Survival Fraction at 2 Gy and γH2AX Expression Kinetics in Peripheral Blood Lymphocytes From Cancer Patients: Relationship With Acute Radiation-Induced Toxicities

Purpose: Predictive assays for acute radiation toxicities would be clinically relevant in radiation oncology. We prospectively examined the predictive role of the survival fraction at 2 Gy (SF2) and of gamma H2AX (double-strand break [DSB]DNA marker) expression kinetics in peripheral blood mononuclear cells (PBMCs) from cancer patients before radiation therapy. Methods and Materials: SF2 was measured with Trypan Blue assay in the PBMCs from 89 cancer patients undergoing radiation therapy at 4 hours (SF2([4h])) and 24 hours (SF2([24h])) after ex vivo irradiation. Using Western blot analysis and band densitometry, we further assessed the expression of gamma H2AX in PBMC DNA at 0 hours, 30 minutes, and 4 hours (33 patients) and 0 hour, 4 hours, and 24 hours (56 patients), following ex vivo irradiation with 2 Gy. Appropriate ratios were used to characterize each patient, and these were retrospectively correlated with early radiation therapy toxicity grade. Results: The SF2((4h)) was inversely correlated with the toxicity grade (P=.006). The gamma H2AX-ratio(30min) (band density of irradiated/ non-irradiated cells at 30 minutes) revealed, similarly, a significant inverse association (P=.0001). The DSB DNA repair rate from 30 minutes to 4 hours, calculated as the relative R gamma H2AX-ratio (gamma H2AX-ratio((4h))/gamma H2AX-ratio(30min)) showed a significant direct association with high toxicity grade (P=.01). Conclusions: Our results suggest that SF2 is a significant radiation sensitivity index for patients undergoing radiation therapy. gamma H2AX Western blot densitometry analysis provided 2 important markers of normal tissue radiation sensitivity. Low gamma H2AX expression at 30 minutes was linked with high toxicity grade, suggesting that poor gamma H2AX repair activity within a time frame of 30 minutes after irradiation predicts for poor radiation tolerance. On the other hand, rapid gamma H2AX content restoration at 4 hours after irradiation, compatible with efficient DSB repair ability, predicts for increased radiation tolerance. (C) 2015 Elsevier Inc. All rights reserved.