Inhibition of histone deacetylases sensitizes EGF receptor-TK inhibitor-resistant non-small-cell lung cancer cells to erlotinib in vitro and in vivo.

Intrinsic and/or acquired resistance of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) commonly occurs in patients with non-small-cell lung cancer (NSCLC). Here, we developed a combined therapy of histone deacetylase inhibition by a novel HDAC inhibitor, YF454A, with erlotinib to overcome EGFR-TKI resistance in NSCLC. The sensitization of the effects of erlotinib by YF454A was examined in a panel of EGFR-TKI-resistant NSCLC cell lines in vitro and two different erlotinib-resistant NSCLC xenograft mouse models in vivo. Western blotting and Affymetrix GeneChip expression analysis were further performed to determine the underlying mechanisms for the effects of the combination of erlotinib and YF454A. YF454A and erlotinib showed a strong synergy in the suppression of cell growth by blocking the cell cycle and triggering cell apoptosis in EGFR-TKI-resistant NSCLC cells. The combined treatment led to a significant decrease in tumour growth and tumour weight compared with single agents alone. Mechanistically, this combination therapy dramatically down-regulated the expression of several crucial EGFR-TKI resistance-related receptor tyrosine kinases, such as Her2, c-Met, IGF1R and AXL, at both the transcriptional and protein levels and consequently blocked the activation of downstream molecules Akt and ERK. Transcriptomic profiling analysis further revealed that YF454A and erlotinib synergistically suppressed the cell cycle pathway and decreased the transcription of cell-cycle related genes, such as MSH6 and MCM7. Our preclinical study of YF454A provides a rationale for combining erlotinib with a histone deacetylase inhibitor to treat NSCLC with EGFR-TKI resistance.