bluuebunny/crossref_metadata_2025_split huggingface dataset:
EMBR-15. PRC2 COMPLEX ENFORCES NEURONAL LINEAGE AND SUPPRESSES TUMOR GROWTH IN SHH MEDULLOBLASTOMA
Authors: Cleveland Abigail , Malawsky Daniel , Churiwal Mehal , Gershon Timothy 
Published: June 2021

Abstract
Hyperactivation of Sonic Hedgehog (SHH) signaling pathway drives tumor progression in the largest medulloblastoma subgroup. During cerebellar development, promoters of SHH target genes show inhibitory trimethylation of histone H3 at lysine 27 (H3K27me3), mediated by the Polycomb Repressive Complex 2 (PRC2). Here, we explored the regulation of cerebellar growth and medulloblastoma tumorigenesis by PRC2 complex components EED and EZH2. For developmental studies, we conditionally deleted Eed or Ezh2 in the Atoh1 lineage that gives rise to the cerebellar granule neuron progenitors (CGNP) that are cells of origin for SHH medulloblastomas. For tumor studies, we bred the conditional Eed- or Ezh2-deleted mouse lines with mice genetically engineered to develop SHH medulloblastoma. Our developmental studies showed that Eed was absolutely required for cerebellar growth. Eed-deleted CGNPs underwent aberrant, myocyte-like differentiation and spontaneous apoptosis, resulting in cerebellar hypoplasia. In contrast, Ezh2 deletion produced no developmental phenotype, despite blocking all H3K27me3 in CGNPs. Our tumor studies showed that Eed-deleted medulloblastomas similarly showed aberrant, myocyte differentiation, but unlike CGNPs, did not undergo widespread apoptosis. Eed-deleted medulloblastomas progressed more rapidly than control tumors, indicating that the inappropriate, muscle-like differentiation did not slow tumor growth. Ezh2-deleted medulloblastomas similarly progressed more rapidly than controls. Our data show that the PRC2 complex acts to enforce neuronal lineage commitment in both development and tumorigenesis and to restrain tumor growth in SHH medulloblastoma. Myocyte differentiation in Eed-deleted tumors suggests that PRC2 loss of function may contribute to the medullomyoblastomas that have been observed in patients. The differences in developmental phenotype show that EZH2 and EED functions are non-identical and can be dissociated, while similar increase in tumor progression show tumor suppressive functions for both EED and EZH2.
EMBR-16. SMOOTHENED-ACTIVATING LIPIDS DRIVE RESISTANCE TO CDK4/6 INHIBITION IN HEDGEHOG-ASSOCIATED MEDULLOBLASTOMA
Authors: Daggubati Vikas , Hochstelter Jordan , Bommireddy Anirudh , Choudhury Abrar , Krup Alexis Leigh , Choski Pervinder , Tong Pakteema , Li Amy , Xu Libin , Reiter Jeremy , Raleigh David 
Published: June 2021

Abstract

Background
Medulloblastoma is an aggressive pediatric brain tumor that is associated with misactivation of the Hedgehog (HH) pathway. Our lab has shown that CDK6, a critical activator of the cell cycle, is a direct transcriptional target of oncogenic HH signaling, and that inhibiting CDK6 blocks the growth of HH-associated medulloblastoma in mice. A clinical trial exploring the efficacy of CDK6 inhibition in medulloblastoma patients is underway, but prior attempts to target the HH pathway in medulloblastoma have been encumbered by resistance to molecular monotherapy. Thus, we sought to identify mechanisms of resistance to CDK6 inhibition in HH-associated medulloblastoma.

Methods
We performed orthogonal CRISPR and CRISPR interference screens in HH-associated medulloblastoma cells treated with pharmacologic inhibitors of CDK6 in vitro, and RNA-sequencing of HH-associated medulloblastomas with genetic deletion of CDK6 in vivo. Mechanistic and functional validation of resistance pathways was performed using CRISPR interference, immunoblotting, immunofluorescence, genetics, and pharmacology. Lipid quantification was carried out by ultra-high performance liquid chromatography-tandem mass spectrometry.

Results
Our results reveal that decreased ribosomal protein expression underlies resistance to CDK6 inhibition in HH-associated medulloblastoma, leading to endoplasmic reticular (ER) stress and activation of the unfolded protein response (UPR). We show that ER stress and the UPR increase the activity of enzymes producing Smoothened-activating sterol lipids that sustain oncogenic HH signaling in medulloblastoma despite CDK6 inhibition. These discoveries suggest that combination molecular therapy against CDK6 and HSD11ß2, an enzyme producing Smoothened-activating lipids, may be an effective treatment for HH-associated medulloblastoma. In support of this hypothesis, we demonstrate that concurrent genetic deletion or pharmacological inhibition of CDK6 and HSD11ß2 additively blocks the growth of multiple models of HH-associated medulloblastoma in mice.

Conclusions
Smoothened-activating lipid biosynthesis underlies resistance to CDK6 inhibition in HH-associated medulloblastoma, revealing a novel combination therapy to treat the most common malignant brain tumor in children.
EMBR-20. ELONGATION CONTROL OF MRNA TRANSLATION DRIVES GROUP 3 MEDULLOBLASTOMA
Authors: Delaidelli Alberto , Negri Gian Luca , Wang Que Xi , Huang Albert , Sidhu Simran , Zhang Joyce , Huang Yue Zhou , Yao Betty , Langman Sofya , Vislovukh Andrii , Hovestadt Volker , Taylor Michael , Leprivier Gabriel , Sorensen Poul 
Published: June 2021

Abstract
Medulloblastoma (MB) is the most common pediatric intracranial tumor and leading cause of childhood related cancer deaths. Group 3 affiliation and genetic amplifications of the MYC oncogene are predictors of adverse outcome in MB, underscoring a dire need for novel and more effective therapeutic approaches. The let-7 family of small non-coding RNAs (miRNAs) is known to inhibit tumor progression and regulate metabolism by targeting and degrading several cellular mRNAs, including MYC. Indeed, let-7 miRNAs are frequently repressed in several cancer types, including in MYC-driven MB. We previously reported that the mRNA translation elongation regulator eukaryotic Elongation Factor-2 Kinase (eEF2K) is a pivotal mediator of cancer cell adaptation to nutrient deprivation. In the current work, we identified a potential binding site for let-7 miRNAs on the eEF2K 3’ untranslated region (UTR). In addition, eEF2K mRNA and let-7 miRNA expressions negatively correlate in MB, suggesting a potential regulation of the former by the latter. Let-7 miRNAs transfection decreases eEF2K mRNA and protein levels (by ~40–50%). Down-regulation of luciferase activity by let-7 miRNAs is impaired upon mutation of the let-7 binding site on the eEF2K 3’UTR. Inhibition of eEF2K significantly reduces survival of MYC-amplified MB cell lines under nutrient deprivation, altering their mRNA translation rates. Knockout of eEF2K increases survival of MYC-amplified MB xenografts when mice are kept under calorie restricted diets. We conclude that let-7 miRNAs degrade the eEF2K mRNA by binding to its 3’UTR, indicating that let-7 repression in MYC-driven MB is partially responsible for increased eEF2K levels. Moreover, the let-7-eEF2K axis constitutes a critical mechanism for MYC-driven MB adaptation to acute metabolic stress, representing a promising therapeutic target. Future therapeutic studies will aim to combine eEF2K inhibition with caloric restriction mimetic drugs, as eEF2K activity appears critical under metabolic stress conditions.
HGG-13. BRAIN DISTRIBUTION AND CLEARANCE OF ALISERTIB IS LIMITED BY PGP AND BCRP EFFLUX PUMPS AND DEPENDENT UPON DELIVERY METHOD
Authors: Power Erica , Oh Juhee , Zhang Liang , Elmquist William , Daniels David 
Published: June 2021

Abstract
Diffuse midline gliomas (DMGs) harboring the H3K27M mutation are highly aggressive, uniformly fatal brain tumors that primarily occur in children. The blood-brain barrier (BBB), including drug efflux pumps, prevent numerous drugs from reaching CNS tumors at cytotoxic concentrations. Alisertib is an aurora kinase inhibitor that was previously identified in a drug screen as a compound of interest. However, its ability to penetrate the BBB is not well established. The goals of this study were two-fold: 1) determine the CNS distribution and clearance rates of alisertib following systemic delivery and if the BBB efflux pumps, Pgp and BCRP, alter distribution and clearance. 2) Compare alisertib distribution and clearance following convection-enhanced delivery to systemic results. WT and Pgp/BCRP knockout mice and Sprague-dawley rats underwent tail vein injection (mice and rats) or convection-enhanced delivery to the brainstem (rats only) of alisertib and sacrificed at 0, 2, 4, 8, 12, 16 and 24hours. The plasma and brain were collected and analyzed for alisertib concentration by HPLC-MS/MS. We found that in both mice and rats, alisertib concentration in the plasma and brain decreased biexponentially. Overall, Alisertib was found to be 3.14% brain penetrant. In Pgp/BCRP knockout mice, alisertib concentration in the plasma and brain decreased biexponentially, but was detected at higher concentration at all time points in the brain compared to WT mice. This resulted in a higher brain penetrance (17.26%). Differences based on anatomical brain region were significant in those rats which received convection-enhanced delivery. Alisertib was found in higher concentration in the pons and cerebellum compared to systemic delivery, but lower concentrations in the cortex and plasma. These results suggest that drug clearance may be a general mechanism limiting efficacy of drugs of interest and should be carefully considered during preclinical evaluation.
HGG-26. SINGLE-CELL RNA-SEQ OF PEDIATRIC HIGH-GRADE GLIOMAS IDENTIFIES COMMON ONCOGENIC PROCESSES AMONG DISTINCT TUMOR HISTOLOGIES
Authors: DeSisto John , Donson Andrew , Fu Rui , Sanford Bridget , Riemondy Kent , Green Adam 
Published: June 2021

Abstract

Background
Pediatric high-grade glioma (PHGG) is a deadly childhood brain tumor that responds poorly to treatment. PHGG comprises two major subtypes: cortical tumors with wild-type H3K27 and diffuse midline gliomas (DMG) that occur in the midline and have characteristic H3K27M mutations. Cortical PHGG is heterogeneous with multiple molecular subtypes. In order to identify underlying commonalities in cortical PHGG that might lead to better treatment modalities, we performed molecular profiling, including single-cell RNA-Seq (scRNA-Seq), on PHGG samples from Children’s Hospital Colorado.

Methods
Nineteen cortical PHGG tumor samples, one DMG and one normal margin sample obtained at biopsy were disaggregated to isolate viable cells. Fifteen were glioblastomas (GBM), including five with epithelioid and/or giant cell features and five radiation-induced glioblastomas (RIG). There were also four non-GBM PHGG. We performed scRNA-Seq using 10X Genomics v.3 library preparation to enable capture of infiltrating immune cells. We also performed bulk RNA-Seq and DNA methylation profiling.

Results
After eliminating patient-specific and cell-cycle effects, RIG, epithelioid GBM, and other GBM each formed identifiable subgroups in bulk RNA-Seq and scRNA-Seq datasets. In the scRNA-Seq data, clusters with cells from multiple tumor samples included a PDGFRA-positive population expressing oligodendrocyte progenitor markers, astrocytic, mesenchymal and stemlike populations, macrophage/monocyte immune cells, and a smaller T-cell population. Analyses of DNA methylation data showed PDGFRA and CDK4 amplification and CDKN2A deletion are common alterations among PHGG. Inferred copy number variation analysis of the single-cell data confirmed that individual tumors include populations that both include and lack the molecular alterations identified in the methylation data. RNA velocity studies to define tumor cells of origin and further analyses of the immune cell populations are underway.

Conclusions
Single-cell analysis of PHGG confirms a large degree of tumor heterogeneity but also shows that PHGG have stemlike, mesenchymal and immune cell populations with common characteristics.
HGG-36. ONC201 TARGETING IN DIPG
Authors: Abuarqoub Alqassem , McAnulty Tatiana , Amiel Eyal , Stafford James 
Published: June 2021

Abstract
Diffuse intrinsic pontine glioma (DIPG) is a group of predominantly pediatric brain tumors with an average age of diagnosis of 6–7 years old, and a poor prognosis (median survival of ~1 year). Given the location of DIPG in the brainstem, surgical approaches are limited. Furthermore, the tumors have limited responsivity to traditional chemotherapy or radiotherapy, ergo new therapeutic options are needed. Recently, the drug ONC201 has emerged as a potential therapeutic option with outcomes sometimes surpassing progression-free and expected survival outcomes. However, the selectivity of its effect and mechanism in DIPG is still unclear. Here, we pursue a better understanding of ONC201 and its mechanism of action directly in DIPG patient-derived cell lines. First, we demonstrate that a range of DIPG cell lines are highly sensitive to ONC201 and compare this sensitivity to other patient-derived brain tumor and normal controls. Next, we directly show that the mitochondrial protease, ClpP is the primary target of ONC201 in DIPG. Given recent literature implicating the activation of ClpP by ONC201 and dysregulation of the metabolome in other tumors, we are currently examining these downstream effects in DIPG. Ultimately we hope to elucidate whether ClpP targeting can be used to better diagnose and improve therapeutic options in DIPG
HGG-43. INTERROGATING THE ROLE OF PEA3 ONCOGENIC TRANSCRIPTION FACTORS IN PEDIATRIC HIGH-GRADE K27M GLIOMAS
Authors: Park Hannah , Kobritz Naomi , Mehdikhani Shaunt , Breunig; Joshua 
Published: June 2021

Abstract
Pediatric high-grade gliomas (HGGs) are an aggressive form of pediatric brain tumors which pose a grim five-year survival with little advancement in therapeutic efficacy, often requiring a multimodal therapeutic combination of chemotherapy, resection, and radiation. We have previously shown that proper function of ETS transcription factors is necessary for gliomagenesis in Ras/MAPK-driven pediatric gliomas. It is our hypothesis that ETS transcription factors are necessary for tumor initiation in HGGs by promoting the necessary glial cell fates in glioma. Further, we hypothesize that functional inhibition of ETS proteins following tumor formation will improve survival and outcome in HGG. Functional inhibition of ETS proteins using a competitive dominant-negative mutant was shown to completely rescue neural stem cell depletion, tumor formation and tumor-free survival in two rodent models of HGGs. Mechanistically, we show evidence that Pea3 factors may induce glial-cell fate by promoting Olig2 expression and activation of glial transcriptional programs. Indeed, transcriptomic analysis of ETS-perturbed HGG tumors revealed that Sox9 and Olig2 transcription factor networks were dependent on proper ETS function. Further, we show evidence that Etv5 can directly interact with promoter regions of glial fate master regulators in human primary glioma cell lines. To empirically determine the effect of Pea3 proteins on tumorigenesis, we have created a novel methodology for inducible gain- and loss-of-function genetic interrogation of these factors in vivo. Our survival results and combined single-cell RNA-sequencing of individual groups show that inhibition of the Pea3 family leads to a marked increase in survival in K27M glioma by regulating key features of glioblasts. All in all, our group provides evidence that the ETS family of transcription factors is necessary for glial specification of tumor cells and induce pro-glial transcriptional programs by activating OPC- and astrocyte-specific genes in K27M-driven tumors.
HGG-44. REVEALING VULNERABILITIES IN DIPG THROUGH ONC201
Authors: Stafford James , Abuarqoub Alqassem , Mcanulty Tatiana , Possemato Richard , Amiel Eyal , Snuderl Matija 
Published: June 2021

Abstract
Emerging evidence from clinical and preclinical studies suggests that the imipridone ONC201 is well tolerated and may have some clinical impact in discrete diffuse intrinsic pontine glioma patients (DIPG). A primary goal of our work is to determine if DIPG are uniquely sensitive to ONC201 and if so, whether ONC201 itself can be used as a tool to illuminate novel vulnerabilities in DIPG. To accomplish this, we are utilizing a combination of patient-derived cell lines as well as mouse xenografts that dovetail with a variety of molecular, epigenetic and metabolomic tools. A central finding from our work is that ONC201 primarily activates the mitochondrial protease, ClpP in DIPG patient-derived cell lines, an effect consistent with recently described ONC201 mechanism of action in other tumors. We further demonstrate that activation of ClpP by ONC201 leads to a host of downstream effects in DIPG model systems including distinctive effects on the metabolome leading to direct alterations in the unique epigenetic signature of DIPG. By directly manipulating these metabolic and epigenetic factors we provide prospective mechanistic insight into how ONC201 as well as ClpP activity impacts DIPG growth and tumorigenicity. These preclinical research findings shed light on potential therapeutic vulnerabilities in DIPG as well as ways that these strategies may be combined to enhance their potential.
IMMU-02. CH14.18 IN THE TREATMENT OF HIGH-RISK NEUROBLASTOMA: A META-ANALYSIS
Authors: Abdel-Khaleq Sameerah , Alim Lina , Johnston Atholl , Adam Khloud 
Published: June 2021

Abstract
High-risk neuroblastoma (HRNB) is a rare malignancy that mainly affects young children. Long-term survival remains low despite aggressive, multimodal treatment regimens. The aim is to assess the effect of Ch14.18, a novel anti-GD2 antibody, on survival in HRNB. In this meta-analysis, Pubmed/MEDLINE, EMBASE, Cochrane CENTRAL and Clinicaltrials.gov bibliographic databases were searched from inception to 1st July 2018. Prospective or retrospective interventional clinical trials with at least two arms or observational cohort or case-control studies were eligible. Participants had to have HRNB. Ch14.18 was the intervention of choice. Any control, comparator treatments were accepted. Studies were appraised for inclusion by two independent reviewers. Data was extracted from published reports. Primary outcomes assessed were Event-Free Survival (EFS) and Overall Survival (OS) and presented as Weighted Mean EFS (%) ± Standard Error (SE) and Weighted Mean OS (%) ± Standard Error (SE), respectively. Combined effect size was elicited for EFS±SE and OS±SE. The search yielded 367 results of which 7 studies conducted on 1727 patients were eligible for inclusion. The weighted mean EFS±SE for Ch14.18 regimens (n=779) and control regimens (n=787) were 55.6±2.0% and 41.2±1.7%, respectively. The weighted mean OS±SE for Ch14.18 regimens (n=430) and control regimens (n=348) were 63.4±2.3% and 53.6±2.7%, respectively. Results of the meta analysis yielded statistical power &gt;94%. The combined effect size of Ch14.18 regimens for EFS±SE was 0.2907±0.05 [95% CI: 0.19–0.39, p&lt;0.001] and the combined effect size for OS±SE was 0.26±0.07 [95% CI: 0.11- 0.4, p&lt;0.001]. Significant superior survival outcomes were achieved with the use of Ch14.18 in the treatment of HRNB. These findings support using Ch14.18 as an adjunct in maintenance therapy in high-risk neuroblastoma. This meta analysis is the first of its kind. Survival outcomes are to be interpreted with caution due to confounding bias.
IMMU-04. FIRST-IN-CHILDREN PHASE 1B STUDY USING THE IDO PATHWAY INHIBITOR INDOXIMOD IN COMBINATION WITH RADIATION AND CHEMOTHERAPY FOR CHILDREN WITH NEWLY DIAGNOSED DIPG (NCT02502708, NLG2105)
Authors: S. Johnson Theodore , Pacholczyk Rafal , Aguilera Dolly , Al-Basheer Ahmad , Bajaj Manish , Berrong Zuzana , Castellino Robert C , Eaton Bree R , Esiashvili Natia , Foreman Nicholas , Heger Ian M , Kennedy Eugene P , Martin William , Ring Eric , Sadek Ramses F , Smith Amy , Smith Chris , Vaizer Rachel , MacDonald Tobey J , Munn David H 
Published: June 2021

Abstract

Background
Diffuse intrinsic pontine glioma (DIPG) is a uniformly fatal brain tumor with no available cure. Indoximod blocks the IDO (indoleamine 2,3-dioxygenase) pathway, thereby reversing IDO-mediated immune suppression in the tumor microenvironment.

Methods
Patients aged 3 to 21 years with treatment-naive DIPG were eligible for this phase 1b dose-confirmation study of indoximod. The treatment regimen comprised continuous oral indoximod (38.4 mg/kg/day divided twice daily) with conformal photon radiation (54 Gy in 30 fractions), followed by cycles of indoximod with temozolomide (200 mg/m2/day, days 1–5 in 28-day cycles).

Results
Thirteen patients (median age 9 years, range 5 to 20 years) with DIPG were treated. Median OS was 14.5 months (follow-up ranged 4.8 to 29.3 months), 12-month OS was 61.5% (8/13), and 18-month OS was 30.8% (4/13), with 1 patient remaining in follow-up at the data cutoff. This compared favorably to expected median OS of approximately 10.8 months, 12-month OS of 45.3%, and 18-month OS of 16.2% taken from published historical data from the Pediatric Brain Tumor Consortium. Two patients showed near-complete responses lasting until relapsing after 7.6 months and 13.3 months of study therapy, respectively. Many patients had increased circulating non-classical monocytes (nc-Monos, CD16+, CD14neg, CD33+, HLA-DR+) within the first 3 treatment cycles, and elevation of this early pharmacodynamic marker was predictive of subsequent OS. Patients with nc-Monos &gt;10% (n=7) had median OS of 19 months, whereas patients with nc-Monos below 10% (n=5) had median OS of 7 months (p=0.0047). No patients stopped therapy for toxicity. The most common indoximod-attributed adverse events were thrombocytopenia, neutropenia, nausea, vomiting, dizziness, and fatigue.

Conclusions
Adding indoximod immunotherapy to conventional radiation and chemotherapy for front-line treatment of pediatric patients with DIPG was well-tolerated. Improved outcomes were observed in patients having evidence of pharmacodynamic response. A follow-on phase 2 study is in progress (NCT04049669).