Effects of entinostat onresistance to cetuximab and EGFR TKIs in non-small cell lung cancer.

Abstract

e18077 Background: Cetuximab, a monoclonal antibody targeting the epidermal growth factor (EGFR) is active in patients with NSCLC. Gate keeper mutations in EGFR, such as T790M and activation of alternative driven pathways such as Met amplification are known mechanisms of acquired resistance to EGFR TKI. Here we evaluated the effects of the class I histone deacetylase inhibitors (HDACi), entinostat with cetuximab or EGFR TKIs in NSCLC cell lines with 3 potential mechanisms of intrinsic and acquired EGFR inhibitor resistance: RAS mutation according to E-cadherin expression, T790M EGFR mutation, and amplified MET. Methods: In vivo efficacy of entinostat alone or in combination with cetuximab or gefitinib was tested in athymic nude mice bearing RAS mutant, E-cadherin positive (A549) and E-cadherin negative (NCI-H460) NSCLC xenograft tumors. NSCLC cell lines were treated with various dilutions of cetuximab, entinostat or erlotinib. The NCI-H1975 and NCI-H1993 cell lines harboring the EGFR-L858R/T790M mutation and MET amplification, respectively, were treated with the combination of entinostat and erlotinib. Cell growth was analyzed by the MTT assay. Expression of e-cadherin was evaluated using affymetix microarrays. Results: When entinostat (E; 5mg/kg) was combined with cetuximab (C; 25mg/kg) in nude mice bearing the E-cadherin positive A549 xenograft, tumor growth inhibition was higher than each drug alone in (C: 65%; E: 70%; E+C: 88%; p=0.001) or what is detected in the E-cadherin negative H460 xenografts (C: 3%, E: 64%, E+C: 75%). Synergistic effects were detected when entinostat was combined with erlotinib in the NCI-H1975 or NCI-H1993 cell lines (combination index, CI<1). Conclusions: Entinostat enhances the effect of Cetuximab in vivo in Ras mutant, E-cadherin positive NSCLC cell lines, or erlotinib in cell lines harboring the EGFR mutation T790M or amplified MET. The combination of entinostat and EGFR inhibitors could provide the rational for developing clinical trials in patients with NSCLC with tumors resistant to EGFR inhibitors.