Enhanced autophagy is required for survival in EGFR-independent EGFR-mutant lung adenocarcinoma cells

• Published in: Laboratory investigation Vol. 93; no. 10; pp. 1137 - 1146
• Main Authors: Sakuma, Yuji, Matsukuma, Shoichi, Nakamura, Yoshiyasu, Yoshihara, Mitsuyo, Koizume, Shiro, Sekiguchi, Hironobu, Saito, Haruhiro, Nakayama, Haruhiko, Kameda, Yoichi, Yokose, Tomoyuki, Oguni, Sachiko, Niki, Toshiro, Miyagi, Yohei
• Format: Journal Article
• Language: English
• Published: New York Nature Publishing Group US 01.10.2013; Nature Publishing Group
• Subjects: 631/67/1612; 631/80/82/39; Adenocarcinoma - drug therapy; Adenocarcinoma - genetics; Adenocarcinoma - metabolism; Adenocarcinoma - ultrastructure; Adenocarcinoma of Lung; Adult; Aged; Antineoplastic Agents - pharmacology; Autophagy - drug effects; Autophagy-Related Protein 5; Cell Hypoxia - drug effects; Cell Line, Tumor; Cell Survival; Drug Resistance, Neoplasm; Epithelial-Mesenchymal Transition; ErbB Receptors - antagonists & inhibitors; ErbB Receptors - genetics; ErbB Receptors - metabolism; Female; Humans; Laboratory Medicine; Lung - drug effects; Lung - metabolism; Lung - pathology; Lung Neoplasms - drug therapy; Lung Neoplasms - genetics; Lung Neoplasms - metabolism; Lung Neoplasms - ultrastructure; Male; Medicine; Medicine & Public Health; Microtubule-Associated Proteins - antagonists & inhibitors; Microtubule-Associated Proteins - genetics; Microtubule-Associated Proteins - metabolism; Mutant Proteins - antagonists & inhibitors; Mutant Proteins - metabolism; Neoplasm Proteins - antagonists & inhibitors; Neoplasm Proteins - genetics; Neoplasm Proteins - metabolism; Pathology; Phagosomes - drug effects; Phagosomes - metabolism; Phagosomes - ultrastructure; Protein Kinase Inhibitors - pharmacology; research-article; RNA Interference; mutation; autophagy; epithelial-to-mesenchymal transition (EMT); acquired resistance; lung adenocarcinoma
• ISSN: 0023-6837; 1530-0307
• DOI: 10.1038/labinvest.2013.102

Lung cancers harboring epidermal growth factor receptor ( EGFR ) mutations depend on constitutive activation of the kinase for survival. Although most EGFR -mutant lung cancers are sensitive to EGFR tyrosine kinase inhibitors (TKIs) and shrink in response to treatment, acquired resistance to TKI therapy is common. We demonstrate here that two EGFR -mutated lung adenocarcinoma cell lines, HCC827 and HCC4006, contain a subpopulation of cells that have undergone epithelial-to-mesenchymal transition and survive independent of activated EGFR. These EGFR-independent cancer cells, herein termed gefitinib-resistant (GR) cells, demonstrate higher levels of basal autophagy than their parental cells and thrive under hypoxic, reduced-serum conditions in vitro ; this somewhat simulates the hypoxic environment common to cancerous tissues. We show that depletion of the essential autophagy gene, ATG5 , by small interfering RNA (siRNA) or chloroquine, an autophagy inhibitor, markedly reduces GR cell viability under hypoxic conditions. Moreover, we show a significant elevation in caspase activity in GR cells following knockdown of ATG5. These results suggest that GR cells can evade apoptosis and survive in hostile, hypoxic environments with constant autophagic flux. We also show the presence of autophagosomes in some cancer cells from patient samples, even in untreated EGFR -mutant lung cancer tissue samples. Together, our results indicate that autophagy inhibitors alone or in combination with EGFR TKIs may be an effective approach for the treatment of EGFR -mutant lung cancers, where basal autophagy of some cancer cells is upregulated.