EGFR-Mutant SCLC Exhibits Heterogeneous Phenotypes and Resistance to Common Antineoplastic Drugs

Approximately 5% of patients with EGFR-activating mutations acquire EGFR tyrosine kinase inhibitor (TKI) resistance through SCLC transformation. However, the reason for the poor outcome and the molecular basis of EGFR-mutant SCLC that has transformed from adenocarcinoma remain unclear.In this study, we established two EGFR-mutant SCLC cell lines from lung adenocarcinoma patients after failed EGFR-TKI treatment to investigate their molecular basis and potential therapeutic strategies in the hope of improving patient outcome.These two EGFR-mutant SCLC cell lines displayed two different phenotypes: suspensive and adherent. Both phenotypes shared the same genomic alterations analyzed by array-based comparative genomic hybridization assay. Increased expression of EGFR and mesenchymal markers and decreased expression of neuroendocrine markers were observed in adherent cells. Principal component analysis and hierarchical clustering analysis of RNA microarray revealed that these two cell lines displayed a unique gene expression pattern that was distinctly different from that in NSCLC and classical SCLC cells. Combined treatment using an EGFR-TKI and an AKT inhibitor attenuated cell viabilities in our two cell lines. Moreover, the use of a histone deacetylase inhibitor significantly inhibited the cell viabilities of both cell lines in vitro and in vivo.Our findings suggest that EGFR-mutant SCLC may be a distinct subclass of SCLC that exhibits epithelial-mesenchymal transition phenotypes, and adding an AKT or histone deacetylase inhibitor to pre-existing therapies may be one of the therapeutic choices for transformed EGFR-mutant SCLC.