The role of miRNAs in the development of brain metastases originating from lung adenocarcinoma.

[INTRODUCTION] Brain metastases (BMs) represent most malignant lesions of the central nervous system. Lung cancer-particularly lung adenocarcinoma (LUAD, ∼25%)-is the most common source of BMs. MicroRNAs (miRNAs) play a crucial role in regulating gene expression, thereby contributing to tumor progression and metastatic spread. Identifying these regulatory molecules may enable a deeper understanding of the mechanisms driving LUAD brain metastasis (LUAD-BM) development and reveal therapeutic targets to prevent or limit disease progression.

[METHODS] Next-generation RNA sequencing (RNA-seq) was performed on six LUAD-BM and six non-tumorous human brain tissue samples to assess miRNA expression profiles. Additionally, RNA-seq data from 20 primary LUAD and 15 normal lung tissue samples were obtained from The Cancer Genome Atlas (TCGA) database. MiRNAs showing the most pronounced alterations in LUAD-BM samples were selected for validation by real time quantitative polymerase chain reaction (RT-qPCR).

[RESULTS] Analysis of RNA-seq data identified 229 differentially expressed (DE) miRNAs between LUAD-BM and control samples. Functional annotation analysis indicated that these DE miRNAs are key regulators of tumorigenesis and metastasis. Using the Mann-Whitney U test, ten miRNAs were confirmed to differ significantly between LUAD-BM and normal brain tissue. Receiver operating characteristic (ROC) curve analysis demonstrated their diagnostic potential. Among the ten validated miRNAs, miR-200c-3p, miR-146b-5p, and miR-3934-5p showed distinct expression patterns between primary LUAD and LUAD-BM, while miR-10a-5p, miR-210-3p, and miR-130b-3p exhibited stepwise dysregulation along the normal lung-LUAD-LUAD-BM axis, suggesting their involvement in metastatic progression.

[CONCLUSION] We identified ten miRNAs that showed preliminary ability to differentiate LUAD-BM from normal brain tissue. These findings indicate possible diagnostic and therapeutic implications. Among these, six miRNAs showed significant expression changes along the normal control-primary LUAD-LUAD-BM axis, highlighting their potential as biomarkers and therapeutic targets in BM development.