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Epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor (TKI) therapy often provides a dramatic response in lung cancer patients with EGFR mutations. In addition, moderate clinical efficacy of the EGFR-TKI, erlotinib, has been shown in lung cancer patients with the wild-type EGFR. Numerous molecular mechanisms that cause acquired resistance to EGFR-TKIs have been identified in lung cancers with the EGFR mutations; however, few have been reported in lung cancers with the wild-type EGFR. We used H358 lung adenocarcinoma cells lacking EGFR mutations that showed modest sensitivity to erlotinib. The H358 cells acquired resistance to erlotinib via chronic exposure to the drug. The H358 erlotinib-resistant (ER) cells do not have a secondary EGFR mutation, neither MET gene amplification nor PTEN downregulation; these have been identified in lung cancers with the EGFR mutations. From comprehensive screening of receptor tyrosine kinase phosphorylation, we observed increased phosphorylation of insulin-like growth factor 1 receptor (IGF1R) in H358ER cells compared with parental H358 cells. H358ER cells responded to combined therapy with erlotinib and NVP-AEW541, an IGF1R-TKI. Our results indicate that IGF1R activation is a molecular mechanism that confers acquired resistance to erlotinib in lung cancers with the wild-type EGFR. [ABSTRACT FROM AUTHOR]

To select the appropriate patients for treatment with epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs), it is important to gain a better understanding of the intracellular pathways leading to EGFR-TKI resistance, which is a common problem in patients with lung cancer. We recently reported that mutant KRAS adenocarcinoma is resistant to gefitinib as a result of amphiregulin and insulin-like growth factor-1 receptor overexpression. This resistance leads to inhibition of Ku70 acetylation, thus enhancing the BAX/Ku70 interaction and preventing apoptosis. Here, we determined the intracellular pathways involved in gefitinib resistance in lung cancers and explored the impact of their inhibition. We analyzed the activation of the phosphatidyl inositol-3-kinase (PI3K)/AKT pathway and the mitogen-activated protein kinase/extracellular-signal regulated kinase (MAPK/ERK) pathway in lung tumors. The activation of AKT was associated with disease progression in tumors with wild-type EGFR from patients treated with gefitinib (phase II clinical trial IFCT0401). The administration of IGF1R-TKI or amphiregulin-directed shRNA decreased AKT signaling and restored gefitinib sensitivity in mutant KRAS cells. The combination of PI3K/AKT inhibition with gefitinib restored apoptosis via Ku70 downregulation and BAX release from Ku70. Deacetylase inhibitors, which decreased the BAX/Ku70 interaction, inhibited AKT signaling and induced gefitinib-dependent apoptosis. The PI3K/AKT pathway is thus a major pathway contributing to gefitinib resistance in lung tumors with KRAS mutation, through the regulation of the BAX/Ku70 interaction. This finding suggests that combined treatments could improve the outcomes for this subset of lung cancer patients, who have a poor prognosis. [ABSTRACT FROM AUTHOR]

Acquired resistance to epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs), such as gefitinib and erlotinib, is a critical problem in the management of patients with EGFR mutant lung cancer. Several mechanisms have been reported involved in this acquired resistance, including hepatocyte growth factor (HGF) activation of an alternative pathway. PI3K and mTOR are downstream molecules of receptor tyrosine kinases, such as EGFR and Met, and are thought to be ideal targets for controlling various tumor types. We assessed whether BEZ235, a dual inhibitor of PI3K and mTOR, could overcome the EGFR-TKI resistance induced by HGF in an EGFR mutant lung cancer model. Exogenous and endogenous HGF triggered resistance to erlotinib in the PC-9 and HCC827, EGFR mutant lung cancer cell lines. BEZ235 alone inhibited the viability of PC-9 and HCC827 cells in vitro, irrespective of the presence or the absence of HGF. Using a xenograft model of severe combined immunodeficient mice with HGF-gene-transfected PC-9 cells (PC-9/HGF), we found that BEZ235 inhibited tumor growth, whereas erlotinib did not. BEZ235 monotherapy also inhibited the phosphorylation of Akt and p70S6K/S6RP, downstream molecules of PI3K and mTOR, respectively, as well as suppressing tumor-cell proliferation and angiogenesis of PC-9/HGF tumors. These results suggest that BEZ235, even as monotherapy, may be useful in managing HGF-induced EGFR-TKI resistance in EGFR mutant lung cancer. [ABSTRACT FROM AUTHOR]