To overcome T790M-mediated acquired resistance of lung cancer cells to epidermal 
growth factor receptor tyrosine kinase inhibitors (EGFR TKIs), second generation 
TKIs such as BIBW2992 (afatinib) and third generation TKIs including WZ4002 have 
been developed. However, clinical data on their efficacy in treating T790M 
mutant tumors are lacking. Histone deacetylase (HDAC) inhibitors have been 
reported to arrest cell growth and to lead to differentiation and apoptosis of 
various cancer cells, both in vitro and in vivo. In the present study, we 
assessed whether the combination of suberoylanilide hydroxamic acid (SAHA, 
vorinostat), a potent HDAC inhibitor, and BIBW2992 or WZ4002 could overcome EGFR 
TKI resistance associated with T790M mutation in lung cancer cells. While 
treatment with BIBW2992 or WZ4002 alone slightly reduced the viability of PC-9G 
and H1975 cells, which possess T790M mutation, combining them with SAHA resulted 
in significantly decreased cell viability through the activation of the 
apoptotic pathway. This combination also enhanced autophagy occurrence and 
inhibition of autophagy significantly reduced the apoptosis induced by the 
combination treatment, showing that autophagy is required for the enhanced 
apoptosis. Caspase-independent autophagic cell death was also induced by the 
combination treatment with SAHA and either BIBW2992 or WZ4002. Finally, the 
combined treatment with SAHA and either BIBW2992 or WZ4002 showed an enhanced 
anti-tumor effect on xenografts of H1975 cells in vivo. In conclusion, the 
combination of new generation EGFR TKIs and SAHA may be a new strategy to 
overcome the acquired resistance to EGFR TKIs in T790M mutant lung cancer.