ABCG2 and leukemia: Furthermore, 14C-AZA IUR in ABCG2-overexpressing leukemia cells (K562-ABCG2B) did not alter with ABCG2 inhibitor KO143 (12.14 ± 1.01 ng vs. 12.24 ± 1.09 ng, p = 0.922) (Figure 4E).