title: Induction of topoisomerase I cleavage complexes by 1-beta -D-arabinofuranosylcytosine (ara-C) in vitro and in ara-C-treated cells.
abstract: 1-beta-d-Arabinofuranosylcytosine (Ara-C) is a nucleoside analog commonly used in the treatment of leukemias. Ara-C inhibits DNA polymerases and can be incorporated into DNA. Its mechanism of cytotoxicity is not fully understood. Using oligonucleotides and purified human topoisomerase I (top1), we found a 4- to 6-fold enhancement of top1 cleavage complexes when ara-C was incorporated at the +1 position (immediately 3') relative to a unique top1 cleavage site. This enhancement was primarily due to a reversible inhibition of top1-mediated DNA religation. Because ara-C incorporation is known to alter base stacking and sugar puckering at the misincorporation site and at the neighboring base pairs, the observed inhibition of religation at the ara-C site suggests the importance of the alignment of the 5'-hydroxyl end for religation with the phosphate group of the top1 phosphotyrosine bond. This study also demonstrates that ara-C treatment and DNA incorporation trap top1 cleavage complexes in human leukemia cells. Finally, we report that camptothecin-resistant mouse P388/CPT45 cells with no detectable top1 are crossresistant to ara-C, which suggests that top1 poisoning is a potential mechanism for ara-C cytotoxicity.
authors.affiliation: Laboratory of Molecular Pharmacology, Division of Basic Sciences, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4255, USA.
authors.forename: P
authors.initials: P
authors.lastname: Pourquier
authors.forename: Y
authors.initials: Y
authors.lastname: Takebayashi
authors.forename: Y
authors.initials: Y
authors.lastname: Urasaki
authors.forename: C
authors.initials: C
authors.lastname: Gioffre
authors.forename: G
authors.initials: G
authors.lastname: Kohlhagen
authors.forename: Y
authors.initials: Y
authors.lastname: Pommier
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D002166:Camptothecin / Q000494:pharmacology; D003561:Cytarabine / Q000494:pharmacology*; D004247:DNA / Q000737:chemistry*; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D004351:Drug Resistance; D004790:Enzyme Induction / Q000187:drug effects*; D006801:Humans; D051379:Mice; D015394:Molecular Structure; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D003561:Cytarabine; D004247:DNA; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin