DNA supercoiling and repair in peripheral lymphocytes as a measure of acute radiation response after radiotherapy

Abstract

DNA supercoiling density and incision kinetics during ultraviolet (UV) excision repair hav been measured in lymphocytes from 20 cancer patients and 17 healthy donors. Nucleoid sedimentation was used, which allows the sensitive detection of both DNA damage and alterations in chromatin structure. The release of DNA supercoiling after ethidium bromide intercalation and the kinetics of the incision step following UV irradiation were compared in lymphocytes derived from cancer patients and those from normal donors. The classification into lymphocytes with normal or reduced repair and normal or altered supercoiling, respectively, revealed that reduced repair as well as altered chromatin structure occurred more frequently in lymphocytes derived from patients (40% and 85%, respectively) than in those from healthy donors (35% and 23%, respectively). Even more striking was the simultaneous occurrence of both characteristics in tumor patients: in 34% of all cases reduced repair was associated with altered supercoiling density, whereas among healthy donors this association occurred in only 18% of all cases. Supercoiling density may be related to functional integrity of lymphocytes and repair capacity to recovery after radiation damage. Since both parameters are important for the radiation response of normal tissue, we consider these measurements a potential prognostic assay aimed at reducing acute reaction of the normal tissue.