Tumor-associated macrophages provide a suitable microenvironment for non-small lung cancer invasion and progression

It remains largely unknown whether tumor-associated macrophages (TAMs) are involved in invasion and metastasis of human lung cancer. The aim of our study was to obtain an accurate overview of the broad range of changes occurring in monocytes that develop into TAMs, and the roles of TAMs during the progression of non-small cell lung cancer.

TAM was isolated from 98 primary lung cancer tissues by short term cultivation in serum-free medium. The mRNA expression levels of 9 genes, including EGF, Cathepsin K, Cathepsin S, COX-2, MMP-9, PDGF, uPA, VEGFA, HGF, were evaluated by real-time PCR in 98 NSCLC. The relationships between those gene expression levels and clinicopathological features were investigated. The effects of conditioned medium from TAMs on the invasive properties of different lung cancer cell lines were measured using Transwell chambers.

We successfully achieved up to 95% purity of TAM, derived from 98 primary lung cancer tissues. TAM expressed high levels of Cathepsin K, COX-2, MMP-9, PDGF-B, uPA, VEGFA, and HGF. Phenotypic expression on TAMs, like MMP9, was shown to be correlated with disease progression by analyzing lung cancer tissues. Conditioned medium from TAM significantly increased cell migration and invasion in SPC-A1 cells, H460 cells and A549 cells. Anti-uPA and anti-MMP-9, but not anti-VEGF monoclonal antibodies, can inhibit TAM-induced invasion. The increase of invasiveness in the lung cancer cell lines was also correlated with their gelatinase activity, through MMP9.

Short-term culture in serum free medium is an effective way to isolate TAM in NSCLC. The results of this study also demonstrated that those up-regulated genes in TAMs contributed to suitable microenvironments for lung cancer invasion and metastasis. These findings may be useful in developing novel therapeutic strategies to prevent lung cancer progression.