ABCG2 and malignant colon neoplasm: Furthermore, TMP195 also reversed ABCG2-mediated resistance to mitoxantrone, a known drug substrate of ABCG2 [25], in S1-M1-80, an ABCG2-overexpressing MDR variant of S1 human colon cancer cells (Figure 1C), and in HEK293 cells transfected with human ABCG2 (R482, Figure 1D and Table 1).