Comparison of Top1 mediated DNA cleavage induced by camptothecin (CPT), LMP-400, LMP-776 and lamellarin D (LamD). (a) Compound structures. (b) (lane 1) DNA alone; (lane 2) Top1 alone; (lane 3–16) Top1 + indicated drugs at 0.3, 0.9, 2.7, and 8.1 μM, respectively. The numbers on the left and arrows indicate cleavage site positions. A 117-bp DNA substrate was used in this assay, but the cleavage sites are numbered to be consistent with the 161-bp DNA substrate traditionally used in this assay in order to facilitate comparison (25).