Growth inhibition of NB4, HL60, U937, and KG-1 cell lines after As₂O₃ or melarsoprol treatment. Various concentrations of As₂O₃ and melarsoprol were added to the media (Materials and Methods): Controls (○), 10⁻⁵ mol/L (▵), 10⁻⁶ mol/L (□), and 10⁻⁷ mol/L (•). As₂O₃ at a concentration of 10⁻⁴ mol/L (⊞) was also used. Representative results from one of three independent experiments are shown as the mean ± SD of triplicates. Inhibition of cell growth and loss of viability are comparable in four different cell lines in which PML-RAR fusion protein is or is not present.