FLASH irradiation‐induced acute lung injury promotes metastatic colonization via neutrophil extracellular trap formation

BACKGROUND: FLASH irradiation, a technique that delivers prescribed dose at ultra-high dose rate, has been described to alleviate normal tissue injury in multiple animal models. However, the underlying mechanism was not fully understood. PURPOSE: We aimed to investigate whether FLASH irradiation-induced acute lung injury could reduce metastatic colonization compared with conventional (CONV) irradiation. METHODS: Healthy lungs of C57BL/6J male mice were irradiated with either FLASH or CONV, SV2 lung adenocarcinoma cells were intravenously injected and healthy lung volume was monitored using micro-computed tomography (micro-CT). The irradiated tissues (tumor + normal parenchyma) were analyzed by proteomic to identify key regulators of cancer progression. Key proteins were preliminarily validated using real-time quantitative PCR and western blot. Further validation was carried out by inhibiting or promoting neutrophil extracellular traps (NETs) formation within in vivo models. RESULTS: In radiation-induced acute lung injury models, both CONV and FLASH involved in equivalent and enhanced metastatic colonization. Follow-up molecular analysis using proteomic profiling revealed NETs formation involved in cancer progression. Both radiation modalities triggered acute lung injury and inflammatory response with a similar pattern. Inhibiting NETs formation significantly delay tumor metastasis in either FLASH or CONV, whereas stimulating NETs formation markedly accelerate cancer progression. CONCLUSION: These experiments suggest that healthy lung spare does not recapitulate at acute time point after exposure to FLASH. Proteomic analyses suggest a possible role for NETs formation within the tumor microenvironment in deriving cancer cell seeding. NETs formation could be served as a prognostic factor in thoracic cancer.