Interleukin-1 increases tumor cell adhesion to endothelial cells through an RGD dependent mechanism: in vitro and in vivo studies

Mechanisms Supporting the Use of Beta-Blockers for the Management of Breast Cancer Bone Metastasis

Simple Summary

Bone represents the most common site of metastasis for breast cancer and the establishment and growth of metastatic cancer cells within the skeleton significantly reduces the quality of life of patients and their survival. The interplay between sympathetic nerves and bone cells, and its influence on the process of breast cancer bone metastasis is increasingly being recognized. Several mechanisms, all dependent on β-adrenergic receptor signaling in stromal bone cells, were shown to promote the establishment of disseminated cancer cells into the skeleton. This review provides a summary of these mechanisms in support of the therapeutic potential of β-blockers for the early management of breast cancer metastasis.

Abstract

The skeleton is heavily innervated by sympathetic nerves and represents a common site for breast cancer metastases, the latter being the main cause of morbidity and mortality in breast cancer patients. Progression and recurrence of breast cancer, as well as decreased overall survival in breast cancer patients, are associated with chronic stress, a condition known to stimulate sympathetic nerve outflow. Preclinical studies have demonstrated that sympathetic stimulation of β-adrenergic receptors in osteoblasts increases bone vascular density, adhesion of metastatic cancer cells to blood vessels, and their colonization of the bone microenvironment, whereas β-blockade prevented these events in mice with high endogenous sympathetic activity. These findings in preclinical models, along with clinical data from breast cancer patients receiving β-blockers, support the pathophysiological role of excess sympathetic nervous system activity in the formation of bone metastases, and the potential of commonly used, safe, and low-cost β-blockers as adjuvant therapy to improve the prognosis of bone metastases.

The Blockade of Tumoral IL1β-Mediated Signaling in Normal Colonic Fibroblasts Sensitizes Tumor Cells to Chemotherapy and Prevents Inflammatory CAF Activation

Heterotypic interactions between newly transformed cells and normal surrounding cells define tumor’s fate in incipient carcinomas. Once homeostasis has been lost, normal resident fibroblasts become carcinoma-associated fibroblasts, conferring protumorogenic properties on these normal cells. Here we describe the IL1β-mediated interplay between cancer cells and normal colonic myofibroblasts (NCFs), which bestows differential sensitivity to cytotoxic drugs on tumor cells. We used NCFs, their conditioned media (CM), and cocultures with tumor cells to characterize the IL1β-mediated crosstalk between both cell types. We silenced IL1β in tumor cells to demonstrate that such cells do not exert an influence on NCFs inflammatory phenotype. Our results shows that IL1β is overexpressed in cocultured tumor cells. IL1β enables paracrine signaling in myofibroblasts, converting them into inflammatory-CAFs (iCAF). IL1β-stimulated-NCF-CM induces migration and differential sensitivity to oxaliplatin in colorectal tumor cells. Such chemoprotective effect has not been evidenced for TGFβ1-driven NCFs. IL1β induces the loss of a myofibroblastic phenotype in NCFs and acquisition of iCAF traits. In conclusion, IL1β-secreted by cancer cells modify surrounding normal fibroblasts to confer protumorogenic features on them, particularly tolerance to cytotoxic drugs. The use of IL1β-blocking agents might help to avoid the iCAF traits acquisition and consequently to counteract the protumorogenic actions these cells.

IL-1 Signaling in Tumor Microenvironment

Interleukin 1 (IL-1) has long been known for its pleiotropic effects on inflammation that plays a complex, and sometimes contrasting, role in different stages of cancer development. As a major proinflammatory cytokine, IL-1β is mainly expressed by innate immune cells. IL-1α, however, is expressed by various cell types under physiological and pathological conditions. IL-1R1 is the main receptor for both ligands and is expressed by various cell types, including innate and adaptive immune cell types, epithelial cells, endothelial cells, adipocytes, chondrocytes, fibroblasts, etc. IL-1 and IL-1R1 receptor interaction leads to a set of common signaling pathways, mainly the NF-kB and MAP kinase pathways, as a result of complex positive and negative regulations. The variety of cell types with IL-1R1 expression dictates the role of IL-1 signaling at different stages of cancer, which under certain circumstances leads to contrasting roles in tumor development. Recent availability of IL-1R1 conditional knockout mouse model has made it possible to dissect the role of IL-1/IL-1R1 signaling transduction in different cell types within the tumor microenvironment. This chapter will focus on the role of IL-1/IL-1R1 in different cell types within the tumor microenvironment and discuss the potential of targeting this pathway in cancer therapy.

β2ARs stimulation in osteoblasts promotes breast cancer cell adhesion to bone marrow endothelial cells in an IL-1β and selectin-dependent manner

Progression and recurrence of breast cancer, as well as reduced survival of patients with breast cancer, are associated with chronic stress, a condition known to impact the hypothalamic-pituitary axis and the autonomic nervous system. Preclinical and clinical evidence support the involvement of the sympathetic nervous system in the control of bone remodeling and in pathologies of the skeleton, including bone metastasis. In experimental mouse models of skeletal metastasis, administration of the βAR agonist isoproterenol (ISO), used as a surrogate of norepinephrine, the main neurotransmitter of sympathetic neurons, was shown to favor bone colonization of metastatic breast cancer cells via an increase bone marrow vascularity. However, successful extravasation of cancer cells into a distant organ is known to be favored by an activated endothelium, itself stimulated by inflammatory signals. Based on the known association between high sympathetic outflow, the expression of inflammatory cytokines and bone metastasis, we thus asked whether βAR stimulation in osteoblasts may alter the vascular endothelium to favor cancer cell engraftment within the skeleton. To address this question, we used conditioned medium (CM) from PBS or ISO-treated bone marrow stromal cells (BMSCs) in adhesion assays with bone marrow endothelial cells (BMECs) or the endothelial cell line C166. We found that ISO treatment in differentiated BMSCs led to a robust induction of the pro-inflammatory cytokines interleukin-1 beta (IL-1β) and interleukin-6 (IL-6). The CM from ISO-treated BMSCs increased the expression of E- and P-selectin in BMECs and the adhesion of human MDA-MB-231 breast cancer cells to these cells in short-term static and dynamic adhesion assays, and a blocking antibody against IL-1β, but not IL-6, reduced this effect. Direct IL-1β treatment of BMECs had a similar effect, whereas the impact of IL-6 treatment on the expression of adhesion molecules by BMECs and on the adhesion of cancer cells to BMECs was negligible. Collectively, these in vitro results suggest that in the context of the multicellular and dynamic bone marrow environment, sympathetic activation and subsequent βAR stimulation in osteoblasts may profoundly remodel the density but also the activation status of bone marrow vessels to favor the skeletal engraftment of circulating breast cancer cells.

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β2AR activation in osteoblasts increases the expression of pro-inflammatory cytokines IL-1β and IL-6.

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IL-1β promotes the adhesion of breast cancer cells to endothelium via an endothelial increase in E- and P-selectin expression.

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IL-1β blockade and selectin inhibition inhibits breast cancer cell adhesion to endothelial cells.

Combination therapy with proteasome inhibitors and TLR agonists enhances tumour cell death and IL-1β production

Proteasome inhibitors have emerged as an effective therapy for the treatment of haematological malignancies; however, their efficacy can be limited by the development of tumour resistance mechanisms. Novel combination strategies including the addition of TLR adjuvants to increase cell death and augment immune responses may help enhance their effectiveness. Although generally thought to inhibit inflammatory responses and NF-κB activation, we found that under specific conditions proteasome inhibitors can promote inflammatory responses by mediating IL-1β maturation and secretion after TLR stimulation. This was dependent on the timing of proteasome inhibition relative to TLR stimulation where reversal of treatment order could alternatively increase or inhibit IL-1β secretion (P < 0.001). TLR stimulation combined with proteasome inhibition enhanced cell death in vitro and delayed tumour development in vivo in NOD SCID mice (P < 0.01). However, unlike IL-1β secretion, cell death occurred similarly regardless of treatment order and was only partially caspase dependent, possessing characteristics of both apoptosis and necrosis as indicated by activation of caspase-1, 3, 8 and RIP3 phosphorylation. Although stimulation of various TLRs was capable of driving IL-1β production, TLR4 stimulation was the most effective at increasing cell death in THP-1 and U937 cells. TLR4 stimulation and proteasome inhibition independently activated the RIP3 necroptotic pathway and ultimately reduced the effectiveness of caspase/necroptosis inhibitors in mitigating overall levels of cell death. This strategy of combining TLR stimulation with proteasome inhibition may improve the ability of proteasome inhibitors to generate immunogenic cell death and increase anti-tumour activity.

The Interleukin (IL)-1R1 pathway is a critical negative regulator of PyMT-mediated mammary tumorigenesis and pulmonary metastasis

Breast cancer is the most common cancer in women and the second leading cause of female cancer-related deaths worldwide. Inflammation is an established hallmark of tumorigenesis and an important determinant of tumor outcome and response to therapy. With advances in cancer immunotherapy, there is an urgent need to dissect the contribution of specific immune effectors in cancer development. Here, we genetically investigated the role of the Interleukin-1 (IL-1) receptor 1 (IL-1R1) pathway in breast cancer tumorigenesis and metastasis using the MMTV-PyMT mouse model. Our results indicate that IL-1R1 signaling suppresses mammary tumor cell proliferation early in tumorigenesis and curbs breast cancer outgrowth and pulmonary metastasis. We show that PyMT/Il1r1^-/- mice had a higher primary tumor burden and increased mortality rate compared with IL-1R1-sufficient PyMT control mice. This phenotype was independent of the inflammatory caspases-1/-11 but driven by IL-1α, as PyMT/Il1a^-/- mice phenocopied PyMT/Il1r1^-/- mice. Collectively, our results suggest that IL-1α-mediated IL-1R1 signaling is tumor-suppressive in PyMT-driven breast cancer.

Selenoglycoproteins attenuate adhesion of tumor cells to the brain microvascular endothelium via a process involving NF-κB activation

Selenium-containing compounds and selenized yeast have anticancer properties. In order to address possible mechanisms involved in these effects, selenoglycoproteins (SGPs) were extracted from selenium-enriched yeast at pH 4.0 and 6.5 (the fractions are called SGP40 and SGP65, respectively), followed by evaluation of their impact on the interactions of lung and breast tumor cells with human brain microvascular endothelial cells (HBMECs). Extracted SGPs, especially SGP40, significantly inhibited adhesion of tumor cells to HBMECs and their transendothelial migration. Because the active components of SGPs are unknown, small selenium-containing compounds [leucyl-valyl-selenomethionyl-arginine (LVSe-MR) and methylselenoadenosine (M-Se-A)], which are normally present in selenized yeast, were introduced as additional treatment groups. Treatment of HBMECs with SGP40, LVSe-MR and M-Se-A induced changes in gene signatures, which suggested a central involvement of nuclear factor (NF)-κB-dependent pathway. These observations were confirmed in the subsequent analysis of NF-κB DNA binding activity, quantitative measurements of the expression of selected genes and proteins, and tumor cell adhesion assay with a specific NF-κB inhibitor as the additional treatment factor. These findings indicate that specific organic selenium-containing compounds have the ability to inhibit tumor cell adhesion to brain endothelial cells via down-regulation of NF-κB. SGPs appear to be more effective than small selenium-containing compounds, suggesting the role of not only selenium but also the glycoprotein component in the observed protective impact.

Report of a phase I evaluation of dose and schedule of interleukin-1 alpha and cyclophosphamide in patients with advanced tumors: An Eastern Cooperative Oncology Group study (PX990) and review of IL-1-based studies of hematopoietic reconstitution

Interleukin-1 (IL-1) is a cytokine critical to inflammation, immunological activation, response to infection, and bone marrow hematopoiesis. Cyclophosphamide downmodulates immune suppressor cells and is cytotoxic to a variety of tumors. A phase I trial of IL-1 and cyclophosphamide was conducted by the Eastern Cooperative Oncology Group. This study evaluated 3 dose levels and 3 schedules in patients with solid tumors. The goal was to evaluate the hematopoietic supportive care effect and possible antitumor effect. Toxicity was fever, chills, hypotension, nausea/emesis, hepatic, and neutropenia. Toxicity increased with dose increases of interleukin-1. Treatment at all dose levels resulted in significant increases in total white blood cell (WBC) counts above baseline. Nadir WBC and nadir absolute neutrophil counts were not significantly different by dose level of IL-1 or schedule of IL-1. Toxicity due to IL-1 at higher doses prohibited further evaluation of this agent for hematopoietic support, particularly in view of the activity and tolerability of more lineage-specific hematopoietic cytokines. Therapeutic interventions in the role of IL-1 in inflammatory conditions and cancer may be further informed by our definition of its clinical and biological effects in this evaluation of dose and schedule.

Why not treat human cancer with interleukin-1 blockade?

The clinical successes of targeting angiogenesis provide a basis for trials of interleukin-1 (IL-1) blockade and particularly anti-IL-1beta as an add-on therapy in human metastatic disease. In animal studies for over 20 years, IL-1 has been demonstrated to increase adherence of tumor cells to the endothelium in vitro, and administration of IL-1 to mice increases the number of metastatic colonies and tumor growth. Importantly, reducing endogenous IL-1 activity, particularly IL-1beta, with the naturally occurring IL-1 receptor antagonist (IL-1Ra) reduces both metastasis as well as tumor burden. Inhibition of IL-1 activity prevents in vivo blood vessel formation induced by products released from hypoxic macrophages or vascular endothelial cell growth factor itself. Mice deficient in IL-1beta do not form blood vessels in matrigels embedded with vascular endothelial cell growth factor or containing products of macrophages. Recombinant IL-1Ra (anakinra) has been administered to over 1,000 patients with septic shock resulting in a consistent reduction in all-cause 28-day mortality. Approved for treatment of rheumatoid arthritis, anakinra has a remarkable safety record. Anakinra resulted in decreased blood vessels in the pannus of affected joints in patients with rheumatoid arthritis. Neutralizing monoclonal antibodies to IL-1beta and a soluble receptor to IL-1 are approved for treating chronic inflammatory diseases. Given the availability of three therapeutic agents for limiting IL-1 activity, the safety of blocking IL-1, and the clear benefit of blocking IL-1 activity in animal models of metastasis and angiogenesis, clinical trials of IL-1 blockade should be initiated, particularly as an add-on therapy of patients receiving antiangiogenesis-based therapies.

Insulin-like growth factor-I regulates the liver microenvironment in obese mice and promotes liver metastasis

Among the mechanisms implicated in the tumor-promoting effects of obesity, signaling by insulin-like growth factor-I (IGF-I) and insulin has received considerable attention. However, the emerging realization that obesity is associated with chronic inflammation has prompted other consideration of how the IGF-I axis may participate in cancer progression. In the present study, we used two mouse models of chronic (LID) and inducible (iLID) igf-1 gene deficiency in the liver to investigate the role of IGF-I in regulating the host microenvironment and colorectal carcinoma growth and metastasis in obese mice. Obese mice had a heightened inflammatory response in the liver, which was abolished in mice with chronic IGF-I deficiency (LID). In control animals changes to the hepatic microenvironment associated with obesity sustained the presence of tumor cells in the liver and increased the incidence of hepatic metastases after intrasplenic/portal inoculation of colon carcinoma cells. These changes did not occur in LID mice with chronic IGF-1 deficiency. In contrast, these changes occurred in iLID mice with acute IGF-1 deficiency, in the same manner as the control animals, revealing a fundamental difference in the nature of the requirement for IGF-1 on tumor growth and metastasis. In the setting of obesity, our findings imply that IGF-1 is critical to activate and sustain an inflammatory response in the liver that is needed for hepatic metastasis, not only through direct, paracrine effect on tumor cell growth, but also through indirect effects involving the tumor microenvironment.

Microcalcifications associated with breast cancer: an epiphenomenon or biologically significant feature of selected tumors?

Radiographic mammary calcifications occur in 30-50% of breast cancers and constitute one of the most important diagnostic markers of both benign and malignant lesions of the breast. The presence of oxalate-type microcalcification appears to be a reliable criterion in favor of the benign nature of the lesion or, at most, of a lobular carcinoma in situ. In contrast, calcium hydroxyapatite (HA) crystals are associated with both benign and malignant breast tumors. Although the diagnostic value of microcalcifications in breast cancer is of great importance, the genesis of these calcifications is unclear. Despite numerous histological ultrastructure studies of HA deposits in breast carcinomas, to date there have been limited investigations of the potential role of these crystals in breast cancer. We review the literature examining the biological effects of HA crystals in breast cancer cell lines, specifically the mechanism of HA-induced mitogenesis and upregulation of gene expression.

IL-18 is produced by prostate cancer cells and secreted in response to interferons

Murine models have shown that IL-18 has antiangiogenic and antitumor effects, but little is known about IL-18 production in human tumors. We investigated IL-18 expression in clinically localized prostate cancers by immunohistochemistry and showed that 75% of the prostate cancers studied (27/36 cases) presented with tumor cells producing IL-18. Prostate tumor cell lines PC-3, DU 145 and LNCaP synthesized the immature form of IL-18 (p24). IFN-gamma produced in prostate cancers induced caspase-1 mRNA and IL-18 secretion of tumor cell lines, which was inhibited by the cell-permeable Tyr-Val-Ala-Asp-aldehyde caspase-1 inhibitor (YVAD-CHO). Interestingly, IFN-alpha also induced IL-18 secretion of the poorly differentiated cell line PC-3. PC-3 and DU 145, but not the well-differentiated cell line LNCaP, expressed IL-18R alpha (IL-1Rrp) protein and transcripts for IL-18R beta (AcPL). Exogenous IL-18 increased mitochondrial activity of both cell lines evaluated by the tetrazolium (MTT) assay but did not influence their proliferation. This indicated that prostate tumor cells could secrete IL-18 in response to IFN-gamma in the tumor microenvironment and that IL-18 could act as a autocrine/paracrine factor for the tumor. In the cohort of patients studied, IL-18 expression in prostate cancers (with up to 10% of tumor cells stained) was associated with a favorable outcome and equally predictive as pathologic stage on multivariate analysis (log rank test, p = 0.02). Tumor IL-18 production is a novel physiopathologic feature of prostate cancer and appears to be a favorable event in the course of the disease. Modulation of IL-18 production by interferons could have a beneficial clinical effect, which deserves further investigation.

Overexpression of a set of genes, including WISP-1, common to pulmonary metastases of both mouse D122 Lewis lung carcinoma and B16-F10.9 melanoma cell lines

Despite advances in the management of solid tumours, the development of metastases continues to be the most significant problem and cause of death for cancer patients. To define genetic determinants of pulmonary metastases, we have applied oligonucleotide microarrays to established murine models of highly metastatic D122 Lewis lung carcinoma and B16-F10.9 melanoma cell lines. These models are characterised by primary subcutaneous growth in C57BL/6J mice, a period of minimal residual disease and spontaneous pulmonary metastases. Microarray analysis defined seven genes, namely - arginase, brain natriuretic peptide (BNP), interleukin-1 alpha (IL-1 alpha), plasminogen activator inhibitor-2 (PAI-2), surfactant protein C (SP-C), uteroglobin (UG) and wnt-1-induced secreted protein-1 (WISP-1), which were consistently elevated in pulmonary metastases compared to the primary tumour of both D122 and B16-F10.9 models. Previous studies demonstrated that two of these seven genes, IL-1 alpha and PAI-2, are involved in the metastatic process. The results obtained by the microarrays were confirmed by real-time quantitative PCR, for three chosen genes - PAI-2, WISP-1 and UG. Our approach aimed to identify genes essential for the metastatic process in general and for pulmonary metastases specifically. Further research should address the precise role of these genes in the metastasising process to the lungs and test if they could be used as targets for future therapies.

Phosphocitrate inhibits calcium hydroxyapatite induced mitogenesis and upregulation of matrix metalloproteinase-1, interleukin-1beta and cyclooxygenase-2 mRNA in human breast cancer cell lines

Microcalcifications containing calcium hydroxyapatite (HA) are often associated with malignant human breast lesions. Frequently, they are the only mammographic features that indicate the presence of a tumoural lesion. We previously reported the induction of both mitogenesis and prostaglandin E2 (PGE2) production and the increased activities of matrix metalloproteinases (MMPs) MMP-2 and MMP-9 in normal human mammary epithelial cells and breast cancer cell lines, treated with HA. In the present study we attempted to elucidate the mechanism of these biological effects. Firstly, we found that direct cell-crystal contact was required for induction of mitogenesis as the effect was not merely a result of isotopic exchange of calcium into the culture medium. Treatment with bafilomycin A1, a proton pump inhibitor, abrogated HA-induced mitogenesis to control cell levels. These results suggest that phagocytosis and intracellular crystal dissolution is required for HA-induced mitogenesis. We also demonstrated that the increase in prostaglandin E2, previously reported, is due, at least in part, to HA-induced upregulation of cyclooxygenase-2 (COX-2) in Hs578T cells. An accumulation of MMP-1 mRNA was also shown in response to HA stimulation in Hs578T cells. Furthermore, a HA-induced increase in interleukin-1beta (IL-1beta), a potent inducer of MMP-1 gene expression, was demonstrated in Hs578T cells at 2 and 4 h. Treatment with phosphocitrate (PC) (a naturally occurring inhibitor of calcium phosphate crystallisation, which is known to block a number of HA-induced biological effects in other cell types) blocked HA-mediated mitogenesis, as well as, COX-2, MMP-1 and IL-1beta induction, at the transcriptional level. These results show that calcium HA crystals are capable of exerting significant biological effects on surrounding cells which can be abrogated by PC and emphasise the role of calcium HA in amplifying the pathological process involved in breast cancer.

Altered expression of several genes in highly metastatic subpopulations of a human pulmonary adenocarcinoma cell line

Non-small cell lung cancer is associated with approximately 85% mortality due to its high metastatic potential. Therapeutic efforts have failed to produce a significant improvement in prognosis. In this situation, a better understanding of the key factors of metastasis may be useful for designing new molecular targets of therapy. In order to identify these factors, we compared the expression profiles of two subpopulations of an adenocarcinoma cell line with a high metastatic potential, PC9/f9 and PC9/f14, with the parent cell line, PC9, using a cDNA array. The expression of 15 genes was found to be significantly enhanced or reduced in the highly metastatic subpopulations. The expression of matrix metalloproteinase-2 (MMP-2), plasminogen activator inhibitor-1 (PAI-1) and interleukin-1 (IL-1 alpha) were upregulated in the highly metastatic subpopulations, while the expression of carcinoembryonic antigen (CEA), caspase-5, Fas ligand, Prk/FNK, cyclin E, cyclin B1, Ki-67, proliferating cell nuclear antigen (PCNA), Smad4, macrophage proinflammatory human chemokine-3 alpha (MIP-3 alpha)/LARC, Met and CD44 were downregulated. Data from the literature suggest that the altered expression of MMP-2, PAI-1, IL-1 alpha, CEA, caspase-5, Fas ligand, Prk/FNK and Smad4 promotes the highly metastatic phenotype. The differential expression of these genes was confirmed by Northern blot analysis, standard reverse transcription-polymerase chain reaction (RT-PCR) and real-time quantitative RT-PCR. This analysis in subpopulations of a lung cancer cell line indicated that the highly metastatic potential of lung cancer may be induced not by an alteration in the expression of a single gene, but by the accumulation of alterations in the expression of several genes involved in extracellular matrix (ECM) adhesion disruption, ECM degradation, escape from apoptosis, and resistance to transforming growth factor-beta(1) (TGF-beta(1)). Strategies for inhibiting metastasis of pulmonary adenocarcinoma should be designed accordingly.

Induction of E-selectin after partial hepatectomy promotes metastases to liver in mice

BACKGROUND

The liver is the most frequent site of tumor metastasis. It has been suggested that partial hepatectomy promotes liver metastasis of malignant disease and that expression of E-selectin, a cell adhesion molecule, plays roles in tumor metastasis. However, no reports are available concerning the expression of E-selectin after hepatectomy.

METHODS

In the present study, we used BALB/c mice subjected to 30% partial hepatectomy after injection of 1 x 10(4) colon 26 cells to determine the effects of partial hepatectomy on tumor metastasis to liver. E-Selectin expression within the liver after partial hepatectomy was evaluated using reverse transcription polymerase chain reaction and Western blotting. In addition, we injected polyclonal antibody to E-selectin into mice in which partial hepatectomy had augmented liver metastasis.

RESULTS

Mice subjected to partial hepatectomy had significantly increased numbers of liver metastases (sham operation, 1.5 +/- 2.0, vs partial hepatectomy, 35.5 +/- 19.3; P < 0.001). Expression of E-selectin mRNA within the liver was markedly increased 4 h after partial hepatectomy, but subsequently decreased at 24 h. E-Selectin protein was detected 8 h after hepatectomy, but subsequently decreased at 24 h as measured by Western blotting. Mice subjected to intraperitoneal injection of neutralizing antibody after operation had significantly decreased numbers of liver metastases (phosphate-buffered saline, 20.6 +/- 9.2, P < 0.05, and normal IgG, 18.0 +/- 8.0, P < 0.05, compared with polyclonal antibody to E-selectin, 5.6 +/- 4.8).

CONCLUSION

Induction of E-selectin by partial hepatectomy promotes hematogenous liver metastasis. Our findings can be applied to surgical treatment of liver tumor to reduce the recurrence of liver metastasis after hepatectomy by inhibiting E-selectin-mediated adhesion using reagents to E-selectin.

Interactions between cancer cells and the endothelium in metastasis

The haematogenous phase of cancer metastasis facilitates the transport of metastatic cells within the blood and incorporates a sequence of interactions between circulating intravascular cancer cells and the endothelium of blood vessels at the sites of tumour cell arrest. Initial interactions involve mechanical contact and transient adhesion, mediated by endothelial selectins and their ligands on the neoplastic cells. This contact initiates a sequence of activation pathways that involves cytokines, growth factors, bioactive lipids, and reactive oxygen species produced by either the cancer cell or the endothelium. These molecules elicit expression of integrin adhesion molecules in cancer cells and the endothelium, matrix metalloproteinases, and chemotactic factors that promote the attachment of tumour cells to the vessel wall and/or transvascular penetration. Induction of endothelial free radicals can be cytotoxic to cancer cells. Collectively, the sum of these interactions constitutes an interdependent relationship, the outcome of which determines the fate of the metastatic process.

IL-18 regulates IL-1beta-dependent hepatic melanoma metastasis via vascular cell adhesion molecule-1

Proinflammatory cytokines, including IL-1beta and tumor necrosis factor-alpha (TNF-alpha), promote cancer cell adhesion and liver metastases by up-regulating the expression of vascular cell adhesion molecule-1 (VCAM-1) on hepatic sinusoidal endothelium (HSE). In this study, hepatic metastasis after intrasplenically injected mouse B16 melanoma (B16M) cells was reduced 84-95% in mice with null mutations for either IL-1beta or the IL-1beta-converting enzyme (ICE, caspase-1) compared with wild-type mice. On day 12, 47% of wild-type mice were dead compared with 19% of either IL-1beta or ICE-deficient mice. In vitro, conditioned medium from B16M cells (B16M-CM) induced the release of TNF-alpha and IL-1beta from cultures of primary murine HSE. The effect of B16M-CM on HSE resulted in increased numbers of B16M cells adhering to HSE, which was completely abrogated by a specific inhibitor of ICE, anti-IL-18 or IL-18-binding protein. Exogenous IL-18 added to HSE also increased the number of adhering melanoma cells; however, this was not affected by IL-1 receptor blockade or TNF neutralization but rather by anti-VCAM-1. These results demonstrate a role for IL-1beta and IL-18 in the development of hepatic metastases of B16M in vivo. In vitro, soluble products from B16M cells stimulate HSE to sequentially release TNF-alpha, IL-1beta, and IL-18. The IL-18 cytokine increases expression of VCAM-1 and the adherence of melanoma cells.

RGD-recognizing integrins mediate interactions of human prostate carcinoma cells with endothelial cells in vitro

BACKGROUND

Interactions of cancer cells with endothelium are a crucial step in metastatic invasion. RGD-recognizing integrins play a definitive role in these interactions.

METHODS

Fluorescence-activated cell sorting (FACS) analysis of RGD-sensitive integrins in prostate epithelial cells was performed. Attachment inhibition assay was used to characterize functionality of particular integrins. Potential partners for RGD-binding integrins in human umbilical vein endothelial cells (HUVEC) were identified by Western blotting and attachment inhibition assay. To determine the RGD-flanking amino acids optimal for interactions with prostate cell integrins, these cells were biopanned with a phage library.

RESULTS

Different expressions of RGD-recognizing integrins and distinctions in RGD-dependent adhesion of nonmalignant and cancer cells were observed. Cancer but not control cells were detached from culture plastic by incubation with RGD peptide. Adhesion of carcinoma cells to HUVEC was RGD-sensitive, in contrast to nonmalignant cells. Antibodies against alpha3, alpha5, beta1, and alpha(v)beta3 inhibited interactions of carcinoma cells with HUVEC. Potential ligands for alpha5beta1, alpha3beta1, and alphaVbeta3 integrins, fibronectin, and vitronectin, were detected on the HUVEC surface. Several phages which preferentially bound to the surface of particular prostate cells were selected.

CONCLUSIONS

Interactions of prostate carcinoma with endothelium are mediated in part via alpha5beta1, alpha3beta1, and alpha(v)beta3 integrins. Because these interactions are RGD-sensitive, synthetic RGD peptides with optimized flanking amino acids can potentially be used as antimetastatic agents.

Regulation of endothelial cell and platelet receptor-ligand binding by the 12- and 15-lipoxygenase monohydroxides, 12-, 15-HETE and 13-HODE

In previous studies, we reported that vascular wall cells such as endothelial cells metabolize linoleic acid to 13-hydroxyoctadecadienoic acid (13-HODE) via the 15-lipoxygenase pathway. Endothelial cell 13-HODE levels vary inversely with endothelial cell reactivity to platelets, which, in turn, varies directly with the expression of the vitronectin receptor (VnR) on the apical surface of endothelial cells. We and others have also found that tumour cell adhesivity is dependent, in part, upon the relative amounts of intracellular 13-HODE and the arachidonic acid monohydroxide(s), 12- and/or 15-hydroxyeicosatetraenoic acids (12-, 15-HETE). In addition, we and others have found that platelet adhesivity is dependent upon the intraplatelet level of its major lipoxygenase metabolite, 12-HETE. Finally, we have demonstrated that 13-HODE and VnR co-localize in nonadhesive endothelial cells but dissociate following endothelial cell injury, at which time, the VnR relocates on the endothelial cell apical surface. These data suggest to us that lipoxygenase-derived monohydroxides regulate the ability of various receptors to recognize their specific ligands. The latter data also suggest that these monohydroxides act directly by a physiochemical mechanism. The present study supports this possibility. Thus, we demonstrate that 13-HODE downregulates VnR binding with vitronectin (Vn) > fibronectin (Fn) > fibrinogen (Fgn), whereas 12- and 15-HETE upregulate specific VnR/ligand binding, using purified VnR/liposomes and purified ligands in an adhesion assay; and that 12- and 15-HETE upregulate GPIIb/IIIa:liposome binding of Fgn > Fn > Vn. We conclude that cell-specific monohydroxides influence cell-specific receptor-ligand binding directly through a physiochemical mechanism.

The surgical treatment of pulmonary metastases

The surgical management of pulmonary metastases remains controversial, as no randomized trials have compared surgical excision with nonoperative treatment (to our knowledge). A Medline-generated review of the literature was undertaken to determine the factors influencing survival following metastasectomy in published trials. In the absence of randomized comparative trials, data must remain inferential and circumstantial. However, the literature does support the anecdotal observation that patients with metastatic disease can achieve long-term survival following surgical excision, irrespective of the source of the primary neoplasm, if there is no demonstrable extrathoracic disease and complete excision of the pulmonary disease is possible. Other factors noted as influencing survival appear to be anecdotal and variable from report to report. Pulmonary metastasectomy should be considered in patients with sufficient pulmonary reserve when the lung is the only site of metastatic disease and the lesions can be totally excised. An algorithm is proposed for a logical approach to the problem.

Inhibition of human HT-29 colon carcinoma cell adhesion by a 4-fluoro-glucosamine analogue

Cell surface glycoconjugates play an important role in cellular recognition and adhesion. Modification of these structures in tumour cells could affect tumour cell growth and behaviour, including metastasis. 2-Acetamido-1,3,6-tri-O-acetyl-4-deoxy-4-fluoro-alpha-D-glycopyranose (4-F-GlcNAc) was synthesized as a potential inhibitor and/or modifier of tumour cell glycoconjugates. The effect of this sugar analogue on the adhesive properties of human colon carcinoma HT-29 cells was evaluated. Treatment of HT-29 cells with 4-F-GlcNAc led to reduced cell surface expression of terminal lactosamine, sialy-Le(x) and sialyl-Le(a), as determined by Western blotting and flow cytometry. The aberrant expression of these oligosaccharide structures on the HT-29 cell surface resulted in: (1) decreased E-selectin mediated adhesion of human colon cells to human umbilical cord endothelial cells (HUVEC); (2) impaired adhesion of HT-29 cells to beta-galactoside binding lectin, galectin-1; and (3) reduced ability to form homotypic aggregates. After exposure to 4-F-GlcNAc, lysosomal associated membrane proteins (lamp) 1 and 2, and carcinoembryonic antigen (CEA) detected in HT-29 cells were of lower molecular weight, probably due to impaired glycosylation. These results strongly suggest that modification of tumour cell surface molecules can alter tumour cell adhesion and that tumour cell surface oligosaccharides may be suitable targets for therapeutic exploitation.

Interleukin-1-mediated H2O2 production by hepatic sinusoidal endothelium in response to B16 melanoma cell adhesion

We have examined H2O2 production by in vitro enriched hepatic sinusoidal endothelium (HSE) during interleukin-1 beta (IL-1 beta) stimulation and B16 melanoma cell adhesion. Production of H2O2 was quantified by flow cytometry and multiwell plate-scanning fluorimetry of intracellular 2', 7'-dichlorofluorescein (DCFH) oxidation in HSE. Under IL-1 beta treatment there was a 6-fold increase in endothelial cells producing H2O2 (67%) and a 4-fold augmentation in the Kupffer cell population (86%). The average H2O2 content per cell size unit significantly (P < 0.01) increased in endothelial cells (2.6-fold) and Kupffer cells (1.7-fold). In contrast to the homogeneity of Kupffer cells, H2O2 production intensity was largely heterogeneous in IL-1 beta-activated HSE. Enhancement of H2O2 production by IL-beta-treated HSE started at the 4th h and peaked 2-3 h later. The addition of increasing concentration of IL-1 beta to HSE for 4 h caused the progressive activation of H2O2 production by treated cells. The addition of 80 M excess of IL-1 receptor antagonist (IL-1 Ra) 10 min before IL-1 beta treatment abrogated IL-1 beta-mediated enhancement of H2O2. From the 2nd h of B16 melanoma adhesion to HSE there was significantly (P < 0.05) enhancement of H2O2 content in HSE. This activation increased 2.25-fold by the 3rd h of coculture and had reduced again by the 5th h. IL-1 Ra (80 ng/ml) given to HSE 10 min before melanoma cells abrogated the HSE response to melanoma cells. The addition of 1% paraformaldehyde (PFA)-fixed B16 melanoma cells to HSE did not affect H2O2 production response, indicating that HSE-activating agents were on the melanoma cell surface. Preincubation of B16 melanoma cells in the presence of 5 micrograms/ml anti-mouse IL-1 beta neutralizing antibody reduced the melanoma cell-induced HSE production of H2O2 by 80%. On the contrary, B16 melanoma cell-conditioned medium did not vary HSE production of H2O2 compared to control HSE. Western blot analysis of cytosolic and membrane sediments from B16 melanoma cells confirmed the presence of IL-1 beta (17.4 kDa) in both cell compartments. Thus, HSE responded to melanoma cell contact with a rapid production of H2O2. HSE activation was IL-1-dependent. This cytokine was directly provided to HSE by the cell surface of adhered melanoma cells.

Antitumor effects of liposomal IL1 alpha and TNF alpha against the pulmonary metastases of the B16F10 murine melanoma in syngeneic mice

Interleukin 1 alpha (IL1 alpha) and tumor necrosis factor alpha (TNF alpha) have been successfully incorporated into specific phosphatidylcholine (PC) and phosphatidylserine (PS) multilamellar vesicle (MLV) liposomes by modifying the concentration of calcium ion and pH of the encapsulation buffer. Under these conditions, some of the cytokines may attach to the exterior surface of the MLV and therefore be readily accessible to target cells for receptor binding and signal transduction. These cytokine-associated liposomes are stable for up to 2 weeks in serum-free buffer, and leakage of cytokines into medium containing 10% fetal bovine serum was about 50% at the end of a 3-day incubation period at 37 degrees C. The biological activities mediated by liposomal IL1 alpha and TNF alpha were specific: the stimulation of thymidine uptake in T-helper D10 lymphocytes and the cytolysis of TNF alpha-sensitive L929 target cells could be blocked by specific neutralizing antibodies in a dose-dependent fashion. When administered intravenously into C57BL/6 mice bearing the syngeneic B16F10 murine melanoma cells, dual entrapment of liposomal IL1 alpha and TNF alpha significantly reduced the number of metastatic tumor nodules in the lungs and prolonged the life span of the animals. Thus, liposomal IL1 alpha and TNF alpha displayed significant in vivo antitumor activity against the IL1 alpha- and TNF alpha-resistant B16F10 metastatic murine melanoma.

Interleukin 1 modulates growth of human renal carcinoma cells in vitro

We have investigated the influence of interleukin 1 (IL-1) on growth of human renal carcinoma cells in vitro. Using a capillary soft-agar cloning system, 18% of freshly explanted renal carcinomas were stimulated to grow by IL-1 and 4% were inhibited. Subsequent experiments with established renal cancer cell lines demonstrated that two out of four cell lines (Caki-2, A-498) were sensitive to IL-1. [3H]Thymidine incorporation as well as monolayer growth was enhanced in Caki-2 cells in the presence of high (10%) and low (1%) serum concentrations. Although clonogenic growth of A-498 cells was stimulated by IL-1, overall [3H]thymidine incorporation and monolayer proliferation were decreased. Using radioligand experiments, 250 cell-surface receptors of high affinity (KD 4.5 x 10(-11) M) and 2500 receptors of low affinity (KD 1.3 x 10(-9) M) were detected on A-498 cells. IL-1 binding was reduced under the influence of IL-1. Competition experiments with inhibiting antibodies against IL-1 receptor type I and type II revealed that signal transduction was performed via type I receptors. After cross-linking to IL-1, receptor type I was immunoprecipitated using anti-IL-1 antibodies. We hypothesise that, since IL-1 modulates in vitro growth of a subgroup of human renal cancer cells, interference with its mechanism of action may be of potential value in order to modulate tumour proliferation.

A novel in vitro assay system for transendothelial tumor cell invasion: significance of E-selectin and alpha 3 integrin in the transendothelial invasion by HT1080 fibrosarcoma cells

The interaction of tumor cells with endothelial cells is a key event in tumor metastasis. We established an in vitro invasion assay system, in which the invasion of tumor cells after interaction with endothelial cells can be examined. Two chamber culture wells separated by porous membrane were used. Human umbilical vein endothelial cells (HUVEC) were placed on porous membranes coated with matrix components. The invasion by HT1080 fibrosarcoma cells was determined in this system by counting the number of cells that moved through the membranes from upper to lower chambers. HUVEC cells did not migrate through the membranes as judged by the staining with UEA-I. Observation by scanning electron microscopy revealed that HT1080 cells bound to HUVEC surfaces and migrated underneath the HUVEC monolayer. Effects of antibodies specific for cell surface adhesion molecules on the migration of HT1080 cells were examined. Invasion of uncoated membranes and membranes coated with HUVEC cells was compared. Antibody against E-selectin significantly suppressed an increase of HT1080 cell invasion of HUVEC monolayers stimulated by IL-1 beta or TNF alpha. Antibody against integrin alpha 3 subunit remarkably inhibited the invasion of HUVEC cell-coated membranes, suggesting that integrins with the alpha 3 subunit may play an important role in the transendothelial invasion by HT1080 cells.

The relative roles of vitronectin receptor, E-selectin and alpha 4 beta 1 in cancer cell adhesion to interleukin-1-treated endothelial cells

Adhesion of cancer cells to endothelium is thought to be a prerequisite to extravasation during the haematogenous phase of metastasis, and is enhanced after perturbation of the endothelium by interleukin-1 (IL-1). The inducible endothelial adhesion molecules, E-selectin, VCAM-1/alpha 4 beta 1 and vitronectin receptor have been reported to mediate attachment of cancer cells to IL-1-treated endothelial cells. We have examined the relative contribution of these molecules by quantifying the adhesion of a panel of 22 human, 125I-labelled cancer cells and the rat W256 tumour to untreated and IL-1-treated endothelial monolayers in the presence of relevant neutralising antibodies. Antibodies against E-selectin inhibited the adhesion of HL-60 leukaemia cells and two colon carcinomas. Anti-alpha 4 beta 1 antibodies blocked adhesion of four melanomas, five sarcomas and one lung carcinoma. Anti-vitronectin receptor antibodies inhibited adhesion of 14 of the 22 human cell lines to IL-1-treated endothelial cells. Adhesion of seven cell lines was inhibited by more than a single antibody. In contrast, adhesion of one of the cancer cell lines was unaffected by any of the antibodies, suggesting involvement of other IL-1-inducible endothelial adhesion molecules. Moreover, none of the antibodies altered the attachment of cancer cells to unstimulated endothelial monolayers. We conclude that the mechanisms of cancer cell adhesion to the endothelium are influenced by endothelial activation and by the adhesive repertoire of the cancer cell.

Rolling and adhesion of human tumor cells on vascular endothelium under physiological flow conditions

We investigated the interaction of different human tumor types with resting and IL-1-activated human umbilical vein endothelial cells under laminar flow conditions using a parallel plate flow chamber. Three tumor cell lines (the HT-29M colon carcinoma, the OVCAR-3 ovarian carcinoma, and the T-47D breast carcinoma) showed limited adhesion to unstimulated endothelial cells at any of the shear stress levels tested, while rolling and massive adhesion of tumor cells were observed on IL-1-activated endothelial cells. Three other tumor cell lines (the A375M and A2058 melanomas and the MG-63 osteosarcoma) did not adhere on resting endothelial cells at high shear stress (> 1.5 dyn/cm2) and started to adhere with decreasing shear stress; the number of adherent cells increased steeply on IL-1-activated endothelial cells, but no cell rolling was observed even at the highest shear stress. These mechanisms of tumor cell interaction with endothelial cells were analyzed in detail using the HT-29M colon carcinoma and the A375M melanoma. Incubation of activated endothelial cells with a monoclonal antibody against E-selectin inhibited rolling and adhesion of HT-29M, but had no effect on the adhesion of A375M cells; monoclonal antibody against vascular cell adhesion molecule-1 reduced the adhesion of A375M cells and had no effect on HT-29M. The selective interaction of these two molecules with tumor cells was confirmed by measuring the adhesion of tumor cells on immobilized soluble proteins. On E-selectin-coated surfaces, HT-29M cells rolled during perfusion experiments without subsequent adhesion, while A375M cells did not adhere. On vascular cell adhesion molecule-1-coated surfaces, HT-29M cells neither adhered nor rolled, while A375M cells adhered massively without rolling. Under flow conditions, therefore, cells from different tumor types interact with the endothelial surface by different mechanisms, depending on adhesion molecules expressed on the tumor and endothelial cell surface.

Decreased adhesion to endothelial cells and matrix proteins of H-2Kb gene transfected tumour cells

Transfection of murine metastatic B78H1 cells (derived from B16 melanoma) with a syngeneic H-2Kb gene was used to study the effect of Major Histocompatibility Complex (MHC) gene products on tumour cell adhesion to endothelial cells and matrix proteins and the involvement in the metastatic process. H-2Kb-expressing transfectants showed a reduced adhesion to endothelial surfaces of different origin (four murine endotheliomas and human umbilical vein endothelial cells) when compared to parental B78H1 cells and to controls transfected with pSV2neo alone. On the average a 50-70% reduction in adhesion to endothelial cells was observed among H-2Kb transfectants. H-2Kb transfectants had a reduced expression of the alpha 4 integrin subunit, moreover the adhesion of Neo-transfected clones to endothelial cells was reduced to the levels of H-2Kb transfectants by antibodies directed against the beta 1 subunit and the endothelial VCAM-1 molecule, thus suggesting an impairment of the VLA-4/VCAM-1 interaction in H-2Kb transfectants. Adhesion to extracellular matrix components was also strongly decreased: in general the adhesion of H-2Kb cells showed a 50-75% inhibition with respect to Neo or parental controls. The highest difference was observed in adhesion to vitronectin and laminin, the lowest in adhesion to fibronectin. Reduction in adhesive properties of H-2Kb-expressing transfectants could be involved in the reduced metastatic ability, evaluated by means of intravenous injection of cells: H-2Kb transfectants yielded less than ten lung colonies, while all controls produced more than 100. Our data indicate that expression of a single class I MHC gene can significantly alter the metastatic phenotype of MHC-negative tumour cells and this could be related to a general alteration of tumour cell adhesive interactions.

Adhesion molecules and their role in cancer metastasis

This article describes various adhesion molecules and reviews evidence to support a mechanistic role for adhesion molecules in the process of cancer metastasis. A variety of evidence supports the involvement of specific adhesion molecules in metastasis. 1. For example, some cancer cells metastasize to specific organs, irrespective of the first organ encountered by the circulating cancer cells. This ability to colonize a specific organ has been correlated with the preferential adhesion of the cancer cells to endothelial cells derived from the target organ. This suggests that cancer cell/endothelial cell adhesion is involved in cancer cell metastasis and that adhesion molecules are expressed on the endothelium in an organ-specific manner. 2. Further, inclusion of peptides that inhibit cell adhesion, such as the YIGSR- or RGD-containing peptides, is capable of inhibiting experimental metastasis. 3. Metastasis can be enhanced by acute or chronic inflammation of target vessels, or by treatment of animals with inflammatory cytokines, such as interleukin-1. In vitro, cancer cell/endothelial cell adhesion can be enhanced by pretreating the endothelial cell monolayer with cytokines, such as interleukin-1 or tumor necrosis factor-alpha. This suggests that, in addition to organ-specific adhesion molecules, a population of inducible endothelial adhesion molecules is involved and is relevant to metastasis. 4. Further support for this model is found in the comparison to leukocyte/endothelial adhesion during leukocyte trafficking. Convincing evidence exists, both in vivo and in vitro, to demonstrate an absolute requirement for leukocyte/endothelial adhesion before leukocyte extravasation can occur. The relevance of this comparison to metastasis is reinforced by the observation that some of the adhesion molecules involved in leukocyte/endothelial adhesion are also implicated in cancer cell/endothelial adhesion. The involvement of adhesion molecules suggests a potential therapy for metastasis based on interrupting adhesive interactions that would augment other treatments for primary tumors.

Interaction of human malignant melanoma tumor spheroids with endothelium and reconstituted basement membrane: modulation by RGDS

Tumor-cell extravasation involves sequential adhesive interactions with vascular endothelium and the subendothelial basement membrane. We have established a 3-dimensional model in vitro to simulate these events and to elucidate targets of the anti-cell-adhesive synthetic peptide RGDS. Tumor spheroids of the melanoma cell line ST-ML-12 served as models of tumor-cell emboli and were transferred onto human umbilical vein endothelial cells. To imitate the vascular anatomy, the latter were grown on reconstituted basement membranes produced by dextran-stimulated bovine corneal endothelial cells. RGDS did not affect the homotypic aggregation of the tumor cells and only minimally inhibited the attachment of the spheroids to the reconstituted vessel. A short-term (20 min) inhibition of adhesion to denuded basement membranes was observed. The attachment was closely associated with damage to the endothelial cells by oxygen-derived free radicals. RGDS retarded endothelial injury for up to 3 hr. The most prominent effect was observed after penetration of the endothelium. RGDS suppressed the emigration of tumor cells from the attached tumor-cell cluster in a dose- and time-dependent fashion. After 12 hr, the inhibitory effect progressively declined. This was not due to loss of activity of the peptide, indicating a resistance mechanism in the melanoma cells. On purified components of the basement membrane, RGDS effectively inhibited the initial spheroid attachment to fibronectin and collagen IV but had no effect on attachment to laminin. By contrast, subsequent migration was significantly suppressed on all substrata. Our model permits the study of dynamic cell-cell and cell-extracellular-matrix interactions and indicates that RGDS might predominantly act on early tumor-cell locomotion after penetration of the endothelium.

Interleukin 1-induced cancer cell/endothelial cell adhesion in vitro and its relationship to metastasis in vivo: role of vessel wall 13-HODE synthesis and integrin expression

Previously, we have demonstrated that stimulation of endothelial cells (ECs) with interleukin-1 alpha (IL-1 alpha) enhances the synthesis and expression of the vitronectin receptor (VnR), promotes VnR-dependent adhesion of human A549 adenocarcinoma cells to ECs, and is associated with decreased EC 13-hydroxyoctadecadienoic acid (13-HODE) synthesis in vitro. To determine whether these observations are relevant in vivo, we examined the acute retention and subsequent metastasis of intravenously-injected B16F10 melanoma cells in murine lungs, in relation to vessel wall 13-HODE. In C57BL/6 mice pretreated with IL-1 alpha, vessel wall 13-HODE was decreased and B16F10 lung entrapment and metastasis were increased. The latter two events were blocked by pretreating the animals with the GRGDS peptide. These data suggest a relationship between vessel wall 13-HODE synthesis, adhesion molecule expression, and adhesion of B16F10 cells to the endothelium.

VLA-4 molecules on tumor cells initiate an adhesive interaction with VCAM-1 molecules on endothelial cell surface

To elucidate the role of VLA-4 (alpha 4 beta 1 integrin) in tumor metastasis, we have transfected cDNA coding alpha 4 subunit into human fibrosarcoma (HT1080) cells. VLA-4-overexpressing HT-VC1 cells exhibited increased ability to interact with known ligands for VLA-4, such as CS1 peptide and VCAM-1 (vascular cell adhesion molecule-1). In addition, the in vitro invasive ability of HT-VC1 cells was augmented and the mRNA for type IV collagenase was increased in HT-VC1 cells. The induction of VCAM-1 molecules on lung endothelial cells of nude mice by tumor necrosis factor-alpha treatment resulted in augmentation of in vivo HT-VC1 cell adhesion to the lung endothelial cells. Thus, the VLA-4 molecules on tumor cells initiate an adhesive interaction with VCAM-1 molecules on endothelial cells, that is important for hematogenous metastasis.

Effect of IL-1 on experimental bone/bone-marrow metastases

Bone metastasis is a common event and a major cause of morbidity in cancer patients. The hematopoietic marrow of the bones, rather than the bone tissue per se, is the target organ in bone metastasis. In the bone marrow, IL-1 induces the release of hematopoietic growth factors that may affect tumor-cell growth. We treated groups of mice with rhuIL-1 alpha to examine its role in the establishment of experimental bone/bone-marrow metastasis. We found that injection of 2 micrograms of rhuIL-1 alpha 24 hr prior to, simultaneously with or 24 hr after the injection of 10(4) B16 melanoma cells into the left cardiac ventricle of mice resulted in a 2-fold increase in the average number of colonized bones per mouse. GM-CSF is produced by bone-marrow stromal cells in response to IL-1, and its receptor has been found on tumor cells, including melanoma cells. However, the administration of rmuGM-CSF to mice by either multiple injections or continuous infusion did not affect the number of colonized bones. Many of the biologic effects of IL-1 are mediated by prostaglandins. Treatment of mice with 100 micrograms of indomethacin, a potent inhibitor of prostaglandin synthesis, prior to the injection of rhuIL-1 alpha, prevented the increase in number of bone metastases. To determine whether constitutive productions of IL-1 and/or prostaglandins are involved in the pathogenesis of bone/bone marrow metastasis, we treated mice with antimouse IL-1 alpha neutralizing antibodies, rhuIRAP (an inhibitor of IL-1 activity) or indomethacin. We found no difference in the average number of colonized bones per mouse between treated and control mice. We conclude that exogenous administration of IL-1 enhances experimental bone/bone-marrow metastases, and that this phenomenon is mediated through prostaglandins. However, neither the constitutive production of IL-1 nor that of prostaglandins appear to play a role in the pathogenesis of bone/bone-marrow metastasis in our murine model system.

Cancer cell interactions with injured or activated endothelium

Blood vessels and lymphatics are the most important pathways for dissemination of cancer cells but the entry and exit of these cells into and from the vasculature requires that they pass through barriers formed by the endothelium and its basement membrane. This review summarizes evidence that this step in metastasis can be regulated by microenvironmental influences which alter the properties of this barrier. These phenomena can be attributed to both 'passive' and 'active' responses of the endothelium. The microvasculature is susceptible to perturbation from environmental agents, host cells and cancer cells. There is clinical and experimental evidence that this can upregulate the metastatic process. Using established animal models of pulmonary microvascular injury it has been shown that endothelial damage promotes the localization and metastasis of circulating cancer cells to the lung and that this effect is lost after endothelial repair. Oxidative stress is an effector of vascular damage in several of the experimental models. While endothelial cells appear to be directly susceptible to free radical attack, basement membranes are not. However, oxidative injury of endothelial cells causes release of proteases which can then degrade the basement membrane. This event is associated with generation of tumor cell chemoattractants and enhances cancer cell invasion of vascular basement membranes in vitro. Vascular endothelial cells are also susceptible to stimulation by systemic mediators including cytokines, thrombin, or endotoxin which induce a series of active responses in the vessel wall. These perturbed endothelial cells synthesize and express cell surface adhesion molecules which can interact with cancer cells. They also release chemoattractants which stimulate cancer cell motility. We postulate that such responses endow the vessel wall with the potential to act as a determinant of metastatic rate.

Eicosanoids, other fatty acid metabolites and the cardiovascular system: are the present antithrombotic approaches rational?

Antiplatelet +/- anticoagulant drugs are currently used as the standard treatment to prevent and treat thrombosis. While this approach is beneficial, it is not optimal. Recent evidence suggests that constituents of the vascular endothelium play an important role in regulating vessel wall thrombogenecity, thereby inhibiting thrombogenesis. These include constituents such as PGI2, tissue plasminogen activator, thrombomodulin and the lipoxygenase fatty acid metabolite derived from linoleic acid, 13-hydroxyoctadecadienoic acid (13-HODE). Consequently, new strategies have been developed to maximize the use of these agents for antithrombotic therapy. We will review these different approaches, discuss their rationale, and based upon recent experimental data, introduce an alternative approach for antithrombotic therapy which may circumvent a number of limitations and side-effect of the currently used drugs.

Effect of inflammatory cytokines on the adherence of tumor cells to endothelium in a murine model

We have demonstrated that pretreatment of mouse brain microvascular endothelial cells (MBE) with tumor necrosis factor-alpha (TNF), IL-1, or LPS augmented the binding of P815 mastocytoma cells in vitro. The effect of these agents was dose and time dependent. PMA was able to mimic the influence of these factors to a limited degree. The effect of TNF on endothelium was accompanied by the appearance of changes in the expression of proteins isolated from endothelial cell membranes. The adherence of tumor cells to endothelium was not inhibited by RGD-containing peptides but could be decreased by preincubation of endothelium with high concentrations of FCS. Our data suggest that cytokines regulate the synthesis of endothelial adhesion proteins which may be involved in tumor cell adherence leading to metastasis. These results raise the possibility that cytokines may exert paradoxical effects in vivo, i.e., a cytotoxic effect that reduces tumor mass accompanied by a metastasis-enhancing effect that actually promotes dissemination of the remaining tumor cells. Definition of the molecular events involved in tumor cell-endothelial cell interactions may lead to strategies for minimizing the latter effect in therapeutic settings.

Chemotherapy enhances endothelial cell reactivity to platelets

Recent studies indicate that chemotherapy is a cause for thrombosis in breast cancer patients. We performed experiments to determine whether the enhanced thrombosis was due, in part, to an effect of chemotherapy on endothelial cell reactivity. Heparinized blood samples were obtained from stage II breast cancer patients receiving monthly adjuvant chemotherapy consisting of cyclophosphamide, epirubicin and 5-fluorouracil. Cultured human endothelial cells were incubated with the plasmas for 2 h, and then the reactivity of the endothelial cells to normal donor platelets was determined isotopically. Endothelial cell reactivity was increased when the endothelial cells were incubated with the post-chemotherapy plasmas. The plasma effect persisted after the chemotherapy drugs were cleared from the circulation, but this plasma effect was abolished when the plasmas were heat-inactivated. Furthermore, the increase in endothelial cell reactivity correlated with the level of interleukin-1 present in the post-chemotherapy plasmas. Finally, the increased endothelial cell reactivity was inhibited by the GRGDS peptide, or by an antibody to the endothelial cell vitronectin receptor. These observations suggest that chemotherapeutic drugs alter endothelial cell reactivity to platelets by inducing the release of interleukin-1 which, in turn, facilitates adhesion molecule expression on the endothelial cell surface. If so, these observations provide a possible explanation for one mechanism which may contribute to the thrombogenic effect seen in breast cancer patients undergoing chemotherapy.