Single-cell transcriptome in the examination of the molecular characteristics of macrophages in lung cancer brain metastasis.

e20546 Background: Brain metastasis is one of the most common distant metastasis types in lung cancer patients. Its mechanism involves multiple factors, including cell-cell interactions, immune evasion, and the influence of the microenvironment. Single-cell RNA sequencing technology has significantly advanced our understanding of tumors at a single-cell resolution. It enables an in-depth understanding of the expression profiles of metastatic cells in brain tissue, providing potential predictive biomarkers for future monitoring, diagnosis, and effective treatment. Methods: We collected 50 samples from the GEO database, including 17 normal lung samples, 17 lung cancer samples, and 16 brain metastasis samples. We used the MNN method for batch correction and performed differential analysis using findAllMarkers and FindMarkers. Additionally, we conducted enrichment analysis using ClusterProfiler. Results: After batch correction and re-clustering of the macrophages, we identified 9 clusters. Based on their biological functions, they were classified into 5 macrophage subtypes: RTMₘacro, Angioₘacro, SEPP1ₘacro, Prolifₘacro, and Monoₗike. The angiogenic macrophages (Angioₘacro) were most prominent in lung cancer brain metastasis samples (52%), followed by lung cancer (25%), and least present in normal samples (17%). Enrichment analysis revealed that iron death, antigen processing and presentation, and endoplasmic reticulum protein processing were more enriched in brain metastasis. This correlates with the high proportion of angiogenic macrophages present in the brain. The SEPP1ₘacro subtype showed high expression of SEPP1 and VCAN, genes associated with angiogenesis. Studies suggest that SEPP1 is associated with poor prognosis as it promotes neovascularization and tumor invasion. This subtype was highly expressed in brain metastasis (40%) and lung cancer (45%), but rare in normal samples (4%). In the SEPP1ₘacro subtype, brain metastasis samples were enriched in signaling pathways such as tumor necrosis factor, PI3K-AKT, NF-kB, and Mitogen-activated protein kinase (MAPK), focusing mainly on the interaction of cytokines and cytokine receptors. Conclusions: In lung cancer and lung cancer brain metastasis, there is a significant presence of macrophages that promote angiogenesis and subpopulations of tumor-promoting cells associated with poor prognosis. The existence of these two cell subsets may indicate their activation during tumor metastasis and their regulatory role in the formation of new blood vessels, thereby promoting tumor growth.