Astrocyte differentiation states and glioma formation

Aloe-Emodin Overcomes Anti-Cancer Drug Resistance to Temozolomide and Prevents Colony Formation and Migration in Primary Human Glioblastoma Cell Lines NULU and ZAR

Glioblastoma, the most dangerous and aggressive type of CNS tumor, appears resistant to many chemotherapy drugs. In the patient-derived glioma cell lines NULU and ZAR, which exhibit drug-resistant phenotypes, we investigated the effect of combined AE (Aloe-emodin) and TMZ (temozolomide) and found a significant additive inhibitory effect on cell growth and a promising cytotoxic effect on both cell lines compared to treatment with single agents. We also examined the effect of combined AE and TMZ treatment on the drug-resistance protein MGMT. The results suggest that using AE combined with traditional drugs restores drug resistance in both primary resistant cell lines (NULU and ZAR). Furthermore, migration assays and scratch tests showed that the combined use of AE and TMZ can slow down the colony formation and migration of glioblastoma cells. These convincing results suggest that AE could be a natural adjuvant agent to potentiate the effects of traditional drugs (TMZ) and overcome drug resistance in glioblastoma cells.

Nidogen-1 expression is associated with overall survival and temozolomide sensitivity in low-grade glioma patients

We investigated the prognostic significance of nidogen-1 (NID1) in glioma. Oncomine, GEPIA, UALCAN, CCGA database analyses showed that NID1 transcript levels were significantly upregulated in multiple cancer types, including gliomas. Quantitative RT-PCR analyses confirmed that NID1 expression was significantly upregulated in glioma tissues compared to paired adjacent normal brain tissue samples (n=9). NID1 silencing enhanced in vitro apoptosis and the temozolomide sensitivity of U251 and U87-MG glioma cells. Protein-protein interaction network analysis using the STRING and GeneMANIA databases showed that NID1 interacts with several extracellular matrix proteins. TIMER database analysis showed that NID1 expression in low-grade gliomas was associated with tumor infiltration of B cells, CD4⁺ and CD8⁺ T cells, macrophages, neutrophils, and dendritic cells. Kaplan-Meier survival curve analysis showed that low-grade gliomas patients with high NID1 expression were associated with shorter overall survival. However, NID1 expression was not associated with overall survival in glioblastoma multiforme patients. These findings demonstrate that NID1 expression in glioma tissues is associated with overall survival of low-grade glioma patients and temozolomide sensitivity. NID1 is thus a potential prognostic biomarker and therapeutic target in low-grade glioma patients.

Characterization of primary glioma cell lines derived from the patients according to 2016 CNS tumour WHO classification and comparison with their parental tumours

BACKGROUND

Gliomas represent about 80% of primary brain tumours and about 30% of malignant ones, which today don't have a resolution therapy because of their variability. A valid model for the study of new personalized therapies can be represented by primary cultures from patient's tumour biopsies.

METHODS

In this study we consider 12 novel cell lines established from patients' gliomas and immunohistochemically and molecularly characterized according to the newly updated 2016 CNS Tumour WHO classification.

RESULTS

Eight of these lines were glioblastoma cells, two grade III glioma cells (anaplastic astrocytoma and oligo astrocytoma) and two low grade glioma cells (grade II astrocytoma and oligodendroglioma). All cell lines were analysed by immunohistochemistry for specific glioma markers, respectively VIMENTIN, GFAP, IDH1R132, and ATRX. The methylation status of the MGMT gene promoter was also determined in all lines. The comparison of the immunohistochemical characteristics and of the MGMT methylation status of the lines with the tissues of origin shows that the cells in culture maintain the same characteristics.

CONCLUSIONS

Human cancer cell lines represent a support in the knowledge of tumour biology and in drug discovery through its facile experimental manipulation.

TRIAL REGISTRATION

NCT04180046.

A new tyrosine kinase inhibitor K905-0266 inhibits proliferation and sphere formation of glioblastoma cancer cells

Glioblastoma (GBM) is the most prevalent malignant tumour of the central nervous system and carries a poor prognosis; average survival time after diagnosis is 14 months. Because of its unfavourable prognosis, novel therapies are needed. The aim of this study was to assess whether inhibition of GBM and GBM-derived cancer stem cells (CSCs) by a new tyrosine kinase inhibitor (TKI), K905-0266, is possible. To do this, we generated GBM (D54 and U87MG) cells expressing luciferase and characterised the inhibitory effects of the TKI with bioluminescent imaging (BLI) and western blot (WB). The effect of the TKI was then evaluated in CSCs. BLI showed significant inhibition of D54 and U87MG cells by TKI treatment. WB showed that the TKI decreased pERK and Bcl-2 level and increased cleaved caspase-3 level. Sphere formation was significantly reduced by the TKI in CSCs. Our results showed that a new TKI, K905-0266, effectively inhibited GBM and CSCs, making this a candidate for GBM therapy.

Effects of aloe emodin on U87MG glioblastoma cell growth: In vitro and in vivo study

Glioblastoma, the most aggressive and malignant form of glioma, appears to be resistant to various chemotherapeutic agents. Hence other approaches have been investigated to target more pathways involved in glioblastoma development and progression. Here we investigate the anticancer effect of Aloe-Emodin (AE), an anthraquinone compound presents in the leaves of Aloe arborescens, on human glioblastoma cell line U87MG. U87MG were treated with various concentrations of AE (20 and 40 μM) for different times (24, 48, and 72 hr). Cell growth was monitored by daily cell count after treatments. Growth analysis showed that AE significantly decrease proliferation of U87MG in a time and dose dependent manner. FACS analysis demonstrates a block of cell cycle in S and G2/M phase. AE probably induced also apoptosis by releasing of apoptosis-inducing factor: PARP and Lamin activation leading to nuclear shrinkage. In addition, exposure of U87MG to AE reduced pAKT phosphorylation. AE inhibition of U87MG growth is a result of more mechanism together. Here we report that AE has a specific growth inhibition on U87MG also in in vivo. The growth of U87MG, subcutaneously injected in nude mice with severe combined immunodeficiency, is inhibited without any appreciable toxic effects on the animals after AE treatment. AE might represent a conceptually new lead antitumor adjuvant drug.

Knockdown of AKT3 (PKBγ) and PI3KCA suppresses cell viability and proliferation and induces the apoptosis of glioblastoma multiforme T98G cells

Glioblastoma multiforme (GBM) is the most malignant and invasive human brain tumor that is difficult to treat and has a very poor prognosis. Thus, new therapeutic strategies that target GBM are urgently needed. The PI3K/AKT/PTEN signaling pathway is frequently deregulated in a wide range of cancers. The present study was designed to examine the inhibitory effect of AKT3 or PI3KCA siRNAs on GBM cell growth, viability, and proliferation.T98G cells were transfected with AKT3 and/or PI3KCA siRNAs. AKT3 and PI3KCA protein-positive cells were identified using FC and Western blotting. The influence of specific siRNAs on T98G cell viability, proliferation, cell cycle, and apoptosis was evaluated as well using FC. Alterations in the mRNA expression of AKT3, PI3KCA, and apoptosis-related genes were analyzed using QRT-PCR. Knockdown of AKT3 and/or PI3KCA genes in T98G cells led to a significant reduction in cell viability, the accumulation of subG1-phase cells and, a reduced fraction of cells in the S and G2/M phases. Additionally, statistically significant differences in the BAX/BCL-2 ratio and an increased percentage of apoptotic cells were found. The siRNA-induced AKT3 and PI3KCA mRNA knockdown may offer a novel therapeutic strategy to control the growth of human GBM cells.

The antiproliferative effect of indomethacin-loaded lipid-core nanocapsules in glioma cells is mediated by cell cycle regulation, differentiation, and the inhibition of survival pathways

Despite recent advances in radiotherapy, chemotherapy, and surgical techniques, glioblastoma multiforme (GBM) prognosis remains dismal. There is an urgent need for new therapeutic strategies. Nanoparticles of biodegradable polymers for anticancer drug delivery have attracted intense interest in recent years because they can provide sustained, controlled, and targeted delivery. Here, we investigate the mechanisms involved in the antiproliferative effect of indomethacin-loaded lipid-core nanocapsules (IndOH-LNC) in glioma cells. IndOH-LNC were able to reduce cell viability by inducing apoptotic cell death in C6 and U138-MG glioma cell lines. Interestingly, IndOH-LNC did not affect the viability of primary astrocytes, suggesting that this formulation selectively targeted transformed cells. Mechanistically, IndOH-LNC induced inhibition of cell growth and cell-cycle arrest to be correlated with the inactivation of AKT and β-catenin and the activation of GSK-3β. IndOH-LNC also induced G0/G1 and/or G2/M phase arrest, which was accompanied by a decrease in the levels of cyclin D1, cyclin B1, pRb, and pcdc2 and an increase in the levels of Wee1 CDK inhibitor p21^WAF1. Additionally, IndOH-LNC promoted GBM cell differentiation, observed as upregulation of glial fibrillary acidic protein (GFAP) protein and downregulation of nestin and CD133. Taken together, the crosstalk among antiproliferative effects, cell-cycle arrest, apoptosis, and cell differentiation should be considered when tailoring pharmacological interventions aimed at reducing glioma growth by using formulations with multiples targets, such as IndOH-LNC.

Neoplasms associated with germline and somatic NF1 gene mutations

INTRODUCTION

Neurofibromatosis 1 is a tumor predisposition genetic syndrome with autosomal dominant inheritance and virtually 100% penetrance by the age of 5 years. NF1 results from a loss-of-function mutation in the NF1 gene, resulting in decreased levels of neurofibromin in the cell. Neurofibromin is a negative regulator of various intracellular signaling pathways involved in the cellular proliferation. Although the loss of heterozygosity in the NF1 gene may predispose NF1 patients to certain malignancies, additional genetic alterations are a prerequisite for their development. The precise nature of these additional genetic alterations is not well defined, and genetic testing of all malignancies in NF1 patients becomes an essential component of future research in this subset of patients. In addition to germline NF1 mutations, alteration of the somatic NF1 gene is associated with sporadic malignancies such as adenocarcinoma of the colon, myelodysplastic syndrome, and anaplastic astrocytoma.

MATERIALS AND METHODS

A comprehensive English and non-English language search for all articles pertinent to malignancies associated with NF1 was conducted using PubMed, a search engine provided by the U.S. National Library of Medicine and the National Institutes of Health. Key words searched included the following: "malignancies associated with NF1", "tumors associated with NF1", and "NF1 and malignancies". A comprehensive analysis in terms age and mode of presentation, investigation and therapeutic modalities, and outcome of the published data was performed and compared with similar information on the sporadic cases.

RESULTS

Malignancies in NF1 patients typically occur at an earlier age and, with an exception of optic pathway gliomas, certain types of malignancies carry a poor prognosis compared with their sporadic counterparts. Malignancies are the leading cause of death in NF1 patients, resulting in a 10- to 15-year decreased life expectancy compared with the general population.

CONCLUSIONS

The lack of well-defined screening tests for early detection and the nonspecific clinical presentation contributes to a poorer outcome in malignancies associated with NF1. Small study group size, mixed patient population, and a lack of uniformity in reporting research results make comparison of treatment outcome for this group difficult. An International Consensus Meeting to address and recommend best practices for screening, diagnosis, management, and follow-up of malignancies associated with NF1 is needed.

[Instability of cell phenotype and tumor initiating cells in gliomas]

Gliomas, the most frequent primitive CNS tumors, have been suggested to originate from astrocytes or from neural progenitors/stem cells. However, the precise identity of the cells at the origin of gliomas remains a matter of debate because no pre-neoplastic state has been yet identified. TGFα, an EGF family member, is frequently over-expressed in the early stages of glioma progression. We questioned whether prolonged TGFα exposure affects the stability of the normal mature astrocyte phenotype and, eventually, their propensity to cancerous transformation. Using mouse astrocyte cultures devoid of residual neural stem cells or progenitors, we demonstrate that several days of TGFα-treatment result in the functional conversion of a population of mature astrocytes into radial glial cells, a population of neural progenitors, without any accompanying sign of cancerous transformation. In contrast, when astrocytes de-differentiated with TGFα were submitted to oncogenic stress using gamma irradiation, they acquired cancerous properties, forming high-grade glioma-like tumors after brain grafting. Gamma irradiation was without effect on astrocytes which were not treated with TGFα. These results suggested that most gliomas should contain tumor cells with stem-like properties (TSCs). Our study of 55 pediatric brain tumors show that tumor cells with stem cell-like or progenitor-like properties can be isolated from a majority of gliomas. Survival analysis showed an association between isolation of TSCs with extended self-renewal capabilities and a patient's higher mortality rate.

Clinical relevance of tumor cells with stem-like properties in pediatric brain tumors

Background

Primitive brain tumors are the leading cause of cancer-related death in children. Tumor cells with stem-like properties (TSCs), thought to account for tumorigenesis and therapeutic resistance, have been isolated from high-grade gliomas in adults. Whether TSCs are a common component of pediatric brain tumors and are of clinical relevance remains to be determined.

Methodology/Principal Findings

Tumor cells with self-renewal properties were isolated with cell biology techniques from a majority of 55 pediatric brain tumors samples, regardless of their histopathologies and grades of malignancy (57% of embryonal tumors, 57% of low-grade gliomas and neuro-glial tumors, 70% of ependymomas, 91% of high-grade gliomas). Most high-grade glioma-derived oncospheres (10/12) sustained long-term self-renewal akin to neural stem cells (>7 self-renewals), whereas cells with limited renewing abilities akin to neural progenitors dominated in all other tumors. Regardless of tumor entities, the young age group was associated with self-renewal properties akin to neural stem cells (P = 0.05, chi-square test). Survival analysis of the cohort showed an association between isolation of cells with long-term self-renewal abilities and a higher patient mortality rate (P = 0.013, log-rank test). Sampling of low- and high-grade glioma cultures showed that self-renewing cells forming oncospheres shared a molecular profile comprising embryonic and neural stem cell markers. Further characterization performed on subsets of high-grade gliomas and one low-grade glioma culture showed combination of this profile with mesenchymal markers, the radio-chemoresistance of the cells and the formation of aggressive tumors after intracerebral grafting.

Conclusions/Significance

In brain tumors affecting adult patients, TSCs have been isolated only from high-grade gliomas. In contrast, our data show that tumor cells with stem cell-like or progenitor-like properties can be isolated from a wide range of histological sub-types and grades of pediatric brain tumors. They suggest that cellular mechanisms fueling tumor development differ between adult and pediatric brain tumors.

Ultrastructural characterization of the optic pathway in a mouse model of neurofibromatosis-1 optic glioma

The purpose of this study was to investigate the progression of changes in retinal ganglion cells and optic nerve glia in neurofibromatosis-1 (NF1) genetically-engineered mice with optic glioma. Optic glioma tumors were generated in Nf1+/- mice lacking Nf1 expression in GFAP+ cells (astrocytes). Standard immunohistochemistry methods were employed to identify astrocytes (GFAP, S100beta), proliferating progenitor cells (sox2, nestin), microglia (Iba1), endothelial cells (CD31) and retinal ganglion cell (RGC) axons (Neurofilament 68k) in Nf1+/-, Nf1(GFAP)CKO (wild-type mice with Nf1 loss in glial cells), and Nf1+/-(GFAP)CKO (Nf1+/- mice with Nf1 loss in glial cells) mice. Ultrastructural changes in the optic chiasm and nerve were assessed by electron microscopy (EM). RGC were counted in whole retina preparations using high-resolution, mosaic confocal microscopy following their delineation by retrograde FluoroGold labeling. We found that only Nf1+/-(GFAP)CKO mice exhibited gross pre-chiasmatic optic nerve and chiasm enlargements containing aggregated GFAP+/nestin+ and S100beta+/sox2+ cells (neoplastic glia) as well as increased numbers of blood vessels and microglia. Optic gliomas in Nf1+/-(GFAP)CKO mice contained axon fiber irregularities and multilamellar bodies of degenerated myelin. EM and EM tomographic analyses showed increased glial disorganization, disoriented axonal projections, profiles of degenerating myelin and structural alterations at nodes of Ranvier. Lastly, we found reduced RGC numbers in Nf1+/-(GFAP)CKO mice, supporting a model in which the combination of optic nerve Nf1 heterozygosity and glial cell Nf1 loss results in disrupted axonal-glial relationships, subsequently culminating in the degeneration of optic nerve axons and loss of their parent RGC neurons.

1p19q LOH patterns and expression of p53 and Olig2 in gliomas: relation with histological types and prognosis

In glial tumors, the loss of heterozygosity of the 1p and 19q chromosomal arms is thought to be a marker of good prognosis in oligodendroglial tumors. However, 1p and 19q loss of heterozygosity may be telomeric, interstitial, centromeric or affect the whole arm of the chromosome and the associations between these different patterns and tumor type, other molecular markers and patient prognosis remain unclear. We analyzed microsatellite markers in a region spanning the chromosome from the telomere to the centromere, to characterize the pattern of 1p and 19q loss of heterozygosity in 39 infiltrative gliomas, including astrocytomas, glioblastomas, oligoastrocytomas and oligodendrogliomas. We then studied the association between loss of heterozygosity and the expression of p53 protein and Olig2, as analyzed using immunohistochemistry, and epidermal growth factor receptor (EGFR) gene amplification, as investigated using fluorescence in situ hybridization (FISH). Finally, we assessed the influence of molecular markers on the overall survival of patients. We identified five different 1p19q loss of heterozygosity patterns among the tumors studied and found that loss of heterozygosity over the whole 1p arm was associated with loss of heterozygosity over the whole 19q arm in 90% of cases. 1p19q whole loss was present in all the classical oligodendrogliomas, whereas other 1p19q loss patterns predominated in oligoastrocytomas. 1p19q whole loss was also significantly associated with Olig2 overexpression, but was never observed in tumors overexpressing p53 protein. We also found that, among patients with contrast-enhancing tumors, those with 1p19q whole loss tended to survive for longer. In combination with classical histological and immunohistochemical data, 1p19q status determination provides pertinent information useful for (1) discriminating between histological types of gliomas and (2) identifying a subgroup of tumors that are associated with a better prognosis.

Apparent diffusion coefficient of glial neoplasms: correlation with fluorodeoxyglucose-positron-emission tomography and gadolinium-enhanced MR imaging

BACKGROUND AND PURPOSE

Gd-enhancement provides essential information in the assessment of brain tumors. However, enhancement does not always correlate with histology or disease activity, especially in the setting of current therapies. Our aim was to compare FDG-PET scans to ADC maps and Gd-enhanced MR images in patients with glial neoplasms to assess whether DWI might offer information not available on routine MR imaging sequences and whether such findings have prognostic significance.

MATERIALS AND METHODS

Institutional review board approval was obtained for this retrospective review, which was conducted in full compliance with HIPAA regulations. Twenty-one patients (11 men and 10 women) with glial tumors underwent FDG-PET and MR imaging, including ADC and Gd- enhancement. Subjectively, regions of interest were drawn around the following areas: 1) increased FDG uptake, 2) decreased signal intensity on ADC maps, and 3) Gd-enhancement. Objectively, FDG-PET and MR images were co-registered, and pixel-by-pixel comparison of ADC to PET values was made for all regions of interest. Correlation coefficients (r values) were calculated for each region of interest. Percentage overlap between regions of interest was calculated for each case.

RESULTS

Subjective evaluation showed 60% of patients with excellent or good correlation between ADC maps and FDG-PET. Pixel-by-pixel comparison demonstrated r values that ranged from -0.72 to -0.21. There was significantly greater overlap between decreased ADC and increased FDG-PET uptake (67.1 +/- 15.5%) versus overlap between Gd-enhancement and increased FDG-PET uptake (54.4 +/- 27.5%) (P < .05). ADC overlap was greater with increased FDG-PET than with Gd-enhancement in 8/9 cases. Survival data revealed that the presence of restricted diffusion on ADC correlated with patient survival (P < .0001).

CONCLUSIONS

ADC maps in patients with brain tumors provide unique information that is analogous to FDG-PET. There is a greater overlap between ADC and FDG-PET compared with Gd-enhancement. ADC maps can serve to approximate tumor grade and predict survival.

Activated BRAF induces gliomas in mice when combined with Ink4a/Arf loss or Akt activation

Mutations in receptor tyrosine kinase (RTK) growth factor receptors (epidermal growth factor receptor, platelet-derived growth factor receptor, MET and ERBB2), which result in downstream activation of the RAS/RAF/MEK/ERK mitogen-activated protein kinase (MAPK) pathway and PI(3)K/Akt pathway, are found in almost all high-grade gliomas and MAPK signaling is necessary for continued glioma maintenance. In addition, BRAF is mutated in the majority of low-grade gliomas and its expression and activity is significantly increased in the majority of high-grade gliomas. Although the importance of RTKs and RAS signaling in glioma development has been shown, the role of BRAF has yet to be characterized. We evaluated the effect of activated BRAF in glioma formation using the retroviral replication-competent avian leukosis virus long terminal repeat, splice acceptor (RCAS)/TVA system to transfer genes encoding activated forms of BRAF, KRas, Akt and Cre to nestin-expressing neural progenitor cells in Ink4a/Arf(lox/lox) mice in vivo. Although expression of activated BRAF alone is not sufficient for tumorigenesis, the combination of activated BRAF and Akt or BRAF with Ink4a/Arf loss is transforming. Interestingly, activated BRAF generates gliomas with characteristics similar to activated KRas in the context of Akt but not Ink4a/Arf loss. Our studies show a role for BRAF activation and signaling in glioma development and as potential target for glioma therapy.

Live cell labeling of glial progenitor cells using targeted quantum dots

This study describes the development of targeted quantum dots (T-QDs) as biomarkers for the labeling of glial progenitor cells (GPCs) that over express platelet derived growth factor (PDGF) and its receptor PDGFR (GPC(PDGF)). PDGFR plays a critical role in glioma development and growth, and is also known to affect multiple biological processes such as cell migration and embryonic development. T-QDs were developed using streptavidin-conjugated quantum dots (S-QDs) with biotinylated antibodies and utilized to label the intracellular and extracellular domains of live, cultured GPC(PDGF) cells via lipofection with cationic liposomes. Confocal studies illustrate successful intracellular and extracellular targeted labeling within live cells that does not appear to impact upstream PDGFR dynamics during real-time signaling events. Further, T-QDs were nontoxic to GPC(PDGF) cells, and did not alter cell viability or proliferation over the course of 6 days. These results raise new applications for T-QDs as ultra sensitive agents for imaging and tracking of protein populations within live cells, which that will enable future mechanistic study of oncogenic signaling events in real-time.

Identification of up-regulated genes in malignant glioma with subtraction hybridization: preliminary screening studies

PURPOSE

This investigation is intended to obtain differentially expressed genes related to human malignant glioma using Subtractive hybridization.

MATERIALS AND METHODS

Subtractive hybridization is potentially faster methods for identifying differentially expressed genes associated with a particular disease state. We identified 7 over-expressed genes which were not homologous to any of the known genes in the Genbank database.

RESULTS

Using semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR), the mRNA expression levels of these 7 genes were higher in human glioblastomas tissue than in non-tumor brain tissue. In order to learn more about the expression profile of these genes, RT-PCR was performed using various commercially available human carcinoma cell lines. Some of these new genes were over-expressed in human glioma cell line, but not the expressed in other human cancer cell line.

CONCLUSION

Theses cloned new genes may play a role in brain tumorigenesis. Further studies including verification of oncogene, cancer protein, and glioblastoma induction in animal model are needed.

N-(4-Hydroxyphenyl)retinamide induced differentiation with repression of telomerase and cell cycle to increase interferon-gamma sensitivity for apoptosis in human glioblastoma cells

Glioblastoma is the most malignant and prevalent brain tumor in humans. It is composed of heterogenic abnormal astroglial cells that avoid differentiation, maintain proliferation, and hardly commit apoptosis. N-(4-Hydroxyphenyl)retinamide (4-HPR) induced astrocytic differentiation and increased sensitivity to interferon-gamma (IFN-gamma) for apoptosis in human glioblastoma A172, LN18, and SNB19 cells. Combination of 4-HPR and IFN-gamma significantly inhibited human telomerase reverse transcriptase (hTERT), cyclin dependent kinase 2 (CDK2), and survivin to up-regulate caspase-8, caspase-9, and caspase-3 for increasing apoptosis in all glioblastoma cell lines. Hence, combination of 4-HPR and IFN-gamma should be considered for controlling growth of different human glioblastoma cells.

Identification of a PTEN-regulated STAT3 brain tumor suppressor pathway

Activation of the transcription factor STAT3 is thought to potently promote oncogenesis in a variety of tissues, leading to intense efforts to develop STAT3 inhibitors for many tumors, including the highly malignant brain tumor glioblastoma. However, the function of STAT3 in glioblastoma pathogenesis has remained unknown. Here, we report that STAT3 plays a pro-oncogenic or tumor-suppressive role depending on the mutational profile of the tumor. Deficiency of the tumor suppressor PTEN triggers a cascade that inhibits STAT3 signaling in murine astrocytes and human glioblastoma tumors. Specifically, we forge a direct link between the PTEN-Akt-FOXO axis and the leukemia inhibitory factor receptor beta (LIFRbeta)-STAT3 signaling pathway. Accordingly, PTEN knockdown induces efficient malignant transformation of astrocytes upon knockout of the STAT3 gene. Remarkably, in contrast to the tumor-suppressive function of STAT3 in the PTEN pathway, STAT3 forms a complex with the oncoprotein epidermal growth factor receptor type III variant (EGFRvIII) in the nucleus and thereby mediates EGFRvIII-induced glial transformation. These findings indicate that STAT3 plays opposing roles in glial transformation depending on the genetic background of the tumor, providing the rationale for tailored therapeutic intervention in glioblastoma.

Overexpression of CDC2/CyclinB1 in gliomas, and CDC2 depletion inhibits proliferation of human glioma cells in vitro and in vivo

Background

Gliomas are the most common and aggressive primary brain tumors for which unfortunately no effective treatment modalities exist despite advances in molecular biology as the knowledge base to unravel the extremely complex molecular mechanisms of tumorigenesis is limited. In this study an attempt has been made to understand the molecular pathological basis of tumorigenesis which led to an identification of an oncogene, CDC2, and an epigenetic strategy has been evaluated to control the tumorigensis by downregulating this oncogene.

Methods

Tissue microarrays were utilized to investigate the expression of genes in a large number of tumor samples and to identify overexpressed genes which could be potentially causing tumorigenesis. Retroviral vectors expressing short hairpin RNAs (shRNAs) targeted against CDC2 were designed and transducted into human glioma cell line ex vivo in order to downregulate the expression of CDC2. Real-Time PCR was used to determine the level of CDC2 mRNA. Western Blotting was used to determine the level of expression of CDC2 protein as measure to quantify down regulation of CDC2 expression along with use of flow cytometry to investigate effect of shRNAs on cell cycles and detection of apoptosis. Following ex vivo study, viral particles containing small interfering RNA for CDC2 were subsequently injected into xenogeneic graft tumor of nude mice and the weight of human glioma xenografts, survival and resulting phenotypic changes of target gene were investigated.

Results

Human glioma tissue microarrays indicated the positive expression rates of CDC2/CyclinB1 with a positive correlation with pathologic grades (r = 0.982, r = 0.959, respectively). Retroviral vectors expressing short hairpin RNAs (shRNAs) against CDC2 caused efficient deletion of CDC2, cellular G2/M arrest concluding in apoptosis and inhibition of proliferation in human glioma cells U251 and SHG-44 cell lines ex vivo. And the viral particles containing small interfering RNA for CDC2 were subsequently injected into subcutaneous and intracranial xenogeneic graft tuomrs of nude mice. For subcutaneous tumors, injection of CDC2-shRNA retroviruses significantly decreased tumor weight and volume compared with control. Immunohistochemistry indicated that CDC2 are negative and TUNEL are positive in tumors treated with recombinant retrovirus. For mice implanted with intracranial gliomas, treatment of CDC2-shRNA retroviruses increased survival times compared with control.

Conclusion

CDC2 gene plays an important role in the proliferation of human gliomas. Downregulation of CDC2 could potentialy inhibit human gliomas cells growth ex vivo and in vivo. From these results, it was suggested that CDC2 might be a potential target on gene therapy of human gliomas.

Immediate early gene IEX-1 induces astrocytic differentiation of U87-MG human glioma cells

The immediate early response gene IEX-1 is involved in the regulation of apoptosis and cell growth. In order to increase the apoptotic sensitivity to chemotherapeutic drugs and gamma-ray, we attempted to establish U87-MG human glioma cell line expressing IEX-1. Unexpectedly, however, transfection of IEX-1 into U87-MG glioma cells resulted in morphological changes to astrocytic phenotype and increase in glial differentiation marker proteins, S-100 and glial fibrillary acidic protein (GFAP). Glial cell differentiation was used to examine in rat C6 glioma cell line, since this cell line express astrocytic phenotypes by increase in intracellular cAMP concentration. Stimulation of human U87-MG glioma cells by membrane-permeable dibutyryl cAMP (dbcAMP) not only elicited their morphological changes but also induced expression of IEX-1 as well as S-100 and GFAP. H89, an inhibitor of protein kinase A (PKA), blocked dbcAMP-induced morphological changes of U87-MG cells and expression of IEX-1. In contrast, morphological changes and expression of S-100 and GFAP induced by IEX-1 were not affected by H89. Morphological changes induced by dbcAMP were totally abolished by functional disruption of IEX-1 expression by anti-sense RNA. These results indicate that IEX-1 plays an important role in astrocytic differentiation of human glioma cells and that IEX-1 functions at downstream of PKA.

Transforming growth factor α promotes sequential conversion of mature astrocytes into neural progenitors and stem cells

An instability of the mature cell phenotype is thought to participate to the formation of gliomas, primary brain tumors deriving from astrocytes and/or neural stem cells. Transforming growth factor alpha (TGFalpha) is an erbB1 ligand overexpressed in the earliest stages of gliomas, and exerts trophic effects on gliomal cells and astrocytes. Here, we questioned whether prolonged TGFalpha exposure affects the stability of the normal mature astrocyte phenotype. We first developed astrocyte cultures devoid of residual neural stem cells or progenitors. We demonstrate that days of TGFalpha treatment result in the functional conversion of a population of mature astrocytes into radial glial cells, a population of neural progenitors. TGFalpha-generated radial glial cells support embryonic neurons migration, and give birth to cells of the neuronal lineage, expressing neuronal markers and the electrophysiological properties of neuroblasts. Lengthening TGFalpha treatment to months results in the delayed appearance of cells with neural stem cells properties: they form floating cellular spheres that are self-renewing, can be clonally derived from a single cell and differentiated into cells of the neuronal lineage. This study uncovers a novel population of mature astrocytes capable, in response to a single epigenetic factor, to regress progressively into a neural stem-like cell stage via an intermediate progenitor stage.

Transplanted glioma cells migrate and proliferate on host brain vasculature: a dynamic analysis

Glioma cells have a remarkable capacity to infiltrate the brain and migrate long distances from the tumor, making complete surgical resection impossible. Yet, little is known about how glioma cells interact with the complex microenvironment of the brain. To investigate the patterns and dynamics of glioma cell infiltration and migration, we stereotactically injected eGFP and DsRed-2 labeled rat C6 glioma cells into neonatal rat forebrains and used time-lapse microscopy to observe glioma cell migration and proliferation in slice cultures generated from these brains. In this model, glioma cells extensively infiltrated the brain by migrating along the abluminal surface of blood vessels. Glioma cells intercalated their processes between the endothelial cells and the perivascular astrocyte end feet, but did not invade into the blood vessel lumen. Dynamic analysis revealed notable similarities between the migratory behavior of glioma cells and that previously observed for glial progenitor cells. Glioma cells had a characteristic leading process and migrated in a saltatory fashion, with bursts of migration separated by periods of immobility, and maximum speeds of over 100 microm/h. Migrating glioma cells proliferated en route, pausing for as short as an hour to divide before the daughter cells resumed migrating. Remarkably, the majority of glioma cell divisions took place at or near vascular branch points, suggesting that mitosis is triggered by local environmental cues. This study provides the first dynamic analysis of glioma cell infiltration in living brain tissue and reveals that the migration and proliferation of transplanted glioma cells is directed by interactions with host brain vasculature.

TWIST is expressed in human gliomas and promotes invasion

TWIST, a basic helix-loop-helix (bHLH) transcription factor that regulates mesodermal development, has been shown to promote tumor cell metastasis and to enhance survival in response to cytotoxic stress. Our analysis of rat C6 glioma cell-derived cDNA revealed TWIST expression, suggesting that the gene may play a role in the genesis and physiology of primary brain tumors. To further delineate a possible oncogenic role for TWIST in the central nervous system (CNS), we analyzed TWIST expression in human gliomas and normal brain by using reverse transcription polymerase chain reaction, Northern blot analysis, in situ hybridization, and immunohistochemistry. TWIST expression was detected in the large majority of human glioma-derived cell lines and human gliomas examined. Levels of TWIST mRNA were associated with the highest grade gliomas, and increased TWIST expression accompanied transition from low grade to high grade in vivo, suggesting a role for TWIST in promoting malignant progression. In accord, elevated TWIST mRNA abundance preceded the spontaneous malignant transformation of cultured mouse astrocytes hemizygous for p53. Overexpression of TWIST protein in a human glioma cell line significantly enhanced tumor cell invasion, a hallmark of high-grade gliomas. These findings support roles for TWIST both in early glial tumorigenesis and subsequent malignant progression. TWIST was also expressed in embryonic and fetal human brain, and in neurons, but not glia, of mature brain, indicating that, in gliomas, TWIST may promote the functions also critical for CNS development or normal neuronal physiology.

Estrogen receptor positivity in mammary tumors of Wnt-1 transgenic mice is influenced by collaborating oncogenic mutations

The majority (75%) of human breast cancers express estrogen receptor (ER). Although ER-positive tumors usually respond to antiestrogen therapies, 30% of them do not. It is not known what controls the ER status of breast cancers or their responsiveness to antihormone interventions. In this report, we document that transgenic (TG) expression of Wnt-1 in mice induces ER-positive tumors. Loss of Pten or gain of Ras mutations during the evolution of tumors in Wnt-1 TG mice has no effect on the expression of ER, but overexpression of Neu or loss of p53 leads to ER-negative tumors. Thus, our results provide compelling evidence that expression of ER in breast cancer may be influenced by specific genetic changes that promote cancer progression. These findings constitute a first step to explore the molecular mechanisms leading to ER-positive or ER-negative mammary tumors. In addition, we find that ER-positive tumors arising in Wnt-1 TG mice are refractory to both ovariectomy and the ER antagonist tamoxifen, but lose ER expression with tamoxifen, suggesting that antiestrogen selects for ER-negative tumor cells and that the ER-positive cell fraction is dispensable for growth of these tumors. This is a first report of a mouse model of antiestrogen-resistant ER-positive breast cancers, and could provide a powerful tool to study the molecular mechanisms that control antiestrogen resistance.

Natural history of neurofibromatosis 1-associated optic nerve glioma in mice

Children affected with the inherited tumor predisposition syndrome, neurofibromatosis 1 (NF1), are prone to the development of low-grade astrocytic optic pathway tumors (optic pathway glioma [OPG]). Previously, we developed a model of NF1-associated astrocytoma (GFAPCre; Nf1(flox/mut) mice) in which mice develop optic nerve and chiasm glioma. To define the molecular pathogenesis of OPG, we used this mouse model to study the natural history of OPG formation using immunohistological and radiographic approaches. We observed that whereas astrocyte hyperplasia is present in the optic nerves associated with gross optic nerve thickening at 3 weeks of age, overt neoplastic changes were not seen until 2 months of age. Astrocyte proliferation was maximal between 3 weeks and 2 months of age, suggesting that the most rapid period of growth occurs early. Mouse OPG tumors were detected by magnetic resonance imaging at 2 months of age and exhibited contrast enhancement, as seen in human OPG. In addition, the mouse OPG tumors exhibited expression of proteins associated with astroglial progenitors, including nestin and brain lipid binding protein. Last, we observed neovascularization and microglial cell infiltration by 3 weeks of age before overt neoplastic transformation, suggesting that these cellular changes participate in the early stages of tumor formation.

Ginsenoside-Rd from Panax notoginseng enhances astrocyte differentiation from neural stem cells

Neural stem cells cultured as neurospheres were used to assess the effects of P. notoginseng on the production of neurons and glia. The crude saponins (PNS) and ginsenoside-Rd promote the differentiation of neurospheres into astrocytes. Ginsenoside-Rd increases the production of astrocytes in a dose-dependent manner. On the other hand, both PNS and ginsenoside-Rd induce a weak but significant effect by decreasing the number of neurons. The other ginsenosides do not induce any differentiation on both neurons and astrocytes.

Stem/progenitor cells in mouse mammary gland development and breast cancer

Breast cancer is a genetically and clinically heterogeneous disease. It is unclear whether different target cells contribute to this heterogeneity and which cell types are most susceptible to oncogenesis. Stem cells are speculated to be the cellular origin of at least a subset of human breast cancers. To begin to address these issues, we have isolated and characterized cell populations enriched in normal mammary stem/progenitors and have studied the expression of putative stem/progenitor markers in tumors derived from genetically engineered mice. Specifically, transgenic activation of Wnt signaling in the mammary gland induces tumors comprised of epithelial and myoepithelial cells harboring the same genetic defect implying that the tumor arose from transformation of a bipotent progenitor cell. On the other hand, transgenic activation of Neu signaling induces tumors comprising cells of more limited lineage capacity. Thus, the heterogeneity of different breast cancers may reflect the activation of different oncogenic pathways, different cellular targets in which these genetic changes occur, or both.

Developmental neurobiology and the origin of brain tumors

Our knowledge of the causes of brain tumors has steadily increased and is leading to a refined understanding of the signaling pathways that may be essential for tumor formation. At the same time, we are gaining insights into the developmental processes that regulate the formation of the diverse range of cell types in the normal brain. Interestingly, many of these pathways seem to overlap and suggest common mechanisms regulating tumor formation and cellular development. This overlap may also inform us about the nature of the cell of origin for different types of brain tumors. By appreciating the inter-relationship between tumor formation and development, we maybe able to design new therapeutics targeting tumors for new modes of treatment.

The oligodendroglial lineage marker OLIG2 is universally expressed in diffuse gliomas

Astrocytomas, oligodendrogliomas, and oligoastrocytomas, collectively referred to as diffuse gliomas, are the most common primary brain tumors. These tumors are classified by histologic similarity to differentiated astrocytes and oligodendrocytes, but this approach has major limitations in guiding modern treatment and research. Lineage markers represent a potentially useful adjunct to morphologic classification. The murine bHLH transcription factors Olig1 and Olig2 are expressed in neural progenitors and oligodendroglia and are essential for oligodendrocyte development. High OLIG expression alone has been proposed to distinguish oligodendrogliomas from astrocytomas, so we critically evaluated OLIG2 as a marker by immunohistochemical and oligonucleotide microarray analysis. OLIG2 protein is faithfully restricted to normal oligodendroglia and their progenitors in human brain. Immunohistochemical analysis of 180 primary, metastatic, and non-neural human tumors shows OLIG2 is highly expressed in all diffuse gliomas. Immunohistochemistry and microarray analyses demonstrate higher OLIG2 in anaplastic oligodendrogliomas versus glioblastomas, which are heterogeneous with respect to OLIG2 levels. OLIG2 protein expression is present but inconsistent and generally lower in most other brain tumors and is absent in non-neuroectodermal tumors. Overall, OLIG2 is a useful marker of diffuse gliomas as a class. However, expression heterogeneity of OLIG2 in astrocytomas precludes immunohistochemical classification of individual gliomas by OLIG2 alone.