Antileukemic effects of cercosporamide. (A) U937 cells were incubated for 5 days in the presence or absence of the indicated doses of cercosporamide. Cell proliferation was assessed by an MTT assay. Data are expressed as means ± standard error (SE) of 5 independent experiments. (B) MM6 cells were incubated for 5 days in the presence or absence of the indicated doses of cercosporamide. Cell proliferation was assessed by an MTT assay. Data are expressed as means ± SE of 3 independent experiments. (C) K562 cells were incubated for 5 days in the presence or absence of the indicated doses of cercosporamide. Cell proliferation was assessed by an MTT assay. Data are expressed as means ± SE of 4 independent experiments. (D) U937 cells were plated in methylcellulose culture assay system with increasing concentrations of cercosporamide, as indicated. Data are expressed as percentage control of leukemic colonies for untreated cells and represent means ± SE of 5 experiments. (E) U937 cells were plated in methylcellulose culture assay system with cytarabine (1 ng/mL) and/or cercosporamide (10 µM), as indicated, and CFU-L leukemic colony formation was assessed. Data are expressed as a percentage control of CFU-L for untreated cells. Means ± SE of the values from 5 independent experiments are shown. Paired t test analysis for the combinations of cytarabine plus cercosporamide showed P = .011 compared with cercosporamide alone and P = .009 compared with cytarabine alone. UT, untreated.