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Originally published as JCO Early Release 10.1200/JCO.2005.12.172 on December 14 2004 © 2005 American Society of Clinical Oncology. Tumor-Associated Macrophages: The Double-Edged Sword in Cancer Progression
From the Institutes of Biomedical Sciences and Molecular Biology, National Chung Hsing University, Taichung; Center for Genomic Medicine, National Taiwan University College of Medicine; Department of Internal Medicine, National Taiwan University Hospital and National Taiwan University College of Medicine; Graduate Institute of Epidemiology, National Taiwan University, Taipei; Department of Forensic Medicine, National Taiwan University Hospital and National Taiwan University College of Medicine; Institute of Statistical Science and Institute of Biomedical Sciences, Academia Sinica; and National Health Research Institute, Taipei, Taiwan, Republic of China Address reprint requests to Pan-Chyr Yang, MD, PhD, Department of Internal Medicine, National Taiwan University Hospital, No. 7, Chung-Shan S Rd, Taipei, Taiwan 100, R.O.C.; e-mail: pcyang{at}ha.mc.ntu.edu.tw.
PURPOSE: Inflammation plays a critical role in cancer progression. In this study we investigate the pro-tumorigenic activities and gene expression profiles of lung cancer cells after interaction with macrophages. MATERIALS AND METHODS: We measured intratumoral microvessel counts and macrophage density in 41 lung cancer tumor specimens and correlated these with the patients' clinical outcome. The interaction between macrophages and cancer cell lines was assessed using a transwell coculture system. The invasive potential was evaluated by in vitro invasion assay. The matrix-degrading activity was assayed by gelatin zymography. The microarray was applied to a large-scale analysis of the genes involved in the interaction, as well as to monitor the gene expression profiles of lung cancer cells responding to anti-inflammatory drugs in cocultures. RESULTS: The macrophage density positively correlated with microvessel counts and negatively correlated with patient relapse-free survival (P < .05). After coculture with macrophages, lung cancer cell lines exhibited higher invasive potentials and matrix-degrading activities. We identified 50 genes by microarray that were upregulated more than two-fold in cancer cells after coculture. Northern blot analyses confirmed some gene expression such as interleukin-6, interleukin-8, and matrix metalloproteinase 9. The two-dimensional hierarchical clustering also demonstrated that the gene expression profiles of lung cancer cells responding to various anti-inflammatory drugs in cocultures are distinct. CONCLUSION: The interaction of lung cancer cells and macrophages can promote the invasiveness and matrix-degrading activity of cancer cells. Our results also suggest that a great diversity of gene expression occurs in this interaction, which may assist us in understanding the process of cancer metastasis.
It is now becoming clear that the inflammatory cells that exist in the tumor microenvironment play an indispensable role in cancer progression. This may explain why many cancers arise from sites of chronic irritation and inflammation.1 Angiogenesis plays an important role in tumor growth, invasion, and metastasis.2,3 This process is meticulously regulated by the local increase of the activity of a variety of angiogenic factors, such as interleukin (IL) -8, vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and transforming growth factor alpha (TGF- ).3-5 Substantial evidence suggests that stroma cells adjacent to the cancer cells, including fibroblasts, inflammatory cells such as macrophages, neutrophils, and lymphocytes, can interact with cancer cells and express angiogenic factors.6-8 The interaction of lung cancer cells and stroma fibroblasts can promote the expression of angiogenic factor IL-8 both in cancer cells as well as in stroma fibroblasts.9 The macrophage is the pivotal member of inflammatory cells within the tumor stroma. Upon activation, the tumor-associated macrophages can release a vast diversity of growth factors, proteolytic enzymes, cytokines, and inflammatory mediators. Many of these factors are key agents in angiogenesis.
We demonstrated that following cancer cell/macrophage coculture, marked IL-8 mRNA expression could be induced in macrophages as well as in lung cancer cells that were controlled via the nuclear factor kappa B (NF- Tumor-infiltrating macrophages (TIMs) have recently been shown to correlate with vessel density in ovarian,12 breast,13 and other malignancies,14 and have been associated with the expression of VEGF and epidermal growth factor receptor (EGFR) in cancer cells.15 Our previous report also indicated that TIM density was positively correlated with tumoral IL-8 mRNA expression and intratumoral microvessel counts, and negatively correlated with patient survival.10 However, little is known about the global pro-tumorigenic gene expression profile in the cancer cells interacting with TIMs. In this study, by using the cDNA microarray,16 we were able to perform a large-scale analysis of the genes involved in the interaction between cancer cells and the infiltrating macrophages. This information may assist us in exploring complex interactions between cancer cells and stroma that orchestrate the process of tumor progression and metastasis. Furthermore, in our previous study,10 we found that several anti-inflammatory drugs can effectively inhibit the expression of angiogenic factor IL-8 in a similar fashion. Therefore, to understand whether the suppression of gene expression profiles of cancer cells responding to anti-inflammatory drugs are similar or not, we also applied microarray analysis to monitor the gene expression profiles of lung cancer cells responding to anti-inflammatory drugs in cancer cell/macrophage cocultures, which can help us to interpret the diversity of different functional mechanisms of the various anti-inflammatory drugs.
Cell Lines Human monocyte cell line THP-1 (ATCC TIB 202; ATCC, Manassas, VA), human nonsmall-cell lung cancer (NSCLC) cell line A549 (ATCC CCL-185), lung adenocarcinoma cell lines CL1-5, CL1-0,17,18 and PC14 were grown with RPMI 1640 media (GIBCO BRL, Gaithersburg, MD) supplemented with 1.5g/L Na2HCO3, 4.5g/L glucose, and 10% fetal bovine serum (FBS; GIBCO-BRL). All cell lines were incubated at 37°C with 20% O2 and 5% CO2. PMA (Sigma Chemical Co, St Louis, MO) 3.2 x 107 M was applied to monocyte cultures. After incubating with PMA for 24 hours, monocytes were differentiated to macrophages. Macrophages were washed three times with RPMI medium containing 10% FBS and incubated for another 24 hours to eliminate the effect of PMA, then were incubated in serum-free media for 24 hours. The culture supernatants were collected as conditioned medium.
Immunohistochemical Staining for Microvessels and Macrophages
Immunohistochemical staining was carried out using a modified avidin-biotin peroxidase complex method.4,19 Microvessel counts and TIM counts were determined as described in our previous reports.10,20
In Vitro Invasion Assay
Lung Cancer CL1-5 Cells/Macrophages Coculture
Human cDNA Microarray Analysis For the second microarray experiment, four copies of each differentially expressed gene identified from the procedures above were re-arrayed per microarray membrane. The copies were used to calculate the CV as the measurement of reproducibility. The details of target preparation, hybridization, color development, image analysis, and spot quantification have been described previously.16,18,21
Northern Blot Analysis
Gelatin Zymography
Gene Expression Profiles of Cancer Cells Responding to Anti-Inflammatory Drugs
Statistical Analysis
TIMs Are Significantly Correlated With Microvessel Counts and Patients' Relapse-Free Survival The immunohistochemical staining showed that the cytoplasm of TIMs was stained brown by anti-CD68 antibodies (Fig 1A), while the microvessels appeared as brown linear fragments, with or without an internal lumen (Fig 1B). Significant correlations were found between the macrophage density and intratumoral microvessel count (linear regression, r = 0.743; P = 2.68 x 108; Fig 1C).
We used a median value of 163 (infiltrating macrophage density per x 200 field) as the cutoff to separate tumors into those with high (n = 21) and low (n = 20) infiltrating macrophage counts. The median relapse-free survival for patients with tumors with a high density of TIMs (7.0 months; 95% CI, 1.02 to 12.91 months) was also significantly shorter than that for patients whose tumors had a low density of TIMs (26.0 months; 95% CI, 9.25 to 42.75; P = .0181, log-rank test; Fig 1D). Taking histologic type into consideration, the results showed that the density of TIMs was higher in adenocarcinoma than in squamous cell carcinoma (P = .001, Fisher's exact test). Interestingly, after stratification by histologic type of tumor, the relapse-free survival of patients with high TIM density was significantly shorter than for patients with low TIM density in squamous cell carcinoma (median ± SE, 5.0 ± 4.90 months v 24.0 ± 4.67 months; P = .0093, log-rank test), and had a trend to be shorter in adenocarcinoma (median ± SE, 7.0 ± 2.58 months v 20.0 ± 5.99 months; P = .35, log-rank test). The results of the multivariate analysis with Cox regression modeling (including sex, age, stage, histologic types, tumor status, lymph-node metastasis, TIM, microvessel count, and other clinicopathologic variables) also showed that the effect of tumor type on relapse-free survival was not significant (P = .4). Due to the sample size, the well- and moderately differentiated samples were merged as one group (more differentiated, n = 31), and the poorly differentiated samples were identified separately (less differentiated, n = 10). The results of survival analysis with stratification by the grade of tumor differentiation showed that TIM density had a trend to correlate with relapse-free survival in the more differentiated subgroup (P = .078, log-rank test), but was less correlated with relapse-free survival in the poorly differentiated group (P = .346, log-rank test).
Macrophage/Cancer Cell Coculture Increases Cancer Cell Invasive Ability
Microarray-Identified, Differentially Expressed Genes of CL1-5 Cells After Coculture With Macrophages Since the CL1-5 cells showed higher response to macrophage stimulation in terms of in vitro invasion ability and IL-8 expression,10 this cell line was chosen to carry out microarray experiments. Biotin-labeled probes derived from mRNAs of CL1-5 cells stimulated with and without macrophage-conditioned medium were hybridized to microarrays with 9,600 putative genes to profile the gene expression patterns (Fig 3A). Figure 3B reveals a collection of cropped microarray images (4 x 4 spots) showing the gene expression patterns of cancer cells before and after coculture with macrophages. The results of microarray analyses indicated that 3,577 out of 9,600 EST clones were identified according to whether the expression level either in the cocultured or in the non-cocultured group was larger than the background (> 3,000 intensity units). The CV for the three replicates of each gene was 10.15%, averaged over the 9,600 genes and the two groups.
By regression analysis, 482 genes that had expression levels beyond a 95% CI of the regression line were considered as differentially expressed genes (Fig 3C). Among these genes, 50 genes displaying more than a two-fold expression level as well as two genes, VEGF-A (1.58-fold) and VEGF-C (1.88-fold), on the borderline of a two-fold change in cocultures compared to the control, were grouped into seven categories by their putative functions (Table 2). All of these genes were verified by sequencing. Genes with multiple roles were included in more than one category. A full list of genes and data related to cancer cell/macrophage cocultures are posted at our Web site (http://w3.mc.ntu.edu.tw/department/genechip/supplement.htm).
Northern Blot Analyses Substantiate the Results of Microarray Studies In this study, we focused on the inducible genes' expression that caused us the most interest. Therefore, 10 gene expressions that showed more than a two-fold change were randomly selected to carry out Northern blot analyses. These clones were sequenced retrospectively after differential expressions were found, to assure that they indeed represented the true transcript. Based on our previous study10 and the zymographic analysis, IL-8 and matrix metalloproteinase 9 (MMP-9) were specifically selected for Northern blot. Otherwise, the other genes were randomly selected, including IL-6, IL-6 signal transducer, IL-7 receptor, CCAAT/enhancer binding protein beta, NF- B inhibitor alpha, intercellular adhesion molecule-1, MMP-1, and stanniocalcin-1. In addition, two genes, VEGF-A and VEGF-C, in which the expression levels are on the borderline of a two-fold change, were also selected. Figure 4 shows that the results of Northern blot analyses were consistent with those from the microarray studies (Table 2). GAPDH was used as an internal control.
Zymography Reveals Higher Gelatinase Activity in Lung Cancer Cells After Coculture With Macrophages Lung cancer cell lines CL1-0, CL1-5, A549, and PC14, were cocultured with macrophages for 24 hours. The medium derived from non-cocultured and macrophage-cocultured cancer cell lines were harvested and subjected to native gel electrophoresis and zymographic analysis. Higher gelatinase activity was observed in all four of these lung cancer cells after coculture with macrophages (Fig 5). Among these cell lines, CL1-0 had the lowest invasive ability (Fig 2) and showed the least increase in gelatinase activity after coculture with macrophages.
Gene Expression Profiles of CL1-5 Cells After Coculture With Macrophages and the Response to Anti-Inflammatory Agents Because the CL1-5 cells revealed a stronger response to macrophage cocultures regardless of the amplification of IL-8 expression or invasive potential, we attempted to use CL1-5 cells to profile the gene expression in cancer cells after coculture with macrophages. The 52 genes identified from microarray were upregulated and were found to have pro-tumorgenic activity. We then examined whether the anti-inflammatory agents could suppress these upregulated gene expressions of cancer cells and return to their basal state. Therefore, those genes that are categorized in Table 2 were used to re-array and profile the gene expression patterns of cancer cells responding to five anti-inflammatory drugs in four different concentrations. Figure 6 shows the gene expression profiles of 52 genes by a two-dimensional hierarchical clustering. The CV for the four copies of each gene was 10.83%, averaged over the 52 genes and the treatment groups. Extracting the data from these 52 genes from the first microarray experiment, the CV for the three replicates of each gene was 9.92%, averaged over the 52 genes and the two groups. The result indicated that there was no significant difference for the CV of these genes between the first and second microarray experiment. Furthermore, the ratio of the gene intensity of untreated cells (coculture without drug) to control (non-coculture) cells is also used to compare to the results of the first microarray experiment. The average of fold-change over the 52 genes for the first microarray was 3.6 ± 2.09, and for the second microarray, 3.2 ± 2.42. The results indicated that the expression patterns of these genes in the second microarray are consistent with those in the first microarray experiment. The gene expression patterns of cells treated with PDTC and dexamethasone are the most similar to that of non-cocultured cells, whereas the gene expression pattern of cells treated with thalidomide is the most dissimilar to that of non-cocultured cells but is the most similar to that of cocultured cells. The anti-inflammatory agents, except for the thalidomide used in this study, revealed the capacity to recover, at least in part, the switched stage. As compared with Figure 6, the multiple scatter plots clearly showed the significance of the differences among the treatments (Fig 7). The results also showed that the inhibitory mechanisms of five anti-inflammatory agents in cancer cell/macrophage cocultures are quite different and can be discriminated from each other by gene expression profiles.
Macrophages perform a multitude of functions essential for tissue remodeling, inflammation, and immune responses against cancer.24 In this study, we demonstrated that TIMs have pro-tumorgenic activity. The TIM density correlated with tumor microvessel density and was related to cancer progression. Coculture of cancer cells with macrophages can enhance cancer cell invasive potential and matrix-degrading activity. Furthermore, the microarray analysis revealed that 52 genes with pro-tumorgenic properties were upregulated and could be partially suppressed by various anti-inflammatory drugs. Previous reports indicate that angiogenic factors, such as IL-8 and VEGF, correlate with tumor angiogenesis and metastasis,20,25,26 and cancer cell-macrophage coculture can promote the expressions of these factors in NSCLC.10,11 The IL-8 expressed by human melanoma cells can also upregulate MMP-2 activity and enhance tumor growth and metastasis.27 In this study, the gelatinolytic activity of MMP-9 is significantly increased in the media of lung cancer cells after coculture with macrophages. It is worth noting that the lung cancer cell lines CL1-0 and CL1-5, derived from the same parental cells, possessed different invasive/metastatic potential in vitro and in vivo, CL1-5 having a greater potential than CL1-0.18 Our results therefore showed that invasive capabilities and matrix-degrading activities increased to a lesser degree in cancer cells with low invasive capacity (CL1-0) than in cancer cells with a higher invasive capacity (CL1-5; Fig 5).
We previously demonstrated that TIMs can upregulate tumor-associated IL-8 mRNA expression through NF- However, many genes have been previously reported to be associated with angiogenesis and metastasis, including the association of IL-6 with a poor prognosis in patients with metastatic breast cancer. Also, many genes have been correlated with the extent of disease28: IL-8 expression was highly associated with distant lymph node metastasis of NSCLC17; urokinase-type plasminogen activator receptor expressed more in tumor tissues of NSCLC patients, as compared with adjacent normal tissues29; STC-1 mRNA level significantly correlated with primary tumor size, number of lymph nodes, and TNM stages in early-stage breast cancer patients30; plasma ICAM-1 was higher in metastatic patients with renal cell carcinoma compared with nonmetastatic patients31; and MMP-1 immunoreactivity of colorectal adenocarcinomas significantly correlated with the presence of lymph node and hepatic metastasis.32 Many genes identified in this study have been confirmed to play a role in metastasis throughout the literature. Further characterization of genes identified in this study is currently in progress.
We previously demonstrated that the interaction between macrophages and cancer cells can upregulate IL-8 expression. This process is mediated, in part, through the NF-
Previous studies have also shown that the tested anti-inflammatory agents significantly inhibit IL-8 mRNA expression in CL1-5 cells cocultured with macrophages in a dose-dependent manner.10 To understand whether the gene expression profiles of cancer cells responding to anti-inflammatory drugs are also dose-dependent, the designated concentrations of drugs were applied to microarray experiments. The concentrations of each anti-inflammatory drug are based on the least effect on cell viability analyses described previously.10 The averages of the cell viability at all of the designated concentrations are as follows: 94.5% for celecoxib (0.01 to 10 µM), 98% for dexamethasone (0.01 to 10 µM), 96.5% for PDTC (0.1 to 10 µM), 93% for aspirin (0.1 to 10 µM), and 98.4% for thalidomide (5 to 50 µM, unpublished data). The concentrations of thalidomide used in microarray experiments were higher than for other drugs, which is due to the lesser effect on suppressing IL-8 induction.38,39 Although the suppressive effects of these drugs on IL-8 mRNA induction were very similar, their possible mechanisms of action are quite different.39-44 Nevertheless, the inhibitory effect of these anti-inflammatory drugs is, for the most part, finally mediated through the NF-
To explore and interpret the differentially functional mechanisms of these five anti-inflammatory drugs, we applied microarray analysis to monitor the gene expression profiles of lung cancer cells responding to drugs in macrophage/cancer cell cocultures. It was evident that the gene expression profile of non-cocultured cells was switched to a novel one after macrophage stimulation. Interestingly, the anti-inflammatory agents tested in this study, except for thalidomide, revealed the capacity to recover, at least in part, the switched stage (Fig 6). Some of the differentially expressed genes in treatment with thalidomide as compared with the other anti-inflammatory drugs are well known to be involved in cancer progression. For example, spermidine/spermine N1-acetyltransferase (SSAT) is induced by hepatotoxins and liver tumor promoters45 and is found specifically in the tumor tissue, not in normal lung tissue.46 Furthermore, SSAT induced by cytokines, IL-1ß, and hepatocyte growth factor controls tumor metabolism and growth, as well as tumor-host interaction.45 Human platelet-derived growth factor beta (PDGF-ß) chain is closely involved in cell growth, oncogenicity, and blood vessel maturation.47,48 Interestingly, the transcription factor NF- In dose-dependent experiments, the results indicated that there is no dose-dependent effect of gene expression patterns on cancer cells responding to anti-inflammatory drugs. Although some drugs, such as celecoxib, dexamethasone, and PDTC, showed a dose-dependent effect in inhibiting IL-8 expression in lung cancer cell/macrophage cocultures in a previous study,10 it was just the result derived from one gene and a different approach. The gene expression profile consisted of many genes, therefore it might not have been suitable to perform a dose-dependent experiment. Taken together, the interaction of lung cancer cells/macrophages can promote the invasiveness and matrix-degrading activity of lung cancer cells. By using microarray technology, we have identified several genes involved in the interaction between cancer cells and macrophages, which may assist us in exploring complex interactions between cancer cells and stroma that orchestrate the process of cancer metastasis. Our results also confirmed the bipolar roles of tumor-associated macrophages more clearly in cancer progression. Furthermore, the gene expression profiles of lung cancer cells responding to anti-inflammatory drugs in cancer cell/macrophage cocultures provide hints in interpreting the differentially functional mechanisms of drugs, as well as for evaluating the potential for new drug discovery in pharmacogenomics by microarray.
The authors indicated no potential conflicts of interest.
Supported by the National Science Council (NSC 91-3112-P-005-008Y; NSC91-3112-P-002-017-Y) and National Health Research Institutes of the Republic of China through the National Research Program for Genomic Medicine Grant (NHRI92A1-NSCLC09-5). Presented in part at the 94th Meeting of the American Association for Cancer Research, Washington, DC, July 11-14, 2003. Drs Chen, Lin, Yao, and Yuan contributed equally to this work. Terms in blue are defined in the glossary, found at the end of this issue and online at www.jco.org. Authors' disclosures of potential conflicts of interest are found at the end of this article.
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