ABCG2 and cancer: Using Hoechst 33342 dye and fluorescence-activated cell sorting (FACS) of cancer cells treated with 20 μM reserpine, we concluded that after 48 h of incubation, UA significantly decreased the percentages of ABCG2-positive BCSCs, representing approximately 86% (from 2.3% to 0.4%) in MDA-MB-231 cells and 78% (from 2.6% to 0.6%) in the flow cytometry assay (Figure 2A,B).