Purpose: To evaluate the interaction between tumor-infiltrating macrophages and cancer cells and its effect on the expression of a potent angiogenic factor, interleukin-8 (IL-8), tumor angiogenesis, and patient outcome in non-small cell lung cancer (NSCLC).
Experimental design: We measured tumor IL-8 mRNA expression (by real-time quantitative reverse transcription-PCR), intratumor microvessel counts, and tumor-infiltrating macrophage density (by immunohistochemical staining) in 35 NSCLC surgical specimens and correlated with the patient's clinical outcome. We then investigated the interaction between macrophages (cell line THP-1) and six different human cancer cell lines (four NSCLCs, one osteosarcoma, and one hepatoma) and its effect on IL-8 mRNA expression using a macrophage/cancer cell coculture system, IL-8 mRNA expression in lung cancer cells, and macrophages being measured separately after coculture in the presence or absence of six anti-inflammatory agents, i.e., pentoxifylline, aspirin, indomethacin, dexamethasone, celecoxib (a selective cyclooxygenase-2 inhibitor), and pyrrolidine dithiocarbamate, a specific nuclear factor kappaB (NF-kappaB) inhibitor. NF-kappaB transcriptional activity and protein levels were measured by reporter gene assay and Western blot.
Results: The tumor-infiltrating macrophage density correlated significantly and positively with tumor IL-8 mRNA expression and intratumor microvessel counts and significantly and negatively with patient survival. In addition, after cell-cell interaction in cancer cell:macrophage cocultures, marked IL-8 mRNA expression was induced in lung cancer cells (approximately 270-fold) and, to a lesser degree, in macrophages (4.5-fold). The increase in IL-8 mRNA expression correlated with the in vitro metastatic potential of the cancer cells. All six anti-inflammatory agents suppressed induction of IL-8 mRNA expression in lung cancer cells by >90%, four (pentoxifylline, celecoxib, pyrrolidine dithiocarbamate, and dexamethasone) having a dose-dependent effect. NF-kappaB transcriptional regulation and protein levels were simultaneously increased in the nuclei of cancer cells in macrophage/cancer cell cocultures, this effect also being suppressed by all six anti-inflammatory agents.
Conclusions: The interaction between infiltrating macrophages and cancer cells up-regulates IL-8 mRNA expression, especially in the cancer cells; this may contribute greatly to the increased tumor angiogenesis and adverse outcome in NSCLC patients with a high density of tumor-infiltrating macrophages. Anti-inflammatory agents can suppress the induction of IL-8 mRNA expression seen in lung cancer cells after coculture with macrophages, and this suppression is mediated, in part, through the NF-kappaB pathway.