Unraveling Heterogeneity in Tumor Evolution Induced by Diverse Radiation Modes: Insights from Systems Biology

The biomedical consequences of space radiation pose a significant concern for astronauts engaged in deep space. However, the effects of long-term low dose-rate exposures in space environments remain elusive. In this study, we simulated the space radiation environment by exposing human bronchial epithelial cells to low dose-rate (0.0067 Gy/day) α-particles, and continuously irradiated them multiple times to achieve cumulative total doses of 0.2 Gy, 0.4 Gy, and 0.5 Gy, respectively. At the same time, the cells were irradiated with the same total dose in a single exposure to investigate the potential of low dose-rate alpha particles to induce malignant transformation of human bronchial epithelial cells. A comprehensive suite of assays was employed to assess tumorigenic potential, including tumor formation in NOD/SCID mice, immunohistochemistry, CCK-8 proliferation assay, invasion assay, and the evaluation of multicellular spheroid formation during subsequent passages post-irradiation. Moreover, we dissected differential malignant mechanisms in tumor evolution ecosystem induced by the two distinct irradiation modes from systems biology views based on scRNA-seq technology. Our results showed that exposure to α-particles, whether through a single acute exposure or long-term low dose-rate exposures, induced the occurrence and development of tumors. Long-term low dose-rate exposures to α-particles increase the malignancy of induced tumors, but not the risk of carcinogenesis, compared to a single acute exposure with the same total dose. In addition, through scRNA-seq, we found that long-term low dose-rate exposures triggered more copy number variation (CNV) and epithelial-mesenchymal transition (EMT) events, and the activation of DNA damage repair pathways occurred significantly later than with a single acute exposure and involved more specific changes in cellular communication dynamics. In conclusion, our findings provide emerging yet convincing evidence that not only sheds light on why cells exposed to long-term low dose-rate exposures exhibit heightened malignancy, but also offers valuable insights into the genetic determinants driving tumor evolution and heterogeneity.