High mobility group box 1 (HMGB1) protein, released from irradiated tumor cells, plays a crucial role in stimulating anti-tumor immune responses. This study investigated whether carbon-ion beams, like X-rays, trigger HMGB1 release from human cancer cells. Five human cancer cell lines (TE2, KYSE70, A549, NCI-H460, and WiDr) were exposed to both X-ray and carbon-ion beam irradiation.
Comparing X-ray and Carbon-Ion Beam Effects on Cell Survival
Cell survival was measured using a clonogenic assay, and the D10 dose (dose at which 10% of cells survive) was calculated. D10 values for X-rays ranged from 2.1 Gy (TE2) to 8.0 Gy (A549). Carbon-ion beams exhibited lower D10 values, ranging from 0.9 Gy (TE2) to 3.5 Gy (WiDr), indicating higher cell-killing efficiency. This difference in D10 highlights the distinct biological effectiveness of carbon-ion beams compared to X-rays.
HMGB1 Release Following Irradiation
Enzyme-linked immunosorbent assay (ELISA) measured HMGB1 levels in cell culture supernatants at 72 and 96 hours post-irradiation with D10 doses. At 72 hours, both X-rays and carbon-ion beams significantly elevated HMGB1 levels in A549, NCI-H460, and WiDr cells. By 96 hours, all five cell lines showed a substantial increase in HMGB1 release after irradiation with either radiation type.
Comparable HMGB1 Induction Across Radiation Types
Importantly, no significant difference in HMGB1 induction was observed between X-rays and carbon-ion beams at most time points, except for NCI-H460 cells at 96 hours. This suggests that comparable levels of HMGB1 are released after irradiation with iso-survival doses of both X-rays and carbon-ion beams. This finding implies that despite differences in cell-killing mechanisms, both radiation modalities trigger a similar immunological response through HMGB1 release.
Conclusion: Implications for Cancer Therapy
This research demonstrates that both X-ray and carbon-ion beam irradiation induce significant HMGB1 release from various human cancer cell lines. The comparable HMGB1 levels observed after irradiation with iso-survival doses suggest that both modalities may trigger similar anti-tumor immune responses. Further research is needed to explore the clinical implications of these findings and to determine the optimal radiation type for maximizing anti-tumor immunity in cancer patients.
