Synergistic Effects of Simvastatin and Irinotecan against Colon Cancer Cells with or without Irinotecan Resistance

Figure 6

Synergistic effect of simvastatin and irinotecan on caspase-3 activity in HT-29 cell and irinotecan-resistant HT-29 cells. The spectrophotometric assay of caspase-3 activity was carried out as described in Section 2. HT-29 cells were treated for 48 h with simvastatin (SV) alone, irinotecan (IR) alone, and combination of SV and IR at 2 : 1 molar ratio in which the concentration of SV and IR was 57.7 μM and 15.625 μM, respectively (a). Following each drug treatment for 48 h, the spectrofluorometric assay of caspase-3 activity was carried out. The data are expressed as the means ± SD from three independent experiments. , compared to untreated control cells; , compared to SV alone; , compared to IR alone. HT-29R cells were treated for 48 h with SV alone, IR alone, and combination of SV and IR at 2 : 1 molar ratio in which the concentration of SV and IR was 111 μM and 49 μM, respectively (b). Following each drug treatment for 48 h, caspase-3 activity was determined spectrophotometrically using a multiplate reader (DTX 880 Multimode Detector). Increased caspase-3 activities were evident in combination treatment group of the cells relative to untreated control and single treatment of SV or IR in HT-29 cells (a) and HT-29R cells (b). The data are expressed as the means ± SD from three independent experiments. , compared to untreated control cells; , compared to SV alone; , compared to IR alone.

(a)

(b)