Table 2.

Sensitization of HCT-15 cells to doxorubicin treatment by selected 3,4-dihydroisocoumarins.

Compound	IC50 (μM)	p-Value	Fold change
Doxorubicin	8.5 ± 0.7	–	1.00
+2.5 μM PSC833	0.3 ± 0.03∗∗	0.0017	28.33
+20 μM 16	8.7 ± 1.6	0.9999	0.98
+50 μM 16	2.3 ± 0.08∗	0.0129	3.70
+20 μM 14	9.6 ± 1.0	0.9498	0.89
+50 μM 14	10.6 ± 2.1	0.6313	0.80

PSC833 was used as positive control. Fold change of cytotoxicity was determined by dividing the IC₅₀ value of cells treated with doxorubicin alone by the IC₅₀ value of cells treated with doxorubicin in combination with the respective test compound. Data show mean ± SEM of three independent experiments performed in quadruplicates. ^∗p < 0.05; ^∗∗p < 0.01 compared to doxorubicin alone (one-way ANOVA followed by Dunnett’s multiple comparisons test).