Cancer Therapy: Preclinical Increased TGF-a as a Mechanism of Acquired Resistance to the Anti-EGFR Inhibitor Cetuximab through EGFR–MET Interaction and Activation of MET Signaling in Colon Cancer Cells

Purpose: Although cetuximab, an anti-EGF receptor (EGFR) monoclonal antibody, is an effective treatment for patients with KRAS wild-type metastatic colorectal cancer (mCRC), its clinical use is limited by onset of resistance. Experimental Design: We characterized two colorectal cancer models to study the mechanisms of acquired resistance to cetuximab. Results: Following chronic treatment of nude mice bearing cetuximab-sensitive human GEO colon xenografts, cetuximab-resistantGEO(GEO-CR)cellswereobtained. InGEO-CRcells,proliferationandsurvival signals were constitutively active despite EGFR inhibition by cetuximab treatment. Whole gene expression profiling identifiedaseriesofgenes involved in thehepatocytegrowthfactor (HGF)-MET–dependentpathways, whichwereupregulatedinGEO-CRcells.Furthermore,activated,phosphorylatedMETwasdetectedinGEO-CR cells. A second colorectal cancer cell line with acquired resistance to cetuximab was obtained (SW48-CR). InhibitionofMET expression by siRNA restored cetuximab sensitivity inGEO-CR and SW48-CR cells, whereas exogenousactivationofMETbyHGFstimulationincetuximab-sensitiveGEOandSW48cells inducedresistance to cetuximab. Treatment ofGEO-CRand SW48-CR cellswith PHA665752, a selectiveMET inhibitor, inhibited cell growth, proliferation, and survival signals and impaired cancer cell migration. Overexpression of TGF-a, a specificEGFR ligand,was involved in theacquisitionof cetuximab resistance inGEO-CRandSW48-CRcells. In fact, TGF-a overexpression induced the EGFR–MET interaction, with subsequent MET phosphorylation and activation of MET downstream effectors in GEO-CR and SW48-CR cells. Conclusions: These results suggest that overexpression of TGF-a through induction of EGFR–MET interaction contributes to cetuximab resistance in colorectal cancer cells. The combined inhibition of EGFR and MET receptor could represent a strategy for preventing and/or overcoming cetuximab resistance in patients with colorectal cancer. Clin Cancer Res; 19(24); 6751–65. 2013 AACR.