bluuebunny/crossref_metadata_2025 huggingface dataset:
EPEN-05. MUTATIONAL ANALYSIS OF THE C11ORF95 DOMAIN AND SINGLE-CELL RNA-SEQ PROFILE OF A MOUSE MODEL OF SUPRATENTORIAL EPENDYMOMA
Authors: Truong Kevin , He James , Birdsall Gavin , Randazzo Ericka , Dunnack Jesse , LoTurco Joseph
Published: June 2021

We used a recently developed mouse model to better understand the cellular and molecular determinants of tumors driven by the oncogenic fusion protein C11orf95-RELA. Our approach makes use of in utero electroporation and a binary transposase system to introduce human C11orf95-RELA sequence, wild type and mutant forms, into neural progenitors. We used single cell RNA-seq to profile the cellular constituents within the resulting tumors in mice. We find that approximately 70% of the cells in the tumors do not express the oncogene C11orf95-RELA and these non-oncogene expressing cells are a combination of different non-tumor cell cell-types, including significant numbers of T-cells, and macrophages. The C11orf95-RELA expressing tumor cells have a unique transcriptomic profile that includes both astrocytic and neural progenitor marker genes, and is distinct from glioblastoma transcriptomic profiles. Since C11orf95-RELA is believed to function through a combination of both activation of NF-κB response genes by constitutive activation of RELA, and genes not activated by NF-κB, we assessed the expression of NF-κB response genes across the populations of cells in the tumor. Interestingly, when tumor cells highly expressing C11orf95-RELA were analyzed further, the subclusters identified were distinguished by upregulation of non-NF-kB pathways involved in cell proliferation, cell fate determination, and immune activation. We hypothesized that the C11orf95 domain may function to bring RELA transcriptional activation to inappropriate non-NF-κB targets, and we therefore performed a point mutation analysis of the C11orf95 domain. We found that mutations in either of the cysteines or histidines that make up a possible zinc finger domain in C11orf95 eliminate the ability of the fusion to induce tumors. In cell lines, these loss-of-function point mutants still trafficked to nuclei, and activated NF-κB pathways. We are currently using RNAseq and CRISPR loss-of function to identify genes downstream of C11orf95-RELA that are required for tumorigenesis.
EPEN-09. SUPER ENHANCER GENES AS MOLECULAR TARGETS IN C11ORF95-RELA FUSION EPENDYMOMA
Authors: Bertrand Kelsey , Mack Stephen
Published: June 2021

Genomic sequencing has driven precision-based oncology therapy; however, genetic drivers remain unknown or non-targetable for many malignancies, demanding alternative approaches to identify therapeutic leads. Ependymomas comprise histologically similar tumor entities driven by distinct molecular mechanisms, such as fusion oncoproteins, genome-wide chromosomal instability, or disruption of DNA methylation patterns. Despite these differences, ependymomas resist chemotherapy and lack available targeted agents for clinical trial development. Based on our previous findings, we hypothesized that mapping chromatin landscapes and super enhancers (SE) could uncover transcriptional dependencies as targets for therapy (Mack, Pajtler, Chavez et al., Nature, 2018). To functionally test the requirement of these SE genes for ependymoma cellular growth, we designed a pooled RNA interference screen against 267 SE associated genes. Our screen was performed in one C11ORF95-RELA-fusion model and two PF-EPN-A models as controls in biological triplicates. As an indication that our screen was successful, positive controls scored among lead hits including KIF11, BUB1B, PHF5A and MYC. Importantly, we identified many subtype specific dependencies in both C11ORF95-RELA-fusion and PF-EPN-A models, thus revealing novel pathways that potentially govern subgroup-specific ependymoma cell growth. Further, several candidates detected across all ependymoma lines were also identified as pan-cancer dependencies or glioma/glioblastoma specific essential genes from the DepMap Cancer Dependency Gene Resource. Our findings reveal novel targets and pathways that are essential for ependymoma cell growth, which may provide new insight into therapeutic strategies against these aggressive brain tumors.
EPEN-10. UNRAVELLING THE TUMOR IMMUNE MICROENVIRONMENT OF POSTERIOR FOSSA A EPENDYMOMAS ON RNA AND PROTEIN EXPRESSION LEVELS
Authors: F. Feenstra Fenna , Calkoen Friso , Kros Johan M , Kester Lennart , Kranendonk Mariëtte , van der Lugt Jasper , Mustafa Dana A M
Published: June 2021

Background

Ependymomas account for 8–10% of pediatric brain tumors, and the standard therapy of surgery and radiation has not changed for the past two decades. Characterization of the tumor immune microenvironment (TIME) is of great importance in order to find better therapies. However, the TIME of ependymomas is still not defined. In this retrospective observational study we aimed to unravel the TIME of ependymomas at mRNA and protein expression levels.

Methods

Ependymoma samples from two locations were selected: Posterior Fossa (PF-A, n=8), and supratentorial (ST, n=5). Targeted gene expression profile using the PanCancer immune profile panel of NanoString technology was performed. Data were analyzed using the nSolver software. In addition, 8 samples were subjected to RNA bulk sequencing, and the sequenced data were connected to the expression data of the same samples. To validate some of the findings, immunohistochemistry was performed.

Results

Unsupervised hierarchical clustering showed that PF-A ependymomas can be divided into two groups based on the expression of their immune-related genes. PF-A that showed high immune-expression clustered closely to the ST ependymomas. Significant expressions of genes related to “antigen-processing” and “adhesion” pathways were found in the immune-active groups. On the contrary, the PF-A that had low expressions of immune-related genes showed a high expression of BMI1 that has a prognostic and therapeutic value. Connecting gene expression to bulk sequence data validated the findings. In addition, immunohistochemical analysis confirmed that protein expression for some of the findings.

Conclusion

The TIME varies in ependymomas based on the location of the tumor. Moreover, the immune-related expression profiles indicated that PF-A ependymomas can be divided into two groups: immune-active and immune-not active PF-A. The prognostic and therapeutic values of the immune activity of PF-A should be further studied.
GERM-03. CLINICAL FEATURES AND OUTCOME OF CHILDREN WITH INTRACRANIAL NON-GERMINOMATOUS GERM CELL TUMORS: A POPULATION-BASED STUDY IN HONG KONG
Authors: P.Y. Liu Anthony , Ku Dennis T L , Fu Eric , Luk Chung-Wing , Yau Jeffrey P W , Ling Siu-Cheung , Chan Godfrey C F , Shing Matthew M K
Published: June 2021

The incidence of central nervous system non-germinomatous germ cell tumor (NGGCT) is four times higher in Chinese children than in the Western population. Reports on the outcome of Asian patients are nonetheless limited. Here we aim to summarize the experience of treating pediatric NGGCT in Hong Kong. Leveraging a population-wide pediatric oncology database, Chinese children with NGGCT diagnosed from 2002–2020 (n=43) were retrospectively studied. The diagnoses of NGGCT were made either with elevation in tumor markers (AFP/hCG; n=19), or by histology with/without concomitant raise in tumor markers (n=24). Most patients were treated with a combination of chemotherapy (cisplatin/etoposide/bleomycin, carboplatin/etoposide or carboplatin/etoposide/ifosfamide) and radiation (craniospinal+boost, whole ventricular+boost, or focal). The male:female ratio was 37:6, and the median age of diagnosis was 11.2 years. Primary tumor locations were pineal in 18, sellar/suprasellar in 12, basal ganglial in 9, supratentorial in 3 and posterior fossa in 1. Three had metastasis. Among the patients diagnosed by histology (n=24), 12 had mixed GCT, 8 had malignant/immature teratoma, 3 had embryonal carcinoma, and 1 had yolk sac tumor. With a median follow-up of 8 years, 8 patients progressed (local=7, distant=1), and 9 patients died (progression=5, palliative treatment for congenital tumors=2, sepsis=1, procedural complication=1). The respective 5-year PFS and OS were 74.9±6.9% and 82.2±6.1%. In multivariate analysis, high serum hCG level and no radiation use were significantly associated with inferior PFS. Outcome did not differ according to chemotherapeutic reagents used or radiation fields. Four patients had growing teratoma syndrome. Long-term neuroendocrine sequalae were common. In conclusion, children with NGGCT had reasonable outcome after multi-modal therapy in Hong Kong. Effort should be made to minimize tumor and treatment-related toxicities. The role of tumor markers for risk-stratification within NGGCT needs to be further interrogated.
HGG-02. NEUROPHYSIOLOGICAL SMALL MOLECULE SCREEN TO TARGET NEURON-GLIOMA INTERACTIONS IN PEDIATRIC HIGH-GRADE GLIOMAS
Authors: Rogawski David , Mulinyawe Sara , Thomas Craig , Monje Michelle
Published: June 2021

Neurons stimulate glioma growth via synaptic and paracrine signaling mechanisms. We recently demonstrated that neurons form AMPA receptor-dependent synapses with glioma cells, and that neuronal activity also induces potassium-evoked currents that are amplified by gap junctions coupling glioma cells. However, our understanding of the neurotransmitters, receptors, and ion channels participating in neuron-glioma signaling remains incomplete. We have recently developed a high-throughput neuron-glioma co-culture strategy to screen small molecules for agents that may disrupt neuron-glioma signaling. Glioma cell proliferation is increased tenfold when cultured together with neurons; this robust biological effect can be probed in a targeted screen of compounds influencing neurotransmitter receptors and ion channels. The neurophysiological small molecule library used was curated to include approved anti-epileptics, neuroleptics, and antidepressants, as well as a variety of other compounds acting on different neurotransmitter types and ion channels. Hits from the primary screen were run through a counter-screen using glioma cells grown alone without neurons, to identify compounds that specifically affect neuron-glioma interactions. Correlation of the screening results with drug mechanisms of action will allow us to map out the key neurotransmitter pathways regulating glioma growth, which can be further validated using genetic and in vivo experiments. Drugs identified in this glioma neuroscience screen may be readily translated into much-needed therapeutics for children with high-grade glioma.
HGG-06. EARLY GABAERGIC NEURONAL LINEAGE DEFINES DEPENDENCIES IN HISTONE H3 G34R/V GLIOMA
Authors: Liu Ilon , Bjerke Lynn , Cruzeiro Gustavo Alencastro Veiga , Rogers Rebecca F , Grabovska Yura , Panditharatna Eshini , Mackay Alan , Barron Tara , Shaw McKenzie , Hoffman Samantha E , Hack Olivia A , Quezada Michael A , Dempster Joshua , Temelso Sara , Englinger Bernhard , Molinari Valeria , Mire Hafsa M , Jiang Li , Madlener Sibylle , Mayr Lisa , Dorfer Christian , Geyeregger Rene , Rota Christopher , Ricken Gerda , Alexandrescu Sanda , Braun Emelie , Danan-Gotthold Miri , Hu Lijuan , Siletti Kimberly , Sundstroem Erik , Hodge Rebecca , Lein Ed , Agnihotri Sameer , Eisenstat David D , Carceller Fernando , Stapleton Simon , Bleil Cristina , Mastronuzzi Angela , Cole Kristina A , Waanders Angela J , Carcaboso Angel Montero , Vinci Maria , Hargrave Darren , Haberler Christine , Gojo Johannes , Slavc Irene , Linnarsson Sten , Monje Michelle , Jones Chris , Filbin Mariella G
Published: June 2021

High-grade gliomas harboring H3 G34R/V mutations exclusively occur in the cerebral hemispheres of adolescents and young adults, suggesting a distinct neurodevelopmental origin. Combining multimodal bulk and single-cell genomics with unbiased genome-scale CRISPR/Cas9 approaches, we here describe a GABAergic interneuron progenitor lineage as the most likely context from which these H3 G34R/V mutations drive gliomagenesis, conferring unique and tumor-selective gene targets essential for glioma cell survival, as validated genetically and pharmacologically. Phenotypically, we demonstrate that while H3 G34R/V glioma cells harbor the neurotransmitter GABA, they are developmentally stalled, and do not induce the neuronal hyperexcitability described in other glioma subtypes. These findings offer a striking counter-example to the prevailing view of glioma origins in glial precursor cells, resulting in distinct cellular, microenvironmental, and therapeutic consequences.
HGG-07. RADIATION INDUCED SENESCENCE IN DIFFUSE INTRINSIC PONTINE GLIOMA CELLS REVEALS SELECTIVE VULNERABILITY TO BCL-XL INHIBITION
Authors: Vardon Ashley , Guiho Romain , Carvalho Diana , Jones Chris , Hargrave Darren , Martinez-Barbera Juan-Pedro
Published: June 2021

Diffuse intrinsic pontine glioma remains a devastating condition with a dismal five year survival rate less than 5%. New approaches for treating this aggressive disease are critical to driving progress. Conventional radiotherapy remains the cornerstone of treatment, with no chemotherapeutic agent found to improve survival. However, radiotherapy is often delivered as a palliative treatment, and disease often recurs 3–6 months after. Radiation causes DNA damage and oxidative stress yielding a senescent state of replicative arrest in susceptible cells. However, increasing evidence demonstrates malignant cells can escape senescence leading to tumour recurrence. Targeted ablation of non-replicating senescent tumour cells following radiation could negate tumour recurrence. It remains unknown whether DIPG undergoes senescence following radiation, and furthermore, whether senolytics can be utilised to target senescent DIPG cells. We employed radiation to induce a senescent state in primary human DIPG cell lines. Senescence was confirmed using SA-β-gal staining, lack of EdU incorporation and qRT-PCR to characterise the SASP in three primary human DIPG cell lines. RNA-sequencing on DIPG cells following radiation revealed senescence and SASP signatures. Viable cells that survive radiation were then utilised to screen candidate senolytic drugs, only Bcl-XL inhibitors demonstrated reproducible senolytic activity in radiation treated DIPG cells. Conversely, Bcl-2 inhibitors failed to show any consistent senolytic activity. These results demonstrate future possibilities of targeting radiation induced senescence in DIPG, using novel senolytic therapies and highlight Bcl-XL dependency as a potential vulnerability of surviving DIPG cells following exposure to radiation.
HGG-11. LEPTOMENINGEAL DISEASE AND TUMOR DISSEMINATION ALONG CSF PATHWAYS IN A MURINE DIPG MODEL: IMPLICATIONS FOR STUDY OF THE TUMOR-CSF-EPENDYMAL MICROENVIRONMENT
Authors: Pan Shelei , Ye Dezhuang , Yue Yimei , Yang Lihua , Pacia Christopher , Dahiya Sonika , Limbrick David , Rubin Joshua , Chen Hong , Strahle Jennifer
Published: June 2021

Background

Leptomeningeal disease and hydrocephalus are present in up to 30% of patients with diffuse intrinsic pontine glioma (DIPG), however there are no animal models of cerebrospinal fluid (CSF) dissemination. As the tumor-CSF-ependymal microenvironment may play an important role in tumor pathogenesis, we identified characteristics of the Nestin-tumor virus A (Nestin-Tva) genetically engineered mouse model (GEMM) that make it ideal to study the interaction of tumor cells with the CSF and its associated pathways with implications for the development of treatment approaches to address CSF dissemination in DIPG.

Methods

A Nestin-TVa model of DIPG utilizing the three most common DIPG genetic alterations (H3.3K27M, PDGF-B, p53) was used for this study. All animals underwent MR imaging and a subset underwent histopathologic analysis with H&E and beta-IV tubulin.

Results

Tumor dissemination within the CSF pathways (ventricles, leptomeninges) was present in 76% (25/33) of animals, with invasion of the choroid plexus, disruption of the ciliated ependyma and regional subependymal fluid accumulation. Ventricular enlargement consistent with hydrocephalus was present in 94% (31/33). Ventricle volume correlated with region specific transependymal CSF flow (periventricular T2 signal), localized anterior to the lateral ventricles. Subependymal tumor cells were also present subjacent to the 4th ventricle in a post-mortem human specimen.

Conclusions

This is the first study to report CSF pathway tumor dissemination an animal model of DIPG and is representative of CSF dissemination seen clinically. Understanding the CSF-tumor-ependymal microenvironment has significant implications for treatment of DIPG through targeting mechanisms of tumor spread within the CSF pathways.
HGG-12. HUMAN IPSC-DERIVED H3.3K27M NEUROSPHERES: A NOVEL MODEL FOR INVESTIGATING DIPG PATHOGENESIS AND DRUG RESPONSE
Authors: Skinner Kasey , Koga Tomoyuki , Miki Shunichiro , Gruener Robert F , Huang R Stephanie , Furnari Frank , Miller C Ryan
Published: June 2021

Diffuse intrinsic pontine glioma (DIPG) is a subset of high-grade glioma that occurs predominantly in children and has no cure. Up to 80% of DIPG harbor a heterozygous point mutation that results in a lysine 27 to methionine substitution in histone variant H3.3 (H3.3K27M). Existing DIPG models have provided insight into the role of H3.3K27M but have limitations: genetically engineered murine models often rely on overexpression of the mutant histone to form tumors; patient-derived xenografts (PDX) are more genetically faithful but preclude examination of the effect of individual mutations on pathogenesis. To address these shortcomings and better recapitulate the genetics of human tumors, we designed a novel DIPG model based on human induced pluripotent stem cells (iPSC) edited via CRISPR to express heterozygous H3.3K27M. Edited iPSC were chemically differentiated into neural progenitor cells, which upon implantation into the brainstems of immunodeficient mice formed diffusely invasive tumors that were histologically consistent with high-grade glioma. Further, neurospheres cultured from primary tumors formed secondary tumors upon reimplantation with more diffuse invasion, suggesting in vivo evolution. To validate this model’s relevance to DIPG transcriptionally, we performed RNA-sequencing on a cohort of primary and secondary tumor neurospheres (termed primary and secondary iDIPG) and compared them to published RNA-seq data from pediatric PDX and patient tumor samples. Hierarchical clustering and principal component analysis on differentially expressed genes (P<0.05) showed that H3.3K27M iDIPG cluster with H3.3K27M PDX and patient tumors. Further, ssGSEA showed that H3.3K27M iDIPG are enriched for astrocytic and mesenchymal signature genes, a defining feature of H3.3K27M DIPG. Finally, we found that primary H3.3K27M iDIPG neurospheres are sensitive to panobinostat, an HDAC inhibitor shown to be effective against H3.3K27M DIPG cells in vitro. Overall, these data suggest that H3.3K27M iDIPG are a promising tool for investigating DIPG biology and new therapeutic strategies.
HGG-15. THE IMIPRIDONE ONC201 IN COMBINATION WITH THE ONCOLYTIC ADENOVIRUS DELTA-24-RGD HAS A SYNERGISTIC EFFECT IN PRECLINICAL MODELS OF PHGGS AND DMGS
Authors: de la Nava Daniel , Ausejo-Mauleon Iker , Laspidea Virginia , Marrodán Lucía , Zalacain Marta , Herrador-Cañete Guillermo , Nazarian Javad , Mueller Sabine , Allen Joshua E , Fueyo Juan , Gomez-Manzano Candelaria , Gupta Sumit , Patiño Ana , Alonso Marta M
Published: June 2021

Pediatric High Grade Gliomas (pHGGs), including Diffuse Midline Gliomas (DMGs), are aggressive pediatric tumors with a poor overall survival. In the last years, ONC201 has emerged as a promising agent in the field of pediatric brain tumors. Another interesting approach is virotherapy; Delta-24-RGD, which is an oncolytic virus, has demonstrated safety and effectiveness in different preclinical models and in clinical trials. Therefore, in this work we set to evaluate whether the combination of ONC201 with Delta-24-RGD could result in an increased therapeutic benefit in pHGGs and DMGs. Given that ONC201 targets mitochondrial metabolism in a preclinical setting, we assessed potential negative interactions of the combination therapy. While ONC201 treatment resulted in decreased viral protein load (E1A and fiber), there was no significant negative impact on the viral replication (measured by hexon staining). ONC201 did not disrupt the activation of mTORC1 pathway by the adenovirus. Furthermore, Delta-24-RGD did not affect the decrease in basal oxygen consumption rate induced by ONC201. Our results suggested that ONC201 and Delta-24-RGD are not antagonistic. Evaluation of the in vitro cytotoxicity in different human pHGG (CHLA-03-AA and SF188) and DMG (TP-54 and SU-DIPG-IV) cell lines showed that the combination treatment was significantly better that either agent alone. In vivo, a single local injection of Delta-24-RGD followed by a weekly ONC201 of mice bearing CHLA-03-AA cell line orthotopically significantly increased the median overall survival (PBS: 48 days; ONC201: 54.5 days; Delta-24-RGD: 62 days; ONC201+Delta-24-RGD: 95 days (P=0.0008)) of these mice leading to 20% long-term survivors, free of disease. Currently, we are evaluating the effect of the combination in immunosuppressed and immunocompetent models of DMGs. In summary, our data indicate ONC201 in combination with Delta-24-RGD could be a potential therapeutic choice for patients affected by pHGGs and DMGs.
HGG-17. FOCUSED ULTRASOUND-ENHANCED DELIVERY OF RADIOLABELED AGENTS TO DIFFUSE INTRINSIC PONTINE GLIOMA
Authors: Ye Dezhuang , Zhang Xiaohui , Yang Lihua , Yue Yimei , Tai Yuan-chuan , Rubin Joshua B , Liu Yongjian , Chen Hong
Published: June 2021

Diffuse intrinsic pontine glioma (DIPG) arising in the brainstem is the deadliest pediatric brain cancer with nearly 100% fatality and a median survival of <1 year. The critical location in the brainstem and the often intact blood-brain barrier (BBB) pose significant challenges in the treatment of DIPG. The objective of this study was to demonstrate the potential for focused ultrasound-induced BBB disruption (FUS-BBBD) to improve DIPG treatment by enhancing the safe and efficient delivery of drugs. A genetically engineered mouse model of DIPG was generated using the RCAS (replication-competent avian sarcoma-leucosis virus long-terminal repeat with splice acceptor)/tumor virus A modeling system. A magnetic resonance-guided FUS (MRgFUS) system was used to induce BBB disruption in these mice with the FUS targeted at the center of the tumor. Two radiolabeled agents with different sizes were used to evaluate the delivery efficiency of the FUS-BBBD technique in DIPG mice: a small-molecular radiotracer, 68Ga-DOTA-ECL1i, and a radiolabeled nanoparticle, 64Cu-labeled copper nanoparticles (64Cu-CuNCs, ~ 5 nm in diameter). 68Ga-DOTA-ECL1i (half-life ~ 1 h) and 64Cu-CuNCs (half-life ~13 h) were intravenously injected into the mice after FUS sonication, and microPET/CT imaging was performed at 1 h and 24 h, respectively, to evaluate the spatial-temporal distribution of these two agents in the brain and quantify the delivery outcome. FUS treatment increased the uptake of 68Ga-DOTA-ECL1i and 64Cu-CuNCs to the DIPG tumor by 3.25 folds and 4.07 folds on average, respectively. These findings demonstrated, for the first time, that FUS can increase BBB permeability in a murine model of DIPG and significantly enhance the delivery of agents of different sizes into the DIPG tumor.
HGG-22. EVALUATING THE REGULATION OF BLOOD-BRAIN BARRIER INTEGRITY IN DIPG MOUSE MODELS
Authors: Wei Xin , Phoenix Timothy
Published: June 2021

Diffuse intrinsic pontine gliomas (DIPGs) are considered to maintain a fairly intact blood-brain barrier (BBB) based on patient imaging tumor histology. In characterizing recently developed DIPG and HGG mouse models, we identified differences in BBB function and increased Angiopoietin1 (Angpt1) in H3 K27M DIPG models. We hypothesize that H3 K27M mutations promote the maintenance of DIPG BBB integrity through upregulation of Angpt1. To determine DIPG and HGG BBB phenotypes we performed an intergrative analysis of vascular histology and endothelial transcriptomes Ongoing studies using electroporation based DIPG mouse models are being performed examine the regulation and function of Angpt1 in DIPG BBB integrity. We have initiated studies comparing H3 K27M DIPG mouse models to H3 WT and G34R cortical HGG mouse models, demonstrating that DIPG models show minimal changes in vascular phenotype, including vessel density, branching, and diameter compared to cortical HGG models. Comparing DIPG and HGG purified endothelial transcriptomes, HGG ECs displayed enrichments of inflammatory signals and proliferation gene sets, and increased expression of tip cell identity genes. We identified Angpt1 as selectively upregulated in H3 K27M mouse models and derived cell lines. Preliminary data suggests Angpt1 supports the maintenance of BBB integrity in DIPG models. BBB phenotype differences are present in DIPG and HGG mouse models. Uncovering mutation specific mechanisms that regulate BBB function in brain tumors will be critical to advance our understanding of brain tumor pathogenesis and treatment response.
HGG-24. PRECLINICAL EFFICACY OF THE BRAIN PENETRANT CYCLIN-DEPENDENT KINASE INHIBITOR ZOTIRACICLIB IN PEDIATRIC DIFFUSE MIDLINE GLIOMAS
Authors: Mueller Timothy , Yadavilli Sridevi , Laternser Sandra , Cianciolo Chiara , Przystal Justyna , Bonner Erin , Biery Matt C , Vitanza Nicholas A , Grotzer Michael , Mueller Sabine , Nazarian Javad
Published: June 2021

Children diagnosed with diffuse midline gliomas (DMG), including diffuse intrinsic pontine glioma (DIPG), have extremely poor outcomes with a median overall survival of 9–12 months from initial diagnosis. Standard-of-care is limited to focal radiation therapy, given the paucity of effective targeted therapies for DMG. To identify effective drugs for treatment of children diagnosed with DMG, we investigated the brain-penetrating multi cyclin-dependent kinase inhibitor Zotiraciclib (ZTR/TG02). ZTR has demonstrated encouraging response rates and a benign safety profile in phase 1 trials of adults with high-grade glioma. It is thought to achieve its anti-cancer activity mainly by transcription disruption, a previously described vulnerability of DMGs, by inhibiting multiple cyclin-dependent kinases 9 and 7 (CDK9, 7). We found that ZTR robustly reduces viability of different patient derived DMG cells in a dose-dependent manner, with a median IC50 of 201 nM across eight tested cell lines (range 11–1258 nM, 72 hrs). Consistently, we observed loss of RNA polymerase II phosphorylation after 24 hours of treatment, indicating effective CDK9 inhibition at low drug concentrations and after short incubation time. This effect was followed by depletion of short-lived proteins including MYC and the anti-apoptotic factor MCL-1. Putative biomarkers of response and resistance were identified in silico using DepMap data analysis. To assess the safety profile of ZTR, we exposed our zebrafish model to various drug concentrations and found the drug to be safe at IC50 molarity. Ongoing in vitro and in vivo studies evaluating the efficacy of ZTR in combination with promising combination therapies for more effective treatment of children with DMG are also underway.
HGG-28. ONCOGENIC TYROSINE KINASE GENE FUSIONS IN SUPRATENTORIAL HIGH GRADE GLIOMAS OF YOUNG CHILDREN - COMPARISON OF RNA- AND DNA-BASED METHODS FOR THEIR RELIABLE DETECTION
Authors: Pietsch Torsten , Gielen Gerrit , Waha Andreas , Doerner Evelyn , von Bueren Andre O , Vokuhl Christian , Kristiansen Glen , Kramm Christof
Published: June 2021

High-grade diffuse gliomas in early childhood are characterized by a more favorable outcome compared to older children. We have shown in previous studies that these tumors are characterized by stable genomes. The occurrence of tyrosine kinase gene fusions in high-grade gliomas of infancy may represent therapeutic targets. 50 glioblastomas (GBM) with supratentorial location occurring in children younger than four years were retrieved from the archives of the Brain Tumor Reference Center, Institute of Neuropathology, Bonn University. DNA and RNA were extracted from FFPE tumor samples. Gene fusions were identified on the DNA level by FISH using break-apart probes for ALK, NTRK1, -2, -3, ROS1 and MET and Molecular Inversion Probe (MIP) methodology. On the RNA level, fusion transcripts were detected by targeted RNA sequencing as well as Nanostring assay with fusion-specific probes. 37 supratentorial GBM occurred in the first year of life, 13 GBM between one and four years. 18 cases showed fusions of ALK to different partners; all occurred in the first year of life (18/37, 48.6%). Fusions of ROS1 were found in 5, MET in 3, NTRK1, -2, -3 in 10 cases. 12 cases showed no and two cases novel fusions. The different methods led to comparable results. Only recurrent fusions with known fusion partners were detectable with fusion sequence-specific Nanostring probes and library construction for targeted RNA sequencing failed in a fraction of cases. Break-apart FISH led to reliable results on the next day, and MIP technology represented the most sensitive method for analysis of FFPE samples. Gene fusions involving the tyrosine kinase genes ALK, MET, ROS1 and NTRK1, -2, -3 occurred in 72% of glioblastomas of young children; most frequent were ALK fusions occurring in infant GBM. DNA-based MIP technology represented the most robust and sensitive assay. A combination of RNA- and DNA-based methods to detect these fusions with high reliability is recommended.
HGG-39. ALTERNATIVE SPLICING OF NEUROFIBROMIN 1 IS ASSOCIATED WITH ELEVATED MAPK ACTIVITY AND POOR PROGNOSIS IN HIGH-GRADE GLIOMA
Authors: Siddaway Robert , Milos Scott , Vadivel Arun , Dobson Tara , Swaminathan Jyothishmathi , Ryall Scott , Pajovic Sanja , Nazarian Javad , Becher Oren , Brudno Michael , Ramani Arun , Gopalakrishnan Vidya , Hawkins Cynthia
Published: June 2021

Despite a good understanding of the coding mutations underlying high-grade gliomas (HGG), their prognosis remains poor. We sought to characterize their transcriptional alterations and how this contributes to pathogenesis. We analyzed a large cohort of pediatric HGG (pHGG) by DNA sequencing (n=79) and RNA-Seq (n=63 plus normal brain, n=20), finding spliceosome mutations that are associated with increased splicing burden. High levels of alternative splicing were found in known cancer driver genes, with enrichment for chromatin regulators (including the SWI/SNF and NuRD complexes) and the RAS/MAPK pathway, in particular neurofibromin 1 (NF1). Both pediatric and adult HGG preferentially expressed NF1-II, a less active RAS GTPase, resulting in increased RAS/MAPK activity resulting from inclusion of exon23a into the GAP-related domain of NF1. In IDH wild-type, adult HGG, NF1-II was associated with reduced survival independently from RAS/MAPK pathway mutations. NF1 exon23a splicing was regulated by REST-mediated suppression of splicing factors controlling its inclusion. Together, our results identify a novel mechanism by which HGG can activate RAS/MAPK signaling and other oncogenic pathways to promote tumorigenesis independently from direct mutations.
HGG-40. FOCUSED ULTRASOUND ENHANCES ETOPOSIDE DELIVERY IN A MURINE PONTINE GLIOMA MODEL
Authors: Englander Zachary , Wei Hong-Jian , Pouliopoulos Antonios , Yoh Nina , McQuillan Nicholas , Tazhibi Masih , Wang Tony , Bruce Jeffrey , Canoll Peter , Feldstein Neil , Zacharoulis Stergios , Konofagou Elisa , Wu Cheng-Chia
Published: June 2021

Background

Diffuse intrinsic pontine glioma (DIPG) is a devastating pediatric brain cancer with limited treatment options and poor survival. The delivery of systemic therapies in this disease is severely limited by the blood-brain barrier (BBB). Focused ultrasound combined with intravenous microbubbles (FUS+MB) can effectively open the BBB permitting the entry of drugs across the cerebrovasculature. Etoposide is a chemotherapy frequently used in pediatric oncology with well-established anti-tumor effects but limited efficacy when administered systemically in DIPG. Given that FUS+MB in DIPG is not well studied, our goal was to determine the feasibility of ultrasound-mediated BBB opening and etoposide delivery in a preclinical murine pontine glioma model.

Methods

A syngeneic, orthotopic model was established by stereotactic injection of PDGF-B+PTEN-/-p53-/- murine glioma cells into the pons of B6 albino mice. Mice were randomly divided into control (n=6) or FUS+MB groups (n=6). A single-element, spherical-segment FUS transducer (center frequency=1.5MHz) driven by a function generator through a power amplifier was used with concurrent microbubble injection to sonicate the tumor and its margins on post-injection day 14. Immediately after treatment, 5 mg/kg of intraperitoneal etoposide was administered to all 12 mice. All animals underwent cardiac puncture and blood sampling, followed by transcardiac perfusion and brain harvesting. Liquid chromatography-mass spectometry was performed on both serum and tumor tissue to measure etoposide levels.

Results

Contrast-enhanced MRI demonstrated successful BBB opening in all FUS+MB mice. Compared to control (mean=20.98ng/g), etoposide concentration in the sonicated tumor tissue (mean=164.77ng/g) was nearly eight times greater. Lastly, the mean brain tumor–to-serum ratio was more than fivefold higher in the treated mice (1.50%) compared with the control mice (0.28%) (P<0.005).

Conclusions

FUS+MB is hereby shown successful in BBB opening and enhanced delivery of etoposide in a preclinical pontine glioma model.
IMMU-06. DELTA-24-RGD EXPRESSING POSITIVE IMMUNE MODULATORS SHOW ANTI-DIPG EFFECT AND INCREASE TUMOR IMMUNE INFILTRATION
Authors: Laspidea Virginia , Gupta Sumit , Puigdelloses Montserrat , Labiano Sara , Ausejo-Mauleon Iker , de la Nava Daniel , Becher Oren J , Gumin Joy , Fueyo Juan , Gomez-Manzano Candelaria , Alonso Marta M
Published: June 2021

Diffuse Intrinsic Pontine Gliomas (DIPG) are aggressive pediatric brain tumors that arise in the pons of children, being the leading cause of pediatric death caused by cancer. We have previously demonstrated that Delta-24-RGD administration is safe and efficacious in DIPG preclinical models, indicating that it could be a good candidate as therapeutic approach for DIPG. However, our data underscore that there is still room to improve the anti-DIPG effect obtained with Delta-24-RGD. For that purpose, we have constructed three new virus by engineering Delta-24-RGD with different T cell activators: 4-1BBL (Delta-24-ACT), OX40-L (Delta-24-RGDOX) and GITRL (Delta-24-GREAT), to further increase the immune response generated by the viral effect. In vitro, the three virus were able to infect murine and human DIPG cell lines, produce oncolytic effect in a dose-dependent manner and express the corresponding functional ligand (4-1BBL, OX40L or GITRL) in the membrane of infected cells (almost 100% of cells expressing them at 10 MOIs). As expected, viral replication was optimal in human cell lines but semipermissive in murine cells. In vivo, the intratumoral administration of armed oncolytic viruses was safe and significantly increased survival of mice bearing orthotopic DIPG murine tumors, leading to long-term survivors. In addition, we analyzed the effect of the virus in the tumor microenvironment by flow cytometry and immunohistochemistry, which indicated that there was a significant increase of immune infiltration in brains of treated mice. Moreover, the immune infiltrated showed a functional active phenotype. Although deeper characterization is needed, these data show that the incorporation of a positive immune modulator into Delta-24-RGD could improve the oncolytic effect of the virus by boosting the immune response, while maintaining a safe profile in immunocompetent models offering a feasible option treatment for DIPG.
IMMU-07. “STROKE MIMICS” ARE NOT BENIGN IN IMMUNOCOMPROMISED CHILDREN
Authors: Mahdi Jasia , Bach Alicia , Smith Alyssa , Tomko Stuart , Fields Melanie , Griffith Jennifer , Morris Stephanie , Guerriero Rejean , Noetzel Michael , Guilliams Kristin , Agner Shannon
Published: June 2021

Objective

To determine the clinical variances between strokes and stroke mimics in a pediatric immunocompromised population that consists of children with central nervous system (CNS) and non-CNS malignancies and a history of solid organ transplantation.

Methods

We performed a retrospective cohort analysis of stroke alert activations in patients with high-grade gliomas, low-grade gliomas, atypical teratoid rhabdoid tumors, rare CNS tumors, B-cell acute lymphoblastic leukemia, T-cell acute lymphoblastic leukemia, osteosarcoma, and solid organ transplants at St. Louis Children’s Hospital between February 2013 and September 2019. We categorized final diagnoses as strokes or stroke mimics. We classified diagnoses as a neurologic emergency if the diagnosis necessitated changes in management.

Results

Out of 217 stroke alerts, 31 alerts occurred for 28 patients meeting inclusion criteria. All final diagnoses constituted neurologic emergencies, including: stroke (39%), chemotherapy-related neurotoxicity (29%), tumor progression (19%), and seizures/posterior reversible encephalopathy syndrome (13%). Patients meeting inclusion criteria with strokes and stroke mimics presented similarly, with the exception of altered mental status, which was more prevalent in patients with strokes than stroke mimics (p = 0.03). One child received hyperacute thrombectomy for stroke. Only 58% of children with stroke mimics had complete resolution of their presenting neurologic symptoms. Children with strokes and stroke mimics had similar mortality incidences of 33% and 37%, respectively.

Conclusions

Although all acute neurologic changes in immunocompromised children are not strokes, stroke mimics in this population are neither benign nor self-limited and carry long-term neurologic morbidity and mortality. This study highlights the utility of an acute stroke evaluation infrastructure and the need for acute and long-term neurology involvement in the care of these patients.
IMMU-10. USE OF A SINGLE PEPTIDE CHECKPOINT INHIBITOR FOR TREATMENT OF CENTRAL NERVOUS SYSTEM TUMORS
Authors: Moertel Christopher , Xiong Zhengming , Pluhar G-Elisabeth , Olin Michael
Published: June 2021

Cancer immunotherapy has revolutionized clinical management of malignancies by generating long-term, durable control of tumors. Unfortunately, these therapies often cause serious immune-related adverse events. In addition, only a small percentage of solid tumors respond to these therapies and there is little efficacy in CNS tumors. Our research is focused on the CD200 immune checkpoint, which modulates the immune system through the inhibitory receptor (CD200R1) and activation receptors (CD200AR). We demonstrated that targeting the CD200AR with a checkpoint peptide ligand (CD200AR-L) activates the immune system and renders it impervious to the inhibitory effects of CD200. In a pre-clinical canine spontaneous high-grade glioma trial, CD200AR-L, with autologous tumor lysate vaccination, resulted in a 20% two-year progression-free survival; no toxicities or adverse effects were observed. We suggest this result was due to the ability of the CD200AR-L to modulate multiple immune checkpoints. During the characterization of the CD200AR-L, we discovered signaling molecules are shared by the CD200 and PD-1/PD-L1 checkpoint pathways, suggesting these immune checkpoints are connected. Our preliminary studies demonstrated that the inhibitory CD200R1 and PD-1 mediate immune checkpoint signaling activities through the SHIP1/2. Moreover, CD200AR-L overpowers the suppressive effects of CD200 and PD-L1, which are both shed by tumors, by downregulating the inhibitory CD200R1 and PD-1 on both antigen-presenting cells (APC) and T-cells. In addition, CD200AR-L downregulates PD-1 on APCs and inhibits the upregulation of PD-L1 and CTLA4. These studies led to the discovery that the novel peptide modulates the CD200, PD-1/PD-L1 and CTLA-4 pathways, providing the basis for the translatable development of a CD200-directed peptide for clinical use against multiple tumors including gliomas. These studies led to FDA approval of this peptide for the first in human phase I single center, open-label, dose-escalation clinical trial (NCT04642937) in adult and pediatric trial for children with recurrent malignant brain tumors.
IMMU-13. CUSTOMIZABLE MULTI-LAMELLAR RNA-NANOPARTICLES FOR PEDIATRIC GLIOMA
Authors: Mendez-Gomez Hector , McGuiness James , grippin Adam , Weidert Frances , Carrera-Justiz Sheila , Mitchell Duane , Sayour Elias
Published: June 2021

Background

Since the preponderance of pediatric gliomas are mutationally ‘bland,’ immune checkpoint inhibitors are unlikely to mediate therapeutic benefit. Alternately, immunologic response can be induced de novo against pediatric gliomas with mRNA cancer vaccines. Messenger RNA represents a paradigm shift in vaccinology (i.e. COVID-19) given its flexibility, commercialization, and propensity to confer rapid protection with only a single vaccine.

Objective

We sought to develop a new mRNA platform with an optimized backbone for insertion of both personalized and/or “off the shelf’ (i.e. H3K27M) transcripts for rapid induction of anti-tumor activity against pediatric gliomas.

Approach

We synthesized an mRNA backbone with optimized 5’ and 3’ UTRs for delivery of gene transcripts pertinent to pediatric brain tumors using a lipid-nanoparticle (NP) delivery vehicle. This vaccine utilizes a novel engineering design that layers tumor derived mRNA into a lipid-nanoparticle (NP) “onion-like” or multi-lamellar package.

Results

We demonstrate immunogenicity of RNA-NPs delivering either personalized glioma mRNA or H3K27M mRNA. RNA-NPs localize to myeloid cells in murine KR158b brain tumors and activate dendritic cells that supplant regulatory intratumoral myeloid populations inducing antigen-recall response with long-term survivor benefit. Our optimized mRNA backbone yielded significantly improved anti-tumor efficacy compared with commercial backbones. We have shown this approach can be refined for co-delivery of immunomodulatory RNAs (i.e. GM-CSF) and/or delivery of siRNAs targeting immunoregulatory axes (PD-L1) in murine brain tumors (GL261). We have since established safety of RNA-NPs in acute/chronic murine GLP toxicity studies without cross-reactivity to normal-brain, and launched a large-animal canine brain tumor trial which demonstrated RNA-NPs to be feasible, safe and immunologically active.

Conclusion

RNA-NPs reprogram the brain tumor microenvironment while inducing a glioma-specific immune response. We have since received FDA-IND approval for first-in-human trials (IND#BB-19304) in pediatric patients with high-grade gliomas (PNOC020 study, NCT04573140).
LGG-04. MULTIOMIC ANALYSIS OF MAPK PATHWAY ACTIVITY IN PEDIATRIC PILOCYTIC ASTROCYTOMA
Authors: Sigaud Romain , Selt Florian , Hielscher Thomas , Stefanski Anja , Overbeck Nina , Usta Diren , Kocher Daniela , Remke Marc , Picard Daniel , Pfister Stefan M , Jones David T W , Brummer Tilman , Witt Olaf , Milde Till
Published: June 2021

Introduction

Pilocytic astrocytomas (PA) are the most common pediatric brain tumors. They are characterized by MAPK pathway alterations, leading to its constitutive activation and modulating the balance between cell proliferation and the oncogene-induced senescence (OIS) sustained by senescence-associated secretory phenotype (SASP) factors. This makes PA suitable for MAPK inhibitor (MAPKi) therapies, showing encouraging results in phase 1/2 clinical trials. Little is known about the molecular implications of MAPK downregulation in the proliferating and senescent compartments.

Methods

DKFZ-BT66 PA cells derived from a primary KIAA:BRAF-fusion positive PA cell line, were used as model system. Gene expression and phospho-proteomic datasets were generated from DKFZ-BT66 cells, in both the proliferative and senescent states, and treated with the MEKi trametinib for different time-spans. A time course analysis based on differentially expressed genes was performed, followed by a single-sample gene set enrichment analysis (ssGSEA). Analysis of the phospho-proteomic data is ongoing.

Results

Differential gene expression analysis revealed that MEK inhibition leads to the inhibition of the OIS-SASP gene program in senescent DKFZ-BT66. ssGSEA showed that most MAPK-related signatures were downregulated upon MEKi treatment, while pathways related to upstream MAPK activators (including FGFR, NTRK and TGFB pathways) were upregulated, in both proliferating and senescent DKFZ-BT66. Genes regulated by the MAPK pathway and involved in OIS-SASP were identified by analyzing genes differentially regulated between proliferating and senescent DKFZ-BT66, and modulated upon MEKi treatment.

Conclusion

This data suggests that MAPKi reverses OIS in senescent PA cells, while inducing the activation of MAPK upstream regulators in proliferating and senescent PA cells, identifying putative co-targets that could help prevent growth rebound upon MAPKi withdrawal. Furthermore, the identification of the MAPK-related OIS-SASP genes provide insight about the regulation of OIS-SASP by the MAPK pathway. Validation of this data with the ongoing phospho-proteomic analysis and in primary samples is needed.
LGG-08. TREATMENT OUTCOMES AND TOLERABILITY OF TRAMETINIB IN PROGRESSIVE CIRCUMSCRIBED LOW-GRADE GLIOMAS
Authors: Hanzlik Emily , Archambault Bridget , Dairi Mays , Schroeder Kristin , Patel Mallika , Lipp Eric S , Boucree Song , Peters Katherine , Ashley David , Landi Daniel
Published: June 2021

Circumscribed low-grade gliomas comprise roughly one-third of pediatric CNS tumors. Most of these tumors are caused by activating mutations in the mitogen-activated protein kinase (MAPK) pathway. Drugs targeting the MAPK pathway are effective in other cancers and are being utilized in low-grade gliomas. We describe treatment outcomes and toxicities in a series of thirteen low-grade glioma patients treated with trametinib. We performed a retrospective chart review to evaluate response on T2/FLAIR MRI images per updated RANO criteria, visual outcomes, tolerability, and durability of response in progressive low-grade glioma patients treated with trametinib. Thirteen patients age 22 months to 34 years were included. Best radiographic response on therapy included 2/13 partial response, 3/13 minimal response, 5/13 stable disease, and 3/13 progressive disease. Diagnoses included pilocytic astrocytoma (n=6), desmoplastic infantile ganglioglioma (DIG; n=1), and low-grade glial neoplasms (n=2). Molecular drivers included BRAF:KIAA1549 fusion (n=3), V600E mutation (n=1), and somatic NF1 mutation (n=1). Three patients had germline NF1. In patients with partial or minimal response, best response was seen after longer durations of therapy; 4 of 5 best responses occurred after at least 12 months on therapy. Five patients completed prescribed therapy. Three patients remain stable off therapy at 6, 12, and 21 months; two patients recurred at 1 and 10 months off therapy. Skin manifestations were the predominant form of toxicity. This was more severe in older males, and symptoms improved with intermittent dosing. All patients with optic pathway tumors showed at least stable vision throughout treatment, with some patients having dramatic improvement. Trametinib is effective and well-tolerated in patients with low-grade glioma. Dermatologic toxicity can be mitigated by intermittent dosing. Best responses tended to occur later in therapy, sometimes after relatively stable MRIs. Patients with optic pathway lesions showed stable to improved vision even in the absence of significant radiographic response.