Representative gels of the TOP1-mediated DNA cleavage assay. Lane 1, DNA alone; lane 2, DNA and TOP1; lane 3, DNA and TOP1 with CPT (1 μM); lane 4, DNA and TOP1 with LMP744 (1 μM); lanes 5–28, DNA and TOP1 with the tested compounds at 0.1, 1.0, 10, and 100 μM concentrations, respectively. The arrows and numbers at left indicate the cleavage site positions.