The individual contributions of TOP2A and TOP2B to DOX-induced DNA damage and to its prevention by DRZ. (A) HTETOP cells were treated for 24 h with DRZ, its analogue ICRF-161 or ICRF-193, alone or combined with 1 μM DOX. TOP2B, TOP2A and γ-H2AX protein levels were determined by Western blot. (B) Western blot of γ-H2AX, TOP2B and TOP2A in mock- or TOP2B siRNA-transfected HTETOP cells incubated with 0.1 or 1 μM DOX for 24 h. TOP2A was depleted from HTETOP cells by 24 h pre-incubation with 1 μg/ml TET, followed by TOP2B siRNA transfection. DOX was added 24 h later following transfection. (C) and (D) HTETOP cells were pre-treated with 1 μg/ml TET (C) or TOP2B siRNA (D) for 24 h, followed by 24 h exposure to DOX alone or in combination with 100 μM DRZ. DRZ was administered 30 min before DOX. γ-H2AX, TOP2A and TOP2B protein levels were determined by Western blot.