The inhibition gels compounds against TOP1 and TOP2. (A) TOP1-mediated (left) and TOP2-mediated (right) relaxation assay gels. Lane 1, supercoiled pBR322 DNA alone; lane 2, DNA and enzyme; lanes 3–6, DNA, enzyme and the tested compound at 25 μM concentration, respectively. Camptothecin (CPT) and etoposide (ETP) were used as positive controls for TOP1 and TOP2, respectively. R, relaxed DNA; Sc, supercoiled DNA. (B) Detection of TOP2-DNA covalent cleavage complexes by in vivo complex of enzyme (ICE) assay using CCRF-CEM cells. Lane 1, untreated control; lanes 2 and 3, cells treated with ETP at 10 and 50 μM concentration, respectively; lanes 4 and 5, cells treated with 74 at 10 and 50 μM concentration, respectively; lane 6, cells co-treated with 10 μM ETP and 50 μM 74.