Alterations of cell viability after treatment with HDAC inhibitors and rhTRAIL variants 4C7 or DHER. DLD-1 cells (A) or WiDr cells (B) were firstly treated with 10 μM HDAC inhibitors including SAHA, Entinostat, RGFP966, or PCI34051, respectively, for 24 h and the day after cells were incubated with rhTRAIL 4C7 or DHER overnight. Cell viability was determined by MTS assay. The values shown are mean ± SD from one of three experiments performed in triplicate. p values were analyzed by one-way ANOVA in Turkey’s multiple comparison with Graphpad Prism version 7.0. ** 0.001 ≤ p ≤ 0.01, **** p ≤ 0.0001.