The Relationship between Cellular Radiosensitivity and Radiation-Induced DNA Damage Measured by the Comet Assay

Abstract

ABSTRACT. The relationship between deoxyribonucleic acid (DNA) damage and the cell death induced by γ-irradiation was examined in three kinds of cells, Chinese hamster ovary fibroblast CHO-K1, human melanoma HMV-II and mouse leukemia L5178Y. Cell survival was determined by a clonogenic assay. The induction and rejoining of DNA strand breaks induced by radiation were measured by the alkaline and neutral comet assays. L5178Y cells were the most radiosensitive, while CHO-K1 cells and HMV-II cells were radioresistant. There was an inverse relationship between the survival fraction at 2 Gy (SF2) and the yield of initial DNA strand breaks per unit dose under the alkaline condition for the comet assay, and also a relationship between SF2 and the residual DNA strand breaks (for 4 hr after irradiation) under the neutral condition for the comet assay, the latter being generally considered to be relative to cellular radiosensitivity. In the present analysis, it was considered that the alkaline condition for the comet assay was optimal for evaluating the initial DNA strand breaks, while the neutral condition was optimal for evaluating the residual DNA strand breaks. Since the comet assay is simpler and more rapid than other methods for detecting radiation-induced DNA damage, this assay appears to be a useful predictive assay for evaluating cellular clonogenic radiosensitivity of tumor cells. KEY WORDS: comet assay, DNA strand break, γ-irradiation, predictive assay, radiosensitivity.J. Vet. Med. Sci. 65(4): 471-477, 2003 Different types of cell lines show different radiosensitivities. In addition, even a tumor of the same origin and pathology, can show radiosensitivity over quite a wide range [4], and therefore, understanding the radiosensitivity of an individual tumor is of great importance in the clinical situation. Knowledge of the intrinsic radiosensitivities of cells from a tumor biopsy can help produce an optimized radiotherapy protocol for individual patients.Reproductive death measured by a clonogenic assay is an important index for the cell death induced by radiation, and the cellular radiosensitivities of fibroblasts and tumor cells have been evaluated by a clonogenic assay [13,17]. A good correlation was found between the reproductive death of fibroblasts measured by the clonogenic assay and the severity of late normal tissue effects, such as fibrosis and erythema, after radiotherapy [7,14]. However, this clonogenic assay consumes a lot of time, and the cells must be proliferated in vitro [4,14]. Hence this assay is not optimal for routine clinical use, and thus there is now much interest in exploiting a more rapid and simple assay to evaluate cellular radiosensitivity [8,25].It is said that the cell death caused by radiation is due to deoxyribonucleic acid (DNA) damage [29]. DNA double strand breaks (dsbs) are considered to be closely related to cell death because it is suggested that they can lead directly to chromosome aberration and the loss of genetic material [22]. To date, the correlation between radiose...

Potential use of the comet assay in the clinical management of cancer

“…0.95) between the two methods in measuring the radiosensitivity of several bladder (25,42) and colorectal (40) tumour cell lines after irradiation with ,10 Gy in vitro, indicating that both initial DNA damage and residual damage can be used to predict for radiosensitivity in these cell lines. Similar studies have also shown a correlation between radiosensitivity measured by the comet assay and SF2 clonogenic survival following in vitro radiation of human melanoma (50), cervical (39) and ovarian (49) tumour cell lines. In normal fibroblasts, initial DNA damage, but not DNA repair, has also been shown to correlate with clonogenic survival (51).…”

Light dependency of resistance to ionizing radiation in Euglena gracilis

“…This result indicates that the radiation resistance of E. gracilis is not related to the dsb content, but related to the dsb rejoining ability. In mammalian cells, it has been shown that the radiation resistance is not related to the dsb content at 0 h after g-irradiation, but related to the dsb rejoining ability (Wada et al, 2002). The tendency of radiation resistance of E. gracilis in this study corresponds with these reports.…”

“…The tail moment values at 0 h after 750-Gy irradiation for light-and dark-grown cells of strain SM-ZK were 57.571.4 and 51.578.7. The reason might be that the yield of dsb produced by irradiation is less than 5% of the ssb (Olive, 1999;Wada et al, 2002). The dsb repair proceeds less efficient compared with the ssb repair (Olive, 1999).…”

Killing of Feline T-Lymphocytes by Gamma-Rays and Energetic Carbon Ions

“…Inactivation cross-section in FeT-J cells exposed to carbon ions is greater than that in CHO-K1 ovarian cells of the Chinese hamster [18] and normal human fibroblast AG01522 cells [8]. FeT-J cells are likely to be more radiosensitive than CHO-K1 cells and human malignant melanoma HMV-II, and less than murine lymphoma L5178Y [28].…”