A standardized G2-assay for the prediction of individual radiosensitivity.
OBJECTIVE
An increased yield of chromatid breaks following G2-phase irradiation could be a marker of radiosensitivity-predisposing genes that respond to DNA damage. We have shown that the dynamic nature of chromatin-nucleoprotein complex, which is capable of rapid unfolding, disassembling, assembling and refolding, affects repair of radiation-induced DNA-lesions and causes chromatid breaks during G2-M transition in damaged DNA sites. Here, we investigate induction and repair kinetics of chromatid breaks, their potential role in radiosensitivity predisposition and a standardized G2-assay is proposed to assess individual radiosensitivity.


METHODS
Lymphocytes from 125 blood donors with significant inter-individual radiosensitivity variation (healthy, cancer, AT-patients) are used to correlate G2-checkpoint efficiency with chromatid breakage and individual radiosensitivity. Experiments involve repair kinetics of chromatid breaks using colcemid-block and treatment with caffeine to abrogate G2-checkpoint, generate internal controls and standardize the G2-assay.


RESULTS
Radiation-induced chromatid breaks during G2-M transition, following 4h repair, remained unchanged and a significant correlation between G2-chromosomal radiosensitivity and G2-checkpoint efficiency to prevent chromatid breakage was found. A standardized G2-assay is developed by introducing normalization to conditions reflecting lack of checkpoint and repair similar to those of AT-patients, generating a unique standard for individual radiosensitivity testing.


CONCLUSIONS
The standardized G2-assay can minimize inter-laboratory and intra-experimental variations and may have straightforward application in clinical practice for individualization of radiotherapy protocols.
Laboratory of Radiobiology & Biodosimetry, National Center for Scientific Research Demokritos, Athens, Greece. gabriel@ipta.demokritos.gr
Gabriel E
GE
Pantelias
Georgia I
GI
Terzoudi
D016022:Case-Control Studies; D002869:Chromosome Aberrations; D004249:DNA Damage / Q000528:radiation effects; D004260:DNA Repair / Q000235:genetics; D005260:Female; D059565:G2 Phase Cell Cycle Checkpoints / Q000235:genetics; D006801:Humans; D008214:Lymphocytes / Q000528:radiation effects*; D008297:Male; D009369:Neoplasms / Q000235:genetics* / Q000473:pathology / Q000532:radiotherapy*; D011237:Predictive Value of Tests; D011829:Radiation Dosage; D011836:Radiation Tolerance / Q000235:genetics* / Q000528:radiation effects; D012016:Reference Values; D012494:Sampling Studies