DNAR-08. THY1 MEDIATES TREATMENT RESISTANCE IN GLIOBLASTOMA THROUGH RAPID REPAIR OF DNA DAMAGE

Abstract Glioblastoma (GBM) is a uniformly lethal primary intracranial neoplasm that inevitably recurs despite treatment by DNA damaging agents radiation (RT) and temozolomide (TMZ). Recurrence may be driven by inherently resistant glioma stem-like cells (GSCs). GSCs have been shown to have constitutive upregulation of DNA damage response (DDR) pathways, resulting from elevated DNA replication stress. This baseline elevated DDR has consequently been shown to confer inherent resistance to DNA damaging agents, TMZ/RT. However, factors mediating elevated replication stress and upregulated DDR in GSCs are poorly defined. Previously, we identified the cell-surface protein, THY1, as a mediator of GSC phenotype and treatment resistance in GBM. To determine mechanisms mediating treatment resistance in THY1+ cells, we engineered patient-derived neurosphere and organoid models, to either overexpress or silence THY1 expression. These models were treated with RT and collected at various time points to measure DNA repair efficiency by assessing the formation and resolution of yH2AX foci and ATM/ATR activation. In parallel, patient-derived GBM tissue from over 20 patients was analyzed using single cell RNA sequencing and spatial transcriptomics to assess pathways associated with THY1 expression. Interestingly, spatial transcriptomics and single cell RNA sequencing data demonstrates significant upregulation of GSC pathways, as well as constitutive upregulation of DDR pathways (p<2e-16) in THY1-high cells. Exploiting our patient-derived lines we determined that DNA repair activation was upregulated at baseline, measured using yH2AX foci and immunoblotting. We then measured DDR in response to radiation and found that high THY1 expression mediated rapid repair of DNA. Overall, we demonstrate that THY1 mediates therapy resistance by constitutively upregulating DDR, likely by upregulating DNA replication stress. We are now working to determine the mechanisms mediating the GSC phenotype and DNA replication stress in THY1 cells in hopes of future translation.