Fig. 1

Effect of HDACis ± HY-PDT on cell growth and mitochondrial membrane dissipation potential. a Cell growth (metabolic activity by MTT), b mitochondrial membrane potential (TMRE+), and c HY content were measured after a sequential treatment starting with HDACis for 24 h followed by activation with hypericin for 48 h (a, b; HT-29 and HCT 116 cells) or for 0–1 h (c; HT-29 cells). The 0 h time point indicates that measurements were done immediately after hypericin activation. Samples treated with drug-free vehicle solvents (<0.1% DMSO) were used as the reference control. The results are expressed as percentage of control and represent the average ± SD of three independent experiments each done in triplicates (a) or singlets (b, c). Data was analyzed using one-way ANOVA with Tukey post hoc test. HCT 116 cell growth was compared to that of HT-29 (▪p < 0.05, ▪▪p < 0.01, ▪▪▪p < 0.001; a, b). All conditions were compared to the reference control (*p < 0.05, **p < 0.01, ***p < 0.001), and the combined treatments were compared to HY-PDT alone (ǂp < 0.05, ǂǂp < 0.01, ǂǂǂp < 0.001) and to correspondingly equal concentrations of HDACis alone (▲p < 0.05, ▲▲p < 0.01, ▲▲▲p < 0.001). The study design is outlined in d