The nuclear DNA repair protein Ku70/80 is a tumor-associated antigen displaying rapid receptor mediated endocytosis

To be of therapeutic relevance, a tumor-associated antigen should be expressed on the surface of neoplastic cells but not, or to a significantly lower extent, on cells of non-transformed nature. The Ku heterodimer (Ku70/80) is involved in DNA double strand break recognition and repair and is ubiquitously expressed in the nucleus of all cells. However, its exclusive nuclear localization has been reassessed by studies that demonstrate Ku to be expressed on the surface of tumor cell lines, displaying functions in cell adhesion, migration and invasion. In this study, we add another feature to the pluripotent role of Ku70/80 by showing that, upon binding the novel human recombinant antibody INCA-X, the Ku70/80 heterodimer is internalized into pancreatic carcinoma cells. The receptor-mediated endocytosis of Ku70/80 is rapid (t(1/) (2) 12 min) and extensive (90% of the receptor pool inside the cell after 100 min) as measured by rotating radioimmunoassay. Ku70/80 was also successfully used as a port of entry for cytotoxic payloads to tumor cells of various origin, as determined by indirect immunotoxin administration of a saporin-conjugated, secondary anti-human antibody. Thus, the internalization properties of the Ku70/80 suggest a potential role of this tumor associated antigen in selective drug-delivery in several human malignancies.     

EGFRvIII as a promising target for antibody-based brain tumor therapy

Cell surface receptors are attractive candidates for targeted therapy of cancer. Growth factors and their receptors play important roles in the regulation of cell division, development, and differentiation. Among those, the epidermal growth factor receptor (EGFR) was the first identified to be amplified and/or rearranged in malignant gliomas. The most common rearranged form, EGFR type III variant (EGFRvIII), has a deletion in its extracellular domain that results in the formation of a new, tumor-specific target found in glioblastoma multiforme, as well as in breast, ovarian, prostate, and lung carcinomas. Monoclonal antibodies have been developed with specific activity against this mutant receptor. These antibodies are internalized into the cell after receptor binding. Specific antibodies, either unarmed or armed with cytotoxic agents, including radioisotopes and toxins, have shown a promising role for EGFRvIII as a target for brain tumor therapy.     

Evaluation of the humoral response of glioma patients to a possible common tumor-associated antigen(S)

Cytotoxic antibodies against glioblastoma-associated antigen(s) have been sought for in glioma patient sera. Complement-dependent cytotoxicity (CDC) and antibody-dependent cell-mediated cytotoxicity (ADCC) assays were used to test sera from 80 patients using ⁵¹Cr labelled target cells derived from eight different glioblastoma lines. As more positive sera were detected with ADCC than with CDC, ADCC assay was used for the remainder of the study. Cytotoxic antibodies were detected in the sera from 8 of 80 glioma patients (10%) by CDC and in 20 of 143 (14%) by ADCC. Fourteen per cent of 27 meningioma patients and 16% of 25 normal donors used as controls were found to react in ADCC against the same glioblastoma cell lines. The positive serum samples showed extensive cross-reactions with the different glioblastoma cells, but the pattern of reactivity was different for each serum tested. The antibodies detected did not seem to be directed against tumor-associated antigen(s), since the positive sera were found to have a similar ADCC reactivity against unrelated tumor cells and normal fibroblasts. Moreover, their antiglioma reactivity was absorbed by cells of unrelated tumors and by normal platelets. These results do not support previous reports of specific humoral responses in glioma patients against common tumor-associated antigen(s).     

Cellular and in vivo activity of a novel PI3K inhibitor, PX-866, against human glioblastoma

The phosphatidylinositol-3-kinase (PI3K)/Akt oncogenic pathway is critical in glioblastomas. Loss of PTEN, a negative regulator of the PI3K pathway or activated PI3K/Akt pathway that drive increased proliferation, survival, neovascularization, glycolysis, and invasion is found in 70%–80% of malignant gliomas. Thus, PI3K is an attractive therapeutic target for malignant glioma. We report that a new irreversible PI3K inhibitor, PX-866, shows potent inhibitory effects on the PI3K/Akt signaling pathway in glioblastoma. PX-866 did not induce any apoptosis in glioma cells; however, an increase in autophagy was observed. PX-866 inhibited the invasive and angiogenic capabilities of cultured glioblastoma cells. In vivo, PX-866 inhibited subcutaneous tumor growth and increased the median survival time of animals with intracranial tumors. We also assessed the potential of proton magnetic resonance spectroscopy (MRS) as a noninvasive method to monitor response to PX-866. Our findings show that PX-866 treatment causes a drop in the MRS-detectable choline-to-NAA, ratio and identify this partial normalization of the tumor metabolic profile as a biomarker of molecular drug action. Our studies affirm that the PI3K pathway is a highly specific molecular target for therapies for glioblastoma and other cancers with aberrant PI3K/PTEN expression.     

Identification of CD70-mediated apoptosis of immune effector cells as a novel immune escape pathway of human glioblastoma

Interactions of CD70, a tumor necrosis factor-related cell surface ligand and its receptor, CD27, are thought to play an important role for T-, B-, and natural killer-cell activation. However, ligation of CD27 can also induce apoptosis. Human glioblastoma is paradigmatic for cancer-associated immunosuppression. We identified CD70 as a radioinducible gene in U87 MG glioma cells. A screening of a panel of human glioma cell lines revealed that 11 of 12 cell lines expressed CD70 mRNA and protein. Two human neuroblastoma cell lines did not express CD70. CD70 mRNA expression was enhanced by irradiation in 8 of 12 glioma cell lines in a p53-independent manner. No alteration in CD70 expression was observed after glioma cell exposure to cytotoxic drugs such as lomustine. CD70 protein was also detected by immunocytochemistry in 5 of 12 glioblastomas and 3 of 4 anaplastic astrocytomas in vivo. CD27 expression was not detected in any glioma cell line, and there was no evidence for autocrine or backward signaling of the CD70 system in human glioma cells. Unexpectedly, CD70 expressed on glioma cells did not increase the immunogenicity of glioma cells in vitro. In contrast, CD70-positive glioma cells induced apoptosis in peripheral blood mononuclear cells (PBMCs) in a CD70-dependent manner. Neutralization of CD70 expressed on glioma cells prevented apoptosis and enhanced the release of tumor necrosis factor-alpha in cocultures of glioma cells and PBMCs. The effects of CD70-expressing glioma cells on PBMCs were mimicked by agonistic CD27 antibodies. Conversely, the shedding of CD27 by PBMCs was identified as a possible escape mechanism from glioma cell-induced CD70-dependent apoptosis. Thus, induction of B-cell and T-cell apoptosis via interactions of CD70 expressed on glioma cells and CD27 expressed on B and T cells may be a novel way for the immune escape of malignant gliomas.     

Immunocytochemical mapping of the phosphatase and tensin homolog (PTEN/MMAC1) tumor suppressor protein in human gliomas

PTEN/MMAC1 (phosphatase and tensin homolog/mutated in multiple advanced cancers 1) is a tumor suppressor gene, the inactivation of which is an important step in the progression of gliomas to end-stage glioblastoma multiforme. We examined the distribution of PTEN protein in 49 primary human gliomas by immunocytochemistry using polyclonal antibodies that we raised against PTEN-glutathione S-transferase fusion proteins expressed in Escherichia coli. The study group consisted of 6 low-grade astrocytomas, 7 anaplastic astrocytomas, 21 glioblastomas multiforme, 4 low-grade oligodendrogliomas, 6 malignant oligodendrogliomas, and 5 malignant mixed oligoastrocytomas. For each tumor, we determined the percentage of tumor cells showing PTEN immunoreactivity in the most cellular regions of the tumor specimen. In both astrocytomas and oligodendrogliomas, there was an inverse relationship between the percentage of PTEN+ cells and malignancy grade, consistent with a role for PTEN as a tumor suppressor gene, the expression of which declines during glioma progression. In nonneoplastic tissue, PTEN was expressed in human fetal brain at 16, 23, and 27 weeks' gestation, but not in adult brain, indicating that PTEN is developmentally regulated in the CNS. In 21 glioblastomas multiforme, we correlated PTEN protein expression with PTEN gene sequence. Although PTEN-mutant tumors showed significantly diminished PTEN protein expression compared with wild-type cases, suppressed expression of PTEN is more prevalent than predicted from mutation frequencies.     

Inhibition of DNA methylation sensitizes glioblastoma for tumor necrosis factor-related apoptosis-inducing ligand-mediated destruction

Life expectancy of patients affected by glioblastoma multiforme is extremely low. The therapeutic use of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been proposed to treat this disease based on its ability to kill glioma cell lines in vitro and in vivo. Here, we show that, differently from glioma cell lines, glioblastoma multiforme tumors were resistant to TRAIL stimulation because they expressed low levels of caspase-8 and high levels of the death receptor inhibitor PED/PEA-15. Inhibition of methyltransferases by decitabine resulted in considerable up-regulation of TRAIL receptor-1 and caspase-8, down-regulation of PED/PEA-15, inhibition of cell growth, and sensitization of primary glioblastoma cells to TRAIL-induced apoptosis. Exogenous caspase-8 expression was the main event able to restore TRAIL sensitivity in primary glioblastoma cells. The antitumor activity of decitabine and TRAIL was confirmed in vivo in a mouse model of glioblastoma multiforme. Evaluation of tumor size, apoptosis, and caspase activation in nude mouse glioblastoma multiforme xenografts showed dramatic synergy of decitabine and TRAIL in the treatment of glioblastoma, whereas the single agents were scarcely effective in terms of reduction of tumor mass, apoptosis induction, and caspase activation. Thus, the combination of TRAIL and demethylating agents may provide a key tool to overcome glioblastoma resistance to therapeutic treatments.     

Adenovirus-mediated expression of a dominant negative Ku70 fragment radiosensitizes human tumor cells under aerobic and hypoxic conditions

Ku70 is one component of a protein complex, the Ku70/Ku80 heterodimer, which binds to DNA double-strand breaks and activates DNA-dependent protein kinase (DNA-PK), leading to DNA damage repair. Our previous work has confirmed that Ku70 is important for DNA damage repair in that Ku70 deficiency compromises the ability of cells to repair DNA double-strand breaks, increases the radiosensitivity of cells, and enhances radiation-induced apoptosis. Because of the radioresistance of some human cancers, particularly glioblastoma, we examined the use of a radio-gene therapy paradigm to sensitize cells to ionizing radiation. Based on the analysis of the structure-function of Ku70 and the crystal structure of Ku70/Ku80 heterodimer, we designed and identified a candidate dominant negative fragment involving an NH(2)-terminal deletion, and designated it as DNKu70. We generated this mutant construct, stably overexpressed it in Rat-1 cells, and showed that it has a dominant negative effect (i.e., DNKu70 overexpression results in decreased Ku-DNA end-binding activity, and increases radiosensitivity). We then constructed and generated recombinant replication-defective adenovirus, with DNKu70 controlled by the cytomegalovirus promoter, and infected human glioma U-87 MG cells and human colorectal tumor HCT-8 cells. We show that the infected cells significantly express DNKu70 and are greatly radiosensitized under both aerobic and hypoxic conditions. The functional ramification of DNKu70 was further shown in vivo: expression of DNKu70 inhibits radiation-induced DNA-PK catalytic subunit autophosphorylation and prolongs the persistence of gamma-H2AX foci. If radiation-resistant tumor cells could be sensitized by down-regulating the cellular level/activity of Ku/DNA-PK, this approach could be evaluated as an adjuvant to radiation therapy.     

Apoptosis-based treatment of glioblastomas with ABT-737, a novel small molecule inhibitor of Bcl-2 family proteins

Defects in the apoptotic signaling cascades contribute to the poor therapeutic response of malignant gliomas. As glioblastomas are characterized by high expression levels of anti-apoptotic Bcl-2 family proteins, we studied the effects of the novel Bcl-2 inhibitor, ABT-737, on malignant glioma cells. ABT-737 treatment released the pro-apoptotic Bax protein from its binding partner Bcl-2 and potently induced apoptotic cell death in glioblastoma cells in vitro and in vivo. The local administration of ABT-737 prolonged the survival in an intracranial glioma xenograft model. Downregulation of Mcl-1 and overexpression of Bcl-2 sensitized the cells to ABT-737-mediated apoptosis. Moreover, ABT-737 potentiated the cytotoxicity of the chemotherapeutic drugs vincristine and etoposide, and of the death ligand TRAIL. As glioma stem cells may play a crucial role for the tumor progression and the resistance to treatment in glioblastomas, we investigated the effects of ABT-737 on the subpopulation of glioma cells exhibiting stem cell characteristics. Inhibition of proliferation and induction of apoptosis by ABT-737 were less efficient in glioma stem cells than in non-stem cell-like glioma cells. As the resistance of glioma stem cells was associated with high Mcl-1 expression levels, ABT-737 treatment combined with downregulation of Mcl-1 could represent a promising novel approach in glioblastoma treatment.     

Reactivation of insulin-like growth factor binding protein 2 expression in glioblastoma multiforme: a revelation by parallel gene expression profiling.

We carried out a gene expression profiling study using cDNA array technology with 24 primary glioma tissues of low-grade (oligodendroglioma), intermediate-grade (anaplastic oligodendroglioma and anaplastic astrocytoma), and high-grade (glioblastomas multiforme) tumors and found that insulin-like growth factor binding protein 2 (IGFBP2) was consistently overexpressed only in glioblastoma multiforme. The cDNA array results were confirmed by Northern and Western blotting. The fact that the IGFBP2 gene, which is normally expressed in fetal cells and turned off in adult cells, becomes reactivated in the most advanced stage of glioma suggests that glioma progression is a result of dedifferentiation or results from a block of differentiation. Identification of IGFBP2 as a gene associated with glioma progression demonstrates the power and utility of high-throughput gene expression profiling in cancer gene discovery.     

Perillyl alcohol induces apoptosis in human glioblastoma multiforme cells

Standard treatment of glioblastoma multiforme consisting of surgical resection, radiation and/or chemotherapy is rarely curative, emphasizing the need for new chemotherapeutic drugs. The monoterpene perillyl alcohol (POH) has preventive and therapeutic effects in a wide variety of pre-clinical tumor models and is currently under phase I and II clinical trials. In the present study, we analyzed its effect on human glioblastoma cell lines (U87 and A172) and a primary cell culture derived from a human glioblastoma tumor specimen (GBM-1). Using MTT, we showed that POH inhibits the viability of glioblastomas in a concentration-dependent way. Glioblastoma cell lines treated with POH showed morphological alterations characteristic of apoptosis. Analysis of cell cycle and quantification of DNA fragmentation, in cells stained with propidium iodide (PI), confirmed the apoptotic effect of POH on glioblastomas. These data support the potential usefulness of perillyl alcohol as an effective chemotherapeutic agent for patients with recurrent glioblastoma multiforme.     

CXCR4 expression mediates glioma cell invasiveness

Glioblastoma multiforme is a highly invasive tumor bearing a dismal prognosis. Experimental strategies that focus on the specific biological cues governing the invasive capacity of these tumors may hold significant therapeutic promise. In this context, we describe the in vitro and in vivo association of the cell surface chemokine receptor, CXCR4, with the development of an invasive phenotype in malignant glioblastoma. We demonstrate that invasive populations of glioma cells overexpress CXCR4 at the message and protein levels, and that this expression ranges from 25- to 89-fold higher than that found in noninvasive tumor cells. Furthermore, neutralization of CXCR4 significantly impairs the in vitro invasive capacity of malignant glial cells. In addition, glioma cells secrete CXCL12 and demonstrate robust invasive capacity toward a CXCL12 gradient in vitro. These findings underscore the importance of CXCR4 as a potential therapeutic target for the treatment of invasive glioblastoma.     

Overexpression of cytosolic,plasma membrane bound and extracellular heat shock protein 70 (Hsp70) in primary glioblastomas

A unique feature in several non-CNS-tumors is the overexpression of heat shock protein 70 (Hsp70, HSPA1A) in the cytosol, but also its unusual plasma membrane expression and release. Although in gliomas, cytosolic Hsp70 levels are not associated with histological grading, the role of membrane bound and released Hsp70 is still completely unknown. Membrane bound as well as cytosolic Hsp70 can be detected in viable tumor cells with the monoclonal antibody (mAb) cmHsp70.1. Herein, we analysed membrane bound Hsp70 levels in primary and secondary gliomas of different grades and on isolated glioma subpopulations (endothelial cells, CD133-positive cells, primary cultures) by immunohistochemistry and flow cytometry using cmHsp70.1 mAb. Extracellular Hsp70 was determined by a commercial Hsp70 sandwich ELISA (R&D) in plasma samples of glioblastoma patients and healthy volunteers. We found an overexpression of Hsp70 in primary glioblastomas compared to low-grade, anaplastic, or secondary gliomas as determined by immunohistochemistry. Especially in flow cytometry, a strong plasma membrane Hsp70 expression was only observed in primary but not secondary glioblastomas. Within the heterogeneous tumor mass, CD133-positive tumor-initiating and primary glioblastoma cells showed a high membrane Hsp70 expression density, whereas endothelial cells, isolated from glioblastoma tissues only showed a weak staining pattern. Also in plasma samples, secreted Hsp70 protein was significantly increased in patients harbouring primary glioblastomas compared to those with secondary and low grade glioblastomas. Taken together, we show for the first time that cytosolic, membrane bound and extracellular Hsp70 is uniquely overexpressed in primary glioblastomas.     

Role of target antigen in bispecific‐antibody‐mediated killing of human glioblastoma cells: A pre‐clinical study

Bispecific antibodies (bsAbs) directed to tumor‐associated antigens and to receptors mediating T‐cell activation, such as the TCR/CD3 complex and the co‐stimulatory CD28 molecule, are capable of activating T cells at the surface of tumor cells, resulting in tumor‐cell killing. Here we report the pre‐clinical characterization of bispecific‐antibody fragments (bsFab₂) directed to 2 different glioblastoma‐associated antigens: the EGF receptor (EGFR) and a chondroitin‐sulfate proteoglycan (CSPG). Using cultured glioblastoma cells expressing both target antigens, we found that the ability of anti‐tumor × anti‐CD28 bsFab₂ to mediate “targeted T‐cell co‐stimulation” is superior for constructs targeting the CSPG molecule, correlating with an approximately 6‐fold higher expression level of this antigen on the cell surface. In contrast, bsFab₂ triggering CD3 are more effective if they contain EGFR‐target specificity. This indicates that the activity of anti‐tumor × anti‐CD3 constructs critically depends on properties of the antigen other than its expression level on the cell surface, e.g., its mobility in the membrane. These findings prompted us to use EGFR‐targeting bsFab₂ in an ongoing clinical trial with glioma patients. Int. J. Cancer 80:612–616, 1999. © 1999 Wiley‐Liss, Inc.     

7B7: a novel antibody directed against the Ku70/Ku80 heterodimer blocks invasion in pancreatic and lung cancer cells

Development of more effective therapeutic strategies for cancers of high unmet need requires the continued discovery of disease-specific protein targets for therapeutic antibody targeting. In order to identify novel proteins associated with cancer cell invasion/metastasis, we present here an alternative to antibody targeting of cell surface proteins with an established role in invasion; our functional antibody screening approach involves the isolation and selection of MAbs that are primarily screened for their ability to inhibit tumour invasion. A clonal population of the Mia PaCa-2, a pancreatic ductal adenocarcinoma (PDAC) cell line, which displays a highly invasive phenotype, was used to generate MAbs with the objective of identifying membrane targets directly involved in cancer invasion. Selected MAb 7B7 can significantly reduce invasion in a dose-responsive manner in Mia PaCa-2 clone 3 and DLKP-M squamous lung carcinoma cells. Using immunoprecipitation and liquid chromatography-tandem mass spectrometry (LC-MS-MS) analysis, the target antigen of anti-invasive antibody, 7B7, was determined to be the heterodimeric Ku antigen, Ku70/80, a core protein composed of the Ku70 and Ku80 subunits which is involved in non-homologous end-joining (NHEJ) DNA repair. RNA interference-mediated knockdown of Ku70 and Ku80 resulted in a marked decrease in the invasive capacity of Mia PaCa-2 clone 3 and DLKP-M cells, indicating that Ku70/Ku80 is functionally involved in pancreatic and lung cancer invasion. Immunohistochemical analysis demonstrated Ku70/Ku80 immunoreactivity in 37 PDAC tumours, indicating that this heterodimer is highly expressed in this aggressive cancer type. This study demonstrates that a functional MAb screening approach coupled with immunoprecipitation/proteomic analyses can be successfully applied to identify functional anti-invasive MAbs and potential novel targets for therapeutic antibody targeting.     

Inhibition of glioblastoma angiogenesis and invasion by combined treatments directed against vascular endothelial growth factor receptor-2, epidermal growth factor receptor, and vascular endothelial-cadherin.

PURPOSE: Inhibition of angiogenesis can influence tumor cell invasion and metastasis. We previously showed that blockade of vascular endothelial growth factor receptor-2 (VEGFR-2) with the monoclonal antibody DC101 inhibited intracerebral glioblastoma growth but caused increased tumor cell invasion along the preexistent vasculature. In the present study, we attempted to inhibit glioma cell invasion using a monoclonal antibody against the epidermal growth factor receptor (EGFR), which in the context of human glioblastomas, has been implicated in tumor cell invasion. In addition, we analyzed whether blockade of vascular endothelial (VE)-cadherin as a different antiangiogenic target could also inhibit glioblastoma angiogenesis and growth. EXPERIMENTAL DESIGNS: Nude mice who received intracerebral glioblastoma xenografts were treated using monoclonal antibodies against VEGFR-2 (DC101), EGFR (C225), and VE-cadherin (E4G10) either alone or in different combinations. RESULTS: Increased tumor cell invasion provoked by DC101 monotherapy was inhibited by 50% to 66% by combined treatment with C225 and DC101. C225 inhibited glioblastoma cell migration in vitro, but had no effect on the volume of the main tumor mass or on tumor cell proliferation or apoptosis in vivo, either alone or in combination with DC101. The anti-VE-cadherin monoclonal antibody E4G10 was a weaker inhibitor of tumor angiogenesis and growth than DC101, and also caused a weaker increase in tumor cell invasion. CONCLUSIONS: Inhibition of angiogenesis achieved by blocking either VEGFR-2 or VE-cadherin can cause increased glioma cell invasion in an orthotopic model. Increased tumor cell invasion induced by potent inhibition of angiogenesis with DC101 could be inhibited by simultaneous blockade of EGFR.     

Dishevelled 2 signaling promotes self-renewal and tumorigenicity in human gliomas

Glioblastoma multiforme is the most common glioma variant in adults and is highly malignant. Tumors are thought to harbor a subpopulation of stem-like cancer cells, with the bulk resembling neural progenitor-like cells that are unable to fully differentiate. Although multiple pathways are known to be involved in glioma tumorigenesis, the role of Wnt signaling has been poorly described. Here, we show that Dishevelled 2 (Dvl2), a key component of the Wnt signaling pathway, is overexpressed in human gliomas. RNA interference-mediated depletion of Dvl2 blocked proliferation and promoted the differentiation of cultured human glioma cell lines and primary, patient-derived glioma cells. In addition, Dvl2 depletion inhibited tumor formation after intracranial injection of glioblastoma cells in immunodeficient mice. Inhibition of canonical Wnt/β-catenin signaling also blocked proliferation, but unlike Dvl2 depletion, did not induce differentiation. Finally, Wnt5a, a noncanonical Wnt ligand, was also required for glioma cell proliferation. The data therefore suggest that both canonical and noncanonical Wnt signaling pathways downstream of Dvl2 cooperate to maintain the proliferative capacity of human glioblastomas.     

ROS fusion tyrosine kinase activates a SH2 domain-containing phosphatase-2/phosphatidylinositol 3-kinase/mammalian target of rapamycin signaling axis to form glioblastoma in mice

Glioblastoma multiforme is the most common and lethal form of primary brain cancer. Diagnosis of this advanced glioma has a poor prognosis due to the ineffectiveness of current therapies. Aberrant expression of receptor tyrosine kinases (RTK) in glioblastoma multiformes is suggestive of their role in initiation and maintenance of these tumors of the central nervous system. In fact, ectopic expression of the orphan RTK ROS is a frequent event in human brain cancers, yet the pathologic significance of this expression remains undetermined. Here, we show that a glioblastoma-associated, ligand-independent rearrangement product of ROS (FIG-ROS) cooperates with loss of the tumor suppressor gene locus Ink4a;Arf to produce glioblastomas in the mouse. We show that this FIG-ROS-mediated tumor formation in vivo parallels the activation of the tyrosine phosphatase SH2 domain-containing phosphatase-2 (SHP-2) and a phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin signaling axis in tumors and tumor-derived cell lines. We have established a fully penetrant preclinical model for adult onset of glioblastoma multiforme in keeping with major genetic events observed in the human disease. These findings provide novel and important insights into the role of ROS and SHP-2 function in solid tumor biology and set the stage for preclinical testing of targeted therapeutic approaches.