Abstract LB-209: Chromatin condensation in KRAS-mutant lung cancer as a therapeutic target: challenging the paradigm of associating KRAS mutation with EGFR inhibitor resistance
Authors: Wang Meng , Kern Ashley M. , Hülskötter Marieke , Greninger Patricia , Singh Anurag , Pan Yunfeng , Chowdhury Dipanjan , Krause Mechthild , Baumann Michael , Benes Cyril H. , Efstathiou Jason A. , Settleman Jeff , Willers Henning 
Published: May 2015

Abstract
Non-small cell lung cancer (NSCLC) with mutations in the KRAS oncogene is generally resistant to targeted agents directed against the epidermal growth factor receptor (EGFR). Although EGFR is active in KRAS-mutant cancers its role in supporting cell survival and its potential utility as a therapeutic target have remained unclear. EGFR-targeted drugs have been shown to enhance the cytotoxic effects of radiation treatments (RT). However, clinical results have been inconsistent suggesting the need for genomic biomarkers to better identify a subset of patients in whom the combination of EGFR inhibitors and RT can be further developed. By carrying out a screen of 40 human NSCLC-derived cell lines, we establish a surprising positive correlation between the presence of a KRAS mutation and radiosensitization by the EGFR tyrosine kinase inhibitor erlotinib and the monoclonal antibody cetuximab. EGFR signaling in KRAS-mutant NSCLC cells promotes chromatin condensation in-vitro and in-vivo, thereby restricting the number of DNA double-strand breaks (DSB) produced by a given dose of RT. Chromatin condensation in interphase cells is characterized by an unexpected mitosis-like co-localization of serine 10 phosphorylation and lysine 9 trimethylation on histone H3. Aurora B kinase promotes this process in a manner that is co-dependent upon EGFR and protein kinase C alpha (PKCα) in KRAS-mutant but not wild-type cells. In keeping with a recently reported role of PKCα in breast cancer stem cells, disrupting the EGFR-PKCα pathway is particularly effective under experimental conditions that enrich for stem cell-like cancer cells including spheres. Interestingly, PKCα as well as MEK/ERK signaling is required for suppression of DSB-inducible premature senescence by EGFR. Blockade of autophagy results in a mutant KRAS-dependent senescence-to-apoptosis switch in cancer cells or spheres treated with RT. In conclusion, we identify EGFR as a molecular target to overcome a novel chromatin-mediated mechanism of RT resistance in KRAS-mutant tumor cells, thereby challenging the current paradigm of resistance of KRAS-mutant cancers to EGFR inhibitors. Our findings may reposition EGFR-targeted agents for combination with DSB-inducing therapies in KRAS-mutant NSCLC, and yield novel therapeutic opportunities to target chromatin modifications in cancer stem cells.
Supported by the Dana-Farber/Harvard Cancer Center SPORE in Lung Cancer, NCI P50 CA090578, NCI R01 CA142698, American Cancer Society 123420RSG-12-224-01-DMC and RSG-12-079-01, UK Wellcome Trust 086357, Deutsche Forschungsgemeinschaft DFG-PAK-190, Federal Share of program income earned by Massachusetts General Hospital on C06 CA059267, Proton Therapy Research and Treatment Center.
Citation Format: Meng Wang, Ashley M. Kern, Marieke Hülskötter, Patricia Greninger, Anurag Singh, Yunfeng Pan, Dipanjan Chowdhury, Mechthild Krause, Michael Baumann, Cyril H. Benes, Jason A. Efstathiou, Jeff Settleman, Henning Willers. Chromatin condensation in KRAS-mutant lung cancer as a therapeutic target: challenging the paradigm of associating KRAS mutation with EGFR inhibitor resistance. [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 LB-209. doi:10.1158/1538-7445.AM2014-LB-209