The epidermal growth factor receptor (EGFR) T790M mutation confers acquired resistance to tyrosine kinase inhibitors (TKIs) in approximately 50% of drug-resistant EGFR mutant lung adenocarcinomas. Experiments using genetically engineered mouse models of EGFR mutant lung cancer have revealed that T790M-mediated resistance can be overcome by a second-generation TKI, afatinib, in combination with the anti-EGFR antibody, cetuximab. This drug combination is currently in clinical trials in patients with TKI-resistant tumors and is showing a promising ∼40% response rate. Nevertheless, cases of afatinib+cetuximab resistance are beginning to emerge.

To identify the molecular mechanisms that play a role in afatinib+cetuximab resistance and test new therapies to overcome resistance to these drugs, we have developed mouse models of afatinib+cetuximab resistance in mice with inducible expression of the EGFRL858R+T790M mutant in type II pneumocytes. Mice harboring lung tumors were treated five days a week with afatinib and twice a week with cetuximab for four weeks. After the first round of treatment, drug-treatments were interrupted for one month. This on/off drug treatment was repeated until lung tumors no longer responded to treatment, as evidenced by imaging as well as clinical symptoms. Resistance to afatinib+cetuximab treatment was also studied in xenografts. Eight-week-old nu/nu athymic nude mice were injected subcutaneously with human lung adenocarcinoma cells, expressing the erlotinib-resistant EGFRDel19+T790M mutant. Notably, both transgenic and xenografts models harboring EGFRT790M-induced tumors developed resistance to EGFR-dual targeting and preliminary molecular studies on the resistant tumors show the absence of additional mutations in EGFR and in the ERBB2 tyrosine kinase domain in resistant tumors. These findings suggest that an alternative pathway or mechanism is involved in mediating resistance to the afatinib and cetuximab combination. We are further exploring mechanisms of resistance by performing genome-wide and signaling pathway analyses of drug-resistant tumors from these models. Findings from mouse models will be validated in repeat biopsy specimens from patients who have developed resistance to the drug combination. An improved understanding of the molecular mechanisms responsible for acquired resistance to EGFR inhibition will provide new insight into the biology of this subset of lung cancers with immediate therapeutic implications for patients.

This content is only available via PDF.