ABCG2 and breast cancer: Similarly, the ABCG2-overexpressing S1-MI-80 human colon cancer cells, MCF7-FLV1000 human breast cancer cells, and H460-MX20 lung cancer cells were significantly resistant to HS-173 as compared to the parental S1 (Figure 1C), MCF7 (Figure 1D), and H460 cells, with calculated RF values of 10, 12, and 5, respectively.