RAS-dependent Manner Chemotherapy in Primary Human Glioblastoma Cells in a Resistance to Sequential Administration of Radiation and The Epidermal Growth Factor Receptor Pathway Mediates

作者:Arnab Chakravarti;Abhijit Chakladar;Meaghan A. Delaney;Douglas E. Latham;Jay Steven Loeffler 刊名: 上传者:王克学

【摘要】Resistance to conventional adjuvant therapies (i.e.; chemotherapy and radiation) has been well documented in malignant gliomas. Unlike many other tumor types; combined modality therapy involving radiation and chemotherapy has failed to appreciably enhance outcome for glioblastoma patients compared with radiation alone. In vitro; we have observed an actual antagonistic effect between sequential administration of radiation and 1;3-bis(2-chloroethyl)-1-nitrosourea (BCNU) chemotherapy in three primary human glioblastoma cell lines (referred as the GBME3-5 cell lines); which also happen to demonstrate strong expression of the epidermal growth factor receptor (EGFR). Upon inhibition of EGFR with the EGFR tyrosine kinase inhibitor; AG1478; it was found that this crossresistance between sequential administration of radiation and BCNU was abrogated. To dissect which of these pathways may be responsible for the observed antagonism; known EGFR-regulated downstream signaling pathways including RAS; phosphatidylinositol 3-kinase (PI3-K); mitogenactivated protein kinase (p44/p42); and protein kinase C were inactivated with both pharmacological inhibitors and transient transfection experiments with dominant-negative and constitutively active constructs in the presence of exogenous EGF stimulation. It was found that BCNU inhibited radiation-induced apoptosis through EGFR-mediated activation of PI3K/AKT via RAS. On the other hand; radiation was found to inhibit BCNU-induced apoptosis through EGFR-mediated activation of both PI3-K and mitogen-activated protein kinase (p44/p42) pathways; also via RAS. Inhibition of either EGFR or RAS activity appears to not only abrogate the observed antagonism between sequentially administered radiation and chemotherapy but actually results in a greater enhancement of apoptosis in the setting of combined modality therapy than when administered with either radiation or chemotherapy as single agents. Therefore; these findings suggest that strategies to inactivate EGFR or RAS signaling may be critical to improving not only the efficacy of single-agent therapy but also of combined modality therapy in gliomas.