Furthermore, we found that the effect of HS-173 on G2/M cell-cycle arrest and apoptosis was substantially reduced in ABCB1-overexpressing KB-V1 and ABCG2-overexpressing S1-MI-80 cancer cell lines when compared to what was observed with their respective parental cell lines (Figure 2 and Figure 3). This evidence concerns the gene ABCG2 and cancer.