The role of tumour-associated macrophages in tumour progression: implications for new anticancer therapies

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.

Proliferative actions of muscarinic receptors expressed in macrophages derived from normal and tumor bearing mice

Macrophages (Mps) are essential cellular components of the innate immune system. They are released from the bone marrow as immature monocytes and after circulating in the blood stream, migrate into tissues to undergo final differentiation into resident Mps. In general terms Mps behavior in breast tumors, was described as being either for or against tumor growth. Under certain well defined circumstances Mps are able to kill cells in two ways: direct tumor cytotoxicity or antibody dependent cytotoxicity. We had previously demonstrated that peritoneal Mps from LMM3 mammary tumor bearing mice (TMps) enhanced in vivo the LMM3 induced angiogenesis, promoting tumor growth while Mps from normal BALB/c mice (NMps) did not. In this work, we demonstrate that Mps, expressing functional muscarinic acetylcholine receptors, are able to proliferate in vitro in response to the muscarinic agonist carbachol. These peritoneal cells use two distinct metabolic pathways: TMps are primed by tumor presence and they proliferate mainly by activating arginase pathway and by producing high levels of prostaglandin E(2) via M(1)-M(3) receptors activation. In NMps, carbachol stimulates M(2) receptors function, triggering protein kinase C activity and induces moderate prostaglandin E(2) liberation via M(1) receptor.

The inflammatory micro-environment in tumor progression: the role of tumor-associated macrophages

The link between inflammation and cancer proposed more than a century ago by Rudolf Virchow, who noticed the infiltration of leukocytes in malignant tissues, has recently found a number of genetic and molecular confirmations. Experimental, clinical and epidemiological studies have revealed that chronic inflammation contributes to cancer progression and even predisposes to different types of cancer. Cancer-associated inflammation includes: the presence of leukocyte infiltration; the expression of cytokines such as tumor necrosis factor (TNF) or interleukin (IL)-1; chemokines such as CCL2 and CXCL8; active tissue remodelling and neo-angiogenesis. Tumor-associated macrophages (TAM) are key regulators of the link between inflammation and cancer. Many observations indicate that, in the tumor micro-environment, TAM have several protumoral functions, including expression of growth factors, matrix proteases, promotion of angiogenesis and suppression of adaptive immunity. In this review we will discuss the role of TAM in the inflammatory micro-environment of solid tumors and will try to identify potential target for future therapeutic approaches.

A fibrotic focus is a prognostic factor and a surrogate marker for hypoxia and (lymph)angiogenesis in breast cancer: review of the literature and proposal on the criteria of evaluation

A fibrotic focus is a scar-like area in the centre of a carcinoma and can be regarded as a focus of exaggerated reactive tumour stroma formation. Although modern surgical pathology uses different histopathological and molecular markers to assess the aggressiveness and predict the behaviour of malignant tumours, markers reflecting stromal cell behaviour and interactions between epithelial cells and stromal cells are scarce. In this review we summarize all studies investigating the value of a fibrotic focus as a prognostic factor and as a surrogate marker for hypoxia and (lymph)angiogenesis in patients with breast cancer. These data show that a fibrotic focus can be used as a practical, easily assessable and reproducible integrative histological prognostic parameter in breast cancer. We propose a consensus methodology to assess the fibrotic focus in breast cancer.

Arginine metabolism in tumor-associated macrophages in cutaneous malignant melanoma: evidence from human and experimental tumors

Tumor-associated macrophages (TAMs) may elicit contrasting effects on tumor growth, depending on their biological activities. Macrophages use arginine either to synthesize nitric oxide (NO) through the inducible NO synthase (iNOS) or to produce ornithine through arginase activity. Although the effects of NO are primarily cytotoxic, production of ornithine may promote tumor cell proliferation. Thus, iNOS/arginase balance in TAMs may be crucial in tumor progression. The aim of this study was (a) to explore iNOS and arginase expression in TAMs associated with human melanoma at different stages of tumor progression and (b) to explore whether melanoma cells influence iNOS and/or arginase expression in TAMs under basal condition and in the presence of interferon gamma and/or lipopolysaccharide. Immunohistochemical analyses performed on tissue sections from in situ melanoma, invasive melanoma of different pT categories, and metastatic melanoma revealed that (a) the percentage of iNOS-positive TAMs was significantly higher in in situ and thin melanomas in comparison with more advanced, thicker tumors; (b) the percentage of arginase-positive TAMs did not change among the pT categories analyzed; and (c) the percentage of iNOS-positive TAMs was greater than that of arginase-positive TAMs in peritumoral and intratumoral locations of thin melanomas (pT1). Moreover, by the use of an in vitro experimental protocol represented by B16 murine melanoma cells cocultivated with inflammatory macrophages, we found that melanoma cells stimulate iNOS expression and NO production in macrophages. In conclusion, our in vivo and in vitro results suggest that, mainly in early melanoma lesions, iNOS prevails over arginase in TAMs, a phenomenon possibly stimulated by contact with tumor cells. However, macrophages stimulated by murine melanoma cells secreted a level of NO compatible with an antitumor activity only in the presence of interferon gamma.

Targeting tumour-associated macrophages

Clinical and experimental evidence have highlighted that a major leukocyte population present in tumours, the so-called tumour-associated macrophages (TAM), is the principal component of the leukocyte infiltrate supporting tumour growth. Over the years the mechanisms supporting the protumoural functions of TAM have become increasingly clear and in several experimental tumour models, the activation of an inflammatory response (most frequently mediated by macrophages) has been shown to play an essential role for full neoplastic transformation and progression. This evidence strongly supports the idea that TAM are central orchestrators of the inflammatory networks expressed in the tumour microenvironment, and suggest these cells as possible targets of anticancer therapies.

IKK beta suppression of TSC1 links inflammation and tumor angiogenesis via the mTOR pathway

TNFalpha has recently emerged as a regulator linking inflammation to cancer pathogenesis, but the detailed cellular and molecular mechanisms underlying this link remain to be elucidated. The tuberous sclerosis 1 (TSC1)/TSC2 tumor suppressor complex serves as a repressor of the mTOR pathway, and disruption of TSC1/TSC2 complex function may contribute to tumorigenesis. Here we show that IKKbeta, a major downstream kinase in the TNFalpha signaling pathway, physically interacts with and phosphorylates TSC1 at Ser487 and Ser511, resulting in suppression of TSC1. The IKKbeta-mediated TSC1 suppression activates the mTOR pathway, enhances angiogenesis, and results in tumor development. We further find that expression of activated IKKbeta is associated with TSC1 Ser511 phosphorylation and VEGF production in multiple tumor types and correlates with poor clinical outcome of breast cancer patients. Our findings identify a pathway that is critical for inflammation-mediated tumor angiogenesis and may provide a target for clinical intervention in human cancer.

Tie2-expressing monocytes and tumor angiogenesis: regulation by hypoxia and angiopoietin-2

Recent findings indicate that tumor-associated macrophages are important drivers of tumor angiogenesis. Here, we review the essential role played by Tie2-expressing monocytes (TEM) in this phenomenon. TEMs are present in human blood and tumors and their elimination in various tumor models suppresses tumor angiogenesis. A ligand for Tie2, angiopoietin-2 (Ang-2), is produced by angiogenic tumor vessels and is a chemoattractant for TEMs. Hypoxia up-regulates Tie2 expression on TEMs and, together with Ang-2, down-regulates their antitumor functions. Learning more about the regulation of TEMs by the tumor microenvironment may yield new strategies to ablate the tumor vasculature.

Inflammation and breast cancer. Microenvironmental factors regulating macrophage function in breast tumours: hypoxia and angiopoietin-2

Considerable evidence has now accumulated for tumour-associated macrophages stimulating key aspects of tumour progression, including the proliferation, survival and metastasis of tumour cells, tumour angiogenesis and suppression of the anti-tumour functions of other immune effectors at the tumour site. Tumour micro-environmental factors such as hypoxia have profound, direct effects on these cells, stimulating many of their pro-tumour functions. Hypoxia also does so indirectly by stimulating the release of the cytokine angiopoietin-2 from tumour cells and tumour blood vessels. This in turn then recruits Tie-2-expressing monocytes into tumours from the bloodstream and inhibits their production of anti-apoptotic and anti-angiogenic cytokines.

Melanophages reside in hypermelanotic, aberrantly glycosylated tumor areas and predict improved outcome in primary cutaneous malignant melanoma

BACKGROUND

Previously, hypermelanotic regions of cutaneous malignant melanoma (CMM) were found to contain a mixture of highly melanized melanoma cells and melanophages. Both cell types produced beta1,6-branched oligosaccharides. These sugars are used for motility by myeloid cells and cancer cells alike and are associated with poor survival in carcinomas of the breast, colon and lung. This study further investigated associations between melanophages and beta1,6-branched oligosaccharides and their potential contributions to patient outcome.

METHODS

Individual archival melanomas and high-throughput melanoma tissue microarrays were stained for melanophages with azure blue/S100 and for beta1,6-branched oligosaccharides with the lectin leukocytic phytohemagglutinin (LPHA, a selective marker for beta1,6-branched oligosaccharides).

RESULTS

In primary CMM, melanophages were highly enriched in hypermelanotic, LPHA-positive tumor regions and correlated with improved outcome at 10- and 20-year follow ups. While the combination of melanophages, LPHA positivity and high pigmentation indicated better outcome, a subset of LPHA-positive cells not associated with melanophages indicated worse outcome.

CONCLUSION

This is the first report of an anti-tumor role for the melanophage in melanoma biology. There appeared to be two classes of beta1,6-branched oligosaccharide-producing melanoma cells with opposing effects on outcome: one that attracted melanophages (better) and another that did not (worse). The findings disclose new aspects of the immune system and aberrant glycosylation in CMM.

Inhibition of HuR and MMP-9 expression in macrophage-differentiated HL-60 myeloid leukemia cells by green tea polyphenol EGCg

Matrix metalloproteinase (MMP)-9 expression is linked with myeloid cell differentiation, as well as inflammation and angiogenesis processes related to cancer progression. MMP-9 secretion and macrophage-like HL-60 myeloid leukemia cells differentiation were triggered by the tumor-promoting agent PMA. The chemopreventive effects of green tea catechins epigallocatechin-gallate, catechin-gallate, and epicatechin-gallate, but not those catechins that lack a 3'-galloyl group, inhibited in a time- and dose-dependent manner MMP-9 secretion. The gene and protein expression of MMP-9 and of the mRNA stabilizing factor HuR were also inhibited, while that of the 67 kDa laminin receptor remained unaffected. Specific catechins may help optimize current chemotherapeutic treatment protocols for leukemia.

Effect of dominant negative transforming growth factor-beta receptor type II on cytotoxic activity of RAW 264.7, a murine macrophage cell line

Transforming growth factor-beta (TGF-beta) is a potent suppressor of the immune system. In the present study, we investigated the effect of TGF-beta resistance on a murine macrophage cell line, RAW 264.7, by overexpressing a dominant negative TGF-beta receptor type II (TbetaRIIDN) construct. As expected, TbetaRIIDN-expressing RAW cells, designated as RAW-TbetaRIIDN, were resistant to TGF-beta signaling. When these cells were cocultured with the murine renal cell carcinoma cell line, Renca, a dramatic increase in apoptosis of Renca cells was observed. Simultaneously, elevated levels of inducible nitric oxide synthase (iNOS) and tumor necrosis factor-alpha (TNF-alpha) in association with IFN-gamma were detected in RAW-TbetaRIIDN cells. When the effects of TNF-alpha and iNOS were neutralized through the use of neutralizing antibody and N(G)-methyl-L-arginine, respectively, the enhanced cytotoxicity of TbetaRIIDN-RAW cells was partially reversed. Taken together, these results show that TGF-beta-resistant RAW 264.7 murine macrophage cells have increased cytotoxic activity that is in part mediated by iNOS and TNF-alpha.

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.

The expression of S100A8 in pancreatic cancer-associated monocytes is associated with the Smad4 status of pancreatic cancer cells

The cross-talk between tumour cells and the surrounding supporting host cells (stroma) is a key regulator of cancer growth and progression. By undertaking 2-DE analysis of laser capture microdissected malignant and stromal components of pancreatic tumours and benign ductal elements, we have identified high levels of S100A8 and S100A9 in tumour-associated stroma but not in benign or malignant epithelia. Immunohistochemical analysis (n = 71 patients) revealed strong expression of both proteins in stromal myeloid cells, subsequently identified as CD14(+)/CD68(- )monocytes/macrophages. Co-immunofluorescence revealed that S100A8 was expressed in a subset of S100A9-positive cells. Correlation of the expression of S100A8 and S100A9 to patient parameters revealed that the microenvironments of tumours which lacked expression of the tumour suppressor protein, Smad4, had significantly reduced numbers of S100A8-immunoreactive (p = 0.023) but not S100A9-immunoreactive (p = 0.21) cells. The ratio of S100A8- to S100A9-positive cells within individual tumours was significantly lower in Smad4-negative tumours than in Smad4-positive tumours (p<0.003). Pancreatitic specimens also contained S100A8- and S100A9-expressing cells, although this was not observed in regions displaying extensive fibrosis. In conclusion, our study provides an extensive analysis of S100A8 and S100A9 in pancreatic disease and highlights a potentially important relationship between pancreatic cancer cells and their surrounding microenvironment.

Cell death recognition model for the immune system

It is essential for the immune system to recognize markers or understand rules required for discriminating antigens that should be actively responded to from those be tolerated. Although the classic self-nonself theory over the past five decades has been challenged by "danger" model and "infectious nonself" model, etc., no theories could fit for all. Cell death is important not only for its role in homeostasis, but also for its decisive effects on the immune responses. Different ways of cell death, apoptosis or necrosis, transmit fundamentally opposite driving forces for the immune system, inducing tolerance or initiating adaptive immune responses. The progress in understanding phagocytosis and process of apoptotic and necrotic cells leads the author to propose "cell death" recognition model for the immune system. Four principles are important in this model. First, only antigens shedding from apoptotic or necrotic cells rather than those from healthy cells, can be presented to naïve T cells. Second, either apoptotic cells or necrotic cells, but not healthy cells, can attract phagocytes, namely dendritic cells (DC) or macrophages that are also antigen presenting cells (APC), to scavenge dead cells. Third, macrophages or DC residing in non-lymphoid tissues phagocytose dying/dead cells, migrate to lymphoid tissues and present antigens to naïve T cells there. Fourth, tolerance or adaptive responses are not dependent on whether the antigens are self or nonself, but on the ways of cell death during antigen presentation. Importantly, tolerance and adaptive immunity are all dominant responses and the impact of cell death on immune responses is a dynamic balance between them. "Cell death" recognition model could more easily explain various immune phenomena, including infection, self tolerance and autoimmunity, tumor immunity as well as transplant rejection. Investigation into the roles and mechanisms of cell death mediated immune responses and finding out key modulators will prompt better understanding the ways of immune recognition and provide novel strategies for the management of autoimmunity, tumors, infections as well as transplantation.

Metabolic mechanisms of cancer-induced inhibition of immune responses

During progression, tumors become refractory to the offensive weapons of the immune system. It has been known for a long time that the tumor microenvironment presents a profound modification in the metabolism of arachidonic acid and amino acids such as l-triptophan and l-arginine. However, only in the last decade we have started to appreciate how these changes might cause dysfunctions in cells of both adaptive and innate immune system. The knowledge of these complex and partially interconnected metabolic pathways is offering new targets for an integrated pharmacological approach aiming at freeing tumor-specific T lymphocytes from the latches of cancer influence.

Tumor cell apoptosis polarizes macrophages role of sphingosine-1-phosphate

Macrophage polarization contributes to a number of human pathologies. This is exemplified for tumor-associated macrophages (TAMs), which display a polarized M2 phenotype, closely associated with promotion of angiogenesis and suppression of innate immune responses. We present evidence that induction of apoptosis in tumor cells and subsequent recognition of apoptotic debris by macrophages participates in the macrophage phenotype shift. During coculture of human primary macrophages with human breast cancer carcinoma cells (MCF-7) the latter ones were killed, while macrophages acquired an alternatively activated phenotype. This was characterized by decreased tumor necrosis factor (TNF)-alpha and interleukin (IL) 12-p70 production, but increased formation of IL-8 and -10. Alternative macrophage activation required tumor cell death because a coculture with apoptosis-resistant colon carcinoma cells (RKO) or Bcl-2-overexpressing MCF-7 cells failed to induce phenotype alterations. Interestingly, phenotype alterations were achieved with conditioned media from apoptotic tumor cells, arguing for a soluble factor. Knockdown of sphingosine kinase (Sphk) 2, but not Sphk1, to attenuate S1P formation in MCF-7 cells, restored classical macrophage responses during coculture. Furthermore, macrophage polarization achieved by tumor cell apoptosis or substitution of authentic S1P suppressed nuclear factor (NF)-kappaB signaling. These findings suggest that tumor cell apoptosis-derived S1P contributes to macrophage polarization.

Scavenger receptor-A-targeted leukocyte depletion inhibits peritoneal ovarian tumor progression

Immunosuppressive leukocytes are emerging as a critical factor in facilitating tumor progression. These leukocytes are converted by the tumor microenvironment to become tolerogenic, facilitate metastasis, and to aid in neovascularization. The predominant variety of suppressive leukocytes found in human and murine ovarian cancer are called vascular leukocytes (VLC), due to sharing functions and cell surface markers of both dendritic cells and endothelial cells. Using the ID8 murine model of ovarian cancer, the aim of this study was to test the efficacy of VLC elimination as an ovarian tumor therapy. We show that carrageenan-mediated depletion of peritoneal tumor-associated leukocytes inhibits ovarian tumor progression. We then identified scavenger receptor-A (SR-A) as a cell surface receptor that is robustly and specifically expressed within human and murine ovarian tumor ascites upon VLCs. Administration of anti-SR-A immunotoxin to mice challenged with peritoneal ID8 tumors eliminated tumor-associated VLCs and, importantly, substantially inhibited peritoneal tumor burden and ascites accumulation. Moreover, the toxin required targeting to SR-A because mice that received untargeted toxin did not exhibit inhibition of tumor progression. We conclude that SR-A constitutes a novel and specific target for efficacious immunotherapeutic treatment of peritoneal ovarian cancer.

Tumor immunoediting and immunosculpting pathways to cancer progression

Recent studies have suggested that a natural function of the immune system is to respond and destroy aberrant, dysfunctional cells by a process called immunosurveillance. These studies also suggest that the tumors that arise despite immunosurveillance have been immunosculpted by the immune system. The purported abilities of tumors to induce immune tolerance and suppression, the increased pathogenic behavior of the tumor cells following exposure to immune effectors and the loss of immunogenicity (i.e. immunoediting) often observed in advanced stage tumors could be the result of immunosculpting. In some cases, these immunosculpting features may be permanent and irreversible. However, in other cases, reversible epigenetic mechanisms may underlie the immune resistant tumor phenotype. Regardless, these immune-induced alterations could contribute to cancer pathogenesis. Understanding the mechanisms by which tumors evade immunity will be important for disease prevention and therapeutics.

Influence of tumor cell and stroma sensitivity on tumor response to radiation

In this study, we evaluated the role of tumor cell and tumor stroma sensitivity as determinants of radiation-induced tumor growth delay. A DNA double-strand break repair-defective DNA-PKcs(-/-) tumor cell line and its radioresistant DNA-PKcs(+/+)-transfected counterpart were used to initiate tumors in nude and hypersensitive severe combined immunodeficient (SCID) mice. Insertion of the human DNA-PKcs(+/+) gene substantially increased the intrinsic radioresistance of the DNA-PKcs(-/-) tumor cells and substantially decreased tumor response to radiation in both nude and hypersensitive SCID mice. Tumor cell radiosensitivity was the major determinant of tumor response in nude mice. In SCID mice, both tumor cell sensitivity and radiation-induced stromal damage contributed to response. The relative contribution of host and tumor cell sensitivity on tumor response was unchanged for single doses of 1 x 15 and 6 x 3 Gy-fractionated dose irradiation.

Altered macrophage differentiation and immune dysfunction in tumor development

Tumors require a constant influx of myelomonocytic cells to support the angiogenesis and stroma remodeling needed for their growth. This is mediated by tumor-derived factors, which cause sustained myelopoiesis and the accumulation and functional differentiation of myelomonocytic cells, most of which are macrophages, at the tumor site. An important side effect of the accumulation and functional differentiation of these cells is that they can induce lymphocyte dysfunction. A complete understanding of the complex interplay between neoplastic and myelomonocytic cells might offer novel targets for therapeutic intervention aimed at depriving tumor cells of important growth support and enhancing the antitumor immune response.

The theory of biological robustness and its implication in cancer

One of the essential issues in systems biology is to identify fundamental principles that govern living organisms at the system level. In this chapter, I argue that robustness is a fundamental feature of living systems where its relationship with evolution-trade-offs among robustness, fragility, resource demands, and performance-provides a possible framework for how biological systems have evolved and been organized. In addition, diseases can be con- sidered as a manifestation of fragility of the system. In some cases, such as cancer, the disease state establishes its own robustness against therapeutic interventions. Understanding robustness and its intrinsic properties will provide us with a more profound understanding of biological systems, their anomalies, and countermeasures.

Inflammation and IGF-I activate the Akt pathway in breast cancer

Akt signaling may promote breast cancer progression and poor disease outcome. We hypothesized that serum insulin-like growth factor I (IGF-I) and a proinflammatory tumor environment induce phosphorylation of Akt and downstream targets of Akt in breast cancer. We studied the relationship between Akt pathway activation, IGF-I and markers of inflammation, e.g., nitric oxide synthase-2 (NOS2), cyclooxygenase-2 (COX2) and tumor phagocyte density, in 248 breast tumors. We also examined the association of Akt phosphorylation with breast cancer survival. We observed that phosphorylation of Akt, BAD and caspase-9 correlated strongly with the expression of the 2 proinflammatory enzymes, NOS2 and COX2, in breast tumors (p < 0.001; Spearman rank correlation). Both NOS2 and COX2 expression were independently associated with Akt phosphorylation in the multivariate analysis. Serum IGF-I concentrations and the IGF-I/IGFBP3 ratio correlated with Akt phosphorylation at Thr308 and Ser473 in breast tumors (p <or= 0.05; Spearman rank correlation). The association with Akt phosphorylation at Thr308 remained statistically significant in the multivariate analysis. Akt pathway activation was not associated with overall survival in the unstratified analysis, but we observed a statistical interaction between Akt phosphorylation and tumor phagocyte density on breast cancer survival (p(interaction) < 0.05). We further corroborated our findings in cell culture models by demonstrating that ANA-1 macrophages, nitric oxide and prostaglandin E(2) induce Akt phosphorylation in human breast cancer cells. In summary, a proinflammatory environment was found to activate the Akt pathway in breast cancer, and may modify the association between the Akt phosphorylation status and breast cancer survival.

Pretreatment levels of peripheral neutrophils and leukocytes as independent predictors of overall survival in patients with American Joint Committee on Cancer Stage IV Melanoma: results of the EORTC 18951 Biochemotherapy Trial

PURPOSE

An elevated count of blood neutrophils and monocytes recently was shown independently to predict short survival in patients with stage IV melanoma undergoing interleukin-2-based immunotherapy. In this study, we aimed to validate this finding in a large cohort of stage IV melanoma patients.

PATIENTS AND METHODS

For this retrospective prognostic study, the data from the European Organisation for the Research and Treatment of Cancer 18951 study were used. Patients were randomly assigned between treatment with dacarbazine, cisplatin, and interferon alfa with or without interleukin-2. Counts of neutrophils and leukocytes were analyzed together with other known prognostic factors: serum lactate dehydrogenase, performance status, metastatic site, and sex. Two multivariate prognostic factor analyses were carried out in the model: one with leukocyte counts and one with neutrophil counts.

RESULTS

A total of 363 patients were randomly assigned and baseline blood neutrophil and leukocyte counts were available from 316 and 350 patients, respectively. A high neutrophil count (> 7.5 x 10(9)/L) was an independent prognostic factor for short overall survival (hazard ratio [HR], 1.5; 95% CI, 1.1 to 2.1; P = 0.02), and a high leukocyte count (> 10 x 10(9)/L) was an independent prognostic factor of both short overall survival (HR, 1.7; 95% CI, 1.3 to 2.4; P = 0.0005) and short progression-free survival (HR, 1.5; 95% CI, 1.1 to 2.1; P = 0.008).

CONCLUSION

A high pretreatment count of neutrophils in blood was confirmed as an independent prognostic factor for short overall survival in stage IV melanoma patients undergoing interleukin-2-based immunotherapy. Furthermore, a high count of leukocytes was an independent prognostic factor for short overall survival and progression-free survival. Both parameters should be useful as stratification factors in clinical trials.

Targeting the tumor microenvironment

Despite some notable successes cancer remains, for the most part, a seemingly intractable problem. There is, however, a growing appreciation that targeting the tumor epithelium in isolation is not sufficient as there is an intricate mutually sustaining synergy between the tumor epithelial cells and their surrounding stroma. As the details of this dialogue emerge, new therapeutic targets have been proposed. The FDA has already approved drugs targeting microenvironmental components such as VEGF and aromatase and many more agents are in the pipeline. In this article, we describe some of the "druggable" targets and processes within the tumor microenvironment and review the approaches being taken to disrupt these interactions.

Immunomodulatory and anti-tumor activities of native and heat denatured Abrus agglutinin

Abrus agglutinin (AAG), a hetero tetrameric gal beta (1-3) NAc gal specific lectin, is isolated from seeds of Abrus precatorius. In our previous studies we found that the protein could act as an immunomodulator and immunoadjuvant in native (NA) and heat denatured (HDA) conditions. An anticancer effect of the lectin is reported, but its mode of action is not clearly known. In the present study, the anti-tumor activity of AAG (NA, HDA) has been evaluated in a murine Dalton's lymphoma (DL) ascites tumorogenic model. We found that treatment with both NA and HDA were able to decrease the tumor cell number in vivo and significantly increased median survival time. In vitro studies showed that AAG (NA, HDA) treatment of Dalton's lymphoma ascites cells (DLAC) resulted in growth inhibition at the concentration of 1 microg/ml and above. Whereas, AAG (NA, HDA) at much lower concentrations (approximately 1 ng/ml) can stimulate peritoneal macrophage and spleen derived NK cells in vitro demonstrating cytotoxicity against DLAC. Cell cycle analysis showed an increased number of cells in Sub-G0/G1 phase for in vitro and in vivo treatments. In summary, AAG (NA, HDA) at non-toxic concentration was able to elicit anti-tumor effects in DL bearing mice by stimulating the innate immune system and Th1 type immunomodulation.

Human and murine macrophages mediate activation of MEN 4901/T-0128: a new promising camptothecin analogue-polysaccharide conjugate

MEN 4901/T-0128 is a new cytotoxic prodrug constituted by the camptothecin analogue T-2513 bound to carboxymethyl dextran through a triglycine linker. MEN 4901/T-0128 was designed to target the active camptothecin at the tumour site. MEN 4901/T-0128 is weakly cytotoxic in vitro and thus T-2513 must be released from the conjugate to become active. Here, we demonstrated that human purified cathepsin B releases T-2513 from MEN 4901/T-0128 at pH values ranging from 3 to 5. pH dependency of this reaction suggests that cleavage of the linker should mainly occur in the lysosomes. As elevated cathepsin B activity has been described in macrophages, human tumour monocytic THP-1 cells differentiated into macrophage-like cells were used to study the cellular mechanisms responsible for MEN 4901/T-0128 antitumour activity. Here, we show that differentiated THP-1 internalizes MEN 4901/T-0128 efficiently in a time-dependent and concentration-dependent manner. After phagocytosis, THP-1 cells can cleave the prodrug and release T-2513 in the media. On the contrary, undifferentiated THP-1 cells or pancreatic ASPC-1 tumour cells, although expressing high levels of cathepsin B, are much less efficient in the release of cytotoxic moieties in the culture media. Moreover, normal murine macrophages, recovered from the peritoneal cavity or from the spleen, when activated (in vitro by 100 ng/ml phorbol 12-myristate-13-acetate and in vivo by 300 microl of 3% w/v thioglycollate solution), were able to release (after incubation with 10 microg/ml MEN 4901/T-0128) cytotoxic moieties in the culture supernatant, in an amount sufficient to kill human carcinoma A2780 cells. Thus, we suggest that tumour-associated macrophages may play a key role in the uptake of MEN 4901/T-0128, cleavage and local release of active moiety T-2513. This mechanism should support a tumour targeting of the cytotoxic moieties, allowing an improved antitumour efficacy/safety ratio for MEN 4901/T-0128.

Direct visualization of macrophage-assisted tumor cell intravasation in mammary tumors

Although the presence of macrophages in tumors has been correlated with poor prognosis, until now there was no direct observation of how macrophages are involved in hematogenous metastasis. In this study, we use multiphoton microscopy to show, for the first time, that tumor cell intravasation occurs in association with perivascular macrophages in mammary tumors. Furthermore, we show that perivascular macrophages of the mammary tumor are associated with tumor cell intravasation in the absence of local angiogenesis. These results show that the interaction between macrophages and tumor cells lying in close proximity defines a microenvironment that is directly involved in the intravasation of cancer cells in mammary tumors.

Tumor-associated macrophages and CD3-zeta expression of tumor-infiltrating lymphocytes in human esophageal squamous-cell carcinoma

The clinical significance of tumor-associated macrophages (TAMs) and CD3-zeta chain expression of tumor-infiltrating lymphocytes (TILs), and their correlation in human esophageal squamous cell carcinoma (SCC) are not very clear. Serial histological slides from 137 esophageal SCC patients who had undergone tumor resection were immunohistochemically studied with anti-CD68, anti-CD3-zeta and anti-CD3-epsilon antibodies. TAMs infiltration (expressed as macrophage index, M(phi)I) and CD3-zeta expression (judged by Z/E = CD3-zeta+ cells/CD3-epsilon+ cells ratio) in different tissue compartments were observed. We found that the total tumor tissue region had significantly higher macrophage density and lower CD3-zeta expression (mean +/- SD: M(phi)I(normal): 225.3 +/- 85.9; Z/E(total): 0.52 +/- 0.25; n = 137) relative to adjacent histologically normal esophageal squamous epithelium (M(phi)I(normal): 60.5 +/- 31.7, P < 0.001; Z/E(normal): 0.79 +/- 0.35, P = 0.001; n = 70). Significantly higher M(phi)I(stroma) (P = 0.006) and lower Z/E(total) (P = 0.016) were detected in patients with lymph node metastasis than in those without. Patients with high M(phi)I(total) and M(phi)I(cancer) but low Z/E(total) had poorer surgical outcomes. Univariate analysis of M(phi)I(total) and multivariate analysis of M(phi)I(total) with specific clinico-pathological parameters demonstrated M(phi)I(total) to be an independent prognostic factor for survival in esophageal SCC patients (Cox proportional hazard model, P = 0.029 and P = 0.031, respectively).

Transcriptional profiling suggests that secondary and primary large B-cell lymphomas of the gastrointestinal (GI) tract are blastic variants of GI marginal zone lymphoma

The pathogenetic relationship of marginal zone B-cell lymphoma (MALT lymphoma) of the gastrointestinal (GI) tract and eventually co-existing aggressive B-cell lymphoma and primary aggressive B-cell lymphoma remains to be elucidated. The RNA of laser-microdissected cells was isolated and amplified from small and/or large cell compartments of eight MALT lymphomas (small cell lymphoma, SCL), 14 GI diffuse large B-cell lymphomas (large cell lymphoma, LCL), and ten GI B-cell lymphomas with composite small and large cell compartments (ComL) and expression analyses were performed using cDNA arrays. Hierarchical cluster analysis clearly separated SCL and LCL and the small and large cell compartments of ComL. Likewise, cluster analysis with all samples of SCL, LCL, and ComL yielded two main 'small cell' and 'large cell' branches. Furthermore, 60 genes were differentially expressed between SCL and LCL, and 82 genes between the small and large cell components of ComL; 26 genes were discriminators in both settings. Use of the profiles of ComL as training sets for class prediction resulted in 95% accuracy for the classification of SCL and LCL. Collectively, the data strongly suggest that both secondary and primary aggressive B-cell lymphomas of the GI tract are blastic marginal zone lymphomas.

Macrophage-targeted photosensitizer conjugate delivered by intratumoral injection

A conjugate between maleylated albumin and a photosensitizer (PS) shows cell type specific targeting to macrophages via the scavenger receptor. Administration of this conjugate to a tumor-bearing mouse followed by illumination may allow selective destruction of macrophages within tumors. There is accumulating evidence that tumor-associated macrophages contribute to tumor growth, invasiveness, metastasis, and immune suppression. We tested the intravenous (IV) injection of a conjugate between maleylated albumin and chlorin(e6) to BALB/c mice bearing three tumor types with differing proportions of tumor-associated macrophages. The accumulation of PS within the tumors after IV injection and 24 h incubation time was disappointing, and we therefore investigated intratumoral (IT) injection. This gave 20-50 times greater concentrations of PS within the tumor compared to IV injection as determined by tissue extraction. Furthermore the amounts of PS in each tumor type correlated well with the numbers of macrophages both as determined by extraction from bulk tumor and fluorescence quantification and as determined by tissue dissociation to a single cell suspension and two-color flow cytometry with macrophage-specific antibodies. IT injection of nonconjugated PS gave lower tumor accumulation that did not correlate with macrophage content. IT injection of targeted macromolecular delivery systems is an underexplored area and worthy of further study.

The multifaceted roles of chemokines in malignancy

Tumor development and progression are multifactorial processes, regulated by a large variety of intrinsic and microenvironmental factors. A key role in cancer is played by members of the chemokine superfamily. Chemokines and their receptors are expressed by tumor cells and by host cells, in primary tumors and in specific metastatic loci. The effects of chemokines on tumorigenesis are diverse: While some members of the superfamily significantly support this process, others inhibit fundamental events required for tumor establishment and metastasis. The current review describes the multifaceted roles of chemokines in malignancy, addressing four major aspects of their activities: (1) inducing leukocyte infiltration to tumors and regulating immune functions, with emphasis on tumor-associated macrophages (and the chemokines CCL2, CCL5), T cells (and the chemokines CXCL9, CXCL10) and dendritic cells (and the chemokines CCL19, CCL20, CCL21); (2) directing the homing of tumor cells to specific metastatic sites (the CXCL12-CXCR4 axis); (3) regulating angiogenic processes (mainly the ELR(+)-CXC and non-ELR-CXC chemokines); (4) acting directly on the tumor cells to control their malignancy-related functions. Together, these different chemokine functions establish a net of interactions between the tumor cells and their microenvironment, and partly dictate the fate of the malignancy cascade.

Role of tumor-derived proinflammatory cytokines GM-CSF, TNF-alpha, and IL-12 in the migration and differentiation of antigen-presenting cells in cervical carcinoma

BACKGROUND

Proinflammatory cytokines are important in modifying the activity, differentiation, and migration of antigen-presenting cells and may influence the survival of cancer patients. The study assessed whether GM-CSF, TNF-alpha, and IL-12, produced by cervical cancer cells, are important for the activity, differentiation, and migration of antigen-presenting cells.

METHODS

In 90 patients with cervical carcinoma the number of monocytes/tumor-associated macrophages (TAM), mature dendritic cells (DC), and Langerhans cells (LHC) was determined using immunohistochemistry. An RNA in situ hybridization technique was used to measure the expression level of GM-CSF, TNF-alpha, IL-12p35, and IL-12p40.

RESULTS

TAM were detected intraepithelial as well as in the stroma of the tumor. LHC were only detected intraepithelial and mature DC only in the tumor stroma. The number of TAM correlated positively with the number of mature DC. The expression levels of GM-CSF and TNF-alpha correlated positively with the number of TAM and DC. TNF-alpha showed a negative correlation with the number of LHC. A significant correlation between the expression of functional IL-12 (IL-12p40) and stromal TAM was found. The expression of GM-CSF, TNF-alpha, and IL-12p40 did not correlate significantly with disease-free survival. However, high IL-12p40 expression was associated with a favorable cumulative overall survival.

CONCLUSIONS

The results suggest that GM-CSF as well as TNF-alpha, produced by cervical carcinoma cells, may play a role in the differentiation of monocytes into mature DC. Furthermore, TNF-alpha may influence the migration of LHC from the tumor.

Macrophage-based anti-cancer therapy: modelling different modes of tumour targeting

Tumour hypoxia is associated with poor drug delivery and low rates of cell proliferation, factors that limit the efficacy of therapies that target proliferating cells. Since macrophages localise within hypoxic regions, a promising way to target hypoxic tumour cells involves engineering macrophages to express therapeutic genes under hypoxia. In this paper we develop mathematical models to compare the responses of avascular tumour spheroids to two modes of action: either the macrophages deliver an enzyme that activates an externally applied prodrug (bystander model), or they deliver cytotoxic factors directly (local model). The models we develop comprise partial differential equations for a multiphase mixture of tumour cells, macrophages and extracellular fluid, coupled to a moving boundary representing the spheroid surface. Chemical constituents, such as oxygen and drugs, diffuse within the multiphase mixture. Simulations of both models show the spheroid evolving to an equilibrium or to a travelling wave (multiple stable solutions are also possible). We uncover the parameter dependence of the wave speed and steady-state tumour size, and bifurcations between these solution forms. For some parameter sets, adding extra macrophages has a counterintuitive deleterious effect, triggering a bifurcation from bounded to unbounded tumour growth. While these features are common to the bystander and local models, the crucial difference is where cell death occurs. The bystander model is comparable to traditional chemotherapy, with poor targeting of hypoxic tumour cells; however, the local mode of action is more selective for hypoxic regions. We conclude that effective targeting of hypoxic tumour cells may require the use of drugs with limited mobility or whose action does not depend on cell proliferation.

Synergism between GM-CSF and IFNgamma: enhanced immunotherapy in mice with glioma

Glioblastoma multiforme is the most common malignant primary brain tumor and also one of the most therapy-resistant tumors. Because of the dismal prognosis, various therapies modulating the immune system have been developed in experimental models. Previously, we have shown a 37-70% cure in a rat glioma model where rats were peripherally immunized with tumor cells producing IFNgamma. On the basis of these results, we wanted to investigate whether a combination of GM-CSF and IFNgamma could improve the therapeutic effect in a mouse glioma model, GL261 (GL-wt). Three biweekly intraperitoneal (i.p.) immunizations with irradiated GM-CSF-transduced GL261 cells (GL-GM) induced a 44% survival in mice with intracranial glioma. While treatment of GL-wt and GL-GM with IFNgamma in vitro induced upregulation of MHC I and MHC II on the tumor cells, it could not enhance survival after immunization. However, immunizations with GL-GM combined with recombinant IFNgamma at the immunization site synergistically enhanced survival with a cure rate of 88%. Tumors from mice receiving only 1 immunization on Day 10 after tumor inoculation were sectioned on Day 20 for analysis of leukocyte infiltration. Tumor volume was reduced and the infiltration of macrophages was denser in mice immunized with GL-GM combined with IFNgamma compared with that of both wildtype and nonimmunized mice. To our knowledge, this is the first study to demonstrate a synergy between GM-CSF and IFNgamma in experimental immunotherapy of tumors, by substantially increasing survival as well as inducing a potent anti-tumor response after only 1 postponed immunization.

Sulfasalazine-induced cystine starvation: potential use for prostate cancer therapy

BACKGROUND

Certain cancers depend for growth on uptake of cystine/cysteine from their environment. Here we examined advanced human prostate cancer cell lines, DU-145 and PC-3, for dependence on extracellular cystine and sensitivity to sulfasalazine (SASP), a potent inhibitor of the x(c)(-) cystine transporter.

METHODS

Cultures were evaluated for growth dependence on exogenous cystine, x(c)(-) transporter expression, response to SASP (growth and glutathione content). In vivo, effect of SASP was determined on subrenal capsule xenograft growth.

RESULTS

Cystine omission from culture medium arrested DU-145 and PC-3 cell proliferation; both cell lines expressed the x(c)(-) transporter and were growth inhibited by SASP (IC(50)s: 0.20 and 0.28 mM, respectively). SASP-induced growth inhibition was associated with vast reductions in cellular glutathione content - both effects based on cystine starvation. SASP (i.p.) markedly inhibited growth of DU-145 and PC-3 xenografts without major toxicity to hosts.

CONCLUSIONS

SASP-induced cystine/cysteine starvation leading to glutathione depletion may be useful for therapy of prostate cancers dependent on extracellular cystine.

Is YKL-40 a new therapeutic target in cancer?

YKL-40 is produced by cancer cells and tumour-associated macrophages. YKL-40 may play a role in cancer cell proliferation, differentiation, survival, invasiveness, metastasis, in angiogenesis and the inflammation and remodelling of the extracellular matrix surrounding the tumour. Serum YKL-40 is a biomarker of prognosis, confirmed in 13 different types of cancer including > 2500 patients. Highest serum YKL-40 is found in patients with metastatic cancer with the shortest recurrence-free interval and shortest overall survival. Serum YKL-40 provides independent information compared with clinical characteristics and biomarkers, such as HER2, carcinoembryonic antigen, CA-125, prostate-specific antigen and lactate dehydrogenase. The authors hypothesise that inhibition of YKL-40 by monoclonal antibodies either directly or towards its receptor may be as efficient a cancer therapeutic as the monoclonal antibodies against HER2, HER1, vascular endothelial growth factor and CD20. Drugs inhibiting YKL-40 should be explored as new cancer therapeutics.

Consistent liver metastases in a rat model by portal injection of microencapsulated cancer cells

Consistent liver metastases in animal models is generally observed only with certain cancer cell lines. With the aim of improving on existing animal models of liver metastases, we hypothesized that cancer cells encased in 300 microm microcapsules, mimicking micrometastatic foci, might be effective seeds of liver metastases. A total of 3,000 microcapsules, containing 700 to 1,500 viable cells/capsule in logarithmic growth phase of three human pancreatic cancer cell lines (SUIT-2, AsPC-1, and BxPC-3), were transplanted in nude rats by portal injection. The rate of liver metastases was 100% (12 of 12), 100% (6 of 6), and 83% (5 of 6) for SUIT-2, AsPC-1, and BxPC-3 microcapsules, respectively. In contrast, the administration of an identical number of single cancer cells (2.1-4.5 x 10(6)) did not lead to liver metastases. Metastases was strictly limited to the liver, was quite stable, and could be proportionately tailored by varying the number of cancer microcapsules administered. Microscopic observation showed that two-thirds of the cancer microcapsules were lodged in the peripheral small (20-50 microm) portal veins, although one-third of the cancer microcapsules were trapped in the central wide (200-400 microm) portal vein. Capsules began to burst at day 3, with recognizable metastases produced at day 7, resulting in overt metastases production at days 28 to 42. The present cancer microcapsule method may be useful for obtaining liver metastases in animal models, especially for cell lines that will not form liver metastases with conventional single cell injection methods and/or for experiments requiring the consistent formation of liver metastases.

Inhibition of carcinoma cell-derived VEGF reduces inflammatory characteristics in xenograft carcinoma

The stroma of carcinomas shares several characteristics with inflamed tissues including a distorted vasculature, active angiogenesis and macrophage infiltration. In addition, the tumor interstitial fluid pressure (P(IF)) of the stroma is pathologically elevated. We show here that bevacizumab [rhuMab vascular endothelial growth factor (VEGF), Avastin], a monoclonal antibody to VEGF, at a dose of 5 mg/kg modulated inflammation in KAT-4 xenograft human anaplastic thyroid carcinoma tissue. At this dose, bevacizumab reduced the density of macrophages, MHC class II antigen expression by macrophages and IL-1beta mRNA expression. Furthermore, bevacizumab lowered tumor extracellular fluid volume, plasma protein leakage from tumor vessels, the number of CD31-positive structures and tumor P(IF). The tumor plasma volume and the number of alpha-smooth muscle actin-positive vessels, however, remained unchanged. Our data suggest that carcinoma cell-derived VEGF either directly or indirectly participates in maintaining an inflammatory microenvironment in experimental KAT-4 carcinoma. Furthermore, our data indicate that the reduction of inflammation resulting in reduced vascular permeability and decrease in the tumor extracellular fluid volume by bevacizumab contributes to reduced tumor P(IF).

Tumor macrophage redox and effector mechanisms associated with hypoxia

Monocytes are recruited from the circulation into solid tumors where they differentiate into macrophages with unique phenotypes. While macrophages utilize oxygen in a broad range of immune effector functions, the generation of reactive oxygen and nitrogen oxide species is less clear in the setting of hypoxia, which can be a prominent feature of solid tumors. The relationships among innate immunity, redox systems, and the plasticity of phenotypic changes tumor-associated macrophages undergo in conjunction with tumor hypoxia will be examined.

Transgenic expression of CSF-1 in CSF-1 receptor-expressing cells leads to macrophage activation, osteoporosis, and early death

CSF-1 is the primary mononuclear phagocyte and osteoclast growth factor. Autocrine regulation by CSF-1 has been reported in macrophages during inflammatory responses and in neoplastic cells. To investigate whether inflammatory disease or neoplasia was the dominant consequence of autocrine regulation by CSF-1 in CSF-1 receptor (CSF-1R)-expressing cells, we created mice that express CSF-1 under the control of the CSF-1R promoter/first intron driver [transgene TgN(Csf1r-Csf1)Ers (TgRC) mice], which have reduced thymic size, a short lifetime, and low body weight and develop osteoporosis. In 4-week-old TgRC mice, osteoclast numbers are elevated, and macrophage densities are increased in bone marrow, spleen, liver, and brain. Cultured TgRC macrophages express CSF-1 and proliferate without exogenous CSF-1 and in the presence of neutralizing antimouse CSF-1 antibody. Compared with macrophages from nontransgenic littermates, TgRC macrophages exhibit a stellate morphology, express elevated mRNAs for proinflammatory cytokines, and despite a lower, steady-state cytokine secretion, secrete elevated levels of inflammatory cytokines in response to LPS, indicating that TgRC macrophages are functionally primed through the CSF-1R. Thus, autocrine regulation of CSF-1R-expressing cells by CSF-1 leads to a severe phenotype that emphasizes the importance of the known, local production of CSF-1 in inflammatory disease.

Random migration precedes stable target cell interactions of tumor-infiltrating T cells

The tumor microenvironment is composed of an intricate mixture of tumor and host-derived cells that engage in a continuous interplay. T cells are particularly important in this context as they may recognize tumor-associated antigens and induce tumor regression. However, the precise identity of cells targeted by tumor-infiltrating T lymphocytes (TILs) as well as the kinetics and anatomy of TIL-target cell interactions within tumors are incompletely understood. Furthermore, the spatiotemporal conditions of TIL locomotion through the tumor stroma, as a prerequisite for establishing contact with target cells, have not been analyzed. These shortcomings limit the rational design of immunotherapeutic strategies that aim to overcome tumor-immune evasion. We have used two-photon microscopy to determine, in a dynamic manner, the requirements leading to tumor regression by TILs. Key observations were that TILs migrated randomly throughout the tumor microenvironment and that, in the absence of cognate antigen, they were incapable of sustaining active migration. Furthermore, TILs in regressing tumors formed long-lasting (≥30 min), cognate antigen–dependent contacts with tumor cells. Finally, TILs physically interacted with macrophages, suggesting tumor antigen cross-presentation by these cells. Our results demonstrate that recognition of cognate antigen within tumors is a critical determinant of optimal TIL migration and target cell interactions, and argue against TIL guidance by long-range chemokine gradients.

The radiosensitizing effect of immunoadjuvant OM-174 requires cooperation between immune and tumor cells through interferon-gamma and inducible nitric oxide synthase

PURPOSE

To explore whether antitumor immunoadjuvant OM-174 can stimulate immune cells to produce interferon-gamma (IFN-gamma) and thereby radiosensitize tumor cells.

METHODS AND MATERIALS

Splenocytes from BALB/c mice were stimulated by OM-174 at plasma-achievable concentrations (0.03-3 mug/mL), and afterward analyzed for the expression and secretion of IFN-gamma by reverse transcriptase-polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. Stimulated splenocytes were used as a source of IFN-gamma to radiosensitize hypoxic EMT-6 tumor cells through the cytokine-inducible isoform of nitric oxide synthase (iNOS).

RESULTS

OM-174 activated the production of IFN-gamma at high levels that reached 70 ng/mL in normoxia (21% oxygen) and 27 ng/mL in tumor-relevant hypoxia (1% oxygen). This caused up to 2.1-fold radiosensitization of EMT-6 tumor cells, which was associated with the iNOS-mediated production of the radiosensitizing molecule nitric oxide, as confirmed by accumulation of its oxidative metabolite nitrite, Western blot analysis, and reverse transcriptase-polymerase chain reaction. Both iNOS activation and radiosensitization were counteracted by neutralizing antibodies against IFN-gamma. The same mechanism of radiosensitization through the IFN-gamma secretion pathway was identified for IL-12 + IL-18, which are known to mediate IFN-gamma responses. Hypoxia displayed a dual effect on the immune-tumor cell interaction, by downregulating the expression of the IFN-gamma gene while upregulating iNOS at transcriptional level.

CONCLUSION

Immunoadjuvant OM-174 is an efficient radiosensitizer of tumor cells through activation of the IFN-gamma secretion pathway in immune cells. This finding indicates a rationale for combining immunostimulatory and radiosensitizing strategies and extends the potential therapeutic applications of OM-174.

Leukocyte infiltration in cancer creates an unfavorable environment for antitumor immune responses: a novel target for therapeutic intervention

The interaction between tumor cells and the nearby environment is being actively investigated to explore how this interplay affects the initiation and progression of cancer. Host-tumor relationship results in the production of pro-inflammatory cytokines and chemokines that promote the recruitment of leukocytes within and around developing neoplasms. Cancer cells, together with newly recruited tumor-infiltrating cells, can also activate fibroblast and vascular responses, thus resulting in a chronic microenvironment perturbation. In this complex scenario, interactions between innate and adaptive immune cells can be disturbed, leading to a failure of immune-mediated tumor recognition and destruction. On the basis of the recent awareness about tumor promotion and immune deregulation by immune/inflammatory cells, novel anti-cancer strategies can be exploited.

Dimerization of CXCR4 in living malignant cells: control of cell migration by a synthetic peptide that reduces homologous CXCR4 interactions

Chemokine receptor CXCR4 (CD184) may play a role in cancer metastasis and is known to form homodimers. However, it is not clear how transmembrane regions (TM) of CXCR4 and receptor homotypic interactions affect the function of CXCR4 in living cells. Using confocal microscopy and flow cytometric analysis, we showed that high levels of CXCR4 are present in the cytoplasm, accompanied by lower expression on the cell surface in CXCR4 transfectants, tumor cells, and normal peripheral blood lymphocytes. CXCR4 homodimers were detected in tumor cells, both on the cell surface membrane and in the cytoplasm using fluorescence resonance energy transfer and photobleaching fluorescence resonance energy transfer to measure energy transfer between CXCR4-CFP and CXCR4-YFP constructs. Disruption of lipid rafts by depletion of cholesterol with methyl-beta-cyclodextrin reduced the interaction between CXCR4 molecules and inhibited malignant cell migration to CXCL12/SDF-1alpha. A synthetic peptide of TM4 of CXCR4 reduced energy transfer between molecules of CXCR4, inhibited CXCL12-induced actin polymerization, and blocked chemotaxis of malignant cells. TM4 also inhibited migration of normal monocytes toward CXCL12. Reduction of CXCR4 energy transfer by the TM4 peptide and methyl-beta-cyclodextrin indicates that interactions between CXCR4s may play important roles in cell migration and suggests that cell surface and intracellular receptor dimers are appropriate targets for control of tumor cell spread. Targeting chemokine receptor oligomerization and signal transduction for the treatment of cancer, HIV-1 infections, and other CXCR4 mediated inflammatory conditions warrants further investigation.

Mammary gland macrophages: pleiotropic functions in mammary development

Mammary gland development is a complex process involving epithelial cells and supporting stromal cells. Macrophages (MØs) are an important component of the mammary gland stroma and are critical for normal mammary gland development; however, the mechanisms by which macrophages regulate these processes are not well understood. MØs are known to interact with numerous cell types, including epithelial cells, fibroblasts, adipocytes, and endothelial cells, all of which are significant components of mammary gland development. Therefore, the purpose of this review is to describe the interactions between MØs and these various cell types and use this knowledge to identify potential functions of MØs in the mammary gland.

The chemokine network: a target in cancer biology?

Chemokine gradients are central to the movement of cells in both homeostatic and pathological processes. Most cancers express a complex array of chemokines that influence the local microenvironment through recruitment of stromal cells and by stimulating angiogenesis. Recently, the discovery of chemokine receptors on tumor cells has led to speculation that the chemokine system may be involved in cancer cell growth and survival, and possibly the development of site-specific spread. Understanding the networks of chemokines and their receptors in cancer will enable manipulation of this system. Both chemokines and their receptors represent targets for therapeutic intervention either with antibodies or small molecule antagonists. However, due to the complexity of the system, and the number of chemokines and receptors that are also expressed by normal cells, issues remain concerning whether systemic or local drug delivery are preferable and whether the redundancy of the system will compensate if one chemokine or receptor is targeted. Nevertheless, efficacy has been demonstrated in a number of experimental models. By targeting this network, it may be possible to generate anti-tumor immune responses by altering the chemokine and/or leukocyte balance in tumors; alternatively, chemokine/chemokine receptor-expressing cancer cells could be directly targeted.

Monocyte/macrophage infiltration in tumors: modulators of angiogenesis

The role of a tumor immune infiltrate in cancer progression and metastasis has been debated frequently. Although often considered to be associated with improved prognosis and leading to the enhanced survival of cancer patients, inflammatory cells have also been described to assist the tumor's capabilities to progress, proliferate, and metastasize. Tumor-associated macrophages (TAMs), for example, have been shown to be symbiotically related to tumor cells: Tumor cells recruit TAMs and provide them with survival factors, and TAMs in turn produce a variety of angiogenic factors in response to the tumor microenvironment. This review will describe the composition of an immune infiltrate in tumors and the angiogenic and angiostatic properties of the cells present. Special emphasis will be on the angiogenesis-associated activities of TAMs. The development of immunotherapy and gene therapy using TAMs to mediate tumor cytotoxicity or to deliver gene constructs will be discussed as well. As immunotherapy has so far not been as effective as anticipated, a combination therapy in which angiostatic agents are used as well is put forward as a novel strategy to treat cancer.