Multi-pronged analysis of pediatric low-grade glioma reveals a unique tumor microenvironment associated with BRAF alterations

Pediatric low-grade gliomas (pLGG) comprise 35% of all brain tumors. Despite favorable survival, patients experience significant morbidity from disease and treatments. A deeper understanding of pLGG biology is essential to identify novel, more effective, and less toxic therapies. We utilized single cell RNA sequencing (scRNA-seq), spatial transcriptomics, and cytokine analyses to characterize and understand tumor and immune cell heterogeneity across pLGG. scRNA-seq revealed tumor and immune cells within the tumor microenvironment (TME). Tumor cell subsets revealed a developmental hierarchy with progenitor and mature cell populations. Immune cells included myeloid and lymphocytic cells. There was a significant difference between the prevalence of two major myeloid subclusters between pilocytic astrocytoma (PA) and ganglioglioma (GG). Bulk and single-cell cytokine analyses evaluated the immune cell signaling cascade with distinct immune phenotypes among tumor samples. KIAA1549-BRAF tumors appeared more immunogenic, secreting higher levels of immune cell activators and chemokines, compared to BRAF V600E tumors. Spatial transcriptomics revealed the differential gene expression of these chemokines and their location within the TME. A multi-pronged analysis of pLGG demonstrated the complexity of the pLGG TME and differences between genetic drivers that may influence their response to immunotherapy. Further investigation of immune cell infiltration and tumor-immune interactions is warranted.

Key points

There is a developmental hierarchy in neoplastic population comprising of both progenitor-like and mature cell types in both PA and GG.A more immunogenic, immune activating myeloid population is present in PA compared to GG. Functional analysis and spatial transcriptomics show higher levels of immune mobilizing chemokines in KIAA1549-BRAF fusion PA tumor samples compared to BRAF V600E GG samples.

Importance of the Study

While scRNA seq provides information on cellular heterogeneity within the tumor microenvironment (TME), it does not provide a complete picture of how these cells are interacting or where they are located. To expand on this, we used a three-pronged approach to better understand the biology of pediatric low-grade glioma (pLGG). By analyzing scRNA-seq, secreted cytokines and spatial orientation of cells within the TME, we strove to gain a more complete picture of the complex interplay between tumor and immune cells within pLGG. Our data revealed a complex heterogeneity in tumor and immune populations and identified an interesting difference in the immune phenotype among different subtypes.

Tumor and immune cell types interact to produce heterogeneous phenotypes of pediatric high-grade glioma

BACKGROUND

Pediatric high-grade gliomas (PHGG) are aggressive brain tumors with 5-year survival rates ranging from <2% to 20% depending upon subtype. PHGG presents differently from patient to patient and is intratumorally heterogeneous, posing challenges in designing therapies. We hypothesized that heterogeneity occurs because PHGG comprises multiple distinct tumor and immune cell types in varying proportions, each of which may influence tumor characteristics.

METHODS

We obtained 19 PHGG samples from our institution's pediatric brain tumor bank. We constructed a comprehensive transcriptomic dataset at the single-cell level using single-cell RNA-Seq (scRNA-Seq), identified known glial and immune cell types, and performed differential gene expression and gene set enrichment analysis. We conducted multi-channel immunofluorescence (IF) staining to confirm the transcriptomic results.

RESULTS

Our PHGG samples included 3 principal predicted tumor cell types: astrocytes, oligodendrocyte progenitors (OPCs), and mesenchymal-like cells (Mes). These cell types differed in their gene expression profiles, pathway enrichment, and mesenchymal character. We identified a macrophage population enriched in mesenchymal and inflammatory gene expression as a possible source of mesenchymal tumor characteristics. We found evidence of T-cell exhaustion and suppression.

CONCLUSIONS

PHGG comprises multiple distinct proliferating tumor cell types. Microglia-derived macrophages may drive mesenchymal gene expression in PHGG. The predicted Mes tumor cell population likely derives from OPCs. The variable tumor cell populations rely on different oncogenic pathways and are thus likely to vary in their responses to therapy.

Genetic Predictors of Neurocognitive Outcomes in Survivors of Pediatric Brain Tumors

Purpose

Neurocognitive deficits are common in pediatric brain tumor survivors. The use of single nucleotide polymorphism (SNP) analysis in DNA repair genes may identify children treated with radiation therapy for brain tumors at increased risk for treatment toxicity and adverse neurocognitive outcomes.

Methods

The Human 660W-Quad v1.0 DNA BeadChip analysis (Illumina) was used to evaluate 1048 SNPs from 59 DNA repair genes in 46 subjects. IQ testing was measured by the Wechsler Intelligence Scale for Children. Linear regression was used to identify the 10 SNPs with the strongest association with IQ scores while adjusting for radiation type.

Results

The low vs high IQ patient cohorts were well matched for time from first treatment to most recent IQ, first treatment age, gender, and treatments received. 5 SNPs on 3 different genes (CYP29, XRCC1, and BRCA1) and on 3 different chromosomes (10, 19, and 17) had the strongest association with most recent IQ score that was not modified by radiation type. Furthermore, 5 SNPs on 4 different genes (WRN, NR3C1, ERCC4, RAD51L1) on 4 different chromosomes (8, 5, 16, 14) had the strongest association with change in IQ independent of radiation type, first IQ, and years between IQ measures.

Conclusions

SNP polymorphisms offer potential to predict adverse neurocognitive outcomes in pediatric brain tumor survivors. Our results require validation in a larger patient cohort. Improving the ability to identify children at risk of treatment related neurocognitive deficits could allow for better treatment stratification and early cognitive interventions.

EPID-06. Transfusion related iron overload in pediatric patients with CNS tumors

BACKGROUND: Patients receiving chemotherapy or autologous hematopoietic stem cell transplant (autoHSCT) routinely receive red cell transfusions as supportive care. Each unit of transfused red cells contains approximately 150mg of iron which the body has no natural mechanism for excreting. Transfusion-related iron overload (TRIO) is an under-recognized complication of therapy which left untreated may result in long-term damage to the liver, heart, or endocrine organs. We sought to identify the prevalence of TRIO in patients with pediatric CNS tumors and evaluate specific risk factors. METHODS: A retrospective record review of pediatric CNS tumor patients treated at Children’s Hospital Colorado was conducted including patients who completing therapy between 1/1/2014 – 12/1/2021. Patients at high risk for TRIO were defined as having a cumulative transfused blood volume of more than 150mL/kg or 4000mL total. The diagnosis of TRIO was confirmed if patients had a serum ferritin greater than 1000ng/mL or elevated liver iron content of 7mg/g dry weight or greater by MRI. RESULTS: There were 173 evaluable patients (40% embryonal tumors, 15% germ cell tumors, 10% ependymomas, 26% low grade gliomas, 5% high grade gliomas, and 3% other tumors). The mean age at completion of therapy was 8 years (range: 0.67 – 25 years). Patients receiving autoHSCT (24% of cohort) were at higher risk for TRIO based on transfused volumes (p&lt;0.0001) than patients not treated with autoHSCT (72% vs 6%, RR 12.0) The prevalence of TRIO in autoHSCT patients was 7.5% (3/40) vs 0.8% (1/121) in patients not undergoing autoHSCT (RR 9.37). For autoHSCT patients at high risk by transfused volume the prevalence of TRIO was 10.3% (3/29). CONCLUSIONS: Pediatric CNS tumor patients who have received an autoHSCT are at higher risk for TRIO than those who have not. Routine screening for TRIO should be offered to patients receiving autoHSCT.

OTHR-03. Oxaliplatin as a hearing-sparing alternative to carboplatin in tandem autologous stem cell transplants in pediatric CNS malignancy

BACKGROUND: Intensive chemotherapy with tandem autologous stem cell transplants (autoSCT) is shown to improve survival for children with CNS malignancy. Platinum-based chemotherapeutic agents in these regimens, mainly cisplatin and carboplatin, have resulted in significant sensorineural hearing loss. Oxaliplatin, a newer platinum-based agent, is considered less ototoxic. Empiric substitution of oxaliplatin for carboplatin in preparative regimens for autoSCT have been tried. However, the survival and ototoxicity outcomes have not been studied. OBJECTIVE: To compare the overall survival and ototoxicity of oxaliplatin versus carboplatin preparatory chemotherapy regimens in children who received tandem autoSCT for treatment of CNS malignancy. METHODS: We performed a retrospective chart review of all pediatric patients with primary CNS tumors who received tandem autoSCT from 2011 to 2018 at Children’s Hospital Colorado. Demographics, clinical outcomes, and medication administration records were extracted from electronic medical records. Hearing evaluations, performed at pre-transplant, after each transplant episode, and at follow-up visits, were reviewed and graded by an audiologist. Comparisons were performed using Fisher’s exact tests and log rank test statistics. RESULTS: 32 pediatric patients with CNS tumors met inclusion criteria. Seven patients received oxaliplatin in place of carboplatin in one or more preparatory regimens. There was no statistically significant difference in overall survival between the two groups (p=0.99). A total of 85 follow-up audiograms were available for assessment, including long-term follow up. Of the 13 audiograms that showed hearing loss, one (8%) had prior oxaliplatin exposure, compared to 18/72 (25%) audiograms without hearing loss had prior oxaliplatin exposure (p=0.28). CONCLUSIONS: Oxaliplatin is effective and well-tolerated when used in lieu of carboplatin in preparatory regimen for autoSCT for pediatric CNS malignancy. This study is limited by its small size. A larger, multi-center study is warranted to confirm oxaliplatin’s safety and effect on survival and ototoxicity in pediatric autoHSCT.

EPCT-01. Pediatric Brain Tumor Consortium (PBTC)-055: A phase I study of trametinib and hydroxychloroquine (HCQ) for BRAF-fusion or Neurofibromatosis type-1 (NF1)-associated pediatric gliomas

INTRODUCTION: Autophagy is a highly conserved process by which intracellular components are degraded and recycled promoting cell survival. Preclinically, autophagy has been implicated as a resistance mechanism in BRAF-mutant glioma cells treated with MAPK-pathway inhibitors. HCQ, an oral autophagy inhibitor, has been evaluated preclinically and clinically to overcome resistance. METHODS: PBTC-055 (NCT04201457) is a phase I/II trial of HCQ combined with trametinib (BRAF-fusion or NF1-associated gliomas) or trametinib and dabrafenib (BRAFV600E gliomas) in patients &lt; 30 years with progressive glioma. Prior treatment with RAF and/or MEK inhibitor with sub-optimal response (no response or response followed by progression on therapy) was required. Here, we present phase I data combining trametinib with HCQ utilizing a rolling-6 design. HCQ was administered at escalating dose levels (8, 15, or 20 mg/kg/day divided BID) in combination with standard pediatric trametinib dosing. All patients received prior MEK inhibitor therapy; 5/18 (28%) exhibited no response and 13/18 (72%) progressed on active therapy. RESULTS: Eighteen eligible/evaluable subjects were enrolled. Median age was 9.6 years (2.5-20.4 years); 10 were male. There were 2 dose-limiting toxicities (both grade 3 rash one each at DL1 and DL3). The highest dose level of HCQ (20 mg/kg/day divided BID) was declared the RP2D. Grade 3 adverse events possibly related to therapy included skin infection, rash, cardiac ejection fraction decrease, weight loss, and anorexia. There were no grade 4 or 5 attributable toxicities. Preliminarily, combination pharmacokinetic assessment revealed similar metabolism of trametinib to that reported as a single agent; HCQ demonstrated more rapid clearance compared to adults. Pharmacodynamic assessments are ongoing. CONCLUSIONS: The combination of trametinib and HCQ is safe with a RP2D of HCQ of 20 mg/kg/day divided BID. Currently, subjects are enrolling on the phase II portion evaluating the efficacy of this novel combination.

LGG-55. Autophagy sensitizes CNS tumors to targeted therapy by lowering their apoptotic threshold

Autophagy inhibition improves the effectiveness and overcomes RAF pathway inhibition (RAFi) resistance across multiple CNS tumors and molecularly distinct resistance mechanisms. Mechanistic links between autophagy and apoptotic cell death may explain this ability to improve RAFi response and reverse resistance. RAFi sensitive (MAF 794, AM38) and resistant (MAF 794R, MAF 905-3, AM38R, B76) BRAFV600E CNS tumor cell lines were analyzed at baseline, following RAFi (vemurafenib), autophagy inhibition (chloroquine or shRNAs), and combination therapy. Growth assays and caspase activation were monitored by Incucyte Zoom. qRT-PCR evaluated key pro-apoptotic BH3-only members of the BCL-2 family. Broad BH-3 profiling was completed using the Letai JC-1 Plate-Based protocol. Western blot analysis assessed protein levels. Combination pharmacologic treatment caused alterations in key pro-apoptotic BH3-only proteins including an increase in BNIP3L and PUMA. Genetically inhibiting autophagy with shRNAs for ATG5 and ATG7 (proteins required for formation of the autophagosome) produced similar results with increases in both protein and mRNA levels of BNIP3L and PUMA following RAFi treatment. This suggested autophagy-mediated regulation of BH3 proteins functions to determine cellular apoptotic threshold. Caspase activation demonstrated increased effectiveness of combined RAFi and autophagy inhibition overcoming the apoptotic threshold compared to single drug treatment. BH3 profiling demonstrated a dependence on BCL-2 to inhibit apoptosis. BH3 mimetics competitively bind to pro-survival BCL-2 family members, blocking their protective effects and pushing tumor cells towards apoptosis. Autophagy inhibition can also improve treatment response by overcoming the apoptotic threshold in RAFi resistant cells and magnifying the apoptotic response in sensitive cells. BH3 profiling reveals CNS BRAFV600E are BCL-2 dependent cells, unprimed for apoptosis, which may be good candidates for additional treatment with BH3 mimetics such as venetoclax. This presents an attractive treatment for MAPK activated CNS tumors by enhancing apoptotic cell death by targeting the MAPK pathway, autophagy and BH3.

491. Persistence of SARS-CoV-2 Iinfection in Immunocompromised Children

Background

The temporal dynamics of SARS-CoV-2 infectivity in immunocompromised children (IC) are unknown but may have important infection control implications. We evaluated SARS-CoV-2 viral persistence and assessed factors associated with viral persistence and cycle threshold (CT) values as a surrogate of viral load for IC.

Methods

We conducted a retrospective cohort study of SARS-CoV-2-positive IC at a large quaternary pediatric hospital from March 2020-2021. Immunocompromised status was defined as primary or secondary/acquired immunodeficiencies due to comorbidities or immunosuppressive treatment. The primary outcome was time to first-of-two consecutively negative SARS-CoV-2 PCR tests ≥ 24 hours apart. Polymerase chain reaction (PCR) testing of sequential patient samples was conducted using the Centers for Disease Control 2019-nCoV Real-Time RT-PCR Diagnostic Panel (CDC assay). Chi-square, Fisher exact, and Wilcoxon tests were used to compare demographic and clinical characteristics. Kaplan-Meier curve median event times and log-rank tests were used to compare outcomes. Subjects without 2 consecutive negative tests censored at the last test. Analyses were conducted using SAS v 9.4.

Results

Ninety-one children met inclusion criteria, and 67 children had more than 1 test (Figure 1). Median age was 15.5 years (IQR 8-18 yrs), 64% were male, 58% of children were white, and 43% were Latinx. Most (67%) were tested in outpatient settings, and 58% of children were asymptomatic. The median time to two negative tests was 42 days (IQR 25.0,55.0), with no difference in duration of positivity with specific diagnoses, degree of lymphopenia, or symptomatic vs asymptomatic illness. Five of 7 (71%) children with samples available for repeat testing had initial CT values &lt; 30, indicating a moderate to high viral load, and of these, 4 (57%) had repeat testing 21 to 30 days later with CT values &lt; 30 (Figure 2), suggesting persistence of moderate to high viral loads.

Figure 1. Plot of immunocompromised children in cohort with positive SARS CoV2 PCR and subsequent testing (n = 67).

Conclusion

The median duration of viral persistence among IC with SARS-CoV-2 infection was 6 weeks, with no significant difference in immunocompromised diagnoses or clinical presentation, with over half of children with testing on the same platform having moderate to high viral loads after 3 weeks, suggesting potential transmission risk.

Disclosures

Samuel R. Dominguez, MD, PhD, BioFire Diagnostics (Consultant, Research Grant or Support)DiaSorin Molecular (Consultant)Pfizer (Grant/Research Support) Samuel R. Dominguez, MD, PhD, BioFire (Individual(s) Involved: Self): Consultant, Research Grant or Support; DiaSorin Molecular (Individual(s) Involved: Self): Consultant; Pfizer (Individual(s) Involved: Self): Grant/Research Support Suchitra Rao, MBBS, MSCS, BioFire (Research Grant or Support)

SARS-CoV-2 persistence in immunocompromised children

OBJECTIVES

We evaluated the length of time immunocompromised children (ICC) remain positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), identified factors associated with viral persistence, and determined cycle threshold (C_T ) values of children with viral persistence as a surrogate of viral load.

METHODS

We conducted a retrospective cohort study of ICC at a pediatric hospital from March 2020 to March 2021. Immunocompromised status was defined as primary, secondary, or acquired due to medical comorbidities/immunosuppressive treatment. The primary outcome was time to first of two consecutive negative SARS-CoV-2 polymerase chain reaction (PCR) tests at least 24 hours apart. Testing of sequential clinical specimens from the same subject was conducted using the Centers for Disease Control (CDC) 2019-nCoV real-time reverse transcriptase (RT)-PCR Diagnostic Panel assay. Descriptive statistics, Kaplan-Meier curve median event times and log-rank tests were used to compare outcomes between groups.

RESULTS

Ninety-one children met inclusion criteria. Median age was 15.5 years (interquartile range [IQR] 8-18), 64% were male, 58% were White, and 43% were Hispanic/Latinx. Most (67%) were tested in outpatient settings and 58% were asymptomatic. The median time to two negative tests was 42 days (IQR 25.0-55.0), with no differences in median time by illness presentation or level of immunosuppression. Seven children had more than one sample available for repeat testing, and five of seven (71%) children had initial C_T values of <30 (moderate to high viral load); four children had C_T values of <30, 3-4 weeks later, suggesting persistent moderate to high viral loads.

CONCLUSIONS

Most ICC with SARS-CoV-2 infection had mild disease, with prolonged viral persistence >6 weeks and moderate to high viral load.

ddPCR Analysis Reveals BRAF V600E Mutations Are Infrequent in Isolated Pituitary Langerhans Cell Histiocytosis Patients

Langerhans cell histiocytosis (LCH) is an inflammatory myeloid neoplasia with a highly variable clinical presentation affecting people of all ages. Mutations in BRAF V600E are the most identifiable molecular alteration in LCH although its incidence in pediatric patients with isolated pituitary stalk involvement is not well described. Pediatric patients with LCH and isolated pituitary stalk involvement typically present with central diabetes insipidus. Diagnosis requires a transcranial biopsy which often yields scant tissue. We sought to determine the prevalence of BRAF V600E mutations in patients with isolated pituitary stalk LCH using digital droplet polymerase chain reaction because this method requires minimal tumor DNA. We identified 8 patients with isolated pituitary stalk thickening who underwent a biopsy at Children's Hospital Colorado from January 2001 to December 2019, as well as 6 patients with systemic LCH diagnosed by biopsy in the same period as a comparison. Only one out of the 8 patients with isolated thickened pituitary stalk was found to have a detectable BRAF V600E mutation. Five out of the 6 patients with systemic LCH had a detectable BRAF V600E mutation. In our series, BRAF V600E mutations are rare in pediatric patients with LCH and isolated pituitary stalk involvement.

QOL-36. USE OF CANNABINOIDS IN THE PEDIATRIC CENTRAL NERVOUS SYSTEM TUMOR POPULATION

BACKGROUND

Cannabinoids, including cannabidiol (CBD) and tetrahydrocannabinol (THC), are a class of compounds found in marijuana. Numerous studies in adults have examined cannabinoid use in management of cancer-related symptoms such as nausea, anorexia, and pain. Less is known about the use in the pediatric oncology population.

METHODS

A prospective observational study has been ongoing since 2016 at Children’s Hospital Colorado to evaluate cannabinoids’ impact using PedsQL™ modules on quality of life of pediatric patients with central nervous system (CNS) tumors who are 2–18 years old. Laboratory assessments of T-cell activity and pharmacokinetics of CBD, THC and associated metabolites are in process. Diaries with exploratory information on cannabinoid use patterns are being collected.

RESULTS

Thirty-three patients (14:19; male:female) have been enrolled with a median age of 6.4 years (range, 2.9–17.7 years). The most common tumor type in enrolled patients is embryonal tumors (13/33; 39%). Nine (27%) patients have low-grade glial/glioneuronal tumors, and eight (24%) had high-grade/diffuse midline gliomas. The remaining patients had ependymoma or craniopharyngioma. The median time on cannabinoids is 9 months. Most (n=20) patients have used oral products with CBD and THC. One patient continues on cannabinoid therapy in follow up. Preliminary immune function analyses identified impaired neutrophil superoxide anion production and chemotaxis in patients taking cannabinoids at early time points on therapy.

CONCLUSIONS

Families of children with various CNS tumors are pursuing cannabinoid therapy for both antitumor and supportive care purposes. Analysis of the impact of cannabinoids on patients’ quality of life is ongoing.

LGG-27. TARGETED THERAPY FOR PEDIATRIC LOW-GRADE GLIOMAS AND PLEXIFORM NEUROFIBROMAS WITH TRAMETINIB

BACKGROUND

Targeted therapy aimed at modulating the RAS/RAF/MEK/ERK pathway is of increasing interest for patients with plexiform neurofibromas and low-grade gliomas. Trametinib is an FDA-approved MEK inhibitor that has little published pediatric experience to date.

METHODS

A retrospective chart review of patients treated with trametinib for low-grade gliomas (LGG) and/or plexiform neurofibromas (PN) between 2015–2018 was conducted at Children’s Hospital Colorado. Data collected included patient demographics, lesion location, Neurofibromatosis type 1 (NF1) status, best response of PN/LGG to trametinib, duration of trametinib therapy, and reported toxicities at least possibly attributed to trametinib.

RESULTS

Thirty (57% male; 73% NF1) patients were identified. Sixteen (53%) patients had PN only, 12 (40%) had LGG only, and two (7%) patients had both PN and LGG. The most common LGG location was the optic pathway/hypothalamus (72%). The most common location of PN was the face (63%). Two-thirds (8/12) of patients with LGG had a BRAF alteration or NF1 mutation. The median age at start of trametinib therapy was 9.9 years (range, 2.0 – 18.8 years). The median duration of trametinib therapy was 0.8 years (range 0.1 – 2.9 years). The most commonly reported adverse event was rash. No patients developed retinal toxicity or cardiotoxicity. Only two (7%) patients discontinued for toxicity and one (3%) for progressive disease.

CONCLUSIONS

Trametinib can be administered without significant toxicity to children with PN or LGG. Clinical benefit is noted in this cohort; however, prospective clinical trials are necessary to characterize efficacy formally.

DDEL-06. DRUG INTERACTION BETWEEN EVEROLIMUS AND CANNABIDIOL IN PEDIATRIC PATIENTS WITH SUBEPENDYMAL GIANT CELL ASTROCYTOMAS: A SINGLE INSTITUTION EXPERIENCE

Tuberous sclerosis complex (TSC) is an autosomal recessive genetic disorder associated with clinical manifestations including subependymal giant cell astrocytomas (SEGA) and seizures. The combination of everolimus and Epidiolex, a purified form of cannabidiol, has become an increasingly common treatment regimen in this population. Everolimus is primarily metabolized via CYP3A4, which may be inhibited by cannabidiol. We seek to describe our institution’s experience with this drug interaction. METHODS: Investigators conducted a retrospective review of neuro-oncology patients with TSC and SEGA who were treated concurrently with everolimus and cannabidiol. Data collected included demographics, body surface area, everolimus dose, everolimus troughs, date of cannabidiol initiation, documented symptoms, liver and renal function tests, and reason for discontinuing therapy. RESULTS: Three patients (ages 11–17 years) met inclusion criteria. All patients were stable on everolimus doses ranging from 6.5 to 9.5 mg/m2/day and achieving trough goals of 5–10 ng/mL. Two to four weeks after initiating cannabidiol, everolimus trough concentrations rose 200–860% above goal. One patient reported new-onset involuntary movements, but no other toxicities were noted. Cannabidiol was discontinued in all cases due to caregiver concerns regarding drug interactions. All patients were able to achieve goal trough concentrations on previously stable doses of everolimus after discontinuing cannabidiol. CONCLUSIONS: Cannabidiol appears to modulate everolimus metabolism leading to significantly elevated serum concentrations. Additional research is required to determine the need for empiric dose adjustments upon cannabidiol initiation. Patient counseling, frequent trough monitoring, and surveillance for adverse effects are crucial for optimizing outcomes in patients prescribed this regimen.

LGG-34. CLINICAL AND MOLECULAR CHARACTERIZATION OF A MULTI-INSTITUTIONAL COHORT OF PEDIATRIC SPINAL CORD LOW-GRADE GLIOMAS

BACKGROUND

The MAPK/ERK pathway is involved in cell growth and proliferation, and mutations in the BRAF paralog of this pathway have made it an oncogene of interest in pediatric cancer. Previous studies have identified that BRAF mutations as well as BRAF-KIAA1549 fusions are common in intracranial low-grade gliomas (LGGs). Fewer studies have tested for the presence of these genetic aberrations in spinal LGGs. The aim of this study was to better understand the prevalence of BRAF and other genetic aberrations in spinal LGG.

METHODS

We analyzed 46 spinal LGGs from children age 1–25 years from two institutions, Children’s Hospital Colorado (CHCO) and The Hospital for Sick Children (Sick Kids) for the presence of BRAF fusions or mutations. Data was correlated with clinical information. A 67 gene panel additionally screened for other possible genetic abnormalities of interest in the patient cohort from CHCO. In the Sick Kids cohort, BRAFV600E was tested for by ddPCR and IHC while BRAF fusions where detected by FISH, RT-PCR or Nanostring platform.

RESULTS

Of the 31 patient samples who underwent fusion analysis, 13 (42%) harbored the BRAF-KIAA1549 fusion. Overall survival (OS) for patients confirmed positive for BRAF-KIAA1549 was 100% compared to 76% for fusion negative patients. Other mutations of interest were also identified in this patient cohort including BRAFV600E, STK11, PTPN11, H3F3A, APC, TP53, PIK3CA (polymorphism), FGFR1, and CDKN2A deletion.

CONCLUSION

BRAF-KIAA1549 was seen in higher frequency than BRAFV600E or other genetic aberrations in pediatric spinal LGGs and trends towards longer OS although not statistically significant.

DDRE-13. DECONVOLUTING MECHANISMS OF RESISTANCE TO BRAF INHIBITORS IN BRAF V600E HUMAN GLIOMA

BACKGROUND

While BRAF-targeted therapy can be effective in a subset of patients with glioma, resistance to treatment can emerge over time. The description and validation of mechanisms of resistance in BRAF-mutant glioma are not previously described.

METHODS

Pre- and post- BRAF inhibitor (BRAFi) or BRAFi/MEK inhibitor (MEKi) treated patient samples were obtained under IRB-approved protocols at University of Colorado Denver, UCSF, and Johns Hopkins. Targeted DNA sequencing or whole exome sequencing (WES), and RNA-seq were conducted on paired samples. Functional validation of putative resistance mechanisms was performed using established glioma cell lines with BRAF V600E mutation (DBTRG-5MG, AM38, B76).

RESULTS

Analysis of 15 tissue sample pairs identified point mutations in 15 genes (including CBL, NF1, PTEN, and MAP2K1) and expression changes in RAF1 leading to putative mechanisms of resistance. We performed functional validation of loss of NF1 and CBL as resistance mechanisms and demonstrated growth inhibition and cell death in response to BRAFi with siRNA/sgRNA-mediated knockdown of each gene. Knockdown of CBL resulted in increased EGFR expression and phosphorylation, a possible mechanism for maintaining ERK signaling within the cell. Combination therapy with a MEKi or EGFR inhibitor was able to overcome resistance to BRAFi, in NF1 knockdown and CBL knockdown, respectively. Restoration of wild-type PTEN in B76 cells (PTEN-/-) restored sensitivity to BRAFi. Ingenuity pathway analysis suggested that a switch from BRAF to CRAF dependence mediated resistance in some tumors. Indeed, inhibition of CRAF expression using siRNA in a patient-derived glioma cell line re-sensitized cells to BRAFi.

CONCLUSIONS

Analysis of pre-/post-treatment BRAF mutant glioma sample pairs, primarily from pediatric patients, identified a variety of putative resistance mechanisms, some of which have been validated in vitro. Resistance mechanisms to BRAFi in glioma are varied and may be susceptible to different combinations of targeted therapy, highlighting the importance of a personalized approach.

Preclinical and clinical investigation of intratumoral chemotherapy pharmacokinetics in DIPG using gemcitabine

Background

Hundreds of systemic chemotherapy trials in diffuse intrinsic pontine glioma (DIPG) have not improved survival, potentially due to lack of intratumoral penetration, which has not previously been assessed in humans.

Methods

We used gemcitabine as a model agent to assess DIPG intratumoral pharmacokinetics (PK) using mass spectrometry.

Results

In a phase 0 clinical trial of i.v. gemcitabine prior to biopsy in children newly diagnosed with DIPG by MRI, mean concentration in 4 biopsy cores in patient 1 (H3K27M diffuse midline glioma) was 7.65 µM. These compare favorably to levels for patient 2 (mean 3.85 µM, found to have an H3K27-wildtype low-grade glioma on histology), and from a similar study in adult glioblastoma (adjusted mean 3.48 µM). In orthotopic patient-derived xenograft (PDX) models of DIPG and H3K27M-wildtype pediatric glioblastoma, gemcitabine levels and clearance were similar in tumor, pons, and cortex and did not depend on H3K27 mutation status or tumor location. Normalized gemcitabine levels were similar in patient 1 and the DIPG PDX.

Conclusions

These findings, while limited to one agent, provide preliminary evidence for the hypotheses that lack of intratumoral penetration is not why systemic chemotherapy has failed in DIPG, and orthotopic PDX models can adequately model intratumoral PK in human DIPG.

Targeted fusion analysis can aid in the classification and treatment of pediatric glioma, ependymoma, and glioneuronal tumors

BACKGROUND

The use of next-generation sequencing for fusion identification is being increasingly applied and aids our understanding of tumor biology. Some fusions are responsive to approved targeted agents, while others have future potential for therapeutic targeting. Although some pediatric central nervous system tumors may be cured with surgery alone, many require adjuvant therapy associated with acute and long-term toxicities. Identification of targetable fusions can shift the treatment paradigm toward earlier integration of molecularly targeted agents.

METHODS

Patients diagnosed with glial, glioneuronal, and ependymal tumors between 2002 and 2019 were retrospectively reviewed for fusion testing. Testing was done primarily using the ArcherDx FusionPlex Solid Tumor panel, which assesses fusions in 53 genes. In contrast to many previously published series chronicling fusions in pediatric patients, we compared histological features and the tumor classification subtype with the specific fusion identified.

RESULTS

We report 24 cases of glial, glioneuronal, or ependymal tumors from pediatric patients with identified fusions. With the exception of BRAF:KIAA1549 and pilocytic/pilomyxoid astrocytoma morphology, and possibly QKI-MYB and angiocentric glioma, there was not a strong correlation between histological features/tumor subtype and the specific fusion. We report the unusual fusions of PPP1CB-ALK, CIC-LEUTX, FGFR2-KIAA159, and MN1-CXXC5 and detail their morphological features.

CONCLUSIONS

Fusion testing proved to be informative in a high percentage of cases. A large majority of fusion events in pediatric glial, glioneuronal, and ependymal tumors can be identified by relatively small gene panels.

The US Experience with Local Economic Development

In this paper the increasing intensity of intermunicipal and interstate economic competition in the USA is noted. It is argued that the federal structure of the USA, the present political climate, and the mobility of capital combine to produce a situation of positive feedback leading to everincreasing subsidies. The situation constitutes a classic prisoner's dilemma. Decreased competition would be in the interests of all units of government. However, there is no way that a state or local government can opt out of the competition unilaterally and no mechanism by which collective action can be taken to reduce the intensity of competition. Also considered in this paper are the aggregate effects of local economic development programs in terms of taxes and public expenditures, efficiency, and equity, and several less commonly discussed considerations.

Late effects of total body irradiation and hematopoietic stem cell transplant in children under 3 years of age

BACKGROUND

Total body irradiation (TBI) is an important component of hematopoietic stem cell transplant (SCT) for pediatric malignancies. With increasing survival rates, late effects of SCT become more important. Younger children may be at particular risk of late effects of radiation and SCT.

METHODS

We retrospectively reviewed outcomes of children less than 3 years of age who received TBI as part of their preparative regimen for SCT at Children's Hospital Colorado. Clinical information including the date of last follow-up, most recent lab values, and physiologic tests were extracted from the medical record.

RESULTS

Of 81 patients who underwent SCT, 19 received TBI and of those, 15 were long-term survivors available for review. Late effects occurring in greater than 50% of the children included abnormalities involving endocrine, metabolic, renal, cataracts, and neurocognitive systems. Other organs involved less commonly included liver, skeletal, and cardiac abnormalities. Solid tumors were a rare finding with only one patient developing a benign osteochondroma and no identified secondary malignancies.

CONCLUSIONS

TBI has been shown to be an important part of the preparative regimen for patients undergoing SCT. Our results, similar to other studies, suggest TBI in patients less than 3 years of age will likely result in multi-organ dysfunction including endocrine, metabolic, renal, eye, and neurocognitive abnormalities. A longitudinal study with standardized testing of these systems would further clarify the late effects concerns in this patient population.

Indication of electron neutrino appearance from an accelerator-produced off-axis muon neutrino beam

The T2K experiment observes indications of ν(μ) → ν(e) appearance in data accumulated with 1.43×10(20) protons on target. Six events pass all selection criteria at the far detector. In a three-flavor neutrino oscillation scenario with |Δm(23)(2)| = 2.4×10(-3)  eV(2), sin(2)2θ(23) = 1 and sin(2)2θ(13) = 0, the expected number of such events is 1.5±0.3(syst). Under this hypothesis, the probability to observe six or more candidate events is 7×10(-3), equivalent to 2.5σ significance. At 90% C.L., the data are consistent with 0.03(0.04) < sin(2)2θ(13) < 0.28(0.34) for δ(CP) = 0 and a normal (inverted) hierarchy.

Favorable selection in the Medicare+Choice program: new evidence

Historically, studying the Medicare managed care favorable-selection issue has been difficult because direct data on managed care enrollees have been unavailable. In this study, we analyzed the first year of Balanced Budget Act (BBA)-mandated inpatient encounter data. Based on this comparison of actual managed care and fee-for-service (FFS) beneficiaries, it appears that there are significant differences between these populations. The most striking differences are found in the comparison of average risk factors, indicating a clear bias in the managed care populations toward beneficiaries predicted to be less costly.

Risk Adjustment for the Medicare program: lessons learned from research and demonstrations

The Balanced Budget Act (BBA) of 1997 requires numerous changes in Medicare. Medicare's managed care program has been reinvented as "Medicare + Choice," offering an expanded range of delivery system options for beneficiaries and a schedule of payment changes that will dramatically affect managed care plans. Preceding some of these BBA-legislated changes to Medicare were years of research and demonstrations. Risk-adjusted payment in the Medicare + Choice program, which is mandated for implementation in 2000, is one example of a longstanding developmental initiative. This paper provides a brief overview of risk adjustment-related research and demonstration activities carried out by the Health Care Financing Administration (HCFA) since the 1980s, and describes a possible technical approach for the implementation of risk-adjusted Medicare managed care payments in 2000.

Delivering home-based case management to families with children with mental retardation and developmental disabilities

To meet the needs of individuals with mental retardation and developmental disabilities (MR/DD) and their families living in urban setting, a noncenter-based model of case management was implemented. In contrast to traditional case management in which families and consumers come to the case manager and most service coordination is done by telephone or in meetings at the case manager/social worker's worksite, the case manager in a noncenter-based model is mobile and able to meet the consumer and family in their domains. In this model, case management is provided in conjunction with in-home residential habilitation and funded by Medicaid under the Home and Community Based Services Waiver. This funding stream provides monies for nontraditional services delivered in noncertified settings. Case managers used the Family Resource Scale to get an immediate indication of the resources and needs of each family. The scale highlights the adequacy of a person's basic and caregiving resources, as well as financial needs. The findings from this study suggest that an understanding of both disability and entitlements is essential for case managers who may have to help advocate for consumers around services and benefits. Moreover, to build and maintain an egalitarian and supportive relationship with families, the importance of caregiver-specified resources and needs must be recognized by case managers. Access to resource information and the ability to engage the family in problem-solving depends on a well-trained staff with the ability to respond to individuals with different needs and from a variety of circumstances. These essential skills prepare a case manager to assist families with their immediate requirements as well as to mobilize them to plan for future needs.