ABCG2 and cancer: We observed that metformin acted on multiple cancer-promoting pathways in DOXRes MCF7 cells by reducing the expression of at least two members of the ABC drug antiporters, MDR-1 and BCRP, reducing cancer-related phosphorylation of S6K on serine 473, and p53 on serine 392 [29], and by reducing the expression of HIF1α (Fig 3A and 3D).