bluuebunny/crossref_metadata_2025 huggingface dataset:
EMBR-02. OLIG2 REPRESENTS A PROGNOSTIC MARKER AND THERAPEUTIC TARGET IN MYC-AMPLIFIED MEDULLOBLASTOMA RELAPSE AND METASTASIS
Authors: Xu Zhenhua , Murad Najiba , Rivero-Hinojosa Samuel , Schüller Ulrich , Zhang Peng , Liu Xiao , Rood Brian , Packer Roger , Pei Yanxin
Published: June 2021

Medulloblastoma (MB) is one of the most common malignant pediatric brain tumors. Among the multiple MB subtypes, MB with MYC amplification confers an extremely poor prognosis with an overall survival rate of less than 30%. Relapse is often mediated by a small population of therapy-resistant tumor cells which expand and ultimately progress to lethal tumors. Moreover, MYC-amplified MB exhibits a high incidence of leptomeningeal metastases. Approximately one-third of patients with MYC-amplified MB present with metastases and nearly all have this complication at relapse. Metastatic MYC-amplified MB is highly fatal. As such, our ability to effectively treat MYC-amplified MB is largely dependent on our capacity to eradicate the therapy resistant tumor cells, particularly the metastatic tumor cells. The development of clinically effective therapies for this disease will be facilitated by the identification of therapy-resistant tumor cell populations and their molecular signatures involved in tumor metastasis and relapse. Using patient-derived xenograft (PDX) mouse models, we recently discovered that a subset of MYC-amplified MB tumors with strong OLIG2 expression (OLIG2-high) is resistant to radiation and prone to metastasize, whereas MYC-amplified MB tumors without OLIG2 expression (OLIG2-low) are sensitive to radiation without dissemination. Irradiation of OLIG2-high tumors led to either a small number of quiescent OLIG2- cancer stem-like cells (CSLCs) remaining in the cerebellar bed or to the dissemination of highly proliferative OLIG2+ tumor cells along the leptomeninges. All mice harboring these radioresistant CSLCs succumbed to relapse. Further studies demonstrated that the quiescent OLIG2- CSLCs did not contribute to tumor recurrence directly, while elimination of OLIG2+ radioresistant CSLCs with a small molecule OLIG2 antagonist significantly prevented metastatic recurrence, delayed tumor growth and prolonged animal survival. Thus, our studies provide new insights into the role of OLIG2 in radiotherapy resistance and metastasis in MYC-amplified MB and propose a novel therapeutic approach to treating metastatic MYC-amplified MB.
EMBR-05. THE TENTATIVE APPLICATION OF EN BLOC CONCEPT IN THE PEDIATRIC BRAIN TUMOR: EXPERIENCE FROM A LARGE PEDIATRIC CENTER IN CHINA
Authors: Cao Liangliang , Ma Jie
Published: June 2021

Background

The less allowable blood loss and tolerance of intraoperative blood loss of children lead to the high rate of massive blood transfusion in the treatment of brain tumor. The surgical concepts of en bloc resection may contribute to the improvement of brain tumor resection.

Objective

To investigate the effects of en bloc concept on short outcomes of pediatric brain tumors and factors associated with the application of en bloc concept.

Methods

According to the surgical concept involved, the patients were divided into three subgroups-complete en bloc concept, partial en bloc concept and piecemeal concept. The matching-comparison (piecemeal group and en bloc group formed from the first two subgroups) was conducted based on age, tumor location, lesion volume, and pathological diagnosis to investigate effect of the en bloc concept on the short-term outcomes. Then the patient data after January 2018, when the en bloc concept was routinely integrated into brain tumor surgery in our medical center, were reviewed and analyzed to find out the predictors associated with the application of en bloc concept.

Results

In the en bloc group, the perioperative outcomes, including hospital stay (p=0.001), PICU stay (p=0.003), total blood loss(p=0.015), transfusion rate(p=0.005) and complication rate(p=0.039), were all significantly improved. The multinomial logistic regression analysis showed that tumor volume and imaging features, like bottom vessel, encasing nerve or pass-by vessel, finger-like attachment, ratio of “limited line” and ratio of “clear line” remained independent factors for the application of en bloc concept in our medical center.

Conclusion

This study supports the application of complete or partial en bloc concept in the pediatric brain tumor surgery referring to the preoperative imaging features, and compared with piecemeal concept, en bloc concept can improve the short outcomes without significant increases in neurological complication. Large series and Additional supportive evidence are still warranted.
EMBR-13. NOVEL SYNERGISTIC APPROACHES FOR TARGETED THERAPY OF MYC-DRIVEN MEDULLOBLASTOMA USING CRISPR/CAS9 GENE EDITING
Authors: Qin Nan , Picard Daniel , Rickert Daniel , Meyer Frauke-Dorothee , Blümel Lena , Göbbels Sarah , Bartl Jasmin , Pauck David , Fischer Ute , Borkhardt Arndt , Reifenberger Guido , Remke Marc
Published: June 2021

Introduction

Resistance to chemotherapy is a common cause of treatment failure in cancer patients and a major problem facing current cancer research. Targeted modulation of oncogenic signaling pathways may be used to systematically characterize drug resistance mechanisms across tumor entities and may help to identify new therapeutic strategies. Since the transcription factor MYC is aberrantly activated in many cancers including pediatric malignant brain tumors, like medulloblastoma (MB), our study focused on MYC-related drug resistance.

Methods and Results

We performed high-throughput drug screening using our in-house semi-automated platform and identified the HDAC inhibitor Entinostat as a drug that shows promising effects in MYC-driven MB. Investigating genome-wide dCas9-based transcriptional activation screening, potential drug response modulators, mainly TGFB1/Erk/MKNK1 signaling including neural EGFL like 2 (NELL2), were discovered. For further validation, we stably overexpressed NELL2 in MYC-driven MB cells and treated overexpressing cells and the corresponding control cells with Entinostat. Using PI staining, cell cycle status was tracked. Entinostat treatment led to modest induction of cell death in MYC-driven MB control cells but only slightly increased cell death rate in MYC-driven MB cells with NELL2-overexpression.

Conclusion

We report that the combination of genetic and pharmacological approaches is a powerful approach to study drug resistance. Our data suggest that activation of the TGFB1/Erk/MKNK1 signaling pathway desensitizes MYC-driven MB cells to Entinostat. Synergistic targeting of TGFB1/Erk/MKNK1 signaling and MYC could therefore provide a novel therapeutic option in this aggressive MB subtype.
EMBR-18. LASER INTERSTITIAL THERMAL THERAPY FOR RECURRENT MEDULLOBLASTOMA
Authors: Xu Jordan , Pathare Jodi , Hoerig Clay , Goldberg Aaron , Abongwa Chenue , Plant Ashley , Olaya Joffre
Published: June 2021

Background

Medulloblastoma is one of the most common malignant childhood brain tumors and is managed by maximal surgical resection followed by cranio-spinal irradiation and adjuvant chemotherapy. The estimates for survival have not significantly improved over the last two decades, and survivors have an increased risk of poor quality of life. Disease relapse occurs in around 30% of children and survival is less than 20%. Laser interstitial thermal therapy (LITT) is a minimally invasive approach that has been increasingly used to treat brain lesions, particularly for high-risk surgeries. While LITT has been described in a variety of primary brain tumors, including glioblastoma multiforme and metastatic brain tumors, there have been few reports of LITT for recurrent medulloblastoma.

Case Description

We describe a case of an 11-year-old female with recurrent medulloblastoma first treated at age 5. She initially underwent gross total resection complicated by severe posterior fossa syndrome followed by chemotherapy and radiation (per ACNS0332). She was unfortunately found to have a new enhancing lesion on surveillance imaging 6 years later, and a biopsy confirmed recurrent tumor. Due to morbidity from initial surgery, the family did not wish to pursue further open resection but agreed to proceed with laser ablation as an alternative. She continues on Avastin/irinotecan/TMZ. Surveillance MRI nearly a year later shows a significant reduction in tumor size and enhancement.

Conclusion

Recurrent medulloblastoma is a highly aggressive tumor that conveys a poor prognosis. LITT offers a less invasive procedure that may serve as an adjunct in treating recurrent tumor or as palliation. Longer term follow-up and additional cases will help understand the efficacy of LITT in recurrent medulloblastoma.
EMBR-22. RATIONAL DEVELOPMENT OF SYNERGISTIC THERAPIES ALONGSIDE BMI1 INHIBITION FOR GROUP 3 MEDULLOBLASTOMA
Authors: Bakhshinyan David , Adile Ashley A , Venugopal Chitra , Brown Kevin , Chan Katherine , Qazi Maleeha A , Chokshi Chirayu , Gwynne William D , Tieu David , Moffat Jason , Singh Sheila
Published: June 2021

Medulloblastoma (MB) is the most common pediatric brain tumor. Of its four distinct molecular subgroups, Group 3 MBs are associated with increased risk of recurrence, metastasis and overall poor patient outcome. In recent years, small molecule inhibitors targeting BMI1 have shown to be efficacious against several types of malignant tumors including pediatric MB. Although in vivo studies provide a promising proof-of-concept for the therapeutic targeting of BMI1 in Group 3 MB, mice that receive treatment eventually succumb to their disease. These results suggest that additional mechanisms may underlie the maintenance of MB and underscores the main obstacle in treating a constantly evolving tumor. After initial preclinical validation of BMI1 inhibitor PTC-596, DNA barcoding clonal tracking technology was leveraged to profile in vivo clonal dynamics of Group 3 MB in response to the established chemoradiotherapy regimen alone and in combination with PTC-596. Comparison of clonal composition of the tumors extracted from the brains and spines post-treatment revealed the persistence of a small number of clones with the ability to escape therapy and drive subsequent tumor expansion. In order to better understand molecular susceptibilities of MB cells post BMI1 inhibition, we undertook an in vitro genome-wide CRISPR/Cas9 screening to identify context-specific MB regulatory pathways to be synergistically targeted along with BMI1. By comparing the results of the in vitro genome wide CRISPR/Cas9 screen to the essential genes in human neural stem cells (hNSCs), we identified several context specific regulators of mTOR, AKT and PLK1 pathways. The combined treatment alongside PTC-596 has demonstrated synergistic efficacy against MB cells with minimal toxicity to hNSCs in vitro and is currently being evaluated in preclinical studies. This study provides the foundation for clinical validation of small-molecule inhibitors synergistic with PTC-596 to improve the durability of remissions and extend survival of patients with treatment-refractory Group 3 MB.
EMBR-24. YB1 IS CRITICAL FOR MEDULLOBLASTOMA TUMOR MAINTENANCE AND DNA REPAIR FOLLOWING THERAPEUTIC INTERVENTION
Authors: McSwain Leon , Kenney Anna , Chen Victor , Huang Tiffany
Published: June 2021

Medulloblastoma (MB) is the most common pediatric central nervous system malignancy. Although the current standard of care leads to ~70% patient survival, the therapies are highly toxic, leading to life-long side effects, and recurrence due to therapeutic resistance is fatal. We sought to investigate mediators of radiation response in mouse models for the Sonic hedgehog (SHH) subgroup MB as well as human cell lines. We previously identified Y-box binding protein 1 (YB1) as a downstream effector of YAP-mediated MB radiation resistance. YB1 is a crucial, yet understudied, protein highly expressed across all 4 subgroups of MB. Through its DNA- and RNA-binding cold shock domain, YB1 mediates both transcriptional and translational changes important for tumor maintenance and therapeutic response. We show that following ionizing radiation, YB1 mediates DNA repair through PARP and that PARP inhibition abrogates YB1-mediated DNA repair in cells overexpressing YB1. Additionally, through its inhibitory effects on p53, YB1 is capable of mediating anti-apoptotic effects in response to genotoxic insult. By targeting YB1 with short hairpin RNA, we show that cells are more amenable to ionizing radiation induced double strand breaks. Additionally, we utilize RNA binding protein immunoprecipitation sequencing to investigate post transcriptional regulation of RNAs bound by YB1. We show that YB1 binds numerous transcripts critical for the identity of early cerebellar progenitor cells, the putative cell of origin for SHH subgroup tumors, in addition to transcripts important for cell cycling and migration.
EMBR-30. A NOVEL PLK1 INHIBITOR ONVANSERTIB EFFECTIVELY SENSITIZES GROUP 3 MEDULLOBLASTOMA TO RADIOTHERAPY
Authors: Wang Dong , Veo Bethany , Pierce Angela , Foamier Susan , Balakrishnan Ilango , Donson Andrew , Alimova Irina , Erlander Mark , Ridinger Maya , Venkataraman Sujatha , Vibhakar Rajeev
Published: June 2021

Medulloblastoma (MB) is often accompanied by MYC amplification. PLK1 is an oncogenic kinase that controls cell cycle and proliferation, and it has been preclinically validated as a cancer therapeutic target. Onvansertib (PCM-075) is a novel, orally available PLK1 inhibitor, which shows tumor growth inhibition in many types of cancer. We examined the effect of Onvansertib on MYC-driven medulloblastoma as a monotherapy or in combination with radiation. A Crisper-Cas9 screen was used to discover essential genes for MB tumor growth. Microarray and immunohistochemistry on pediatric patient samples were performed to examine the expression of PLK1. The effect of Onvansertib in vitro was measure by cell viability, colony-forming assays, extreme limiting dilution assay, and RNA-Seq. ALDH activity, cell-cycle distribution, and apoptosis were analyzed by flow cytometry. DNA damage was assessed by immunofluorescence staining. Medulloblastoma xenografts were generated to explore the monotherapy or radio-sensitizing effect. PLK1 is overexpressed in Group 3 MB. The IC50 concentrations of Onvansertib in Group 3 MB cell lines were between 4.9 and 6 nM. Onvansertib reduced colony formation, cell proliferation, stem cell renewal, and induced G2/M arrest in vitro. Moreover, Onvansertib in combination with radiation increased DNA damage and apoptosis compared with radiation alone. The combination of Onvansertib with radiotherapy resulted in marked tumor regression in orthotopic xenografts. These findings suggest that Onvansertib is an effective strategy in combination with radiotherapy in MB.
EMBR-32. INTEGRATED STRESS RESPONSE PLAYS A PRO-SURVIVAL ROLE IN MYC-DRIVEN MEDULLOBLASTOMA
Authors: Langman Sofya , Delaidelli Alberto , Huang Yue Zhou , Sorensen Poul
Published: June 2021

Medulloblastoma (MB) accounts for 20% of diagnosed brain tumors in children. Group 3 (G3) MB subtype is the most aggressive. Molecularly, G3 MB is characterized by MYC overexpression, which drives elevated mRNA translation in tumor cells. PERK is an eukaryotic translation initiation factor 2 (eIF2α) kinase that inhibits mRNA translation under endoplasmic reticulum (ER) stress conditions, such as in response to accumulation of unfolded proteins. When unfolded proteins accumulate in the ER, activated PERK phosphorylates eIF2α. This shuts down global translation and triggers integrated stress response (ISR) to help cells adapt through selective translation of mRNA encoding pro-survival proteins. High mRNA expression of PERK correlates with poor survival in G3 MB patients. In vitro, combination of ER or hypoxic stress with PERK knockdown induces apoptosis in MB cells. ISRIB is an ISR inhibitor that maintains translation rates despite eIF2α phosphorylation. Combining ISRIB with stress such as hypoxia induces apoptosis in MB cells and prevents accumulation of key ISR mediators such as ATF4. In addition, combination of ISRIB and hypoxia induces oxidative stress. Current G3 MB treatment regimens include vincristine, a known ISR inducer. Combination of ISRIB with vincristine amplifies vincristine-induced apoptosis, potentially suggesting novel therapeutic approach for MB. Our findings show that inhibition of ISR in G3 MB represents a powerful inducer of cancer cell death.
EPEN-02. FUNCTION AND DEPENDENCY OF NF-KB ACTIVITY IN C11ORF95-RELA FUSION EPENDYMOMA
Authors: Stuckert Austin , Arabzade Amir , Zhao Yanhua , Chen Hsiao-Chi , Mack Stephen
Published: June 2021

Introduction

Ependymoma is an aggressive type of pediatric brain tumor resistant to chemotherapy, with treatment to date limited to surgical resection and radiation. Thus, identification and validation of molecular targets that can translate into clinical trials in ependymoma is desperately needed to improve patient outcomes. Over 70% of supratentorial ependymoma are driven by an oncogenic fusion between C11orf95 and Rela (denoted CRFUS). CRFUS expression initiates ependymoma development in mice by potentially acting as an oncogenic transcription factor and disrupting gene expression programs. We hypothesized that specific CRFUS interacting proteins are required for tumor formation and could represent lead therapeutic targets.

Methods

To study CRFUS ependymoma, a natively-forming tumor model of CRFUS generated by in utero electroporation of the developing mouse brain was utilized. Tumor cells were isolated and then subjected to nuclear Rapid Immunoprecipitation and Mass Spectrometry Analysis of Endogenous Proteins (RIME) of HA-tagged CRFUS protein. Immunoprecipitation and Western Blot (IP-WB) were utilized to probe for leading protein interactions.

Results

We identified NF-kB proteins consistent with canonical Rela mediated transcription (NFKB1 and NFKB2) as well as novel protein interactomes that converged on RNA splicing and translational regulation. In addition, we identified a large series of novel chromatin-binding proteins as candidates potentially required for CRFUS mediated tumorigenesis.

Conclusions

Further study is ongoing to validate key CRFUS protein interaction dependency on tumor development. ChIP-Seq (chromatin immunoprecipitation with massively parallel DNA sequencing) and CUT&RUN (cleavage under target and release using nuclease) assays have been employed to further analyze the functional role of canonical Rela pathway members. By interrogating these mechanisms, novel therapeutic targets and pathways may be identified in parallel with dissecting the molecular basis of CRFUS driven ependymoma.
GERM-01. RECURRENCE PATTERN AND SURVIVAL FOR RELAPSED INTRACRANIAL NON-GERMINOMATOUS GERM CELL TUMORS: A SINGLE-INSTITUTION EXPERIENCE
Authors: Wen Lei
Published: June 2021

Purpose

Intracranial non-germinomatous germ cell tumors (NGGCTs) have lower overall survival than germinoma because relatively higher recurrence usually occurs after first line therapy.

Methods

Between January 2003 and December 2018, 111 consecutive patients diagnosed with NGGCTs reviewed. Those who progressed after first line therapy were included in this study. Data of first line treatment, salvage treatment, clinicopathological features and survival were collected and analyzed.

Results

Totally, thirty patients (30/111, 27.0%) relapsed in our cohort, including 19 patients with accurate relapse information detail, and 11 patients who died of disease progression during follow up but without exact time and site of relapse. The median OS from diagnosis of the disease was 49.2 months (95% CI: 14.1 to 84.3 months) and 3-year OS was 54.3%. Patients who received both CSI and chemotherapy relapsed less than those who received reduced volume of radiotherapy or only CSI or only chemotherapy (22.5% vs. 45.5%, p=0.034). Of 19 patients who had detail information of recurrence time and site, the median time from diagnosis of disease to relapse was 9.5 months (2.2 to 72.1 months). Regarding to recurrence site, most patients relapsed in primary site (10/19, 52.6%) or distant intracranial (6/19, 31.6%). The recurrence site of other 3 patients were spinal (n=1), ventricular (n=1) and peritoneal (n=1).

Conclusion

Protracted follow-up is recommended because late recurrence is not uncommon. Primary tumor site and distant intracranial are the most prevalent relapsed location. Patients who relapsed could benefited from both CSI and salvage chemotherapy.
GERM-02. MANAGEMENT STRATEGY FOR CHEMO-REFRACTORY, PROGRESSIVE PEDIATRIC IMMATURE TERATOMA
Authors: McNutt Sarah , Shah Nidhi , Rizk Elias
Published: June 2021

Background

Localized NGGCT, a heterogeneous entity, treated with chemo-radiotherapy harbors an overall survival of around 93% based. Here, we present a case of a child whose immature teratoma progressed on chemotherapy, while tumor markers remain within normal range. Salvage therapy for progressive immature teratoma is variable, and can include surgery, chemotherapy and/or craniospinal radiation. Case: 10 year old boy with precocious puberty presented to the local Emergency room with tonic-clonic seizures. Imaging showed a localized pineal mass, with mixed cystic and solid components. Biopsy results were diagnostic for mixed germ cell tumor with components of immature teratoma. Prior to the start of chemotherapy, serum and cerebrospinal fluid (CSF) tumor markers showed slight elevation of both alpha feto- protein (AFP) and beta-human chorionic gonadotropin hormone (β-HCG). The patient underwent two cycles of chemotherapy per ACNS1123, stratum 1, with normalization of tumor markers. Unfortunately, near the end of Cycle 2 of chemotherapy, patient presented with clinical signs of herniation, and was noted to have significant progression of pineal mass on imaging. Tumor was gross totally resected, with pathology conclusive for only immature teratoma. Pre- and post-operative tumor markers remained normal. Proton-beam craniospinal radiation was then administered. Patient is now almost 6 months off therapy, with unremarkable serum and CSF tumor markers, as well as serial imaging that remains negative for disease, with neurological development appropriate for age.

Conclusion

This case highlights the unusual nature of progression of an immature teratoma with no elevation of tumor markers while on chemotherapy. While salvage chemotherapy, in the form of a metronomic regimen or high-dose consolidative regimen, can be considered, these do present quite a bit of short-term and long-term toxicity to the growing child. Craniospinal irradiation followed by close monitoring is a reasonable alternative, with less short-term toxicity, for an entity that is radio-sensitive.
HGG-08. CREATION OF AN IN VITRO AND IN VIVO MODEL SYSTEM FOR THE STUDY OF H3.1K27M DIPG
Authors: Lagas Joseph , Yang Lihua , Becher Oren , Rubin Joshua
Published: June 2021

Diffuse Intrinsic Pontine Glioma (DIPG) is a devastating pediatric high-grade glioma that occurs in the brainstem with a median survival of less than 1 year. A greater understanding of the early tumorigenic events is essential for the development of effective therapeutics. DIPG is characterized by founder mutations in histone H3, either H3.1K27M or H3.3K27M. These mutations cause global hypomethylation, resulting in aberrant gene expression. Little is known about how this mechanism contributes to tumorigenesis. Interestingly, H3.1K27M DIPG show an increased incidence in females, whereas H3.3K27M DIPG shows no sex difference. This illustrates that the tumorigenic potential of H3.1K27M may be different between the sexes. Few models of DIPG incorporate the study of H3.1K27M despite the fact that it represents a unique opportunity to obtain valuable information on the tumorigenesis of DIPG through the study of the sex difference. Thus, we have created an in vitro and in vivo model system for H3.1K27M DIPG utilizing the RCAS mouse model system. This system utilizes RCAS vectors and a RCAS-ntva transgenic mouse line to deliver specific mutations to nestin expressing cells in the brainstem, including oligodendrocyte progenitor cells (OPCs), the predicted cell of origin. Delivering H3.1K27M, ACVR1 R206H, and PDGFaa at postnatal day 7 produces DIPG-like tumors in vivo, confirmed by H and E staining, between 60–110 days post injection. Additionally, confirmed through immunofluorescence staining, we can isolate a pure population of OPCs via immunopanning and infect them with RCAS vectors in vitro to produce stable expression of H3.1K27M. Introduction of H3.1K27M alone into male and female OPC cultures provides an opportunity to compare the early tumorigenic effects of H3.1K27M between the sexes in vitro. These results demonstrate that we have created an in vitro and in vivo H3.1K27M DIPG model system for the study of sex differences and tumorigenesis in DIPG.
HGG-19. 5-AMINOLEVULINIC ACID (5-ALA)-GUIDED RESECTION OF PEDIATRIC BRAIN TUMORS
Authors: Schwake Michael , Bruns Ann-Katrin , Müther Michael , Schipmann Stephanie , Stummer Walter
Published: June 2021

Between tumor and normal brain, allowing a higher degree of resection, and improved patient outcomes. In recent years, several reports have emerged regarding the use of 5-ALA in other brain tumor entities, including pediatric brains tumors. Since gross total resection (GTR) of many brain tumors in children is crucial, the role of 5-ALA-guided resection requires elucidation.

Methods

A systematic literature review of EMBASE and MEDLINE/PubMed databases revealed 20 eligible publications encompassing 186 5-ALA-guided operations on pediatric brain tumors. To reduce bias, publications were revised independently by two authors.

Results

5-ALA-guided resection enabled the surgeons to identify the tumor more easily and was considered helpful mainly in cases of glioblastoma (GBM, 21/27, 78%), anaplastic ependymoma WHO grade III (10/14, 71%), and anaplastic astrocytoma (4/6, 67%). In contrast, cases of pilocytic astrocytomas (PAs) and medulloblastomas 5-ALA-guided surgery did not show consistent fluorescent signals and 5-ALA was considered helpful only in 12% and 22% of cases, respectively. Accumulation of fluorescent porphyrins seems to depend on WHO tumor grading. In case fluorescence signal was considered helpful, it was associated with a greater degree of resection. One study showed an association between visible fluoresce signal and concentration of protopophyrin IX (PPIX) concentration. A threshold of 4μg/ml was required in order to visualize the fluorescence signal. The rate of adverse events related to 5-ALA was negligible, especially new postoperative sequelae.

Conclusion

5-ALA could play a role in resection of malignant, contrast enhancing, supratentorial pediatric brain tumors. At present, we are conducting a prospective phase I-II multicenter clinical trial to evaluate side effects and feasibility of 5-ALA guided surgery.
HGG-23. IN VITRO AND IN VIVO PRECLINICAL DRUG SCREENING OF PROMISING THERAPEUTICS FOR DIFFUSE MIDLINE GLIOMA (DMG)
Authors: Cosentino Chiara Cianciolo , Laternser Sandra , Przystal Justyna M , Yadavilli Sridevi , Zhang Jie , Müller Timothy , Kritzer Bettina , Müller Sabine , Nazarian Javad
Published: June 2021

Introduction

Diffuse midline gliomas (DMGs) are amongst the most unforgiving pediatric brain tumors, characterized by an intrinsic resistance to therapy. Despite major advances in understanding of tumor biology, the prognosis remains exceedingly poor, and treatment options are limited. New therapeutics are being evaluated at a fast rate by different laboratories. In order to prioritize effective drug candidates for DMG treatment, we comprehensively characterized a panel of promising therapeutic agents in in vitro and in different vivo systems.

Methods

We determined the sensitivity of primary DMG cell lines to a panel of small molecule inhibitors targeting known DMG targets and pathways. Dose response curves were generated for more than 20 different compounds and possible synergistic effects were investigated by SynergieFinder. In an effort to highlight potential toxicities and associated mechanisms at a large scale, we performed a preclinical toxicity evaluation in zebrafish larvae, with a slightly modified version of the official Fish Embryo Acute Toxicity (FET) test. Drug toxicity was tested by continuous exposure of zebrafish larvae to increasing concentrations of the different compounds. Survival curves, morphological analyses and behavioral tests were performed at a maximum tolerated dose (MTD). To confirm the findings obtained in zebrafish, we further performed in vivo studies in mice for promising candidates.

Results

Among the tested drugs in vitro we found 10 drugs showing promising dose- dependent reduction in cell viability with IC50 in nM to µM range. These were further evaluated for toxicity in zebrafish. The zebrafish larvae toxicities observations strongly correlated with the findings in murine in vivo studies, reinforcing the importance of zebrafish as an accurate investigative toxicology model to assess acute toxicity of molecules in preclinical studies.

Conclusions

By testing a wide range of drugs, targeting different pathways on DMG cells and in different in vivo systems we identified promising drug candidates for clinical management of children diagnosed with DMG.
HGG-27. HNRNPA1 SPLICED VARIANT SENSITIZATION EFFECT DISCLOSED IN GLIOMA CELLS
Authors: Yadav Ajay
Published: June 2021

Glioblastoma is aggressive brain tumor. Glioma heterogeneity builds in hypoxic condition due to its intrinsic high apoptosis rate cause to develop a high selection clonal pressure. HnRNPA1 plays a key role in developing glycolytic tumor, shows its high expression exclusively in hypoxic glioma cells. Recently we observed one more spliced variant of hnRNPA1, encoding higher isoform, exclusively abundant in resistant glioma cell lines. Widely around the scientific community HnRNPA1 splice factor family protein was found distinctly regulating resistant glioma phenotype. To support our hypothesis, methodology we perform includes various apoptosis assays to critically understand hnRNPA1 spliced variant dependent pathway in Temozolomide resistant U87 glioma cells. Proteomic based apoptotic array and angiogenic array enable us to visualize selective knock down of hnRNPA1 has dominant role in promoting apoptotic cascade. Additionally, flow cytometry base annexin V-PI staining technique to understand early and late apoptosis was measured in selective hnRNPA1 spliced variant knockdown cells in presence or absence of PI3 kinase inhibitor wortmannin (5 micro molar). Results showed hnRNPA1 higher isoform knock down promotes more apoptosis compare to lower isoform. Interestingly, overexpression of HnRNPA1 higher isoform or lower isoform alone doesn’t promote apoptosis, however is prominently higher apoptosis in Bortezomib treated U87 glioma cells. These both isoforms are presently majorly in gliomas, but somehow for long was not recognized. Conclusion is to explore more related novel finding or therapeutic strategy to target higher isoform of hnRNPA1, using invivo mouse xenograft model.
HGG-31. HISTONE H3.3 G34R/V MUTATIONS STIMULATE PEDIATRIC HIGH-GRADE GLIOMA FORMATION THROUGH THE INDUCTION OF CHROMOSOMAL INSTABILITY
Authors: Grigore Florina , Robinson James , Langfald Alyssa , Hinchcliffe Edward , Day Charles
Published: June 2021

The histone H3.3 G34R/V mutations are known drivers of high-grade pediatric glioma (pHGG). However, the mechanism(s) for H3.3 G34R/V induced tumor formation are unclear. Chk1 phosphorylates H3.3 S31 at the pericentromere during early mitosis, suggesting a novel mitotic function. We observed that H3.3 G34 mutant pHGG cells have reduced mitotic H3.3 S31 phosphorylation compare to WT H3.3 cell lines. The H3.3 G34R mutation reduced Chk1 phosphorylation at S31 by >90% in an in vitro kinase assay. Overexpression of either H3.3 G34R or non-phosphorylatable S31A in H3.3 WT, diploid cells led to a significant increase in chromosome mis-segregations. Likewise, H3.3 G34 mutant pHGG cells have significantly elevated rates of mis-segregation as compare to H3.3 WT pHGG cells. During normal cell division, phospho-S31 is lost in late anaphase. However, when chromosome missegregation occurs, phospho-S31 spreads and stimulates p53 accumulation in G1 – thus suppressing aneuploid cell proliferation. Here we show that cells expressing mutant G34 fail to arrest following mis-segregation, despite having WT p53. These studies demonstrate that the H3.3 G34R/V mutations are sufficient to transform normal, diploid cells into proliferative, chromosomally instable cells. To determine if this process contributes to tumorigenesis, we used the RCAS/TVA mouse model to overexpress H3.3 WT, G34R, or S31A in the glial precursor cells of mice pups. Over 100 days, S31A and G34R mice had drastically reduced survival (averaging 77, 81, and 100 days for S31A, G34R, and WT mice). Furthermore, most G34R and S31A mice developed HGG, while H3.3 WT mice remained tumor-free and did not develop high-grade tumors. Our work strongly indicates that a major factor in H3.3 G34R pHGG formation is the induction of chromosomal instability – which occurs directly through the suppression of H3.3 S31 phosphorylation.
HGG-32. ONC201 AND ONC206 TARGET TUMOR CELL METABOLISM IN PEDIATRIC DIFFUSE MIDLINE GLIOMA PRECLINICAL MODELS
Authors: Przystal Justyna M , Cosentino Chiara Cianciolo , Yadavilli Sridevi , Zhang Jie , Laternser Sandra , Bonner Erin R , Biery Matt , Vitanza Nicholas A , Koschmann Carl , Cain Jason , Waszak Sebastian M , Mueller Sabine , Nazarian Javad
Published: June 2021

Diffuse midline gliomas (DMGs) remain incurable cancers and new treatments are urgently needed. One promising new therapeutic avenue for these cancers is targeting of metabolic vulnerabilities including a heightened dependence on mitochondrial metabolism. We and others have shown that the oral, brain-penetrant imipridone drugs ONC201 and ONC206 target mitochondrial metabolism in cancer cells. In particular, ONC201 and ONC206 hyper-activate the mitochondrial protease ClpP, impair mitochondrial oxidative phosphorylation (OXPHOS), activate the integrated stress response (ISR) signaling pathway, and induce apoptosis in DMG preclinical models. We validated ClpP as a key target of ONC206 by showing that CRISPR/Cas9-mediated CLPP knockout significantly decreased ONC206 sensitivity in DMG cells. We further showed that imipridone-mediated ClpP activation resulted in significant degradation of the chaperone protein ClpX. Moreover, ONC201 and ONC206 treatment inhibited mitochondrial respiration, decreased mitochondrial membrane potential and triggered extensive mitochondrial structural damage, including disintegration of mitochondrial cristae. Time-course RNA sequencing of five DMG cell lines treated with ONC201 and ONC206, alone or in combination, revealed robust ATF4 and CHOP upregulation, indicating potent activation of ISR signaling. Notably, ATF4/CHOP upregulation was strongest in ONC201/6 combination-treated cells, indicating synergy between the two drugs. We further explored drug combinations by testing ONC201 together with ONC206, Panobinostat, JQ1, and Osimertinib to identify synergistic combination treatments. The strongest synergistic effect was found over a broad IC50 range for ONC201 and ONC206. Finally, we showed that ONC201 and ONC206 significantly prolonged survival of mice bearing brainstem DIPG xenografts. Ongoing studies include assessment of the in vivo efficacy of ONC201 and ONC206 across different CNS tumor models, as well as investigation and validation of clinically relevant biomarkers of response to treatment. In summary, our preclinical data strongly support the utility of the mitochondrial targeting agents ONC201 and ONC206 for the treatment of DMG and other malignant brain tumors.
HGG-33. EXPLOITING METABOLIC DEFECTS WITH NAMPT INHIBITORS IN DIPG
Authors: Muraleedharan Ranjithmenon , Heer Collin , Sundam Ranjini , Brenner Charles
Published: June 2021

Diffuse intrinsic pontine glioma (DIPG) are universally lethal pediatric brain tumors with limited treatment options. We recently performed synthetic lethal drug screen with a panel of DNA repair and metabolic inhibitors in vitro, in patient-derived DIPG cells and isogenic cell lines engineered to contain key DIPG-associated mutations. Nearly 80% of DIPGs harbor a recurrent H3K27M mutation in H3.3 (H3F3A) or H3.1 (HIST1H3B) histones. This has prompted us to consider H3K27M mutation-induced exploitable defects for a therapeutic gain. This screen identified synthetic lethal interactions between H3K27M mutations and the nicotinamide phosphoribosyl transferase (NAMPT) inhibitor, FK866. The association between H3K27M mutations and NAMPTi sensitivity was validated in follow-up studies using isogenic WT and H3K27M-mutant expressing pairs of human immortalized astrocytes and neural progenitor cells (NPCs). In addition, we tested the effects of FK866 in a panel of unique DIPG patient-derived tumor neurospheres in short-term viability assays. We found that FK866 induced depletion of NAD and exhibited toxicity towards H3K27M mutant DIPG cell lines with an IC50 of ~2.5 nM. These findings were consistent across three structurally unique NAMPT inhibitors. Finally, we found that inducible expression of mutant H3K27M results in a gradual, 50% decrease in cellular NAD levels over the course of five days, suggesting that H3K27M mutations may induce an inherent NAD metabolic defect that is exploited by NAMPTi’s. We now seek to understand the mechanistic basis for the observed metabolic defect and NAMPTi sensitivity associated with mutant H3K27M. In addition, we aim to identify specific NAMPTi and DNA damaging agent combinations which maximally exploit this H3K27M-associated NAD metabolic defects.
HGG-34. A DNA DAMAGE REPAIR SIGNATURE IN PRIMARY AND RECURRENT PEDIATRIC HIGH-GRADE GLIOMAS: PROGNOSTIC AND THERAPEUTIC VALUE
Authors: Entz-Werle Natacha , Poidevin Laetitia , Nazarov Petr , Lhermitte Benoit , Chenard Marie Pierre , Poch Olivier , Dontenwill Monique , Van Dyck Eric
Published: June 2021

Pediatric high-grade gliomas (pHGGs), including diffuse intrinsic pontine gliomas (DIPGs), despite their low incidence, are the leading cause of mortality in pediatric neuro-oncology. Frequently, pHGGs, harboring mainly histone mutations, are or become resistant to standard therapies like irradiation or chemotherapies. Recent insights showed in adult HGG the predominant role of DNA damage repair (DDR) as a way of prognostic classification. Given the recent evidence that transcription conflicts like in histone-mutated gliomas can induce replication stress and be linked to DDR abnormalities, this study is aiming to establish a DDR signature able to classify specifically pHGGs and to cluster among them poor responders to radiation. Transcriptomic analyses were performed to discriminate seven pHGGs comparatively to a cohort of 10 pilocytic astrocytomas with specific DDR deregulations. The specific transcriptomic signature obtained from this differential gene expression analysis was compared to the aHGG signature already established. To strengthen, refine and finalize the DDR signature able to classify and cluster the pHGGs, we explored both signatures and their common genes in already published transcriptomic analyses of DIPGs and sus-tentorial pHGGs. To check DDR protein expressions correlated to loss of trimethylation as well as histone and TP53 mutations, an immunohistochemical assessment of several DDR markers was performed on a collection of 21 pHGG diagnostic samples and 9 paired relapses. To validate the DDR functional inhibition, we used 3 patient-derived cell lines bearing H3.3K27M mutations. A finalized signature of 28 genes involved in DNA repair and cell cycle machineries was used to cluster in two groups the pHGG cohorts. The differential protein expression of PARP1, XRCC1, p53 and stem cell markers was linked significantly to the more resistant pHGGs and the rapid progressions after radiotherapy. Those DDR makers might be used as theranostic and therapeutic targets, which were screened in PDCLs with promising results.
HGG-37. UPFRONT TARGETED THERAPY FOR THE TREATMENT OF BRAFV600E-MUTANT PEDIATRIC HIGH-GRADE GLIOMA – A MULTI-INSTITUTIONAL EXPERIENCE
Authors: Rosenberg Tom , Yeo Kee Kiat , Joshirao Mrinal , Michaiel George , Tran Hung , Dahiya Sonika , Kachurak Kara , Friedman Gregory , Huang Michael , Wright Karen , Aguilera Dolly , MacDonald Tobey , Chi Susan , Karajannis Matthias
Published: June 2021

Introduction

Sustained responses to molecular targeted therapy with BRAF with or without MEK inhibitors have been reported in patients with recurrent BRAFV600E-mutant pediatric high-grade gliomas (pHGG). The role of upfront targeted therapy in this population, however, has not yet been established.

Methods

We performed a retrospective, multi-institutional record review of patients with BRAFV600E-mutant pHGGs, treated with off-label BRAF and/or MEK inhibitors as part of their initial adjuvant therapy.

Results

Seventeen patients were identified (median age at diagnosis, 8.8 years, range 1.8–20.2). Histologic diagnoses included HGG/glioblastoma (n=10), anaplastic ganglioglioma (n=3), high-grade neuroepithelial tumor (n=2), diffuse midline glioma (n=1) and anaplastic astroblastoma (n=1). Ten patients underwent biopsy (n=8) or subtotal resection (n=2), while near-total or complete resection was accomplished in seven. Concomitant genetic alterations including CDKN2A/B loss, H3K27M and TERT promotor mutations were found in eight tumors. Thirteen patients received focal radiation therapy (RT) and one received craniospinal irradiation prior to targeted therapy. Adjuvant targeted therapy was initiated shortly after diagnosis or completion of RT. Five patients received BRAF-inhibitor monotherapy (dabrafenib or vemurafenib). Twelve patients received combination therapy with the addition of a MEK inhibitor (trametinib). For patients with measurable disease, best responses per COG criteria were CR (n=3), PR (n=7), SD (n=3) and PD (n=1). With median follow-up of 29 months (range 8–78), two-year PFS and OS for the cohort were 74.7% and 81.1%, respectively. Ten (59%) patients remain free of disease recurrence or progression. Grade 3 or higher toxicities were reported in four patients (neutropenia, skin toxicity/photosensitivity, fatigue and weight loss), leading to therapy discontinuation in two.

Conclusions

Upfront targeted therapy for patients with BRAFV600E mutant pHGG appears tolerable and effective, with a durable disease control rate that is superior to historical data. This promising paradigm is currently being evaluated prospectively in the COG ACNS1723 clinical trial.
HGG-38. DE NOVO PYRIMIDINE SYNTHESIS INHIBITION INDUCES REPLICATION CATASTROPHE MEDIATED CELL DEATH IN DIFFUSE MIDLINE GLIOMA
Authors: Pal Sharmistha , Kaplan Jakub , Stopka Sylwia , Regan Michael , Kann Benjamin , Agar Nathalie , Stiles Charles , Cooney Tabitha , Mueller Sabine , Chowdhury Dipanjan , Haas-Kogan Daphne
Published: June 2021

Diffuse midline gliomas (DMG) are aggressive and lethal pediatric brain tumors that cannot be cured by conventional therapeutic modalities. Using a genome wide CRISPR screen we identified the de novo pyrimidine biosynthesis pathway as a metaboilic vulnerability in DMGs. BAY2402234 is a small molecule inhibitor of DHODH -a rate liminting enzyme in the de novo pyrimidine biosynthesis pathway. BAY2402234 induces cell death in DMG cells at low nanomolar concentrations while sparing adult glioblastoma cells and normal astrocytes. Further investigations revealed drammatic reduction in cellular UMP pools, the precursor for all pyrimidine nucleotides, after DHODH inhibition, specifically in DMG cells. Cytotoxicity of DHODH inhibition in DMG cells is rescued by exogenous uridine, supporting UMP depletion as the mechanism underlying DMG cell death and also showing that cell death is an “on target” response to BAY2402234. Cell death induced by BAY2402234 is a consequence of replication fork stalling as evident by accumulation of chromatin-bound RPA foci and g-H2AX. Stalled replication forks eventually collapse, resulting in replication catastrophy and apoptosis. Cytotoxic effects of DHODH inhibition are further exacerbated by inhibition of the intra-S checkpoint protein, ATR. Combined treatment of DMG cells with DHODH and ATR inhibitors resulted in enhanced accumulation of chromatin-bound RPA, g-H2AX, replication fork collapse and apoptosis. Importantly, in vivo studies verify that both BAY2402234 (DHODHi), and BAY1895344 (ATRi), cross the blood-brain barrier, accumulate in the brain at therapeutically relevant concentrations, and induce DNA damage in intracranial DMG xenografts in mice. Taken together, our studies have identified DHODH inhibition as a DMG-specific vulnerability resulting in cell death; the mechanism of DHODHi-induced cell death led us to identify combined inhibition of DHODH and ATR as a synergistic therapy against DMG tumors.
IMMU-14. COMPUTATIONAL DECONVOLUTION OF TUMOR-INFILTRATING IMMUNE COMPONENTS IN PEDIATRIC NERVOUS SYSTEM TUMORS
Authors: Beck Pengbo , Nabbi Arash , Sill Martin , Sudhaman Sumedha , Kool Marcel , Resnick Adam C , Jones David T W , Pfister Stefan M , Pugh Trevor J , Jäger Natalie
Published: June 2021

Introduction

In the last decade, checkpoint inhibitor-based immunotherapy has been a groundbreaking development in the treatment of cancer. However, only a subset of patients treated with immune checkpoint inhibitors show long-lasting clinical benefit. Studies showed the tumor immune microenvironment (TME) as a particularly important factor influencing treatment response, critical for the design of other or combinatorial immunotherapy treatment strategies. Extensive research has been performed in the adult cancer field to unravel its immunogenomic aspects. However, in pediatric cancer this insight into tumor-infiltrating immune components is still lacking. This study aims to provide insight into the landscape of the immune microenvironment in pediatric primary nervous system tumors.

Methods

Bulk RNA-seq data of 936 pediatric primary solid tumors acquired from multiple international initiatives including Therapeutically Applicable Research To Generate Effective Treatments (TARGET), the International Cancer Genome Consortium (ICGC) and the Children’s Brain Tumor Tissue Consortium (CBTTC) were included in this study. We applied computational tumor immune microenvironment deconvolution, repurposed RNA-seq data to recover infiltrating T- and B-cell clonotypes and studied checkpoint gene expression across pediatric neural tumors.

Results

Among pediatric neural tumors, embryonal tumors with multilayered rosettes (ETMR) and medulloblastomas (MB) were least immune infiltrated. Neuroblastomas (NBL) had the highest T-cell infiltration among pediatric cancers, while atypical teratoid/rhabdoid tumors (ATRT) had the highest levels of CD8 T cell infiltration among pediatric CNS tumors. While tumor mutational burden (TMB) was associated with immune cell infiltration in adult lung cancers and melanomas, we found no significant associations in pediatric cancers. The majority of NBL samples expressed LAG3, but ~10% of samples had elevated levels of TIM3 gene expression, suggesting a distinct mode of immunosuppression in this subset.