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.