ZOL alters the cell cycle and induces apoptosis in BV173 cells. The effect of ZOL was evaluated by cell cycle analysis using flow cytometry. BV173 cells were exposed to different concentrations of ZOL for 12 or 24 hours. ZOL at 20 μM decreased the percentage of cells in G₂/M phase and increased the proportion of cells between G₀/G₁ and G₂/M without appropriate BrdUrd incorporation (indicated by arrows in panels A-C). A TUNEL assay with PI counterstaining revealed that ZOL induces widespread apoptosis from the S phase to G₂/M boundary (D-F). The data shown are representative of 3 independent experiments.