The radioenhancement of two human head and neck squamous cell carcinomas by 2'-2' difluorodeoxycytidine (gemcitabine; dFdC) is mediated by an increase in radiation-induced residual chromosome aberrations but not residual DNA DSBs.
OBJECTIVE
The present study aimed at investigating if 2'-2' difluorodeoxycytidine (dFdC) radioenhancement was mediated by an effect on induction and/or repair of radiation-induced DNA DSBs and chromosome aberrations in cells with different intrinsic radiosensitivity.


METHODS
Confluent human head and neck squamous cell carcinoma cell lines designated SCC61 and SQD9 were treated with 5 microM dFdC for 3 or 24 h prior to irradiation. DNA DSBs induction and repair were analyzed by PFGE. Radiation-induced chromosome aberrations were examined with a FISH technique.


RESULTS
In both cell lines, dFdC did not modify radiation-induced DNA DSBs in a dose range between 0 and 40 Gy. After a single dose of 40 Gy, dFdC affected neither the kinetic of repair nor the residual amount of DNA DSBs up to 4 h after irradiation. Whereas dFdC did not increase the induction of chromosome aberrations, after a single dose of 5 Gy, the percentage of aberrant cells and the number of aberrations per aberrant cells were significantly higher in combination with dFdC.


CONCLUSIONS
Our data suggest that under experimental conditions yielding substantial radioenhancement, dFdC decreases the repair of genomic lesions inducing secondary chromosome breaks but has no effect on DNA DSBs repair as measured by PFGE.
Rosier
Jean-François
JF
Department of Radiation Oncology, UCL St-Luc University Hospital, Avenue Hippocrate 10, 1200, Brussels, Belgium
Michaux
Lucienne
L
Ameye
Geneviève
G
Cedervall
Björn
B
Libouton
Jeanne-Marie
JM
Octave-Prignot
Michèle
M
Verellen-Dumoulin
Christine
C
Scalliet
Pierre
P
Grégoire
Vincent
V
D000970:Antineoplastic Agents / Q000494:pharmacology*; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy* / Q000473:pathology; D002869:Chromosome Aberrations / Q000187:drug effects* / Q000528:radiation effects*; D003131:Combined Modality Therapy; D004249:DNA Damage / Q000187:drug effects / Q000528:radiation effects; D004273:DNA, Neoplasm / Q000187:drug effects / Q000528:radiation effects; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D006258:Head and Neck Neoplasms / Q000188:drug therapy* / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D011836:Radiation Tolerance; D011839:Radiation, Ionizing; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D013997:Time Factors; D014407:Tumor Cells, Cultured; D000093542:Gemcitabine
D000970:Antineoplastic Agents; D004273:DNA, Neoplasm; D011838:Radiation-Sensitizing Agents; D003841:Deoxycytidine; D000093542:Gemcitabine