Abstract 736: Mechanisms of EGFR and c-Met inhibitor resistance in NSCLC

Abstract

Abstract While tyrosine kinase inhibitors (TKI's) such as gefitinib and erlotinib against EGFR have positive therapeutic effects in a subset of Non-Small Cell Lung Cancer (NSCLC) patients, their clinical efficacies are limited due to drug resistance, which may be due to secondary T790M mutations in EGFR and/or c-MET gene amplification. Current clinical trials using both c-Met/EGFR-TKIs have found longer progression free states. However, since resistance has been observed in a subset of patients, it is vital to determine the mechanism of combined TKI acquired resistance. To study this mechanism further, we established two NSCLC cell lines (H2170 and H358) which are resistant to EGFR-TKI, erlotinib and c-Met-TKI SU11274 and had IC50 concentrations which were of 10-20 fold higher. To determine the key pathways involved in TKI resistance, immunoblots were performed with the IC50 of resistant cell lines (erlotinib 8µM and SU11274 9µM) in the presence and absence of EGF (15ng/ml), HGF (40ng/ml) or both for 2.5 minutes. We found a 2 and 5 fold decrease in expression of p-c-Met in H2170 ESR and H358 ESR cells respectively in the presence of HGF compared to parental control cells. Downregulation of p-c-Met in both resistant cell lines would imply that these cells were not selected to harbor amplified c-MET expression. These results indicate that EGFR-TKI resistant NSCLC could be due to other factors besides selection of c-Met amplified cells as has been currently suggested and is thus a novel concept which needs further studies. c-Met independent pathways such as VEGF or IGF-1 could also mediate tumor proliferation in the presence of low levels of c-Met. In H2170 ESR cells, EGFR was constitutively autophosphorylated at Tyr1068 (19 fold increase) which resulted in the upregulation of downstream signaling protein p-ERK (Thr202/Tyr204) (2 Fold) in the absence of EGF. We also found upregulation of p-mTOR (Ser2448) (2.5 fold) and phospho p70S6 kinase (Thr389) (2 fold) in the presence and absence of erlotinib which could be modulated by p-ERK or p-mTOR. Modulation of these proteins could result in increased proliferation and cause resistance in NSCLC. Conversely, in H358 ESR, an increase in p-ERK (Thr202/Tyr204) (1.3 fold) was seen in the absence of constitutive autophosphorylation of EGFR. Similar to H2170, an upregulation of p-mTOR (Ser2448) (2 fold) and phospho p70S6 kinase (Thr389) (4 fold) was observed in H358 ESR in the presence of erlotinib in comparison to the parental cell line. These results indicate that other pathways described above may have an important role in mediating resistance. No changes in total protein levels of EGFR, ERK or p70S6 kinase were observed. Thus, in these resistant lines, the p-mTOR pathway may mediate downstream EGFR and c-Met signaling, and our current preliminary studies with rapamycin indicate that mTOR may play a major role in resistance to EGFR/c-Met TKI's. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 736. doi:10.1158/1538-7445.AM2011-736