(A) DNA relaxation assay. Lane 1: 0.3 pmol of negatively supercoiled DNA substrate and no protein; lane 2: DNA, TOP2, and DMSO; lanes 3–4: DNA, TOP2, and NPRL-Z-1; and lane 5: DNA, TOP2 and etoposide. (B) A498 cells were treated with NPRL-Z-1 or etoposide for 1 h to detect the depletion of free enzymes, TOP2α and TOP2β, using the band depletion assay. (C) A498 cells were treated with NPRL-Z-1 or camptothecin for 1 h to detect the depletion of free enzymes, TOP1, using the band depletion assay. (D) Restoration of depleted TOP2 expression. After treatment with NPRL-Z-1 or etoposide for 1 h, the medium was replaced with fresh growth medium and cells were incubated for another hour (R). Cells were then harvested and prepared for TOP2α and TOP2β detection via western blotting. N10 and E25 indicated as NPRL-Z-1 10 µM and etoposide 25 µM, respectively.