(−)-Xanthatin does not affect topoisomerase I (Topo I)-mediated DNA relaxation. Effects of (−)-xanthatin and (−)-dihydrox-anthatin on Topo I-catalyzed DNA relaxation are shown. The filled vs unfilled arrowheads refer to the positions of supercoiled DNA and relaxed DNA, respectively. After the incubation of Topo I alone or in combination with xanthanolides, each sample was subjected to agarose gel electrophoresis, followed by staining with ethidium bromide. A 1-kbp DNA ladder marker was also loaded. Xa, (−)-xanthatin; and Di, (−)-dihydroxanthatin. A representative data image is shown.