Rbio-09. hmgb2 inhibition radio-sensitizes glioblastoma cells independently of their tp53-mutation status

Abstract Alterations in TP53 are major drivers of radiation resistance in gliomas. High Mobility Group Box 2 (HMGB2) has been implicated in resistance to temozolomide through p53-phosphorylation during DNA double-strand break repair and in silico analysis suggests its involvement in the p53-p21-RB signaling pathway. Nevertheless, the role of HMGB2 in radiation response has not been fully explored in gliomas. While HMGB2 is virtually not expressed in the normal adult brain, increasing expression with histopathological glioma grade correlates with poor patient survival. We confirmed increased HMGB2 expression in grade 3 compared to grade 2 gliomas using ClariomD and observed spatial heterogeneous HMGB2 expression in glioblastomas (GBMs) in histopathology-targeted supervised proteomic analysis employing liquid chromatography tandem mass spectroscopy (LC-MS-MS). Here, we aimed to study HMGB2 effects in cell proliferation and response to radiation in a set of molecularly distinct genetically engineered GBM cell lines (IDHwt). Using an established U87 GBM cell line and isogenic primary GBM cell lines GBM3359 TP53wt and CRISPR/Cas9-engineered mutant TP53 (R248W) generated in our laboratory, we successfully produced clones with either HMGB2 shRNA knockdown (KD – over 70% reduction) or HMGB2 lentiviral-mediated overexpression (OE – 3-76x higher expression). HMGB2-KD reduced cell proliferation (10% in U87; 20-25% in isogenic GBM3359 cell lines) and colony formation (more than 50% reduction), which was further rescued with HMGB2 OE in all cell lines. Half maximal inhibitory concentration (IC50) for radiation was determined by methylene blue cell proliferation and clonogenic assays, which showed that HMGB2-KD decreased the IC50 while rescued HMGB2 OE increased RT resistance of all clones. Taken together, our data suggest that HMGB2 inhibition may improve radiation response independently of TP53 status in gliomas. Further mechanistic studies to elucidate the relationship between HMGB2 and TP53 are underway to unfold the contribution of heightened HMGB2 expression to radiation resistance mechanisms in gliomas.