Growth inhibitory effects of topo II poisons in the presence or absence of a fixed concentration of NU7026. K562 cells were treated with increasing concentrations of (A) etoposide, (B) idarubicin, (C) doxorubicin, or (D) mAMSA in the absence (▪) or presence (○) of 10 μM NU7026. After 5 days of exposure, cells were stained with XTT and OD_450nm was quantified. Results are means of at least 4 experiments ± SE.