Abstract 1890: Novel targets mediating resistance to EGFR/c-Met tyrosine kinase inhibitors in NSCLC
Authors: Jacobs Ryan , Fong Jason , Bomgarden Ryan , Rogers John , Puri Neelu 
Published: August 2012

Abstract
c-Met and EGFR are therapeutic targets in NSCLC with a direct role in tumor progression. Highly specific TKIs against c-Met, have limited efficacy individually, and resistance to c-Met TKIs could be due to activation/mutations in EGFR, or c-Met amplification/mutations which could lead to increased expression and constitutive phosphorylation of c-Met. In recent clinical trials, simultaneous treatment with tyrosine kinase inhibitors (TKIs) against c-Met/EGFR has improved patient prognosis, however, their efficacy has been limited due to the development of resistance to TKIs. To establish the mechanism of TKI resistance in NSCLC, two cell lines (H2170 and H358) were made resistant to c-Met and EGFR TKIs (15-30 fold increase in IC50 of SU11274 and 8-10 fold increase in IC50 of Erlotinib) by exposing the cells to progressively increasing concentrations of both drugs simultaneously. In H2170 cell lines, a 4-fold downregulation p-cMet 1003 (c-cbl binding site) and a 5-fold increase in p-c-Met 1234/1235 (autophosphorylation site) was observed. Additionally, several proteins in signaling pathways (mTOR and Wnt) linked to EGFR and c-Met, were also found to be differentially modulated in H2170 and H358 resistant lines: active β-catenin (1.5-2.5 fold increase), p-mTOR (2-4 fold increase), and phospho-pS6kinase (2-20 fold increase). Interestingly, few differences were observed in p-ERK or p-AKT, which are EGFR/c-Met downstream signaling proteins, indicating that other pathways such as mTOR and Wnt may cause TKI resistance. To confirm the role of mTOR and Wnt pathways in resistance and to break their resistance, parental and resistant cell lines were treated with the mTOR inhibitor everolimus and the Wnt inhibitor XAV 939 in addition to c-Met and EGFR TKIs. An MTT viability assay showed resistant cell lines to be 2-4 fold more susceptible in comparison to parental cells with the addition of everolimus to TKI combination treatment. In response to the Wnt inhibitor XAV 939, parental cell lines showed no significant increase in sensitivity while resistant lines showed a 2.5-3 fold decrease in viability when compared to c-Met and EGFR TKI combination treatment. Our results suggest novel mechanisms of resistance to c-Met TKI which are mediated by increased c-Met stability, resulting in increases in Wnt expression/mTOR activation. The decreased phosphorylation of c-Met 1003 may lead to decreased binding/activity of Cbl and/or deficient ubiquitination of c-Met. This may result in increased stabilization of c-Met as evidenced by the increased phosphorylation of c-Met 1234/1235 and the subsequent activation of PI3K/Akt/mTOR and Wnt pathways which has been shown. These studies suggest a new treatment modality since inhibitors of Wnt pathway or agents targeting β-catenin have not entered clinical testing. These results suggest that Wnt/ mTOR inhibitors combined with c-Met/EGFR TKIs may be a novel combination therapy for lung cancer.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1890. doi:1538-7445.AM2012-1890