Dose-dependent X-ray irradiation-induced bystander effects in MCF-7 breast cancer cells

Emerging evidence shows that exposure of cancer cells to ionizing radiation may trigger signal-mediated events in unirradiated cells called the radiation-induced bystander effects (RIBE). Manifestation of the effect is highly variable, dependent on the treatment parameters such as methodology, radiation type, LET, or cell lines. This study aims to investigate RIBE in MCF-7 after irradiation using an X-ray benchtop irradiator. MCF-7 cells were cultured at 2 × 10⁵ cells per T25 flask and irradiated using a CellRad™ bench-top irradiator at 130 kV, 5 mA, with an additional 0.5 mm aluminum filter. The irradiation setup placed the flask within a circular field size of 19.8 cm, delivering a dose rate of 2.096 Gy/min. Acute doses investigated included 0 Gy (sham), 0.5 Gy, 1.5 Gy, 3.36 Gy, 8 Gy, and 12 Gy. Twenty-four hours post-irradiation, medium transfer from irradiated cells (ICM) was performed to initiate radiation-induced bystander effects in non-irradiated cells. Subsequent assessments included viability assays and colony formation assays to validate observed effects, with relative survival calculated relative to sham-irradiated cells. Results show that exposure of the cells to the irradiated cell medium resulted in a significant decrease in cell viability and clonogenic ability, demonstrating bystander effects. This decrease in survival is dose-dependent where the effect is more significant at higher doses 3.36 Gy-12 Gy.