A standardized G2-assay for the prediction of individual radiosensitivity

Abstract

Background and purposeAn 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 methodsLymphocytes 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. ResultsRadiation-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. ConclusionsThe standardized G2-assay can minimize inter-laboratory and intra-experimental variations and may have straightforward application in clinical practice for individualization of radiotherapy protocols.