Background Glioblastoma (GBM) is a highly aggressive brain tumor with rapid subclonal diversification, harboring molecular abnormalities that vary temporo-spatially, a contributor to therapy resistance. Fluorescence guided neurosurgical resection utilizes administration of 5-aminolevulinic acid (5ALA) generating individually fluorescent tumor cells within a background population of non-neoplastic cells in the invasive tumor region. The aim of the study was to specifically isolate and interrogate the invasive GBM cell population using a novel 5ALA based method. Methods We have isolated the critical invasive GBM cell population by developing 5ALA-based metabolic fluorescence activated cell sorting. This allows purification and study of invasive cells from GBM without an overwhelming background “normal brain” signal to confound data. The population was studied using RNAseq, rtPCR and immunohistochemistry, with gene targets functionally interrogated on proliferation and migration assays using siRNA knockdown and known drug inhibitors. Results RNAseq analysis identifies specific genes such as SERPINE1 which is highly expressed in invasive GBM cells but at low levels in the surrounding normal brain parenchyma. siRNA knockdown and pharmacological inhibition with specific inhibitors of SERPINE1 reduced the capacity of GBM cells to invade in an in vitro assay. Rodent xenografts of 5ALA positive cells were established and serially transplanted, confirming tumorigenicity of the fluorescent patient derived cells but not the 5ALA negative cells. Conclusions Identification of unique molecular features in the invasive GBM population offer hope for developing more efficacious targeted therapies compared to targeting the tumor core and for isolating tumor sub-populations based upon intrinsic metabolic properties.

The lack of treatment options for high-grade brain tumors has led to searches for alternative therapeutic modalities. Electrical field therapy is one such area. The Optune™ system is an FDA-approved novel device that delivers continuous alternating electric fields (tumor treating fields—TTFields) to the patient for the treatment of primary and recurrent Glioblastoma multiforme (GBM). Various mechanisms have been proposed to explain the effects of TTFields and other electrical therapies. Here, we present the first study of genome-wide expression of electrotherapy (delivered via TTFields or Deep Brain Stimulation (DBS)) on brain tumor cell lines. The effects of electric fields were assessed through gene expression arrays and combinational effects with chemotherapies. We observed that both DBS and TTFields significantly affected brain tumor cell line viability, with DBS promoting G0-phase accumulation and TTFields promoting G2-phase accumulation. Both treatments may be used to augment the efficacy of chemotherapy in vitro. Genome-wide expression assessment demonstrated significant overlap between the different electrical treatments, suggesting novel interactions with mitochondrial functioning and promoting endoplasmic reticulum stress. We demonstrate the in vitro efficacy of electric fields against adult and pediatric high-grade brain tumors and elucidate potential mechanisms of action for future study.

While specific microRNA (miRNA) signatures have been identified in glioblastoma (GBM), the intratumour heterogeneity in miRNA expression has not yet been characterised. In this study, we reveal significant alterations in miRNA expression across three GBM tumour regions: the core, rim, and invasive margin. Our miRNA profiling analysis showed that miR-330-5p and miR-215-5p were upregulated in the invasive margin relative to the core and the rim regions, while miR-619-5p, miR-4440 and miR-4793-3p were downregulated. Functional analysis of newly identified miRNAs suggests their involvement in regulating lipid metabolic pathways. Subsequent liquid chromatography–mass spectrometry (LC–MS) and tandem mass spectroscopy (LC–MS/MS) profiling of the intracellular metabolome and the lipidome of GBM cells with dysregulated miRNA expression confirmed the alteration in the metabolite levels associated with lipid metabolism. The identification of regional miRNA expression signatures may underlie the metabolic heterogeneity within the GBM tumour and understanding this relationship may open new avenues for the GBM treatment.

Despite significant improvements in treatment and survival in paediatric cancers, outcomes for children with brain tumours remain poor. Novel therapeutic approaches are needed to improve survival and quality of survival. Extracellular arginine dependency (auxotrophy) has been recognised in several tumours as a potential therapeutic target. This dependency is due to the inability of cancer cells to recycle or synthesise intracellular arginine through the urea cycle pathway compared to normal cells. Whilst adult glioblastoma exhibits this dependency, the expression of the arginine pathway enzymes has not been delineated in paediatric brain tumours. We used immunohistochemical (IHC) methods to stain for arginine pathway enzymes in paediatric high-grade glioma (pHGG), low-grade glioma (pLGG), ependymoma (EPN), and medulloblastoma (MB) tumour tissue microarrays (TMAs). The antibodies detected protein expression of the metaboliser arginase (Arg1 and Arg2); recycling enzymes ornithine transcarbamoylase (OTC), argininosuccinate synthetase (ASS1), and argininosuccinate lyase (ASL); and the transporter SLC7A1. Deficiency of OTC, ASS1, and ASL was seen in 87.5%, 94%, and 79% of pHGG samples, respectively, consistent with an auxotrophic signature. Similar result was obtained in pLGG with 96%, 93%, and 91% of tumours being deficient in ASL, ASS1, and OTC, respectively. 79%, 88%, and 85% of MB cases were ASL, ASS1, and OTC deficient whilst ASL and OTC were deficient in 57% and 91% of EPN samples. All tumour types highly expressed SLC7A1 and Arginase, with Arg2 being the main isoform, demonstrating that they could transport and utilise arginine. Our results show that pHGG, pLGG, EPN, and MB demonstrate arginine auxotrophy based on protein expression and are likely to be susceptible to arginine depletion. Pegylated arginase (BCT-100) is currently in phase I/II trials in relapsed pHGG. Our results suggest that therapeutic arginine depletion may also be useful in other tumour types and IHC analysis of patient tumour samples could help identify patients likely to benefit from this treatment.

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NEURO-ONCOLOGY • NOVEMBER 2017 this end, we mapped active chromatin landscapes in 42 primary ependymomas in discovery and validation cohorts using H3K27 acetylation ChIP-seq. Enhancer regions revealed novel oncogenes, molecular targets, and pathways, which when subjected to small molecule inhibitor or shRNA treatment, increased survival and halted proliferation in mouse and neurosphere patient-derived models of ependymomas. Reconstruction of enhancer networks permitted the identification of core transcription factors (TFs) that establish ependymoma cell state, and lineage-specifying TFs that dictate molecular subgroup identity. Lineage-associated TFs point to distinct spatiotemporal origins of ependymoma subgroups such as FOXJ1 TF activity and expression observed preferentially in subsets of hindbrain ependymomas. To translate our results into a potential clinical paradigm, we demonstrate cancer dependencies on super enhancer associated genes and lineage TFs, and establish the utility of chromatin landscape analysis to predict novel targets for cancer therapy.

Introduction Approximately 400 children in the UK are diagnosed with a CNS tumor each year, which represents a quarter of childhood cancer cases in the UK. The 5-year survival rate of paediatric brain tumor patients is approximately 75%, but survival remains much worse for some brain tumor patients, particularly high-grade gliomas. Pre-clinical and clinical studies have demonstrated efficacy of TTFields as a treatment for high-grade glioma leading to the approval of TTFields for adult Glioblastoma multiforme (GBM) patients. The lack of overlapping toxicities associated with TTFields has made electric field therapy an attractive treatment strategy for poor prognosis paediatric brain tumors.Methods The inovitro is the laboratory based testing system used to deliver TTFields to cell cultures. inovitro was used to deliver TTFields over 72 hours at a range of clinically relevant frequencies (100-400kHz) to our panel of paediatric GBM, Medulloblastoma and Ependymoma cell lines. The effects of TTFields on cell viability and cell cycle was assessed using Resazurin based metabolic viability tests and flow cytometry. The determined optimal frequency for each cell line was also combined with a mitotic inhibitor to explore synergistic effects. Gene expression changes of TTFields treated cells was investigated. Results TTFields treatment reduces cell viability of all cell lines tested within the frequency panel. The optimum frequencies were between 100 and 400kHz for all cell lines tested. TTFields treatment had effects on cell cycling with increased G2 accumulation of treated cells being observed. Combining TTFields with mitotic inhibitors increased efficacy in an additive fashion. Conclusions This preliminary study has demonstrated efficacy of TTFields on paediatric brain tumor cell lines. The optimal frequencies for all the paediatric GBM cell lines used did not match the 200kHz as previously reported for U-87 MG cells. This report warrants further study into the potential for TTFields therapy for paediatric brain tumor patients. Citation Format: Joshua Branter, Maria Estevez-Cebrero, Richard Grundy, Surajit Basu, Stuart Smith. Tumor treating fields (TTFields) have antiproliferative effects on high-grade pediatric brain tumor cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4637.