(A-D) Effect of curcumin, TSA or combined curcumin and TSA treatment on the putative TICs in the resistant (A, B) and sensitive (C, D) cell lines. Bar graphs show colony (top), sphere (middle) and side population (SP) (bottom) frequencies. The data are means ± SD of three independent experiments. *, P < 0.05; **, P < 0.01. ***, P < 0.001, ns. = not significant