Fig. 7

Augmentation of cisplatin treatment by treatment with napabucasin. a Napabucasin decreased expression of ALDH1A1 and ALDH1A3 isoforms in NOY-1 CisR cells. ALDH1A2 expression was upregulated after napabucasin treatment. Chemosensitive HT-29/EGFP cells were used as a positive control for the ALDH1A1 expression and chemoresistant HT-29/EGFP/FUR cells as a positive control for the ALDH1A2, ALDH1A3 and ALDH1B1. b Flow cytometric analysis revealed decreased expression of CD133 in napabucasin treated NOY-1 CisR cells. c Combinatorial treatment with cisplatin and high concentration of napabucasin had synergistic effect. d Data obtained by luminescent viability assay were analyzed by Calcusyn software, and Fa-CI plots were created—CI (combination index) on the y-axis is a function of effect level (fraction affected, fa) on the x-axis (fa = 1−% of viable cells/100). Plots display synergism (CI < 1), additivity (CI = 1) or antagonism (CI > 1) for the entire spectrum of effects [66]. Red arrows indicates the synergy of cisplatin and 0.18 µg/ml napabucasin. e Pre-treatment of the cells with napabucasin (0.06 µg/ml) and following treatment with cisplatin (1 µg/ml) reduced the number of clones in a clonogenic assay. f Pre-treatment with napabucasin (0.06 µg/ml) did not change viability of cells treated with cisplatin (1 µg/ml). g Combination of cisplatin (1 μg/ml) with napabucasin (0.06 µg/ml) significantly inhibited tumor growth in vivo. NOY-1 CisR cells were treated with 1 μg/ml cisplatin for six days (group A) or pretreated with 0.06 µg/ml napabucasin and then exposed to 1 μg/ml cisplatin for six days (group B). h Tumors were significantly smaller in the group of mice injected with cells pre-treated with napabucasin compared to mice injected with cells treated with cisplatin alone. i Image of representative tumors at the end of the experiment showing improved effect of combinatorial treatment. cispt-cisplatin, napa-napabucasin, *P < 0.05, **P < 0.01, ***P < 0.001