Phosphorylated histone H2AX in relation to cell survival in tumor cells and xenografts exposed to single and fractionated doses of X-rays.
OBJECTIVE
Human tumor cell lines grown as monolayers or xenograft tumors were exposed to single or multiple fractions of X-rays and the ability to use residual gammaH2AX to identify radiosensitive cells was assessed.


METHODS
Twenty-four hour after exposure to single or daily fractions of X-rays, human tumor cells from monolayers or xenografts were analyzed for clonogenic surviving fraction. Cells were also fixed and labeled with anti-gammaH2AX antibodies for analysis by flow and image cytometry. The relative amount of residual gammaH2AX and the percentage of cells with <3 foci were compared with the clonogenic surviving fraction measured for the same population.


RESULTS
The fraction of gammaH2AX remaining 24h after X-irradiation relative to peak levels 1h after exposure was correlated with radiosensitivity (SF2) for 18 human tumor cell lines. The fraction of SiHa, C33A and WiDr cells with <3 gammaH2AX foci was predictive of clonogenic surviving fraction for both monolayer cells exposed to either single doses or up to 5 fractions. Similar results were obtained using cells from xenograft tumors of irradiated mice.


CONCLUSIONS
The percentage of tumor cells that retain gammaH2AX foci 24h after single or fractionated doses appears to be a useful measure of cellular radiosensitivity that is potentially applicable in the clinic.
Klokov
Dmitry
D
Medical Biophysics Department, British Columbia Cancer Research Centre, Vancouver, BC, Canada.
MacPhail
Susan M
SM
Banáth
Judit P
JP
Byrne
James P
JP
Olive
Peggy L
PL
D000818:Animals; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000528:radiation effects; D003110:Colonic Neoplasms / Q000378:metabolism* / Q000473:pathology / Q000532:radiotherapy*; D019583:Dose Fractionation, Radiation; D005260:Female; D006657:Histones / Q000096:biosynthesis / Q000378:metabolism*; D006801:Humans; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D010766:Phosphorylation / Q000528:radiation effects; D002583:Uterine Cervical Neoplasms / Q000378:metabolism* / Q000473:pathology / Q000532:radiotherapy*; D014965:X-Rays; D023041:Xenograft Model Antitumor Assays
C468783:H2AX protein, human; D006657:Histones