2547 - Monocyte-Macrophage Modulation in Radiation-Immunotherapy-Induced Pneumonitis in NSCLC

Purpose/Objective(s): The combination of thoracic radiotherapy and immunotherapy has significantly improved the prognosis of non-small cell lung cancer (NSCLC) patients. However, the risk of pneumonitis from this combination remains a concern. The pathophysiological mechanisms of radiation-immunotherapy-induced pneumonitis (RIP) are complex and not fully understood, with limited treatment options. ACT001, a derivative of parthenolide, has demonstrated anti-tumor and anti-inflammatory effects in prior studies. Its specific anti-inflammatory role in RIP, however, remained unclear.

Materials/Methods: Peripheral blood was collected from untreated NSCLC patients (Control group) and from NSCLC patients who developed pneumonitis during or within 3 months of receiving thoracic radiotherapy, immunotherapy, or combined radiotherapy-immunotherapy. A total of 12 patients were included, with 3 patients per group. Single-cell RNA sequencing and Olink proteomics were performed.RIP mouse models were established with treatment groups: control, radiotherapy, immunotherapy, combined radiotherapy-immunotherapy, and combined radiotherapy-immunotherapy plus ACT001. CMT167 cell lines stably expressing luciferase were used to generate an orthotopic lung tumor mouse model, and bioluminescence signals were recorded to assess whether ACT001 could alleviate pneumonitis without compromising anti-tumor efficacy.

Results: A total of 126,172 cells were analyzed through single-cell RNA sequencing and classified into B cells, NK/T cells, monocytes, dendritic cells, and neutrophils. The monocyte subset showed the largest differential abundance between the control and treatment-related pneumonitis groups, with an increase observed in the pneumonitis group. Differential expression analysis revealed a marked upregulation of CCR2+ monocytes in the treatment groups, suggesting their key role in RIP pathogenesis. Olink proteomics identified a significant increase in MCP-1 levels in the peripheral blood of pneumonitis patients compared to controls. Gene Ontology (GO) enrichment analysis revealed activation of monocyte-macrophage-related pathways in the pneumonitis cohort. In pneumonitis mouse models, the combined radiotherapy-immunotherapy treatment group exhibited the most severe pneumonitis, with increased CD11b+ M1 macrophages in lung tissue. ACT001 treatment reversed this and alleviated pneumonitis. Macrophage depletion using clodronate liposomes significantly reduced RIP severity, and the addition of ACT001 did not further reduce pneumonitis. In the orthotopic lung tumor RIP model, ACT001 mitigated pneumonitis without diminishing anti-tumor efficacy.

Conclusion: This study highlighted the critical pro-inflammatory role of monocyte-macrophages in RIP and demonstrated that ACT001, by targeting macrophages, mitigated lung injury induced by combined radiotherapy and immunotherapy, without compromising anti-tumor efficacy.