, 2008, Oliveira-Brett et al., 2002 and Rauf et al., 2005).

2,2-Dimethyl-(3H)-3-(N-3′-nitrophenylamino)naphtho[1,2-b]furan-4,5-dione (QPhNO2, C20H16O5N2, molecular mass ABT-263 cost 364.35 g/mol) was prepared as described previously ( da Silva Júnior et al., 2007). Stock solutions for pharmacological assays were prepared by dissolving QPhNO2 and nor-beta in 0.1% DMSO immediately prior to use. Doxorubicin hydrochloride (adriamycin, CAS No. 25316-40-9) (Dox) was purchased from Sigma Aldrich Co. (St. Louis, MO, USA). RPMI 1640 growth medium supplemented with 2% glutamine, fetal bovine serum, streptomycin and penicillin was purchased from Gibco® (Invitrogen, Carlsbad, CA, USA). Calf thymus dsDNA (sodium salt, type I) was purchased from Sigma (St. Louis, MO, USA). Aqueous acetate buffer solutions (0.1 M, pH 4.5), which were used in the electrochemical

experiments involving DNA, were prepared from analytical grade reagents and purified water (conductivity < 0.1 μS/cm) Z-VAD-FMK obtained from a Millipore (Milford, MA, USA) Milli-Q system. Dimethylformamide (DMF) and tetrabutylammonium tetrafluoroborate (TBABF4) were used in the electrochemical experiments (aprotic medium) and prepared from analytical grade reagents supplied by Sigma Aldrich. HL-60 cells (human promyelocytic leukemia line) were grown in RPMI-1640 medium supplemented with 10% fetal bovine serum, 100 μg/mL streptomycin and 100 U/mL penicillin 17-DMAG (Alvespimycin) HCl at 37 °C in a 5% CO2 atmosphere. The cytotoxicity

of compounds (0.009–5 μg/mL) was evaluated using the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) reduction assay ( Mosmann, 1983) after 24 h of incubation. Doxorubicin was used as a positive control. In a second set of experiments, N-acetyl-l-cysteine (NAC, 5 mM) was pre-incubated with the cells for 1 h before drug addition, and after 24 h, cytotoxicity was measured, as previously described. Additional experiments were performed to elucidate the mechanisms involved in the cytotoxic action of nor-beta and QPhNO2 using HL-60 cells (3 × 105 cells mL−1) after drug exposure for 24 h. Compounds were dissolved in DMSO to make a 1 mg mL−1 stock solution and added to the cell culture to obtain a final concentration of 0.5, 1.0 or 2.0 μM QPhNO2, based on its IC50 value, or 1.0 or 2.0 μM nor-beta. Doxorubicin (0.5 μM) was used as a positive control. After the quinone treatment, cells were loaded with 2′,7′-dichlorodihydrofluorescein diacetate (H2-DCF-DA) (20 μM) and incubated at 37 °C for 30 min in the dark, as proposed by Lebel et al. (1992). Doxorubicin and beta-lapachone were used as positive controls. The experiments were repeated in the presence of NAC (5 mM) pre-incubated with the cells for 1 h before drug addition. The cells were then harvested, washed, resuspended in PBS and analyzed immediately by flow cytometry at excitation and emission wavelengths of 490 and 530 nm, respectively.