Enhanced responsiveness of endothelium in the growing/motile state to tumor necrosis factor/cachectin

Synergistic Antitumor Effect of an Angiogenesis Inhibitor (TNP-470) and Tumor Necrosis Factor in Mice

PURPOSE

We investigated the potentiation of combination therapy using tumor necrosis factor (TNF) with TNP-470, a potent angiogenesis inhibitor.

METHODS

We evaluated the antitumor effect in vivo against subcutaneous (s.c.) MC38 mouse colon adenocarcinoma tumors in C57BL/6 mice. The mice were treated with a single bolus injection via the tail vein of 3 or 8 microg rhTNF in 0.5% bovine serum albumin/normal saline (BSA/NS), or with 0.5% BSA/NS alone as a control, with or without TNP-470 pretreatment, given as 30 or 60 mg/kg x 2 days, s.c. DNA synthesis in human umbilical endothelial cells (HUVEC) was assessed by [(3)H]thymidine uptake after incubation with TNF, with or without TNP-470.

RESULTS

The antitumor effect of TNP-470 pretreatment combined with 3 microg recombinant human (rh) TNF injection resulted in an 80% reduction of tumor volume compared with the control. This was significantly better than that induced by 3 microg rhTNF alone (P < 0.005). DNA synthesis in HUVEC was inhibited by TNF with TNP-470 in a dose-dependent manner, but there was no enhanced effect against MC38 in vitro.

CONCLUSIONS

These results suggest that the combination of the angiogenesis inhibitor TNP-470 and TNF might have a synergistic antitumor effect on solid tumors in vivo.

Combining radiotherapy and immunotherapy: a revived partnership

Ionizing radiation therapy (RT) is an important local modality for the treatment of cancer. The current rationale for its use is based largely on the ability of RT to kill the cancer cells by a direct cytotoxic effect. Nevertheless, considerable evidence indicates that RT effects extend beyond the mere elimination of the more radiosensitive fraction of cancer cells present within a tumor at the time of radiation exposure. For instance, a large body of evidence is accumulating on the ability of RT to modify the tumor microenvironment and generate inflammation. This might have far-reaching consequences regarding the response of a patient to treatment, especially if radiation-induced tumor cell kill were to translate into the generation of effective antitumor immunity. Although much remains to be learned about how radiation can impact tumor immunogenicity, data from preclinical studies provide the proof of principle that different immunotherapeutic strategies can be combined with RT to enhance antitumor effects. Conversely, RT could be a useful tool to combine with immunotherapy. This article will briefly summarize what is known about the impact of RT on tumor immunity, including tumor-associated antigens, antigen-presenting cells, and effector mechanisms. In addition, the experimental evidence supporting the contention that RT can be used as a tool to induce antitumor immunity is discussed, and a new approach to radioimmunotherapy of cancer is proposed.

Radiation-induced tumour necrosis factor-alpha expression: clinical application of transcriptional and physical targeting of gene therapy

Promising data are emerging on a new anticancer agent, Ad.EGR-TNF, an adenoviral vector, which contains radio-inducible DNA sequences from the early growth response (EGR1) gene promoter and cDNA for the gene encoding human tumour necrosis factor-alpha. Ad.EGR-TNF combines the well-documented broad-spectrum anticancer activity of TNFalpha with the proven clinical usefulness of radiotherapy. Systemic delivery of the TNFalpha protein has had limited success clinically because of severe dose-limiting toxic effects. This limitation has been overcome by the use of a gene delivery approach, combined with a radiation-inducible promoter to express the TNFalpha protein in the irradiated tumour tissue. Preclinical and early phase I clinical testing indicates that effective concentrations of TNFalpha can be delivered to the tumour site without significant systemic exposure or toxic effects. The combination of radiation and TNFalpha gene delivery has produced striking antitumour effects in model systems in animals. In the clinical setting, potent anticancer activity has been observed with a high rate of complete and partial objective tumour responses. A novel mechanism of destruction of the tumour vasculature seems to be central to this distinct antitumour activity. This review summarises the rationale, mechanistic basis, preclinical data, and preliminary clinical findings for this new treatment model.

Induction of permeability across endothelial cell monolayers by tumor necrosis factor (TNF) occurs via a tissue factor–dependent mechanism: relationship between the procoagulant and permeability effects of TNF

Tumor necrosis factor (TNF) has marked effects on permeability and procoagulant activity on tumor-associated neovasculature when used in isolation perfusion, the latter effect primarily mediated via induction of cell surface expression of tissue factor (TF) on endothelial tissue. However, the cellular events that result in rapid alterations in endothelial cell (EC) permeability after intravascular TNF administration in isolation perfusion are not well characterized. We demonstrate that short exposure intervals to TNF induces TF expression on ECs but has no effect on permeability as assessed by flux of Evans blue–bound albumin across confluent EC monolayers using a 2-compartment model under basal culture conditions. However, a rapid and significant increase in EC permeability occurred with TNF in the presence of factor VIII–deficient plasma. Permeability was induced only with luminal versus abluminal TNF exposure and was blocked by antithrombin III, TF pathway inhibitor, or anti-TF antibody cotreatment. These data indicate that EC surface expression of TF and extrinsic clotting factors are critical in augmenting capillary leak following intravascular TNF administration. Alterations in permeability were associated with intercellular gap formation at sites of down-regulation of vascular endothelial (VE)–cadherin expression, the primary endothelial intercellular adhesion molecule, and intracellular contraction and alignment of F-actin cytoskeletal elements. Rapid induction of TF by TNF may be the primary EC response that results in alterations in permeability and procoagulant activity observed following intravascular TNF administration in isolation perfusion.

Endothelial tissue factor stimulation by proteinase 3 and elastase

In ANCA-associated vasculitis the activation of primed leucocytes by autoantibodies with subsequent release of proteases such as myeloperoxidase (MPO), proteinase 3 (PR3) and elastase is thought to play an important pathogenetic role. Whether these proteases contribute to the vascular lesions by stimulating the procoagulant activity of these cells is unknown. Tissue factor (TF) expression and activity were investigated in human umbilical vein endothelial cells after stimulation with MPO, PR3 and elastase. TF activity was measured using a one-stage clotting assay. Polyclonal antibodies to TF were used to prove specificity. TF mRNA was detected by reverse transcriptase-polymerase chain reaction. PR3 and elastase led to a significant increase in TF mRNA expression and increased activity. The stimulation was not mediated by IL-1. The stimulatory effect of PR3 did not depend on its proteolytic activity (no inhibition by alpha-1-antitrypsin), whereas the effect of elastase was blocked by alpha-1-antitrypsin. MPO had no effect on TF activity. These results show that PR3 and elastase stimulate TF expression in human endothelial cells. In ANCA-associated vasculitis the increased release of proteases may contribute to the development of microthrombi and consecutive necrosis.

Endothelial-monocyte activating polypeptide II, a novel antitumor cytokine that suppresses primary and metastatic tumor growth and induces apoptosis in growing endothelial cells

Neovascularization is essential for growth and spread of primary and metastatic tumors. We have identified a novel cytokine, endothelial-monocyte activating polypeptide (EMAP) II, that potently inhibits tumor growth, and appears to have antiangiogenic activity. Mice implanted with Matrigel showed an intense local angiogenic response, which EMAP II blocked by 76% (P < 0.001). Neovascularization of the mouse cornea was similarly prevented by EMAP II (P < 0.003). Intraperitoneally administered EMAP II suppressed the growth of primary Lewis lung carcinomas, with a reduction in tumor volume of 65% versus controls (P < 0.003). Tumors from human breast carcinoma-derived MDA-MB 468 cells were suppressed by >80% in EMAP II-treated animals (P < 0.005). In a lung metastasis model, EMAP II blocked outgrowth of Lewis lung carcinoma macrometastases; total surface metastases were diminished by 65%, and of the 35% metastases present, approximately 80% were inhibited with maximum diameter <2 mm (P < 0.002 vs. controls). In growing capillary endothelial cultures, EMAP II induced apoptosis in a time- and dose-dependent manner, whereas other cell types were unaffected. These data suggest that EMAP II is a tumor-suppressive mediator with antiangiogenic properties allowing it to target growing endothelium and limit establishment of neovasculature.

Endothelial cell-specific expression of tumor necrosis factor-alpha from the KDR or E-selectin promoters following retroviral delivery

The tumor vasculature offers a target for anti-cancer gene therapy which has the advantages both of good accessibility to systemically delivered therapy and comparative homogeneity across solid tumor types. We aimed to develop retroviruses carrying endothelial-specific promoters for the delivery of genes to proliferating endothelial cells in vitro and to tumor endothelial cells in vivo. This paper reports the generation of such retroviral vectors and the level of expression of murine tumor necrosis factor-alpha (mTNF-alpha) cDNA following infection into endothelial cells and stromal fibroblasts. Retroviral vectors carrying mTNF-alpha have been generated whose expression is controlled either by the retroviral long terminal repeat or by 5' proximal promoter sequences from the endothelial-specific kinase insert domain receptor (KDR)/VEGF receptor and E-Selectin promoters within the context of a self-inactivating (SIN) vector backbone. Both KDR and E-Selectin have been shown to be upregulated on tumor endothelium. A putative polyadenylation sequence AAATAAA within the E-Selectin promoter was mutated to permit faithful transmission of retroviral vectors carrying this promoter. We demonstrate a 10- to 11-fold increase in mTNF-alpha expression from promoter elements within sEND endothelioma cells as compared to NIH-3T3 fibroblasts. Suggestions for further improvements in vector design are discussed.

Interendothelial junctions: structure, signalling and functional roles

Endothelial cell-cell adhesive junctions are formed by transmembrane adhesive proteins linked to a complex cytoskeletal network. These structures are important not only for maintaining adhesion between endothelial cells and, as a consequence, for the control of vascular permeability, but also for intracellular signalling properties. The establishment of intercellular junctions might affect the endothelial functional phenotype by the downregulation or upregulation of endothelial-specific activities.

Intracarotid recombinant human tumor necrosis factor-alpha reduces cerebral blood flow and methionine uptake in rat brain tumors

The aim of the present study is to understand the therapeutic effects of recombinant human tumor necrosis factor-alpha (rH-TNF) on hemocirculation and metabolism of brain tumors. Using double-label autoradiographic technique, we have monitored changes in regional cerebral blood flow (rCBF) and protein-bound fraction of (3H-methyl)-L-methionine, expressed as acid-insoluble fraction (AIF), in rat brain tumors following treatment with intracarotid rH-TNF. The central portion of tumors showed a significant decrease in rCBF and AIF at 4 hours after the injection (p < 0.01, p < 0.05, respectively, as compared with non-treated control rats), turned microscopically necrotic at 24 hours, and became more extensively necrotic at 72 hours. Tumor cells remained viable only in the peripheral portion of the tumors after the treatment. The peripheral portion also showed a moderate decrease in rCBF, but less change in AIF to 4 to 72 hours after the treatment. Neither ipsilateral nor contralateral non-involved cortex demonstrated appreciable changes in rCBF and AIF during the observed period. Intracarotid rH-TNF selectively reduces tumor rCBF and AIF, resulting in histological modification.

Synergistic effects of TNF-alpha and melphalan in an isolated limb perfusion model of rat sarcoma: a histopathological, immunohistochemical and electron microscopical study

Isolated limb perfusion (ILP) with tumour necrosis factor alpha (TNF-alpha) and melphalan has shown impressive results in patients with irresectable soft tissue sarcomas and stage III melanoma of the extremities. The mechanisms of the reported in vivo synergistic anti-tumour effects of TNF-alpha and melphalan are not precisely understood. We have developed an ILP model in the rat using a non-immunogenic sarcoma in which similar in vivo synergy is observed. The aim of this present study was to analyse the morphological substrate for this synergistic response of TNF-alpha in combination with melphalan to shed more light on the pathomechanisms involved. Histology of the tumours from saline- (n = 14) and melphalan-treated (n = 11) rats revealed apparently vital tumour cells in over 80% of the cross-sections. Interstitial oedema and coagulation necrosis were observed in the remaining part of the tumour. Haemorrhage was virtually absent. TNF-alpha (n = 22) induced marked oedema, hyperaemia, vascular congestion, extravasation of erythrocytes and haemorrhagic necrosis (20-60% of the cross-sections). Oedema and haemorrhage suggested drastic alterations of permeability and integrity of the microvasculature. Using light and electron-microscopy, we observed that haemorrhage preceded generalised platelet aggregation. Therefore, we suggest that the observed platelet aggregation was the result of the microvascular damage rather than its initiator. Remarkably, these events hardly influenced tumour growth. However, perfusion with the combination of TNF-alpha and melphalan (n = 24) showed more extensive haemorrhagic necrosis (80-90% of the cross-sections) and revealed a prolonged remission (mean 11 days) in comparison with the other groups of rats. Electron microscopical analysis revealed similar findings as described after TNF-alpha alone, although the effects were more prominent at all time points after perfusion. In conclusion, our findings suggest that the enhanced anti-tumour effect after the combination of TNF-alpha with melphalan results from potentiation of the TNF-alpha-induced vascular changes accompanied by increased vascular permeability and platelet aggregation. This may result in additive cytotoxicity or inhibition of growth of residual tumour cells.

Release of thrombomodulin from endothelial cells by concerted action of TNF-alpha and neutrophils: in vivo and in vitro studies

Inflammatory cytokines decrease the expression of thrombomodulin (TM) on the endothelial cell surface by suppression of TM transcription and translation or internalization with subsequent degradation. Nevertheless, elevated serum TM levels are found in diseases associated with systemical or locally increased levels of inflammatory cytokines. To study directly the in vivo effects of tumour necrosis factor-alpha (TNF-alpha) we determined the course of serum TM after systemic recombinant human (rh)TNF-alpha therapy. The TM levels were determined by enzyme-linked immunosorbent assay (ELISA). Systemic rhTNF-alpha therapy resulted in a marked and significant increase of serum TM. Using a mouse model we studied whether increased serum TM is associated with a decreased expression of TM on the endothelial surface in vivo. The immunohistochemical staining of the vasculature of meth-A sarcoma transplanted in mice showed a loss of TM immunoreactivity 4 hr after intravenous TNF-alpha application. To study the mechanism of TNF-alpha mediated release of TM, cultured endothelial cells were incubated with neutrophils and TNF-alpha. Incubation with TNF-alpha alone did not lead to an increase of TM in vitro. However TM was released into the culture supernatant when endothelial cells pretreated with TNF-alpha were exposed to neutrophils. This was associated with morphological evidence of endothelial cell damage. Therefore, the concerted action of cytokine-stimulated endothelial cells and neutrophils results in release of TM from cultured endothelial cells after rhTNF-alpha therapy. This might explain the increased serum TM levels observed in diseases associated with increased systemic or local levels of inflammatory cytokines despite the induced internalization and the direct inhibitory effects of TNF-alpha on TM transcription and translation.

Regulation of Cellular Gene Expression and Function by the Human Immunodeficiency Virus Type 1 Tat Protein

The human immunodeficiency virus type 1 Tat protein is a potent activator of viral gene expression and replication. Tat can also affect the expression of cellular genes including cytokines, extracellular matrix proteins, enzymes degrading the basement membrane and cell cycle-related proteins, and can regulate cellular functions such as growth, migration and angiogenesis. In addition, under certain circumstances, Tat may have tumorigenic effects. These activities of Tat appear to be mediated by different mechanisms such as the transactivation of cellular gene expression or the interaction of extracellular Tat with the cell membrane through both receptor-mediated and nonreceptor-mediated interactions. Deregulation of cellular gene expression and function by Tat cause abnormalities which may participate in AIDS pathogenesis and in the development of AIDS-associated disorders. Copyright 1995 S. Karger AG, Basel

Transient perturbation of endothelial integrity induced by natural antibodies and complement

The barrier function of blood vessels is though to be regulated at least in part by endothelium. This concept is supported by the dramatic loss of barrier function occurring in the hyperacute rejection of vascularized grafts mediated by anti-endothelial cell (EC) antibodies and complement. In this process, the endothelium is not destroyed but instead loses the ability to retain blood cells and plasma proteins within capillaries. The noncytotoxic mechanism that allows this change in EC function has been unknown. Here we report that within 10 to 20 min of exposure to human xenoreactive natural antibodies and complement, porcine EC undergo alterations in cell shape and in the cytoskeleton that disrupt monolayer integrity and lead to formation of intercellular gaps. Gap formation is not associated with cell death but requires the complement complex C5b67. The gaps induced by anti-EC antibodies and complement are transient; gap closure requires formation of C5b-9 complexes on the cells and the rate of recovery depends on the release of cellular products into the medium. Preincubation of EC with dibutyryl cAMP (0.5 mM) prevents gap formation and disruption of the cytoskeleton caused by antibodies and complement. These results provide evidence that the integrity of endothelium is regulated by components of the complement system and suggest a mechanism that may explain the prominent loss of endothelial integrity seen in humoral immune responses.

Spontaneous abortion in immunodeficient SCID mice

PROBLEM

Immunodeficient SCID mice on the CB-17 have been used to test the role of "rejection" in a xenogeneic blastocyst transfer model of recurrent miscarriage, but interpretation of the data requires knowing syngeneic within-species matings have a high success rate and do not require immunotrophic factors expected only in immunocompetent non-T-cell deficient mice.

METHOD

Resorption rates were studied in a SCID CB-17 barrier facility that provided the mice used to test the role of immunology in the resorption model.

RESULTS

Spontaneous resorption in syngeneically mated immunodeficient SCID mice on the CB-17 background occurred at an unexpectedly high rate and could not be prevented by treatment with anti-asialo GM1 antibody or GM-CSF, both of which are effective in ameliorating abortion in DBA/2J-mated CBA/J mice. Immunocompetent CB-17 +/+ mice showed an even higher rate of loss. The latter was also not affected by treatment with antiasialo GM1 antibody or by GM-CSF and was not prevented by tetracycline (which is effective in the DBA/2-CBA/J system) or progesterone treatment. Mating experiments showed a scid/+ x scid@+ cross gave the highest rate of loss, and it appeared that the presence of +/(+)-type embryos in the uterus could be augmenting abortion with selective discrimination against scid/scid embryos. High abortion rates were associated both with appearance of a coagulase-negative Staphylococcus sp. in feces and with loss of one component of the SPF flora. Decidual tissue from mated CB-17 +/+ mice showed premature release of TNF-alpha in absence of TGF-beta 2-related suppressor activity, and vascular lesions (fibrinoid necrosis), varying in extent, were associated with both scid/scid x scid/scid and +/+ x +/+ pregnancies. TNF-alpha also appeared prematurely in pregnant scid/scid mice, but the levels were lower (and areas of necrosis smaller than in +/+ x +/+ pregnancies). Outcrossing onto a C57B1/6 background dramatically reduced the abortion rate, indicating an important genetic effect on susceptibility with heterogeneity protecting against abortion.

CONCLUSIONS

SCID mice on the CB-17 background do not have a high rate of successful syngeneic pregnancies, and a TNF-alpha induced vasculopathy may be responsible. Abortion was not caused by immunodeficiency leading to loss of immunotrophism because immunocompetent non-SCID CB-17 mice had a higher rate of loss. Factors augmenting the abortion rate included the presence of embryos of the +/+ genotype in the uterus and treatment with anti-asialo GM1 antibody. Abortion rates were not reduced by treatments effective in the DBA/2-mated CBA/J mouse model but were reduced by re-establishing a new colony with defined flora (a temporary effect) and by outcrossing mice with a different (C57B1/6) background. Together, the data suggest an infectious trigger (identity uncertain) of the vasculopathy and an important genetic influence on susceptibility with heterozygosity and a SCID mouse mutation providing against abortion a degree of protection.

Association between biosynthesis of nitric oxide and changes in immunological and vascular parameters in patients treated with interleukin-2

Hypotension is a dose-limiting side effect of interleukin-2 (IL-2) therapy. This may be due to increased biosynthesis of the potent vasodilator nitric oxide (NO) induced by cytokines such as tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma), which are known to be generated during IL-2 therapy. We describe the relationship between NO biosynthesis and changes in immunological and vascular parameters during IL-2 therapy in 13 patients with metastatic cancer. Plasma concentrations of neopterin and nitrite plus nitrate (NOx) were higher in cancer patients prior to treatment compared with normal subjects (neopterin; 10.8 +/- 1.4 vs. 2.0 +/- 0.4 ng ml-1, P < 0.001: NOx; 45 +/- 6 vs. 28 +/- 2 microM, P < 0.005). Pretreatment TNF-alpha and IFN-gamma plasma concentrations were not significantly different in cancer patients from those in controls. During infusion of IL-2 (18 x 10(6) international units m-2 per day for 5 days) these parameters increased, reaching maximal concentrations at day 3 for IFN-gamma and day 5 for TNF-alpha, neopterin and NOx. The maximal induced NOx correlated with maximal TNF-alpha (r = 0.60, P < 0.04), IFN-gamma (r = 0.63, P < 0.02) and neopterin (r = 0.66, P < 0.01). As plasma NOx concentrations increased, systolic blood pressure fell, reaching a minimum at day 3 despite a continued rise in NOx concentrations. These changes were accompanied by a continuous increase in pulse rate throughout the infusion period. These findings indicate that induction of NO biosynthesis contributes to hypotension induced during IL-2 therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Aetiology and pathogenesis of chronic inflammatory bowel disease

While Crohn's disease and ulcerative colitis are both conditions characterized by intestinal inflammation, with some overlap in their clinical and histological features, they are essentially different in pathogenesis. Crohn's disease appears to be primarily a condition of chronic T-lymphocyte activation, with tissue damage induced by secondary macrophage activation. What activates the T-cells is unknown. In this chapter we look at the evidence for and against cell-wall deficient mycobacteria species, viral infection of vascular endothelium and luminal contents as potential mechanisms of chronic activation. In ulcerative colitis, by contrast, there is no strong evidence for T-cell activation, and humoral mechanisms predominate. While the finding of atypical anti-neutrophil cytoplasmic antibodies (P-ANCAs) may be useful in screening, the only novel pathogenetic discovery is the co-localization of a 40 kD colonic autoantibody with immunoglobulins and complement on the apical enterocyte surface. Despite the fundamental differences in initiating mechanisms, the two conditions have many 'downstream' inflammatory processes in common. We discuss the evidence for local production of cytokines, arachidonic acid metabolites and reactive oxygen and nitrogen radicals, highlighting the potential adverse consequences for intestinal vascular integrity.

Location of tumour necrosis factor alpha by immunohistochemistry in chronic inflammatory bowel disease

This study determined the location and tissue density of cells immunoreactive for tumour necrosis factor alpha (TNF alpha) in intestinal specimens from 24 patients with chronic inflammatory bowel disease (15 with Crohn's disease, nine with ulcerative colitis) and 11 controls. There was significantly increased density of TNF alpha immunoreactive cells in the lamina propria of both ulcerative colitis and Crohn's disease specimens, although the distribution of these cells differed in the two conditions. In ulcerative colitis most of the TNF alpha immunoreactivity was seen in the subepithelial macrophages, with comparatively less in the deep lamina propria, while in Crohn's disease immunoreactive cells were distributed evenly throughout the lamina propria. Increased submucosal immunoreactivity was found only in Crohn's disease, in which TNF alpha positive macrophages tended to cluster around arterioles and venules, often infiltrating and disrupting vascular endothelium. It is suggested that this degree of TNF alpha production probably contributes significantly to the pathogenesis of both Crohn's disease and ulcerative colitis, by impairing the integrity of epithelial and endothelial membranes, increasing inflammatory cell recruitment, and by prothrombotic effects on the vascular endothelium.

Diarrhoeal disease: current concepts and future challenges. Intestinal cytokines in inflammatory bowel disease and invasive diarrhoea

In the intestine large numbers of bacteria and their products are separated by a single epithelial layer from resident inflammatory cells (macrophages and lymphocytes). Many of these bacterial products, such as lipopolysaccharides and peptidoglycans, are potent stimulators of free radical and inflammatory cytokine production by macrophages. This can occur in vivo in response to mucosal invasion by enteropathogenic bacteria or because of inappropriate activation of these cells, as in chronic inflammatory bowel disease. In this review we present evidence for production of cytokines in normal intestine and in intestinal inflammatory conditions. The adverse effects of cytokine production upon intestinal homeostasis, in particular disruption of epithelial integrity and prothrombotic changes in the vascular endothelium, are also discussed.

Tumor necrosis factor and its receptors in human ovarian cancer. Potential role in disease progression

The gene for tumor necrosis factor, TNF, was expressed in 45 out of 63 biopsies of human epithelial ovarian cancer. In serous tumors, there was a positive correlation between level of TNF expression and tumor grade. TNF mRNA was found in epithelial tumor cells and infiltrating macrophages, whereas TNF protein localized primarily to a subpopulation of macrophages within and in close proximity to tumor areas. mRNA and protein for the p55 TNF receptor gene localized to the tumor epithelium and tumor, but not to stromal macrophages. The p75 TNF receptor was confined to infiltrating cells. Cells expressing TNF mRNA were also found in ovarian cancer ascites and TNF protein was detected in some ascitic fluids. In 2 out of 12 biopsies of normal ovary, TNF mRNA was detected in a minority of cells in the thecal layer of the corpus luteum. Serum levels of TNF and its soluble receptor did not correlate with extent of TNF expression in matched biopsies. Northern and Southern analysis revealed no gross abnormality of the TNF gene. The coexpression of TNF and its receptor in ovarian cancer biopsies suggests the capacity for autocrine/paracrine action. TNF antagonists may have therapeutic potential in this malignancy.

Role of cyclic AMP in promoting the thromboresistance of human endothelial cells by enhancing thrombomodulin and decreasing tissue factor activities

1. The effects of forskolin, prostaglandin E1 (PGE1), dibutyryl cyclic AMP (db cyclic AMP), dibutyryl cyclic GMP (db cyclic GMP) and 3-isobutyl-l-methyl-xanthine (IBMX) were investigated on the expression of tissue factor and thrombomodulin activities on the surface of human saphenous vein endothelial cells (HSVEC) in culture. 2. Forskolin (10(-6) to 10(-4) M), PGE1 (10(-7) to 10(-5) M) and db cyclic AMP (10(-4) to 10(-3) M) caused a concentration-dependent decrease of cytokine-induced tissue factor activity. 3. Similar concentrations of forskolin, PGE1 and db cyclic AMP enhanced significantly constitutive thrombomodulin activity and reversed the decrease of this activity caused by interleukin-1 (IL-1). 4. IBMX (10(-4) M) decreased tissue factor activity and enhanced the effect of forskolin on tissue factor and thrombomodulin activities. 5. Forskolin (10(-4) M) decreased the IL-1-induced tissue factor mRNA and increased the thrombomodulin mRNA level. IL-1 did not change the thrombomodulin mRNA level after 2 h of incubation with HSVEC in culture. 6. Dibutyryl cyclic GMP (10(-4) M to 10(-3) M) did not influence tissue factor or thrombomodulin activity. 7. Our data suggest that elevation of intracellular cyclic AMP levels may participate in the regulation of tissue factor and thrombomodulin expression, thus contributing to promote or restore antithrombotic properties of the endothelium.

Tumor necrosis factor activities and cancer therapy--a perspective

Tumor necrosis factor (TNF) is a multifunctional cytokine which has excited and fascinated numerous investigators and commercial entities due to its promise as a therapeutic agent against cancer and as a target for drugs treating septic shock. TNF is a protein having cytotoxic, cytostatic, immunomodulatory as well as several other activities and is also involved in septic shock. This review covers the structure of TNF and its receptors, various in vitro activities and in vivo activities based on studies in animal model systems. The role of TNF as an anticancer therapeutic agent, based on various phase I and phase II clinical studies, has also been considered. The review concludes with several considerations for increasing the therapeutic utility of TNF in terms of targeting, toxicity and half-life.

Induction of soluble tumour necrosis factor receptors during treatment with interleukin-2

Interleukin-2 (IL-2) treatment induces other cytokines such as tumour necrosis factor (TNF) TNF may mediate some of the anti-tumour activity of IL-2, but conversely, may contribute to its dose limiting toxicities. Cleaved extracellular domains of the p55 and the p75 TNF receptors (sTNF-R1 and R2) bind to and inhibit the biological activity of TNF in vitro, but may also act as carrier molecules. We have assayed TNF and sTNFR-1 and 2 in the plasma of advanced cancer patients, before and during treatment with IL-2. Plasma levels of TNF in 22 patients were not significantly different from 25 normal controls, but levels of sTNFR-1 and sTNFR-2 were higher (P < 0.001). Levels of TNF and both its soluble receptors were significantly increased in 13 patients receiving IL-2 therapy. Maximum induced levels of sTNFR-1 and sTNFR-2 correlated closely with maximum induced levels of TNF (P < 0.001), but peak levels of sTNFR-1 and two were achieved 24-48 h after peak TNF. Levels of TNF and sTNF-Rs did not correlate with toxicity. Treatment with IL-2 leads not only to induction of TNF but also soluble binding proteins at levels which may modulate its biological activity.

The effect of Mycobacterium tuberculosis on the susceptibility of human cells to the stimulatory and toxic effects of tumour necrosis factor

It has previously been shown that the inherently tumour necrosis factor-alpha (TNF-alpha)-sensitive L929 murine fibroblast cell line becomes much more sensitive to the cytotoxic effect of this cytokine after exposure to Mycobacterium tuberculosis in culture. In this study it is now shown that normal human cells of types likely to be involved in tuberculous lesions are affected in a similar way. Growth of normal human fibroblasts is usually stimulated by TNF-alpha in vitro, but after exposure to M. tuberculosis or to extracts of this organism, these cells are killed rather than stimulated by subsequent exposure to TNF-alpha. Similarly, human endothelial cells become susceptible to doses to TNF-alpha which do not normally affect viability. Moreover this enhancement of sensitivity to TNF-alpha is not confined to its toxicity. Endothelial cells and HeLa cells exposed to M. tuberculosis express increased levels of ICAM-1 after subsequent exposure to TNF-alpha, implying synergy between the two stimuli. It is suggested that these effects contribute to the ability of M. tuberculosis to distort the normal protective role of TNF-alpha so that the cytokine becomes detrimental to the host.

Viral neuroinvasion and encephalitis induced by lipopolysaccharide and its mediators

The present study was designed to test the effect of bacterial endotoxin on penetration of viruses into the central nervous system (CNS). As a model we used two neurovirulent viruses that lack neuroinvasive capacity: West Nile virus-25 (WN-25) and neuroadapted Sindbis virus (SVN). Administration of lipopolysaccharide (LPS, 100 micrograms/mouse) to CD-1 mice, followed by WN-25 inoculation resulted in 83% encephalitis and death, compared with less than 5% in controls. The results in SVN-inoculated CD-1 mice were quite similar. LPS-treated mice suffered 62% mortality compared with 6% in the nontreated group. No changes in viral neuroinvasiveness were demonstrated in viruses isolated from brains of encephalitic mice, suggesting that neuroinvasion is not due to a selection process for an invasive variant, but to direct penetration of the viruses through the blood-brain barrier (BBB). LPS did not induce WN-25 encephalitis in LPS-insensitive C3H/HeJ mice, compared with 100% neuroinvasion in C3H/HeB mice. Induction of neuroinvasion could be transferred to C3H/HeJ mice by transfusion with serum obtained from LPS-treated, LPS-responsive mice. Passive immunization of CD-1 mice with anti-mTNF antibodies before LPS administration did not prevent LPS-induced WN-25 encephalitis. Furthermore, neutralization of tumor necrosis factor activity in the serum of LPS-treated mice did not abolish its activity, and transfusion-associated encephalitis was observed after the administration of the neutralized serum with WN-25. We suggest that LPS can contribute to virus penetration from the blood into the CNS, a process which turns a mild viral infection into a severe lethal encephalitis. This effect is mediated by soluble factors, and is probably achieved by injury to cerebral microvascular endothelium and modulation of BBB permeability.

Tumour necrosis factor induction of ELAM-1 and ICAM-1 on human umbilical vein endothelial cells--analysis of tumour necrosis factor-receptor interactions

Induction of the adhesion molecules ELAM-1 and ICAM-1 on endothelial cells is a key pro-inflammatory effect of tumour necrosis factor (TNF). Earlier work in non-human systems has suggested that unlike other cell types, endothelial cells interact with the N-terminus of the TNF molecule, thereby implying novel TNF receptors on endothelial cells. This is also supported by 125I-TNF cross-linking studies on bovine endothelial cells. The present study aimed to see whether TNF induction of ELAM-1 and ICAM-1 on human umbilical vein endothelial cells (HUVECs) involved novel TNF-receptor interactions. Three approaches were employed. First, antibodies directed at different sites on the TNF molecule were tested for inhibition of TNF-induction of ELAM-1 and ICAM-1 on HUVECs. Inhibition was seen only with antibodies reacting with epitopes outside the N-terminal region. Second, an N-terminal TNF peptide (residues 1-26) failed to induce ELAM-1 and ICAM-1 on HUVECs or antagonise TNF induction of these molecules. Third, HUVEC/125I-TNF cross-linking revealed a major complex characteristic of the known 55 kDa TNF receptor: this was confirmed with receptor-specific monoclonal antibodies. It is concluded that (a) the same part of the TNF molecule interacts with TNF-receptors on HUVECs and other cell types and (b) TNF induction of ELAM-1 and ICAM-1 on HUVECs is mediated via the well-characterized 55 kDa TNF receptor.

Hypoxia-induced increased permeability of endothelial monolayers occurs through lowering of cellular cAMP levels

Prolonged exposure to hypoxia, as at high altitude, results in increased vascular permeability that may be ameliorated by administration of glucocorticoids. To understand mechanisms underlying these observations, cultured bovine aortic and pulmonary artery endothelial cells (ECs) were subjected to hypoxia, and changes in monolayer permeability and adenosine 3',5'-cyclic monophosphate (cAMP) levels were assessed. Exposure of both types of cultured ECs to hypoxia (PO2 approximately 14 Torr) led to a time- and dose-dependent increase in monolayer permeability, as measured by diffusion of radiolabeled solutes, which was associated with a progressive decrease in EC cAMP levels from 60 to 15 pmol/mg protein, and a decrease in EC adenylate cyclase activity. The change in endothelial barrier function was prevented by addition of cAMP analogues. Pertussis toxin protected EC monolayers from hypoxia-mediated increase in permeability while maintaining cAMP levels and adenylate cyclase activity. Addition of dexamethasone to EC monolayers before or simultaneously with their incubation under hypoxic conditions blocked the hypoxia-mediated increase in monolayer permeability. Dexamethasone pretreatment also prevented the decline in cAMP and adenylate cyclase levels in oxygen-deprived cultures. These data indicate that hypoxia decreases EC barrier function by lowering adenylate cyclase activity and cellular cAMP levels. They suggest that dexamethasone may exert its protective effect, in part, by preventing the hypoxia-induced decline in adenylate cyclase activity, leading to an increase in cellular cAMP and maintenance of EC barrier function.

Effects of interferons and other cytokines on tumors in animals: a review

The term cytokine describes a group of protein cell regulators involved in the control of cell growth and differentiation in embryogenesis, immunity and inflammation. They are of low molecular weight, are produced locally, and act in an autocrine or paracrine manner. In the past decade their use as cancer therapy has become a reality. Thirty years ago mice were treated with the antiviral protein interferon (IFN) which not only produced a reduction in the incidence of virus-induced tumors but also slowed the development of transplantable tumors. This was one of the first indications that cytokines can be negative regulators of cell growth. Here we outline current knowledge of the actions of IFNs and other cytokines in animal models, and draw parallels with clinical trials to illustrate the invaluable nature of this preclinical and mechanistic work.

Flavone acetic acid potentiates the induction of endothelial procoagulant activity by tumour necrosis factor

Treatment of human umbilical vein endothelial cells with flavone acetic acid (FAA) at 800 micrograms/ml for 4 h resulted in a 3-11-fold increase in procoagulant activity. This increase was due to enhanced tissue factor expression on the endothelial cell surface, as evidenced by the blocking of the enhanced clotting with antibody to tissue factor, by substitution of normal with factor VII deficient plasma, or by simultaneous treatment of the endothelial cells with cycloheximide or actinomycin D. FAA was not toxic to endothelial cell at concentrations up to 1.6 mg/ml over 4 h. Combined treatment with FAA and tumour necrosis factor alpha (TNF-alpha) (100 pg/ml) produced a 675-fold (range 160-1980) increase in tissue factor activity, compared to 5-fold and 50-fold increases for the individual agents respectively. Northern blotting of total RNA from cells treated with the combination of agents or either agent alone, followed by probing with a cDNA to human tissue factor demonstrated a synergistic increase in tissue factor mRNA after combination treatment. In vivo, the combination of FAA and TNF-alpha could be shown to induce greater growth delay in two murine tumours than would be predicted on the basis of the activity of either agent alone.

Relation between lipopolysaccharide-induced endothelial cell injury and entry of macromolecules into the rat aorta in vivo

Lipopolysaccharide (LPS) causes endothelial cell injury both in vitro and in vivo. It is widely believed that this injury in vivo enhances the transport of macromolecules from plasma into the interstitial space of the underlying artery wall. A new technique was used in rats to obtain high resolution transmural profiles of macromolecules in vivo. We compared the time course of the macromolecular transport into the aortic tissue in vivo after LPS injection to that of LPS-induced endothelial cell death and the proliferative response of the endothelium to LPS injury. At a dose of 1 mg LPS/kg body wt, endothelial cell death reached a maximum by 36 hours after LPS injection and remained elevated for 96 hours; the peak of the S phase of endothelial cell proliferation was observed 48 hours after injection. To examine the effect of LPS on macromolecular accumulation, we measured aortic intimal and medial transmural concentration profiles of horseradish peroxidase (HRP) after circulation of HRP for 15 minutes. The data revealed a transient increase in total aortic accumulation (reflecting predominantly the media), which was maximal between 12 and 48 hours after LPS injection. Although total medial accumulation was found to return to near control levels by 72 hours after LPS injection, intimal accumulation remained elevated above control levels for 120 hours. When HRP was added to the perfusate of an in situ aorta preparation at a near zero transmural pressure gradient, the resulting transmural concentration profiles across aortas from control rats and from rats given LPS 24 hours previously were indistinguishable, whereas a pressure gradient of 60 mm Hg revealed LPS-altered concentration profiles analogous to those in vivo. This suggests that the accumulation of HRP observed in vivo was driven by increased convective transport. These results reveal that LPS enhances entry of macromolecules into the aorta wall in vivo. The changes in macromolecular transport do not, however, correlate temporally with endothelial cell death or proliferation. The results are consistent with an LPS-induced decrease in the endothelial barrier function, which precedes, and may be independent of, cell death and a transient increase in convective transport across the media due to alterations in the barrier function of the internal elastic lamina.

In vitro and in vivo activation of endothelial cells by colony-stimulating factors

This study was designed to identify the set of functions activated in cultured endothelial cells by the hematopoietic growth factors, granulocyte colony-stimulating factor (G-CSF) and granulocyte macrophage-colony-stimulating factor (GM-CSF), and to compare them with those elicited by prototypic cytokines active on these cells. Moreover, indications as to the in vivo relevance of in vitro effects were obtained. G-CSF and GM-CSF induced endothelial cells to proliferate and migrate. In contrast, unlike appropriate reference cytokines (IL-1 and tumor necrosis factor, IFN-gamma), G-CSF and GM-CSF did not modulate endothelial cell functions related to hemostasis-thrombosis (production of procoagulant activity and of platelet activating factor), inflammation (expression of leukocyte adhesion molecule-1 and production of platelet activating factor), and accessory function (expression of class II antigens of MHC). Other colony-stimulating factors (IL-3 and macrophage-colony-stimulating factor) were inactive on all functions tested. In comparison to basic fibroblast growth factor (bFGF), G-CSF and GM-CSF induced lower maximal proliferation of endothelial cells, whereas migration was of the same order of magnitude. G-CSF and GM-CSF stimulated repair of mechanically wounded endothelial monolayers. Exposure to both cytokines induced shape changes and cytoskeletal reorganization consistent with a migratory phenotype. To explore the in vivo relevance of the in vitro effects of these cytokines on endothelium, we studied the angiogenic activity of human G-CSF in the rabbit cornea. G-CSF, but not the heat-inactivated molecule, had definite angiogenic activity, without any sign of inflammatory reactions. G-CSF was less active than bFGF. However, the combination of a nonangiogenic dose of bFGF with G-CSF resulted in an angiogenic response higher than that elicited by either individual cytokines. Thus, G-CSF and GM-CSF induce endothelial cells to express an activation/differentiation program (including proliferation and migration) related to angiogenesis.

Heterogeneous regulation of constitutive thrombomodulin or inducible tissue-factor activities on the surface of human saphenous-vein endothelial cells in culture following stimulation by interleukin-1, tumour necrosis factor, thrombin or phorbol ester

Thrombomodulin and tissue-factor activities were measured on the surface of confluent human saphenous-vein endothelial cells (HSVEC) cultivated in 96-multiwell plates. Thrombomodulin activity was measured in the presence of purified human thrombin (2.2 nM) and protein C (65 nM). Tissue-factor activity was measured with purified human Factor VII (5 nM) and Factor X (400 nM). Generated activated protein C and Factor Xa released in the supernatant were assayed with chromogenic substrates. Resting cells exhibited significant thrombomodulin activity, but no detectable tissue-factor activity. After 4 h of preincubation with tumour necrosis factor (TNF, 22-2200 pM), interleukin-1 (IL-1, 5.7-570 nM) or phorbol myristate acetate (PMA, 1.61-161 nM) there was an increase in tissue-factor activity and a concomitant decrease in thrombomodulin activity. However, the extent of both responses varied according to the nature of the stimulus. Thrombin (0.44-44 nM) also induced an increase in tissue-factor activity, but had no effect on thrombomodulin activity. Kinetic studies showed that for all stimuli the increase in tissue factor was transient, reaching a maximum after 4-8 h of preincubation with the stimulating agent and returning to normal values after 24 h. IL-1 and TNF induced a time-dependent decrease in thrombomodulin, by respectively 47% and 67% of control values after 24 h. However, PMA induced only a transient down-regulation of thrombomodulin, full activity being recovered after 18 h. Hence this simultaneous assay system, using intact HSVEC and purified human coagulation factors, enabled us to observe that the regulation of thrombin generation could be diversely affected by various substances known to stimulate the endothelium. This suggests that the simultaneous and opposite modulation of these proteins does not represent an unified response of the endothelial cells to procoagulant stimuli. These results also confirm the absence of effect of thrombin on the expression of thrombomodulin on the cell surface.

Macrovascular and microvascular endothelium during long-term hypoxia: alterations in cell growth, monolayer permeability, and cell surface coagulant properties

In bovine aortic or capillary endothelial cells (ECs) incubated under hypoxic conditions, cell growth was slowed in a dose-dependent manner at lower oxygen concentrations, as progression into S phase from G1 was inhibited, concomitant with decreased thymidine kinase activity. Monolayers grown to confluence in ambient air, wounded, and then transferred to hypoxia showed decreased ability to repair the wound, as a result of both decreased motility and cell division. Hypoxic ECs demonstrated a approximately 3-fold increase in the total number of high-affinity fibroblast growth factor receptors, and levels of endogenous FGF were suppressed. Consistent with the presence of functional FGF receptors, addition of basic FGF overcame, at least in part, hypoxia-mediated suppression of EC growth, and enhanced wound repair in hypoxia, stimulating both motility and cell division. Despite slower growth in hypoxia, ECs could achieve confluence, and the monolayers consisted of larger cells with altered assembly of the actin-based cytoskeleton and small gaps between contiguous cells. The permeability of these hypoxic EC monolayers to macromolecules and lower molecular weight solutes was increased. Cell surface coagulant properties were also perturbed: the anticoagulant cofactor thrombomodulin was suppressed, and a novel Factor X activator appeared on the EC surface. These data indicate that micro- and macrovascular ECs can grow and be maintained at low oxygen tensions, but hypoxic endothelium exhibits a range of altered functional properties which can potentially contribute to the pathogenesis of vascular lesions.

Inhibition of tumor angiogenesis as a strategy to circumvent acquired resistance to anti-cancer therapeutic agents

Cancers have a formidable capacity to develop resistance to a large and diverse array of chemical, biologic, and physical anti-neoplastic agents. This can be largely traced to the instability of the tumor cell genome, and the resultant ability of tumor cell populations to generate phenotypic variants rapidly. It is therefore argued that anti-cancer strategies should be directed at eliminating those genetically stable normal diploid cells that are required for the progressive growth of tumors. Microvascular endothelial cells comprising the tumor vasculature represent such a normal cell target. Moreover, specificity for tumor associated vasculature by anti-cancer agents may be achieved by virtue of the fact that many of the endothelial cells that comprise these blood vessels are in an immature, cycling, and 'activated' state, in contrast to the endothelial cells associated with normal tissue and organ blood vessels.

Alternative patterns of mitogenesis and cell scattering induced by acidic FGF as a function of cell density in a rat bladder carcinoma cell line

The dual function exerted by acidic fibroblast growth factor (aFGF) in a rat bladder carcinoma cell line has been explored under two different conditions of culture density. At low cell density, aFGF promotes the epithelium-to-mesenchyme transition of NBT-II cells characterized by cell dissociation, morphological changes toward a fibroblastic-like phenotype, and acquisition of cell motility. Under these conditions, NBT-II cells are unresponsive to the growth-promoting effect of aFGF. At high cell density, aFGF is a potent mitogenic factor, but its scattering activity is essentially abrogated. Slight modifications in the binding of aFGF to its specific receptors were observed at high cell density; these changes correlated with a downregulation of receptors with no apparent change in their molecular form. NBT-II cells located at the edge of artificial wounds mimicked the behavior of subconfluent cells, because they did not proliferate upon aFGF treatment. Furthermore, in large-sized NBT-II colonies, peripheral cells were the first to dissociate in response to aFGF. Altogether, our results suggest that the cellular response to multifunctional growth factors might depend on the localization within the responding cell population.

Vascular permeability factor: a tumor-derived polypeptide that induces endothelial cell and monocyte procoagulant activity, and promotes monocyte migration

Systemic infusion of low concentrations of tumor necrosis factor/cachectin (TNF) into mice that bear TNF-sensitive tumors leads to activation of coagulation, fibrin formation, and occlusive thrombosis exclusively within the tumor vascular bed. To identify mechanisms underlying the localization of this vascular procoagulant response, a tumor-derived polypeptide has been purified to homogeneity from supernatants of murine methylcholanthrene A-induced fibrosarcomas that induces endothelial tissue factor synthesis and expression (half-maximal response at approximately 300 pM), and augments the procoagulant response to TNF in a synergistic fashion. This tumor-derived polypeptide was identified as the murine homologue of vascular permeability factor (VPF) based on similar mobility on SDS-PAGE, an homologous NH2-terminal amino acid sequence, and recognition by a monospecific antibody to guinea pig VPF. In addition, VPF was shown to induce monocyte activation, as evidenced by expression of tissue factor. Finally, VPF was shown to induce monocyte chemotaxis across collagen membranes and endothelial cell monolayers. Taken together, these results indicate that VPF can modulate the coagulant properties of endothelium and monocytes, and can promote monocyte migration into the tumor bed. This suggests one mechanism through which tumor-derived mediators can alter properties of the vessel wall.

The effect of hypoxia on capillary endothelial cell function: modulation of barrier and coagulant function

As the cells forming the luminal vascular surface, endothelium is exposed to alterations in the vascular microenvironment, such as hypoxaemia. In this report we demonstrate that hypoxia, with pO2 as low as 12-14 mmHg, was not toxic to endothelium, but reversibly modulated central cellular functions essential for maintenance of homeostasis: permeability of monolayers to solutes increased in a dose-dependent manner, and cell surface coagulant properties were shifted to promote activation of coagulation. The anticoagulant cofactor thrombomodulin was suppressed and an apparently novel activator of factor X, distinct from the classical extrinsic and intrinsic systems, was induced. The hypoxia-induced factor X activator was cell surface-associated, had properties of a cysteine protease, had Mr corresponding to approximately 100 kDa, based on sodium dodecyl sulphate-polyacrylamide electrophoresis (SDS-PAGE), and isoelectric point (pI) approximately 5.0. These findings indicate that hypoxia dynamically modulates endothelial function providing insights into the contribution of microvascular endothelial dysfunction in the pathogenesis of vascular lesions.