143PD - Met Activation by Autocrine Loop Rescues Colon Cancer Cells From Sensitivity to EGFR Inhibition

Abstract

ABSTRACT Background Cetuximab, a monoclonal antibody targeting the epidermal growth factor receptor (EGFR), is active in K-RAS wild type colorectal cancer (CRC). However, initially in responding patients cancer cells would become resistant to EGFR inhibition by the activation of alternative growth controlling pathways including the hepatocyte growth factor (HGF)/MET-dependent signal. Methods mRNA expression profiles of cetuximab-sensitive human GEO colon cancer cells and of their cetuximab-resistant derived GEO-CR cells were analyzed by microarrays. Protein expression levels were evaluated by western blot (WB). Growth factors were measure in the culture medium by Luminex technology. The in vitro antitumor activity of MET inhibitor (METi), was tested in a panel of ten human colon cancer cell lines by MTT assay. Results Evaluation of gene expression profile identified a series of genes that were up-regulated in GEO-CR cells possibly involved in acquired resistance to EGFR inhibition. Among these we found several genes involved in the MET pathway. WB analysis detected activated, phosphorylated MET in GEO-CR but not in GEO and in the other colon cancer cell lines tested. We also found in GEO-CR cells up-regulation of EGFR ligands such as transforming growth factor – α (TGFa) and Heparin Binding- Epidermal Growth Factor (HB-EGF). We further observed expression of HGF in GEO-CR cells, supporting HGF/MET autocrine activation following acquired resistance to cetuximab treatment. In fact, the RAS/RAF/MEK/MAPK pathway was constitutively active despite of EGFR inhibition by cetuximab in GEO-CR cells possibly due to HGF-induced MET activation. Treatment with a potent and selective METi was able to overcome cetuximab resistance in GEO-CR cells and causes cell growth inhibition. Conclusion These results suggest that autocrine activation of HGF/MET could be a relevant therapeutic target in colorectal cancer patients that become resistant to anti-EGFR treatment. Disclosure All authors have declared no conflicts of interest.