(A) Effect of As₂O₃and/or RA on NB4 and NB4-As^R cell growth. NB4 and NB4-As^R were seeded at 10⁵ cells/mL and incubated with 10⁻⁷ mol/L As₂O₃(•), with 10⁻⁶ mol/L RA (⧫), with the combination of 10⁻⁶ mol/L RA and 10⁻⁷ mol/L As₂O₃ (▴) or without As₂O₃ (□). A representative experiment among three separate assays is shown. Each value represents the mean ± SD of three determinations. (B) Effect of As₂O₃and/or RA on NB4 or NB4-As^R cell apoptosis. NB4 and NB4-As^R were treated for 3 days as indicated in the pictures. The percentage of apoptosis (%) was determined by a TUNEL assay (abscissa) and PI staining (ordinate), and analyzed by flow cytometry.