IMMU-37. ANTI-CD47 TREATMENT POTENTIATES PHAGOCYTOSIS OF MEDULLOBLASTOMA BY M1 POLARIZED MACROPHAGES FOLLOWING IRRADIATION

Medulloblastoma (MB) is the most common malignant brain tumor of childhood and accounts for 15–20% of all pediatric brain tumors. Despite significant advancements over the last decade in our understanding of the molecular underpinnings of MB, the overall risk of recurrence remains high, prognosis remains poor, and available treatment modalities remain limited for patients with this disease. Accordingly, the area of targeting tumor immune resistance has garnered increasing interest as a potentially safe and effective adjunctive therapy. CD47 is a cell surface protein that acts as a primary “don’t eat me” signal to the innate immune system and has been shown to be crucial in allowing tumor cells to evade phagocytosis by tumor-associated macrophages. Several preclinical studies aimed at blocking this “don’t eat me signal” through the application of a mouse anti-human monoclonal antibody (Ab) to CD47 (anti-CD47) have shown promise in pediatric brain tumor models. Further, chemotherapy and irradiation have been shown to increase the expression of pro-phagocytic signals on the surfaces of tumor cells. The authors examined the use of anti-CD47 Ab on the rates of phagocytosis of MB cells undergoing different single-fraction doses of external beam irradiation in vitro. The use of anti-CD47 Ab in the D425 MB cell line phagocytosis assay significantly increased rates of phagocytosis for 0 Gy (4.1% without vs. 20.3% with anti-CD47 Ab; p < 0.0001), 2 Gy (7.4% without vs. 23.4% with anti-CD47 Ab; p < 0.0001), 5 Gy (11.9% without vs. 27.3% with anti-CD47 Ab; p < 0.0001), 10 Gy (21.7% without vs. 34% with anti-CD47 Ab; p < 0.0001), and 20 Gy treatment groups (27.2% without vs. 43.9% with anti-CD47 Ab; p < 0.0001). A similar pattern of phagocytosis potentiation through use of anti-CD47 Ab with increasing doses of radiation was seen in D458 and D341 MB cell lines.

Treatment of a symptomatic thalamic pilocytic astrocytoma with reservoir placement and laser interstitial thermal therapy: illustrative case

BACKGROUND

Treatment of pilocytic astrocytomas (PAs) in children can be challenging when they arise in deep midline structures because complete surgical resection may result in significant neurological injury. Laser interstitial thermal therapy (LITT) has provided an alternative treatment modality for lesions that may not be amenable to resection. However, many patients with PAs may be symptomatic from a compressive cyst associated with the PA, and LITT does not obviate the need for cystic decompression in these patients.

OBSERVATIONS

A 12-year-old male presented with left-sided weakness. Magnetic resonance imaging (MRI) revealed an enhancing mass with a large cyst involving the right thalamus and basal ganglia. The patient underwent a reservoir placement for cyst drainage and biopsy of the mass, revealing a pilocytic astrocytoma. He then underwent LITT followed by adjuvant chemotherapy. Sixteen months after LITT, follow-up MRI of the brain revealed no tumor growth.

LESSONS

This is the first case to describe reservoir placement to treat the cystic portion of a pilocytic astrocytoma followed by LITT and targeted chemotherapy. Reservoir placement reduced the cyst’s mass effect and resolved the patient’s symptoms, allowing for treatment options beyond resection.

Multiple Intraspinal Gangliogliomas in a Child With Neurofibromatosis Type 1: Case Report and Literature Review

Neurofibromatosis type 1 (NF1)-associated primary intramedullary spinal cord ganglioglioma has only rarely been reported. Because of frequent nonresectability, they pose significant management challenges despite clinical indolence. This report describes a 4-year-old girl with NF1 who was found to have multiple discrete, infiltrative intramedullary cord masses, and biopsy demonstrated World Health Organization grade I ganglioglioma. Panel-based next-generation sequencing showed her previously identified germline NF1 mutation and a second somatic NF1 mutation. This represents the first report of multiple primary intramedullary gangliogliomas in a child with NF1 and demonstrates how biopsy with panel-based next-generation sequencing provides potential targets for MAPK/MEK/BRAF pathway inhibitor therapy.

RARE-24. IDENTIFYING INDIVIDUALS WITH PRIMARY CENTRAL NERVOUS SYSTEM TUMORS AT RISK FOR HEREDITARY CANCER SYNDROMES USING THE UTAH POPULATION DATABASE

Background

CNS tumors are the most common solid tumors and the deadliest cancers in children. Approximately 10% of children with a CNS tumor harbor a hereditary cancer syndrome (HCS), but many will not be tested for a HCS. The Utah Population Database (UPDB) contains comprehensive cancer registry data for Utah families and can determine multigenerational cancer pedigrees across an archive of 5.8 million individuals. We hypothesize that the UPDB can identify children and families with HCSs not previously identified.

Methods

We queried the UPDB for individuals ages 0–39 diagnosed with a primary CNS tumor (malignant and benign) between 1966–2017 and generated cancer pedigrees of 3 generations or more for probands, extending to at least third-degree relatives. Specialized software calculated a familial standardized incidence ratio (FSIR) to determine families with excess clustering of CNS tumors. Clinical cancer genetics experts reviewed pedigrees to confirm patterns of HCS.

Results

We identified 4,634 CNS tumors in 4,550 individuals, of whom 2,233 (49%) reside in high-quality pedigrees containing ≥2 grandparents, at least 1 from both maternal and paternal sides. To identify families with excess clustering of CNS tumors, we selected pedigrees with an FSIR P<0.05 and ≥2 affected patients, resulting in 161 high-risk families with a mean of 170 (median 96) relatives per pedigree of 3–6 generations. Among these 161 families, there were 2,017 unique relatives (first-third degree) of CNS probands with 2,355 tumors (any site), for a per pedigree average of 14.7 tumors in 12.5 relatives. Review of the 10 highest risk pedigrees indicated that 4 meet HCS criteria, including Li-Fraumeni (n=2), von Hippel-Lindau (n=1), and rhabdoid tumor predisposition (n=1).

Conclusion

The UPDB can produce multigenerational cancer pedigrees that identify individuals and families at risk of harboring a HCS who warrant germline testing. These findings should encourage clinicians to perform thorough family history screening.

Identifying individuals with primary central nervous system tumors at risk for hereditary cancer syndromes using the Utah Population Database

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Background: CNS tumors are the most common solid tumors and the deadliest cancers in children. Approximately 10% of children with a CNS tumor harbor a hereditary cancer syndrome (HCS), but many will not be tested for a HCS. The Utah Population Database (UPDB) contains comprehensive cancer registry data for Utah families and can determine multigenerational cancer pedigrees across an archive of 5.8 million individuals. Early identification of HCSs results in improved cancer surveillance and outcomes, reducing the impact of CNS tumors in children. We hypothesize that the UPDB can identify children and families with HCSs not previously identified. Methods: We queried the UPDB for individuals ages 0-39 diagnosed with a primary CNS tumor (malignant and benign) between 1966-2017 and generated cancer pedigrees of 3 generations or more for probands, extending to at least third-degree relatives. Specialized software calculated a familial standardized incidence ratio (FSIR) to determine families with excess clustering of CNS tumors. Clinical cancer genetics experts reviewed pedigrees to confirm patterns of HCS. Results: We identified 4,634 CNS tumors in 4,550 individuals, of whom 2,233 (49%) reside in high-quality pedigrees containing ≥2 grandparents, at least 1 from both maternal and paternal sides. To identify families with excess clustering of CNS tumors, we selected pedigrees with an FSIR P< 0.05 and ≥2 affected patients, resulting in 161 high-risk families with a mean of 170 (median 96) relatives per pedigree of 3-6 generations. Among these 161 families, there were 2,017 unique relatives (first-third degree) of CNS probands with 2,355 tumors (any site), for a per pedigree average of 14.7 tumors in 12.5 relatives. Review of the 10 highest risk pedigrees indicated that 4 meet HCS criteria, including Li-Fraumeni (n = 2), von Hippel-Lindau (n = 1), and rhabdoid tumor predisposition (n = 1). Conclusions: The UPDB can produce multigenerational cancer pedigrees that identify individuals and families at risk of harboring a HCS who warrant germline testing. These findings should encourage clinicians to perform thorough family history screening and to always consider workup for associated HCSs.

Microglia in the Brain Tumor Microenvironment

Microglia are the brain resident phagocytes that act as the primary form of the immune defense in the central nervous system. These cells originate from primitive macrophages that arise from the yolk sac. Advances in imaging and single-cell RNA-seq technologies provided new insights into the complexity of microglia biology.Microglia play an essential role in the brain development and maintenance of brain homeostasis. They are also crucial in injury repair in the central nervous system. The tumor microenvironment is complex and includes neoplastic cells as well as varieties of host and infiltrating immune cells. Microglia are part of the glioma microenvironment and play a critical part in initiating and maintaining tumor growth and spread. Microglia can also act as effector cells in treatments against gliomas. In this chapter, we summarize the current knowledge of how and where microglia are generated. We also discuss their functions during brain development, injury repair, and homeostasis. Moreover, we discuss the role of microglia in the tumor microenvironment of gliomas and highlight their therapeutic implications.

IMG-13. MRI-BASED RADIOMICS PROGNOSTIC MARKERS OF POSTERIOR FOSSA EPENDYMOMA

PURPOSE

Posterior fossa ependymomas (PFE) are common pediatric brain tumors often assessed with MRI before surgery. Advanced radiomic analysis show promise in stratifying risk and outcome in other pediatric brain tumors. Here, we extracted high-dimensional MRI features to identify prognostic, image-based, radiomics markers of PFE and compared its performance to clinical variables.

METHODS

93 children from five centers (median age=3.3yrs; 59 males; mean PFS=50mos) were included. Tumor volumes were manually contoured on T1-post contrast and T2-weighted MRI for PyRadiomics feature extraction. Features include first-order statistics, size, shape, and texture metrics calculated on the original, log-sigma, and wavelet transformed images. Progression free survival (PFS) served as outcome. 10-fold cross-validation of a LASSO Cox regression was used to predict PFS. Model performance was analyzed and concordance metric (C) was determined using clinical variable (age at diagnosis and sex) only, radiomics only, and radiomics plus clinical variable.

RESULTS

Six radiomic features were selected (all T1): 1 first-order kurtosis (log-sigma) and 5 texture features (3 wavelet, 2 original). This model demonstrated significantly higher performance than a clinical model alone (C: 0.69 vs 0.58, p<0.001). Adding clinical features to the radiomic features didn’t improve prediction (p=0.67). For patients with molecular subtyping (n=48), adding this feature to the clinical plus radiomics models significantly improved performance over clinical features alone (C = 0.79 vs. 0.66, p=0.02). Further validation and model refinement with additional datasets are ongoing.

CONCLUSION

Our pilot study shows potential role for MRI-based radiomics and machine learning for PFE risk stratification and as radiographic biomarkers.

IMMU-19. HDAC INHIBITORS SENSITIZE MYC-AMPLIFIED MEDULLOBLASTOMA TO IMMUNOTHERAPY BY ACTIVATING THE NF-kB PATHWAYS

Medulloblastoma is the most common malignant brain tumor in childhood and comprises four distinct molecular subgroups with further layers of intertumoral heterogeneity. Amplification of the oncogene MYC drives tumorigenesis and constitutes a hallmark feature underlying Group 3 biology. Employing our in-house drug screening pipeline, we evaluated a library of epigenetic inhibitors (n=78) in various brain tumor cell lines followed by a secondary HDACi library (n=20) screen, we identified the clinically established, class I selective HDACi CI-994 as the compound with the most preferential antitumoral effect in MYC-driven medulloblastoma. We confirmed that the inhibitor response was in part MYC-dependent as our lentiviral-based MYC-overexpression model showed higher sensitivity towards CI-994 treatment as compared to the isogenic control with low endogenous MYC expression. CI-994 showed significant antitumoral effects at the primary site and at the metastatic compartment in two orthotopic mouse models of MYC-driven medulloblastoma. RNA sequencing profiling of tumor cells treated with CI-994 at IC50 revealed an up-regulation of multiple innate inflammatory pathways like NFκB, TLR4, Interferon-gamma, and TGFbeta. Flow cytometry analysis revealed an increased surface expression of MHC-I. We combined CI-994 with an anti-body against the innate checkpoint CD47 which acts as a “don’t eat me” signal previously shown by us to have significant anti-tumor activity against MYC-driven MB. Combining CI-994 with anti-CD47 shows a significant increase in macrophage-mediated phagocytosis of tumor cells and a significant increase in the survival of tumor-bearing mice.

IMG-10. MRI-BASED RADIOMIC PROGNOSTIC MARKERS OF DIFFUSE MIDLINE GLIOMA

BACKGROUND

Diffuse midline gliomas (DMG) are lethal pediatric brain tumors with dismal prognoses. Presently, MRI is the mainstay of disease diagnosis and surveillance. We aimed to identify prognostic image-based radiomics markers of DMG and compare its performance to clinical variables at presentation.

METHODS

104 treatment-naïve DMG MRIs from five centers were used (median age=6.5yrs; 18 males, median OS=11mos). We isolated tumor volumes of T1-post-contrast (T1gad) and T2-weighted (T2) MRI for PyRadiomics high-dimensional feature extraction. 900 features were extracted on each image, including first order statistics, 2D/3D Shape, Gray Level Co-occurrence Matrix, Gray Level Run Length Matrix, Gray Level Size Zone Matrix, Neighboring Gray tone Difference Matrix, and Gray Level Dependence Matrix, as defined by Imaging Biomarker Standardization Initiative. Overall survival (OS) served as outcome. 10-fold cross-validation of LASSO Cox regression was used to predict OS. We analyzed model performance using clinical variable (age at diagnosis and sex) only, radiomics only, and radiomics plus clinical variable. Concordance metric was used to assess the Cox model.

RESULTS

Nine radiomic features were selected from T1gad (2 texture wavelet) and T2 (5 first-order features (1 original, 4 wavelet), 2 texture features (1 wavelet, 1 log-sigma). This model demonstrated significantly higher performance than a clinical model alone (C: 0.68 vs 0.59, p&lt;0.001). Adding clinical features to radiomic features slightly improved prediction, but was not significant (C=0.70, p=0.06).

CONCLUSION

Our pilot study shows a potential role for MRI-based radiomics and machine learning for DMG risk stratification and as image-based biomarkers for clinical therapy trials.

MBRS-31. COMBINING IRRADIATION AND ANTI-CD47 TO ENHANCE THE TREATMENT OF GROUP 3 MEDULLOBLASTOMA

Medulloblastoma (MB) is the most common malignant primary pediatric brain tumor. The Group 3 molecular subgroup of Medulloblastoma (Group 3 MB) is the deadliest with only 30% long term survival. Irradiation for Group 3 Medulloblastoma is required for long term survival of children. Methods to enhance the effect of irradiation against Group 3 MB are an active area of investigation. Immunotherapy using the anti-CD47 treatment has shown promise in treating Group 3 MB. We recently demonstrated that irradiation significantly enhanced anti-CD47-mediated phagocytosis of high-grade glioma cells in vitro. Furthermore, mice engrafted with human high-grade glioma that received anti-CD47 combined with irradiation showed a significant increase in the survival rate and a significant decrease in tumor growth than those that received a single treatment. We have now extended these studies to demonstrate the enhancement of anti-CD47-dependent phagocytosis of human Group 3 MB with irradiation. We also analyzed normal human neural stem cells exposed to the same treatments to assess for the potential toxicity that uniquely exists with this treatment combination.

IMG-22. A DEEP LEARNING MODEL FOR AUTOMATIC POSTERIOR FOSSA PEDIATRIC BRAIN TUMOR SEGMENTATION: A MULTI-INSTITUTIONAL STUDY

BACKGROUND

Brain tumors are the most common solid malignancies in childhood, many of which develop in the posterior fossa (PF). Manual tumor measurements are frequently required to optimize registration into surgical navigation systems or for surveillance of nonresectable tumors after therapy. With recent advances in artificial intelligence (AI), automated MRI-based tumor segmentation is now feasible without requiring manual measurements. Our goal was to create a deep learning model for automated PF tumor segmentation that can register into navigation systems and provide volume output.

METHODS

720 pre-surgical MRI scans from five pediatric centers were divided into training, validation, and testing datasets. The study cohort comprised of four PF tumor types: medulloblastoma, diffuse midline glioma, ependymoma, and brainstem or cerebellar pilocytic astrocytoma. Manual segmentation of the tumors by an attending neuroradiologist served as “ground truth” labels for model training and evaluation. We used 2D Unet, an encoder-decoder convolutional neural network architecture, with a pre-trained ResNet50 encoder. We assessed ventricle segmentation accuracy on a held-out test set using Dice similarity coefficient (0–1) and compared ventricular volume calculation between manual and model-derived segmentations using linear regression.

RESULTS

Compared to the ground truth expert human segmentation, overall Dice score for model performance accuracy was 0.83 for automatic delineation of the 4 tumor types.

CONCLUSIONS

In this multi-institutional study, we present a deep learning algorithm that automatically delineates PF tumors and outputs volumetric information. Our results demonstrate applied AI that is clinically applicable, potentially augmenting radiologists, neuro-oncologists, and neurosurgeons for tumor evaluation, surveillance, and surgical planning.

Right frontotemporal craniotomy for ECA-to-MCA direct and indirect bypass and occipital artery indirect bypass to the posterior circulation: case report

Moyamoya is an uncommon disease that presents with stenoocclusion of the major vasculature at the base of the brain and associated collateral vessel formation. Many pediatric patients with moyamoya present with transient ischemic attacks or complete occlusions. The authors report the case of a 9-year-old girl who presented with posterior fossa hemorrhage and was treated with an emergency suboccipital craniotomy for evacuation. After emergency surgery, an angiogram was performed, and the patient was diagnosed with moyamoya disease. Six months later, the patient was treated for moyamoya using direct and indirect revascularization; after surgery there was excellent vascularization in both regions of the bypass and no further progression of moyamoya changes. This case illustrates a rare example of intracerebral hemorrhage associated with moyamoya changes in the posterior vascularization in a pediatric patient and subsequent use of direct and indirect revascularization to reduce the risk of future hemorrhage and moyamoya progression.

In Vitro Macrophage-Mediated Phagocytosis Assay of Brain Tumors

Tumor-associated macrophages (TAMs) have recently emerged as potentially crucial therapeutic targets for cancer. Thus, the development of macrophage-mediated phagocytosis assays is vital for preclinical drug screening of different tumor cells. This assay can be used to evaluate the effect of anti-cancer therapy, such as immunotherapy, radiotherapy, and chemotherapy, on different tumor cells. Here, we describe the in-vitro phagocytosis assay in detail. As an example of immunotherapy treatment, we used a monoclonal antibody to block an anti-phagocytic signal (CD47) to evaluate the assay using human brain tumor cells and monocyte-derived macrophages. We also demonstrated that this assay can be used to evaluate the effect of different irradiation doses on the phagocytosis of brain tumor cells. This functional assay is fast, accurate, and highly reproducible. Furthermore, the results successfully demonstrate that anti-CD47 antibodies and irradiation can enhance the macrophage-mediated phagocytosis of brain tumors.

Pediatric bithalamic gliomas have a distinct epigenetic signature and frequent EGFR exon 20 insertions resulting in potential sensitivity to targeted kinase inhibition

Brain tumors are the most common solid tumors of childhood, and the genetic drivers and optimal therapeutic strategies for many of the different subtypes remain unknown. Here, we identify that bithalamic gliomas harbor frequent mutations in the EGFR oncogene, only rare histone H3 mutation (in contrast to their unilateral counterparts), and a distinct genome-wide DNA methylation profile compared to all other glioma subtypes studied to date. These EGFR mutations are either small in-frame insertions within exon 20 (intracellular tyrosine kinase domain) or missense mutations within exon 7 (extracellular ligand-binding domain) that occur in the absence of accompanying gene amplification. We find these EGFR mutations are oncogenic in primary astrocyte models and confer sensitivity to specific tyrosine kinase inhibitors dependent on location within the kinase domain or extracellular domain. We initiated treatment with targeted kinase inhibitors in four children whose tumors harbor EGFR mutations with encouraging results. This study identifies a promising genomically-tailored therapeutic strategy for bithalamic gliomas, a lethal and genetically distinct brain tumor of childhood.

Locoregionally administered B7-H3-targeted CAR T cells for treatment of atypical teratoid/rhabdoid tumors

Atypical teratoid/rhabdoid tumors (ATRTs) typically arise in the central nervous system (CNS) of children under 3 years of age. Despite intensive multimodal therapy (surgery, chemotherapy and, if age permits, radiotherapy), median survival is 17 months^1,2. We show that ATRTs robustly express B7-H3/CD276 that does not result from the inactivating mutations in SMARCB1 (refs. ^3,4), which drive oncogenesis in ATRT, but requires residual SWItch/Sucrose Non-Fermentable (SWI/SNF) activity mediated by BRG1/SMARCA4. Consistent with the embryonic origin of ATRT^5,6, B7-H3 is highly expressed on the prenatal, but not postnatal, brain. B7-H3.BB.z-chimeric antigen receptor (CAR) T cells administered intracerebroventricularly or intratumorally mediate potent antitumor effects against cerebral ATRT xenografts in mice, with faster kinetics, greater potency and reduced systemic levels of inflammatory cytokines compared to CAR T cells administered intravenously. CAR T cells administered ICV also traffic from the CNS into the periphery; following clearance of ATRT xenografts, B7-H3.BB.z-CAR T cells administered intracerebroventricularly or intravenously mediate antigen-specific protection from tumor rechallenge, both in the brain and periphery. These results identify B7-H3 as a compelling therapeutic target for this largely incurable pediatric tumor and demonstrate important advantages of locoregional compared to systemic delivery of CAR T cells for the treatment of CNS malignancies.

Myxoid glioneuronal tumor, PDGFRA p.K385-mutant: clinical, radiologic, and histopathologic features

"Myxoid glioneuronal tumor, PDGFRA p.K385-mutant" is a recently described tumor entity of the central nervous system with a predilection for origin in the septum pellucidum and a defining dinucleotide mutation at codon 385 of the PDGFRA oncogene replacing lysine with either leucine or isoleucine (p.K385L/I). Clinical outcomes and optimal treatment for this new tumor entity have yet to be defined. Here, we report a comprehensive clinical, radiologic, and histopathologic assessment of eight cases. In addition to its stereotypic location in the septum pellucidum, we identify that this tumor can also occur in the corpus callosum and periventricular white matter of the lateral ventricle. Tumors centered in the septum pellucidum uniformly were associated with obstructive hydrocephalus, whereas tumors centered in the corpus callosum and periventricular white matter did not demonstrate hydrocephalus. While multiple patients were found to have ventricular dissemination or local recurrence/progression, all patients in this series remain alive at last clinical follow-up despite only biopsy or subtotal resection without adjuvant therapy in most cases. Our study further supports "myxoid glioneuronal tumor, PDGFRA p.K385-mutant" as a distinct CNS tumor entity and expands the spectrum of clinicopathologic and radiologic features of this neoplasm.

Spatiotemporal Tracking of Brain-Tumor-Associated Myeloid Cells in Vivo through Optical Coherence Tomography with Plasmonic Labeling and Speckle Modulation

By their nature, tumors pose a set of profound challenges to the immune system with respect to cellular recognition and response coordination. Recent research indicates that leukocyte subpopulations, especially tumor-associated macrophages (TAMs), can exert substantial influence on the efficacy of various cancer immunotherapy treatment strategies. To better study and understand the roles of TAMs in determining immunotherapeutic outcomes, significant technical challenges associated with dynamically monitoring single cells of interest in relevant live animal models of solid tumors must be overcome. However, imaging techniques with the requisite combination of spatiotemporal resolution, cell-specific contrast, and sufficient signal-to-noise at increasing depths in tissue are exceedingly limited. Here we describe a method to enable high-resolution, wide-field, longitudinal imaging of TAMs based on speckle-modulating optical coherence tomography (SM-OCT) and spectral scattering from an optimized contrast agent. The approach's improvements to OCT detection sensitivity and noise reduction enabled high-resolution OCT-based observation of individual cells of a specific host lineage in live animals. We found that large gold nanorods (LGNRs) that exhibit a narrow-band, enhanced scattering cross-section can selectively label TAMs and activate microglia in an in vivo orthotopic murine model of glioblastoma multiforme. We demonstrated near real-time tracking of the migration of cells within these myeloid subpopulations. The intrinsic spatiotemporal resolution, imaging depth, and contrast sensitivity reported herein may facilitate detailed studies of the fundamental behaviors of TAMs and other leukocytes at the single-cell level in vivo, including intratumoral distribution heterogeneity and roles in modulating cancer proliferation.

Pediatric parapharyngeal infection resulting in cervical instability and occipital-cervical fusion-case report and review of the literature

Parapharyngeal infection is the most common deep neck space infection in children and, in rare instances, can result in bony destruction of the cervical spine. We report one such case that required occipital to cervical fusion and halo-vest fixation. We also review the literature and discuss the etiology, diagnosis, and treatment options for managing pediatric cervical bony destruction secondary to infection.

Evaluation of pediatric glioma outcomes using intraoperative MRI: a multicenter cohort study

BACKGROUND

The use of intraoperative MRI (iMRI) during treatment of gliomas may increase extent of resection (EOR), decrease need for early reoperation, and increase progression-free and overall survival, but has not been fully validated, particularly in the pediatric population.

OBJECTIVE

To assess the accuracy of iMRI to identify residual tumor in pediatric patients with glioma and determine the effect of iMRI on decisions for resection, complication rates, and other outcomes.

METHODS

We retrospectively analyzed a multicenter database of pediatric patients (age ≤ 18 years) who underwent resection of pathologically confirmed gliomas.

RESULTS

We identified 314 patients (mean age 9.7 ± 4.6 years) with mean follow-up of 48.3 ± 33.6 months (range 0.03-182.07 months) who underwent surgery with iMRI. There were 201 (64.0%) WHO grade I tumors, 57 (18.2%) grade II, 24 (7.6%) grade III, 9 (2.9%) grade IV, and 23 (7.3%) not classified. Among 280 patients who underwent resection using iMRI, 131 (46.8%) had some residual tumor and underwent additional resection after the first iMRI. Of the 33 tissue specimens sent for pathological analysis after iMRI, 29 (87.9%) showed positive tumor pathology. Gross total resection was identified in 156 patients (55.7%), but this was limited by 69 (24.6%) patients with unknown EOR.

CONCLUSIONS

Analysis of the largest multicenter database of pediatric gliomas resected using iMRI demonstrated additional tumor resection in a substantial portion of cases. However, determining the impact of iMRI on EOR and outcomes remains challenging because iMRI use varies among providers nationally. Continued refinement of iMRI techniques for use in pediatric patients with glioma may improve outcomes.

Nanoparticle enhanced MRI can monitor macrophage response to CD47 mAb immunotherapy in osteosarcoma

CD47 monoclonal antibodies (mAbs) activate tumor-associated macrophages (TAMs) in sarcomas to phagocytose and eliminate cancer cells. Though CD47 mAbs have entered clinical trials, diagnostic tests for monitoring therapy response in vivo are currently lacking. Ferumoxytol is an FDA-approved iron supplement which can be used "off label" as a contrast agent: the nanoparticle-based drug is phagocytosed by TAM and can be detected with magnetic resonance imaging (MRI). We evaluated if ferumoxytol-enhanced MRI can monitor TAM response to CD47 mAb therapy in osteosarcomas. Forty-eight osteosarcoma-bearing mice were treated with CD47 mAb or control IgG and underwent pre- and post-treatment ferumoxytol-MRI scans. Tumor enhancement, quantified as T2 relaxation times, was compared with the quantity of TAMs as determined by immunofluorescence microscopy and flow cytometry. Quantitative data were compared between experimental groups using exact two-sided Wilcoxon rank-sum tests. Compared to IgG-treated controls, CD47 mAb-treated tumors demonstrated significantly shortened T2 relaxation times on ferumoxytol-MRI scans (p < 0.01) and significantly increased F4/80+CD80+ M1 macrophages on histopathology (p < 0.01). CD47 mAb-treated F4/80+ macrophages demonstrated significantly augmented phagocytosis of ferumoxytol nanoparticles (p < 0.01). Thus, we conclude that ferumoxytol-MRI can detect TAM response to CD47 mAb in mouse models of osteosarcoma. The ferumoxytol-MRI imaging test could be immediately applied to monitor CD47 mAb therapies in clinical trials.

Quantification of Macrophages in High-Grade Gliomas by Using Ferumoxytol-enhanced MRI: A Pilot Study

Purpose To investigate ferumoxytol-enhanced MRI as a noninvasive imaging biomarker of macrophages in adults with high-grade gliomas. Materials and Methods In this prospective study, adults with high-grade gliomas were enrolled between July 2015 and July 2017. Each participant was administered intravenous ferumoxytol (5 mg/kg) and underwent 3.0-T MRI 24 hours later. Two sites in each tumor were selected for intraoperative sampling on the basis of the degree of ferumoxytol-induced signal change. Susceptibility and the relaxation rates R2* (1/T2*) and R2 (1/T2) were obtained by region-of-interest analysis by using the respective postprocessed maps. Each sample was stained with Prussian blue, CD68, CD163, and glial fibrillary acidic protein. Pearson correlation and linear mixed models were performed to assess the relationship between imaging measurements and number of 400× magnification high-power fields with iron-containing macrophages. Results Ten adults (four male participants [mean age, 65 years ± 9 {standard deviation}; age range, 57-74 years] and six female participants [mean age, 53 years ± 12 years; age range, 32-65 years]; mean age of all participants, 58 years ± 12 [age range, 32-74 years]) with high-grade gliomas were included. Significant positive correlations were found between susceptibility, R2*, and R2' and the number of high-power fields with CD163-positive (r range, 0.64-0.71; P < .01) and CD68-positive (r range, 0.55-0.57; P value range, .01-.02) iron-containing macrophages. No significant correlation was found between R2 and CD163-positive (r = 0.33; P = .16) and CD68-positive (r = 0.24; P = .32) iron-containing macrophages. Similar significance results were obtained with linear mixed models. At histopathologic analysis, iron particles were found only in macrophages; none was found in glial fibrillary acidic protein-positive tumor cells. Conclusion MRI measurements of susceptibility, R2*, and R2' (R2* - R2) obtained after ferumoxytol administration correlate with iron-containing macrophage concentration, and this shows their potential as quantitative imaging markers of macrophages in malignant gliomas. © RSNA, 2018 Online supplemental material is available for this article.

High-resolution 3D volumetric contrast-enhanced MR angiography with a blood pool agent (ferumoxytol) for diagnostic evaluation of pediatric brain arteriovenous malformations

OBJECTIVE Patients with brain arteriovenous malformations (AVMs) often require repeat imaging with MRI or MR angiography (MRA), CT angiography (CTA), and digital subtraction angiography (DSA). The ideal imaging modality provides excellent vascular visualization without incurring added risks, such as radiation exposure. The purpose of this study is to evaluate the performance of ferumoxytol-enhanced MRA using a high-resolution 3D volumetric sequence (fe-SPGR) for visualizing and grading pediatric brain AVMs in comparison with CTA and DSA, which is the current imaging gold standard. METHODS In this retrospective cohort study, 21 patients with AVMs evaluated by fe-SPGR, CTA, and DSA between April 2014 and August 2017 were included. Two experienced raters graded AVMs using Spetzler-Martin criteria on all imaging studies. Lesion conspicuity (LC) and diagnostic confidence (DC) were assessed using a 5-point Likert scale, and interrater agreement was determined. The Kruskal-Wallis test was performed to assess the raters' grades and scores of LC and DC, with subsequent post hoc pairwise comparisons to assess for statistically significant differences between pairs of groups at p < 0.05. RESULTS Assigned Spetzler-Martin grades for AVMs on DSA, fe-SPGR, and CTA were not significantly different (p = 0.991). LC and DC scores were higher with fe-SPGR than with CTA (p < 0.05). A significant difference in LC scores was found between CTA and fe-SPGR (p < 0.001) and CTA and DSA (p < 0.001) but not between fe-SPGR and DSA (p = 0.146). A significant difference in DC scores was found among DSA, fe-SPGR, and CTA (p < 0.001) and between all pairs of the groups (p < 0.05). Interrater agreement was good to very good for all image groups (κ = 0.77-1.0, p < 0.001). CONCLUSIONS Fe-SPGR performed robustly in the diagnostic evaluation of brain AVMs, with improved visual depiction of AVMs compared with CTA and comparable Spetzler-Martin grading relative to CTA and DSA.

Abstract LB-004: A novel theranostic strategy for MMP-14 expressing glioblastomas impacts survival

Glioblastoma (GBM) has a dismal prognosis due to therapy resistance of GBM initiating cells (GICs). GICs are preferentially found in the perivascular niche and novel therapeutic strategies are needed that target GICs and the vascular niche. The efficacy of current GBM therapies is hindered by their limited trans-endothelial permeability to the GIC perivascular niche and associated systemic toxicities. Here, we propose a new treatment option with tumor enzyme-activatable, combined therapeutic and diagnostic (theranostic) nanoparticles, which caused specific toxicity against GBM tumor cells and GICs. The theranostic cross-linked iron oxide nanoparticles (CLIO) were conjugated to a highly potent vascular disrupting agent (ICT) and secured with a matrix-metalloproteinase (MMP-14) cleavable protein cap. The purpose of this study was to evaluate tumor retention of CLIO-ICT through MR imaging and demonstrate its anti-GBM affects in vivo settings. Methods: GBM-bearing were treated i.v. with CLIO-ICT (80mg/kg of ICT), ICT (80mg/kg of ICT), CLIO (0.5 mmol Fe/kg) or PBS twice a week for 14 days. For combination treatment with temozolomide (33mg/kg), mice were treated with ICT and CLIO-ICT twice a week for 21 days. MRI studies of GBM-bearing mice were performed on a 7T MR scanner (Bruker-Agilent Technologies-General Electric Healthcare), using T2-weighted imaging sequences. BioLuminescent imaging was performed on an IVIS spectrum scanner (PerkinElmer). TNP delivery across the blood brain barrier (BBB) was confirmed by intra-vital microscopy (IVM) studies with a microscope (IV-100; Olympus, Tokyo, Japan). Flow cytometry and histopathology were performed to evaluate apoptosis in GICs upon CLIO-ICT treatment. Results are presented as mean ± SD unless otherwise presented. Tumor and organ relaxation rates and fluorescence signals were compared using one-way ANOVA. Kaplan-Meier survival curves were compared using the log-rank (Mantel-Cox) test. The level of significance was set at p &lt; 0.05, as compared with the control group. Results: Treatment with CLIO-ICT disrupted tumor vasculature of MMP-14 expressing GBM, induced GIC apoptosis and significantly (p&lt; 0.05) impaired tumor growth compared to PBS-treated animals. In addition, the iron core of CLIO-ICT enabled in vivo drug tracking with MR imaging. T2-weighted MR images before and after intravenous injection of CLIO-ICT in mice showed a signal drop or negative enhancement and significant (p&lt; 0.05) tumor retention of CLIO-ICT in GBM tissue, which was confirmed with Prussian blue histopathological evaluations. Treatment with CLIO-ICT plus temozolomide achieved tumor remission and significantly (p&lt; 0.05) increased survival of human GBM bearing mice compared to temozolomide alone. Conclusion: We present a new, clinically translatable therapeutic strategy with significant impact on survival. Further our approach of combining CLIO-ICT with TMZ offers refinements to current less optimal standards of care in order to achieve GBM remission.

Citation Format: suchismita mohanty, Zixin Chen, Kai Li, Goreti Morais, Jessica Klockow, Ketan Yerneni, Laura Pisani, Frederick Chin, Siddhartha Mitra, Samuel Cheshier, Edwin Chang, Sanjiv Gambhir, Jianghong Rao, Paul M. Loadman, Robert A. Falconer, Heike E. Daldrup-Link. A novel theranostic strategy for MMP-14 expressing glioblastomas impacts survival [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-004.

Long-term outcomes of primarily metastatic juvenile pilocytic astrocytoma in children

OBJECTIVE Primarily metastatic juvenile pilocytic astrocytoma (JPA) is rare, likely representing 2%-3% of all cases of JPA. Due to the rarity of primarily metastatic JPA, there is currently no standard treatment paradigm and the long-term outcomes are not fully known. The goal of this case series was to add to the current understanding of this disease process. METHODS The authors searched a comprehensive database of pediatric patients with brain and spinal cord tumors treated at Lucile Packard Children's Hospital from 1997 to 2016 and identified 5 patients with primarily metastatic JPA. A retrospective chart review was performed and details of the patients' treatment and clinical course were recorded for further analysis. RESULTS For the 5 patients with primarily metastatic JPA, the mean follow-up period was 12.3 years. All patients in our series had biopsies or subtotal resections and upfront treatment. Three patients were treated with chemotherapy alone, one was treated with chemotherapy and radiotherapy, and one was treated with radiotherapy alone. Four patients had stable disease after initial treatment, and one patient had multiple episodes of progressive disease but underwent successful salvage therapy and has had stable disease for 19 years. One patient died of an intracerebral hemorrhage 10 years following initial radiation treatment believed to be secondary to radiation vasculopathy. CONCLUSIONS Evaluation of the entire neuraxis should be performed in all instances of initial JPA diagnosis to properly assess for primarily metastatic disease. Many patients with primarily metastatic JPA will have stable disease after upfront treatment, although the higher rate of stable disease found in this series relative to other reports is likely secondary to the small sample size.

A Novel Theranostic Strategy for MMP-14-Expressing Glioblastomas Impacts Survival

Glioblastoma (GBM) has a dismal prognosis. Evidence from preclinical tumor models and human trials indicates the role of GBM-initiating cells (GIC) in GBM drug resistance. Here, we propose a new treatment option with tumor enzyme-activatable, combined therapeutic and diagnostic (theranostic) nanoparticles, which caused specific toxicity against GBM tumor cells and GICs. The theranostic cross-linked iron oxide nanoparticles (CLIO) were conjugated to a highly potent vascular disrupting agent (ICT) and secured with a matrix-metalloproteinase (MMP-14) cleavable peptide. Treatment with CLIO-ICT disrupted tumor vasculature of MMP-14-expressing GBM, induced GIC apoptosis, and significantly impaired tumor growth. In addition, the iron core of CLIO-ICT enabled in vivo drug tracking with MR imaging. Treatment with CLIO-ICT plus temozolomide achieved tumor remission and significantly increased survival of human GBM-bearing mice by more than 2-fold compared with treatment with temozolomide alone. Thus, we present a novel therapeutic strategy with significant impact on survival and great potential for clinical translation. Mol Cancer Ther; 16(9); 1909-21. ©2017 AACR.

Neural Placode Tissue Derived From Myelomeningocele Repair Serves as a Viable Source of Oligodendrocyte Progenitor Cells

BACKGROUND

The presence, characteristics, and potential clinical relevance of neural progenitor populations within the neural placodes of myelomeningocele patients remain to be studied. Neural stem cells are known to reside adjacent to ependyma-lined surfaces along the central nervous system axis.

OBJECTIVE

Given such neuroanatomic correlation and regenerative capacity in fetal development, we assessed myelomeningocele-derived neural placode tissue as a potentially novel source of neural stem and progenitor cells.

METHODS

Nonfunctional neural placode tissue was harvested from infants during the surgical repair of myelomeningocele and subsequently further analyzed by in vitro studies, flow cytometry, and immunofluorescence. To assess lineage potential, neural placode-derived neurospheres were subjected to differential media conditions. Through assessment of platelet-derived growth factor receptor α (PDGFRα) and CD15 cell marker expression, Sox2+Olig2+ putative oligodendrocyte progenitor cells were successfully isolated.

RESULTS

PDGFRαCD15 cell populations demonstrated the highest rate of self-renewal capacity and multipotency of cell progeny. Immunofluorescence of neural placode-derived neurospheres demonstrated preferential expression of the oligodendrocyte progenitor marker, CNPase, whereas differentiation to neurons and astrocytes was also noted, albeit to a limited degree.

CONCLUSION

Neural placode tissue contains multipotent progenitors that are preferentially biased toward oligodendrocyte progenitor cell differentiation and presents a novel source of such cells for use in the treatment of a variety of pediatric and adult neurological disease, including spinal cord injury, multiple sclerosis, and metabolic leukoencephalopathies.

Abstract PR12: Overcoming immune evasion in pediatric hematologic and solid tumor malignancies: A preclinical study using a humanized anti-CD47 antibody

CD47 is an anti-phagocytic cell surface protein mediating cancer cell evasion of phagocytosis by the innate immune system. Preclinical data suggest that CD47 is appears to be an indispensable means by which many cancer cells, including cancer stem cells, overcome intrinsic expression of their pro-phagocytic “eat me” signals. Blockade of CD47 with mAbs enables phagocytosis of cancer cells in vitro and in vivo. We have developed a novel humanized mAb (huCD47-Ab) that specifically binds CD47 and blocks it from interacting with its ligand, signal regulatory protein–α; (SIRPα), on phagocytic cells, resulting in the phagocytosis and elimination of cancer cells through their “eat me” signals. Normal cells generally do not express eat me signals, and are unaffected by CD47 blocking mAb. We observed expression of CD47 on aggressive pediatric tumors, including acute lymphoblastic leukemia (ALL), acute myelogenous leukemia (AML), Ewing's sarcoma, neuroblastoma, and several cancers of the central nervous system (CNS), including atypical tetroid rhabdoid tumor (ATRT), primitive neuroectodermal tumor (PNET), medulloblastoma (MB), and pediatric high-grade glioma (pHGG). In-vitro phagocytosis assays, of primary patient samples shows significant engulfment by human peripheral blood derived macrophages upon incubation with the HuCD47-Ab antibody as compared to control. Furthermore we observe potent anti-tumor efficacy and survival benefit in MB, pHGG, ATRT and PNET orthotopic xenografts models establishing the ability of the huCD47 antibody to across the blood brain barrier by the CD47 blocking antibody. Using a novel human neural stem cell/brain tumor co-engraftment orthotopic xenograft model we show specificity of the HuCD47 antibody to only tumor cells and not normal human cells. We further observe potent anti-tumor efficacy in non-CNS tumor (ALL, AML and Osteosarcoma) xenograft models as well.

Furthermore we demonstrate that HuCD47-Ab can be administered safely to non-human primates at therapeutic serum levels. Pre-IND and IMPD meetings with the FDA in the US and the MHRA in the UK, have been held, and the clinical trials for adult patients with advanced stage malignancies will start in early 2014. After determining safety in these phase I trials, we initiate protocols for adult CNS tumors as part of expansion cohorts, and subsequently extend the trials to pediatric cancer patients, given manageable toxicity and signs of efficacy in the adult patients.

This abstract is also presented as Poster A86.

Citation Format: Siddhartha S. Mitra, Sharareh Gholamin, Jens-Peter Volkmer, Abdullah Feroze, Jie Liu, Achal Achrol, Lijuan Wang, Leanne Sayles, Michael Zhang, Kathleen Sakamoto, Michelle Monje-Deisseroth, Yoon-Jae Cho, Alejandro Sweet-Cordero, Ravi Majeti, Samuel Cheshier, Irving Weissman. Overcoming immune evasion in pediatric hematologic and solid tumor malignancies: A preclinical study using a humanized anti-CD47 antibody. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr PR12.

Abstract 4041: Involvement of Notch1 signaling pathway in medulloblastoma metastasis

Medulloblastoma (MB) is a malignant brain tumor that originates in the cerebellum in children and spreads via the cerebrospinal fluid to the leptomeningeal spaces of the brain and of the spinal cord. MB is stratified into four distinct groups, according to genetic and clinical features, and patients from group 3 (also known as c-Myc-amplified group) have the highest risk of developing metastatic disease and, consequently, a poor prognosis. Treatment protocols involve surgery, craniospinal radiation, and high-dose chemotherapy, which frequently cause disabling neurotoxic effects in long-term survivors. We used MB cell lines and primary cells isolated from patients from the c-Myc-amplified group to develop a spontaneous spinal metastasis orthotopic xenograft model as a tool to understand the cellular determinants of leptomeningeal and spinal dissemination. Human cells isolated from the primary site tumors expressed 10 fold higher NICD1 (Notch1 Intracellular Domain), the active form of Notch1, than cells isolated from spinal metastatic sites (as quantified by western blot and imunohistochemistry), suggesting the downregulation of canonical Notch1 signaling pathway in MB metastasis. Moreover, flow cytometry analyses revealed that a higher percentage of cells isolated from metastatic sites expressed full-length surface Notch1 as compared to the primary site tumor. These differences cannot be explained by enrichment in the stem cell population at primary tumor sites, as we observed that MB cells isolated from primary tumors and metastatic sites exhibit equivalent self-renewal potential and express equivalent levels of CD133 and CD15. Our goal is to understand the role of notch in regulating medulloblastoma metastasis.

Citation Format: Suzana A. Kahn, Sharareh Gholamin, Michael Zhang, Ryan Nitta, Irving Weissman, Siddhartha Mitra, Samuel Cheshier. Involvement of Notch1 signaling pathway in medulloblastoma metastasis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4041. doi:10.1158/1538-7445.AM2014-4041

Abstract LB-207: mTORC2/Akt signaling is modulated by noncanonical mitochondrial Notch1/PINK1 interaction in myc-amplified medulloblastoma tumorigenesis

Medulloblastoma is known to be the most malignant pediatric brain tumor. The armamentarium of targeted therapies to currently treat medulloblastoma and similar pediatric central nervous system malignancies is extremely limited, often necessitating the need to combat such tumors with modified regimens of therapeutic options designed originally to target adult neoplasms. Given such limited therapies, a budding focus on the role of mitochondrial dysregulation in the tumorigenesis of such pathologies merits consideration. Mitochondria are known to play fundamental roles in multiple processes conserved across eukaryotic species. Aside from their key role in energy production through oxidative phosphorylation, the organelles also serve as the sites of essential metabolic pathways, redox regulation, calcium homeostasis, apoptosis, and cell fate determination and differentiation.

Recently, we documented the role of noncanonical Notch signaling and mitochondrial involvement in adult glioblastoma brain tumor-initiating cells (Lee KS et al., Genes and Development, 2013). Although the canonical Notch pathway and is generally well-characterized, involving the ligand-induced cleavage of Notch for transcriptional regulation, only more recently has credible evidence surfaced documenting the role of a second noncanonical pathway, where Notch can function independently of ligand and transcription through a mechanism that remains to be fully elucidated. The regulatory self-renewal versus differentiation choice of Drosophila and mammalian human neural stem cells requires Notch signaling, and in our work, we found noncanonical Notch pathway interaction with PTEN-induced putative kinase 1 (PINK1) to influence mitochondrial function, activating mTORC2/Akt signaling. siRNA-induced knockdown preferentially impaired the maintenance of Drosophila and human glioblastoma cancer stem cell-like tumor-forming cells to a far greater degree than normal stem cell counterparts.

Further experiments have elucidated similar findings of increased Notch1/PINK1 mitochondrial interaction and mTORC2/Akt activity in patient-derived Group 3 (myc-amplified) medulloblastoma primary lines to levels greater than normal or glioblastoma samples. Additionally these medulloblastoma samples appear to be more susceptible to siRNA-induced knockdown of PINK1 than their counterparts. In vivo experiments are ongoing to address the role of mitochondrial Notch1/Pink1 interaction in tumor initiation and its targeting by small molecule inhibitors. Such results underscore the importance of mitochondria in both normal and cancer stem cell biology, a highly conserved mechanism across species, with exciting implications for the treatment of pediatric central nervous system malignancies.

Citation Format: Abdullah H. Feroze, Kyu-Sun Lee, Sharareh Gholamin, Zhihao Wu, Irving Weissman, Bingwei Lu, Siddhartha S. Mitra, Samuel Cheshier. mTORC2/Akt signaling is modulated by noncanonical mitochondrial Notch1/PINK1 interaction in myc-amplified medulloblastoma tumorigenesis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-207. doi:10.1158/1538-7445.AM2014-LB-207