Evaluation of Exosomal miRNA in Blood as a Potential Diagnostic Biomarker for Human Non-Small Cell Lung Cancer

BACKGROUND: Tumor-derived exosomes have been used as diagnostic biomarkers to discriminate between tumor patients and healthy people. This study explored the roles of exosomal miRNAs in lung adenocarcinoma metastasis by microarray and developed a novel method for diagnosis of lung adenocarcinoma. MATERIAL/METHODS: Four lung adenocarcinoma patients’ peripheral blood, including 2 metastasis and 2 N-metastasis, were used for exosomes miRNA microarray analysis. Exosomes were extracted by ultracentrifugation and identified by transmission electron microscopy. All the raw data were normalized by R software with limma packet. qRT-PCR was used to validate the microarray results. A549 cells were used to identify the functions of miR-4448. Western blot, qRT-PCR, RNAi, CCK8, and transwell invasion assay were used to verify the metastasis and proliferation abilities. RESULTS: miR-4436a and miR-4687-5p were upregulated between the metastasis and N-metastasis group, while miR-22-3p, miR-3666, miR-4448, miR-4449, miR-6751-5p and miR-92a-3p were downregulated. miR-4448 was also downregulated between the metastasis and control group, whereas there was no significant difference between the N-metastasis group and control group. qRT-PCR confirmed the downregulation of miR-4448 in exosomes from lung adenocarcinoma patients compared with N-metastasis patients and healthy people. CCK8 and transwell invasion assay showed that A549 cells transfected with miR-4448 inhibitor had higher proliferation and metastasis ability. qRT-PCR and Western blot confirmed the high expression of MMP2 and MMP9 in A549 cells transfected with miR-4448 inhibitor. CONCLUSIONS: miR-4448 can inhibit A549 cell proliferation and metastasis. miR-4448 in exosomes has the potential to serve as a diagnostic marker of patients with adenocarcinoma metastasis.