Glioblastomas are characterized by fast uncontrolled growth leading to hypoxic areas and necrosis. Signalling from EGFR via mammalian target of rapamycin complex 1 (mTORC1) is a major driver of cell growth and proliferation and one of the most commonly altered signalling pathways in glioblastomas. Therefore, epidermal growth factor receptor and mTORC1 signalling are plausible therapeutic targets and clinical trials with inhibitors are in progress. However, we have previously shown that epidermal growth factor receptor and mTORC1 inhibition triggers metabolic changes leading to adverse effects under the conditions of the tumour microenvironment by protecting from hypoxia-induced cell death. We hypothesized that conversely mTORC1 activation sensitizes glioma cells to hypoxia-induced cell death. As a model for mTORC1 activation we used gene suppression of its physiological inhibitor TSC2 (TSC2sh). TSC2sh glioma cells showed increased sensitivity to hypoxia-induced cell death that was accompanied by an earlier ATP depletion and an increase in reactive oxygen species. There was no difference in extracellular glucose consumption but an altered intracellular metabolic profile with an increase of intermediates of the pentose phosphate pathway. Mechanistically, mTORC1 upregulated the first and rate limiting enzyme of the pentose phosphate pathway, G6PD. Furthermore, an increase in oxygen consumption in TSC2sh cells was detected. This appeared to be due to higher transcription rates of genes involved in mitochondrial respiratory function including PPARGC1A and PPARGC1B (also known as PGC-1α and -β). The finding that mTORC1 activation causes an increase in oxygen consumption and renders malignant glioma cells susceptible to hypoxia and nutrient deprivation could help identify glioblastoma patient cohorts more likely to benefit from hypoxia-inducing therapies such as the VEGFA-targeting antibody bevacizumab in future clinical evaluations.

An essential mode of acquired resistance to radiotherapy (RT) appears to be promotion of tumor cell motility and invasiveness in various cancer types, including glioblastoma, a process resembling 'evasive resistance'. Hence, a logical advancement of RT would be to identify suitable complementary treatment strategies, ideally targeting cell motility. Here we report that the combination of focal RT and mammalian target of rapamycin (mTOR) inhibition using clinically relevant concentrations of temsirolimus (CCI-779) prolongs survival in a syngeneic mouse glioma model through additive cytostatic effects. In vitro, the mTOR inhibitor CCI-779 exerted marked anti-invasive effects, irrespective of the phosphatase and tensin homolog deleted on chromosome 10 status and counteracted the proinvasive effect of sublethal irradiation. Mechanistically, we identified regulator of G-protein signaling 4 (RGS4) as a novel target of mTOR inhibition and a key driver of glioblastoma invasiveness, sensitive to the anti-invasive properties of CCI-779. Notably, suppression of RGS4-dependent glioma cell invasion was signaled through both mTOR complexes, mTORC1 and mTORC2, in a concentration-dependent manner, indicating that high doses of CCI-779 may overcome tumor-cell resistance associated with the sole inhibition of mTORC1. We conclude that combined RT and mTOR inhibition is a promising therapeutic option that warrants further clinical investigation in upfront glioblastoma therapy.Oncogene advance online publication, Word Count:5,868 words Condensed title:Radiation-enhanced mTOR inhibition in glioblastomaWeiler et al. 2 AbstractA relevant mode of resistance to antiangiogenic and radiotherapy appears to be promotion of tumour cell motility and invasiveness in various cancer types, a process commonly referred to as 'evasive resistance' that may underlie progressive disease and complicates further treatment. Hence, a logical advancement in current oncology consists in optimizing antiangiogenic regimens by identifying suitable complementary strategies, ideally targeting cell motility. Here we report that clinically relevant radiation-enhanced inhibition of the mTOR complexes 1 and 2 exercises such a dual control of angiogenesis and invasiveness independent from PTEN/AKT activation in glioblastoma, a tumour entity that is paradigmatic for both excessive vascular proliferation and cell invasion. This is due to a concerted disrupture of the VEGF/VEGFR-2 signalling axis and likewise suppression of RGS4, which we identified to be a key driver of glioblastoma invasiveness. This combined antiangiogenic/antiinvasive approach might be a promising therapeutic option and warrants further clinical investigation in upfront glioblastoma therapy.Weiler et al.3

BackgroundHypoxia is a key driver for infiltrative growth in experimental gliomas. It has remained elusive whether tumor hypoxia in glioblastoma patients contributes to distant or diffuse recurrences. We therefore investigated the influence of perioperative cerebral ischemia on patterns of progression in glioblastoma patients.MethodsWe retrospectively screened MRI scans of 245 patients with newly diagnosed glioblastoma undergoing resection for perioperative ischemia near the resection cavity. 46 showed relevant ischemia nearby the resection cavity. A control cohort without perioperative ischemia was generated by a 1:1 matching using an algorithm based on gender, age and adjuvant treatment. Both cohorts were analyzed for patterns of progression by a blinded neuroradiologist.ResultsThe percentage of diffuse or distant recurrences at first relapse was significantly higher in the cohort with perioperative ischemia (61.1%) compared to the control cohort (19.4%). The results of the control cohort matched well with historical data. The change in patterns of progression was not associated with a difference in survival.ConclusionsThis study reveals an unrecognized association of perioperative cerebral ischemia with distant or diffuse recurrence in glioblastoma. It is the first clinical study supporting the concept that hypoxia is a key driver of infiltrative tumor growth in glioblastoma patients.

BackgroundCurrent pathological diagnostics include the analysis of (epi-)genetic alterations as well as oncogenic pathways. Deregulated mammalian target of rapamycin complex 1 (mTORC1) signaling has been implicated in a variety of cancers including malignant gliomas and is considered a promising target in cancer treatment. Monitoring of mTORC1 activity before and during inhibitor therapy is essential. The aim of our study is to provide a recommendation and report on pitfalls in the use of phospho-specific antibodies against mTORC1-targets phospho-RPS6 (Ser235/236; Ser240/244) and phospho-4EBP1 (Thr37/46) in formalin fixed, paraffin embedded material.Methods and FindingsPrimary, established cell lines and brain tumor tissue from routine diagnostics were assessed by immunocyto-, immunohistochemistry, immunofluorescent stainings and immunoblotting. For validation of results, immunoblotting experiments were performed. mTORC-pathway activation was pharmacologically inhibited by torin2 and rapamycin. Torin2 treatment led to a strong reduction of signal intensity and frequency of all tested antibodies. In contrast phospho-4EBP1 did not show considerable reduction in staining intensity after rapamycin treatment, while immunocytochemistry with both phospho-RPS6-specific antibodies showed a reduced signal compared to controls. Staining intensity of both phospho-RPS6-specific antibodies did not show considerable decrease in stability in a timeline from 0–230 minutes without tissue fixation, however we observed a strong decrease of staining intensity in phospho-4EBP1 after 30 minutes. Detection of phospho-signals was strongly dependent on tissue size and fixation gradient. mTORC1-signaling was significantly induced in glioblastomas although not restricted to cancer cells but also detectable in non-neoplastic cells.ConclusionHere we provide a recommendation for phospho-specific immunohistochemistry for patient-orientated therapy decisions and monitoring treatment response.

B10 is a glycosylated derivative of betulinic acid with promising activity against glioma cells. Lysosomal cell death pathways appear to be essential for its cytotoxicity. We investigated the influence of hypoxia, nutrient deprivation and current standard therapies on B10 cytotoxicity. The human glioma cell lines LN-308 and LNT-229 were exposed to B10 alone or together with irradiation, temozolomide, nutrient deprivation or hypoxia. Cell growth and viability were evaluated by crystal violet staining, clonogenicity assays, propidium iodide uptake and LDH release assays. Cell death was examined using an inhibitor of lysosomal acidification (bafilomycin A1), a cathepsin inhibitor (CA074-Me) and a short-hairpin RNA targeting cathepsin B. Hypoxia substantially enhanced B10-induced cell death. This effect was sensitive to bafilomycin A1 and thus dependent on hypoxia-induced lysosomal acidification. Cathepsin B appeared to mediate cell death because either the inhibitor CA074-Me or cathepsin B gene silencing rescued glioma cells from B10 toxicity under hypoxia. B10 is a novel antitumor agent with substantially enhanced cytotoxicity under hypoxia conferred by increased lysosomal cell death pathway activation. Given the importance of hypoxia for therapy resistance, malignant progression, and as a result of antiangiogenic therapies, B10 might be a promising strategy for hypoxic tumors like malignant glioma.

The value of bevacizumab (BEV) in recurrent glioblastoma is unclear. Imaging parameters and progression-free survival (PFS) are problematic endpoints. Few data exist on clinical factors influencing overall survival (OS) in unselected patients with recurrent glioblastoma exposed to BEV. We retrospectively analyzed 174 patients with recurrent glioblastoma treated with BEV at two German brain tumor centers. We evaluated general patient characteristics, MGMT status, pretreatment, concomitant oncologic treatment and overall survival. Karnofsky performance score, number of prior chemotherapies, number of prior recurrences and combined treatment with irinotecan (IRI) were significantly associated with OS in univariate analysis. We did not find differences in OS related to sex, age, histology, MGMT status, prior surgical treatment or number of prior radiotherapies. Combined treatment with IRI and higher KPS both remained significantly associated with prolonged survival in multivariate analysis, but patients receiving IRI co-treatment had less advanced disease. Grouping into clinically relevant categories revealed an OS of 16.9 months from start of BEV in patients with first recurrence and KPS ≥ 80 % (n = 25). In contrast, in patients with second recurrence and KPS < 80 %, OS was 3.6 months (n = 27). Our observational data support an early use of BEV in patients with good performance status. The benefit of co-treatment with IRI in our cohort seems to be the result of biased patient recruitment.

Moderate, but not severe, leukopenia or related complications could be prevented by prophylactic pegfilgrastim in patients treated with a nitrosourea and teniposide for recurrent glioma. Our results, therefore, do not support routine prophylactic use of pegfilgrastim in these patients.

Abstracts iv3 NEURO-ONCOLOGY • OCTOBER 2016monocytic myeloid derived suppressor cells (MDSCs). No differences were found with respect to granulocytic MDSCs. Depletion of macrophages with Clodronate liposomes however did not alter tumor growth of NDRG1 KD tumors. Cytokine array analysis on U87MG NDRG1 KD and control supernatants showed a marked increase in CCL2 secretion in the NDRG1 KD cells. CCL2 is secreted by tumor cells and is responsible for macrophage recruitment into the tumor tissue. Macrophages showed an increased migration rate towards NDRG1 knockdown environment in vitro.CONCLUSIONS: NDRG1 is shaping the glioma tumor microenvironment by regulating angiogenesis and influencing macrophage recruitment in vivo and in vitro. CCL2 was identified as a relevant cytokine dependent of the NDRG1 status in this human glioma model. These data could help to better understand the relationship between NDRG1 and the tumor microenvironment. Glioblastoma is an incurable brain cancer with median survival of less than 1 year in unselected cohorts. Current treatment options include surgical resection and radiotherapy, alkylating chemotherapy with temozolomide or nitrosoureas. Hypoxia and nutrient depletion in the tumor microenvironment are thought to induce alterations of signaling and metabolism that may affect response to these therapies. OS1.4 CURRENT TREATMENT REGIMENSRegulated in development and DNA damage response (REDD1) was first described in 2002 as a protein regulated by hypoxia and in response to DNA stress and later shown to protect human breast carcinoma cells from hypoxia-induced cell death. Mechanistically, REDD1 inhibits mTORC1 signaling by activation of the TSC1/2 complex. We have previously found that mTORC1 inhibition protects human glioblastoma cells from hypoxiainduced cell death.Database analysis revealed that REDD1 is upregulated in glioblastomas. We found an intact REDD1-mTORC1 signaling axis in human glioblastoma cells inducible by hypoxia. Temozolomide and radiotherapy also induced REDD1 and repressed mTOR activity.In this study, we investigated the effects of temozolomide, radiotherapy and hypoxia on REDD1 and mTORC1 signaling with a focus on potential effects on therapeutic resistance. Using the Tet-Off system and a human glioblastoma cell line we constructed an in vitro system in which REDD1 expression is dynamically controllable.Our data demonstrate that overexpression of REDD1 reduces the sensitivity of glioma cells towards hypoxia and chemotherapy. Thus, REDD1 may pose a resistance mechanism and a candidate target for inhibition to improve or restore treatment efficacy. OS1.5 FLUVOXAMINE (SSRI), INHIBITS GLIOBLASTOMA INVASION BY INHIBITION OF ACTIN POLYMERIZATIONH. Michiue, K. Hayashi, H. Matsushita, T. Nishiki, H. Matsui Okayama University, Okayama City, Japan.INTRODUCTION: Invasion of Glioblastoma (GBM) cells into normal brain is the major cause of poor prognosis and requires dynamic reorganization of the actin cytoskeleton, which includes lamellipodial protrusions, focal adhesions, and st...