Involvement of DNA polymerase beta in repairing oxidative damages induced by antitumor drug adriamycin

Adriamycin (ADM) is a widely used antineoplastic drug. However, the increasing cellular resistance has become a serious limitation to ADM clinical application. The most important mechanism related to ADM-induced cell death is oxidative DNA damage mediated by reactive oxygen species (ROS). Base excision repair (BER) is a major pathway in the repair of DNA single strand break (SSB) and oxidized base. In this study, we firstly applied the murine embryo fibroblasts wild-type (pol β +/+) and homozygous pol β null cell (pol β −/−) as a model to investigate ADM DNA-damaging effects and the molecular basis underlying these effects. Here, cellular sensitivity to ADM was examined using colorimetric assay and colony forming assay. ADM-induced cellular ROS level and the alteration of superoxide dismutase (SOD) activity were measured by commercial kits. Further, DNA strand break, chromosomal damage and gene mutation were assessed by comet assay, micronucleus test and hprt gene mutation assay, respectively. The results showed that pol β −/− cells were more sensitive to ADM compared with pol β +/+ cells and more severe SSB and chromosomal damage as well as higher hprt gene mutation frequency were observed in pol β −/− cells. ROS level in pol β −/− cells increased along with decreased activity of SOD. These results demonstrated that pol β deficiency could enable ROS accumulation with SOD activity decrease, further elevate oxidative DNA damage, and subsequently result in SSB, chromosome cleavage as well as gene mutation, which may be partly responsible for the cytotoxicity of ADM and the hypersensitivity of pol β −/− cells to ADM. These findings suggested that pol β is vital for repairing oxidative damage induced by ADM.