Extracellular ascorbic acid generates ROSs and augments the cytotoxicity of As₂O₃. Cell viability of HL60 (A) and U266 cells (B) treated with 1, 2, 3, and 5 μMAs₂O₃ with (▪) or without (□) 100 μM extracellular ascorbic acid for 48 hours. (C, left) Annexin V (FL1) and PI (FL3) flow cytometry analysis of apoptotic HL60 cells treated with AA or DHA for 20 hours. (Right) Percentage of apoptotic cells after treatment with either AA, DHA, As₂O₃, or the combination of DHA and As₂O₃.NT indicates cells not treated. (D) Cell viability of HL60 cells containing (•) or depleted of (○) GSH and treated with increasing concentrations of ascorbic acid in culture media. Cell viability was determined 48 hours after treatment. (E) Production of ROSs in HL60 cells loaded with vitamin C using DHA (•) and in cells where ascorbic acid was added in culture media (○). Data are expressed as the mean ± SD of 3 (A-B) and 2 (C-E) independent experiments.