Targeting mTOR to overcome epidermal growth factor receptor tyrosine kinase inhibitor resistance in non-small cell lung cancer cells

• Published in: PloS one Vol. 8; no. 7; p. e69104
• Main Authors: Fei, Shi-Jiang, Zhang, Xu-Chao, Dong, Song, Cheng, Hua, Zhang, Yi-Fang, Huang, Ling, Zhou, Hai-Yu, Xie, Zhi, Chen, Zhi-Hong, Wu, Yi-Long
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 16.07.2013; Public Library of Science (PLoS)
• Subjects: AKT protein; Analysis; Antineoplastic Agents - pharmacology; Biology; Biotechnology; Cancer; Cancer therapies; Carcinoma, Non-Small-Cell Lung - drug therapy; Carcinoma, Non-Small-Cell Lung - metabolism; Cell cycle; Cell Line, Tumor; Cytometry; Drug Resistance, Neoplasm - drug effects; Enzyme inhibitors; Epidermal growth factor; Epidermal growth factor receptors; Epidermal growth factors; Feasibility studies; Flow cytometry; FOXO1 protein; Humans; Immunoprecipitation; In Vitro Techniques; Inhibitors; Kinases; Lung cancer; Lung diseases; Medicine; Morpholines - pharmacology; Mutation; Non-small cell lung cancer; Non-small cell lung carcinoma; Phenols (Class of compounds); Phosphorylation; Protein Kinase Inhibitors - therapeutic use; Protein-tyrosine kinase receptors; Pyrimidines - pharmacology; Rapamycin; Receptor, Epidermal Growth Factor - antagonists & inhibitors; Receptor, Epidermal Growth Factor - metabolism; Signal transduction; Signal Transduction - drug effects; Signaling; Small cell lung cancer; Substrates; TOR protein; TOR Serine-Threonine Kinases - metabolism; Tyrosine; United States > US; China
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0069104

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) have shown dramatic clinical benefits in advanced non-small cell lung cancer (NSCLC); however, resistance remains a serious problem in clinical practice. The present study analyzed mTOR-associated signaling-pathway differences between the EGFR TKI-sensitive and -resistant NSCLC cell lines and investigated the feasibility of targeting mTOR with specific mTOR inhibitor in EGFR TKI resistant NSCLC cells. We selected four different types of EGFR TKI-sensitive and -resistant NSCLC cells: PC9, PC9GR, H1650 and H1975 cells as models to detect mTOR-associated signaling-pathway differences by western blot and Immunoprecipitation and evaluated the antiproliferative effect and cell cycle arrest of ku-0063794 by MTT method and flow cytometry. In the present study, we observed that mTORC2-associated Akt ser473-FOXO1 signaling pathway in a basal state was highly activated in resistant cells. In vitro mTORC1 and mTORC2 kinase activities assays showed that EGFR TKI-resistant NSCLC cell lines had higher mTORC2 kinase activity, whereas sensitive cells had higher mTORC1 kinase activity in the basal state. The ATP-competitive mTOR inhibitor ku-0063794 showed dramatic antiproliferative effects and G1-cell cycle arrest in both sensitive and resistant cells. Ku-0063794 at the IC50 concentration effectively inhibited both mTOR and p70S6K phosphorylation levels; the latter is an mTORC1 substrate and did not upregulate Akt ser473 phosphorylation which would be induced by rapamycin and resulted in partial inhibition of FOXO1 phosphorylation. We also observed that EGFR TKI-sensitive and -resistant clinical NSCLC tumor specimens had higher total and phosphorylated p70S6K expression levels. Our results indicate mTORC2-associated signaling-pathway was hyperactivated in EGFR TKI-resistant cells and targeting mTOR with specific mTOR inhibitors is likely a good strategy for patients with EGFR mutant NSCLC who develop EGFR TKI resistance; the potential specific roles of mTORC2 in EGFR TKI-resistant NSCLC cells were still unknown and should be further investigated.