FLASH altered early molecular responses without improving breast cell survival

KEY POINTS

• Researchers compared non-tumorigenic MCF10A breast cells with triple-negative MDA-MB-231 cancer cells under normoxic conditions. Cells received electron doses of 2, 4, 6, 9, 11, or 15 Gy at either 230 Gy/s or the conventional rate of 6 Gy/min.
• Clonogenic survival was comparable between FLASH and conventional irradiation in both cell lines across the evaluated doses. The experiment therefore did not demonstrate preferential normal-cell sparing or improved tumor-cell killing.
• FLASH produced more γ-H2AX foci at one hour after irradiation in both cell lines, particularly after 5 Gy. MDA-MB-231 cells also showed greater persistence of 53BP1 foci at 24 hours, but these DNA-damage differences did not translate into altered survival.
• At 9 Gy, FLASH caused less microtubule disruption in MDA-MB-231 cells than conventional irradiation, with a highly significant difference in the quantitative microtubule signal (p < 0.0001). No significant difference was found at 4 or 6 Gy.
• RNA sequencing at 9 and 15 Gy showed broader gene-expression changes after FLASH. MCF10A cells preferentially upregulated mitochondrial genes, while MDA-MB-231 cells showed increased expression of structural and signal-transduction genes.
• Cytokine profiling showed no wholly different qualitative response between dose rates, but MDA-MB-231 cells produced higher levels of several inflammatory and immunomodulatory mediators after FLASH, particularly at 15 Gy and 72 hours. MCF10A cells showed comparatively little variation.
• The glutathione redox ratio did not differ between modalities at 24 hours. The work was confined to two cell lines in normoxia and assessed early responses, so it cannot explain normal-tissue protection observed in intact organisms with immune, vascular, and oxygen-dependent interactions.

CLINICAL TAKEAWAY

SOURCE

Frontiers in Oncology