Bystander signaling between glioma cells and fibroblasts targeted with counted particles

Radiation‐induced bystander effects may play an important role in cancer risks associated with environmental, occupational and medical exposures and they may also present a therapeutic opportunity to modulate the efficacy of radiotherapy. However, the mechanisms underpinning these responses between tumor and normal cells are poorly understood. Using a microbeam, we investigated interactions between T98G malignant glioma cells and AG01522 normal fibroblasts by targeting cells through their nuclei in one population, then detecting cellular responses in the other co‐cultured non‐irradiated population. It was found that when a fraction of cells was individually irradiated with exactly 1 or 5 helium particles (3He2+), the yield of micronuclei (MN) in the non‐irradiated population was significantly increased. This increase was not related to the fraction of cells targeted or the number of particles delivered to those cells. Even when one cell was targeted with a single 3He2+, the induction of MN in the bystander non‐irradiated population could be increased by 79% for AG01522 and 28% for T98G. Furthermore, studies showed that nitric oxide (NO) and reactive oxygen species (ROS) were involved in these bystander responses. Following nuclear irradiation in only 1% of cells, the NO level in the T98G population was increased by 31% and the ROS level in the AG0 population was increased by 18%. Treatment of cultures with 2‐(4‐carboxyphenyl)‐4,4,5,5‐tetramethyl‐imidazoline‐1‐oxyl‐3‐oxide (c‐PTIO), an NO scavenger, abolished the bystander MN induction in non‐irradiated AG01522 cells but only partially in non‐irradiated T98G cells, and this could be eliminated by treatment with either DMSO or antioxidants. Our findings indicate that differential mechanisms involving NO and ROS signaling factors play a role in bystander responses generated from targeted T98G glioma and AG0 fibroblasts, respectively. These bystander interactions suggest that a mechanistic control of the bystander effect could be of benefit to radiotherapy. © 2005 Wiley‐Liss, Inc.