HG-123: AN EPIGENOMIC SCREEN REVEALS THE CHROMATIN REMODELING PROTEIN BPTF AS A DRIVER OF HIGH-GRADE GLIOMA AND DIFFUSE INTRINSIC PONTINE GLIOMA GROWTH IN VITRO AND IN VIVO

INTRODUCTION: High-grade gliomas (HGG) and diffuse intrinsic pontine gliomas (DIPG) account for the majority of pediatric brain tumor deaths and respond poorly to chemotherapy. Individual epigenetic regulators exert widespread control over gene expression and represent novel, druggable targets in cancer therapy. METHODS: We performed sequential pooled small hairpin RNA (shRNA) inhibition screens of all known epigenetic regulators (n = 449) in two patient-derived HGG lines using a neurosphere culture model, followed by a murine orthotopic xenograft model. Each regulator's impact on tumor growth was measured by how significantly shRNAs targeting it dropped in overall frequency, as measured by Illumina sequencing. Targets were validated by correlating single shRNA knockdown, measured by qPCR, with growth effect in multiple patient-derived HGG and DIPG lines compared to a non-targeted shRNA. RNA-Seq was used to compare expression with target knockdown versus non-targeted shRNA. RESULTS: BPTF, the histone-binding component of the NURF chromatin remodeling complex, was found to be the most significant tumor growth driver in vitro (p = 0.00034) and in vivo (p = 0.00028) overall. Using single shRNA screen validation, BPTF knockdown decreased HGG growth by 99.3% and DIPG growth 99.5% in neurosphere culture. BPTF knockdown decreased HGG cell stemness by neurosphere dilution assay. The most significant effects of BPTF knockdown in HGG by RNA-Seq were downregulation of MYC and upregulation of TP53. CONCLUSIONS: The chromatin remodeling protein BPTF was the most significant driver of HGG growth in an unbiased in vitro/in vivo epigenomic screen. It may control HGG and DIPG stemness through regulation of MYC and TP53.