Abstract 752: Elucidating the mechanisms of acquired resistance in lung adenocarcinomas
Authors: Ortiz-Cuarán Sandra , Fernandez-Cuesta Lynnette , Lovly Christine M. , Bos Marc , Scheffler Matthias , Michels Sebastian , Albus Kerstin , Meyer Lydia , König Katharina , Dahmen Ilona , Mueller Christian , Ozretić Luca , Tharun Lars , Schaub Philipp , Florin Alexandra , Pinther Berit , Bahlmann Nike , Ansén Sascha , Peifer Martin , Heukamp Lukas C. , Buettner Reinhard , Sos Martin L. , Wolf Jürgen , Pao William , Thomas Roman K. 
Published: August 2015

Abstract
In EGFR mutant lung adenocarcinomas, targeted therapy with the EGFR tyrosine kinase inhibitors (TKIs) erlotinib, gefitinib, and afatinib performs better than standard chemotherapy in terms of progression free survival (PFS) and radiographic response (RR) rates. In the ALK rearranged cases, targeted therapy with crizotinib is associated with PFS of about 9,7 months and RR of 60.8%. Unfortunately, all patients relapse with a median PFS of 7 to 16 months. The mechanisms of acquired resistance to first generation EGFR TKIs include a secondary EGFR mutation (T790M) in about 50% and, with less frequency, MET amplification, HER2 amplification, PTEN loss, transformation to small cell histology, EMT and rare mutations in BRAF and PI3KCA. Resistance to crizotinib is caused by ALK kinase mutations, by ALK or cKIT amplification or by alterations in IGF1R/IRS1, 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. To this aim, we used rebiopsy samples from patients that had either prolonged stable disease or partial response to therapy, and developed radiographic progression under TKI therapy. To model the emergence of resistance mechanisms in vitro, we generated resistant cell lines to a variety of ALK inhibitors. Patient samples and resistant cell lines that were negative for any of the previously reported mechanisms of resistance were analyzed by genome or exome; validation of mutation calls was performed by Sanger sequencing. Sequencing of the erlotinib resistant samples revealed a deletion in the transmembrane domain of ABCD4, an ATP-binding cassette (ABC) transporter. Stable transduction of this mutation in BaF3 cells, showed that neither the expression of ABCD4 nor the mutation resulted in a reduced sensitivity to erlotinib. Results of the functional validation of a mutation found in a Fms-related tyrosine kinase are currently ongoing. Crizotinib resistant samples showed a mutation in the IPT/TIG domain of the RON kinase that, when expressed in sensitive cells, did not confer resistance to crizotinib. However, a mutation in the PSI domain of the semaphorin SEMA3E lead to an prologned Akt activation, thus sustained downstream PI3K signaling in cells treated with crizotinib. The molecular mechanisms behind this finding are being analyzed. Crizotinib resistant samples also showed mutations in SWI/SNF-regulator of chromatin and a GTPase of the Rab family. Cells resistant to different ALK inhibitors harbor mutations in a mitogen activated protein kinase and an ephrin receptor, among others. The functional impact of such mutations and the efficacy of combination therapies in the setting of resistance to these inhibitors are currently being tested. Our results imply a wide range of cellular pathways might be involved in the process of acquired resistance to EGFR and ALK inhibitors in lung adenocarcinomas.
Citation Format: Sandra Ortiz-Cuarán, Lynnette Fernandez-Cuesta, Christine M. Lovly, Marc Bos, Matthias Scheffler, Sebastian Michels, Kerstin Albus, Lydia Meyer, Katharina König, Ilona Dahmen, Christian Mueller, Luca Ozretić, Lars Tharun, Philipp Schaub, Alexandra Florin, Berit Pinther, Nike Bahlmann, Sascha Ansén, Martin Peifer, Lukas C. Heukamp, Reinhard Buettner, Martin L. Sos, Jürgen Wolf, William Pao, Roman K. Thomas. Elucidating the mechanisms of acquired resistance in lung adenocarcinomas. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 752. doi:10.1158/1538-7445.AM2015-752