Inhibition of neutrophil degranulation by Nexinhib20 delays the development of radiation-induced pulmonary fibrosis

Despite advances in radiation delivery techniques that enhance tumour targeting and minimise collateral exposure, healthy tissues remain susceptible to radiation-induced fibrosis, a chronic and progressive condition that can severely compromise patient quality of life. Therapeutic options to prevent or treat radiation-induced fibrosis remain limited. Recent work has shown that neutrophils infiltrating healthy lung tissue after irradiation adopt an activated phenotype capable of perturbing cellular responses of both epithelial and mesenchymal cells. However, the contribution of these radiation-educated neutrophils to the development of radiation-induced fibrosis remains unclear. Using targeted, image-guided lung irradiation to deliver a dose sufficient to induce fibrosis within four months, we demonstrate that neutrophils are essential for the efficient development of clinically evident fibrosis. Lung irradiation educates neutrophils, enabling them to promote early alterations in the extracellular matrix shortly after radiation exposure. We further show that this “educated” phenotype depends on neutrophil degranulation activity. Pharmacological inhibition of degranulation with Nexinhib20 redirected these cells toward a pro-angiogenic and anti-fibrotic phenotype. Importantly, this treatment was also associated with a transcriptional shift in mesenchymal cells away from a pro-fibrotic program, resulting in a marked delay in the onset of radiation-induced fibrosis. Importantly, Nexinhib20 did not impair the efficacy of cancer radiotherapy, underscoring its potential as a therapeutic strategy to prevent fibrotic complications without diminishing anti-tumour effectiveness.