ABCG2 and breast cancer: In a study by Chen and co-workers127 using parental and mitoxantrone-selected breast-cancer cell lines MCF and MCF/MX, respectively; the lung-carcinoma cell line A549, with moderate endogenous expression of ABCG2; and the prostate-cancer cell line DU145, with no detectable ABCG2 expression, showed that siRNA knockdown of ABCG2 and use of a transporter inhibitor drastically reduced the proliferation of cells with moderate to high expression of ABCG2127.