K562 cells with ABCG2 overexpression exhibited attenuated apoptosis and were no longer arrested in S phase by mitoxantone treatment.

<p>(<b>a</b>, <b>b</b>) After exposure to 10 nM, 100 nM or 1 µM of mitoxantone for 72 h, the cell lines were subjected to flow cytometry to quantify the number of apoptotic cells, and an increased drug resistance was observed in K562/ABCG2, K562/AO2 and K562/IMR cells compared with wild-type K562 cells. (<b>c</b>) The cell cycle phase was determined by flow cytometry after treatment with different concentrations of mitoxantone, which decreased the inhibition of DNA synthesis at S phase in K562/ABCG2, K562/AO2 and K562/IMR cells compared with wild-type K562 cells. The histogram represented the means ± s.d. for three replicates. *<i>P</i><0.05.