title: The epidermal growth factor receptor pathway mediates resistance to sequential administration of radiation and chemotherapy in primary human glioblastoma cells in a RAS-dependent manner.
abstract: 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 cross-resistance 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), mitogen-activated 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 PI3-K/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.
authors.affiliation: Department of Radiation Oncology, Massachusetts General Hospital/Harvard Medical School, Charlestown, Massachusetts 02129, USA. achakravarti@partners.org
authors.forename: Arnab
authors.initials: A
authors.lastname: Chakravarti
authors.forename: Abhijit
authors.initials: A
authors.lastname: Chakladar
authors.forename: Meaghan A
authors.initials: MA
authors.lastname: Delaney
authors.forename: Douglas E
authors.initials: DE
authors.lastname: Latham
authors.forename: Jay S
authors.initials: JS
authors.lastname: Loeffler
mesh_terms: D018906:Antineoplastic Agents, Alkylating / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D001932:Brain Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000532:radiotherapy*; D002330:Carmustine / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D003131:Combined Modality Therapy; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation; D066246:ErbB Receptors / Q000502:physiology*; D005909:Glioblastoma / Q000188:drug therapy* / Q000201:enzymology / Q000532:radiotherapy*; D006801:Humans; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D011836:Radiation Tolerance; D014407:Tumor Cells, Cultured; D018631:ras Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*
chemical_list: D018906:Antineoplastic Agents, Alkylating; D002330:Carmustine; D066246:ErbB Receptors; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D018631:ras Proteins; C494918:AKT1 protein, human