Abstract 956: Elucidating the mechanisms of acquired resistance in lung adenocarcinomas
Authors: Ortiz-Cuarán Sandra , Fernandez-Cuesta Lynnette , Bos Marc , Heukamp Lukas , Lovly Christine M. , Peifer Martin , Gardizi Masyar , Scheffler Matthias , Dahmen Ilona , Müller Christian , König Katharina , Albus Kerstin , Florin Alexandra , Ansén Sascha , Buettner Reinhard , Wolf Jürgen , Pao William , Thomas Roman K. 
Published: May 2015

Abstract
In lung adenocarcinomas, targeted therapy with the EGFR tyrosine kinase inhibitors (TKIs) erlotinib, gefitinib and afatinib is associated with longer progression free survival (PFS) and higher radiographic response (RR) rates when compared to standard first-line chemotherapy. In ALK rearranged lung cancers, targeted therapy with crizotinib is associated with PFS of approximately 9,7 months and RR of 60.8%. However, despite the initial success of these agents, all patients progress with a median PFS of 7 to 16 months. Acquired resistance in EGFR mutant tumors is driven by the occurrence of a secondary EGFR mutation (T790M) in about 50% of the cases and by MET amplification in 5 to 10 % of the cases. Other mechanisms include HER2 amplification, PTEN loss, phenotypic change to small cell histology, rare mutations in BRAF and AXL activation. Resistance to crizotinib, on the other hand, is caused by secondary mutations in the ALK kinase domain, by ALK or cKIT amplification or by alterations in EGFR and KRAS. Here, we made use of next generation sequencing techniques to better understand the mechanisms that drive resistance in lung adenocarcinomas treated with erlotinib or crizotinib. For this purpose, we used transbronchial or CT-guided rebiopsies from patients that had either prolonged stable disease or partial response to therapy, and developed radiographic progression under TKI therapy. Samples were analyzed by FISH and sequenced on a benchtop Illumina platform (MiSeq) in order to evaluate the presence of known mechanisms of resistance. Samples that were negative for any of the reported mechanisms were analyzed by genome, exome or trascriptome sequencing. From the sequencing output of the pan-negative samples, filtering of mutation candidates included: absence of the mutation in the pre-treatment sample (when available), expression of the candidate gene in lung adenocarcinomas, absence of the mutation in primary lung adenocarcinomas, high impact of the mutation at protein level (Polyphen), mutant allelic fraction in the tumor higher than 10%, among other factors. After filtering, validation of mutation calls was performed by Sanger sequencing. Sequencing of the erlotinib resistant samples revealed mutations in members of a functionally wide spectrum of protein families including the proteoglycan family, the ATP-binding cassette (ABC) transporters family, an Fms-related tyrosine kinase receptor and a member of the transforming growth factor beta family of cytokines. On the other hand, crizotinib resistant samples showed mutations in a cell surface receptor for macrophage-stimulating protein with tyrosine kinase activity, in a C2H2 type zinc finger gene, a semaphorin, a mitogen-activated protein kinase and a member of the SWI/SNF family of proteins. Our results evidence the possible contribution of a wide range of cellular pathways in the process of acquired resistance to EGFR and ALK inhibitors in lung adenocarcinomas.
Citation Format: Sandra Ortiz-Cuarán, Lynnette Fernandez-Cuesta, Marc Bos, Lukas Heukamp, Christine M. Lovly, Martin Peifer, Masyar Gardizi, Matthias Scheffler, Ilona Dahmen, Christian Müller, Katharina König, Kerstin Albus, Alexandra Florin, Sascha Ansén, Reinhard Buettner, Jürgen Wolf, William Pao, Roman K. Thomas. Elucidating the mechanisms of acquired resistance in lung adenocarcinomas. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 956. doi:10.1158/1538-7445.AM2014-956