Histone deacetylase inhibitor romidepsin enhances anti-tumor effect of erlotinib in non-small cell lung cancer (NSCLC) cell lines

Most epidermal growth factor receptor (EGFR) mutant non-small cell lung cancers (NSCLCs) are sensitive to EGFR tyrosine kinase inhibitors (TKIs) such as erlotinib or gefitinib, but many EGFR wild type NSCLCs are resistant to TKIs. In this study, we examined the effects of the histone deacetylase inhibitor, romidepsin, in combination with erlotinib, in NSCLC cell lines and xenografts. Methods: For in vitro studies, nine NSCLC cell lines with varying mutation status and histology were treated with erlotinib and romidepsin alone or in combination. 3-(4, 5-dimethylthiazol-2-yl)-5- (3-carboxymethoxyphenyl)-2-(4- sulfophenyl)-2H-tetrazolium assays were performed to determine the concentration that inhibits 50% (IC50) value of each drug or the combination. For in vivo studies, NCIH1299 xenografts were inoculated subcutaneously into athymic nude mice. Romidepsin and/or erlotinib were injected intraperitoneally after tumors developed and tumor sizes were measured. Results: We found that romidepsin increased the sensitivity of erlotinib synergistically in all nine NSCLC cell lines including EGFR and KRAS wild type cell lines, KRAS mutant cell lines, and TKI resistant EGFR mutant cell lines. This effect was partially due to enhanced apoptosis. Furthermore, cotreatment of erlotinib and romidepsin inhibited NCIH1299 xenograft growth in athymic nude mice. Conclusions: These observations support a role for the combination of a histone deacetylase inhibitor and a TKI in the treatment of NSCLCs.