Increased chemoresistance in PXR overexpressing cells to irinotecan and SN38. For neutral red assays, cells were treated for 72 h by increasing concentrations of irinotecan (A) or SN38 (B). Columns, mean viability as a percentage of control (i.e., cells without chemotherapeutics treatment, 100%) from replicates (n = 6) from six separate experiments; bars, SEM. a, viability percentages of PXR2, PXR3 and PXR6 compared to pcDNA3-transfected cells (p < 0.05) (Mann and Whitney test). b, viability percentages of PXR2, PXR3 and PXR6 compared to each other using Kruskal Wallis test (p < 0.05).