Fig. 4.

Suppression of topoisomerase I-mediated relaxation of supercoiled plasmid DNA by RL compounds. a RL90 and RL91 did not stimulate DNA cleavage mediated by topoisomerase I. No topoisomerase I-mediated DNA cleavage was observed in RL90 and RL91 at 100 μM. Camptothecin is included as an example of drug-induced in topoisomerase I mediated DNA cleavage. The gel was run in the presence of ethidium bromide. Arrow, Nicked DNA. b RL90 and RL91 inhibit the catalytic activity of DNA topoisomerase I. DNA relaxation assay was performed in the presence of RL90 (100 μM, lane 5) and RL91 (100 μM, lane 6). CPT (100 μM, lane 4) and DMSO (lane 3) was included as control. Agarose gel stained with ethidium bromide was shown. Arrow, supercoiled DNA. LM linear marker; SC supercoiled DNA (0.25 μg); R relaxed DNA; N Nicked DNA; Topo topoisomerase I 1 unit (a), 0.25 units (b); CPT: camptothecin (100 μM); RL90, 100 μM; RL91, 100 μM