Abstract
Radioresistant cells are one of the obstacles of tumor radiotherapy. In order to understand the molecular mechanisms of radioresistance and develop more effective tumor radiotherapy, clinically relevant radioresistant (CRR) cells were established from several cancer cell lines. Those cells continue to proliferate under exposure to 2 Gy/day of X-rays for more than 30 days, a standard protocol for tumor radiotherapy. Our previous study indicated that CRR cells are resistant to anticancer drug docetaxel (DOC). One of the factors of cellular DOC resistance is thought to be the resistance against hydrogen peroxide because DOC produce hydrogen peroxide in the cells. It is well known that X-ray exposure generates reactive oxygen species (ROS) in cells and inadequate removal of ROS results in oxidative stress that leads to damage to biological macromolecules; the products of lipid peroxidation can cause DNA damage leading to cell death. Therefore, we hypothesized that more efficient removal of ROS in CRR cells would be the reason for DOC resistance and radioresistance. Both the modified high density survival assay and MTT assay showed that all clinically relevant radioresistant cells are resistant to hydrogen peroxide. We think that DOC resistance of CRR cells is due to the resistance against hydrogen peroxide.
