Targeting NFKB by autophagy to polarize hepatoma-associated macrophage differentiation

Tumor-associated macrophages (TAMs) have been linked to promoting tumor progression by stimulating angiogenesis, cell growth and inflammation. NFKB activity in TAMs may mediate inflammation-associated tumor formation. However, most isolated TAMs from established tumors express a M2 phenotype with less NFKB activation and show a strong immunosuppressive phenomenon. How tumors affect the dynamic of NFKB activity in TAMs, and hence maintain their pro-tumor M2 phenotype is still poorly understood. We recently found that hepatoma-derived toll-like receptor 2 (TLR2)-related ligands are capable of stimulating M2 macrophage differentiation via controlling NFKB RELA/p65 protein homeostasis by selective autophagy. TLR2 signal induces NFKB RELA cytosolic ubiquitination and leads to its degradation by SQSTM1/p62-mediated autophagy. Inhibition of autophagy will rescue NFKB activity and shape the phenotype of hepatoma-polarized M2 macrophages. This suggests that autophagy might play a role in manipulating TAM functions and tumor-associated immune responses. Our study also demonstrates that autophagy can directly control a transcriptional factor in addition to its regulatory molecules. This finding uncovers a new role of autophagy in controlling cellular functions.

Molecular targeting of liposomal nanoparticles to tumor microenvironment

Liposomes are biodegradable and can be used to deliver drugs at a much higher concentration in tumor tissues than in normal tissues. Both passive and active drug delivery by liposomal nanoparticles can significantly reduce the toxic side effects of anticancer drugs and enhance the therapeutic efficacy of the drugs delivered. Active liposomal targeting to tumors is achieved by recognizing specific tumor receptors through tumor-specific ligands or antibodies coupled onto the surface of the liposomes, or by stimulus-sensitive drug carriers such as acid-triggered release or enzyme-triggered drug release. Tumors are often composed of tumor cells and nontumor cells, which include endothelial cells, pericytes, fibroblasts, stromal, mesenchymal cells, innate, and adaptive immune cells. These nontumor cells thus form the tumor microenvironment, which could be targeted and modified so that it is unfavorable for tumor cells to grow. In this review, we briefly summarized articles that had taken advantage of liposomal nanoparticles as a carrier to deliver anticancer drugs to the tumor microenvironment, and how they overcame obstacles such as nonspecific uptake, interaction with components in blood, and toxicity. Special attention is devoted to the liposomal targeting of anticancer drugs to the endothelium of tumor neovasculature, tumor associated macrophages, fibroblasts, and pericytes within the tumor microenvironment.

Tumor-associated macrophages: function, phenotype, and link to prognosis in human lung cancer

Macrophages are the dominant leukocyte population found in the tumor microenvironment. Accumulating evidence suggests that these tumor-associated macrophages (TAMs) actively promote all aspects of tumor initiation, growth, and development. However, TAMs are not a single uniform population; instead, they are composed of multiple distinct pro- and anti-tumoral subpopulations with overlapping features depending on a variety of external factors. Defining and differentiating these subsets remains a challenging work-in-progress. These difficulties are apparent in prognostic studies in lung cancer that initially demonstrated conflicting evidence regarding the significance of TAMs but which have more recently clarified and confirmed the clinical importance of these subsets through improved phenotypic capabilities. Thus, these cells represent potential targets for cancer therapeutic initiatives through translational approaches. In this review, we summarize the current understanding of how the tumor microenvironment takes advantage of macrophage plasticity to mold an immunosuppressive population, the phenotypic heterogeneity of TAMs, and their link to prognosis in human lung cancer.

Instruction of myeloid cells by the tumor microenvironment: Open questions on the dynamics and plasticity of different tumor-associated myeloid cell populations

The versatility and plasticity of myeloid cell polarization/differentiation has turned out to be crucial in health and disease, and has become the subject of intense investigation during the last years. On one hand, myeloid cells provide a critical contribution to tissue homeostasis and repair. On the other hand, myeloid cells not only play an important role as first line defense against pathogens but also they are involved in a broad array of inflammation-related diseases such as cancer. Recent studies show that macrophages can exist in different activation states within the same tumor, underlining their plasticity and heterogeneity. In this review, we will discuss recent evidence on how the tumor microenvironment, as it evolves, shapes the recruitment, function, polarization and differentiation of the myeloid cell compartment, leading to the selection of myeloid cells with immunosuppressive and angiogenic functions that facilitate tumor progression and dissemination.

Irradiation promotes an m2 macrophage phenotype in tumor hypoxia

Macrophages display different phenotypes with distinct functions and can rapidly respond to environmental changes. Previous studies on TRAMP-C1 tumor model have shown that irradiation has a strong impact on tumor microenvironments. The major changes include the decrease of microvascular density, the increase of avascular hypoxia, and the aggregation of tumor-associated macrophages in avascular hypoxic regions. Similar changes were observed no matter the irradiation was given to tissue bed before tumor implantation (pre-IR tumors), or to established tumors (IR tumors). Recent results on three murine tumors, TRAMP-C1 prostate adenocarcinoma, ALTS1C1 astrocytoma, and GL261 glioma, further demonstrate that different phenotypes of inflammatory cells are spatially distributed into different microenvironments in both IR and pre-IR tumors. Regions with avascular hypoxia and central necrosis have CD11b^high/Gr-1+ neutrophils in the center of the necrotic area. Next to them are CD11b^low/F4/80+ macrophages that sit at the junctions between central necrotic and surrounding hypoxic regions. The majority of cells in the hypoxic regions are CD11b^low/CD68+ macrophages. These inflammatory cell populations express different levels of Arg I. This distribution pattern, except for neutrophils, is not observed in tumors receiving chemotherapy or an anti-angiogenesis agent which also lead to avascular hypoxia. This unique distribution pattern of inflammatory cells in IR tumor sites is interfered with by targeting the expression of a chemokine protein, SDF-1α, by tumor cells, and this also increases radiation-induced tumor growth delay. This indicates that irradiated-hypoxia tissues have distinct tumor microenvironments that favor the development of M2 macrophages and that is affected by the levels of tumor-secreted SDF-1α.

Upregulation of B7-H1 expression is associated with macrophage infiltration in hepatocellular carcinomas

The overexpression of B7-H1 in hepatocellular carcinoma (HCC) mediates HCC immune escape and obstructs the immunotherapy based on tumor-specific CD8+ T cells. Tumor-associated macrophages (TAM) are a major component of cancer-related inflammation and play a central role in tumor promotion. To classify the mechanism underlying the overexpression of B7-H1 in HCC, we examined B7-H1 expression and TAM infiltration in 63 cases of human HCC samples using immunohistochemistry method and found that B7-H1 overexpression was associated with TAM infiltration in HCC tissues. Furthermore, B7-H1 expression was upregulated at both mRNA level and protein level in HCC cells (BEL-7402 and SMMC-7721) cocultured with macrophages in a transwell system. The upregulation of B7-H1 expression induced by macrophage was inhibited by blocking NF-κB or STAT3 signal pathways. These results suggest that overexpression of B7-H1 in HCC may be induced by inflammatory microenvironment involving macrophages and imply that anti-inflammation therapy might be preventive for immune escape and assistant for immunotherapy of HCC.

Longitudinal study of tumor-associated macrophages during tumor expansion using MRI

MRI is being used increasingly for the noninvasive longitudinal monitoring of cellular processes in various pathophysiological conditions. Macrophages are the main stromal cells in neoplasms and have been suggested to be the major cell type ingesting superparamagnetic iron oxide (SPIO) nanoparticles. However, no MRI study has described longitudinally the presence of tumor-associated macrophages (TAMs) during tumorigenesis with histological confirmation. To address this, we injected SPIO nanoparticles into the circulation of tumor-bearing mice and used MRI and post-mortem histology to monitor TAMs at different time points. The MRI results demonstrated that TAMs, as hypointense signals, appeared continually with the expansion of the tumor. The histological findings also revealed that SPIO-labeled TAMs tended to deposit closer to the vessel lumen with time prior to rapid tumor growth. The present study demonstrates the potential of using MRI to assess longitudinally TAM accumulation during tumorigenesis, and provides the first in vivo insight into the topographical arrangement of TAMs in relation to the progression of tumors. In vivo monitoring of the presence of TAMs could be useful for the development of tumor treatments that target TAM functions.

M2-polarized tumor-associated macrophages are associated with poor prognoses resulting from accelerated lymphangiogenesis in lung adenocarcinoma

OBJECTIVES

Tumor-associated macrophages have been implicated in promoting tumor growth, progression and metastasis. However, the activated phenotype (M1 or M2) of tumor-associated macrophages remains unknown in solid tumors. Therefore, this study examined the density and prognostic significance of M2-polarized tumor-associated macrophages in lung adenocarcinoma.

METHODS

Tumor specimens from 65 lung adenocarcinoma patients were assessed by ELISA for Th1/Th2 cytokine concentrations. The activated phenotype (M1 or M2) of tumor-associated macrophages was determined utilizing immunofluorescence staining. Additionally, to evaluate lymphangiogenesis, peritumoral lymphatic microvessel density was measured using D2-40. The correlation between tumor-associated macrophage subtype and overall patient survival was analyzed using the Kaplan-Meier method and compared using the log-rank test.

RESULTS

A shift toward Th2 cytokine expression was detected within lung adenocarcinoma microenvironments. Approximately 79.71±16.27% of tumor-associated macrophages were M2 polarized; the remaining 20.35±5.31% were M1 polarized. The infiltration of M2-polarized macrophages was significantly associated with P-TNM staging and lymph node metastasis. The peritumoral lymphatic microvessel density was significantly higher in the high M2-polarized tumor-associated macrophage group than in the low M2-polarized tumor-associated macrophage group. A significant difference in overall patient survival was detected not only between patients with tumors with high and low macrophage counts but also between patients with tumors with high and low counts of M2-polarized macrophages.

CONCLUSION

Tumor-associated macrophages in lung adenocarcinoma have an M2-polarized subtype and are associated with poor prognoses, perhaps resulting from accelerated lymphangiogenesis and lymph node metastasis.

Macrophages in breast cancer: do involution macrophages account for the poor prognosis of pregnancy-associated breast cancer?

Macrophage influx is associated with negative outcomes for women with breast cancer and has been demonstrated to be required for metastasis of mammary tumors in mouse models. Pregnancy-associated breast cancer is characterized by particularly poor outcomes, however the reasons remain obscure. Recently, post-pregnancy mammary involution has been characterized as having a wound healing signature. We have proposed the involution-hypothesis, which states that the wound healing microenvironment of the involuting gland is tumor promotional. Macrophage influx is one of the prominent features of the involuting gland, identifying the macrophage a potential instigator of tumor progression and a novel target for breast cancer treatment and prevention.

Activation of complement C3, C5, and C9 genes in tumors treated by photodynamic therapy

Cancer therapies, which deliver a rapidly induced massive tumor tissue injury, such as photodynamic therapy (PDT), provoke a strong host response raised for dealing with the inflicted local trauma. Activated complement system was identified as an important element of host response elicited by tumor PDT. The expression of genes encoding complement proteins C3, C5, and C9 was studied following tumor PDT mediated by photosensitizer Photofrin using mouse Lewis lung carcinoma (LLC) model. Treated tumors and the livers of host mice were collected at different times after PDT and the expression of the investigated genes was analyzed by RT-PCR. The results show a significant up-regulation of C3, C5, and C9 genes in PDT-treated tumors at 24 h after therapy, while no significant increase in the expression of these genes was found in the liver tissues. The expression of C3, C5, and C9 genes also became up-regulated in untreated tumor-associated macrophages (TAMs) co-incubated in vitro with PDT-treated LLC cells. This effect was abolished or drastically reduced in the presence of antibodies blocking heat shock protein 70 (HSP70), Toll-like receptor (TLR) 2 and TLR4, and specific peptide inhibitors of TIRAP adapter protein and transcription factor NF-kappaB. The presented study reveals that complement genes C3, C5, and C9 become up-regulated in tumors treated by PDT, but not in the host's liver. Tumor-localized up-regulation of these genes can be largely attributed to monocytes/macrophages invading the treated lesion after PDT. This effect appears to be induced by the recognition of danger signals from PDT-treated tumor cells such as HSP70 by TAMs that involve the TLR2- and TLR4-triggered signal transduction pathways leading to the activation of NF-kappaB.

Inhibitory effect of locally produced and exogenous interleukin-6 on tumor growth in vivo

In order to define the potential antitumor activity of the multifunctional cytokine interleukin-6 (IL-6), retrovirus-mediated gene transfer was used to introduce and express a cDNA encoding human IL-6 in the murine fibrosarcoma cell line Fsa-R. Although these genetically modified tumor cells appeared morphologically and phenotypically identical to control Fsa-R cells and had a similar plating efficiency in vitro, they were found to exhibit greatly reduced tumorigenicity in vivo following intravenous injection into syngeneic recipients. Exogenous IL-6 was shown to produce a similar inhibition of tumor growth in the lung if administered intraperitoneally. In contrast, tumor growth in subcutaneous sites was inhibited only if the tumor cells were engineered to express IL-6 locally, or if IL-6 was administered intratumorally. Intraperitoneal injection of IL-6 had no inhibitory effect. Tumors that did grow from IL-6-producing tumor cell inocula in subcutaneous sites were found to contain large numbers of macrophages. These results demonstrate that the antitumor activity of systemically administered IL-6 varies depending on the site of tumor growth and suggest an important role for IL-6 in the recruitment, proliferation and/or survival of tumor-associated macrophages.