Figure 5. Nutlin-3-induced p21^waf1 protein leads to reversible G₁/G₂ arrest. (A) p53 wild-type cells (top panel) and p53- and p21^waf1-defective cells (bottom panel) were incubated with 10 µM Nutlin-3 for 0–24 h. Cells were harvested and assayed for DNA content by flow cytometry. (B) After 24 h of 10 µM Nutlin-3, the drug was removed and cells were incubated for an additional 24 h in fresh medium before assaying by flow cytometry.