ABCG2 and cancer: To determine if this pattern of expression of MDR-associated ABC transporters following below IC50 selection was drug and cell line independent, we selected MCF-7 cells with a single-step selection using 300 nM etoposide and two additional cancer lines, IGROV-1 ovarian cancer cells and S-1 colon tumor cells, with 14 and 21 nM doxorubicin, respectively (Figure 1B–D).