DNA histogram of U937, HL-60, and K562 cells after treatment with dCF and dAd. Cells were cultured with 1 (2) and 10 (3) nmol/L dCF in the presence of 10 μmol/L dAd for 2 days. 1, Untreated control cells. Cells were fixed and stained with propidium iodide, and the DNA content was analyzed by flow cytometry. The apoptotic cell population is shown by the first peak (Apo).