Abstract
Purpose: To investigate the LET and ion species dependence in PLDR-related mutation induction at the hypoxanthine-guanine phosphoribosyltransferase (HPRT) locus in normal human embryonic lung fibroblasts irradiated with high- or low-LET radiations. Materials and Methods: Normal human embryonic lung fibroblasts distributed by the RIKEN BRC Cell Bank were irradiated with X-ray or heavy-ion beams, such as carbon- (290MeV/u and 135MeV/u), silicon- (490MeV/u) and iron- (500Mev/u) ions with different LET ranging from 13keV/um to 200keV/um,generated by the Heavy Ion Medical Accelerator in Chiba (HIMAC).Cell-killing efficiencies were measured using a colony-formation assay at either immediate plating (IP) method or delayed plating (DP) method keeping at 370C for 24hours. Mutation induction was detected to measure 6-thioguanine resistant colonies. The cells were irradiated with D20 dose, which was determined as the dose (Gy) required to reduce the surviving fraction to 20%, for PLDR-related mutation induction at the hprt assayed by IP or DP method. Results and Conclusion: The ratio for mutation frequency of DP/IP was ranging from 0.13 to 3.3. Then we calculated the radio of mutation frequency (IP or DP) against surviving fraction (IP or DP) and found that the ratio of mutation frequency (IP)/surviving fraction (IP) was higher than that of mutation frequency (DP)/surviving fraction (DP) in X rays, carbon, and iron-ion beams. However, the result for silicon-ion beams was ratio opposite. The result suggested that DNA repair fidelity in X-ray- and carbon-ion-induced damage in the DP method was more accurate than that in the IP method, although the results for silicon- and iron-ion beams were different. When the cells were irradiated with the same ion species, the higher LET beams showed the higher ratio of mutation frequency/surviving fraction in both IP and DP cases. These results showed that hprt mutation at IP and DP methods depended on LET and ion species.
