title: Sequence-selective DNA cleavage by a topoisomerase I poison, NB-506.
abstract: An indolocarbazole compound, NB-506, inhibits the activity of topoisomerase I by stabilizing the DNA-topoisomerase I complex (cleavable complex). NB-506 inhibited the religation step of topoisomerase I activity more potently than camptothecin or its derivative, topotecan. A cleavage assay using an end-labeled fragment of DNA revealed that the pattern of cleavage induced by NB-506 was different from that induced by camptothecin. The preferred cleavage sites of NB-506 were found to be not only T but also A or C at the 3'-terminus of the cleaved DNA (position -1), while the DNA cleavage sites of camptothecin always had T at position -1. At the 5'-terminus of the cleaved DNA (position +1), NB-506 showed a preference for G, which is a feature shared in common with camptothecin. Therefore, the difference in cleavage patterns was most likely due mainly to the preferred base at position -1. Moreover, the re-ligation rate was significantly slower at NB-506-selective sites, which had C at position-1, than at camptothecin-selective sites or at sites cleaved by both NB-506 and camptothecin. Our data suggest that NB-506 is an unique topoisomerase I poison and that its potent inhibition of topoisomerase I is partly dependent on retardation of re-ligation at sites selectively induced by NB-506.
authors.affiliation: Banyu Tsukuba Research Institute (in collaboration with Merck Research Laboratories), Tsukuba, Japan. biomedl@banyu.co.jp
authors.forename: K
authors.initials: K
authors.lastname: Fukasawa
authors.forename: H
authors.initials: H
authors.lastname: Komatani
authors.forename: Y
authors.initials: Y
authors.lastname: Hara
authors.forename: H
authors.initials: H
authors.lastname: Suda
authors.forename: A
authors.initials: A
authors.lastname: Okura
authors.forename: S
authors.initials: S
authors.lastname: Nishimura
authors.forename: T
authors.initials: T
authors.lastname: Yoshinari
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D001483:Base Sequence; D002166:Camptothecin / Q000494:pharmacology; D002227:Carbazoles / Q000494:pharmacology*; D004247:DNA / Q000187:drug effects* / Q000235:genetics; D004260:DNA Repair; D005960:Glucosides / Q000494:pharmacology*; D008969:Molecular Sequence Data; D059004:Topoisomerase I Inhibitors
chemical_list: D000970:Antineoplastic Agents; D000972:Antineoplastic Agents, Phytogenic; D002227:Carbazoles; D005960:Glucosides; C092476:NB 506; D059004:Topoisomerase I Inhibitors; D004247:DNA; D002166:Camptothecin