Figure 5. Pharmacological inhibition of Rac1 decreases proliferation and slows progression through the G₁ phase of the cell cycle. (A) The effects of NSC23766 on Rac and Rho activity were measured by active Rac or Rho pull-down. Quantitative densitometry was conducted to determine the ratio of active GTPase to total GTPase detected in the immunoblots. The values are normalized to densitometric values obtained from ECL-Western blots of cells not treated with NSC23766. Results are the mean ± SE from three independent experiments. (B) Proliferation of NCI-H1703 cells was assayed by measuring [³H]thymidine uptake after a 24 h incubation with the indicated concentrations of the Rac inhibitor NSC23766. The values are normalized to [³H]thymidine uptake by cells treated without the drug. Results are the mean ± SE from three independent experiments conducted with six replicates for each treatment in each experiment. (C) The rate of proliferation was assessed by measuring [³H]thymidine uptake at the indicated times after incubation with NSC23766 for 24 h. (D) Changes in cell cycle progression were determined by incubation of NCI-H1703 cells with the Rac inhibitor NSC23766 (100 μg/ml) for 24, followed by flow cytometry analysis. (E) Histograms of cell cycle analysis conducted with NCI-H1703 cells treated with or without the Rac1 inhibitor NSC23766. Results are the mean ± SE from three independent experiments. Symbols above a column indicate a statistical comparison of cells treated with NSC23766 and control cells treated without NSC23766 (NS, not significant; *p < 0.01).