Fig. 7. Effects of cytostatic agents on U937 cells. U937 cells were incubated in the absence (Control) or presence of hydroxyurea (100 µg/ml) or phenylbutyrate (1.5 mM) with or without GM-CSF (200 units/ml) for 120 h and then assessed for clonogenic leukemia growth (A) and CD11b expression (B). Results represent means of five separate experiments; bars, SE. Ps are as determined by ANOVA for the comparison of all treatment groups.