Differences in the topoisomerase I cleavage complexes formed by camptothecin and wakayin, a DNA-intercalating marine natural product

Wakayin is a bispyrroloiminoquinone isolated from a Clavelina sp, ascidian by cytotoxicity directed fractionation, Like camptothecin, it has been found to inhibit the topoisomerase I catalyzed relaxation of supercoiled DNA, Wakayin enhanced cleavage complex formation at the same DNA sequences as camptothecin, Both compounds showed dose-related increases in cleavage complex formation, though wakayin's effect is attenuated at high concentrations. Wakayin is a strong DNA binder, Wakayin also differed from camptothecin in that its cleavage complexes were much less stable than those of camptothecin in 0.5 M NaCl. Again in contrast to camptothecin, wakayin stabilized cleavage complexes poorly, if at all, at 0 degrees C.