Cotreatment with PS and DZNep synergistically induces apoptosis of cultured AML cells and significantly prolongs survival of mice implanted with AML cells. (A) OCI-AML3 and HL-60 cells were treated with DZNep and/or PS as indicated for 48 hours. At the conclusion of treatment, cell death was assessed by trypan blue dye uptake in a hemocytometer. Columns represent the mean of 3 independent experiments; bars represent SEM. (B) OCI-AML3 and HL-60 cells were treated with the indicated concentrations of DZNep and/or PS for 24 hours. Cell lysates were prepared and immunoblot analysis was performed for PARP cleavage. The levels of β-actin in the lysates served as the loading control. Vertical lines have been inserted to indicate a repositioned gel lane. (C) Analysis of dose-effect relationship for DZNep (100-750 nmol/L) and PS (5-20 nmol/L) for the apoptotic effects after 48 hours of exposure in OCI-AML3 and HL-60 cells was performed according to the median dose-effect method of Chou and Talalay. After this, the CI values were calculated. CI < 1, CI = 1, and CI > 1 represent synergism, additivity, and antagonism of the 2 agents, respectively. (D) Female NOD/SCID mice were injected in the lateral tail vein with HL-60 cells. The cells were allowed to engraft for 7 days before initiation of treatment. Mice were treated intraperitoneally with dimethylsulfoxide, 1 mg/kg DZNep 2 days per week for 2 weeks, and/or 10 mg/kg PS 3 days per week for 4 weeks. n = 7 per group. Survival of the mice in all groups (vehicle, DZNep alone, PS alone, and combination) is represented by Kaplan-Meier plot.