Radiation-induced DNA damage and repair in lymphocytes from breast cancer patients and their correlation with acute skin reactions to radiotherapy.

PURPOSE: Repair of radiation-induced DNA damage plays a critical role for both the susceptibility of patients to side effects after radiotherapy and their subsequent cancer risk. The study objective was to evaluate whether DNA repair data determined in vitro are correlated with the occurrence of acute side effects during radiotherapy. METHODS AND MATERIALS: Breast cancer patients receiving radiation therapy after a breast-conserving surgery were recruited in a prospective epidemiologic study. As an indicator for clinical radiosensitivity, adverse reactions of the skin were recorded. Cryo-preserved lymphocytes from 113 study participants were gamma-irradiated with 5 Gy in vitro and analyzed using the alkaline comet assay. Reproducibility of the assay was determined by repeated analysis (n = 26) of cells from a healthy donor. A coefficient of variation of 0.3 was calculated. RESULTS: The various parameters determined to characterize the individual DNA repair capacity showed large differences between patients. Eleven patients were identified with considerably enhanced DNA damage induction, and 7 patients exhibited severely reduced DNA repair capacity after 15 and 30 min. Six patients were considered as clinically radiosensitive, indicated by moist desquamation of the skin after a total radiation dose of about 50 Gy. CONCLUSIONS: Using the alkaline comet assay as described here, breast cancer patients were identified showing abnormal cellular radiation effects, but this repair deficiency corresponded only at a very limited extent to the acute radiation sensitivity of the skin. Because impaired DNA repair could be involved in the development of late irradiation effects, individuals exhibiting severely reduced DNA repair capacity should be followed for the development of late clinical symptoms.

New measure of DNA repair in the single-cell gel electrophoresis (comet) assay.

Since its introduction by Ostling and Johanson [1984; Biochem Biophys Res Commun 123:291-298] and independent modifications by Singh et al. [1990; Exp Cell Res 175:184-191] and Olive et al. [1988; Radiat Res 112:86-94], the comet assay has been widely used in genetic toxicology, environmental biomonitoring, molecular and human epidemiology, and clinical investigations. There are still several issues to be resolved before the comet assay is accepted as a standard assay for detecting DNA damage and repair in a single cell. One of the major issues is the proper quantification of DNA damage/repair. The aim of this article is to develop a new quantitative measure of DNA damage/repair which is represented in the dose-time-response surface. We propose to use the second derivative (2D) of the dose-time-response surface for measuring DNA repair activity. This approach enables us to represent the DNA repair activity of cells exposed to a DNA-damaging agent with a single number by combining all the information of a dose-time-response experiment. The computation procedure includes the application of linear regression. An SAS/AF-based program, "Comet Assay," was developed for this computation and is freely available on the Internet. We considered the response of each of four DNA damage parameters: tail moment, tail length, tail DNA, and tail inertia for constructing the dose-time-response surface. Using data from 25 patients, we observed that 2Ds based on tail moment and tail DNA were highly correlated and that tail inertia might provide information on a somewhat different aspect of DNA damage/repair.