Immunotherapy is a promising new therapeutic field that has demonstrated significant benefits in many solid-tumor malignancies, such as metastatic melanoma and non-small cell lung cancer. However, only a subset of these patients responds to treatment. Glioblastoma (GBM) is the most common malignant primary brain tumor with a poor prognosis of 14.6 months and few treatment advancements over the last 10 years. There are many clinical trials testing immune therapies in GBM, but patient responses in these studies have been highly variable and a definitive benefit has yet to be identified. Biomarkers are used to quantify normal physiology and physiological response to therapies. When extensively characterized and vigorously validated, they have the potential to delineate responders from non-responders for patients treated with immunotherapy in malignancies outside of the central nervous system (CNS) as well as GBM. Due to the challenges of current modalities of radiographic diagnosis and disease monitoring, identification of new predictive and prognostic biomarkers to gauge response to immune therapy for patients with GBM will be critical in the precise treatment of this highly heterogenous disease. This review will explore the current and future strategies for the identification of potential biomarkers in the field of immunotherapy for GBM, as well as highlight major challenges of adapting immune therapy for CNS malignancies.

Preclinical models that reliably recapitulate the immunosuppressive properties of human gliomas are essential to assess immune-based therapies. GL261 murine glioma cells are widely used as a syngeneic animal model of glioma, however, it has become common practice to transfect these cells with luciferase for fluorescent tumor tracking. The aim of this study was to compare the survival of mice injected with fluorescent or non-fluorescent GL261 cells and characterize the differences in their tumor microenvironment. Mice were intracranially implanted with GL261, GL261 Red-FLuc or GL261-Luc2 cells at varying doses. Cytokine profiles were evaluated by proteome microarray and Kaplan-Meier survival analysis was used to determine survival differences. Median survival for mice implanted with 5 × 10 4 GL261 cells was 18 to 21 days. The GL261 Red-FLuc implanted mice cells did not reach median survival at any tumor dose. Mice injected with 3 × 10 5 GL261-Luc2 cells reached median survival at 23 days. However, median survival was significantly prolonged to 37 days in mice implanted with 5 × 10 4 GL261-Luc2 cells. Additionally, proteomic analyses revealed significantly elevated inflammatory cytokines in the supernatants of the GL261 Red-FLuc cells and GL261-Luc2 cells. Our data suggest that GL261 Red-FLuc and GL261-Luc2 murine models elicit an anti-tumor immune response by increasing pro-inflammatory modulators. Glioblastoma (GBM) is the most common malignant primary brain tumor in adults 1. Despite ongoing studies and numerous clinical trials, the prognosis remains poor 2. There is an urgent need to provide these patients with new therapies, as the standard of care treatment has gone unchanged for more than a decade 3. In light of the promising advances made in the area of immune therapy as a treatment for various solid cancers 4-7 , the field of neuro-oncology has embraced immunotherapies for gliomas as a promising area of preclinical and clinical investigation 8. However, recent trials like the Phase III CheckMate-143 9 and Phase III CheckMate-498 10 show poor efficacy despite promising results from pre-clinical studies 11-15. The lack of translation from preclinical to clinical studies illustrates the need for a more rigorous characterization of the pre-clinical models currently being used in the scientific community. The development of novel immune therapeutics is not possible without a reliable preclinical animal model that accurately mimics the complex immune landscape of GBM. Of the various classes of preclinical mouse models, syngeneic models have been indispensable for evaluating immune therapies in GBM 16. Syngeneic murine models are models that rely on allografts of immortalized cancer cells from the same mouse strain from which the model originates.

Background Despite multi-model therapy of maximal surgical resection, radiation, chemotherapy, and tumor treating fields, the median survival of Glioblastoma (GBM) patients is less than 15 months. Protein Arginine Methyltransferase 5 (PRMT5) catalyzes the symmetric di-methylation of arginine residues and is overexpressed in GBM. Inhibition of PRMT5 causes senescence in stem-like GBM tumor cells. LB100, a first-in-class small molecular inhibitor of Protein Phosphatase 2A (PP2A) can sensitize therapy-resistant tumor cells. Here, we tested the anti-GBM effect of concurrent PRMT5 and PP2A inhibition. Methods Patient-derived primary GBM neurospheres (GBMNS), transfected with PRMT5 target-specific siRNA were treated with LB100 and subjected to in vitro assays including PP2A activity and western blot. The intracranial mouse xenograft model was used to test the in vivo antitumor efficacy of combination treatment. Results We found that PRMT5-depletion increased PP2A activity in GBMNS. LB100 treatment significantly reduced the viability of PRMT5-depleted GBMNS compared to PRMT5 intact GBMNS. LB100 enhanced G1 cell cycle arrest induced by PRMT5-depletion. Combination therapy also increased the expression of phospho-MLKL. Necrostatin-1 rescued PRMT5-depleted cells from the cytotoxic effects of LB100, indicating that necroptosis caused the enhanced cytotoxicity of combination therapy. In the in vivo mouse tumor xenograft model, LB100 treatment combined with transient depletion of PRMT5 significantly decreased tumor size and prolonged survival, while LB100 treatment alone had no survival benefit. Conclusion Overall, combined PRMT5 and PP2A inhibition had significantly greater antitumor effects than PRMT5 inhibition alone.

Background The prognosis of glioblastoma (GBM) remains dismal because therapeutic approaches have limited effectiveness. A new targeted treatment using MEK inhibitors, including trametinib, has been proposed to improve GBM therapy. Trametinib had a promising preclinical effect against several cancers but its adaptive treatment resistance precluded its clinical translation in glioblastoma. Previously, we have demonstrated that Protein Arginine Methyltransferase 5 (PRMT5) is upregulated in GBM and its inhibition promotes apoptosis and senescence in differentiated and stem-like tumor cells, respectively. We tested whether inhibition of PRMT5 can enhance the efficacy of trametinib against GBM. Methods Patient-derived primary GBM neurospheres (GBMNS) with transient PRMT5 knockdown were treated with trametinib and cell viability, proliferation, cell cycle progression, ELISA, and western blot were analyzed. In vivo, NSG mice were intracranially implanted with PRMT5-intact and -depleted GBMNS, treated with trametinib by daily oral gavage, and observed for tumor progression and mice survival rate. Results PRMT5 depletion enhanced trametinib-induced cytotoxicity in GBMNS. PRMT5 knockdown significantly decreased trametinib-induced AKT and ERBB3 escape pathways. However, ERBB3 inhibition alone failed to block trametinib-induced AKT activity suggesting that the enhanced antitumor effect imparted by PRMT5 knockdown in trametinib treated GBMNS resulted from AKT inhibition and not ERBB3 inhibition. In orthotopic murine xenograft models, PRMT5-depletion extended the survival of tumor-bearing mice, and combination with trametinib further increased survival. Conclusion Combined PRMT5/MEK inhibition synergistically inhibited glioblastoma in animal models and is a promising strategy for glioblastoma therapy.

Purpose Diffuse midline gliomas are rare midline CNS malignancies that primarily affect children but can also affect adults. While radiation is standard treatment, prognosis remains fatal. Furthermore, due to its sensitive anatomic location, many physicians have been reluctant to perform biopsies without potential for improved prognosis. However, recent advancements in molecular-targeted therapeutics have encouraged greater tissue sampling. While the literature reflects this progress, the landscape of how clinicians actually manage these patients remains unclear. Our goal was to assess the attitudes of current practicing neurosurgical oncologists towards management of adult diffuse midline gliomas, reasons behind their practices, and factors that might influence these practices. Methods We created and distributed a survey with 16 multiple choice and open-ended questions to members of the Tumor Section of the Congress of Neurological Surgeons. Results A total of 81 physicians responded to the survey. Although time since training and volume of glioma patients did not significantly affect the decision to consider clinical trials or to offer biopsy, those that operated on fewer gliomas (< 25/ year) were more likely to cite surgical morbidity as the primary reason not to biopsy these midline locations. Further, surgeons with access to more advanced molecular testing were significantly more likely to consider clinical trial eligibility when offering biopsies. Conclusion Factors that affect the management of diffuse midline gliomas and the role of biopsy are relatively uniform across the field, however, there were a few notable differences that reflect the changes within the neuro-oncology field in response to clinical trials.

BACKGROUND: Despite multi-model therapy of maximal surgical resection, radiation, chemotherapy, and tumor treating fields, median survival of Glioblastoma (GBM) patients is less than two years. Protein Arginine Methyltransferase 5 (PRMT5) catalyzes the symmetric di-methylation of arginine residues and is overexpressed in GBM. Inhibition of PRMT5 causes senescence of immature GBM tumor cells. LB100, first-in-class small molecule inhibitor of Protein Phosphatase 2A (PP2A) can sensitize therapy-resistant tumor cells. Here, we tested the anti-GBM effect of concurrent PRMT5 and PP2A inhibition. Methods: Patient-derived primary GBM neurospheres (GBMNS), transfected with PRMT5 target-specific siRNA were treated with LB100 and subjected to in vitro assays including PP2A activity and western blot. The intracranial mouse xenograft model was used to test the in vivo antitumor efficacy of combination treatment. Results: We found that PRMT5-depletion increased PP2A activity in GBMNS. LB100 treatment significantly reduced the viability of PRMT5-depleted GBMNS compared to PRMT5 intact GBMNS. LB100 enhanced the G1 cell cycle arrest induced by PRMT5-depletion. Combination therapy also increased the expression of phospho-MLKL. Necrostatin-1 rescued PRMT5-depleted cells from the cytotoxic effects of LB100, indicating that necroptosis caused the enhanced cytotoxicity of combination therapy. In the in vivo mouse tumor xenograft model, LB100 treatment combined with transient depletion of PRMT5 significantly decreased tumor size and prolonged mice survival, while LB100 treatment alone had no survival benefit. Conclusion: Overall, combined PRMT5 and PP2A inhibition had significantly greater antitumor effects than PRMT5 inhibition alone.

Background Brain microdialysis is a minimally invasive technique for monitoring analytes, metabolites, drugs, neurotransmitters, and/or cytokines. Studies to date have centered on adults with traumatic brain injury, with a limited number of pediatric studies performed. Objective This scoping review details past use of brain microdialysis in children and identifies potential use for future neuro-oncology trials. Methods In December 2020, Cochrane Library: CENTRAL, Embase, PubMed, Scopus, and Web of Science: Core Collection were searched. Two reviewers screened all articles by title and abstract review and then full study texts, using microdialysis in patients less than 18yo. Results Of the 1,171 articles screened, 49 were included. The 49 studies included 472 pediatric patients (age range 0–17yo), in the brain (21), abdominal (16), and musculoskeletal (12) regions. Intracerebral microdialysis was performed in 64 collective patients, with a median age of 11yo, and predominance in metabolic evaluations. Conclusion Historically, pediatric microdialysis was safely performed within the brain in varied neurologic conditions, except neuro-oncology. Adult brain tumor studies using intratumoral/peritumoral microdialysis sampling can inform future pediatric studies to advance diagnosis and treatment options for such aggressive tumors.

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