Src kinase inhibitor PP2 blocked the incorporation of [³H]-thymidine into KVL-1 cells and caused the reduction of cells in the S phase of the cell cycle. (A) KVL-1 cells (1 × 10⁶) were treated with the Src kinase inhibitor PP2, its inactive analog PP3, or the Syk kinase inhibitor piceatannol (all 2.5 μMor5.0 μM), in a growth medium. After 16 hours, the cells were pulsed with [³H]-thymidine for 4 hours, and the radioactivity incorporated into the cells was measured as described in “Materials and methods.” Results represent the means (± SD) of 3 separate experiments. Marked decreases in [³H]-thymidine incorporation were observed only with PP2 (P < .001). (B) KVL-1 cells (1 × 10⁶) were treated with 2.5 μM or 5.0 μM PP2 for 20 hours. Cell cycle profiles of the propidium iodide–stained cells were analyzed by flow cytometry, and the percentages of the cells in the G₀G₁,G₂M, and S phases of cell cycle were calculated using the ModFit software program. Proliferation index (PI) was calculated from the SG₂/G₀G₁ ratios. Results are representative of 3 independent experiments. DNA content (FL2-A) is depicted on the x axis and the number of cells after staining with propidium iodide is depicted on the y axis.