PDTB-11. DISRUPTING THE EPIGENETIC MODIFIER HMGA2 IN LETHAL PEDIATRIC AND ADULT GLIOMAS INHIBITS INVASION, GROWTH AND TUMORIGENICITY

Abstract

Diffuse intrinsic pontine glioma (DIPG) and glioblastoma (GBM) are highly infiltrative, incurable pediatric and adult brain tumors characterized by the presence of tumor stem-like cells. Although DIPG and GBM have different epigenetic drivers, we found increased expression of an epigenetic modifier and stem cell factor HMGA2 in both tumors by immunohistochemistry and western blotting. HMGA2 is a DNA-binding protein that regulates transcription in normal and cancer stem cells. We hypothesized that HMGA2 contributes to high grade glioma tumorigenicity through its ability to alter the transcription of many genes. Lentiviral short hairpin RNA (shRNA)-mediated reduction of HMGA2 in multiple patient-derived GBM cell lines significantly reduced invasion in transwell assay and colony formation in soft agar assay (shHMGA2 vs. shControl, P<0.01). Similarly, shRNA mediated suppression of HMGA2 in DIPG cell lines reduced proliferation (BrdU incorporation), reduced invasion (transwell assay) and increased apoptosis (cleaved caspase-3 immunofluorescence, shHMGA2 vs. shControl, P<0.001). Pharmacological inhibition of HMGA proteins using the DNA minor-groove binding drug Netropsin significantly inhibited proliferation and increased apoptosis of DIPG cell lines (P<0.01). Mice bearing orthotopic GBM xenografted cells transduced with HMGA2 shRNA lived significantly longer (108 days) compared to control shRNA (67.5 days, P<0.0001 by log-rank analysis). To investigate the mechanism of HMGA2-mediated malignancy, we discovered high levels of CD44 (a known mediator of invasion and stemness) that correlated with high HMGA2 expression in DIPG and GBM tumors. Suppression of HMGA2 led to decreased CD44 protein expression. Knockdown of CD44 in HMGA2-high DIPG and GBM neurospheres reduced invasion and proliferation (P<0.01). Our studies suggest an oncogenic role of HMGA2 and its downstream effectors in gliomas and identify this important pathway as a potential therapeutic target. We conclude that minor groove binding agents similar to Netropsin may be effective agents for HMGA2-expressing pediatric and adult high grade gliomas.