Effect of harmine on cell cycle progression. B16F-10 melanoma cells were treated with harmine for 48 h and analyzed for propidium iodide stained-DNA content by flow cytometry. Values indicate the percentage of the cell population at the phase of the cell cycle. M1 = G1 (Diploid), M2 = G2/M (Tetraploid), M3 = S (Synthetic phase), M4 = Sub-G1 phase. The population of cells in the sub-G0/G1 phase represents cellular fragments due to apoptosis.