Macrophages direct tumour histology and clinical outcome in a colon cancer model

Role of macrophage polarization in tumor angiogenesis and vessel normalization: implications for new anticancer therapies

Angiogenesis, the formation of new capillary blood vessels from preexisting vasculature, is one of the hallmarks of cancer that is pivotal for tumor growth and metastasis. Tumor vessels are known to be abnormal, with typically aberrant, leaky and disordered vessels. Thus, the combination of angiogenesis inhibition and vessel normalization is a potential strategy for anticancer therapy. The solid tumor is composed of not only cancer cells, but also the nonmalignant resident stromal cells, such as bone-marrow-derived cells (BMDCs) and cancer-associated fibroblasts (CAFs). Tumor-associated macrophages (TAMs) are the most abundant cell components of BMDCs, which play a significant role in promoting tumor progression. Accumulating evidences from both patient biopsies and experimental animal models have shown that TAMs function in tumor angiogenesis and vessel abnormalization in a density- and phenotype-dependent manner. This chapter will discuss the evidence for the factors and signaling pathways that are involved in macrophage recruitment and polarization in the tumor microenvironment, and it summarizes the role and underlying molecular mechanisms of macrophage polarization in tumor angiogenesis and vessel normalization. In addition, an overview of the potential of targeting TAM polarization for anticancer therapy will be provided.

Recruitment of monocytes/macrophages in different tumor microenvironments

After emigration from the bone marrow into the peripheral blood, monocytes enter tissues and differentiate into macrophages. Monocytes/macrophages have many roles in immune regulation, angiogenesis, and tumor metastasis and invasion. In addition, studies have revealed that these cells are essential to tumor progression. Recently, an accumulation of evidence has indicated that macrophages in distinct regions of tumor masses have distinct origins. For instance, classical monocytes appear to be a major source of macrophages in tumor epithelial, perivascular, and hypoxic regions. In contrast, non-classical monocytes are an important source of macrophages in the tumor perivascular region. During the past century, it has been demonstrated that several chemoattractants can regulate the recruitment of monocytes/macrophages to tumor sites. Despite the importance of monocytes/macrophages in tumor progression, there had been, until recently, no efforts to summarize receptor-ligand pairs between tumor-derived chemokines and corresponding receptors in monocytes in different microenvironments. In this review, we present a cohesive view of the distinct expression patterns of chemokine receptors in two different monocyte subsets (classical and non-classical monocytes) and describe their roles in monocyte/macrophage recruitment into distinct tumor microenvironments. This review provides insight into the behavior of monocytes/macrophages in different tumor microenvironments.

Prognostic significance of tumor-associated macrophages in solid tumor: a meta-analysis of the literature

PURPOSE

Tumor associated macrophages (TAMs) are considered with the capacity to have both negative and positive effects on tumor growth. The prognostic value of TAM for survival in patients with solid tumor remains controversial.

EXPERIMENTAL DESIGN

We conducted a meta-analysis of 55 studies (n = 8,692 patients) that evaluated the correlation between TAM (detected by immunohistochemistry) and clinical staging, overall survival (OS) and disease free survival (DFS). The impact of M1 and M2 type TAM (n = 5) on survival was also examined.

RESULTS

High density of TAM was significantly associated with late clinical staging in patients with breast cancer [risk ratio (RR)  = 1.20 (95% confidence interval (CI), 1.14-1.28)] and bladder cancer [RR = 3.30 (95%CI, 1.56-6.96)] and with early clinical staging in patients with ovarian cancer [RR = 0.52 (95%CI, 0.35-0.77)]. Negative effects of TAM on OS was shown in patients with gastric cancer [RR = 1.64 (95%CI, 1.24-2.16)], breast cancer [RR = 8.62 (95%CI, 3.10-23.95)], bladder cancer [RR = 5.00 (95%CI, 1.98-12.63)], ovarian cancer [RR = 2.55 (95%CI, 1.60-4.06)], oral cancer [RR = 2.03 (95%CI, 1.47-2.80)] and thyroid cancer [RR = 2.72 (95%CI, 1.26-5.86)],and positive effects was displayed in patients with colorectal cancer [RR = 0.64 (95%CI, 0.43-0.96)]. No significant effect was showed between TAM and DFS. There was also no significant effect of two phenotypes of TAM on survival.

CONCLUSIONS

Although some modest bias cannot be excluded, high density of TAM seems to be associated with worse OS in patients with gastric cancer, urogenital cancer and head and neck cancer, with better OS in patients with colorectal cancer.

M2-polarized macrophages promote metastatic behavior of Lewis lung carcinoma cells by inducing vascular endothelial growth factor-C expression

OBJECTIVES

Tumor-associated macrophages that generally exhibit an alternatively activated (M2) phenotype have been linked to tumor progression and metastasis. However, the role of M2-polarized macrophages in the growth and metastasis of lung adenocarcinoma remains enigmatic. The aim of this study was to explore the effect of M2 macrophages on the proliferation and migration of mouse Lewis lung carcinoma cells and tumor-induced lymphangiogenesis.

METHODS

Trypan blue staining and the Transwell migration assay were performed to evaluate the effects of activated (M1 or M2) macrophages on the proliferation and migration of Lewis cells. Furthermore, vascular endothelial growth factor-C expression in Lewis cells and nitric oxide secretion from activated macrophages were detected during the co-culture assay. Following treatment with activated macrophages, lymphatic endothelial cells differentiated into capillary-like structures, and the induction of Lewis cell migration was assessed using a two-dimensional Matrigel-based assay.

RESULTS

In the co-culture Transwell system, the proliferation and migration of Lewis cells were promoted by M2 macrophages. Moreover, the co-culture significantly increased the expression of vascular endothelial growth factor-C by Lewis cells and reduced the secretion of nitric oxide from M2 macrophages, which subsequently led to the capillary morphogenesis of lymphatic endothelial cells. Interestingly, following co-culture with Lewis cells, the function of RAW264.7 cells was polarized toward that of the M2 macrophage phenotype.

CONCLUSION

M2-polarized macrophages promoted the metastatic behavior of Lewis cells by inducing vascular endothelial growth factor-C expression. Thus, the interruption of signaling between M2 macrophages and Lewis cells may be considered to be a new therapeutic strategy.

Liposomal clodronate treatment for tumour macrophage depletion in dogs with soft-tissue sarcoma

Increased numbers of tumour-associated macrophages correlate with rapid tumour growth and metastasis in tumours. Thus, macrophage depletion has potential as a novel cancer therapy and positive responses have been reported in rodent tumour models. To investigate the effectiveness of this approach in dogs with cancer, we evaluated the effects of the macrophage-depleting agent liposomal clodronate (LC) in dogs with soft-tissue sarcoma (STS). To this end, we conducted a clinical trial of LC therapy in 13 dogs with STS. Repeated LC administration was well tolerated clinically. Preliminary examination of tumour biopsy sets from 5 of the 13 dogs demonstrated that the density of CD11b(+) macrophages was significantly decreased after LC treatment. Circulating concentrations of interleukin-8 were also significantly reduced. These preliminary studies are the first to suggest that LC can be used as a systemic macrophage-depleting agent in dogs to reduce numbers of tumour-associated macrophages.

Tumour macrophages as potential targets of bisphosphonates

Tumour cells communicate with the cells of their microenvironment via a series of molecular and cellular interactions to aid their progression to a malignant state and ultimately their metastatic spread. Of the cells in the microenvironment with a key role in cancer development, tumour associated macrophages (TAMs) are among the most notable. Tumour cells release a range of chemokines, cytokines and growth factors to attract macrophages, and these in turn release numerous factors (e.g. VEGF, MMP-9 and EGF) that are implicated in invasion-promoting processes such as tumour cell growth, flicking of the angiogenic switch and immunosuppression. TAM density has been shown to correlate with poor prognosis in breast cancer, suggesting that these cells may represent a potential therapeutic target. However, there are currently no agents that specifically target TAM's available for clinical use.

Bisphosphonates (BPs), such as zoledronic acid, are anti-resorptive agents approved for treatment of skeletal complication associated with metastatic breast cancer and prostate cancer. These agents act on osteoclasts, key cells in the bone microenvironment, to inhibit bone resorption. Over the past 30 years this has led to a great reduction in skeletal-related events (SRE's) in patients with advanced cancer and improved the morbidity associated with cancer-induced bone disease. However, there is now a growing body of evidence, both from in vitro and in vivo models, showing that zoledronic acid can also target tumour cells to increase apoptotic cell death and decrease proliferation, migration and invasion, and that this effect is significantly enhanced in combination with chemotherapy agents. Whether macrophages in the peripheral tumour microenvironment are exposed to sufficient levels of bisphosphonate to be affected is currently unknown. Macrophages belong to the same cell lineage as osteoclasts, the major target of BPs, and are highly phagocytic cells shown to be sensitive to bisphosphonates in model studies; In vitro, zoledronic acid causes increased apoptotic cell death; in vivo the drug has been shown to inhibit the production of pro-angiogenic factor MMP-9, as well as most recent evidence showing it can trigger the reversal of the TAMs phenotype from pro-tumoral M2 to tumoricidal M1. There is thus accumulating evidence supporting the hypothesis that effects on TAMs may contribute to the anti-tumour effect of bisphosphonates. This review will focus in detail on the role of tumour associated macrophages in breast cancer progression, the actions of bisphosphonates on macrophages in vitro and in tumour models in vivo and summarise the evidence supporting the potential for the targeting of tumour macrophages with bisphosphonates.

Cytokines, inflammation and colon cancer

Patients with inflammatory bowel diseases, such as ulcerative colitis and Crohn's disease, are at increased risk of developing colon cancer, confirming that chronic inflammation predisposes to development of tumors. Moreover, it appears that colon cancers that do not develop as a complication of inflammatory bowel disease are also driven by inflammation, because it has been shown that regular use of nonsteroidal anti-inflammatory drugs (NSAIDs) lowers the mortality from sporadic colon cancer and results in regression of adenomas in familial adenomatous polyposis (FAP) patients, who inherit a mutation in the Apc gene. Colorectal cancer therefore represents a paradigm for the link between inflammation and cancer. Inflammation is driven by soluble factors, cytokines and chemokines, which can be produced by tumor cells themselves or, more often, by the cells recruited to the tumor microenvironment. Inflammatory cytokines and chemokines promote growth of tumor cells, perturb their differentiation, and support the survival of cancer cells. Tumor cells become addicted to inflammatory stroma, suggesting that the tumor microenvironment represents an attractive target for preventive and therapeutic strategies. Proinflammatory cytokines, such as TNFα, IL-6 and IL-1β, or transcription factors that are required for signaling by these cytokines, including NF-κB and STATs, are indeed emerging as potential targets for anticancer therapy. TNFα antagonists are in phase I/II clinical trials and have been shown to be well tolerated in patients with solid tumors, and IL-1β antagonists that ameliorate several inflammatory disorders characterized by excessive IL-1β production, will likely follow. Therefore, development of drugs that normalize the tumor microenvironment or interrupt the crosstalk between the tumor and the tumor microenvironment is an important approach to the management of cancer.

Combined blockade of integrin-α4β1 plus cytokines SDF-1α or IL-1β potently inhibits tumor inflammation and growth

Tumor-associated macrophages promote tumor growth by stimulating angiogenesis and suppressing antitumor immunity. Thus, therapeutics that inhibit macrophage recruitment to tumors may provide new avenues for cancer therapy. In this study, we showed how chemoattractants stromal cell-derived growth factor 1 alpha (SDF-1α) and interleukin 1 beta (IL-1β) collaborate with myeloid cell integrin-α4β1 to promote tumor inflammation and growth. We found that SDF-1α and IL-1β are highly expressed in the microenvironments of murine lung, pancreatic, and breast tumors; surprisingly, SDF-1α was expressed only by tumor cells, whereas IL-1β was produced only by tumor-derived granulocytes and macrophages. In vivo, both factors directly recruited proangiogenic macrophages to tissues, whereas antagonists of both factors suppressed tumor inflammation, angiogenesis, and growth. Signals induced by IL-1β and SDF-1α promoted the interaction of talin and paxillin with the cytoplasmic tails of integrin-α4β1, thereby stimulating myeloid cell adhesion to endothelium in vitro and in vivo. Inhibition of integrin-α4β1, SDF-1α, or IL-1β was sufficient to block tumor inflammation and growth, and the combined blockade of these molecules greatly accentuated these effects. Furthermore, antagonists of integrin-α4β1 inhibited chemotherapy-induced tumor inflammation and acted synergistically with chemotherapeutic agents to suppress tumor inflammation and growth. These results show that targeting myeloid cell recruitment mechanisms can be an effective approach to suppress tumor progression.

Bioincompatible impact of different peritoneal dialysis fluid components and therapeutic interventions as tested in a rat peritoneal dialysis model

Peritoneal dialysis (PD) is associated with functional and structural changes of the peritoneal membrane. In this paper, we describe the impact of different factors contributing to peritoneal incompatibility of PD fluid installation including presence of a catheter, volume loading, and the PD fluid components itself. These factors initiate recruitment and activation of peritoneal immune cells such as macrophages and mast cells, as well as activation of peritoneal cells as mesothelial cells in situ. We provide an overview of PD-associated changes as seen in our rat PD-exposure model. Since these changes are partly reversible, we finally discuss therapeutic strategies in the rat PD model with possible consequences of long-term PD in the relevant human setting.

Transition of tumor-associated macrophages from MHC class II(hi) to MHC class II(low) mediates tumor progression in mice

Background

Tumor-associated macrophages (TAMs) are the most abundant immune cells within the tumor stroma and play a crucial role in tumor development. Although clinical investigations indicate that high levels of macrophage (MΦ) infiltration into tumors are associated with a poor prognosis, the exact role played by TAMs during tumor development remains unclear. The present study aimed to investigate dynamic changes in TAM major histocompatibility complex (MHC) class II expression levels and to assess the effects of these changes on tumor progression.

Results

Significant inhibition of tumor growth in the murine hepatocellular carcinoma Hepa1-6 model was closely associated with partial TAM depletion. Strikingly, two distinct TAM subsets were found to coexist within the tumor microenvironment during Hepa1-6 tumor development. An MHC class II^hi TAM population appeared during the early phase of tumor development and was associated with tumor suppression; however, an MHC class II^low TAM population became increasingly predominant as the tumor progressed.

Conclusions

Tumor progression was positively correlated with increasing infiltration of the tumor tissues by MHC class II^low TAMs. Thus, targeting the transition of MΦ may be a novel strategy for drug development and immunotherapy.

T cells contribute to tumor progression by favoring pro-tumoral properties of intra-tumoral myeloid cells in a mouse model for spontaneous melanoma

Tumors affect myelopoeisis and induce the expansion of myeloid cells with immunosuppressive activity. In the MT/ret model of spontaneous metastatic melanoma, myeloid cells are the most abundant tumor infiltrating hematopoietic population and their proportion is highest in the most aggressive cutaneous metastasis. Our data suggest that the tumor microenvironment favors polarization of myeloid cells into type 2 cells characterized by F4/80 expression, a weak capacity to secrete IL-12 and a high production of arginase. Myeloid cells from tumor and spleen of MT/ret mice inhibit T cell proliferation and IFNγ secretion. Interestingly, T cells play a role in type 2 polarization of myeloid cells. Indeed, intra-tumoral myeloid cells from MT/ret mice lacking T cells are not only less suppressive towards T cells than corresponding cells from wild-type MT/ret mice, but they also inhibit more efficiently melanoma cell proliferation. Thus, our data support the existence of a vicious circle, in which T cells may favor cancer development by establishing an environment that is likely to skew myeloid cell immunity toward a tumor promoting response that, in turn, suppresses immune effector cell functions.

Avenanthramides inhibit proliferation of human colon cancer cell lines in vitro

A high intake of whole grain foods is associated with reduced risk of colon cancer, but the mechanism underlying this protection has yet to be elucidated. Chronic inflammation and associated cyclooxygenase-2 (COX-2) expression in the colon epithelium are causally related to epithelial carcinogenesis, proliferation, and tumor growth. We examined the effect of avenanthramides (Avns), unique polyphenols from oats with anti-inflammatory properties, on COX-2 expression in macrophages, colon cancer cell lines, and on proliferation of human colon cancer cell lines. We found that Avns-enriched extract of oats (AvExO) had no effect on COX-2 expression, but it did inhibit COX enzyme activity and prostaglandin E(2) (PGE(2)) production in lipopolysaccharide-stimulated mouse peritoneal macrophages. Avns (AvExO, Avn-C, and the methylated form of Avn-C (CH3-Avn-C)) significantly inhibited cell proliferation of both COX-2-positive HT29, Caco-2, and LS174T, and COX-2-negative HCT116 human colon cancer cell lines, CH3-Avn-C being the most potent. However, Avns had no effect on COX-2 expression and PGE(2) production in Caco-2 and HT29 colon cancer cells. These results indicate that the inhibitory effect of Avns on colon cancer cell proliferation may be independent of COX-2 expression and PGE(2) production. Thus, Avns might reduce colon cancer risk through inhibition of macrophage PGE(2) production and non-COX-related antiproliferative effects in colon cancer cells. Interestingly, Avns had no effect on cell viability of confluence-induced differentiated Caco-2 cells, which display the characteristics of normal colonic epithelial cells. Our results suggest that the consumption of oats and oat bran may reduce the risk of colon cancer not only because of their high fiber content but also due to Avns, which attenuate proliferation of colonic cancer cells.

Macrophage diversity enhances tumor progression and metastasis

There is persuasive clinical and experimental evidence that macrophages promote cancer initiation and malignant progression. During tumor initiation, they create an inflammatory environment that is mutagenic and promotes growth. As tumors progress to malignancy, macrophages stimulate angiogenesis, enhance tumor cell migration and invasion, and suppress antitumor immunity. At metastatic sites, macrophages prepare the target tissue for arrival of tumor cells, and then a different subpopulation of macrophages promotes tumor cell extravasation, survival, and subsequent growth. Specialized subpopulations of macrophages may represent important new therapeutic targets.

The NF-κB/AKT-dependent Induction of Wnt Signaling in Colon Cancer Cells by Macrophages and IL-1β

Progression of colon cancer from microadenoma to macroscopic tumors is coupled to augmentation of canonical Wnt signaling. We recently reported that tumor associated macrophages, through interleukin 1β (IL-1β) dependent phosphorylation of GSK3β, promote Wnt signaling in colon cancer cells, demonstrating that proinflammatory cytokines can enhance TCF4/β-catenin transcriptional activity in tumor cells. Here we investigated the pathway whereby IL-1β inactivates GSK3β and promotes Wnt signaling in colon cancer cells. We showed that normal human monocytes, THP1 macrophages and IL-1 failed to induce Wnt signaling in tumor cells expressing dominant negative IκB (dnIκB), demonstrating that macrophages and IL-1 activate Wnt signaling in a NF-κB-dependent manner. NF-κB activity was required for macrophages and IL-1 to activate PDK1 and AKT in tumor cells and thereby inhibit GSK3β activity. Consistently, dominant negative AKT (dnAKT), or pharmacological inhibition of AKT in tumor cells, prevented macrophage/IL-1 mediated phosphorylation of GSK3β, activation of Wnt signaling, and induction of c-jun and c-myc, confirming that macrophages and IL-1 promote Wnt signaling in an AKT dependent manner. Finally, we showed IL-1 and macrophages failed to promote growth of colon cancer cells with impaired NF-κB or AKT signaling, confirming the requirement for NF-κB and AKT activation for the protumorigenic activity of tumor associated macrophages. Thus, we showed that IL-1 and tumor associated macrophages activate NF-κB-dependent PDK1/AKT signaling in tumor cells, and thereby inactivate GSK3β, enhance Wnt signaling and promote growth of colon cancer cells, establishing a novel molecular link between inflammation and tumor growth.

Monocyte transplantation for neural and cardiovascular ischemia repair

Neovascularization is an integral process of inflammatory reactions and subsequent repair cascades in tissue injury. Monocytes/macrophages play a key role in the inflammatory process including angiogenesis as well as the defence mechanisms by exerting microbicidal and immunomodulatory activity. Current studies have demonstrated that recruited monocytes/macrophages aid in regulating angiogenesis in ischemic tissue, tumours and chronic inflammation. In terms of neovascularization followed by tissue regeneration, monocytes/macrophages should be highly attractive for cell-based therapy compared to any other stem cells due to their considerable advantages: non-oncogenic, non-teratogenic, multiple secretary functions including pro-angiogenic and growth factors, straightforward cell harvesting procedure and non-existent ethical controversy. In addition to adult origins such as bone marrow or peripheral blood, umbilical cord blood (UCB) can be a potential source for autologous or allogeneic monocytes/macrophages. Especially, UCB monocytes should be considered as the first candidate owing to their feasibility, low immune rejection and multiple characteristic advantages such as their anti-inflammatory properties by virtue of their unique immune and inflammatory immaturity, and their pro-angiogenic ability. In this review, we present general characteristics and potential of monocytes/macrophages for cell-based therapy, especially focusing on neovascularization and UCB-derived monocytes.

Macrophage-derived IL-1beta stimulates Wnt signaling and growth of colon cancer cells: a crosstalk interrupted by vitamin D3

Tumor associated macrophages mediate the link between inflammation and cancer progression. Here we showed that macrophage-derived soluble factors induce canonical Wnt signaling in colon cancer cells and promote their growth. Tumor cells induced the release of IL-1β from macrophages, which induced phosphorylation of GSK3β, stabilized β-catenin, enhanced TCF-dependent gene activation, and induced the expression of Wnt target genes in tumor cells. Neutralization experiments using anti IL-1β specific antibodies, or silencing of IL-1β in THP1 macrophages, revealed that IL-1β was required for macrophages to induce Wnt signaling and to support the growth of tumor cells. Constitutive activation of STAT1 in THP1 macrophages was essential for the induction of IL-1β and thus for the activation of β–catenin signaling in tumor cells.

Vitamin D₃, an effective chemopreventive agent, interrupted this crosstalk by blocking the constitutive activation of STAT1 and the production of IL-1β in macrophages, and therefore- in a vitamin D receptor dependent manner- inhibited the ability of macrophages to activate Wnt signaling in colon carcinoma cells. Our data therefore established that vitamin D₃ exerts its chemopreventive activity by interrupting a cross-talk between tumor epithelial cells and the tumor microenvironment.

Modulation of macrophage cytokine profiles during solid tumor progression: susceptibility to Candida albicans infection

BACKGROUND

In order to attain a better understanding of the interactions between opportunist fungi and their hosts, we investigated the cytokine profile associated with the inflammatory response to Candida albicans infection in mice with solid Ehrlich tumors of different degrees.

METHODS

Groups of eight animals were inoculated intraperitoneally with 5 x 106 C. albicans 7, 14 or 21 days after tumor implantation. After 24 or 72 hours, the animals were euthanized and intraperitoneal lavage fluid was collected. Peritoneal macrophages were cultivated and the levels of IFN-gamma, TNF-alpha, IL-12, IL-10 and IL-4 released into the supernatants were measured by ELISA. Kidney, liver and spleen samples were evaluated for fungal dissemination. Tumor-free animals and animals that had only been subjected to C. albicans infection were used as control groups.

RESULTS

Our results demonstrated that the mice produced more IFN-gamma and TNF-alpha and less IL-10, and also exhibited fungal clearance, at the beginning of tumor evolution. With the tumor progression, this picture changed: IL-10 production increased and IFN-gamma and TNF-alpha release decreased; furthermore, there was extensive fungal dissemination.

CONCLUSION

Our results indicate that solid tumors can affect the production of macrophage cytokines and, in consequence, affect host resistance to opportunistic infections.

The perioperative period is an underutilized window of therapeutic opportunity in patients with colorectal cancer

OBJECTIVE

In this review, we address the underlying mechanisms by which surgery augments metastases outgrowth and how these insights can be used to develop perioperative therapeutic strategies for prevention of tumor recurrence.

SUMMARY BACKGROUND DATA

Surgical removal of the primary tumor provides the best chance of long-term disease-free survival for patients with colorectal cancer (CRC). Unfortunately, a significant part of CRC patients will develop metastases, even after successful resection of the primary tumor. Paradoxically, it is now becoming clear that surgery itself contributes to development of both local recurrences and distant metastases.

METHODS

Data for this review were identified by searches of PubMed and references from relevant articles using the search terms "surgery," "CRC," and "metastases."

RESULTS

Surgical trauma and concomitant wound-healing processes induce local and systemic changes, including impairment of tissue integrity and production of inflammatory mediators and angiogenic factors. This can lead to immune suppression and enhanced growth or adhesion of tumor cells, all of which increase the chance of exfoliated tumor cells developing into secondary malignancies.

CONCLUSIONS

Because surgery remains the appropriate and necessary means of treatment for most CRC patients, new adjuvant therapeutic strategies that prevent tumor recurrence after surgery need to be explored since the perioperative therapeutic window of opportunity offers promising means of improving patient outcome but is unfortunately underutilized.

Cytokine signalling by gp130 regulates gastric mucosal healing after ulceration and, indirectly, antral tumour progression

The cytokines IL-6 and IL-11, which signal via the receptor gp130, have been implicated in various gut pathologies, including inflammation and wound healing. We used mouse cytokine signalling mutants to evaluate the role of gp130 pathways in gastric ulceration and healing and the effect of spatially remote fundic ulceration on antral tumour progression, since compromised wound healing may impact tumourigenesis. Glacial acetic acid applied to the serosal surface of stomachs from wild-type, gp130(757FF), IL-6(-/-) and IL-11 receptor (R)alpha(-/-) mice was used to induce discrete haemostasis/necrosis and resultant mucosal ulceration. Wound pathology and mRNA expression of key cytokine target genes were examined 2 and 14 weeks after ulcer induction. The outcome of fundic ulceration on antral tumour development in gp130(757FF) mice was also examined. Chemical haemostasis in gp130(7575FF) mice produces more severe gastric ulcers than in wild-type mice. Lack of IL-6 produces more severe ulceration, while loss of IL-11Ralpha less severe ulcers, suggesting a role for IL-11 in ulcer induction. Increased expression of ulcer-associated IL-11 and its established mitogenic target genes RegI, IIIbeta and IIIgamma paralleled severe ulceration in gp130(757FF) mice. In this model, coincident with fundic ulceration, antral tumour development was inhibited and correlated with decreased RegI, IIIbeta and IIIgamma and reduced MMP9 and 13 expression. IL-11-driven transcription via gp130 contributes to the gastric mucosal response to ulceration. Fundic mucosal ulceration modulates antral growth factor and metalloproteinase gene expression, thereby contributing to restricted tumour growth.

Tumor-associated macrophages: effectors of angiogenesis and tumor progression

Tumor-associated macrophages (TAMs) are a prominent inflammatory cell population in many tumor types residing in both perivascular and avascular, hypoxic regions of these tissues. Analysis of TAMs in human tumor biopsies has shown that they express a variety of tumor-promoting factors and evidence from transgenic murine tumor models has provided unequivocal evidence for the importance of these cells in driving angiogenesis, lymphangiogenesis, immunosuppression, and metastasis. This review will summarize the mechanisms by which monocytes are recruited into tumors, their myriad, tumor-promoting functions within tumors, and the influence of the tumor microenvironment in driving these activities. We also discuss recent attempts to both target/destroy TAMs and exploit them as delivery vehicles for anti-cancer gene therapy.

Cyclooxygenase-2/carbonic anhydrase-IX up-regulation promotes invasive potential and hypoxia survival in colorectal cancer cells

Inflammation promotes colorectal carcinogenesis. Tumour growth often generates a hypoxic environment in the inner tumour mass. We here report that, in colon cancer cells, the expression of the pro-inflammatory enzyme cyclooxygenase-2 (COX-2) associates with that of the hypoxia response gene carbonic anhydrase-IX (CA-IX). The COX-2 knockdown, achieved by the stable infection of a COX-2 specific short harpin RNA interference (shCOX-2), down-regulates CA-IX gene expression. In colorectal cancer (CRC) cells, PGE₂, the main COX-2 gene products, promotes CA-IX gene expression by ERK1/2 activation. In normoxic environment, shCOX-2 infected/CA-IX siRNA transfected CRC cells show a reduced level of active metalloproteinase-2 (MMP-2) that associates with a decreased extracellular matrix invasion capacity. In presence of hypoxia, COX-2 gene expression and PGE₂ production increase. The knockdown of COX-2/CA-IX blunts the survival capability of CRC cells in hypoxia. At a high cell density, a culture condition that creates a mild pericellular hypoxic environment, the expression of COX-2/CA-IX genes is increased and triggers the invasive potential of colon cancer cells. In human colon cancer tissues, COX-2/CA-IX protein expression levels, assessed by Western blot and immunohistochemistry, correlate each other and increase with tumour stage. In conclusion, these data indicate that COX-2/CA-IX interplay promotes the aggressive behaviour of CRC cells.

New roles for mononuclear phagocytes in cancer biology

The primary focus in the pathogenesis and treatment of human malignancies has been the tumor cell. However, the biologic properties of a malignancy are not all intrinsically determined. Interactions between heterogeneous cell populations influence the growth and survival of both normal and malignant cells. Studies defining the origin of endothelial cells involved in tumor angiogenesis first demonstrated the contributions of normal cellular environment. Recently, the mononuclear phagocyte lineage has been found to have biologically and clinically significant tumor enhancing and tumor suppressive effects. This article reviews the multiple roles of mononuclear phagocytes in cancer biology. A companion manuscript (J Pediatr Hematol Oncol. 2008, in press) describes the targeting of these cells for therapeutic benefit. Incorporating these strategies into future childhood cancer protocols could be an innovative approach for improving patient outcome.

Anti-angiogenic active immunotherapy: a new approach to cancer treatment

Tumor angiogenesis plays an important role in tumor growth, aggression and metastasis. Many molecules have been demonstrated as positive regulators of angiogenesis, including vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), epidermal growth factor (EGF), and others. In recent years, significant progress has been made in the research on anti-angiogenic strategies for tumor therapies. In this review, anti-angiogenic active immunotherapies for tumors based on vaccination with xenogeneic homologous molecules and non-xenogeneic homologous molecules are discussed.

Effect of senescence on macrophage polarization and angiogenesis

There is mounting evidence that as the immune system ages, a progressive deterioration in normal function occurs. Termed immunosenescence, aging impacts both the innate and adaptive immune responses. This review discusses the age-related alterations in the innate immune system, with a specific focus on macrophages. The downstream effect of altered macrophage function on aberrant angiogenesis in the pathophysiology of age-related eye disease is also discussed.

Immune cells as mediators of solid tumor metastasis

Outgrowths of disseminated metastases remain the primary cause of mortality in cancer patients; however, molecular and cellular mechanisms regulating metastatic spread remain largely elusive. Recent insights into these mechanisms have refined the seed and soil hypothesis and it is now recognized that metastasis of solid tumors requires collaborative interactions between malignant cells and a diverse assortment of "activated" stromal cells at both primary and secondary tumor locations. Specifically, persistent pro-tumor immune responses (inflammation), now generally accepted as potentiating primary tumor development, are also being recognized as mediators of cancer metastasis. Thus, novel anti-cancer therapeutic strategies targeting molecular and/or cellular mechanisms regulating these collaborative interactions may provide efficacious relief for metastatic disease. This review focuses on recent literature revealing new mechanisms whereby immune cells regulate metastatic progression, with a primary focus on breast cancer.

A Legumain-based minigene vaccine targets the tumor stroma and suppresses breast cancer growth and angiogenesis

Tumor associated macrophages (TAMs) are well known to play a very important role in tumor angiogenesis and metastasis. The suppression of TAMs in the tumor-microenvironment (TME) provides a novel strategy to inhibit tumor growth and dissemination by remodeling the tumor's stroma. Here, we tested our hypothesis that suppression of TAMs can be achieved in syngeneic BALB/c mice with oral minigene vaccines against murine MHC class I antigen epitopes of Legumain, an asparaginyl endopeptidase and a member of the C13 family of cystine proteases which is overexpressed on TAMs in the tumor stroma. Vaccine vectors were constructed and transformed into attenuated Salmonella typhimurium (Dam ( - ) , AroA ( - )) for oral delivery. Groups of mice received either the expression vectors encoding the Legumain H-2D or 2K epitopes or the control empty vector by gavage. The efficacy of the minigene vaccines was determined by their ability to protect mice from lethal tumor cell challenges, the induction of a specific CTL response as well as IFN-gamma release, and inhibition of tumor angiogenesis. We demonstrated that the Legumain minigene vaccine provided effective protection against tumor cell challenge by inducing a specific CD8+ T-cell response against Legumain+ TAMs in our breast tumor model. The protection, induced by this T-cell response, mediated by the Legumain Kd minigene, is also responsible for lysing D2F2 breast carcinoma cells in syngeneic BALB/c mice and for suppressing tumor angiogenesis. Importantly, in a prophylactic setting, the minigene vaccine proved to be of similar anti-tumor efficacy as a vaccine encoding the entire Legumain gene. Together, our findings establish proof of concept that a Legumain minigene vaccine provides a more flexible alternative to the whole gene vaccine, which may facilitate the future design and clinical applications of such a vaccine for cancer prevention.

Tumor infiltrating macrophages reduce development of peritoneal colorectal carcinoma metastases

Macrophages generally constitute a major component of tumor stroma, and possess either tumor growth promoting or inhibiting capabilities. Classically activated macrophages exert cytotoxicity and produce inflammatory cytokines, which limits tumor growth. By contrast, alternatively activated or M2 macrophages induce tumor progression by stimulating angiogenesis and proliferation. Previously we showed that resident macrophages control metastatic spread of coloncarcinoma cells in liver and peritoneal tumor models. However, it is proposed that newly recruited macrophages develop into tumor-associated M2 macrophages, as they are exposed to a microenvironment that favors alternative activation. Previously we showed that monocyte migration was diminished after flavonoid treatment in an experimental autoimmune encephalomyelitis animal model. In the present study, we investigated the role of newly recruited macrophages in colon carcinoma development, by using the flavonoids rutin and luteolin to reduce monocyte migration into peritoneal tumors. Increased tumor development was observed in animals that were treated with rutin and luteolin. Immunohistochemical analyses showed that the number of ED2(+) resident macrophages was normal in tumors of animals that received rutin and luteolin treatment. However, the number of ED1(+) cells (marker immature macrophages) was reduced, indicating decreased macrophage recruitment. Thus, inhibition of monocyte migration promotes tumor growth, supporting that not only resident, but also newly recruited macrophages limit peritoneal colon carcinoma metastases development.

A cellular Trojan Horse for delivery of therapeutic nanoparticles into tumors

Destruction of hypoxic regions within tumors, virtually inaccessible to cancer therapies, may well prevent malignant progression. The tumor's recruitment of monocytes into these regions may be exploited for nanoparticle-based delivery. Monocytes containing therapeutic nanoparticles could serve as "Trojan Horses" for nanoparticle transport into these tumor regions. Here we report the demonstration of several key steps toward this therapeutic strategy: phagocytosis of Au nanoshells, and photoinduced cell death of monocytes/macrophages as isolates and within tumor spheroids.

Angiostatin inhibits monocyte/macrophage migration via disruption of actin cytoskeleton

In light of the involvement of tumor-associated macrophages (TAM) in the promotion of tumor growth and metastasis, strategies to prevent TAM recruitment within the tumor microenvironment are currently under investigation. The recent observation that angiostatin reduces macrophage infiltration in an atherosclerosis model prompted our laboratory to further explore the use of human plasminogen angiostatin (hK1-3) protein as a macrophage modulatory agent. We demonstrate that hK1-3 blocks migration of murine peritoneal macrophages (91% decrease, P<0.00005) and human monocytes (85% decrease, P<0.05) in vitro. Cell viability of hK1-3-treated cells is not affected, as determined by fluorochrome-labeled inhibitors of caspase-propidium iodide (FLICA/PI) flow cytometry analysis. Furthermore, confocal microscopy of phalloidin-stained cells reveals that hK1-3 leads to disruption of actin filopodia/lamellipodia in human monocytes and induces distinct podosome accumulation in mature differentiated macrophages. Paradoxically, we observed a 3.5-fold increase in secretion and a 3- to 5.5-fold increase in gelatinolytic activity of macrophage-produced matrix metalloproteinase-9, which we suggest is a cellular response to compensate for the dominant static effect of hK1-3 on actin. We also demonstrate that hK1-3 induces the phosphorylation of extracellular signal-regulated kinase (ERK1/2) in human monocytes. hK1-3-mediated macrophage immobilization has the potential to be exploited therapeutically in pathological conditions associated with cellular hypoxia, such as cancer and atherosclerosis.

Radiation-enhanced vascular targeting of human lung cancers in mice with a monoclonal antibody that binds anionic phospholipids

PURPOSE

New treatment strategies aimed at damaging tumor vasculature could potentially improve tumor response to radiation therapy. We recently showed that anionic phospholipids, principally phosphatidylserine, are specifically exposed on the luminal surface of tumor blood vessels. Here we tested the hypothesis that radiation therapy can increase phosphatidylserine exposure on lung tumor vasculature, thereby enhancing the antitumor properties of the anti-phosphatidylserine antibody 2aG4.

EXPERIMENTAL DESIGN

The therapeutic efficacy of radiation therapy plus 2aG4 was tested in nude mice bearing radiation-resistant A549 human lung tumors. Radiation-induced phosphatidylserine exposure on endothelial cells and A549 tumor cells was analyzed by immunofluoresence staining. The mechanism of the enhanced antitumor effect was examined by histology and antibody-dependent cell-mediated cytotoxicity experiments.

RESULTS

Focal irradiation of A549 human lung cancer xenografts increased the percentage of tumor vessels with exposed phosphatidylserine from 4% to 26%. Treatment of mice bearing A549 tumors with 2aG4 plus focal radiation therapy inhibited tumor growth by 80% and was superior to radiation therapy or 2aG4 alone (P < 0.01). Combination therapy reduced blood vessel density and enhanced monocyte infiltration into the tumor mass beyond that observed with individual treatments. In vitro, 2aG4 enhanced the ability of macrophages to kill endothelial cells with exposed phosphatidylserine in an Fc'-dependent manner.

CONCLUSION

These results suggest that 2aG4 enhances the antitumor effects of radiation therapy by increasing antibody-dependent cell-mediated cytotoxicity toward tumor vessels with externalized phosphatidylserine. Bavituximab, a chimeric version of 2aG4 in clinical trials, has the potential to enhance the therapeutic efficacy of radiation therapy in lung cancer patients.

TGF-beta receptor 2 downregulation in tumour-associated stroma worsens prognosis and high-grade tumours show more tumour-associated macrophages and lower TGF-beta1 expression in colon carcinoma: a retrospective study

BACKGROUND

Histological phenotype and clinical behaviour of malignant tumours are not only dependent on alterations in the epithelial cell compartment, but are affected by their interaction with inflammatory cells and tumour-associated stroma. Studies in animal models have shown influence of tumour-associated macrophages (TAM) on histological grade of differentiation in colon carcinoma. Disruption of transforming growth factor beta (TGF-beta) signalling in tumour cells is related to more aggressive clinical behaviour. Expression data of components of this pathway in tumour-associated stroma is limited.

METHODS

Tissue micro arrays of 310 colon carcinomas from curatively resected patients in UICC stage II and III were established. In a first step we quantified amount of CD68 positive TAMs and expression of components of TGF-beta signalling (TGF-beta1, TGF-beta receptors type 1 and 2, Smad 3 and 4) in tumour and associated stroma. Further we analyzed correlation to histological and clinical parameters (histological grade of differentiation (low-grade (i.e. grade 1 and 2) vs. high-grade (i.e. grade 3 and 4)), lymph node metastasis, distant metastasis, 5 year cancer related survival) using Chi-square or Fisher's exact test, when appropriate, to compare frequencies, Kaplan-Meier method to calculate 5-year rates of distant metastases and cancer-related survival and log rank test to compare the rates of distant metastases and survival. To identify independent prognostic factors Cox regression analysis including lymph node status and grading was performed.

RESULTS

High-grade tumours and those with lymph node metastases showed higher rates of TAMs and lower expression of TGF-beta1. Loss of nuclear Smad4 expression in tumor was associated with presence of lymph node metastasis, but no influence on prognosis could be demonstrated. Decrease of both TGF-beta receptors in tumour-associated stroma was associated with increased lymph node metastasis and shorter survival. Stromal TGF-beta receptor 2 expression was an independent prognostic factor for cancer related survival.

CONCLUSION

Histological phenotype and clinical behaviour of colon cancer is not only influenced by mutational incidents in tumour cells but also affected by interaction of tumour tissue with inflammatory cells like macrophages and associated stroma and TGF-beta signalling is one important part of this crosstalk. Further studies are needed to elucidate the exact mechanisms.

TGF-beta receptor 2 downregulation in tumour-associated stroma worsens prognosis and high-grade tumours show more tumour-associated macrophages and lower TGF-beta1 expression in colon carcinoma: a retrospective study

BACKGROUND

Histological phenotype and clinical behaviour of malignant tumours are not only dependent on alterations in the epithelial cell compartment, but are affected by their interaction with inflammatory cells and tumour-associated stroma. Studies in animal models have shown influence of tumour-associated macrophages (TAM) on histological grade of differentiation in colon carcinoma. Disruption of transforming growth factor beta (TGF-beta) signalling in tumour cells is related to more aggressive clinical behaviour. Expression data of components of this pathway in tumour-associated stroma is limited.

METHODS

Tissue micro arrays of 310 colon carcinomas from curatively resected patients in UICC stage II and III were established. In a first step we quantified amount of CD68 positive TAMs and expression of components of TGF-beta signalling (TGF-beta1, TGF-beta receptors type 1 and 2, Smad 3 and 4) in tumour and associated stroma. Further we analyzed correlation to histological and clinical parameters (histological grade of differentiation (low-grade (i.e. grade 1 and 2) vs. high-grade (i.e. grade 3 and 4)), lymph node metastasis, distant metastasis, 5 year cancer related survival) using Chi-square or Fisher's exact test, when appropriate, to compare frequencies, Kaplan-Meier method to calculate 5-year rates of distant metastases and cancer-related survival and log rank test to compare the rates of distant metastases and survival. To identify independent prognostic factors Cox regression analysis including lymph node status and grading was performed.

RESULTS

High-grade tumours and those with lymph node metastases showed higher rates of TAMs and lower expression of TGF-beta1. Loss of nuclear Smad4 expression in tumor was associated with presence of lymph node metastasis, but no influence on prognosis could be demonstrated. Decrease of both TGF-beta receptors in tumour-associated stroma was associated with increased lymph node metastasis and shorter survival. Stromal TGF-beta receptor 2 expression was an independent prognostic factor for cancer related survival.

CONCLUSION

Histological phenotype and clinical behaviour of colon cancer is not only influenced by mutational incidents in tumour cells but also affected by interaction of tumour tissue with inflammatory cells like macrophages and associated stroma and TGF-beta signalling is one important part of this crosstalk. Further studies are needed to elucidate the exact mechanisms.

Myeloid cell trafficking and tumor angiogenesis

Tumor growth and metastasis depend on neovascularization, the growth of new blood vessels. Recent findings have revealed that tumor neovascularization is regulated in part by monocytes, which are myeloid lineage cells from the bone marrow. Tumors exhibit significant monocyte infiltrates, which are actively recruited to the tumor microenvironment. Upon tumor infiltration, monocytes can participate in tumor neovascularization. Monocytes can either differentiate into macrophages, which express proangiogenic growth factors, or into endothelial-like cells, which may directly participate in neovascularization. Preliminary studies in animals suggest that modulation of bone marrow-derived cell trafficking into tumors will provide a useful new approach in cancer therapy.

High macrophage infiltration along the tumor front correlates with improved survival in colon cancer

PURPOSE

The role of macrophages in tumorigenesis is complex because they can both prevent and promote tumor development.

EXPERIMENTAL DESIGN

Four hundred forty-six colorectal cancer specimens were stained with the pan-monocyte/macrophage marker CD68, and average infiltration along the tumor front was semiquantitatively evaluated using a four-grade scale. Each section was similarly scored for the presence of CD68 hotspots. Some aspects of macrophage-tumor cell interactions were also studied using in vitro coculture systems.

RESULTS

Including all patients, regardless of surgical outcome and localization, survival increased incrementally with CD68TF(Mean) infiltration grade (P = 0.0001) but not in curatively resected colon cancers (P = 0.28). CD68 hotspot score (CD68TF(Hotspot)) was divided into high and low. A high hotspot score conferred a highly significant survival advantage also in curatively resected colon cancer cases (n = 199, P = 0.0002) but not in rectal cancers. CD68TF(Hotspot) high turned out as an independent prognostic marker for colon cancer in multivariate analyses including gender, age, localization, grade, stage, tumor type, and lymphocytes at the tumor front, conferring a relative risk of 0.49 (P = 0.007). In vitro coculture experiments, using phorbol 12-myristate 13-acetate-activated U937 cells as macrophage model, revealed that a high ratio of macrophages to colon cancer cells inhibited cancer cell growth. This was partially dependent on cell-to-cell contact, whereas Boyden chamber cocultivation without cell-to-cell contact promoted cancer cell spread.

CONCLUSIONS

In conclusion, our data indicate that a dense macrophage infiltration at the tumor front positively influences prognosis in colon cancer and that the degree of cell-to-cell contact may influence the balance between protumorigenic and antitumorigenic properties of macrophages.

Carcinoembryonic antigen-stimulated THP-1 macrophages activate endothelial cells and increase cell–cell adhesion of colorectal cancer cells

The liver is the most common site for metastasis by colorectal cancer, and numerous studies have shown a relationship between serum carcinoembryonic antigen (CEA) levels and metastasis to this site. CEA activates hepatic macrophages or Kupffer cells via binding to the CEA receptor (CEA-R), which results in the production of cytokines and the up-regulation of endothelial adhesion molecules, both of which are implicated in hepatic metastasis. Since tissue macrophages implicated in the metastatic process can often be difficult to isolate, the aim of this study was to develop an in vitro model system to study the complex mechanisms of CEA-induced macrophage activation and metastasis. Undifferentiated, human monocytic THP-1 (U-THP) cells were differentiated (D-THP) to macrophages by exposure to 200 ng/ml phorbol myristate acetate (PMA) for 18 h. Immunohistochemistry showed two CEA-R isoforms present in both U- and D-THP cells. The receptors were localized primarily to the nucleus in U-THP cells, while a significant cell-surface presence was observed following PMA-differentiation. Incubation of D-THP-1 cells with CEA resulted in a significant increase in tumor necrosis factor-alpha (TNF-alpha) release over 24 h compared to untreated D-THP-1 or U-THP controls confirming the functionality of these cell surface receptors. U-THP cells were unresponsive to CEA. Attachment of HT-29 cells to human umbilical vein endothelial cells significantly increased at 1 h after incubation with both recombinant TNF-alpha and conditioned media from CEA stimulated D-THP cells by six and eightfold, respectively. This study establishes an in vitro system utilizing a human macrophage cell line expressing functional CEA-Rs to study activation and signaling mechanisms of CEA that facilitate tumor cell attachment to activated endothelial cells. Utilization of this in vitro system may lead to a more complete understanding of the expression and function of CEA-R and facilitate the design of anti-CEA-R therapeutic modalities that may significantly diminish the metastatic potential of CEA overexpressing colorectal tumors.

Decreased response rates by the combination of histamine and IL-2 in melphalan-based isolated limb perfusion

Histamine (Hi) combined to melphalan in a rat experimental model of isolated limb perfusion (ILP) for lower limb soft tissue sarcoma, resulted in overall response rates (OR) of 66%. Likewise, ILP with interleukin-2 (IL-2) resulted in OR of 67%, when combined to melphalan, in the same experimental model. In systemic immunotherapy, the combination of IL-2 and Hi has been used for solid tumor treatment based on immunomodulatory effects. In this study, we used our well-established ILP experimental model to evaluate whether the synergistic effect between the two drugs seen in the systemic setting, could further improve response rates in a loco-regional setting. Histological evaluation was done directly and 24 h after ILP. Melphalan uptake by tumor and muscle were measured. Hi and IL-2 together, combined to melphalan in the ILP led to OR of only 28%. Histology of tumors demonstrated partial loss of Hi-induced hemorrhagic effect when IL-2 was present. Melphalan accumulation in the tumor when both Hi and IL-2 were added (3.1-fold) was very similar to accumulation with Hi only (2.8-fold), or IL-2 only (3.5-fold) combined to melphalan. In vitro there was no synergy between the drugs. In conclusion there was a negative synergistic effect between IL-2 and Hi in the regional setting.

Legumain/asparaginyl endopeptidase controls extracellular matrix remodeling through the degradation of fibronectin in mouse renal proximal tubular cells

Legumain/asparaginyl endopeptidase (EC 3.4.22.34) is a novel cysteine protease that is abundantly expressed in the late endosomes and lysosomes of renal proximal tubular cells. Recently, emerging evidence has indicated that legumain might play an important role in control of extracellular matrix turnover in various pathological conditions such as tumor growth/metastasis and progression of atherosclerosis. We initially found that purified legumain can directly degrade fibronectin, one of the main components of the extracellular matrix, in vitro. Therefore, we examined the effect of legumain on fibronectin degradation in cultured mouse renal proximal tubular cells. Fibronectin processing can be inhibited by chloroquine, an inhibitor of lysosomal degradation, and can be enhanced by the overexpression of legumain, indicating that fibronectin degradation occurs in the presence of legumain in lysosomes from renal proximal tubular cells. Furthermore, in legumain-deficient mice, unilateral ureteral obstruction (UUO)-induced renal interstitial protein accumulation of fibronectin and renal interstitial fibrosis were markedly enhanced. These findings indicate that legumain might have an important role in extracellular matrix remodeling via the degradation of fibronectin in renal proximal tubular cells.

Relaxin-induced matrix metalloproteinase-9 expression is associated with activation of the NF-κB pathway in human THP-1 cells

Matrix metalloproteinases (MMPs) and relaxin (RLX) are reported to play an important role in tissue remodeling and wound repair. When macrophages populate wound sites, they secrete biologically active substances, including MMPs. The transcription factor NF-kappaB is important in MMP gene regulation in macrophage cells. Thus, a monocyte/macrophage cell line, THP-1, was used to study the molecular mechanism of RLX action on MMP-2 and MMP-9 expression. After 24 h incubation with porcine RLX (100 ng/ml), conditioned media (CM) and THP-1 cells were collected. Gelatin zymography demonstrated an increase in pro-MMP-9 activity in response to RLX in CM, and no significant change in pro-MMP-2 expression was observed. Immunoblot analysis also revealed an increase in pro-MMP-9 in CM from RLX-treated THP-1 cells. Gel EMSA showed that NF-kappaB DNA-binding activity was elevated in THP-1 cells treated with RLX for 10 min and reached a peak at 30 min. The NF-kappaB DNA complex was supershifted using antibodies against NF-kappaB subunits p50 and p65. Increased expression of the p50 and p65 NF-kappaB subunits was also detected in THP-1 cells after RLX treatment. Incubation with RLX (90 min) reduced THP-1 expression of the NF-kappaB inhibitor protein, IkappaB-alpha. Using a specific NF-kappaB inhibitor, pyrrolidine dithiocarmate (PDTC) inhibited nuclear binding of NF-kappaB. Pre-exposure to PDTC suppressed pro-MMP-9 activity and protein levels in RLX-treated THP-1 cells. In conclusion, these data suggest that RLX-induced tissue remodeling through increasing MMP-9 expression is dependent on NF-kappaB activation.

Targeting tumor-associated macrophages as a novel strategy against breast cancer

Tumor-associated macrophages (TAMs) are associated with tumor progression and metastasis. Here, we demonstrate for the first time that legumain, a member of the asparaginyl endopeptidase family functioning as a stress protein, overexpressed by TAMs, provides an ideal target molecule. In fact, a legumain-based DNA vaccine served as a tool to prove this point, as it induced a robust CD8+ T cell response against TAMs, which dramatically reduced their density in tumor tissues and resulted in a marked decrease in proangiogenic factors released by TAMs such as TGF-beta, TNF-alpha, MMP-9, and VEGF. This, in turn, led to a suppression of both tumor angiogenesis and tumor growth and metastasis. Importantly, the success of this strategy was demonstrated in murine models of metastatic breast, colon, and non-small cell lung cancers, where 75% of vaccinated mice survived lethal tumor cell challenges and 62% were completely free of metastases. In conclusion, decreasing the number of TAMs in the tumor stroma effectively altered the tumor microenvironment involved in tumor angiogenesis and progression to markedly suppress tumor growth and metastasis. Gaining better insights into the mechanisms required for an effective intervention in tumor growth and metastasis may ultimately lead to new therapeutic targets and better anticancer strategies.

Macrophages: obligate partners for tumor cell migration, invasion, and metastasis

Macrophages within the tumor microenvironment facilitate angiogenesis and extracellular-matrix breakdown and remodeling and promote tumor cell motility. Recent studies reveal that direct communication between macrophages and tumor cells leads to invasion and egress of tumor cells into the blood vessels (intravasation). Thus, macrophages are at the center of the invasion microenvironment and are an important drug target for cancer therapy.

Distinct Role of Macrophages in Different Tumor Microenvironments

Macrophages are prominent in the stromal compartment of virtually all types of malignancy. These highly versatile cells respond to the presence of stimuli in different parts of tumors with the release of a distinct repertoire of growth factors, cytokines, chemokines, and enzymes that regulate tumor growth, angiogenesis, invasion, and/or metastasis. The distinct microenvironments where tumor-associated macrophages (TAM) act include areas of invasion where TAMs promote cancer cell motility, stromal and perivascular areas where TAMs promote metastasis, and avascular and perinecrotic areas where hypoxic TAMs stimulate angiogenesis. This review will discuss the evidence for differential regulation of TAMs in these microenvironments and provide an overview of current attempts to target or use TAMs for therapeutic purposes.