Author: Beatriz Allyne Dia Carandang, Chitho P Feliciano, Teresa Sy-Ortin 👨🔬
Affiliation: Department of Physical Sciences and Mathematics, University of the Philippines Manila, Health Physics Research Section, Atomic Research Division, Department of Science and Technology-Philippine Nuclear Research Institute (DOST-PNRI), Graduate School, University of Santo Tomas 🌍
Purpose: To investigate the X-ray radiation-induced bystander effect (RIBE), where unirradiated cells mimic the responses of directly irradiated cells, in MCF-7 breast cancer cells in vitro to understand its potential role in radiotherapy.
Methods: MCF-7 cancer cells were seeded at 200,000 cells per T25 flask and subjected to irradiation using the CellRad™ bench-top irradiator at 130 kV, 5 mA, and an additional 0.5 mm aluminum filter. 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, the medium was transferred from irradiated MCF-7 cells (ICM) to non-irradiated MCF-7 cells to initiate radiation-induced bystander effects. Subsequent assessments of cell viability and colony formation were performed to validate the observed effects, with relative survival calculated with respect to sham-irradiated cells
Results: The investigation shows a significant decrease in cell survival for cells exposed to the medium of irradiated MCF-7 cells, as evaluated using cell viability and clonogenic assays, demonstrating bystander effects. This decrease in survival is dose-dependent (p < 0.0001), with the effect being more pronounced at higher doses (3.36 Gy, p = 0.0004; 8 Gy, p < 0.0001; 12 Gy, p < 0.0001). Comparison of the survival fraction between the treatment groups (direct irradiation vs. exposure to the irradiated cell medium) shows that both dose and treatment scheme significantly affect cell survival (p < 0.0001). Although differences in survival exist between the treatment groups, the decrease in survival of the ICM-exposed MCF-7 cells suggests that exposure to the irradiated medium alone may lead to cell killing
Conclusion: This work highlights the potential of X-ray radiation-induced bystander effects in tumor cell killing, suggesting that bystander effects could play a significant role radiotherapy.