title: Spatial organization of topoisomerase I-mediated DNA cleavage induced by camptothecin-oligonucleotide conjugates.
abstract: Triple helix-forming oligonucleotides covalently linked to topoisomerase I inhibitors, in particular the antitumor agent camptothecin, trigger topoisomerase I-mediated DNA cleavage selectively in the proximity of the binding site of the oligonucleotide vector. In the present study, we have performed a systematic analysis of the DNA cleavage efficiency as a function of the positioning of the camptothecin derivative, either on the 3' or the 5' side of the triplex, and the location of the cleavage site. A previously identified cleavage site was inserted at different positions within two triplex site-containing 59 bp duplexes. Sequence-specific DNA cleavage by topoisomerase I occurs only with triplex conjugates bearing the inhibitor at the 3'-end of the oligonucleotide and on the oligopyrimidine strand of the duplex. The lack of targeted cleavage on the 5' side is attributed to the structural differences of the 3' and 5' duplex-triplex DNA junctions. The changes induced in the double helix by the triple-helical structure interfere with the action of the enzyme according to a preferred spatial organization. Camptothecin conjugates of oligonucleotides provide efficient tools to probe the organization of the topoisomerase I-DNA complex and will be useful to understand the functioning of topoisomerase I in living cells.
authors.affiliation: Laboratoire de Biophysique, USM0503 Muséum National d'Histoire Naturelle, UMR8646 CNRS, UR565 INSERM, 43 Rue Cuvier, 75231 Paris Cedex 05, France. arimondo@mnhn.fr
authors.forename: Paola B
authors.initials: PB
authors.lastname: Arimondo
authors.forename: Stéphane
authors.initials: S
authors.lastname: Angenault
authors.forename: Ludovic
authors.initials: L
authors.lastname: Halby
authors.forename: Alexandre
authors.initials: A
authors.lastname: Boutorine
authors.forename: Frédéric
authors.initials: F
authors.lastname: Schmidt
authors.forename: Claude
authors.initials: C
authors.lastname: Monneret
authors.forename: Thérèse
authors.initials: T
authors.lastname: Garestier
authors.forename: Jian-Sheng
authors.initials: JS
authors.lastname: Sun
authors.forename: Christian
authors.initials: C
authors.lastname: Bailly
authors.forename: Claude
authors.initials: C
authors.lastname: Hélène
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D002166:Camptothecin / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology*; D004247:DNA / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009841:Oligonucleotides / Q000737:chemistry / Q000235:genetics / Q000494:pharmacology*
chemical_list: C478602:7-ethyl-10-hydroxycamptothecin acetic acid; D009841:Oligonucleotides; C051802:triplex DNA; D004247:DNA; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin