Abstract C90: Dependence of afatinib and cetuximab resistant lung adenocarcinomas on mTOR signaling.

Abstract

Abstract Lung adenocarcinomas harboring mutations in the tyrosine kinase domain of the EGFR are sensitive to tyrosine kinase inhibitors (TKIs) erlotinib or gefitinib. Despite a ∼70% response rate to these agents, patients almost inevitably develop resistance on average within a year of starting drug treatment. In 50% of cases, acquired resistance to EGFR TKIs is due to the emergence of a secondary mutation in the tyrosine kinase domain of the receptor (the T790M mutation). Additional less common mechanisms of resistance include activation of bypass signaling pathways via amplification of other receptor tyrosine kinases (RTKs) like MET and HER2 or mutations in genes encoding downstream signaling components such as PIK3CA or BRAF. In rare instances, tumors biopsied at progression show phenotypic transformations such as epithelial-to-mesenchymal transition (EMT) or neuroendocrine differentiation. We previously generated transgenic mice that develop EGFRL858R+T790M-induced lung adenocarcinomas and showed that T790M-mediated resistance could be overcome using a combination of a second generation TKI BIBW-2992 (afatinib) with the anti-EGFR antibody, cetuximab. This preclinical study prompted a Phase IB/II clinical trial testing this drug combination in patients with progressive disease after erlotinib or gefitinib treatment that is showing a promising 30% response rate. Unfortunately patients eventually develop disease progression on this drug combination and the mechanisms of resistance to afatinib+cetuximab are currently unknown. Here, we used an intermittent dosing strategy, previously used to generate erlotinib-resistant tumors in mice, to generate afatinib+cetuximab resistant tumors in xenograft and transgenic mouse models of EGFR mutant lung cancer. In these models, afatinib+cetuximab resistant tumors lacked detectable mutations in the EGFR transgene, the ERBB2 kinase domain or KRAS. Molecular analysis of resistant tumors revealed high levels of activation of the mTOR signaling pathway. Consistent with these findings, two patients with afatinib+cetuximab-resistant tumors exhibited alterations in genes (TSC1 and NF2) that activate the mTOR pathway. In cell culture and in mouse models, such resistance can be overcome by addition of the mTOR pathway inhibitor, rapamycin. These studies are the first to demonstrate mechanisms of acquired resistance to dual inhibition of EGFR in EGFR mutant lung cancer and provide new insight into the biology of this subset of lung cancers with immediate therapeutic implications for patients. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C90. Citation Format: Valentina Pirazzoli, Caroline Nebhan, Xiaoling Song, Zenta Walter, Guoping Cai, Anna Wurtz, Zhongming Zhao, Elisa Elisa de Stanchina, Leora Horn, David Carbone, Philip J. Stevens, Vincent Miller, Scott Gettinger, William Pao, Katerina Politi. Dependence of afatinib and cetuximab resistant lung adenocarcinomas on mTOR signaling. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C90.