Figure 5.
Modulation of topoisomerase I activity by gimatecan (ST1481) or topotecan in HT1376 cell line. Cells were treated with ST1481 (0.01 µg/ml) or topotecan (1 µg/ml) for 1 hour. After 4 hours (A), 24 hours (B), and 72 hours (C) of incubation in drug-free medium, nuclear protein was extracted from 5 x 106 cells as indicated in Material and Methods section. Supercoiled plasmid DNA (375 ng) was unwinded by 30-minute incubation at 37°C with adequately diluted nuclear protein extract and resolved on 1% agarose gel. Arrow: Bands of supercoiled plasmid DNA. Bracket: Bands of plasmid DNA unwinded by topoisomerase I. Figures are representatives of at least three experiments.