ABCG2 and cancer: First, the intrinsic cytotoxicity of hydroxygenkwanin was determined in the ABCB1-overexpressing cancer cell lines KB-V1 (Figure 1A) and NCI-ADR-RES (Figure 1B); in the ABCG2-overexpressing cancer cell lines NC-H460/MX20 (Figure 1C) and A549-Bec150 (Figure 1D); and in the respective drug-sensitive parental cancer cell lines KB-3-1, OVCAR-8, NCI-H460, and A549.