title: DNA mismatch repair proficiency executing 5-fluorouracil cytotoxicity in colorectal cancer cells.
abstract: BACKGROUND
  5-fluorouracil (5FU)-based chemotherapy is the standard treatment for advanced stage colorectal cancer (CRC) patients. Several groups including ours have reported that stage II-III colorectal cancer patients whose tumors retain DNA Mismatch repair (MMR) function derive a benefit from 5FU, but patients with tumors that lost MMR function do not. Although MMR recognition of 5FU incorporated in DNA has been demonstrated biochemically, it has not been demonstrated within cells to execute 5FU cytotoxicity.
  
  
  OBJECTIVE
  To establish an efficient construction model for 5FU within DNA and demonstrate that 5FU incorporated into DNA can trigger cellular cytotoxicity executed by the DNA MMR system.
  
  
  METHODS
  We constructed a 5FdU-containing heteroduplex plasmid (5FdU plasmid) and 5FdU-containing linear dsDNA (5FdU linear DNA), and transfected these into MMR-proficient, hMLH1-/- and hMSH6-/- cells. We observed cell growth characteristics of both transfectants for 5FU-induced cytotoxicity.
  
  
  RESULTS
  MMR- proficient cells transfected with the 5FdU plasmid but not the 5FdU linear DNA showed reduced cell proliferation by MTS and clonogenic assays, and demonstrated cell morphological change consistent with apoptosis. In MMR-deficient cells, neither the 5FdU plasmid nor 5FdU linear DNA induced cell growth or morphological changes different from controls.
  
  
  CONCLUSIONS
  5FdU as heteroduplex DNA in plasmid but not linear form triggered cytotoxicity in a MMR-dependent manner. Thus 5FU incorporated into DNA, separated from its effects on RNA, can be recognized by DNA MMR to trigger cell death.
authors.affiliation: Division of Gastroenterology, Department of Internal Medicine, University of Michigan, Ann Arbor, MI, USA.
authors.forename: Moriya
authors.initials: M
authors.lastname: Iwaizumi
authors.forename: Stephanie
authors.initials: S
authors.lastname: Tseng-Rogenski
authors.forename: John M
authors.initials: JM
authors.lastname: Carethers
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000096:biosynthesis / Q000235:genetics; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology / Q000627:therapeutic use*; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000235:genetics* / Q000473:pathology; D053843:DNA Mismatch Repair; D004273:DNA, Neoplasm / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics; D005472:Fluorouracil / Q000378:metabolism / Q000494:pharmacology*; D045325:HCT116 Cells; D006801:Humans; D000070957:MutL Protein Homolog 1; D009687:Nuclear Proteins / Q000096:biosynthesis / Q000235:genetics; D010957:Plasmids / Q000235:genetics; D014162:Transfection
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000964:Antimetabolites, Antineoplastic; D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; C094443:G-T mismatch-binding protein; C501486:MLH1 protein, human; D009687:Nuclear Proteins; D000070957:MutL Protein Homolog 1; D005472:Fluorouracil