Involvement of Intracellular Fe2+ Against Oxidative Stress in CRR Cells

To achieve more effective cancer treatment, we have established and analyzed "clinically relevant radioresistant (CRR) cells" that can survive exposing to 2 Gy/day X-rays for more than 30 days. CRR cells show resistance against hydrogen peroxide (H2O2) that is one of the reactive oxygen species. However, the resistant mechanism to H2O2 has not been elucidated yet. Therefore, we investigated the involvement of iron ion in the resistant mechanism to H2O2 in CRR cells because iron ion has been reported to react with H2O2 and produce hydroxyl radical (・OH). ・OH have been shown to react with plasma membrane phospholipid and lead to cell death. Internal Fe2+ and ・OH amount were decreased in CRR cells compared with its parental cells. In addition, expression of ferritin, which is iron-binding protein, was increased in CRR cells. No internal H2O2 increase and no lipid peroxidation were seen in CRR cells after 50 µM H2O2 treatment for 2 hours, whereas internal H2O2 uptake and lipid peroxidation was increased after 50 µM H2O2 treatment for 2 hours in parental cells. Furthermore, Pretreatment of 10 µM of FeCl2 leads to more cell death after administration of 50 µM H2O2 in CRR cells. Administration of phospholipid also led to further cell death after 50 µM H2O2 treatment in CRR cells. These results suggest that intracellular Fe2+ content is very important against oxidative stress response in CRR cells and control of Fe2+ amount may be an effective option for cancer that is resistant to treatment.