Figure 3

Cytotoxic activity of doxorubicin (DOX) towards (A) HL60 cells, (B) HL60/VINC cells and (C) HL60/DOX cells. The enzymatic samples contained as follows: for DOX ‘recycling’: 100 μ M DOX, 100 μ M NADPH and 0.1 mg ml⁻¹ CPR; for DOX activated (undergoing reductive conversion): 100 μ M DOX, 500 μ M NADPH and 0.1 mg ml⁻¹ CPR; for DOX activated+SOD: 100 μ M DOX, 500 μ M NADPH, 0.1 mg ml⁻¹ CPR and 500 U ml⁻¹ SOD (0.01 M K₂HPO₄/KH₂PO₄ buffer, pH 7.25; 37°C). The appropriate volumes of the enzymatic sample were added directly to the cell suspension to yield the DOX concentration varying in the range of 0.1–100 nM, 5 nM–3 μ M and 5 nM–5 μ M for HL60 (A), HL60/VINC (B) and HL60/DOX (C) cells, respectively. The cytotoxic effect of DOX was determined by incubating cells (10⁵) with 10 different concentrations of the compound for 72 h. The data points are from a representative experiment.