title: Role of glutathione and nucleotide excision repair in modulation of cisplatin activity with O6-benzylguanine.
abstract: OBJECTIVE
  Modulation of platinating agent cytotoxicity has important clinical implications as a result of their widespread use in the treatment of many different cancers. O6-Benzylguanine (BG) enhances the cytotoxicity of cisplatin against several human tumor lines. The purpose of our work was to elucidate whether BG affects pathways prior to DNA damage (i.e., glutathione, GSH) or following DNA damage (i.e., nucleotide excision repair, NER).
  
  
  METHODS
  In efforts to determine the mechanism of enhancement we: (1) evaluated whether different sequences of BG plus cisplatin treatment differed in their ability to enhance cisplatin-induced cytotoxicity and DNA platination; (2) determined the effect of BG on GSH and glutathione S-transferase (GST) activity and; (3) determined whether BG enhanced cisplatin-induced cytotoxicity in cells lacking specific enzymes in the NER pathway. Colony-forming assay, atomic absorption spectroscopy and HPLC were employed to measure tumor cell growth inhibition, quantitate the amount of platinum on DNA, and determine intracellular GSH concentrations, respectively.
  
  
  RESULTS
  Increased cytotoxicity and platination of DNA was observed when cells were exposed to BG prior to and/or during cisplatin treatment and not when BG followed cisplatin treatment. BG did not significantly alter GST activity with minimal depletion of GSH. In contrast, buthionine sulfoximine (BSO) caused a much more dramatic decrease in GSH than BG that was not accompanied by a dramatic increase in sensitivity to cisplatin. Furthermore, BG enhanced the cytotoxicity of cisplatin in a series of cell lines deficient in NER.
  
  
  CONCLUSIONS
  Overall, our results suggest that the mechanism of enhancement involves neither the GSH nor the NER pathways, but triggers an event prior to DNA platination damage that ultimately results in increased cytotoxicity, apoptosis and increased platination levels.
authors.affiliation: Department of Medicine, Committee on Cancer Biology and Cancer Research Center, University of Chicago, Chicago, IL, 60637, USA.
authors.forename: Melissa L
authors.initials: ML
authors.lastname: Fishel
authors.affiliation: Duke University Medical Center, Durham, NC, 27701, USA.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Gamcsik
authors.affiliation: Department of Medicine, Committee on Cancer Biology and Cancer Research Center, University of Chicago, Chicago, IL, 60637, USA.
authors.forename: Shannon M
authors.initials: SM
authors.lastname: Delaney
authors.affiliation: University of Pittsburgh Cancer Institute, Pittsburgh, PA, 15213, USA.
authors.forename: Eleanor G
authors.initials: EG
authors.lastname: Zuhowski
authors.affiliation: The Carcinogenesis Laboratory, Michigan State University, East Lansing, MI, 48824, USA.
authors.forename: Veronica M
authors.initials: VM
authors.lastname: Maher
authors.affiliation: Department of Health Studies, University of Chicago, Chicago, IL, 60637, USA.
authors.forename: Theodore
authors.initials: T
authors.lastname: Karrison
authors.affiliation: Laboratory of Comparative Carcinogenesis, National Cancer Institute at Frederick, Frederick, MD, 21702-1201, USA.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Moschel
authors.affiliation: University of Pittsburgh Cancer Institute, Pittsburgh, PA, 15213, USA.
authors.forename: Merrill J
authors.initials: MJ
authors.lastname: Egorin
authors.affiliation: Department of Medicine, Committee on Cancer Biology and Cancer Research Center, University of Chicago, Chicago, IL, 60637, USA. edolan@medicine.bsd.uchicago.edu.|University of Chicago, 5841 S. Maryland Ave., P.O. Box MC2115, Chicago, IL, 60637, USA. edolan@medicine.bsd.uchicago.edu.
authors.forename: M Eileen
authors.initials: ME
authors.lastname: Dolan
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D002945:Cisplatin / Q000494:pharmacology*; D004249:DNA Damage; D004260:DNA Repair / Q000187:drug effects*; D004357:Drug Synergism; D005978:Glutathione / Q000378:metabolism*; D006147:Guanine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D006801:Humans; D010984:Platinum / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; C064976:O(6)-benzylguanine; D010984:Platinum; D006147:Guanine; D005978:Glutathione; D002945:Cisplatin