Glioblastoma is one of the most aggressive central nervous system tumors, which constitutes 50% of all primary brain tumors. Glioblastomas have a very poor prognosis, approximately 12-15 months even with standard therapy. Current treatment protocols include surgery, chemotherapy, and radiotherapy. High rates of recurrence after treatment, genetic heterogeneity, and developing resistance to chemotherapy and radiotherapy are challenges to overcome in glioblastoma treatment. Therefore, developing models of chemo- or radio-resistance is of priority to understand the molecular mechanisms that operate during the transition of cells to therapy-refractory state, and to develop new therapeutic approaches. In this study, we generated ionizing radiation (IR)-exposed glioblastoma cell populations to investigate molecular alterations associated with acquired radiotherapy resistance. To generate a clinically relevant radioresistance model, we have exposed glioblastoma cells to a total dose of 60 Gy IR over a 6-week period and cultured age-matched parental cells. We successfully generated sustainable radioresistant cells, as demonstrated by cell viability and colony formation assays. RNA sequencing, performed on these matched cell lines revealed major alterations in the expression of genes of the cell cycle, DNA damage recognition, and repair machinery in the radioresistant cells. Specifically, elements of the DNA double strand break (DSB) recognition and repair, such as ATM, ATR, and CHK1 were markedly upregulated in the radioresistant cell populations. In line with these findings, DNA repair capacity of the radioresistant cell populations was increased, as revealed by the faster clearance of H2AX and 53BP1 in the radioresistant populations. Complementing this approach, pharmacological inhibition of major DNA damage response elements, such as ATM, ATR, as well as CHK1 markedly sensitized the radioresistant cells. Our results prepare a groundwork for studying the molecular mechanisms of radiotherapy resistance and developing novel combination therapy strategies for glioblastomas.
Citation Format: Nareg Pinarbasi, Tugba Bagci-Onder, Ilknur Sur Erdem, Ugur Selek. Investigation of ionizing radiation response in new resistance models of glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3064.
