title: Activation of downstream epidermal growth factor receptor (EGFR) signaling provides gefitinib-resistance in cells carrying EGFR mutation.
abstract: Patients with pulmonary adenocarcinoma carrying the epidermal growth factor receptor (EGFR) mutation tend to display dramatic clinical response to treatment with the EGFR tyrosine kinase inhibitor gefitinib. Unfortunately, in many cases the cancer cells eventually acquire resistance, and this limits the duration of efficacy. To gain insight into these acquired resistance mechanisms, we first prepared HEK293T cell line stably transfected with either wild-type (WT) or mutant (L858R) EGFR, and then expressed oncogenic K-Ras12V mutant in the latter transfectant. Although 293T cells expressing wild-type EGFR did not show any growth inhibition by gefitinib treatment similarly to the non-transfected cells, the cells expressing the EGFR-L858R were exquisitely sensitive. Consistently, phospho-Akt levels were decreased in response to gefitinib in cells expressing EGFR-L858R but not in cells with EGFR-WT. In contrast, 293T cells expressing both EGFR-L858R and oncogenic K-Ras were able to proliferate even in the presence of high concentration of gefitinib probably by inducing Erk1/2 activation. We also expressed K-Ras12V in the gefitinib-sensitive pulmonary adenocarcinoma cell line PC-9, which harbors an in-frame deletion in the EGFR gene. The activated K-Ras inhibited the effects of gefitinib treatment on cell growth, cell death induction and levels of phospho-Akt, as well as phospho-Erk. These data indicate that activated Ras could substitute most of the upstream EGFR signal, and are consistent with the hypothesis that mutational activation of targets immediately downstream from the EGFR could induce the secondary resistance to gefitinib in patients with lung cancer carrying EGFR mutation.
authors.affiliation: Department of Hematology, Oncology and Respiratory Medicine, Graduate School of Medicine and Dentistry, Okayama University, Okayama, Okayama 700-8558, Japan.
authors.forename: Akiko
authors.initials: A
authors.lastname: Uchida
authors.forename: Seiki
authors.initials: S
authors.lastname: Hirano
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kitao
authors.forename: Atsuko
authors.initials: A
authors.lastname: Ogino
authors.forename: Kanmei
authors.initials: K
authors.lastname: Rai
authors.forename: Shinichi
authors.initials: S
authors.lastname: Toyooka
authors.forename: Nagio
authors.initials: N
authors.lastname: Takigawa
authors.forename: Masahiro
authors.initials: M
authors.lastname: Tabata
authors.forename: Minoru
authors.initials: M
authors.lastname: Takata
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Kiura
authors.forename: Mitsune
authors.initials: M
authors.lastname: Tanimoto
mesh_terms: D000230:Adenocarcinoma / Q000188:drug therapy / Q000235:genetics / Q000473:pathology; D000970:Antineoplastic Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm; D066246:ErbB Receptors / Q000235:genetics* / Q000378:metabolism; D000077156:Gefitinib; D011905:Genes, ras; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000473:pathology; D009154:Mutation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011799:Quinazolines / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection
chemical_list: D000970:Antineoplastic Agents; D011799:Quinazolines; D066246:ErbB Receptors; D051057:Proto-Oncogene Proteins c-akt; D000077156:Gefitinib