For analysis of apoptosis, cells (2 × 105 cells per well) were seeded into 6-well plates and cultured for 24 h, and then exposed to DFMO (0, 0.25, 0.5, 1, or 1.5 mM) for 72 h. Cells were trypsinized and washed twice with cold phosphate-buffered saline (PBS) solution, and then resuspended with PBS and incubated for 5 min at room temperature with annexin V-fluorescein isothiocyanate (FITC) plus propidium iodide. Cells were analyzed using a FACS Calibur flow cytometer (BD Biosciences, San Jose, CA). For cell cycle analysis, cells were treated with DFMO, harvested and washed twice with PBS, and fixed with cold 70% ethanol overnight at −20 °C. Stained cells were detected and quantified by flow cytometry.