bluuebunny/crossref_metadata_2025 huggingface dataset:
IMG-13. Role of diffusion weighted imaging of spine in pediatric brain tumors showing diffusion restriction and CSF metastases
Authors: Sahu Arpita , Dasgupta Archya , Lad Shradha , Chatterji Abhishek , Jain Ayushi , Sridhar Epari , Gupta Tejpal
Published: June 2022

INTRODUCTION: Early detection of leptomeningeal metastases (LM) with paediatric brain tumors cases can change the prognosis as well as course of treatment. Conventional MR imaging and CSF (cerebrospinal fluid) analysis plays a vital role in detection of metastases, however, due to certain limitations these can be missed. In our study, diffusion weighed imaging (DWI) of spine was able to bridge this gap and increased the detection rate in MRI equivocal cases in which CSF study was negative. AIMS: To evaluate the incremental value of DWI over the conventional sequences in detection of LM. MATERIALS & METHODS: Paediatric patients with primary brain tumors known to show restriction and propensity for CSF metastasis underwent MRI on 1.5T Philip’s machine. CSF analysis and radiological follow up were used to confirm the diagnosis. RESULTS: Of the 26 patients proven to have LM, linear leptomeningeal metastases (LLP) were seen in 7 patients and nodular leptomeningeal metastases (NLM) were seen in 6 patients and both were seen in 13 patients. Of the 20 patients with LLM, 18 were detected on contrast; however, these were not detected on T2W and DWI except one patient with thick LLP. In 19 patients with NLM, a total of 84 lesions were detected. All were appreciated on contrast with additional 6 lesions which were false positive (FP). Total 96 lesions were detected on T2W, of which 80 were true positive and 16 were FP. About 80 lesions were detected on DWI. Thus, on contrast sequence FP were 6 while on T2W 16 were FP. DISCUSSION: DWI showed a lower FP rate than conventional sequences. CONCLUSION: Contrast sequence remains most reliable sequence for the detection of LM. However, DWI is useful in equivocal cases. The role of DWI in Group 3 and 4 Medulloblastoma with non-enhancing metastases needs to be further explored.
IMG-15. Radiomic Profiling of Pediatric Low-Grade Glioma Improves Risk Stratification Beyond Clinical Measures
Authors: Kazerooni Anahita Fathi , Arif Sherjeel , Haldar Debanjan , Madhogarhia Rachel , Familiar Ariana , Bagheri Sina , Anderson Hannah , Ware Jeffrey B , Vossough Arastoo , Storm Phillip B , Resnick Adam C , Davatzikos Christos , Nabavizadeh Ali
Published: June 2022

PURPOSE: Treatment response is heterogeneous among patients with pediatric low-grade glioma (pLGG), the most frequent childhood brain tumor. Upfront prediction of progression-free survival (PFS) may facilitate more personalized treatment planning and improve outcomes for the pLGG patients. In this work, we explored the additive value of radiomics to clinical measures for prediction of PFS in pLGGs. We further sought associations between the derived risk groups and underlying alterations in key genomic and transcriptomic variables. METHODS: Quantitative radiomic features were extracted from pre-operative multi-parametric MRI scans (T1, T1-post, T2, T2-FLAIR) of 96 patients with newly diagnosed pLGG (median age, 8.59, range, 0.35-18.87 years; median PFS, 25.23, range, 3.03-124.83 months). Multivariate Cox proportional hazard’s (Cox-PH) regression models were fitted using 5-fold cross-validation on a training cohort of 68 subjects and tested on 28 patients. Three models were generated using (1) only clinical variables (age, sex, and extent of tumor resection), (2) radiomic features, and (3) clinical and radiomic variables. The dimensionality of radiomic features in Cox-PH models was reduced by applying Elastic Net regularization penalty to identify a subset of variables that are most predictive of PFS. The patients were then stratified into three groups of high, medium, and low-risk based on model predictions. RESULTS: Cox-PH modeling resulted in a concordance index (c-index) of 0.55 for clinical data, 0.65 for radiomics, and 0.73 for a combination of clinical and radiomic variables, highlighting the additive value of radiomics to the readily available clinical information in prediction of PFS. Radiogenomic assessments revealed significant differences in expression of BRAF, NF1, TSC1, ALK (p<0.01), and RB1 (p<0.05) genes in the high-risk group, compared to the medium and low-risk groups. CONCLUSION: Our results demonstrate the value of integrating radiomics with clinical measures to improve risk assessment of patients with pLGG through improved pretreatment prediction of PFS.
IMG-17. Advanced MRI On The Cellular and Vascular Phenotype of Mouse Ependymoma Models and Chemo-Radiation Treatment Response
Authors: Serkova Natalie , Manalo Jane , Steiner Jenna , Griesinger Andrea , Pierce Angela , Foreman Nicholas
Published: June 2022

Ependymoma (EPN) is an aggressive pediatric brain tumor, for which the benefits of chemotherapy in pediatric patients have not been defined. EPN treated with surgery and radiation recur in 23-66% of patients. Our group has previously established aggressive behaviors of EPN, including high tumor cellularity, cytological anaplasia, high mitotic index, tumor necrosis, and the presence of inflammatory cells such as M2-type myeloid cells. Here we report on an advanced 9.4 Tesla MRI protocol for characterizing the cellular and vascular phenotype and treatment response to chemo-radiation therapy (CRT) in an orthotopic mouse model of patient derived xenografts (PDX) of pediatric EPN . Female severely immune deficient (SCID) mice were used for intracranial inoculation of disaggregated tumors from pediatric EPN patients (n=22). High-resolution T2w-MRI was able to detect cerebellar microlesions as small as 0.2 mm diameter; the median tumor volumes at the baseline were 21±12 mm3. Using diffusion-weighted based cell-size imaging, iron-oxide based vessel-size imaging and quantitative T2-maps, the EPN-specific phenotype was characterized by an increased cell size (S=14 microns), increased vessel density index (Q=0.54), and low ADC values (0.63x10-3). Once the intracranial tumors reached at least 5 mm3, animals were treated with CRT (10 Gy radiation plus 30 mg/kg 5-fluorouracil, n=6). CRT resulted in a tumor shrinkage, tumor necrosis with decreased cell sizes and increased ADC values, and a dramatic vascular-inflammatory response (decreased Q and DT2 values with the injection of iron oxide nanoparticles as macrophage-specific contrast). In summary, orthotopically implanted PDX EPN in mice closely mimic histological features, anatomical location and radiological features of the primary tumors. A significant decrease in vessel size density and an increase in inflammatory cells were seen as soon as 2 days after CRT. The late response (2 weeks post CRT) is characterized by decreased cellularity, cell size, and tumor volumes.
IMMU-11. Evaluation of CAR-T cells targeting CD276 in medulloblastoma
Authors: da Silva Patricia Benites Goncalves , Sieber Laura , Mack Norman , Atar Daniel , Kutscher Lena M , Schlegel Patrick , Ebinger Martin , Kawauchi Daisuke , Seitz Christian , Pfister Stefan M
Published: June 2022

Brain tumors are the most frequent category of solid tumors in children and have the highest mortality rate among all pediatric cancers. Although diagnosis and treatment have improved prognosis over the past decades for some childhood brain tumors, others remain lethal and current treatments are highly toxic to the developing brain, resulting in severe sequelae and considerably affecting the patient’s quality of life. Thus, new therapeutic options with reduced secondary effects are urgently needed. From this perspective, immunotherapies have gained a lot of attention due to their effectiveness in targeting tumor cells specifically. Chimeric-antigen receptor (CAR) T-cells recognize the target antigen on the surface of. CD276 is an immune checkpoint molecule that is expressed in a variety of solid tumor entities, including pediatric brain tumors. We analyzed the CD276 expression in our Patient-Derived-Xenograft (PDX) biobank of brain tumors and found that CD276 is ubiquitously expressed (ATRT, MB, EPN, GBM, ETMR, etc). Flow cytometry of MB PDX (n=4) confirmed CD276 expression of 97-99% of tumor cells, indicating that CD276 might be a good antigen target for CAR-T cell therapy of MBG3 and MBSHH. We found that second generation CAR-T cells targeting CD276 antigen significantly decreased tumor burden of the most aggressive MB subgroups (G3 and SHH-TP53mut PDX models) in NSG mice. We further treated NSG mice carrying a high tumor burden of the aggressive SHH-TP53mut PDX BT084 with second (CD28) and third generation (CD28-41BB) CD276-CAR-T cells. While both 2nd and 3rd generation improved the survival rates compared with CD19-CAR-T control cells, we found no difference in survival between the CD276 CAR-T generations, with no severe secondary effect during treatment. In conclusion, CD276 is a good antigen target for medulloblastoma, and warrants further evaluation for the treatment of medulloblastoma patients at relapse or as a maintenance therapy after standard treatment.
IMMU-14. SynNotch chimeric antigen receptor (CAR) T-cells as a potential treatment for diffuse intrinsic pontine glioma (DIPG)/diffuse midline glioma (DMG)
Authors: Ferrerosa Lauren , Simic Milos , Watchmaker Payal , Diebold David , Pineo-Cavanaugh Psalm , Deucker Jason , Lim Wendall , Okada Hideho
Published: June 2022

BACKGROUND: The development of effective chimeric antigen receptor (CAR) T-cell therapies for malignant pediatric brain tumors remains a challenge due to multiple barriers, including antigenic heterogeneity, on-target off-tumor toxicities, and T cell exhaustion. We have adopted a novel synthetic Notch “synNotch” receptor system and developed innovative T-cell circuits that recognize tumor cells based on the “prime-and-kill” strategy.

METHODS: We created a novel synNotch-CAR circuit in which the brain/glioma-specific antigen Brevican (BCAN) primes the T cells to induce expression of a CAR that recognizes interleukin-13 receptor α2 (IL-13Rα2) and ephrin type A receptor (EphA2), thereby eradicating glioma cells expressing either antigen. Immunocompromised mice bearing the SF8628 DIPG cell line in the frontal lobe or brain stem received a single intravenous (IV) infusion of synNotch CAR T-cells (2.5 x 106 each of CD4+ and CD8+ T cells) on day 6 following the tumor inoculation. Mice were monitored for toxicity and tumor growth.

RESULTS: Following this synNotch CAR T-cell dose, although tumors in the brainstem did not regress, 3 of the 5 mice with frontal lobe tumors demonstrated complete and sustained remission. Our histological analyses revealed primed CAR T-cells both within and surrounding the tumor in both settings. By flow cytometry, we confirmed the CAR T-cells in the CNS were primed and mostly did not express an exhaustive phenotype. In the spleen, we also found the CAR T-cells in a more naïve and central memory state.

CONCLUSIONS: Our work so far has demonstrated that synNotch-CAR T-cells are able to traffic to the tumor microenvironment even in the brainstem, are primed to express the CAR, and most do not express an exhaustive phenotype. Future work will include CAR T-cell dose optimization, continued assessments of the tumor microenvironment, and investigating for antigen escape.
IMMU-15. The immunologic context of pediatric central nervous system malignancies and identification of pan-histology immunomodulatory targets
Authors: Galvin Robert , Nikrad Julia , Jubenville Tyler , Maeser Danielle , Gruener Robert , Jena Sampreeti , Moertel Christopher , Largaspaeda David , Huang R Stephanie
Published: June 2022

Central nervous system tumors account for the most childhood cancer mortality. Immunotherapies have made major contributions to treat adult cancers, but application of immunotherapy for childhood brain tumors has been limited, in part due to the unique CNS microenvironment and mechanisms of immune escape in this context. To investigate the immunologic context, we query the transcriptomic profile of ~700 primary brain tumors released by the Children’s Brain Tumor Network. An immune subtype classification from The Cancer Genome Atlas project reveals that 81% of high-grade tumors across molecular subtypes are characterized by an immunosuppressive phenotype (C4) while an inflammatory phenotype (C3) is more common in low-grade lesions (p<0.001). Adjusting for histologic grade and extent of resection, C4 associates with worse overall (OS) and progression-free survival (PFS) in this cohort (HR 3.1, p=0.008 and 1.6, p=0.03 respectively). Deconvolution of the transcriptome reveals that relative to C3, C4 tumors have decreased T-cell signature, OR 0.4 (0.2–0.8), and increased macrophage and tumor-proliferation signature (OR 2.0, 1.3–3.3, and 3.1, 2.3–4.2, respectively). In contrast to C3 tumors, T-cell signature in C4 tumors adversely impacts survival and correlates with multiple immunosuppressive genes and cytokines. Among them, the immune checkpoint CD276 has the highest associated impact on survival in C4 tumors (HR of log increase is 1.9, p<0.001). Additionally, high-grade lesions have suppressed expression of antigen-presenting genes. EZH2 is implicated in downregulating antigen presentation and is found to be significantly upregulated in all high-grade lesions in this cohort. Treatment with the EZH1/2 inhibitor valemetostat resulted in upregulation of antigen-presenting genes and tissue differentiation pathways across three murine syngeneic models, one modeling diffuse midline glioma and two embryonal models. Future in-vivo studies with genetic and chemical modification of immunomodulatory genes of interest aim to identify immunotherapeutic targets with potential for broad applicability in pediatric neuro-oncology.
IMMU-23. Novel gene-edited CAR-T cell therapy against Diffuse Intrinsic Pontine Glioma
Authors: Balakrishnan Ilango , Leach Lillie , Lakshmanachetty Senthilnath , Pierce Angela , Madhavan Krishna , Chatwin Hannah , Fosmire Susan , Meadows Christina , Green Adam , Fry Terry , Vibhakar Rajeev , Kohler Eric M , Venkataraman Sujatha
Published: June 2022

BACKGROUND: We identified high expression of CD99 in DIPG tumors and developed a CAR using our newly identified single chain variable fragment (scFv) targeting CD99 incorporating a 4-1BB co-stimulatory domain. This CD99 CAR demonstrated the ability to dramatically shrink the established orthotopic DIPG tumor, however tumor recurrence remains an obstacle to cure, due to a loss of the CAR-T cells as they also express the target antigen, CD99 (fratricide). To overcome this obstacle, we modified these CAR-T by editing out CD99. METHODS: CD99 was knocked-out from the human T cells using CRISPR-cas9 gene-editing and subsequently transduced with our CD99 CAR-encoding virus, and isolated the pure population of CD99KO T-cells. These novel, gene-edited T-cells expressing CD99 CAR (“CD99KO CARs”) and the un-edited ones (“CD99 CAR”) were tested for tumor-lysis function when co-cultured with DIPG cells. DIPG tumor-bearing mice infused with a one-time dose of CD99KO CAR-T cells or CD99 CAR- or CD19 control CAR-T cells and were monitored for changes in the tumor burden. At the endpoint spleen and bone marrow were isolated to test for CAR+ cell persistence. RESULTS: The CD99KO CAR-T cells demonstrated effective tumor-lysis when co-cultured with DIPG cells. CD99KO CAR-T cells targeting CD99 showed complete clearance of DIPG tumor in orthotopic DIPG mouse models, and no tumor recurrence was seen well-beyond the time frame of expected tumor recurrence after treatment with un-edited CD99 CAR-T cells. There was an un-precedented increase in the xenograft survival, > 200 days, in mice treated with CD99KO CARs and at which time point sustained persistence of CAR+ cells were evident in the animal spleen and bone marrow. CONCLUSIONS: We have generated a new and promising CAR-T cell therapy that is effective against DIPG with enhanced persistence in animal models which is critical for clinical translation.
LGG-05. A Nine-month-old Boy with Regression of Milestones and Severe Constipation: An Unusual Case of a Spinal Pilocytic Astrocytoma
Authors: Offenbacher Rachel , Kobets Andrew , Dalvi Nagma , Hsu Kevin , Chin Steven , Snuderl Matija , Levy Adam , Martin Allison
Published: June 2022

Pilocytic astrocytoma (PA), a World Health Organization Grade 1 tumor, is the most common brain tumor in children between 5 and 14 years of age and the second most common in children younger than 5 and older than 14. Although classical to the cerebellum and hypothalamic regions, it can also arise in the spinal cord. A nine-month-old boy with a history of torticollis and plagiocephaly presented with a four-month history of regression of milestones, irritability and severe constipation. He was noted to have flaccid paralysis of the lower extremities and decreased reflexes. Ophthalmologic exam was significant for papilledema and magnetic resonance imaging of the spine were notable for a large infiltrative heterogeneously enhancing lesion extending from T4 to the conus containing several loculated intratumoral cysts with abnormal enhancing margins from T4 to T8. He underwent embolization and complete tumor resection. Post-op MRI was notable for an oval shape non-enhancing soft tissue measuring 8 mm along the medial wall of the left lateral ventricle. Comprehensive tumor molecular profiling on the resected spinal tumor tissue (Caris MI), revealed an NTRK1 fusion, MEF2D-NTRK1, Exon 12. Larotrectinib was initiated at 100mg/m2 per dose oral twice daily to target this specific mutation. Follow up imaging 3 months later showed decrease in the size of intracranial lesions. To date, there is only one other case report demonstrating intracranial metastasis from a spinal PA. Due to the size of his spinal lesion, we believe this was his primary site; however, as described in the literature, there is no definitive way to determine the initiating lesion. The use of comprehensive molecular profiling facilitated the discovery of a targetable oncogenic mutation that changed initial management. To the best of our knowledge there has been only one other case report describing this specific fusion in a pediatric spinal CNS tumor.
LGG-08. MR Imaging of pediatric low-grade gliomas: Pretherapeutic differentiation ofBRAF V600E mutation,BRAF-Fused and Wild-Type tumors in patients without Neurofibromatosis-1
Authors: Trasolini Andrew , Erker Craig , Cheng Sylvia , Crowell Cameron , McFadden Kathryn , Moineddin Rahim , Sargent Michael , Mata-Mbemba Daddy
Published: June 2022

OBJECTIVE: The prognosis and treatment of pediatric low-grade gliomas (pLGGs) is influenced by their molecular subtype. MRI remains the mainstay for initial work-up and surgical planning. We aimed to determine the relationship between imaging patterns and molecular subtypes of pLGGs. METHODS: This is a bi-institutional retrospective study for patients diagnosed from 2004 to 2021 with pathologically confirmed pLGG, molecularly defined as BRAF fusion (KIAA1549-BRAF), BRAF V600E mutation, or wild-type (negative for both BRAF V600E mutation and BRAF fusion). Two neuroradiologists, blinded, independently reviewed imaging parameters on the initial MRI and discrepancies were solved by consensus. Bivariate analysis was used followed by pairwise comparison of Dwass, Steel, and Critchlow-Fligner methods to compare the 3 molecular subtypes. Agreement between reviewers was assessed using Kappa (k). RESULTS: 70 patients were included: 30 with BRAF fusion, 19 with BRAF V600E mutation, and 21 wild-type. There was substantial agreement between the two readers for overall imaging variables (k=0.75). BRAF fusion tumors compared to V600E and wild-type had larger size (p=0.0022), greater mass effect (p=0.0053), and increased rate of hydrocephalus (p=0.0002). BRAF fusion tumors had increased frequency of diffuse enhancement compared with BRAF V600E and wild-type (p <0.0001). BRAF V600E mutant tumors were more often located in a cerebral hemisphere (p <0.0001). Diffusion restriction (qualitatively) was uncommon but only seen in BRAF V600E (p=0.0042) with lower ADC ratio (quantitatively) (p=0.003). Additionally, BRAF V600E mutant tumors appeared more infiltrative than BRAF fusion and wild-type (p=0.0002). CONCLUSION:BRAF fusion and BRAF V600E mutant pLGG have unique imaging features that can be used to differentiate from each other and wild-type pLGG using standard radiology review with high inter-reader agreement. In the era of targeted therapy, these features can be useful for therapeutic planning prior to surgery.
LGG-18. Inhibition of Bcl-xL targets the senescent compartment of pilocytic astrocytoma
Authors: Selt Florian , Sigaud Romain , Valinciute Gintvile , Sievers Philipp , Zaman Julia , Alcon Clara , Peterziel Heike , Tsai Jessica W , Guiho Romain , Martínez-Barbera Juan Pedro , Pusch Stefan , Schuhmann Martin U , El Damaty Ahmed , Bandopadhayay Pratiti , von Deimling Andreas , Pfister Stefan M , Montero Joan , Capper David , Herold-Mende Christel , Oehme Ina , Sahm Felix , Jones David T W , Witt Olaf , Milde Till
Published: June 2022

INTRODUCTION: Pilocytic astrocytoma (PA) is a mitogen-activated protein kinase (MAPK)-driven disease. Treatment of sub-totally resected PA remains challenging and relapses occur even after MAPK-targeted therapies such as MEK inhibition. Oncogenic activation of the MAPK-pathway drives the majority of cells into oncogene-induced senescence (OIS). OIS might represent a complementary vulnerability exploitable by senolytic agents. Here we investigated the senolytic properties of BH3-mimetics in PA. METHODS: Four patient-derived PA cell lines, DKFZ-BT66, -BT308, -BT317 (KIAA1549:BRAF-fusion) and DKFZ-BT314 (BRAF V600E-mutation) were treated with different BH3-mimetics, chemotherapeutics and MEK-inhibitors in proliferation (expression of SV40 large T (TAg)) and OIS (repression of TAg) states. Inhibition of metabolic activity (CellTiterGlo® 2.0) and reduction of viability (trypan blue) was assessed after 72 hours. Target expression was determined using gene expression data and Western blot. On-target activity was verified by immunoprecipitation. Dependence on Bcl-xL was investigated by shRNA-mediated knockdown and BH3-profiling. Gene expression data of primary PA and 751 cancer cell lines (GDSC dataset) was analyzed. RESULTS: BH3-mimetics inhibiting Bcl-xL (Bcl-xLi; Navitoclax, A-1131852, A-1155463, AZD4320) showed activity in 3/4 models (DKFZ-BT66, -BT314 and -BT317) in the OIS state (IC50s <300nM). Other BH3-mimetics, chemotherapeutics and MEK-inhibitors had no effect on all models in OIS. Bcl-xL mRNA expression levels were similar, on-target activity and dependence on Bcl-xL protein was comparable in all models. Bcl-xLi-resistance of DKFZ-BT308 was linked to upregulation of genes of the HALLMARK_XENOBIOTICS_METABOLISM gene set involved in drug metabolism. Correlation of these genes with IC50s of navitoclax was validated in an independent dataset (GDSC). CONCLUSION: Treatment with Bcl-xLi is a promising strategy targeting the senescent part of PA. IC50s of the clinically available drug navitoclax were >20-fold below achievable plasma concentration indicating translatability. Genes from the gene set HALLMARK_XENOBIOTICS_METABOLISM could represent a predictive biomarker.
LGG-22. SJ901: Phase I/II evaluation of single agent mirdametinib (PD-0325901), a brain-penetrant MEK1/2 inhibitor, for the treatment of children, adolescents, and young adults with low-grade glioma (LGG)
Authors: Vinitsky Anna , Chiang Jason , Bag Asim K , Campagne Olivia , Stewart Clinton F , Dunphy Paige , Shulkin Barry , Li Qian , Lin Tong , Hoehn Mary Ellen , Johnson Jason N , Towbin Jeffrey A , Khan Raja , Tatevossian Ruth G , Armstrong Gregory T , Potter Brian , Conklin Heather , Shearer Todd , Scott Susan , Robinson Giles W
Published: June 2022

BACKGROUND: MEK inhibitor trials in pediatric low-grade glioma (pLGG) have yielded promising results, but there remains room for improvement since objective responses are rarely complete and disease recurrence after completion of therapy is common. Mirdametinib (PD-0325901) is a highly selective MEK1/MEK2 inhibitor that, in preclinical studies, has been reported to have superior blood-brain-barrier penetration compared to other MEK inhibitors. As such, we recently launched the SJ901 clinical trial (NCT04923126) to determine the safety, recommended phase 2 dose, pharmacokinetics, and preliminary efficacy of mirdametinib in patients with pLGG when administered continuously. Here, we present preliminary phase 1 data. METHODS: SJ901 is a multi-arm phase I/II trial of mirdametinib in patients >2 and <25 years with LGG. Phase I requires participants to have no prior exposure to MEK inhibitors and recurrent/progressive disease with biopsy-proven evidence of MAPK pathway activation. Three escalating dose levels (2 mg/m2/dose BID, 2.5mg/m2/dose BID and 3mg/m2/dose BID) are planned using a rolling 6 design. RESULTS: Accrual began in June 2021. As of Jan 13, 2022, eleven patients enrolled: 5 on dose level 1 (DL1) and 6 on dose level 2 (DL2). Median age is 10 (3-21) years. Ten patients have somatic gene rearrangements (7 BRAF, 1 MYB, 1 RAF1, 1 FGFR1) and one has an NF1 germline mutation. Four have metastatic disease. No dose-limiting toxicities occurred for DL1 (whereas data are pending for DL2) and only grade 1/2 treatment-related adverse events have been observed. No MEK-related retinopathy or cardiopathy has been observed. Four of the six patients with at least one follow-up disease evaluation have a minor response (>25%-<50% decrease). Median time on therapy is 6.6 (2.2-7) months. No disease progressions have occurred. CONCLUSION: Thus far, mirdametinib is well-tolerated and clinically promising when dosed continuously in patients with recurrent/progressive pLGG. More information will be forthcoming.
LGG-23. Cardiac function in children and young adults treated with MEK inhibitors: a single institution retrospecive cohort study
Authors: Robison Nathan , Su Jennifer , Fang Melody , Malvar Jemily , Menteer Jondavid
Published: June 2022

INTRODUCTION: MEK inhibitors (MEKi) have shown efficacy in pediatric low-grade glioma, among other tumors, but have been associated with acute cardiac dysfunction in adults. Cardiac consequences in children are unknown. MATERIAL AND METHODS: We performed a single center retrospective cohort study evaluating cardiac function by echocardiography (echo) in children and young adults <21 years old receiving MEKi at Children’s Hospital Los Angeles between October 2013 and May 2018. Blinded assessment of left ventricular function by fractional shortening (FS) and ejection fraction (EF) was performed on all available echocardiograms obtained before, during, and following therapy, as well as after re-initiation of therapy. RESULTS: Twenty-six patients underwent MEKi therapy with echo follow-up during the study period. Twenty-four of these had complete echo data. Median follow-up was 12 months. Borderline EF (EF 53-57.9%) occurred in 12 (50%) patients; and 3 (12.5%) progressed to abnormal EF (EF <53%). Cardiac dysfunction, when it occurred, was mild (lowest documented EF was 45%, and lowest FS was 24.4%). EF abnormalities typically fluctuated during therapy, resolved off therapy, and recurred with MEKi re-initiation. No clinical or demographic differences were detected between those who maintained normal cardiac function and those who developed borderline or overt cardiac dysfunction. Symptomatic heart failure did not occur. CONCLUSION: In this cohort of children and young adults, MEKi use was associated with a relatively high incidence of borderline decrease in left ventricular function, often of uncertain clinical significance. There was no evidence of permanent cardiac dysfunction. Further evaluation in larger prospective trials is needed.
LGG-24. Neurocognitive impairment and functional independence in adult survivors of childhood glioma: A report from the Childhood Cancer Survivor Study (CCSS)
Authors: Papini Chiara , Xing Mengqi , Salehabadi Sedigheh Mirzaei , Olsson Ingrid Tonning , Lange Katharine , de Blank Peter , Salloum Ralph , Srivastava Deo Kumar , Leisenring Wendy M , Howell Rebecca M , Oeffinger Kevin , Robison Leslie L , Armstrong Gregory T , Krull Kevin R , Brinkman Tara M
Published: June 2022

PURPOSE: Survivors of pediatric glioma are at risk of developing physical and neurocognitive sequelae secondary to their tumor and its treatment. The contribution of these conditions to attainment of functional independence has not previously been examined. METHODS: 1,284 adult survivors of pediatric glioma (48% male, median [range] 30 [18-51] years at assessment, 22 [15-34] years since diagnosis) completed the CCSS Neurocognitive Questionnaire with impairment defined as scores > 90th %ile of sibling norms. Treatment exposures were categorized as surgery only, chemotherapy (± surgery), or cranial radiation (± chemotherapy/surgery). Self-reported chronic health conditions (CHCs) were graded by organ system using NCI’s CTCAE v4.3. Latent class analysis utilized six factors (employment, marital status, independent living, driver’s license, assistance with routine needs, assistance with personal care needs) to identify classes of functional independence. Multivariable modified Poisson regression evaluated relative risk (RR) of neurocognitive impairment between the classes, adjusting for sex, race, age at assessment, and age at diagnosis. Path analysis explored the impact of treatment exposures on functional independence, mediated by Grade 2-4 CHCs and neurocognitive impairment. RESULTS: Three latent classes of functional independence were identified: independent (58%), moderately independent (20%), and non-independent (22%). Compared to the independent class, non-independent survivors were at elevated risk for impaired task efficiency (RR=3.86, 95% CI, 2.97-5.01), memory (RR=2.39, 95% CI, 1.91-2.98), organization (RR=2.04, 95% CI, 1.64-2.54), and emotional regulation (RR=1.67, 95% CI, 1.30-2.15). Path analysis revealed significant direct paths from cranial radiation (β=0.14), impaired task efficiency (β=0.42), and sensorimotor (β=0.22) and endocrine conditions (β=0.24) to non-independence. Cranial radiation also was indirectly associated with non-independence through impaired task efficiency (β=0.06), and sensorimotor (β=0.06) and endocrine conditions (β=0.10). CONCLUSIONS: Neurocognitive impairment and chronic health conditions partially mediate the association between treatment exposures and attainment of independence in adulthood, identifying potential intervention targets to promote independence in long-term survivors.
LGG-32. Integrated biologic, radiologic and clinical analysis of pediatric low-grade gliomas during and after targeted therapy treatment
Authors: Tsai Jessica W , Choi Jungwhan John , Ouaalam Hakim , Murrillo Efrain Aguilar , Yeo Kee Kiat , Vogelzang Jayne , Sousa Cecilia , Woods Jared K , Ligon Keith L , Warfield Simon K , Bandopadhayay Pratiti , Cooney Tabitha M
Published: June 2022

BACKGROUND: Pediatric low grade gliomas (pLGGs) are the most common central nervous system tumor in children, characterized by driver alterations in the RAS and MAPK pathways. Genomic advances have facilitated use of molecular targeted therapies, however their long-term impact on tumor behavior remains critically unanswered. METHODS: We performed an IRB-approved, retrospective chart and imaging review of pLGGs treated with off-label targeted therapy at Dana-Farber/Boston Children’s Cancer and Blood Disorders Center from 2010 to 2020. Volumetric analysis was performed for BRAFV600E and BRAF fusion/duplication driven pLGG subsets. RESULTS: Fifty-five patients were identified (dabrafenib n = 15, everolimus n = 26, trametinib n = 11, and vemurafenib n = 3). Targeted agent was used as first or second-line therapy for 58% (32/55). Median duration of targeted therapy was 0.79 years (0.01 – 4.87), and overall median follow-up was 2.50 years (0.01 – 7.39). The 1-year, 3-year, and 5-year EFS from targeted therapy initiation were 62.1%, 38.2%, and 31.8%, respectively. Mean volumetric change for BRAFV600E mutated pLGG on BRAF inhibitors was -54.11%, and median time to best volumetric response was 8.28 months (n = 12). Median time to largest volume post-treatment was 2.86 months. Mean volumetric change for BRAF fusion/duplication pLGG on MEK inhibitors was +7.34% with median time to best volumetric response of 6.71 months (n = 7). Median time to largest volume post-treatment was 2.38 months. CONCLUSIONS: Our integrated clinical and volumetric data suggest the majority of patients receiving BRAF inhibitors or trametinib achieve reduction in tumor volume while on therapy and that tumor stability can be achieved following targeted therapy cessation. Moreover, volumetric analysis shows promise as a tool to assess targeted therapeutic response in pLGGs.
LGG-38. Dose-dependent seizure control for an NF1 patient treated via MEK-inhibition for optic pathway glioma
Authors: Cantor Evan , Meyer Ashley , Ogle Andrea , Shatara Margaret , Cluster Andrew , Abdelbaki Mohamed S , Morris Stephanie , Weisenberg Judith , Brossier Nicole M
Published: June 2022

BACKGROUND: Low-grade gliomas (LGG) are the most common solid tumor of childhood and can result in neurologic complications, including seizures, focal neurologic deficits, and learning difficulties. Molecularly targeted agents are increasingly being utilized to treat LGG, but the effect of these agents on accompanying neurologic complications are poorly understood. CASE: An 8-years old male with Neurofibromatosis Type 1 (NF1), medically refractory epilepsy and deep extensive glioma (extending from the optic pathway and involving the basal ganglia and corpus collosum) began selumetinib therapy due to radiographic and symptomatic tumor progression. Radiographic response (resolution of enhancement) was observed at 12 weeks of therapy, accompanied by improvement in seizure frequency, hemiparesis, and academic performance. Due to cardiotoxicity observed at that time (asymptomatic decreased ejection fraction and shortening fraction on echocardiogram), selumetinib was reduced to 50% dosing. On this reduced dose of selumetinib, seizures increased in frequency with subsequent worsening hemiparesis and recurrence of learning difficulties. One month later, dosing was escalated back to 100% due to interval resolution of cardiotoxicity, resulting in resolution of seizures and improvement in focal neurologic deficits and cognition. DISCUSSION: Dose-dependent response to MEK inhibition was observed without concurrent changes in anti-epileptic medications. The tumor was stable in size despite improved enhancement with treatment, suggesting that objective response by RANO criteria is not necessary for improved seizure control in LGG. Recent work has implicated the RAS/MEK/ERK pathway in neuronal precursor cells as a cause for epilepsy, suggesting that MEK inhibition of NF1-heterozygous neurons could be contributing to treatment response in this patient. Improvements in weakness and academic performance may have been due to improved seizure control or a direct effect of MEK inhibition on NF1-heterozygous neurons. CONCLUSION: MEK inhibition may have a clinically relevant anti-seizure effect for patients with pediatric LGG or NF1.
LGG-45. Genetic dependencies inMYB/MYBL1-driven pediatric low-grade glioma models
Authors: Condurat Alexandra-Larisa , Jones Jill , Gonzalez Elizabeth , Doshi Jeyna , Zhou Kevin , Tsai Jessica W , Khadka Prasidda , Buchan Graham B J , Rouleau Cecile , Pelton Kristine , Abid Tanaz , Goodale Amy , Persky Nicole , Beroukhim Rameen , Ligon Keith , Root David , Piccioni Federica , Bandopadhayay Pratiti
Published: June 2022

AIM: Pediatric low-grade gliomas (pLGGs) are a heterogenous group of tumors, diverse in their localization, histology, mutational landscape, clinical behavior, and treatment response. Genomic alterations impacting the MYB family of transcription factors were identified in two distinct pLGG subtypes: Angiocentric Gliomas (AG) and Diffuse Astrocytomas (DA). The molecular profiles and therapeutic vulnerabilities associated with these genomic alterations remain unexplored. In this study we highlight the use of genome-wide CRISPR/Cas9 knock-out screens for an unbiased identification of translatable therapeutic targets. METHODOLOGY: Given the lack of patient-derived pLGG cell lines, we engineered in vitro pLGG mouse and human neural stem cell (NSC) models to harbor pLGG-relevant genomic alterations. We performed single cell RNA sequencing to investigate the transcriptional profiles driven by these mutations and to dissect the central regulatory networks enabling tumorigenesis. Specific genetic dependencies associated with MYB/MYBL1 mutations were screened using the Brie genome-wide mouse CRISPR lentiviral knock-out pooled library, consisting of 78,637 single guide RNAs (sgRNAs) targeting 19,674 mouse genes. RESULTS: We have successfully generated in vitro NSC-based pLGG models crucial to deepening our knowledge on pLGG biology and the identification of translatable therapeutic targets. Genome-scale CRISPR/Cas9 knock-out screens in isogenic NSCs models, expressing distinct MYB/MYBL1 alterations or a control transgene, revealed several differential genetic dependencies. Among the top identified dependencies are regulators of cell-stress response, cell-cycle progression, and modulators of the ubiquitin-proteasome degradation pathway. CONCLUSION: Genome-wide CRISPR knock-out screens are a powerful tool for the unbiased identification of mutation-specific genetic dependencies that can be explored as candidates for precision medicine approaches.
LGG-49. Subependymal giant cell astrocytoma associated with a cortical tuber: A case report
Authors: Quinot Valerie Anne , Rössler Karl , Feucht Martha , Kasprian Gregor , Gelpi Ellen , Haberler Christine
Published: June 2022

Subependymal giant cell astrocytomas (SEGAs) are circumscribed gliomas strongly associated with tuberous sclerosis (TS). TS, a rare genetic disorder caused by inactivating mutations in either of the TSC genes (TSC1/2), leads to upregulation of the mTOR pathway and consecutive cell growth. CNS manifestations other than SEGAs include cortical tubers, white matter glioneuronal hamartomas and subependymal nodules (SENs), which, although regarded as distinct morphological phenotypes, share certain histological characteristics including ballooned astrocytes and giant ganglion-like cells. SEGAs, thought to develop from the median ganglionic eminence (MGE), are most commonly located periventricularly. However, rare cases of extraventricular SEGAs have been reported. We report a case of a cortico-subcortically located SEGA in a TS patient. A two-month-old female TS patient with multiple cortical tubers presented with treatment-resistant epilepsy. A 4cm sized tuber located in the right temporal lobe, showing a transmantle sign on MRI but no typical imaging appearance of SEGA, was surgically resected. Histological evaluation revealed typical morphological characteristics of a tuber with dysmorphic neurons, balloon cells and calcifications in the cortex and adjacent white matter. Focally, a cortico-subcortically located, well delineated area with increased cellularity and morphological features of a SEGA was found. Single mitotic figures were detectable. Immunhistochemically, these cells were strongly positive for GFAP, vimentin, and nestin. Scattered S100-, NeuN-, MAP2- and SMI32-positive cells were present. No expression of class-III-b-tubulin and TTF1a was found. pS6 was expressed in a small fraction of cells. CD34 showed a dense capillary network within the lesion. This case is consistent with prior case reports of SEGA-tissue in tubers of TS patients. However, the SEGA tissue of this case did not display TTF1a-expression, characteristic for SEGAs and considered as a marker for cells originating from the MGE, thus implying a different cellular lineage.
LGG-59. Identifying hidden drivers of low-grade glioma tumor growth
Authors: Misek Sean , Fultineer Aaron , Condurat Alexandra , Zhou Kevin , Root David , Persky Nicole , Boehm Jesse , Bandopadhayay Pratiti , Beroukhim Rameen
Published: June 2022

Genomic drivers of pediatric low-grade gliomas (pLGGs) converge on alterations that activate the MAPK pathway. However, expression of individual driver oncogenes fails to induce tumor formation with high penetrance and, paradoxically, expression of these oncogenes suppresses growth in vitro. This, combined with the non-monotonic tumor growth rate in patients, suggests that there are “hidden drivers” beyond a single driver oncogene that are necessary to support tumor growth. The goal of this project is to leverage high-throughput functional genomics strategies to identify these hidden drivers of pLGG. Our preliminary data indicates that genes which modulate differentiation are required for the survival of LGG cells, suggesting that these genes may be hidden drivers of LGG tumor growth. Additionally, we hypothesize that secreted factors in the tumor microenvironment regulate pLGG tumor growth, potentially by modulating differentiation. In total, genes which cooperate with pLGG driver oncogenes to promote tumor growth may represent a new class of therapeutic targets and may explain the complex patterns of tumor growth that are observed in patients.
MEDB-02. The identification and functional characterization of circular RNA Circ_63706 in sonic hedgehog medulloblastomas
Authors: Pokhrel Rudramani , Katsushima Keisuke , Stapleton Stacie , Jallo George , Raabe Eric , Eberhart Charles G , Perera Ranjan J
Published: June 2022

Circular RNAs (circRNAs) are increasingly recognized as stable and specific biomarkers and therapeutic targets in many cancers, but little is known about their function, subtype specificity, and biomarker potential in medulloblastomas. Medulloblastoma is a central nervous system tumor that predominantly affects children and always requires aggressive therapy. Understanding and identifying novel disease-related molecular mechanisms and pathways are essential for developing optimal and novel therapies. To identify medulloblastoma subgroup-specific circRNAs, we subjected RNA-seq data from 175 clinical medulloblastoma samples representing the four subgroups to a statistical and machine learning (random forest classification) pipeline. Circular RNA circ_63706 expression was specific to the sonic hedgehog (SSH) group, which was confirmed through in situ hybridization analysis of clinical tissue samples. Functional characterization of circ_63706 by siRNAs and shRNAs demonstrated that cell proliferation, invasion, and apoptosis are perturbed in circ_63706 cells and inhibited in vivo tumor growth. These novel medulloblastoma-specific circular RNAs are emerging as important oncogenes that not only provide valuable mechanistic insights into how medulloblastomas develop but also how they can be used as biomarkers and therapeutic targets. These results pave the way for the specific identification and personalized treatment of different medulloblastoma subgroups.
MEDB-08. Inhibition of different mitotic targets demonstrated distinct DNA damage and cell death response in p53-mutant medulloblastoma
Authors: Huang Shiying , Pan Jie-Ling , Karthik Sekar , Du YuChen , Lin Qi , Lau Ching C , Adekunle Adesina , Su Jack M F , Major Angela , Elghetany M Tarek , Hui Kam-Man , Li Xiaonan , Teo Wan-Yee
Published: June 2022

BACKGROUND: In normal cells, cell cycle is tightly regulated by mitotic proteins to ensure smooth transition through each phase of cell division. Here, we examine two proteins – KIF11, a mitotic kinesin, responsible for assembly and maintenance of mitotic spindle during mitosis; and MELK, a serine/threonine kinase, essential for mitotic progression. Cancer cells can upregulate MELK and KIF11 to promote uncontrolled cell division and protect the cells from apoptotic cell death, leading to tumorigenesis. AIMS: We investigated the response of p53-mutant medulloblastoma (MB) by inhibiting KIF11 and MELK separately to study the effects on cell cycle progression and cell death mechanisms. RESULTS: Cell proliferation was suppressed by inhibition of either KIF11 or MELK in MB, independent of p53-mutant status. Regardless of p53-mutant status, inhibiting KIF11 induced cell cycle arrest at G2/M. In contrast, inhibiting MELK (IC50 dose) induced more prominent G2/M arrest in p53-mutant cells compared to p53-wildtype cells. In p53-mutant MB, arrested cells during MELK inhibition subsequently underwent apoptotic cell death at 24h and 48h. With KIF11 inhibition, p53-mutant cells at 24h were already in necrotic stage. p53-mutant cells reached necrotic stage in a shorter time with KIF11 inhibition than MELK inhibition. On immunoblotting, independent of p53-mutant status, KIF11 inhibition produces more significant increase in DNA damage marker and c-PARP indicative of apoptosis, compared to MELK inhibition. Treatment with KIF11 or MELK inhibitor increased p53 protein expression in p53-wildtype (normal stress response). However, in p53-mutant cells, p53 protein expression decreased post-KIF11-inhibition, but remained unchanged post-MELK inhibition. In-vivo, inhibiting KIF11 was less tolerable in a patient-derived orthotopic xenograft model with p53-mutation. CONCLUSION: Inhibition of either mitotic target KIF11 or MELK, can induce anti-proliferative effects in MB. In p53-mutant MB, DNA damage and cell death response with KIF11-inhibition are more marked.
MEDB-09. Unraveling the role of unfolded protein response in medulloblastoma cancer stem cells
Authors: Spinello Zaira , Abballe Luana , Splendiani Elena , Giannatale Angela Di , Giangaspero Felice , Mastronuzzi Angela , Ferretti Elisabetta , Miele Evelina , Catanzaro Giuseppina
Published: June 2022

Medulloblastoma (MB) is the most common malignant childhood brain tumor. The current clinical approach consists of multimodal strategies with debilitating long-term effects and risk of tumor recurrence. Medulloblastoma stem cells (MBSCs) are a fraction of tumor cells with high proliferation potential and the capability to adapt to adverse/restrictive conditions in tumor milieu thus driving the refractoriness to conventional therapies. Recently, high basal levels of Unfolded Protein Response (UPR) molecules have been found in tumors of different tissue-origin and are correlated with poor prognosis and low patient survival. However, little is known about the role of UPR in MB. We investigated the expression and activation of UPR players in MBSCs. Human group 3 MB (G3MB) cell lines, specifically CHLA-01, D283- and D341-Med, were grown in Vitamin A and/or FBS or in stem selective medium (B27™) for 72 h before collection. Cells were fixed, stained with proper primary antibodies and images were acquired by confocal microscopy. The analysis of the transcription factors ATF-4 and CHOP revealed their elevated nuclear expression and co-localization, which resulted to be more marked in G3MB stem-like cells than in the differentiated ones. Also the ATF-6 branch was investigated, in differentiating conditions D283 and D341-Med showed a greater activation of ATF-6, represented by its nuclear localization, in respect to stem cells, while CHLA-01 did not show differences. Conversely XBP1, the transcription factor downstream IRE1 signaling, was not expressed in the three cell lines. Lastly, a Kaplan-Meier analysis on MB patients showed a worse prognosis with a shorter survival rate of patients expressing high ATF4 transcript levels. Our results reveal, even in resting conditions, preferential activation of the PERK branch in G3MB cells grown in stem-like condition suggesting that ATF-4 might be a promising therapeutic and prognostic factor to specifically target the stem compartment in aggressive MB.