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Despite being the leading cause of cancer-related childhood mortality, pediatric gliomas have been relatively understudied, and the repurposing of immunotherapies has not been successful. Whole- transcriptome sequencing, single-cell sequencing, and sequential multiplex immunofluorescence were used to identify an immunotherapeutic strategy that could be applied to multiple preclinical glioma models. MAPK-driven pediatric gliomas have a higher IFN signature relative to other molecular subgroups. Single-cell sequencing identified an activated and cytotoxic microglia (MG) population designated MG-Act in BRAF-fused, MAPK-activated pilocytic astrocytoma (PA), but not in high-grade gliomas or normal brain. T cell immunoglobulin and mucin domain 3 (TIM3) was expressed on MG-Act and on the myeloid cells lining the tumor vasculature but not normal brain vasculature. TIM3 expression became upregulated on immune cells in the PA microenvironment, and anti-TIM3 reprogrammed ex vivo immune cells from human PAs to a proinflammatory cytotoxic phenotype. In a genetically engineered murine model of MAPK-driven, low-grade gliomas, anti-TIM3 treatment increased median survival over IgG- and anti-PD-1-treated mice. Single-cell RNA-Seq data during the therapeutic window of anti-TIM3 revealed enrichment of the MGAct population. The therapeutic activity of anti-TIM3 was abrogated in mice on the CX3CR1 MG-KO background. These data support the use of anti-TIM3 in clinical trials of pediatric low-grade, MAPK- driven gliomas., Introduction Immunological studies of adult gliomas have been numerous, whereas pediatric gliomas are relatively understudied despite the fact that they are the leading cause of cancer-related childhood mortality (1). Among [...]

Pediatric and adult high-grade gliomas (HGGs) frequently harbor PDGFR[alpha] alterations. We hypothesized that cotreatment with everolimus may improve the efficacy of dasatinib in PDGFR[alpha]-driven glioma through combinatorial synergism and increased tumor accumulation of dasatinib. We performed dose-response, synergism, P-glycoprotein inhibition, and pharmacokinetic studies in in vitro and in vivo human and mouse models of HGG. Six patients with recurrent PDGFR[alpha]-driven glioma were treated with dasatinib and everolimus. We found that dasatinib effectively inhibited the proliferation of mouse and human primary HGG cells with a variety of PDGFR[alpha] alterations. Dasatinib exhibited synergy with everolimus in the treatment of HGG cells at low nanomolar concentrations of both agents, with a reduction in mTOR signaling that persisted after dasatinib treatment alone. Prolonged exposure to everolimus significantly improved the CNS retention of dasatinib and extended the survival of PPK tumor-bearing mice (mutant TP53, mutant PDGFR[alpha], H3K27M). Six pediatric patients with glioma tolerated this combination without significant adverse events, and 4 patients with recurrent disease (n = 4) had a median overall survival of 8.5 months. Our results show that the efficacy of dasatinib treatment of PDGFR[alpha]-driven HGG was enhanced with everolimus and suggest a promising route for improving targeted therapy for this patient population., Introduction High-grade gliomas (HGGs) are common and aggressive pediatric and adult brain tumors. The median overall survival (OS) of adult patients diagnosed with glioblastoma (GBM), grade IV glioma, is 12.6 [...]

Atypical Teratoid/Rhabdoid tumors (AT/RT) of the central nervous system are rare but aggressive tumors of childhood. Median survival with surgery and standard chemotherapy is less than 12 months. In an attempt to improve outcome, patients were treated with aggressive surgical resection and multi-agent chemotherapy, followed by high dose chemotherapy with autologous stem cell rescue. Nine consecutive children (median age 21 months) were diagnosed with AT/RT at the University of California San Francisco Childrens Hospital from 1997 to 2007 and treated with this aggressive approach. Diagnosis was confirmed using molecular markers. There are two long-term survivors (78 and 98 months from diagnosis). One additional patient is alive with disease. Three patients died of disease during therapy. Three patients died of disease after therapy was complete. There were no toxic deaths. Two of nine patients treated for AT/RT at our institution with high dose chemotherapy and autologous bone marrow transplant are long-term survivors, suggesting that a subset of patients can be cured with this approach.

Vemurafenib (Zelboraf) is an orally available BRAFV600E inhibitor approved for the treatment of unresectable or metastatic BRAFV600E‐mutant melanoma. The primary objective of this work was to characterize the pharmacokinetics (PK) of vemurafenib in pediatric patients with recurrent/refractory astrocytomas harboring the BRAFV600E mutation. The study was also designed to evaluate the feasibility of replacing whole vemurafenib tablets with crushed tablets in young children unable to swallow tablets. Twenty‐five pediatric patients (median age, 8.8 years; range, 3.3‐19.2) with recurrent/refractory BRAFV600E‐mutant astrocytomas received whole (n = 19) or crushed (n = 6) vemurafenib tablets twice daily. Plasma samples were collected on days 1, 15, and 22 in cycle 1 of vemurafenib treatment. Descriptive PK analyses demonstrated significant variability (approximately 6‐fold) in drug exposure. A 1‐compartment model with first‐order absorption and elimination was developed by adjusting the vemurafenib PK model previously validated in adults with mutant BRAFV600E melanoma. After inclusion of allometric scaling on total body weight, the model adequately described the PK of vemurafenib in children between a wide age range of 3 to 19 years old. In the crushed‐tablet cohort, relative bioavailability was approximately 96% (95% confidence interval, 49%‐142%) compared to that seen in pediatric patients receiving whole tablets based on the preliminary comparison analysis results. Moderate intrapatient variability (48%) of vemurafenib clearance was observed. There was significant correlation (R2 = 0.83) between area under the plasma concentration–time curve and trough concentration at steady state. These results will help increase the number of pediatric patients for whom vemurafenib is accessible and facilitate improved dosing in pediatric patients with recurrent/refractory BRAFV600E astrocytomas. [ABSTRACT FROM AUTHOR]

Pleomorphic xanthoastrocytoma (PXA) is an astrocytic neoplasm that is typically well circumscribed and can have a relatively favorable prognosis. Tumor progression to anaplastic PXA (WHO grade III), however, is associated with a more aggressive biologic behavior and worse prognosis. The factors that drive anaplastic progression are largely unknown. We performed comprehensive genomic profiling on a set of 23 PXAs from 19 patients, including 15 with anaplastic PXA. Four patients had tumor tissue from multiple recurrences, including two with anaplastic progression. We find that PXAs are genetically defined by the combination of CDKN2A biallelic inactivation and RAF alterations that were present in all 19 cases, most commonly as CDKN2A homozygous deletion and BRAF p.V600E mutation but also occasionally BRAF or RAF1 fusions or other rearrangements. The third most commonly altered gene in anaplastic PXA was TERT, with 47% (7/15) harboring TERT alterations, either gene amplification (n = 2) or promoter hotspot mutation (n = 5). In tumor pairs analyzed before and after anaplastic progression, two had increased copy number alterations and one had TERT promoter mutation at recurrence. Less commonly altered genes included TP53,BCOR,BCORL1,ARID1A,ATRX,PTEN, and BCL6. All PXA in this cohort were IDH and histone H3 wildtype, and did not contain alterations in EGFR. Genetic profiling performed on six regions from the same tumor identified intratumoral genomic heterogeneity, likely reflecting clonal evolution during tumor progression. Overall, anaplastic PXA is characterized by the combination of CDKN2A biallelic inactivation and oncogenic RAF kinase signaling as well as a relatively small number of additional genetic alterations, with the most common being TERT amplification or promoter mutation. These data define a distinct molecular profile for PXA and suggest additional genetic alterations, including TERT, may be associated with anaplastic progression. [ABSTRACT FROM AUTHOR]

The article presents a study which identifies the in-frame genomic rearrangements resulting from nuclear respiratory factor 1 (NRF1)-BRAF gene and autophagy related 7 (ATG7)-RAF1 active kinase fusions in anaplastic pleomorphic xanthoastrocytoma (PXA) without BRAF p.V600E mutation. It suggests the potential of the molecular characterization of BRAF pV600E to improve the diagnosis of anaplastic PXA.

Although malignant astrocytomas are a leading cause of cancer-related death in children, rational therapeutic strategies are lacking. We previously identified activating mutations of v-raf murine sarcoma viral oncogene homolog B1 (BRAF) (BRAFTI799A encoding BRAFV600E) in association with homozygous cyclin-dependent kinase inhibitor 2A (CDKN2A, encoding p14ARF and p16Ink4a) deletions in pediatric infiltrative astrocytomas. Here we report that BRAFV600E expression in neural progenitors (NPs) is insufficient for tumorigenesis and increases NP cellular differentiation as well as apoptosis. In contrast, astrocytomas are readily generated from NPs with additional Ink4a-Arf deletion. The BRAFV600E inhibitor PLX4720 significantly increased survival of mice after intracranial transplant of genetically relevant murine or human astrocytoma cells. Moreover, combination therapy using PLX4720 plus the Cyclin-dependent kinase (CDK) 4/6-specific inhibitor PD0332991 further extended survival relative to either monotherapy. Our findings indicate a rational therapeutic strategy for treating a subset of pediatric astrocytomas with BRAFV600E mutation and CDKN2A deficiency. [ABSTRACT FROM AUTHOR]

Identifying cellular programs that drive cancers to be stem-like and treatment resistant is critical to improving outcomes in patients. Here, we demonstrate that constitutive extracellular signal-regulated kinase 1/2 (ERK1/2) activation sustains a stem-like state in glioblastoma (GBM), the most common primary malignant brain tumor. Pharmacological inhibition of ERK1/2 activation restores neurogenesis during murine astrocytoma formation, inducing neuronal differentiation in tumorspheres. Constitutive ERK1/2 activation globally regulates miRNA expression in murine and human GBMs, while neuronal differentiation of GBM tumorspheres following the inhibition of ERK1/2 activation requires the functional expression of miR-124 and the depletion of its target gene SOX9. Overexpression of miR124 depletes SOX9 in vivo and promotes a stem-like-to-neuronal transition, with reduced tumorigenicity and increased radiation sensitivity. Providing a rationale for reports demonstrating miR-124-induced abrogation of GBM aggressiveness, we conclude that reversal of an ERK1/2-miR-124-SOX9 axis induces a neuronal phenotype and that enforcing neuronal differentiation represents a therapeutic strategy to improve outcomes in GBM. • Stem cell-derived glioma formation is accompanied by loss of neurogenesis • miR-124-dependent neuronal differentiation reduces glioblastoma (GBM) aggressiveness • An ERK1/2-miR-124-SOX9 axis regulates neuronal differentiation in GBM cells • An miR-124-induced neuronal phenotype sensitizes GBM cells to radiation Sabelström et al. show that the loss of neurogenesis is reversible during neural stem cell-derived glioma formation. Pharmacological inhibition of ERK1/2 globally regulates miRNAs and induces neuronal differentiation, a process that is dependent on the modulation of an miR-124-SOX9 axis in glioblastoma (GBM) cells. The overexpression of miR-124 induces neuronal differentiation that abrogates GBM aggressiveness. [ABSTRACT FROM AUTHOR]

Summary Although signaling from phosphatidylinositol 3-kinase (PI3K) and AKT to mechanistic target of rapamycin (mTOR) is prominently dysregulated in high-grade glial brain tumors, blockade of PI3K or AKT minimally affects downstream mTOR activity in glioma. Allosteric mTOR inhibitors, such as rapamycin, incompletely block mTORC1 compared with mTOR kinase inhibitors (TORKi). Here, we compared RapaLink-1, a TORKi linked to rapamycin, with earlier-generation mTOR inhibitors. Compared with rapamycin and Rapalink-1, TORKi showed poor durability. RapaLink-1 associated with FKBP12, an abundant mTOR-interacting protein, enabling accumulation of RapaLink-1. RapaLink-1 showed better efficacy than rapamycin or TORKi, potently blocking cancer-derived, activating mutants of mTOR. Our study re-establishes mTOR as a central target in glioma and traces the failure of existing drugs to incomplete/nondurable inhibition of mTORC1. [ABSTRACT FROM AUTHOR]