bystander effect induced in breast cancer (mcf7) and human osteoblast cell lines (hfob 1.19) with hdr-brachytherapy

Background: radiation induced bystander effects (ribes) occurs in unirradiated cells exhibiting indirect biological effect as a consequence of signals from other irradiated cells in the population. objective: in this study, bystander effects in mcf7 breast cancer cells and hfob 1.19 normal osteoblast cells irradiated with gamma emitting hdr brachytherapy ir192 source were investigated.material and methods: in this invitro study, bystander effect stimulation was conducted using medium transfer technique of irradiated cells to the nonirradiated bystander cells. cell viability, reactive oxygen species (ros) generation and colony forming assay was employed to evaluate the effect. results: results indicate that the exposure to the medium irradiated mcf7 induced significant bystander killing and decreased the survival fraction of bystander mcf7 and hfob from 1.19 to 81.70 % and 65.44 %, respectively. a significant decrease in survival fraction was observed for hfob 1.19 bystander cells (p < 0.05). we found that the rate of hfob 1.19 cell growth significantly decreases to 85.5% when added with media from irradiated cells. the ros levels of bystander cells for both cell lines were observed to have an increase even after 4 h of treatment. our results suggest the presence of bystander effects in unirradiated cells exposed to the irradiated medium. conclusion: these data provide evidence that irradiated mcf7 breast cancer cells can induce bystander death in unirradiated mcf7 and hfob 1.19 bystander cells. increase in cell death could also be mediated by the ros generation during the irradiation with hdr brachytherapy.