Figure 4.

Effect of gimatecan (ST1481) or topotecan treatment on topoisomerase I expression in MCR cell line. Nuclear protein extract was obtained from cells treated with ST1481 (0.1 µg/ml) or topotecan (1 µg/ml) for 1 hour, immediately after treatment (A), or after 4 hours of washout (B), or after 24 hours of washout (C), or after 72 hours of washout (D). Equal amounts of nuclear protein (3 µg) were resolved on 8% SDS polyacrylamide gel, blotted onto nitrocellulose membrane, and probed with antihuman DNA topoisomerase I monoclonal antibody. The bands of topoisomerase I were visualized using chemiluminescence system. Actin was used as a control of protein loading.