Abstract #2304: Effects of reirradiation on human glioblastoma cells previously treated with low dose fractionated radiotherapy

Abstract

Glioblastoma multiforme is the most common primary brain tumor in adults and radiotherapy is an important adjuvant treatment in the management of glioblastoma. The radiosensitivities of glioblastomas vary widely with respect to clinically relevant radiation doses. Reirradiation is applied to relapsing primary malignant brain tumors. We treated human glioblastoma cells U87 and SNB19 with low dose fractionated irradiation (FIR) and established sublines. This study aims to focus on biological responses of irradiation on parental and established sublines of FIR. Cells of parental and FIR were exposed to different doses of radiation and cell survival was assessed by the colony formation assay. Induction of apoptosis was measured by cell cycle analysis and Hoechst 33258 staining. MMP-9 activity was evaluated by zymography and tumor cell invasion by in vitro Matrigel assay. We also assessed how reirradiation modulates in vitro angiogenesis. Human microvascular endothelial cells were exposed to conditioned medium from irradiated parental and FIR sublines and endothelial migration and capillary-like structure formation were studied. Reirradiation caused an increase in clonogenic cell survival. A decrease in induction of apoptosis was observed in FIR sublines compared with parental cells and this was found to be associated with an increase in survivin, a member of the inhibitor of apoptosis family and downregulation in the activation of Caspase-9, Caspase-3 and PARP. Increase in MMP-9 activity and invasiveness was found in FIR sublines exposed to irradiation. Reirradiation results in increased activation of ERK and PI3K/Akt signaling pathways in FIR sublines compared with parental cells. The results suggest that glioblastoma tumor cells surviving low dose fractionated radiation therapy, afterwards exhibit enhanced angiogenic potential and increased resistance to induction of apoptosis to a new radiation exposure.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 2304.