Insulin-like growth factor-1 receptor/epidermal growth factor receptor (EGFR) heterodimerization and resistance to epidermal growth factor receptor tyrosine kinase inhibitors in non-small-cell lung cancer

13032 Background: Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) have been used to treat lung cancers, but resistance to these agents has been observed. This study was designed to investigate whether the insulin-like growth factor (IGF)-mediated signaling pathway induces resistance to the EGFR TKIs in lung cancer. Methods: The antitumor activities and action mechanisms of EGFR inhibitors (erlotinib, gefinitib, cetuximab), single or in combination with IGF-IR inhibitors, were assessed in vitro in a subset of non-small-cell lung cancer (NSCLC) cell lines by the MTT assay, flow cytometry-based TUNEL assay, soft agar, confocal microscopy, metabolic labeling, coimmunoprecipitation, and northern and western blot analyses, and in vivo in animal models. Correlation of EGFR and IGF-1R expression was assessed using lung tissues from patients with NSCLC. Results: EGFR TKI inhibited the proliferation and anchorage-dependent and -independent colony-forming ability of NSCLC cells, which induced apoptosis, only when IGF-1R signaling was blocked. Treatment with EGFR TKIs, but not with the EGFR antibody, induced EGFR:IGF-1R heterodimerization on cell surface and activation of the IGF-1R, resulting in the stimulation of PI3K/Akt/ mTOR pathway, promoting the de novo protein biosynthesis of survivin and EGFR, resulting in the survival of NSCLC cells. When IGF-IR and mTOR were blocked, treatment of EGFR-TKIs induced apoptosis in NSCLC cells, resulting in suppression of the NSCLC tumor growth. When we tested the expression of IGF-R and EGFR in human lung tissue, 9/14 tumor samples exhibited increased expression of EGFR and 7/9 samples showed a correlative increases in IGF-IR protein levels compared to their paired normal counterparts. Conclusions: These findings suggest that simultaneous targeting of EGFR and IGF-1R signaling pathways might be an effective therapeutic strategy against NSCLC. No significant financial relationships to disclose.