The epidermal growth factor receptor (EGFR) kinase inhibitors gefitinib and erlotinib are effective treatments for lung cancers with EGFR activating mutations, but these tumors invariably develop drug resistance. Here, we describe a gefitinib-sensitive lung cancer cell line that developed resistance to gefitinib as a result of focal amplification of the MET proto-oncogene. inhibition of MET signaling in these cells restored their sensitivity to gefitinib. MET amplification was detected in 4 of 18 (22%) lung cancer specimens that had developed resistance to gefitinib or erlotinib. We find that amplification of MET causes gefitinib resistance by driving ERBB3 (HER3)-dependent activation of PI3K, a pathway thought to be specific to EGFR/ERBB family receptors. Thus, we propose that MET amplification may promote drug resistance in other ERBB-driven cancers as well.

Summary MET amplification activates ERBB3/PI3K/AKT signaling in EGFR mutant lung cancers, and causes resistance to EGFR kinase inhibitors. We demonstrate that MET activation by its ligand, HGF, also induces drug resistance, but through GAB1 signaling. Using high-throughput FISH analyses in both cell lines and in lung cancer patients, we identify subpopulations of cells with MET amplification prior to drug exposure. Surprisingly, HGF accelerates the development of MET amplification both in vitro and in vivo. EGFR kinase inhibitor resistance, due to either MET amplification or autocrine HGF production, was cured in vivo by combined EGFR and MET inhibition. These findings highlight the potential to prospectively identify treatment naïve EGFR mutant lung cancer patients who will benefit from initial combination therapy.

The epidermal growth factor receptor directed antibody, cetuximab, is an effective clinical therapy for patients with colorectal, head and neck and non-small cell lung cancer patients particularly for those with KRAS and BRAF wild type cancers. Treatment in all patients is limited eventually by the development of acquired resistance but little is known about the underlying mechanism. Here we show, that activation of ERBB2 signaling, either through ERBB2 amplification or through heregulin upregulation, leads to persistent ERK 1/2 signaling and consequently cetuximab resistance. Inhibition of ERBB2 or disruption of ERBB2/ERBB3 heterodimerization restores cetuximab sensitivity in vitro and in vivo. A subset of colorectal cancer patients that exhibit either de novo or acquired resistance to cetuximab based therapy possess ERBB2 amplification or high levels of circulating heregulin. Collectively, these findings identify two distinct resistance mechanisms, both of which promote aberrant ERBB2 signaling, that mediate cetuximab resistance. Moreover, these results suggest that ERBB2 inhibitors, in combination with cetuximanb, represent a rational therapeutic strategy that should be assessed in cetuximab-resistant cancers.

The clinical efficacy of EGFR kinase inhibitors is limited by the development of drug resistance. The irreversible EGFR kinase inhibitor WZ4002 is effective against the most common mechanism of drug resistance mediated by the EGFR T790M mutation. Here we show, in multiple complementary models, that resistance to WZ4002 develops through aberrant activation of ERK signaling caused by either an amplification of MAPK1 or by downregulation of negative regulators of ERK signaling. Inhibition of MEK or ERK restores sensitivity to WZ4002 and prevents the emergence of drug resistance. We further identify MAPK1 amplification in an erlotinib resistant EGFR mutant NSCLC patient. In addition, the WZ4002 resistant MAPK1 amplified cells also demonstrate an increase both in EGFR internalization and a decrease in sensitivity to cytotoxic chemotherapy. Our findings provide insights into mechanisms of drug resistance to EGFR kinase inhibitors and highlight rationale combination therapies that should be evaluated in clinical trials.