Trolox enhances arsenic-mediated apoptosis in NB4, AR2, and IM9 cells. (A-B) NB4, AsR2, and IM9 cells were treated with As₂O₃ and trolox (T) for 48 hours. Apoptosis was detected by PI staining. Flow cytometric histograms are shown in panel A. Quantitation of PI-positive cells in a hypotonic fluorochrome solution was performed. Apoptotic cells were also stained with annexin V–FITC and propidium iodide in binding buffer and quantified (B). Each bar represents an average of 3 independent samples, and standard deviation bars are shown. Asterisks indicate significant differences from As₂O₃-treated cells (^**P < .01; ^***P < .001). (C) Cells were treated as indicated for 48 hours. Caspase-3 activation was measured using Red-DEVD-FMK. Its binding to activated caspase-3 was analyzed by flow cytometry. Asterisks indicate significant differences (P < .001) from As₂O₃-treated cells. (D) Western blotting was performed to determine PARP protein levels after 48 hours of treatment. β-Actin was used to show equal loading of lanes. Results are representative of 3 independent experiments each performed in duplicate. (E) NB4 cells were treated with doxorubicin, AraC, or etoposide with or without trolox (T) for 48 hours. Apoptosis was detected by PI staining as described in “Materials and methods.” Each bar represents an average of 3 independent samples, and standard deviation bars are shown.