Effect of Gradient Ionizing Radiation on ROS Formation in Human Breast Cancer Cells

Abstract

The application of ionizing radiation (IR) in cancer radiotherapy can induce collective cellular damages via non‐targeted effects, in which neighboring cells are affected by irradiated cells. This so‐called bystander effect (BE) remains an area of interest. Since reactive oxygen species (ROS) play a vital role in biological systems, ROS induced by IR may contribute to BE. However, this mechanism has not been fully elucidated in carcinomas such as human breast cancer cells (MCF‐7). Hereby, we hypothesized that the application of gradient radiation (GR) can reduce the damage to neighboring healthy cells, compared to uniform radiation (UR). We studied radiation dose responses by evaluating ROS generation in MCF‐7 exposed to UR (5 Gy) or GR (8‐2 Gy). Using dihydroethidium (DHE)/ethidium (ET), a fluorescent probe for intracellular superoxide (O2•–, one major ROS), we measured ROS as an indication of cellular oxidative stress. Our results have shown that at 48 hours after irradiation, there is no difference in intracellular ROS formation in GR vs. UR treatment. Antioxidant Tiron treatment eliminated fluorescence, confirming the presence of intracellular ROS. Our project suggests a potential advantage of GR over UR to reduce the damage to neighboring healthy cells via a BE.