Investigation of MYC-driven group 3 medulloblastoma using novel regulable cell based models

Abstract

Introduction: Medulloblastoma (MB) is the most common malignant brain tumour to occur in children, accounts for 10% deaths in children and has four distinct molecular subgroups. These subgroups are known as MBWNT, MBSHH, MBGRP3, MBGRP4. Patients with MBGRP3 have the worst outcome with an overall survival of ~ 50%. MBGRP3 patients commonly present with metastatic disease, large cell/anaplastic (LCA) histology and/or high MYC expression or gene amplification. MYC amplification is the strongest adverse prognostic factor, however MYC-dependent biology within MBGRP3 tumours remains poorly understood. Method: Doxycycline (DOX)-inducible MYC silencing isogenic models (D425Med and HDMB03, two MYC amplified MBGRP3 cell lines) were generated and used to characterize MYC-dependent phenotypic changes by measurement of parameters including: cellular proliferation, cell cycle and induction of apoptosis. mRNAseq analysis was performed in these isogenic models to investigate the effect of MYC modulation on the transcriptional profile and to identify key downstream pathways which may highlight suitable therapeutic approaches. Results: Silencing of MYC within D425Med resulted in a significant reduction in proliferation, G1 growth arrest and decreased apoptosis compared with controls. A less pronounced effect was seen in HDMB03. These results demonstrate that D425Med depends on and needs MYC for rapid proliferation. RNAseq analysis highlighted specific pathways and genes regulated by MYC and dysregulated in primary MBGRP3 such as the mTOR signalling pathway. Conclusion: Transcriptome analysis in the DOX-inducible MYC silencing isogenic models identified key pathways and genes regulated by MYC and dysregulated in primary MBGRP3. These pathways identified are those involved in cell cycle control, metabolism, differentiation and signalling pathways which could be therapeutically targeted.