title: Gemcitabine (2',2'-difluoro-2'-deoxycytidine), an antimetabolite that poisons topoisomerase I.
abstract: OBJECTIVE
  Gemcitabine-containing regimens are among standard therapies for the treatment of advanced non-small cell lung,pancreatic, or bladder cancers. Gemcitabine is a nucleoside analogue and its cytotoxicity is correlated with incorporation into genomic DNA and concomitant inhibition of DNA synthesis. However, it is still unclear by which mechanism(s) gemcitabine incorporation leads to cell death.
  
  
  METHODS
  We used purified oligodeoxynucleotides to study the effects of gemcitabine incorporation on topoisomerase I (top1) activity and tested the role of top1 poisoning in gemcitabine-induced cytotoxicity in cancer cells.
  
  
  RESULTS
  We found that top1-mediated DNA cleavage was enhanced when gemcitabine was incorporated immediately 3' from a top1 cleavage site on the nonscissile strand. This position-specific enhancement was attributable to an increased DNA cleavage by top1 and was likely to have resulted from a combination of gemcitabine-induced conformational and electrostatic effects. Gemcitabine also enhanced camptothecin-induced cleavage complexes. We also detected top1 cleavage complexes in human leukemia CEM cells treated with gemcitabine and a 5-fold resistance of P388/CPT45 top1-deficient cells to gemcitabine, indicating that poisoning of top1 can contribute to the antitumor activity of gemcitabine.
  
  
  CONCLUSIONS
  The present results extend our recent finding that incorporation of 1-beta-D-arabinofuranosylcytosine into DNA can induce top1 cleavage complexes [P. Pourquier et al. Proc. Natl. Acad. Sci. USA, 97: 1885-1890, 2000]. The enhancement of camptothecin-induced top1 cleavage complexes may, at least in part, contribute to the synergistic or additive effects of gemcitabine in combination with topotecan and irinotecan in human breast or lung cancer cells.
authors.affiliation: Laboratory of Molecular Pharmacology, Division of Basic Sciences, NCI, National Institutes of Health, Bethesda, Maryland 20892-4255, USA.
authors.forename: Philippe
authors.initials: P
authors.lastname: Pourquier
authors.forename: Christopher
authors.initials: C
authors.lastname: Gioffre
authors.forename: Glenda
authors.initials: G
authors.lastname: Kohlhagen
authors.forename: Yoshimasa
authors.initials: Y
authors.lastname: Urasaki
authors.forename: François
authors.initials: F
authors.lastname: Goldwasser
authors.forename: Lary W
authors.initials: LW
authors.lastname: Hertel
authors.forename: Shuyuan
authors.initials: S
authors.lastname: Yu
authors.forename: Richard T
authors.initials: RT
authors.lastname: Pon
authors.forename: William H
authors.initials: WH
authors.lastname: Gmeiner
authors.forename: Yves
authors.initials: Y
authors.lastname: Pommier
mesh_terms: D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D051379:Mice; D008956:Models, Chemical; D009841:Oligonucleotides / Q000737:chemistry; D013997:Time Factors; D059004:Topoisomerase I Inhibitors; D014407:Tumor Cells, Cultured; D000093542:Gemcitabine
chemical_list: D000964:Antimetabolites, Antineoplastic; D004791:Enzyme Inhibitors; D009841:Oligonucleotides; D059004:Topoisomerase I Inhibitors; D003841:Deoxycytidine; D000093542:Gemcitabine