines by quantitative real-time polymerase chain reaction. The effect of overexpression of miR-429 on in vitro cell proliferation, apoptosis and invasion was examined. Western blot analysis was used to detect the influence of miR-429 on the expression of target gene, and Pearson analysis was used to calculate the correlation between the expression of targets gene and the miR-429 in GBM tissues. Our study shows that miR-429 is downregulated in GBM tissues compared with noncancerous tissues (P < .01). In addition, the expression of miR-429 in GBM cell lines is also significantly lower (P < .01). Enforced expression of miR-429 inhibits GBM cells proliferation, induces apoptosis and suppresses invasion and leads to the downregulation of the SOX2 protein. Moreover, the expression level of miR-429 in GBM tissues shows inverse relationship with the expression level of SOX2 protein. Our findings suggest that miR-429 represents a potential tumour-suppressive miRNA and plays an important role in GBM progression by directly targeting SOX2.

MiR-592 functions as a tumor suppressor in glioma by targeting IGFBP2

A growing body of evidence suggests that microRNA-592 is involved in tumor initiation and development in several types of human cancers. However, the biological functions and molecular mechanism of microRNA-592 in glioma remain unclear. In this study, we explored the potential role of microRNA-592 in glioma as well as the possible molecular mechanisms. Our results proved that microRNA-592 expression was significantly downregulated in glioma tissues and cell lines (p < 0.01). Functional assays revealed that overexpression of microRNA-592 dramatically reduced the cell proliferation, migration, and invasion and induced cell arrest at G1/G0 phase in vitro. Mechanistic investigations defined insulin-like growth factor binding protein 2 as a direct and functional downstream target of microRNA-592, which was involved in the microRNA-592-mediated tumor-suppressive effects in glioma cells. Moreover, the in vivo study showed that microRNA-592 overexpression produced the smaller tumor volume and weight in nude mice. In summary, these results elucidated the function of microRNA-592 in glioma progression and suggested a promising application of it in glioma treatment.

Synthetic miR-145 Mimic Enhances the Cytotoxic Effect of the Antiangiogenic Drug Sunitinib in Glioblastoma

Although aggressive therapeutic regimen has been applied in the treatment of Glioblastoma (GBM), the prognosis of patients with GBM remains poor. Preclinical studies have demonstrated the efficacy of Suntinib in GBM both in vitro and in vivo. In this study, we showed that the cytotoxicity was enhanced by transfection with miR-145 mimic. In addition, we suggested that the enhanced cytotoxicity of Sunitinib by miR-145 mimic was mediated by inhibition of both P-gp and Bcrp.

Icaritin inhibits the invasion and epithelial-to-mesenchymal transition of glioblastoma cells by targeting EMMPRIN via PTEN/AKt/HIF-1α signalling

Icaritin, a hydrolytic product of icariin from the Epimedium genus, exerts anti-tumour effects on a variety of tumour cell types, mainly by inhibiting cell proliferation and inducing apoptosis. However, little is known about the role of icaritin in cancer invasion and epithelial-to-mesenchymal transition (EMT). In the present study, the glioblastoma (GBM) cell line U87MG was used as a model to investigate the effects of icaritin on the invasion and EMT of cancer cells. The results showed that icaritin significantly inhibited the invasion and EMT of GBM cells by targeting extracellular matrix metalloproteinase (EMMPRIN). Furthermore, the findings strongly indicate that the modulatory effect of icaritin on EMMPRIN is mediated via the PTEN/Akt/HIF-1α signalling pathway. The data provide the first experimental evidence of the inhibitory effect of icaritin on cancer cell invasion and EMT, thus highlighting the potential of icaritin to be employed as a promising anti-cancer agent in the treatment of GBM.

Silver nanoparticles outperform gold nanoparticles in radiosensitizing U251 cells in vitro and in an intracranial mouse model of glioma

Radiotherapy performs an important function in the treatment of cancer, but resistance of tumor cells to radiation still remains a serious concern. More research on more effective radiosensitizers is urgently needed to overcome such resistance and thereby improve the treatment outcome. The goal of this study was to evaluate and compare the radiosensitizing efficacies of gold nanoparticles (AuNPs) and silver nanoparticles (AgNPs) on glioma at clinically relevant megavoltage energies. Both AuNPs and AgNPs potentiated the in vitro and in vivo antiglioma effects of radiation. AgNPs showed more powerful radiosensitizing ability than AuNPs at the same mass and molar concentrations, leading to a higher rate of apoptotic cell death. Furthermore, the combination of AgNPs with radiation significantly increased the levels of autophagy as compared with AuNPs plus radiation. These findings suggest the potential application of AgNPs as a highly effective nano-radiosensitizer for the treatment of glioma.

RTVP-1 promotes mesenchymal transformation of glioma via a STAT-3/IL-6-dependent positive feedback loop

Glioblastomas (GBMs), the most aggressive primary brain tumors, exhibit increased invasiveness and resistance to anti-tumor treatments. We explored the role of RTVP-1, a glioma-associated protein that promotes glioma cell migration, in the mesenchymal transformation of GBM. Analysis of The Cancer Genome Atlas (TCGA) demonstrated that RTVP-1 expression was higher in mesenchymal GBM and predicted tumor recurrence and poor clinical outcome. ChiP analysis revealed that the RTVP-1 promoter binds STAT3 and C/EBPβ, two master transcription factors that regulate mesenchymal transformation of GBM. In addition, IL-6 induced RTVP-1 expression in a STAT3-dependent manner. RTVP-1 increased the migration and mesenchymal transformation of glioma cells. Similarly, overexpression of RTVP-1 in human neural stem cells induced mesenchymal differentiation, whereas silencing of RTVP-1 in glioma stem cells (GSCs) decreased the mesenchymal transformation and stemness of these cells. Silencing of RTVP-1 also increased the survival of mice bearing GSC-derived xenografts. Using gene array analysis of RTVP-1 silenced glioma cells we identified IL-6 as a mediator of RTVP-1 effects on the mesenchymal transformation and migration of GSCs, therefore acting in a positive feedback loop by upregulating RTVP-1 expression via the STAT3 pathway. Collectively, these results implicate RTVP-1 as a novel prognostic marker and therapeutic target in GBM.

RTVP-1 regulates glioma cell migration and invasion via interaction with N-WASP and hnRNPK

Glioblastoma (GBM) are characterized by increased invasion into the surrounding normal brain tissue. RTVP-1 is highly expressed in GBM and regulates the migration and invasion of glioma cells. To further study RTVP-1 effects we performed a pull-down assay using His-tagged RTVP-1 followed by mass spectrometry and found that RTVP-1 was associated with the actin polymerization regulator, N-WASP. This association was further validated by co-immunoprecipitation and FRET analysis. We found that RTVP-1 increased cell spreading, migration and invasion and these effects were at least partly mediated by N-WASP. Another protein which was found by the pull-down assay to interact with RTVP-1 is hnRNPK. This protein has been recently reported to associate with and to inhibit the effect of N-WASP on cell spreading. hnRNPK decreased cell migration, spreading and invasion in glioma cells. Using co-immunoprecipitation we validated the interactions of hnRNPK with N-WASP and RTVP-1 in glioma cells. In addition, we found that overexpression of RTVP-1 decreased the association of N-WASP and hnRNPK. In summary, we report that RTVP-1 regulates glioma cell spreading, migration and invasion and that these effects are mediated via interaction with N-WASP and by interfering with the inhibitory effect of hnRNPK on the function of this protein.

RasGRP3 regulates the migration of glioma cells via interaction with Arp3

Glioblastoma (GBM), the most aggressive primary brain tumors, are highly infiltrative. Although GBM express high Ras activity and Ras proteins have been implicated in gliomagenesis, Ras-activating mutations are not frequent in these tumors. RasGRP3, an important signaling protein responsive to diacylglycerol (DAG), increases Ras activation. Here, we examined the expression and functions of RasGRP3 in GBM and glioma cells. RasGRP3 expression was upregulated in GBM specimens and glioma stem cells compared with normal brains and neural stem cells, respectively. RasGRP3 activated Ras and Rap1 in glioma cells and increased cell migration and invasion partially via Ras activation. Using pull-down assay and mass spectroscopy we identified the actin-related protein, Arp3, as a novel interacting protein of RasGRP3. The interaction of RasGRP3 and Arp3 was validated by immunofluorescence staining and co-immunoprecipitation, and PMA, which activates RasGRP3 and induces its translocation to the peri-nuclear region, increased the association of Arp3 and RasGRP3. Arp3 was upregulated in GBM, regulated cell spreading and migration and its silencing partially decreased these effects of RasGRP3 in glioma cells. In summary, RasGRP3 acts as an important integrating signaling protein of the DAG and Ras signaling pathways and actin polymerization and represents an important therapeutic target in GBM.

Overexpression of miR-100 inhibits cell proliferation, migration, and chemosensitivity in human glioblastoma through FGFR3

Background

Glioblastoma multiforme is one of the most deadly forms of brain cancer. We investigated the regulatory effects of microRNA-100 (miR-100) on cell proliferation, migration, and chemosensitivity in human glioblastoma.

Methods

miR-100 expression was assessed by quantitative real-time polymerase chain reaction in both glioblastoma cells and human tumors. Lentiviruses of miR-100 mimics and inhibitors were transfected into U251 and T98G cells. The regulatory effects of either overexpressing or downregulating miR-100 on glioblastoma were evaluated by a viability assay, growth assay, migration assay, chemosensitivity assay, and an in vivo tumor transplantation assay. Expression of fibroblast growth factor receptor 3 (FGFR3), the bioinformatically predicted target of miR-100, was examined by Western blot in glioblastoma. FGFR3 was then ectopically overexpressed in U251 and T98G cells, and its effects on miR-100-mediated cancer regulation were evaluated by growth, migration, and chemosensitivity assays.

Results

MiR-100 was markedly downregulated in both glioblastoma cell lines and human tumors. Overexpressing miR-100 through lentiviral transfection in U251 and T98G cells significantly inhibited cancer growth (both in vitro and in vivo) and migration and increased chemosensitivity to cisplatin and 1, 3-bis (2-chloroethyl)-l-nitrosourea, whereas downregulation of miR-100 had no effects on development of cancer. FGFR3 was directly regulated by miR-100 in glioblastoma. Ectopically overexpressing FGFR3 was able to ameliorate the anticancer effects of upregulation of miR-100 on glioblastoma growth, migration, and chemosensitivity.

Conclusion

MiR-100 was generally downregulated in glioblastoma. Overexpressing miR-100 had anticancer effects on glioblastoma, likely through regulation of FGFR3. The MiR-100/FGFR3 signaling pathway might be a biochemical target for treatment in patients with glioblastoma.

Compound 331 selectively induces glioma cell death by upregulating miR-494 and downregulating CDC20

Malignant gliomas are the most common malignant tumors in the central nervous system (CNS). Up to date, the prognosis of glioma is still very poor, effective therapy with less side-effect is very necessary. Herein, we identify a compound named as "331" selectively induced cell death in glioma cells but not in astrocytes. Compound 331 upregulated miR-494 and downregulated CDC20 in glioma cells but not in astrocytes. These results suggest that compound 331 could be a potential drug selectively targeting glioma cells through upregulating miR-494 and downregulating CDC20.

PARP3 interacts with FoxM1 to confer glioblastoma cell radioresistance

Poly(ADP-ribose) polymerase 3 (PARP3), a critical player in cellular response to DNA double-strand breaks (DSBs), plays an essential role in the maintenance of genome integrity. However, the role of PARP3 in tumorigenesis especially in glioblastoma remains largely unknown. In the present study, we found that the mRNA and protein levels of PARP3 were upregulated in primary glioblastoma tissues. Knockdown of PARP3 expression by lentivirus-based shRNA decreased cell glioblastoma proliferation and inhibited tumor growth in vivo by using a xenograft mouse model. Furthermore, we found that silencing the expression of PARP3 resulted in a synergistic radiosensitizing effect when combined with radiotherapy in glioblastoma cell lines. At the molecular level, we found that PARP3 interacted with FoxM1 to enhance its transcriptional activity and conferred glioblastoma cell radioresistance. Thus, our data suggest that PARP3 could be a therapeutic target to overcome radioresistance in glioblastoma.

Associations between SOX2 and miR-200b expression with the clinicopathological characteristics and prognosis of patients with glioma

The aim of the present study was to investigate the associations between microRNA (miR)-200b and sex determining region Y-box 2 (SOX2) expression with gender, age, clinical staging and pathological staging in 123 patients with glioma. The results revealed higher miR-200b expression levels in the glioma tissue than in the normal brain tissues, and a reduction in miR-200b expression with increasing pathological grading of the gliomas. Immunohistochemistry revealed a 53.7% gross expression rate of SOX2 in the glioma tissues. SOX2 and miR-200b expression levels were significantly correlated with the histological grading of the gliomas (P<0.05); however, no associations were observed with patient gender, age, pathological classification or clinical staging of the glioma (P>0.05). In patients with grade I and II gliomas, no correlation was detected between miR-200b and SOX2, while a significant correlation was observed in grade III and IV gliomas. A median 52-month follow-up revealed 1-, 3- and 5-year gross survival rates of 82.1, 50.0 and 30.7%, respectively, in the 123 patients with a glioma. Univariate analysis revealed no association between survival rate and patient age, gender, Karnofsky Performance Scale score, histological grading or clinical staging (P>0.05). However, miR-200b and SOX2 were independent prognostic factors for glioma (P<0.05). Patients with positive SOX2 expression exhibited a significantly reduced 5-year survival rate, compared with those with negative SOX2 expression (P<0.001). Furthermore, a significantly higher 5-year survival rate was observed in patients with high miR-200b expression than those with low miR-200b expression (P<0.001). The results indicated that SOX2 and miR-200b expression levels are associated with the histological grading of gliomas, but do not correlate with patient gender or age, or the pathological classification or clinical staging of the gliomas. Thus, miR-200b and SOX2 offer useful independent prognostic factors for glioma.

Tunneling nanotubes between rat primary astrocytes and C6 glioma cells alter proliferation potential of glioma cells

The tunneling nanotube (TNT) is a newly discovered, long and thin tubular structure between cells. In this study, we established a co-culture system for rat primary astrocytes and C6 glioma cells and found that TNTs formed between them. Most of the TNTs initiated from astrocytes towards C6 glioma cells. The formation of TNTs depended on p53. In addition, hydrogen peroxide increased the number of TNTs in the co-culture system. Established TNTs reduced the proliferation of C6 glioma cells. Our data suggest that TNTs between astrocytes and glioma cells facilitate substance transfer and therefore alter the properties, including the proliferation potential, of glioma cells.

miR-135b contributes to the radioresistance by targeting GSK3β in human glioblastoma multiforme cells

Radioresistance remains a major challenge in the treatment of glioblastoma multiforme (GBM). Recent data strongly suggests the important role of miRNAs in cancer progression and therapeutic response. Here, we have established a radioresistant human GBM cell line U87R derived from parental U87 and found miR-135b expression was upregulated in U87R cells. miR-135b knockdown reversed radioresistance of U87R cells, and miR-135b overexpression enhanced radioresistance of U87 cells. Mechanically, bioinformatics analysis combined with experimental analysis demonstrated GSK3β (Glycogen synthase kinase 3 beta) was a novel direct target of miR-135b. Moreover, GSK3β protein expression was downregulated in U87R cells and restored expression of GSK3β increased radiosensitivity of U87R cells. In addition, clinical data indicated that the expression of miR-135b or GSK3β was significantly association with IR resistance of GBM samples. Our findings suggest miR-135b is involved in the radioresistance of human GBM cells and miR-135b-GSK3β axis may be a novel candidate for developing rational therapeutic strategies for human GBM treatment.

A functional screen identifies miRs that induce radioresistance in glioblastomas

The efficacy of radiotherapy in many tumor types is limited by normal tissue toxicity and by intrinsic or acquired radioresistance. Therefore, it is essential to understand the molecular network responsible for regulating radiosensitivity/resistance. Here, an unbiased functional screen identified four microRNAs (miR1, miR125a, miR150, and miR425) that induce radioresistance. Considering the clinical importance of radiotherapy for patients with glioblastoma, the impact of these miRNAs on glioblastoma radioresistance was investigated. Overexpression of miR1, miR125a, miR150, and/or miR425 in glioblastoma promotes radioresistance through upregulation of the cell-cycle checkpoint response. Conversely, antagonizing with antagomiRs sensitizes glioblastoma cells to irradiation, suggesting their potential as targets for inhibiting therapeutic resistance. Analysis of glioblastoma datasets from The Cancer Genome Atlas (TCGA) revealed that these miRNAs are expressed in glioblastoma patient specimens and correlate with TGFβ signaling. Finally, it is demonstrated that expression of miR1 and miR125a can be induced by TGFβ and antagonized by a TGFβ receptor inhibitor. Together, these results identify and characterize a new role for miR425, miR1, miR125, and miR150 in promoting radioresistance in glioblastomas and provide insight into the therapeutic application of TGFβ inhibitors in radiotherapy.

IMPLICATIONS

Systematic identification of miRs that cause radioresistance in gliomas is important for uncovering predictive markers for radiotherapy or targets for overcoming radioresistance.

Connexin 30 expression inhibits growth of human malignant gliomas but protects them against radiation therapy

BACKGROUND

Glioblastomas remain ominous tumors that almost invariably escape treatment. Connexins are a family of transmembrane, gap junction-forming proteins, some members of which were reported to act as tumor suppressors and to modulate cellular metabolism in response to cytotoxic stress.

METHODS

We analyzed the copy number and expression of the connexin (Cx)30 gene gap junction beta-6 (GJB6), as well as of its protein immunoreactivity in several public and proprietary repositories of glioblastomas, and their influence on patient survival. We evaluated the effect of the expression of this gap junction protein on the growth, DNA repair and energy metabolism, and treatment resistance of these tumors.

RESULTS

The GJB6 gene was deleted in 25.8% of 751 analyzed tumors and mutated in 15.8% of 158 tumors. Cx30 immunoreactivity was absent in 28.9% of 145 tumors. Restoration of Cx30 expression in human glioblastoma cells reduced their growth in vitro and as xenografts in the striatum of immunodeficient mice. Cx30 immunoreactivity was, however, found to adversely affect survival in 2 independent retrospective cohorts of glioblastoma patients. Cx30 was found in clonogenic assays to protect glioblastoma cells against radiation-induced mortality and to decrease radiation-induced DNA damage. This radioprotection correlated with a heat shock protein 90-dependent mitochondrial translocation of Cx30 following radiation and an improved ATP production following this genotoxic stress.

CONCLUSION

These results underline the complex relationship between potential tumor suppressors and treatment resistance in glioblastomas and single out GJB6/Cx30 as a potential biomarker and target for therapeutic intervention in these tumors.

FET-PET-based reirradiation and chloroquine in patients with recurrent glioblastoma: first tolerability and feasibility results

BACKGROUND

Treatment of recurrent glioblastoma (rGBM) remains an unsolved clinical problem. Reirradiation (re-RT) can be used to treat some patients with rGBM, but as a monotherapy it has only limited efficacy. Chloroquine (CQ) is an anti-malaria and immunomodulatory drug that may inhibit autophagy and increase the radiosensitivity of GBM.

PATIENTS AND METHODS

Between January 2012 and August 2013, we treated five patients with histologically confirmed rGBM with re-RT and 250 mg CQ daily.

RESULTS

Treatment was very well tolerated; no CQ-related toxicity was observed. At the first follow-up 2 months after finishing re-RT, two patients achieved partial response (PR), one patient stable disease (SD), and one patient progressive disease (PD). One patient with reirradiated surgical cavity did not show any sign of PD.

CONCLUSION

In this case series, we observed encouraging responses to CQ and re-RT. We plan to conduct a CQ dose escalation study combined with re-RT.

RAD18 mediates resistance to ionizing radiation in human glioma cells

Radioresistance remains a major challenge in the treatment of glioblastoma multiforme (GBM). RAD18 a central regulator of translesion DNA synthesis (TLS), has been shown to play an important role in regulating genomic stability and DNA damage response. In the present study, we investigate the relationship between RAD18 and resistance to ionizing radiation (IR) and examined the expression levels of RAD18 in primary and recurrent GBM specimens. Our results showed that RAD18 is an important mediator of the IR-induced resistance in GBM. The expression level of RAD18 in glioma cells correlates with their resistance to IR. Ectopic expression of RAD18 in RAD18-low A172 glioma cells confers significant resistance to IR treatment. Conversely, depletion of endogenous RAD18 in RAD18-high glioma cells sensitized these cells to IR treatment. Moreover, RAD18 overexpression confers resistance to IR-mediated apoptosis in RAD18-low A172 glioma cells, whereas cells deficient in RAD18 exhibit increased apoptosis induced by IR. Furthermore, knockdown of RAD18 in RAD18-high glioma cells disrupts HR-mediated repair, resulting in increased accumulation of DSB. In addition, clinical data indicated that RAD18 was significantly higher in recurrent GBM samples that were exposed to IR compared with the corresponding primary GBM samples. Collectively, our findings reveal that RAD18 may serve as a key mediator of the IR response and may function as a potential target for circumventing IR resistance in human GBM.

MicroRNA-137 is downregulated in glioblastoma and inhibits the stemness of glioma stem cells by targeting RTVP-1

Glioblastomas (GBM), the most common and aggressive malignant astrocytic tumors, contain a small subpopulation of cancer stem cells (GSCs) that are implicated in therapeutic resistance and tumor recurrence. Here, we study the expression and function of miR-137, a putative suppressor miRNA, in GBM and GSCs. We found that the expression of miR-137 was significantly lower in GBM and GSCs compared to normal brains and neural stem cells (NSCs) and that the miR-137 promoter was hypermethylated in the GBM specimens. The expression of miR-137 was increased in differentiated NSCs and GSCs and overexpression of miR-137 promoted the neural differentiation of both cell types. Moreover, pre-miR-137 significantly decreased the self-renewal of GSCs and the stem cell markers Oct4, Nanog, Sox2 and Shh. We identified RTVP-1 as a novel target of miR-137 in GSCs; transfection of the cells with miR-137 decreased the expression of RTVP-1 and the luciferase activity of RTVP-1 3'-UTR reporter plasmid. Furthermore, overexpression of RTVP-1 plasmid lacking its 3'-UTR abrogated the inhibitory effect of miR-137 on the self-renewal of GSCs. Silencing of RTVP-1 decreased the self-renewal of GSCs and the expression of CXCR4 and overexpression of CXCR4 abrogated the inhibitory effect of RTVP-1 silencing on GSC self-renewal. These results demonstrate that miR-137 is downregulated in GBM probably due to promoter hypermethylation. miR-137 inhibits GSC self-renewal and promotes their differentiation by targeting RTVP-1 which downregulates CXCR4. Thus, miR-137 and RTVP-1 are attractive therapeutic targets for the eradication of GSCs and for the treatment of GBM.

Mesenchymal stem cells deliver synthetic microRNA mimics to glioma cells and glioma stem cells and inhibit their cell migration and self-renewal

MicroRNAs (miRNAs) have emerged as potential cancer therapeutics; however, their clinical use is hindered by lack of effective delivery mechanisms to tumor sites. Mesenchymal stem cells (MSCs) have been shown to migrate to experimental glioma and to exert anti-tumor effects by delivering cytotoxic compounds. Here, we examined the ability of MSCs derived from bone marrow, adipose tissue, placenta and umbilical cord to deliver synthetic miRNA mimics to glioma cells and glioma stem cells (GSCs). We examined the delivery of miR-124 and miR-145 mimics as glioma cells and GSCs express very low levels of these miRNAs. Using fluorescently labeled miRNA mimics and in situ hybridization, we demonstrated that all the MSCs examined delivered miR-124 and miR-145 mimics to co-cultured glioma cells and GSCs via gap junction- dependent and independent processes. The delivered miR-124 and miR-145 mimics significantly decreased the luciferase activity of their respected reporter target genes, SCP-1 and Sox2, and decreased the migration of glioma cells and the self-renewal of GSCs. Moreover, MSCs delivered Cy3-miR-124 mimic to glioma xenografts when administered intracranially. These results suggest that MSCs can deliver synthetic exogenous miRNA mimics to glioma cells and GSCs and may provide an efficient route of therapeutic miRNA delivery in vivo.

E1a promotes c-Myc-dependent replicative stress: implications in glioblastoma radiosensitization

The E1a gene from adenovirus is known to be a potent inducer of chemo/radiosensitivity in a wide range of tumors. However, the molecular bases of its radiosensitizer properties are still poorly understood. In an attempt to study this effect, U87MG cells, derived from a radio-resistant tumor as glioblastoma, where infected with lentivirus carrying E1a gene developing an acute sensitivity to ionizing radiation. The induction of radiosensitivity correlated with a marked G 2/M phase accumulation and a potent apoptotic response. Our findings demonstrate that c-Myc plays a pivotal role in E1a-associated radiosensitivity through the induction of a replicative stress situation, as our data support by genetic approaches, based in interference and overexpression in U87MG cells. In fact, we present evidence showing that Chk1 is a novel transcriptional target of E1a gene through the effect exerted by this adenoviral protein onto c-Myc. Moreover, c-Myc upregulation also explains the marked phosphorylation of H2AX associated to E1a expression in the absence of DNA damage. Indeed, all these observations were applicable to other experimental models, such as T98G, LN-405 and A172, rendering the same pattern in terms of radiosensitivity, cell cycle distribution, upregulation of Chk1, c-Myc, and phosphorylation pattern of H2AX. In summary, our data propose a novel mechanism to explain how E1a mediates radiosensitivity through the signaling axis E1a→c-Myc→ replicative stress situation. This novel mechanism of E1a-mediated radiosensitivity could be the key to open new possibilities in the current therapy of glioblastoma.

Circadian gene Clock contributes to cell proliferation and migration of glioma and is directly regulated by tumor-suppressive miR-124

Although the roles of circadian Clock genes and microRNAs in tumorigenesis have been profoundly studied, mechanisms of cross-talk between them in regulation of gliomagenesis are poorly understood. Here we show that the expression level of CLOCK is significantly increased in high-grade human glioma tissues and glioblastoma cell lines. In contrast miR-124 is attenuated in similar samples. Further studies show that Clock is a direct target of miR-124, and either restoration of miR-124 or silencing of CLOCK can reduce the activation of NF-κB. In conclusion, we suggest that as a target of glioma suppressor miR-124, CLOCK positively regulates glioma proliferation and migration by reinforcing NF-κB activity.

MicroRNA-145 is downregulated in glial tumors and regulates glioma cell migration by targeting connective tissue growth factor

Glioblastomas (GBM), the most common and aggressive type of malignant glioma, are characterized by increased invasion into the surrounding brain tissues. Despite intensive therapeutic strategies, the median survival of GBM patients has remained dismal over the last decades. In this study we examined the expression of miR-145 in glial tumors and its function in glioma cells. Using TCGA analysis and real-time PCR we found that the expression of miR-145/143 cluster was downregulated in astrocytic tumors compared to normal brain specimens and in glioma cells and glioma stem cells (GSCs) compared to normal astrocytes and neural stem cells. Moreover, the low expression of both miR-145 and miR-143 in GBM was correlated with poor patient prognosis. Transfection of glioma cells with miR-145 mimic or transduction with a lentivirus vector expressing pre-miR 145 significantly decreased the migration and invasion of glioma cells. We identified connective tissue growth factor (CTGF) as a novel target of miR-145 in glioma cells; transfection of the cells with this miRNA decreased the expression of CTGF as determined by Western blot analysis and the expression of its 3′-UTR fused to luciferase. Overexpression of a CTGF plasmid lacking the 3′-UTR and administration of recombinant CTGF protein abrogated the inhibitory effect of miR-145 on glioma cell migration. Similarly, we found that silencing of CTGF decreased the migration of glioma cells. CTGF silencing also decreased the expression of SPARC, phospho-FAK and FAK and overexpression of SPARC abrogated the inhibitory effect of CTGF silencing on cell migration. These results demonstrate that miR-145 is downregulated in glial tumors and its low expression in GBM predicts poor patient prognosis. In addition miR-145 regulates glioma cell migration by targeting CTGF which downregulates SPARC expression. Therefore, miR-145 is an attractive therapeutic target for anti-invasive treatment of astrocytic tumors.

Treatment outcome and prognostic factors of adult glioblastoma multiforme

INTRODUCTION

This study aimed to report the characteristics, prognostic factors and treatment outcome of 223 patients with glioblastoma multiforme (GBM).

SUBJECTS AND METHOD

This retrospective study was carried out by reviewing the medical records of 223 adult patients diagnosed at a tertiary academic hospital between 1990 and 2008. Patients' follow up ranged from 1 to 69 months (median 11 months). Surgery was attempted in all patients in whom complete resection in 15 patients (7%), subtotal resection in 77 patients (34%), partial resection in 73 patients (33%) and biopsy alone in 58 patients (26%) were done. In addition, we performed a literature review of PubMed to find out and analyze major related series. In all, we collected and analyzed the data of 33 major series including more than 11,000 patients with GBM.

RESULTS

There were 141 men and 82 women. The median progression free- and overall survival were 6 (95% CI=5.711-8.289) and 11 (95% CI=9.304-12.696) months respectively. In univariate analysis for overall survival, age (P=0.003), tumor size (P<0.013), performance status (P<0.001), the extent of surgical resection (P=0.009), dose of radiation (P<0.001), and adjuvant chemotherapy (P<0.001) were prognostic factors. However, in multivariate analysis, only radiation dose, extent of surgical resection, and adjuvant chemotherapy were independent prognostic factors for overall survival.

CONCLUSION

The prognosis of adult patients with GBM remains poor; however, complete surgical resection and adjuvant treatments improve progression-free and overall survival.

Pediatric glioblastoma multiforme: A single-institution experience

Background:

Glioblastoma multiforme (GBM) is the most common astrocytoma in adults and has a poor prognosis, with a median survival of about 12 months. But, it is rare in children. We report our experience on the pediatric population (20 years or younger) with GBM.

Patients and Methods:

Twenty-three patients with GBM who were treated at our hospital during 1990–2008 were evaluated.

Results:

The mean age was 15.2 years, and the majority of them (14/23) were male. All had received radiotherapy and some had also received chemotherapy. The mean survival was 16.0 months. Two cases survived more than 5 years. Age, radiation dose and performance status were significantly related to survival.

Conclusion:

GBM in pediatric patients were not very common in our center, and prognosis was unfavorable.

Expression of eukaryotic initiation factor 5A and hypusine forming enzymes in glioblastoma patient samples: implications for new targeted therapies

Glioblastomas are highly aggressive brain tumors of adults with poor clinical outcome. Despite a broad range of new and more specific treatment strategies, therapy of glioblastomas remains challenging and tumors relapse in all cases. Recent work demonstrated that the posttranslational hypusine modification of the eukaryotic initiation factor 5A (eIF-5A) is a crucial regulator of cell proliferation, differentiation and an important factor in tumor formation, progression and maintenance. Here we report that eIF-5A as well as the hypusine-forming enzymes deoxyhypusine synthase (DHS) and deoxyhypusine hydroxylase (DOHH) are highly overexpressed in glioblastoma patient samples. Importantly, targeting eIF-5A and its hypusine modification with GC7, a specific DHS-inhibitor, showed a strong antiproliferative effect in glioblastoma cell lines in vitro, while normal human astrocytes were not affected. Furthermore, we identified p53 dependent premature senescence, a permanent cell cycle arrest, as the primary outcome in U87-MG cells after treatment with GC7. Strikingly, combined treatment with clinically relevant alkylating agents and GC7 had an additive antiproliferative effect in glioblastoma cell lines. In addition, stable knockdown of eIF-5A and DHS by short hairpin RNA (shRNA) could mimic the antiproliferative effects of GC7. These findings suggest that pharmacological inhibition of eIF-5A may represent a novel concept to treat glioblastomas and may help to substantially improve the clinical course of this tumor entity.

NADPH oxidase subunit 4 mediates cycling hypoxia-promoted radiation resistance in glioblastoma multiforme

Cycling hypoxia is a well-recognized phenomenon within animal and human solid tumors. It mediates tumor progression and radiotherapy resistance through mechanisms that involve reactive oxygen species (ROS) production. However, details of the mechanism underlying cycling hypoxia-mediated radioresistance remain obscure. We have previously shown that in glioblastoma, NADPH oxidase subunit 4 (Nox4) is a critical mediator involved in cycling hypoxia-mediated ROS production and tumor progression. Here, we examined the impact of an in vivo tumor microenvironment on Nox4 expression pattern and its impact on radiosensitivity in GBM8401 and U251, two glioblastoma cell lines stably transfected with a dual hypoxia-inducible factor-1 (HIF-1) signaling reporter construct. Furthermore, in order to isolate hypoxic tumor cell subpopulations from human glioblastoma xenografts based on the physiological and molecular characteristics of tumor hypoxia, several techniques were utilized. In this study, the perfusion marker Hoechst 33342 staining and HIF-1 activation labeling were used together with immunofluorescence imaging and fluorescence-activated cell sorting (FACS). Our results revealed that Nox4 was predominantly highly expressed in the endogenous cycling hypoxic areas with HIF-1 activation and blood perfusion within the solid tumor microenvironment. Moreover, when compared to the normoxic or chronic hypoxic cells, the cycling hypoxic tumor cells derived from glioblastoma xenografts have much higher Nox4 expression, ROS levels, and radioresistance. Nox4 suppression in intracerebral glioblastoma-bearing mice suppressed tumor microenvironment-mediated radioresistance and enhanced the efficiency of radiotherapy. In summary, our findings indicated that cycling hypoxia-induced Nox4 plays an important role in tumor microenvironment-promoted radioresistance in glioblastoma; hence, targeting Nox4 may be an attractive therapeutic strategy for blocking cycling hypoxia-mediated radioresistance.

Brain tumors in children--current therapies and newer directions

Brain tumors are the second most common malignancy and the major cause of cancer related mortality in children. Though significant advances in neuroimaging, neurosurgery, radiation therapy and chemotherapy have evolved over the years, overall survival rate remains less than 75%. Malignant gliomas, high risk medulloblastoma with recurrence and infant brain tumors continue to be a major cause of therapeutic frustration. Even today diffuse pontine gliomas are universally fatal. Though tumors like low grade glioma have an overall excellent survival, recurrences and progression in eloquent areas pose therapeutic challenges. As research continues to unravel the biology including key molecules and signaling pathways responsible for the oncogenesis of different childhood brain tumors, novel targeted therapies are profiled. Identification of major targets like the Epidermal Growth factor Receptor (EGFR), Platelet Derived Growth Factor Receptor (PDGFR), Vascular Endothelial Growth factor (VEGF) and key signaling pathways like the MAPK and PI3K/Akt/mTOR has enabled us over the recent years to better understand tumor behavior and design tailored therapy. These efforts have improved overall survival of children with brain tumors. This review article discusses the current status of common brain tumors in children and the newer therapeutic approaches.

The role of adjuvant radiation therapy in the management of high-grade gliomas

The purpose of this article is to update the neurosurgical community on the role of adjuvant radiation therapy in the management of patients with high-grade glioma. This information guides clinicians in the multidisciplinary management of these patients via a review of the literature describing current treatment paradigms as well as new avenues of investigation.

Towards tailored therapy of glioblastoma multiforme

Gliobastoma multiform (GBM) is the most common and aggressive brain tumor, which is characterized by its infiltrative nature. Current standard therapy for GBMs consists of surgery followed by radiotherapy combined with the alkylating agent temozolomide (TMZ). Recent clinical trials have demonstrated that this chemo-irradiation approach results in a significant increase in survival compared to radiotherapy alone. Nevertheless, due to tumor recurrence, the median survival time is still limited to approximately 15 months. Recently, several studies have focused on aberrant signal transduction in GBM, resistance mechanisms of GBM to TMZ and to radiotherapy. Attention has been focused on molecular targets including phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway, protein kinase C (pKC) pathway, Ras/mitogen-activated protein kinase pathway (MAPK), Wnt pathway and intrinsic or extrinsic apoptosis pathways. In addition, research has been directed to radiotherapy and radiosensitizing agents, and cancer gene therapy as well. This article will address several resistance mechanisms of GBM to chemotherapy and radiotherapy and the recent preclinical and clinical studies on targeted therapy.

Radioresistance of human glioma spheroids and expression of HSP70, p53 and EGFr

BACKGROUND

Radiation therapy is routinely prescribed for high-grade malignant gliomas. However, the efficacy of this therapeutic modality is often limited by the occurrence of radioresistance, reflected as a diminished susceptibility of the irradiated cells to undergo cell death. Thus, cells have evolved an elegant system in response to ionizing radiation induced DNA damage, where p53, Hsp70 and/or EGFr may play an important role in the process. In the present study, we investigated whether the content of p53, Hsp70 and EGFr are associated to glioblastoma (GBM) cell radioresistance.

METHODS

Spheroids from U-87MG and MO59J cell lines as well as spheroids derived from primary culture of tumor tissue of one GBM patient (UGBM1) were irradiated (5, 10 and 20 Gy), their relative radioresistance were established and the p53, Hsp70 and EGFr contents were immunohistochemically determined. Moreover, we investigated whether EGFr-phospho-Akt and EGFr-MEK-ERK pathways can induce GBM radioresistance using inhibitors of activation of ERK (PD098059) and Akt (wortmannin).

RESULTS

At 5 Gy irradiation UGBM1 and U-87MG spheroids showed growth inhibition whereas the MO59J spheroid was relatively radioresistant. Overall, no significant changes in p53 and Hsp70 expression were found following 5 Gy irradiation treatment in all spheroids studied. The only difference observed in Hsp70 content was the periphery distribution in MO59J spheroids. However, 5 Gy treatment induced a significant increase on the EGFr levels in MO59J spheroids. Furthermore, treatment with inhibitors of activation of ERK (PD098059) and Akt (wortmannin) leads to radiosensitization of MO59J spheroids.

CONCLUSIONS

These results indicate that the PI3K-Akt and MEK-ERK pathways triggered by EGFr confer GBM radioresistance.

STAT6 expression in glioblastoma promotes invasive growth

BACKGROUND

Glioblastoma (GBM) is a highly aggressive malignant primary brain tumor, characterized by rapid growth, diffuse infiltration of cells into both adjacent and remote brain regions, and a generalized resistance to currently available treatment modalities. Recent reports in the literature suggest that Signal Transducers and Activators of Transcription (STATs) play important roles in the regulation of GBM pathophysiology.

METHODS

STAT6 protein expression was analyzed by Western blotting in GBM cell lines and by immunohistochemistry in a tissue microarray (TMA) of glioma patient tissues. We utilized shRNA against STAT6 to investigate the effects of prolonged STAT6 depletion on the growth and invasion of two STAT6-positive GBM cell lines. Cell proliferation was assessed by measuring (3)H-Thymidine uptake over time. Invasion was measured using an in vitro transwell assay in which cells invade through a type IV collagen matrix toward a chemoattractant (Fetal Bovine Serum). Cells were then stained and counted. Kaplan-Meyer survival curves were generated to show the correlation between STAT6 gene expression and patient survival in 343 glioma patients and in a subset of patients with only GBM. Gene expression microarray and clinical data were acquired from the Rembrandt 1 public data depository (https://caintegrator.nci.nih.gov/rembrandt/). Lastly, a genome-wide expression microarray analysis was performed to compare gene expression in wild-type GBM cells to expression in stable STAT6 knockdown clones.

RESULTS

STAT6 was expressed in 2 GBM cell lines, U-1242MG and U-87MG, and in normal astrocytes (NHA) but not in the U-251MG GBM cell line. In our TMA study, STAT6 immunostaining was visible in the majority of astrocytomas of all grades (I-IV) but not in normal brain tissue. In positive cells, STAT6 was localized exclusively in the nuclei over 95% of the time. STAT6-deficient GBM cells showed a reduction in (3)H-Thymidine uptake compared to the wild-type. There was some variation among the different shRNA- silenced clones, but all had a reduction in (3)H-Thymidine uptake ranging from 35%- 70% in U-1242MG and 40- 50% in U-87MG cells. Additionally, STAT6- depleted cells were less invasive than controls in our in vitro transmembrane invasion assay. Invasiveness was decreased by 25-40% and 30-75% in U-1242MG and U-87MG cells, respectively. The microarray analysis identified matrix metalloproteinase 1 (MMP-1) and urokinase Plasminogen activator (uPA) as potential STA6 target genes involved in the promotion of GBM cell invasion. In a Kaplan-Meier survival curve based on Rembrandt 1 gene expression microarray and clinical data, there was a significant difference in survival (P < 0.05) between glioma patients with up- and down-regulated STAT6. Decreased STAT6 expression correlated with longer survival times. In two subsets of patients with either grade IV tumors (GBM) or Grade II/III astrocytomas, there was a similar trend that however did not reach statistical significance.

CONCLUSIONS

Taken together, these findings suggest a role for STAT6 in enhancing cell proliferation and invasion in GBM, which may explain why up-regulation of STAT6 correlates with shorter survival times in glioma patients. This report thus identifies STAT6 as a new and potentially promising therapeutic target.

Molecular heterogeneity in glioblastoma: therapeutic opportunities and challenges

Glioblastoma (GBM) has been recognized as a clinical and pathologic entity for more than a century. Throughout its history, its cells of origin have been in question. Its behavior is aggressive and despite decades of effort, median survival is just beginning to improve. Surgical techniques and radiotherapy schemas continue to be refined, but the most recent progress has been achieved through improved medical therapies. These are the result of both pharmacological advances and a deeper understanding of the biological characteristics of GBM. Due to a combination of its complex phenotype and organ-specific clinical manifestations, efforts to refine GBM treatment with targeted therapies largely have been frustrated. In this review, we discuss recent attempts to exploit new molecular insights, consider the reasons for slow progress in developing better treatments, and examine future therapeutic options.

γ-secretase inhibitor-I enhances radiosensitivity of glioblastoma cell lines by depleting CD133+ tumor cells

BACKGROUND AND AIMS

Glioblastoma is a deadly primary brain tumor with great resistance to radiotherapy. To reverse its radioresistance is important for improving prognosis. Gamma-secretase inhibitors (GSI) have been proven to have anti-tumor effects, yet the knowledge of their influences on glioblastomas is still limited.

METHODS

The cytotoxic effects of GSI-I (a tripeptide GSI) on glioblastoma cell lines U87 and U251 were assessed by MTT assay, and the low concentration that did not induce significant cell death was determined. The in vitro radiosensitization effects of this low concentration of GSI-I were evaluated by cell colony forming assays. The CD133+ cell fractions before and after radiation with or without treatment of GSI-I were analyzed by flow cytometry. Then CD133+ and CD133- glioblastoma cells were sorted by magnetic activated cell sorting (MACS), and the radiosensitization effects of GSI-I on the two cell subtypes were investigated separately. Finally, the cytotoxic effects of GSI-I on CD133+and CD133- glioblastoma cells were examined, respectively, and the expression of the Notch pathway components between the two cell subtypes were compared. In addition, the anti-tumor effects of GSI-I were confirmed by in vivo experiments.

RESULTS

GSI-I at a low concentration sensitized U87 and U251 cells to radiation by depletion of radioresistant CD133+ cells. CD133+ U87/U251 cells displayed preferential sensitivity to low concentrations of GSI-I, which may be related to the higher expression of the Notch signaling pathway in these cells.

CONCLUSIONS

Combining GSI-I with radiotherapy may represent a promising strategy for treating radioresistant gliomas.

Exciting new advances in neuro-oncology: the avenue to a cure for malignant glioma

Malignant gliomas are the most common and deadly brain tumors. Nevertheless, survival for patients with glioblastoma, the most aggressive glioma, although individually variable, has improved from an average of 10 months to 14 months after diagnosis in the last 5 years due to improvements in the standard of care. Radiotherapy has been of key importance to the treatment of these lesions for decades, and the ability to focus the beam and tailor it to the irregular contours of brain tumors and minimize the dose to nearby critical structures with intensity-modulated or image-guided techniques has improved greatly. Temozolomide, an alkylating agent with simple oral administration and a favorable toxicity profile, is used in conjunction with and after radiotherapy. Newer surgical techniques, such as fluorescence-guided resection and neuroendoscopic approaches, have become important in the management of malignant gliomas. Furthermore, new discoveries are being made in basic and translational research, which are likely to improve this situation further in the next 10 years. These include agents that block 1 or more of the disordered tumor proliferation signaling pathways, and that overcome resistance to already existing treatments. Targeted therapies such as antiangiogenic therapy with antivascular endothelial growth factor antibodies (bevacizumab) are finding their way into clinical practice. Large-scale research efforts are ongoing to provide a comprehensive understanding of all the genetic alterations and gene expression changes underlying glioma formation. These have already refined the classification of glioblastoma into 4 distinct molecular entities that may lead to different treatment regimens. The role of cancer stem-like cells is another area of active investigation. There is definite hope that by 2020, new cocktails of drugs will be available to target the key molecular pathways involved in gliomas and reduce their mortality and morbidity, a positive development for patients, their families, and medical professionals alike.

Proton-beam therapy for tumors of the CNS

The focus of this review is proton radiotherapy for primary neoplasms of the brain. Although glial cells are among the most radioresistant in the body, the presence of sensitive critical structures and the high doses needed to control CNS tumors present a formidable challenge to the treating radiation oncologist. Treatment with conventional photon radiation at doses required to control disease progression all too often results in unacceptable toxicity. Protons have intrinsic properties that often allow radiation oncologists to deliver a higher dose to the tumor compared with photons, while at the same time offering better sparing of normal tissues. Recognition of these advantages has resulted in development of many new proton treatment facilities worldwide.