ABCG2 and lung cancer: A dual ABCG2/ABCB1 inhibitor in S1-M1-80 (mitoxantrone (MX)-selected ABCG2-overexpressing of human colorectal cancer cell line S1), NCI-H460/MX20 (MX-selected ABCG2-overexpressing of human lung cancer cell line NCI-H460)