Time course of response of THP-1 and HL-60 cells to GO. The THP-1 and HL-60 cell lines were cultured in the presence of 300 ng/mL, and cells were fixed at the beginning of culture (T0) or after 24 hours (T24), 48 hours (T48), or 72 hours (T72). Cells were then stained with propidium iodide (PI) and analyzed for cell cycle. The results are representative of at least 2 independent experiments.