DDRE-38. MAGMAS INHIBITION IN MEDULLOBLASTOMA CELL CULTURES AND PATIENT-DERIVED XENOGRAFT MODELS: POTENTIAL THERAPEUTIC IMPLICATIONS

BACKGROUND Brain tumors are the second most common type of pediatric cancer and are the leading cause of all cancer-related deaths in children. Medulloblastoma (MB) is the most common type of malignant pediatric brain tumor and has a five-year overall survival ranging from 40-75%, depending on the patient’s age and other prognostic features. There are current anti-cancer therapies against medulloblastoma, but the treatment of recurrent disease remains a challenge. Magmas (mitochondria-associated protein involved in granulocyte-macrophage colony-stimulating factor signal transduction) overexpression has been reported in multiple types of metabolically active tissue and cancer cells, including prostate cancer, pituitary adenoma, and glioma. Limited data suggest that specific subgroups of medulloblastoma may also overexpress Magmas. This study aims to examine whether Magmas inhibition by compound “BT#9” could be beneficial for the treatment of medulloblastoma. METHODS We studied the ability of a Magmas inhibitor (BT#9) as a therapeutic agent in stable medulloblastoma cell lines (DAOY and D283) and patient-derived primary cultures with MTT assays, migration assays, and invasion assays. RESULTS Similar to the adult GBM studies, Magmas inhibition by BT9 had significant cytotoxic effects, causing both decreased cell proliferation and blocked cell migration in medulloblastoma cell lines DAOY and D283. IC50s determined for each during different time points demonstrated an average range of less than 3μM compared to the average range seen in adult glioblastoma cell cultures (< 10 μM). These findings suggest that the inhibition of Magmas warrants further investigation as a potential therapeutic target to optimize clinical outcomes in medulloblastoma. Our future studies will include the determination of IC50s for primary cell cultures and in vitro testing with patient-derived xenograft models.

MBRS-27. EXOSOMES CARRY DISTINCT miRNAs THAT DRIVE MEDULLOBLASTOMA PROGRESSION

INTRODUCTION Extracellular vesicles (EVs) represent an ideal source of functional biomarkers due to their role in intercellular communication and their ability to protect cargo, including RNA, from degradation. The most investigated EV’s are exosomes, nanovesicles secreted by all cell types and able to cross the blood-brain-barrier. Here we characterised the RNA of exosomes isolated from medulloblastoma cell lines, with the aim of investigating exosomal RNA cargo as potential functional biomarkers for medulloblastoma. METHODS Exosomes derived from a panel of matched (original tumour and metastasis) medulloblastoma cell lines were isolated and characterised by NanoSight, electron microscopy, western blotting and Nanoscale flow cytometry. Exosomal miRNA and mRNA from our matched cell lines and foetal neuronal stem cells, which were used as a normal control, were analysed by RNA-sequencing technology. RESULTS Based on hierarchical clustering, malignant derived exosomes were distinctly separated from normal control exosomes. miRNA profiling revealed several established oncomiRs identified in our malignant derived exosomes compared to control samples. Using interaction pathway analysis, we identified that our malignant exosomes carry numerous miRNAs implicated in migration, proliferation, cellular adhesion and tumour growth. Several previously identified oncomiRs were also identified to be present at higher levels in metastatic exosomes compared to primary and normal, including hsa-miR-455-3p and hsa-miR-92a-3p. CONCLUSION This study shows that exosomes from MB cells carry a distinct miRNA cargo which could enhance medulloblastoma progression. The use of circulating exosomes as markers of metastatic disease could be an innovative and powerful non-invasive tool.

Characterization of G-CSF receptor expression in medulloblastoma

Background Identifying mechanisms of medulloblastoma recurrence is a key to improving patient survival, and targeting treatment-resistant subpopulations within tumors could reduce disease recurrence. Expression of the granulocyte colony-stimulating factor receptor (G-CSF-R, CD114) is a potential marker of cancer stem cells, and therefore we hypothesized that a subpopulation of medulloblastoma cells would also express CD114 and would demonstrate chemoresistance and responsiveness to G-CSF. Methods Prevalence of CD114-positive (CD114+) cells in medulloblastoma cell lines, patient-derived xenograft (PDX) tumors, and primary patient tumor samples were assessed by flow cytometry. Growth rates, chemoresistance, and responses to G-CSF of CD114+ and CD114-negative (CD114−) cells were characterized in vitro using continuous live cell imaging and flow cytometry. Gene expression profiles were compared between CD114+ and CD114− medulloblastoma cells using quantitative RT-PCR. Results CD114+ cells were identifiable in medulloblastoma cell lines, PDX tumors, and primary patient tumors and have slower growth rates than CD114− or mixed populations. G-CSF accelerates the growth of CD114+ cells, and CD114+ cells are more chemoresistant. The CD114+ population is enriched when G-CSF treatment follows chemotherapy. The CD114+ population also has higher expression of the CSF3R, NRP-1, TWIST1, and MYCN genes. Conclusions Our data demonstrate that a subpopulation of CD114+ medulloblastoma cells exists in cell lines and tumors, which may evade traditional chemotherapy and respond to exogenous G-CSF. These properties invite further investigation into the role of G-CSF in medulloblastoma therapy and methods to specifically target these cells.