8226/S-ATOR05 cell line is resistant to ATO and resistance is not due to changes in uptake.

<p>(<b>A</b>) 8226/S, 8226/S-CR, 8226/S-ATOR05 cell lines were treated with the indicated concentrations of ATO for 24 h and apoptosis was assessed by flow cytometry using Annexin V-FITC and PI staining and graphed as percent of control Annexin V positive cells versus drug concentration. (<b>B</b>) 8226/S, 8226/S-CR, 8226/S-ATOR05 cells were treated with 2 µM ATO for 24 h and then collected for intracellular arsenic determination. The data are presented as the mean ± SD of at least 3 independent experiments. Student’s <i>t</i>-test was used to compare differences between 8226/S and 8226-CR and 8226/S-ATOR05 cells, with 95% confidence intervals. *, P<0.05; **, P<0.01; ***, P<0.001.