Drug Resistance in Medulloblastoma Is Driven by YB-1, ABCB1 and a Seven-Gene Drug Signature

SIMPLE SUMMARY: Medulloblastoma is the most common malignant childhood brain tumour. Under standard therapy, relapse occurs in 30% of patients and is almost universally fatal, accounting for 10% of all childhood cancer deaths. A barrier to effective medulloblastoma treatment is cellular resistance to standard-of-care therapies. Here, we investigate mechanisms surrounding medulloblastoma therapy resistance, both related to and independent from oncoprotein YB-1. Accordingly, we reveal roles for YB-1 in therapy sensitivity and the regulation of the multi-drug resistance gene ABCB1. We also identify functions for YB-1 in cell invasion, lipid metabolism and activation of the MYC oncoprotein. Importantly, through the generation of cell lines resistant to standard-of-care medulloblastoma therapies, we identify a drug-tolerant gene expression signature which may represent global, targetable mediators of medulloblastoma drug resistance. Together, our findings reveal important mechanisms and genes underlying therapy resistance in medulloblastoma and provide routes to their intervention. ABSTRACT: Therapy resistance represents an unmet challenge in the treatment of medulloblastoma. Accordingly, the identification of targets that mark drug-resistant cell populations, or drive the proliferation of resistant cells, may improve treatment strategies. To address this, we undertook a targeted approach focused on the multi-functional transcription factor YB-1. Genetic knockdown of YB-1 in Group 3 medulloblastoma cell lines diminished cell invasion in 3D in vitro assays and increased sensitivity to standard-of-care chemotherapeutic vincristine and anti-cancer agents panobinostat and JQ1. For vincristine, this occurred in part by YB-1-mediated transcriptional regulation of multi-drug resistance gene ABCB1, as determined by chromatin immunoprecipitation. Whole transcriptome sequencing of YB-1 knockdown cells identified a role for YB-1 in the regulation of tumourigenic processes, including lipid metabolism, cell death and survival and MYC and mTOR pathways. Stable cisplatin- and vincristine-tolerant Group 3 and SHH cell lines were generated to identify additional mechanisms driving resistance to standard-of-care medulloblastoma therapy. Next-generation sequencing revealed a vastly different transcriptomic landscape following chronic drug exposure, including a drug-tolerant seven-gene expression signature, common to all sequenced drug-tolerant cell lines, representing therapeutically targetable genes implicated in the acquisition of drug tolerance. Our findings provide significant insight into mechanisms and genes underlying therapy resistance in medulloblastoma.