A. NTC and BRCA1-kd SKOV-3 cells were treated with 5 μM etoposide, 0.75 μM triapine, or both agents in combination for 4 hr. Total protein was analyzed for the levels of phospho-RPA32 (S4/S8), RPA32, CtIP, γ-H2AX, HSC70 by western blotting. The HSC70 level was used as a loading control. B. Cells were transfected with 50 nM CtIP-siRNA1. After 48 hr, cells were treated with 5 μM etoposide for 4 hr and total protein was analyzed by western blotting as described in A. C. NTC SKOV-3 cells were treated with various concentrations of etoposide in combination with fixed concentrations of triapine as indicated. BRCA1-kd cells were also treated with various concentrations of etoposide in the absence of triapine. Colonies were stained and clonogenic survival was determined. Data are means ± SD. D. NTC and BRCA1-kd SKOV-3 cells were treated with 5 μM etoposide, 0.75 μM triapine, or both agents in combination for 4 hr. Cells were stained with an anti-BRCA1 antibody and counterstained for nuclei. Immunofluorescence of BRCA1 foci (green) and nuclei (blue) were visualized by confocal microscopy.