title: The relation between deoxycytidine kinase activity and the radiosensitising effect of gemcitabine in eight different human tumour cell lines.
abstract: BACKGROUND
  Gemcitabine (dFdC) is an active antitumour agent with radiosensitising properties, shown both in preclinical and clinical studies. In the present study, the relation between deoxycytidine kinase (dCK) activity and the radiosensitising effect of gemcitabine was investigated in eight different human tumour cell lines.
  
  
  METHODS
  Tumour cells were treated with dFdC (0-100 nM) for 24 h prior to radiotherapy (RT) (gamma-Co60, 0-6 Gy, room temperature). Cell survival was determined 7, 8, or 9 days after RT by the sulforhodamine B test. dCK activity of the cells was determined by an enzyme activity assay.
  
  
  RESULTS
  A clear concentration-dependent radiosensitising effect of dFdC was observed in all cell lines. The degree of radiosensitisation was also cell line dependent and seemed to correlate with the sensitivity of the cell line to the cytotoxic effect of dFdC. The dCK activity of our cell lines varied considerably and differed up to three fold from 5 to 15 pmol/h/mg protein between the tested cell lines. In this range dCK activity was only weakly related to radiosensitisation (correlation coefficient 0.62, p = 0.11).
  
  
  CONCLUSIONS
  Gemcitabine needs to be metabolised to the active nucleotide in order to radiosensitise the cells. Since dFdCTP accumulation and incorporation into DNA are concentration dependent, the degree of radiosensitisation seems to be related to the extent of dFdCTP incorporated into DNA required to inhibit DNA repair. The activity of dCK does not seem to be the most important factor, but is clearly a major factor. Other partners of the intracellular metabolism of gemcitabine in relation to the cell cycle effects and DNA repair could be more responsible for the radiosensitising effect than dCK activity.
authors.affiliation: Laboratory of Cancer Research and Clinical Oncology, Department of Medical Oncology, University of Antwerp (UA/UZA), Wilrijk, Belgium. bea.pauwels@ua.ac.be
authors.forename: Bea
authors.initials: B
authors.lastname: Pauwels
authors.forename: Annelies E C
authors.initials: AE
authors.lastname: Korst
authors.forename: Greet G O
authors.initials: GG
authors.lastname: Pattyn
authors.forename: Hilde A J
authors.initials: HA
authors.lastname: Lambrechts
authors.forename: Juliette A E
authors.initials: JA
authors.lastname: Kamphuis
authors.forename: Christel M J
authors.initials: CM
authors.lastname: De Pooter
authors.forename: Godefridus J
authors.initials: GJ
authors.lastname: Peters
authors.forename: Filip
authors.initials: F
authors.lastname: Lardon
authors.forename: Jan B
authors.initials: JB
authors.lastname: Vermorken
mesh_terms: D002470:Cell Survival; D004260:DNA Repair; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D003842:Deoxycytidine Kinase / Q000187:drug effects / Q000378:metabolism*; D004354:Drug Screening Assays, Antitumor; D006801:Humans; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D000093542:Gemcitabine
chemical_list: D011838:Radiation-Sensitizing Agents; D003841:Deoxycytidine; D003842:Deoxycytidine Kinase; D000093542:Gemcitabine