Effect of various fixed ratio combinations of simvastatin and irinotecan on cell viability in HT-29 cells and irinotecan-resistant HT-29 cells. Simvastatin (SV) and irinotecan (IR) were administered at molar ratios of 4 : 1, 2 : 1, 1 : 1, 1 : 2, and 1 : 4 based on IC50 values of these two drugs on HT-29 cells and HT-29R cells. Cell proliferation of HT-29 (a) and HT-29R cells (b) at various molar ratios of both drugs was measured by MTT assay. These results showed that combined treatment of irinotecan with simvastatin more potently suppressed cell proliferation of HT-29 cells even with resistance to irinotecan as well as without resistance to irinotecan. The data are expressed as the means ± SD from three independent experiments.