Liver macrophage-mediated cytotoxicity toward mastocytoma cells involves phagocytosis of tumor targets

Liver Immune Microenvironment and Metastasis from Colorectal Cancer-Pathogenesis and Therapeutic Perspectives

A drastic difference exists between the 5-year survival rates of colorectal cancer patients with localized cancer and distal organ metastasis. The liver is the most favorable organ for cancer metastases from the colorectum. Beyond the liver-colon anatomic relationship, emerging evidence highlights the impact of liver immune microenvironment on colorectal liver metastasis. Prior to cancer cell dissemination, hepatocytes secrete multiple factors to recruit or activate immune cells and stromal cells in the liver to form a favorable premetastatic niche. The liver-resident cells including Kupffer cells, hepatic stellate cells, and liver-sinusoidal endothelial cells are co-opted by the recruited cells, such as myeloid-derived suppressor cells and tumor-associated macrophages, to establish an immunosuppressive liver microenvironment suitable for tumor cell colonization and outgrowth. Current treatments including radical surgery, systemic therapy, and localized therapy have only achieved good clinical outcomes in a minority of colorectal cancer patients with liver metastasis, which is further hampered by high recurrence rate. Better understanding of the mechanisms governing the metastasis-prone liver immune microenvironment should open new immuno-oncology avenues for liver metastasis intervention.

Myeloid tumor necrosis factor and heme oxygenase-1 regulate the progression of colorectal liver metastases during hepatic ischemia-reperfusion

The liver ischemia-reperfusion (IR) injury that occurs consequently to hepatic resection performed in patients with metastases can lead to tumor relapse for not fully understood reasons. We assessed the effects of liver IR on tumor growth and the innate immune response in a mouse model of colorectal (CR) liver metastasis. Mice subjected to liver ischemia 2 days after intrasplenic injection of CR carcinoma cells displayed a higher metastatic load in the liver, correlating with Kupffer cells (KC) death through the activation of receptor-interating protein 3 kinase (RIPK3) and caspase-1 and a recruitment of monocytes. Interestingly, the immunoregulatory mediators, tumor necrosis factor-α (TNF-α) and heme oxygenase-1 (HO-1) were strongly upregulated in recruited monocytes and were also expressed in the surviving KC following IR. Using TNF^flox/flox LysM^cre/wt mice, we showed that TNF deficiency in macrophages and monocytes favors tumor progression after IR. The antitumor effect of myeloid cell-derived TNF involved direct tumor cell apoptosis and a reduced expression of immunosuppressive molecules such as transforming growth factor-β, interleukin (IL)-10, inducible nitric oxyde synthase (iNOS), IL-33 and HO-1. Conversely, a monocyte/macrophage-specific deficiency in HO-1 (HO-1^flox/flox LysM^cre/wt ) or the blockade of HO-1 function led to the control of tumor progression post-liver IR. Importantly, host cell RIPK3 deficiency maintains the KC number upon IR, inhibits the IR-induced innate cell recruitment, increases the TNF level, decreases the HO-1 level and suppresses the tumor outgrowth. In conclusion, tumor recurrence in host undergoing liver IR is associated with the death of antitumoral KC and the recruitment of monocytes endowed with immunosuppressive properties. In both of which HO-1 inhibition would reinforce their antitumoral activity.

Liver Tropism in Cancer: The Hepatic Metastatic Niche

The liver is the largest organ in the human body and is prone for cancer metastasis. Although the metastatic pattern can differ depending on the cancer type, the liver is the organ to which cancer cells most frequently metastasize for the majority of prevalent malignancies. The liver is unique in several aspects: the vascular structure is highly permeable and has unparalleled dual blood connectivity, and the hepatic tissue microenvironment presents a natural soil for the seeding of disseminated tumor cells. Although 70% of the liver is composed of the parenchymal hepatocytes, the remaining 30% is composed of nonparenchymal cells including Kupffer cells, liver sinusoidal endothelial cells, and hepatic stellate cells. Recent discoveries show that both the parenchymal and the nonparenchymal cells can modulate each step of the hepatic metastatic cascade, including the initial seeding and colonization as well as the decision to undergo dormancy versus outgrowth. Thus, a better understanding of the molecular mechanisms orchestrating the formation of a hospitable hepatic metastatic niche and the identification of the drivers supporting this process is critical for the development of better therapies to stop or at least decrease liver metastasis. The focus of this perspective is on the bidirectional interactions between the disseminated cancer cells and the unique hepatic metastatic niche.

Liver metastases: Microenvironments and ex-vivo models

The liver is a highly metastasis-permissive organ, tumor seeding of which usually portends mortality. Its unique and diverse architectural and cellular composition enable the liver to undertake numerous specialized functions, however, this distinctive biology, notably its hemodynamic features and unique microenvironment, renders the liver intrinsically hospitable to disseminated tumor cells. The particular focus for this perspective is the bidirectional interactions between the disseminated tumor cells and the unique resident cell populations of the liver; notably, parenchymal hepatocytes and non-parenchymal liver sinusoidal endothelial, Kupffer, and hepatic stellate cells. Understanding the early steps in the metastatic seeding, including the decision to undergo dormancy versus outgrowth, has been difficult to study in 2D culture systems and animals due to numerous limitations. In response, tissue-engineered biomimetic systems have emerged. At the cutting-edge of these developments are ex vivo 'microphysiological systems' (MPS) which are cellular constructs designed to faithfully recapitulate the structure and function of a human organ or organ regions on a milli- to micro-scale level and can be made all human to maintain species-specific interactions. Hepatic MPSs are particularly attractive for studying metastases as in addition to the liver being a main site of metastatic seeding, it is also the principal site of drug metabolism and therapy-limiting toxicities. Thus, using these hepatic MPSs will enable not only an enhanced understanding of the fundamental aspects of metastasis but also allow for therapeutic agents to be fully studied for efficacy while also monitoring pharmacologic aspects and predicting toxicities. The review discusses some of the hepatic MPS models currently available and although only one MPS has been validated to relevantly modeling metastasis, it is anticipated that the adaptation of the other hepatic models to include tumors will not be long in coming.

Kupffer cells decrease metastasis of colon cancer cells to the liver in the early stage

Although Kupffer cells (KCs) play an important role in the liver's immune response, their role in colon cancer metastasis to the liver is unclear. We here analyzed the relationship between KCs and tumor cells (TCs) in colon cancer metastasis to the liver. Fischer 344 (F344) rats were divided into control group (KC+ group) and KC elimination group (KC‑ group), in which KC elimination was induced by Cl2MDP liposome injection. RCN‑H4 colon cancer cells were injected into the rats of both groups, and the relationship between the two types of cells was observed by intravital microscopy (IVM) for 6 h. Moreover, to investigate the effect of KCs on liver metastasis formation, KCs were eliminated at different time points before and after the TC injection. The number of metastatic nodules 2 weeks after the injection was evaluated. In the KC‑ group, IVM revealed that the number of adherent TCs had increased 1.5‑fold at 6 h after the TC injection as compared with in the KC+ group. Moreover, in the KC+ group, 74% of the TCs adhered to the KCs, and KC activation and KC phagocytosis of the TCs were observed. Two weeks after the injection, the number of metastatic nodules was significantly increased in rats in which the KCs had been eliminated before the injection, but not in rats in which the KCs had been eliminated after the injection. KC activation and KC phagocytosis of TCs decreased colon cancer cell metastasis to the liver.

Natural history of hepatic metastases from colorectal cancer - pathobiological pathways with clinical significance

Colorectal cancer hepatic metastases represent the final stage of a multi-step biological process. This process starts with a series of mutations in colonic epithelial cells, continues with their detachment from the large intestine, dissemination through the blood and/or lymphatic circulation, attachment to the hepatic sinusoids and interactions with the sinusoidal cells, such as sinusoidal endothelial cells, Kupffer cells, stellate cells and pit cells. The metastatic sequence terminates with colorectal cancer cell invasion, adaptation and colonisation of the hepatic parenchyma. All these events, termed the colorectal cancer invasion-metastasis cascade, include multiple molecular pathways, intercellular interactions and expression of a plethora of chemokines and growth factors, and adhesion molecules, such as the selectins, the integrins or the cadherins, as well as enzymes including matrix metalloproteinases. This review aims to present recent advances that provide insights into these cell-biological events and emphasizes those that may be amenable to therapeutic targeting.

Macrophages as mediators of tumor immunosurveillance

Tumor immunosurveillance is a well-established mechanism for regulation of tumor growth. In this regard, most studies have focused on the role of T- and NK-cells as the critical immune effector cells. However, macrophages play a major role in the recognition and clearance of foreign, aged, and damaged cells. Macrophage phagocytosis is negatively regulated via the receptor SIRPalpha upon binding to CD47, a ubiquitously expressed protein. We recently showed that CD47 is up-regulated in myeloid leukemia and migrating hematopoietic progenitors, and that the level of protein expression correlates with the ability to evade phagocytosis. These results implicate macrophages in the immunosurveillance of hematopoietic cells and leukemias. The ability of macrophages to phagocytose tumor cells might be exploited therapeutically by blocking the CD47-SIRPalpha interaction.

Role of Kupffer cells in the outgrowth of colorectal cancer liver metastases

Colorectal cancer is one of the commonest malignancies in the "developed" world. The liver constitutes the main host organ for its distant metastases which, when present, augur a bad prognosis for the disease. Kupffer cells (KCs) are macrophages that constantly reside within the liver and form an effective first line defence against multiple harmful agents which reach the hepatic sinusoids via the portal circulation. KCs remove chemical compounds and dead or damaged cells, eliminate bacteria and protect against invading tumour cells. They may play a crucial tumouricidal role, exerting cytotoxic and cytostatic functions through the release of multiple cytokines and chemokines. Subsequently, colorectal metastasising cells are destroyed either by KC-performed phagocytosis or via the stimulation of other immune cells which migrate into the sinusoids and act accordingly. On the contrary, KC products, including cytokines, growth factors and matrix-degrading enzymes may promote liver metastasis, supporting tumour cell extravasation, motility and invasion. Current research aims to exploit the antineoplastic properties of KCs in new therapeutic approaches of colorectal cancer liver metastasis. Numerous agents, such as the granulocyte macrophage-colony stimulating factor, interferon gamma, muramyl peptide analogues and various antibody based treatments, have been tested in experimental models with promising results. Future trials may investigate their use in everyday clinical practice and compare their therapeutic value with current treatment of the disease.

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.

The prometastatic microenvironment of the liver

The liver is a major metastasis-susceptible site and majority of patients with hepatic metastasis die from the disease in the absence of efficient treatments. The intrahepatic circulation and microvascular arrest of cancer cells trigger a local inflammatory reaction leading to cancer cell apoptosis and cytotoxicity via oxidative stress mediators (mainly nitric oxide and hydrogen peroxide) and hepatic natural killer cells. However, certain cancer cells that resist or even deactivate these anti-tumoral defense mechanisms still can adhere to endothelial cells of the hepatic microvasculature through proinflammatory cytokine-mediated mechanisms. During their temporary residence, some of these cancer cells ignore growth-inhibitory factors while respond to proliferation-stimulating factors released from tumor-activated hepatocytes and sinusoidal cells. This leads to avascular micrometastasis generation in periportal areas of hepatic lobules. Hepatocytes and myofibroblasts derived from portal tracts and activated hepatic stellate cells are next recruited into some of these avascular micrometastases. These create a private microenvironment that supports their development through the specific release of both proangiogenic factors and cancer cell invasion- and proliferation-stimulating factors. Moreover, both soluble factors from tumor-activated hepatocytes and myofibroblasts also contribute to the regulation of metastatic cancer cell genes. Therefore, the liver offers a prometastatic microenvironment to circulating cancer cells that supports metastasis development. The ability to resist anti-tumor hepatic defense and to take advantage of hepatic cell-derived factors are key phenotypic properties of liver-metastasizing cancer cells. Knowledge on hepatic metastasis regulation by microenvironment opens multiple opportunities for metastasis inhibition at both subclinical and advanced stages. In addition, together with metastasis-related gene profiles revealing the existence of liver metastasis potential in primary tumors, new biomarkers on the prometastatic microenvironment of the liver may be helpful for the individual assessment of hepatic metastasis risk in cancer patients.

Interactions between rat colon carcinoma cells and Kupffer cells during the onset of hepatic metastasis

Liver sinusoids harbor populations of 2 important types of immunocompetent cells, Kupffer cells (KCs) and natural killer (NK) cells, which are thought to play an important role in controlling hepatic metastasis in the first 24 hr upon arrival of the tumor cells in the liver. We studied the early interaction of KCs, NK and CC531s colon carcinoma cells in a syngeneic rat model by confocal laser scanning microscopy. Results showed a minority of KCs (19% periportal and 7% pericentral) involved in the interaction with 94% of tumor cells and effecting the phagocytosis of 92% of them. NK cell depletion decreased the phagocytosis of tumor cells by KCs by 33% over a period of 24 hr, leaving 35% of the cancer cells free, as compared to 6% in NK-positive rats. Surviving cancer cells were primarily located close to the Glisson capsule, suggesting that metastasis would initiate from this region.

A potential role of macrophage activation in the treatment of cancer

One of the functions of macrophages is to provide a defense mechanism against tumor cells. In the last decades the mechanism of tumor cell killing by macrophages have been studied extensively. The tumor cytotoxic function of macrophages requires stimulation either with bacterial cell wall products such as lipopolysaccharide (LPS) or muramyldipeptide (MDP) or with cytokines such as interferon-gamma (IFN-gamma) and granulocyte-macrophage colony-stimulating factor (GM-CSF). Activated macrophages secrete several substances that are directly involved in tumor cell killing i.e. tumor necrosis factor (TNF) and nitric oxide (NO). On the other hand, substances are secreted that are able to stimulate tumor cell growth, depending on the stage and the nature of the tumor. Several clinical trials have been performed aiming at the activation of macrophages or dendritic cells, a subpopulation of the macrophages. In this review we will summarize and discuss experimental studies and clinical trials based on the activation of macrophages.

Structure and function of sinusoidal lining cells in the liver

The hepatic sinusoid harbors 4 different cells: endothelial cells (100, 101), Kupffer cells (96, 102, 103), fat-storing cells (34, 51, 93), and pit cells (14, 107, 108). Each cell type has its own specific morphology and functions, and no transitional stages exist between the cells. These cells have the potential to proliferate locally, either in normal or in special conditions, that is, experiments or disease. Sinusoidal cells from a functional unit together with the parenchymal cells. Isolation protocols exist for all sinusoidal cells. Endothelial cells filter the fluids, exchanged between the sinusoid and the space of Disse through fenestrae (100), which measure 175 nm in diameter and are grouped in sieve plates. Fenestrae occupy 6-8% of the surface (106). No intact basal lamina is present under these cells (100). Various factors change the number and diameter of fenestrae [pressure, alcohol, serotonin, and nicotin; for a review, see Fraser et al (32)]. These changes mainly affect the passage of lipoproteins, which contain cholesterol and vitamin A among other components. Fat-storing cells are pericytes, located in the space of Disse, with long, contractile processes, which probably influence liver (sinusoidal) blood flow. Fat-storing cells possess characteristic fat droplets, which contain a large part of the body's depot of vitamin A (91, 93). These cells play a major role in the synthesis of extracellular matrix (ECM) (34, 39-41). Strongly reduced levels of vitamin A occur in alcoholic livers developing fibrosis (56). Vitamin A deficiency transforms fat-storing cells into myofibroblast-like cells with enhanced ECM production (38). Kupffer cells accumulate in periportal areas. They specifically endocytose endotoxin (70), which activates these macrophages. Lipopolysaccharide, together with interferon gamma, belongs to the most potent activators of Kupffer cells (28). As a result of activation, these cells secrete oxygen radicals, tumor necrosis factor, interleukin 1, interleukin 6, and a series of eicosanoids (28) and become cytotoxic against tumor cells [e.g., colon carcinoma cells (19, 22, 48)]. Toxic secretory products can cause necrosis of the liver parenchyma, which constitutes a crucial factor in liver transplantation (55). Pit cells possess characteristic azurophylic granules and display a high level of spontaneous cytolytic activity against various tumor cells, identifying themselves as natural killer cells (10). The number and cytotoxicity of pit cells can be considerably enhanced with biological response modifiers, such as Zymosan or interleukin 2 (8). Pit cell proliferation occurs within the liver, but recent evidence indicates that blood large granular lymphocytes develop into pit cells in 2 steps involving high- and low-density pit cells (88). Kupffer cells control the motility, adherence, viability, and cytotoxicity of pit cells (89), whereas cytotoxicity against tumor cells is synergistically enhanced (80, 81).

An electron microscopy study of Kupffer cells in livers of mice having Friend erythroleukemia hepatic metastases

Kupffer cells, which are part of the reticuloendothelial system, play an important role in clearing pathogenic substances, including tumor cells, from the liver. The role of Kupffer cells in tumor development is very important as Kupffer cells can be manipulated to a tumoricidal state with biological response modifiers to kill tumor cells and thus to decrease tumor burden and extend survival time. To gain additional information on the role of Kupffer cells and their interaction with tumor cells in hepatic metastases, we studied an established experimental hematogenous metastatic model (Friend erythroleukemia) in mouse livers by light and electron microscopy. Highly activated Kupffer cells were observed in close contact with tumor cells in sinusoids and also in tumor forming foci within the hepatic parenchyma. The Kupffer cells were activated by the presence of the hematogenous tumor cells and were able to lyse and phagocytose them. However, some tumor cells evaded the Kupffer cells as metastases still occurred. Kupffer cells and other macrophages were found to leave the sinusoids and migrate to sites of potential tumor development where they interacted with tumor cells and intimately wrapped their processes around fat storing cells. It is possible that these macrophages which cross biological barriers could be used to deliver drug-loaded microparticles (liposomes and microcapsules) to tumors.

Kupffer cell/tumor cell interactions and hepatic metastasis in colorectal cancer

The degree of interaction with Kupffer cells of two moderately well differentiated cell lines, CX-1 and CCl-188 of high metastatic potential (61%) were compared to two poorly differentiated cell lines, MIP-101 and Clone A of low metastatic potential (6%) in the intrasplenic injection model for liver metastasis. MIP-101 and Clone A bound significantly better to mouse Kupffer cells in vitro than either CX-1 or CCL-188. We also identified specific cell surface proteins mediating attachment of colorectal carcinoma cells to murine Kupffer cells. Kupffer cells were radiolabelled and their surface proteins incubated with MIP-101 and CX-1. Two radiolabelled proteins from murine Kupffer cells of 14 and 34 kDa were identified consistently binding to the tumor cells. Binding of both proteins was inhibited by asialofetuin but not by fetuin. This suggests that the major binding proteins between Kupffer cells and colorectal cancer cells are galactose binding lectins.

Desialylation of metastatic human colorectal carcinoma cells facilitates binding to Kupffer cells

Cell surface hypersialylation of human colorectal carcinoma (HCRC) cells correlates with increased metastatic potential after intrasplenic injection, while desialylation with various agents has been shown to inhibit hepatic metastases. In this study we examined the effects of desialylation of HCRC cell lines with a novel intracellular inhibitor of the CMP-sialic acid transport protein (KI-8110). HCRC cells, which are poorly differentiated and poorly metastatic in nude mice (Clone A and MIP-101) were compared to well-differentiated, highly metastatic cells (CX-1 and CCL-235). KI-8110 treatment has previously been shown to reduce sialic acid levels in each of these cell lines and to reduce hepatic metastases in CX-1 and CCL-235 cell lines. This study attempts to identify a mechanism by which desialylation inhibits hepatic metastases. After KI-8110 treatment, in vitro adhesion assays were performed with each cell line to examine binding to Kupffer cells and the extracellular matrix protein fibronectin. Binding of Clone A, CX-1, and CCL-235 to Kupffer cells was significantly increased after KI-8110 treatment. Desialylation had no significant effect on binding of HCRC cell lines to fibronectin. While the metastatic cascade involves many complex interactions, the cytotoxic effects of Kupffer cells in the hepatic sinusoid are known to be an important mechanism of host defense against tumor cells. Cell surface sialic acids may well mask Kupffer cell binding to HCRC cells, preventing their cytotoxic effects and enhancing the metastatic potential of circulating tumor cells.

Lipopolysaccharide treatment of rats alters antigen expression and oxidative metabolism in hepatic macrophages and endothelial cells

Endothelial cells and macrophages are located within the hepatic sinusoids. These two cell types play an important role in the clearance of bacterially derived lipopolysaccharide from the portal circulation. Our laboratory has previously demonstrated that treatment of rats with lipopolysaccharide results in the accumulation of macrophages in the liver that display properties of activated mononuclear phagocytes. This study was designed to analyze the effects of lipopolysaccharide on hepatic endothelial cells. Female Sprague-Dawley rats were treated with 5 mg/kg of lipopolysaccharide. Macrophages and endothelial cells were isolated from the rats 48 hr later by in situ perfusion of the liver with collagenase and pronase followed by differential centrifugation and centrifugal elutriation. We found that lipopolysaccharide treatment of rats resulted in an increase in the number of both macrophages and endothelial cells recovered from the liver. Using specific monoclonal antibodies and flow cytometry, both macrophages and endothelial cells were found to express cell surface markers for Ia antigen, leukocyte common antigen, CD4 and the macrophage antigen, ED2. Macrophages expressed greater levels of these markers than endothelial cells. Flow cytometric analysis also revealed considerable subpopulation heterogeneity in the endothelial cells in antigen expression, physical characteristics and functional activity. Treatment of rats with lipopolysaccharide decreased expression of cell surface markers on the macrophages but not on the endothelial cells. This may be due to the distinct origin of these cells. To determine whether endothelial cells, like macrophages, were activated by lipopolysaccharide, we examined their ability to produce reactive oxygen intermediates.(ABSTRACT TRUNCATED AT 250 WORDS)