Osimertinib exacerbates immune checkpoint inhibitor-related severe adverse events by activating the IL-6/JAK/STAT3 pathway in macrophages.

Objective: The combination of epithelial growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) and immune checkpoint inhibitors (ICIs) leads to an increased incidence of severe immune-related adverse events (irAEs). However, the mechanisms underlying macrophages in irAEs have not been elucidated.

Methods: An osimertinib and ICI-induced irAE mouse model was constructed. Lung micro-CT scans were used to assess the degree of inflammatory infiltration. Hematoxylin-eosin staining was used to analyze the histopathologic inflammatory infiltration in mouse liver and lung tissues. Flow cytometry was used to detect the percentages of T cells, NK cells, and macrophages and the expression of EGFR. Enzyme-linked immunosorbent assay (ELISA) was used to detect the serum interleukin (IL)-6, alanine transaminase (ALT), ferritin, and tumor necrosis factor (TNF)-α levels. Total RNA extracted from mouse liver macrophages was analyzed by RNA-seq. Simple Western blot analysis was used to detect the IL-6/JAK/STAT3 pathway activation state.

Results: Osimertinib combined with ICIs upregulated EGFR expression on macrophages with increased serum IL-6, ALT, and ferritin levels. RNA-seq and simple Western blot analysis of mouse liver macrophages confirmed that that the IL-6/JAK/STAT3 pathway was activated in the combination treatment group. Ruxolitinib blocked the IL-6/JAK/STAT3 pathway and significantly decreased the serum IL-6, ALT, and ferritin levels in the combination treatment group.

Conclusions: An osimertinib and ICI-induced irAE mouse model was constructed that showed osimertinib combined with ICIs inhibited EGFR phosphorylation and activated the IL-6/JAK/STAT3 signaling pathway in mouse liver macrophages, which led to the release of relevant cytokines.