Abstract 4736: Amplification of ERK2 mediates resistance to the novel irreversible EGFR inhibitor WZ4002
Authors: Ercan Dalia , Zhou Wenjun , Yanagita Masahiko , Capelletti Marzia , Rogers Andrew , Xiao Yun , Gray Nathanael S. , Janne Pasi A. 
Published: June 2012

Abstract
Background: EGFR T790M causes clinical resistance to the quinazoline EGFR kinase inhibitors gefitinib and erlotinib in non-small cell lung cancer. Amplification of EGFR T790M causes resistance to the irreversible quinazoline EGFR inhibitor PF00299804 (Ercan etl al. Oncogene 2010). A novel T790M selective irreversible pyrimidine EGFR kinase inhibitor, WZ4002, is effective in NSCLC models harboring EGFR T790M (Zhou, W, Ercan, D et al., Nature 2009). The mechanism(s) of resistance to this class of irreversible EGFR inhibitors have not been explored.
Methods and Results: We exposed the Gefitinib resistant PC9 GR cells (EGFR del E746_A750/T790M; IC50 to WZ4002: ∼30nM) to increasing concentrations of WZ4002 to generate PC9 GW resistant cells (IC50 to WZ4002 ∼10µM) and isolated several resistant clones. The PC9 GWR cells contain EGFR del E746_A750/T790M but do not harbor additional EGFR mutations and are cross resistant to the irreversible quinazoline EGFR inhibitor BIBW2992. The PC9 GWR cells demonstrate an increase in basal phosphorylation of ERK2 but not ERK1 as well as total protein compared to parental PC9 GR cells. WZ4002 effectively inhibits EGFR phosphorylation but not ERK 2 phosphorylation in the PC9 GWR cells whereas in the PC9 GR cells WZ4002 inhibits both EGFR and ERK 1/2 phosphorylation. Furthermore, unlike in the PC9 GR cells, EGFR inhibition does not lead to BIM induction or apoptosis in the PC9 GWR cells. Genomic analyses of the PC9 GWR compared with the PC9 GR cells, using single nucleotide polymorphism (SNP) arrays, identify a focal amplification in the PC9 GWR cells on chromosome 22 which includes ERK2 (MAP2K). Using fluorescence in situ hybridization (FISH), we confirm amplified intra-chromosomal regions mapping to MAP2K. Inhibition of ERK signaling by either an ERK2 specific shRNA or by the MEK inhibitor CI-1040, restores sensitivity to WZ4002 and BIBW2992. In addition, combination of WZ4002 and CI-1040 results in BIM induction and apoptosis in the PC9 GWR cells. In contrast inhibition of PI3K signaling using the PI3K inhibitor PI-103 does not restore WZ4002 sensitivity. Ectopic activation of ERK signaling using an activated MEK1 allele (MEK K57N) found in lung cancer, in different lung cancer cell lines (PC9 (EGFR del E746_A750), PC9 GR (EGFR del E746_A750), and H1975 (L858R/T790M), is sufficient to cause resistance to WZ4002 and block WZ4002 mediated apoptosis.
Conclusions: We identify amplification of ERK2, a component downstream component of EGFR signaling, as a mechanism of resistance to structurally distinct irreversible EGFR kinase inhibitors. The combination of an EGFR inhibitor and a MEK inhibitor is effective in against these drug resistant cancers.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4736. doi:10.1158/1538-7445.AM2011-4736