A standardized G2-assay for the prediction of individual radiosensitivity.

Background And Purpose: 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.

Materials And 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.