Fibrin as a component of the tumor stroma: origins and biological significance

Colon cancer metastasis in mouse liver is not affected by hypercoagulability due to Factor V Leiden mutation

Clinical trials have shown life-prolonging effects of antithrombotics in cancer patients, but the molecular mechanisms remain unknown due to the multitude of their effects. We investigated in a mouse model whether one of the targets of antithrombotic therapy, fibrin deposition, stimulates tumour development. Fibrin may provide either protection of cancer cells in the circulation against mechanical stress and the immune system, or form a matrix for tumours and/or angiogenesis in tumours to develop. Mice homozygous for Factor V Leiden (FVL), a mutation in one of the coagulation factors that facilitates fibrin formation, were used to investigate whether hypercoagulability affects tumour development in an experimental metastasis model. Liver metastases of colon cancer were induced in mice with the FVL mutation and wild-type littermates. At day 21, number and size of tumours at the liver surface, fibrin/fibrinogen distribution, vessel density and the presence of newly formed vessels in tumours were analysed. Number and size of tumours did not differ between mice with and without the FVL mutation. Fibrin/fibrinogen was found in the cytoplasm of hepatocytes and cancer cells, in blood vessels in liver and tumour tissue and diffusely distributed outside vessels in tumours, indicating leaky vessels. Vessel density and angiogenesis varied widely between tumours, but a pre-dominance for vessel-rich or vessel-poor tumours or vessel formation could not be found in either genotype. In conclusion, the FVL mutation has no effect on the development of secondary tumours of colon cancer in livers of mice. Fibrin deposition and thus inhibition of fibrin formation by anticoagulants do not seem to affect tumour development in this model.

A meta-analysis and systematic review of the efficacy and safety of anticoagulants as cancer treatment: impact on survival and bleeding complications

BACKGROUND

Preclinical evidence suggests that anticoagulants, in particular the low-molecular-weight heparins (LMWH), exert an antitumor effect, whereas clinical trials have reported conflicting results. The authors conducted a comprehensive, systematic review and meta-analysis of the evidence from randomized controlled trials (RCTs), to evaluate the impact of anticoagulants on survival and safety in cancer patients without venous thromboembolism.

METHODS

A comprehensive systematic literature review of RCTs was performed without language restrictions through May 2006 with subsequent updates to the end of 2006, including an exhaustive search of electronic databases, major conference proceedings, article references, and content experts. Two reviewers extracted data independently. Primary study outcomes were 1-year overall mortality and all bleeding complications. Major and fatal bleeding complications were secondary outcomes.

RESULTS

Across all 11 studies that were identified, anticoagulation significantly decreased 1-year overall mortality with a relative risk (RR) of 0.905 (95% confidence interval [95% CI], 0.847-0.967; P = .003). The RR for mortality was 0.877 (95% CI, 0.789-0.975; P = .015) for LMWH, compared with an RR of 0.942 (95% CI, 0.854-1.040; P = .239) for warfarin, resulting in an absolute risk difference (ARD) of 8% for LMWH and an ARD of 3% for warfarin. Improved survival with anticoagulation may be dependent on tumor type. Major bleeding episodes occurred less frequently in patients who received LMWH (ARD, 1%) compared with patients who received warfarin (ARD, 11.5%; P < .0001). Overall, fatal bleeding occurred rarely (ARD, 0.32%; P = .542).

CONCLUSIONS

Anticoagulants, particularly LMWH, significantly improved overall survival in cancer patients without venous thrombosis while increasing the risk for bleeding complications. However, given the limitations of available data, the use of anticoagulants as antineoplastic therapy cannot be recommended until additional RCTs confirm these results.

The emergence of ECM mechanics and cytoskeletal tension as important regulators of cell function

The ability to harvest and maintain viable cells from mammalian tissues represented a critical advance in biomedical research, enabling individual cells to be cultured and studied in molecular detail. However, in these traditional cultures, cells are grown on rigid glass or polystyrene substrates, the mechanical properties of which often do not match those of the in vivo tissue from which the cells were originally derived. This mechanical mismatch likely contributes to abrupt changes in cellular phenotype. In fact, it has been proposed that mechanical changes in the cellular microenvironment may alone be responsible for driving specific cellular behaviors. Recent multidisciplinary efforts from basic scientists and engineers have begun to address this hypothesis more explicitly by probing the effects of ECM mechanics on cell and tissue function. Understanding the consequences of such mechanical changes is physiologically relevant in the context of a number of tissues in which altered mechanics may either correlate with or play an important role in the onset of pathology. Examples include changes in the compliance of blood vessels associated with atherosclerosis and intimal hyperplasia, as well as changes in the mechanical properties of developing tumors. Compelling evidence from 2-D in vitro model systems has shown that substrate mechanical properties induce changes in cell shape, migration, proliferation, and differentiation, but it remains to be seen whether or not these same effects translate to 3-D systems or in vivo. Furthermore, the molecular "mechanotransduction" mechanisms by which cells respond to changes in ECM mechanics remain unclear. Here, we provide some historical context for this emerging area of research, and discuss recent evidence that regulation of cytoskeletal tension by changes in ECM mechanics (either directly or indirectly) may provide a critical switch that controls cell function.

VEGF increases the fibrinolytic activity of endothelial cells within fibrin matrices: involvement of VEGFR-2, tissue type plasminogen activator and matrix metalloproteinases

Proteolysis of fibrin matrices by endothelial cells plays essential roles in the migratory and morphogenic differentiation processes underlying angiogenesis. Using an in vitro fibrinolysis model consisting of human umbilical vein endothelial cells (HUVECs) embedded in a three dimensional fibrin matrix, we show that VEGF, an angiogenic cytokine that plays a crucial role in the onset of angiogenesis, is a potent activator of HUVEC-mediated fibrinolysis. This VEGF-dependent fibrin degradation was completely abrogated by inhibitors of either the plasminogen activator/plasmin or matrix metalloproteinases (MMP) proteolytic systems, suggesting the involvement of both classes of proteases in fibrin degradation. Accordingly, VEGF-induced fibrinolysis correlated with an increase in the expression of tPA and of some MMPs, such as MT2-MMP and was completely blocked by a neutralizing antibody against tPA. Overall, these results indicate that efficient proteolysis of three dimensional fibrin matrices during VEGF-mediated angiogenesis involves a complex interplay between the MMP and plasmin-mediated proteolytic systems.

A novel three-dimensional model to quantify metastatic melanoma invasion

Although attempts to develop any viable chemotherapeutic approaches to combat metastatic cancers have largely failed, potential genetic targets to halt metastatic progression continue to be identified. As drugs are developed to address these targets, there is a need for high-throughput systems that accurately reproduce in vivo microenvironments to gauge their efficacy. Accordingly, we have developed a three-dimensional in vitro culture system representative of the environment present upon secondary metastasis to quantitatively measure tumor cell invasion in this setting three-dimensionally. Culturing melanomas of different metastatic capacities within the system showed that each cell type invades the matrix in a manner commensurate to its known metastatic potential in vivo. Moreover, the developed quantitative schemes were put to use to characterize the effect of microenvironmental influences (i.e., matrix components, interstitial cell presence) on planar and vertical melanoma invasion. We propose this novel, quantitative system as a useful tool to assess the effects of pharmacologic and/or microenvironmental influences on tumor cell invasion at a metastatic site.

Treatment of solid tumors and metastases by fibrinogen-targeted anticancer drug therapy

The accumulation of fibrin/fibrinogen and other coagulation factors in and around solid tumors and metastatic foci has been recognized for a century as an aspect of cancer pathology. On this basis, anticoagulants and fibrinolytic agents have been deployed as adjuvant anticancer therapies, but they have proved clinically useful for only a small proportion of tumors and they only control the functions of the coagulant components. Overuse or long-term application of anticoagulants and fibrinolytic agents often lead to undesirable side-effects. Here, we propose that anticancer drugs that act by different mechanisms can inhibit tumor-associated coagulation, and it may be possible to develop drugs that specifically targeting tumor-related coagulation, have specific cytotoxic effects on tumor and metastatic cells. We provide laboratory and clinical evidence supporting the hypothesis and offer proposals for future applications.

Tumour-expressed tissue factor inhibits cellular cytotoxicity

AIMS

The association between tissue factor (TF) expression and increased rate of tumour metastasis is well established. In this study, we have examined the hypothesis that the expression of TF by disseminated tumour cells confers protection against immune recognition and cytotoxicity.

MATERIALS AND METHODS

A hybrid EGFP-TF protein was expressed in HT29 colon carcinoma and K562 lymphoblast cell lines. To assess the cytotoxic activity against tumour cells over-expressing TF, a novel method was used, based on the direct measurement of fluorescently labelled HT29 or K562 target cells.

RESULTS

Upon challenge with peripheral blood mononuclear cells (PBMC), tumour cells expressing TF partially evaded cellular cytotoxicity (Delta=15-40% reduction in cytotoxicity). Moreover, the influence of TF was not primarily dependent on its procoagulant function, although the inclusion of 20% (v/v) plasma did lower the rate of cytotoxicity against untransfected cells. However, expression of a truncated form of TF, devoid of the cytoplasmic domain, did not mediate any degree of inhibition of cytotoxicity, suggesting that the protective function of TF is principally due to this domain.

CONCLUSIONS

We conclude that TF can promote immune evasion in tumour cells expressing this protein leading to increased survival and therefore metastatic rate in such cells.

Genetic variation in platelet integrin alphabeta (GPIIb/IIIa) and the metastatic potential of renal cell carcinoma

OBJECTIVE

To explore whether genetic polymorphisms in platelet receptors known to be associated with platelet activity have any association with haematogenous metastases in renal cell carcinoma (RCC), as platelets and their fibrinogen receptors may be central to haematogenous cancer spread, in addition to various adhesive proteins on both platelets and tumour cells on themselves.

PATIENTS AND METHODS

The glycoprotein alpha(IIb)beta3 (GPIIb/IIIa) is the main fibrinogen receptor on platelets, with GPIb-IX-V and GPIa/IIa being the von Willebrand Factor and collagen receptors, respectively. In a cross-sectional survey of 128 men treated for RCC (55 with disseminated disease and 73 with a local disease), they were genotyped using DNA extracted from freshly drawn blood, and central clinical data were recorded.

RESULTS

The frequency of possessing the GPIIIaPl(A2) allele among patients with metastatic RCC was 43.6%, and with local disease was 24.7% (P = 0.024). The frequencies of the different alleles of the GIB-IX-V, C3550T and GPIa/IIa C807T polymorphisms did not differ between the groups. In a stepwise logistic regression (metastatic vs local RCC) the Pl(A2) allele remained a significant risk factor, with an odds ratio of 2.7 (95% confidence interval, 1.1-6.5; P = 0.02).

CONCLUSION

The prothrombotic Pl(A2) allele of platelet fibrinogen receptor GPIIb/IIIa increased the risk of metastases in RCC in men.

Anti-thrombotics in thrombosis and cancer

Many cancer patients have a reportedly hypercoagulable state, with recurrent thrombosis due to the impact of cancer cells and chemotherapy or radiotherapy on the coagulation cascade. Studies have demonstrated that unfractionated heparin or its low-molecular-weight fractions interfere with various processes involved in tumor growth and metastasis. These include fibrin formation; binding of heparin to angiogenic growth factors, such as basic fibroblast growth factor and vascular endothelial growth factor; modulation of tissue factor; and perhaps other more important modulatory mechanisms, such as enhanced tissue factor pathway inhibitor (TFPI) release and inhibition of various matrix-degrading enzymes. Clinical trials have suggested a clinically relevant effect of low-molecular-weight heparin (LMWH), as compared with unfractionated heparin, on the survival of cancer patients with deep vein thrombosis. Similarly, the impact of warfarin on the survival of cancer patients with thromboembolic disorders was demonstrated. Studies from the author's laboratory demonstrated a significant role for LMWH, warfarin, anti-VIIa, and LMWH-releasable TFPI on the regulation of angiogenesis, tumor growth and tumor metastasis. Thus, modulation of tissue factor/VIIa noncoagulant activities by LMWH, warfarin, anti-VIIa, or TFPI may be a useful therapeutic method for the inhibition of angiogenesis associated with human tumor growth and metastasis. Additionally, antiplatelet drugs may have an impact on tumor metastasis, and the combination of antiplatelets and anticoagulants at adjusted doses may provide greater benefits to cancer patients.

Effect of inhibition of vascular endothelial growth factor signaling on distribution of extravasated antibodies in tumors

Antibodies and other macromolecular therapeutics can gain access to tumor cells via leaky tumor vessels. Inhibition of vascular endothelial growth factor (VEGF) signaling can reduce the vascularity of tumors and leakiness of surviving vessels, but little is known about how these changes affect the distribution of antibodies within tumors. We addressed this issue by examining the distribution of extravasated antibodies in islet cell tumors of RIP-Tag2 transgenic mice and implanted Lewis lung carcinomas using fluorescence and confocal microscopic imaging. Extravasated nonspecific immunoglobulin G (IgG) and antibodies to fibrin or E-cadherin accumulated in irregular patchy regions of stroma. Fibrin also accumulated in these regions. Anti-E-cadherin antibody, which targets epitopes on tumor cells of RIP-Tag2 adenomas, was the only antibody to achieve detectable levels within tumor cell clusters at 6 hours after i.v. injection. Treatment for 7 days with AG-013736, a potent inhibitor of VEGF signaling, reduced the tumor vascularity by 86%. The overall area density of extravasated IgG/antibodies decreased after treatment but the change was less than the reduction in vascularity and actually increased when expressed per surviving tumor vessel. Accumulation of anti-E-cadherin antibody in tumor cell clusters was similarly affected. The patchy pattern of antibodies in stroma after treatment qualitatively resembled untreated tumors and surprisingly coincided with sleeves of basement membrane left behind after pruning of tumor vessels. Together, the findings suggest that antibody transport increases from surviving tumor vessels after normalization by inhibition of VEGF signaling. Basement membrane sleeves may facilitate this transport. Antibodies preferentially distribute to tumor stroma but also accumulate on tumor cells if binding sites are accessible.

The cancer stem cell: evidence for its origin as an injured autoreactive T cell

This review explores similarities between lymphocytes and cancer cells, and proposes a new model for the genesis of human cancer. We suggest that the development of cancer requires infection(s) during which antigenic determinants from pathogens mimicking self-antigens are co-presented to the immune system, leading to breaking T cell tolerance. Some level of autoimmunity is normal and necessary for effective pathogen eradication. However, autoreactive T cells must be eliminated by apoptosis when the immune response is terminated. Apoptosis can be deficient in the event of a weakened immune system, the causes of which are multifactorial. Some autoreactive T cells suffer genomic damage in this process, but manage to survive. The resulting cancer stem cell still retains some functions of an inflammatory T cell, so it seeks out sites of inflammation inside the body. Due to its defective constitutive production of inflammatory cytokines and other growth factors, a stroma is built at the site of inflammation similar to the temporary stroma built during wound healing. The cancer cells grow inside this stroma, forming a tumor that provides their vascular supply and protects them from cellular immune response.

As cancer stem cells have plasticity comparable to normal stem cells, interactions with surrounding normal tissues cause them to give rise to all the various types of cancers, resembling differentiated tissue types. Metastases form at an advanced stage of the disease, with the proliferation of sites of inflammation inside the body following a similar mechanism. Immunosuppressive cancer therapies inadvertently re-invigorate pathogenic microorganisms and parasitic infections common to cancer, leading to a vicious circle of infection, autoimmunity and malignancy that ultimately dooms cancer patients. Based on this new understanding, we recommend a systemic approach to the development of cancer therapies that supports rather than antagonizes the immune system.

Regulation of urokinase receptor mRNA stability by hnRNP C in lung epithelial cells

Increased urokinase receptor (uPAR) expression as well as stabilisation of uPAR mRNA contribute to the pathogenesis of lung inflammation and neoplasia. Post-transcriptional regulation of uPAR mRNA involves interaction of both coding and 3'-UTR sequences with regulatory uPAR mRNA binding proteins (Bps). In order to identify novel regulatory interactions, we performed gel mobility shift and UV cross-linking assays and found two distinct uPAR mRNA-protein complexes. We identified a rapidly migrating 40 kDa uPAR mRNABp that selectively bound a 110 nucleotide (nt) fragment of the uPAR mRNA 3'UTR. Chimeric beta-globin/uPAR mRNA containing the 110 nt 40 kDa protein binding fragment destabilised stable beta-globin mRNA with a rate of decay identical to that of chimeric beta-globin/uPAR containing the full uPAR 3'UTR. The 40 kDa uPAR 3'UTR Bp was purified using poly (U) sepharose and identified as heterogeneous nuclear ribonucleoprotein C (hnRNPC). Finally, we confirmed its interaction with the uPAR mRNA 3' UTR by gel mobility supershift assay using an anti-hnRNPC antibody. Direct in vivo interaction of hnRNPC with the uPAR mRNA 3'UTR was demonstrated by immunoprecipitation and combined RT PCR-Southern blotting assay. Co-transfection of hnRNPC cDNA in Beas2B cells reversed destabilisation of chimeric beta-globin/uPAR 3'UTR mRNA and its over-expression also induced uPAR protein and mRNA expression through stabilisation of uPAR mRNA. These observations indicate a novel mechanism of uPAR gene regulation in lung epithelial cells in which cis elements within a 110 nt uPAR mRNA 3'UTR sequence interact with hnRNPC to regulate uPAR mRNA stability.

Regulation of urokinase receptor expression by phosphoglycerate kinase is independent of its catalytic activity

Posttranscriptional regulation of urokinase-type plasminogen activator receptor (uPAR) mRNA involves the interaction of a uPAR mRNA coding region sequence with phosphoglycerate kinase (PGK), a 50-kDa uPAR mRNA binding protein. PGK catalyzes a reversible transfer of a phosphoryl group from 1,3-biphosphoglycerate to ADP in the glycolytic pathway. Our previous studies showed that overexpression of PGK in uPAR-overproducing H157 lung carcinoma cells results in decreased cytoplasmic uPAR mRNA and cell surface uPAR protein expression through destabilization of the mRNA. In order to determine the role of PGK enzymatic activity on uPAR mRNA stability we mutated PGK by changing amino acid P204H and amino acid D219A. The mutant proteins were expressed in Epicurian coli BL21 cells, and the purified proteins were analyzed for PGK activity. We found that mutation of amino acid P204H and D219A reduced PGK activity by 99 and 83%, respectively. By gel mobility shift and Northwestern assay, we found that the mutant proteins were able to bind to uPAR mRNA as effectively as wild-type PGK. Overexpression of mutant, inactive PGK in H157 cells reduced cell surface uPAR protein as well as uPAR mRNA expression. Run-on transcription analysis indicated that overexpression of mutant PGKs fails to alter the rate of synthesis of uPAR mRNA, whereas transcription chase experiments demonstrated that both mutants and wild-type PGK reduce the stability of the uPAR mRNA transcripts to a similar extent. Overexpression of mutant PGK also inhibited the rate of DNA synthesis and the invasion-migration ratio. These results demonstrate that uPAR mRNA binding activity as well as PGK-mediated regulation of uPAR mRNA are independent of PGK enzymatic activity.

Rationale for the treatment of cancer with sodium selenite

Epidemiological studies conducted during several decades of the last century have demonstrated the importance of sufficient nutritional supply of selenium (Se) for human health. More importantly, low blood Se levels were found to be associated with an increased incidence and mortality from various types of cancers. Recently, attention of researchers was drawn to the relationship between free radical generation, known otherwise as oxidative stress, and carcinogenesis. It was therefore thought that antioxidants should be beneficial for prevention and inhibition of different malignancies. However, there appeared to be a paradox, because tumor growth is associated with tissue hypoxia that is accompanied by the formation of reductive rather than oxidative free radicals. Various organic and inorganic Se compounds, generally considered to be antioxidants, produced mixed results when tested in animal models and human subjects. Amongst them, sodium selenite has been shown to be the most effective in an in vitro and in vivo carcinogenesis studies. As recently demonstrated, selenite is not an antioxidant, but possesses oxidizing properties in the presence of specific substrates. Thus selenite is capable of oxidizing polythiols to corresponding disulfides, but does not react with monothiols. Such polythiols associated with cancer membrane-bound proteins appear under the reducing conditions of hypoxic tumor tissue. These thiol groups can, in turn, initiate a disulfide exchange reaction with plasma proteins, predominantly with fibrinogen, to form an insoluble and protease-resistant fibrin-like polymer. As the result, tumor cells become surrounded by a coat which masks specific tumor antigens thus allowing cancer cells to escape immune recognition and elimination by natural killer (NK) cells. Selenite by virtue of oxidizing cell membrane thiols, can prevent the formation of the coat and consequently makes cancer cells vulnerable to the immune surveillance and destruction. In addition, selenite may directly activate NK cells, as well as inhibit angiogenesis without undesirable decrease in the oxidative potential of cellular environment. It is, therefore, postulated that sodium selenite, in view of its relative low toxicity, might become a drug of choice for many types of cancer including leukemia.

Port-Site Metastasis: The Influence of Biology

OBJECTIVE

Several surgical and technical mechanisms have been proposed for the development of port-site metastasis, but the influence of tumor and host biologic factors has not been emphasized. We present a case of a pelvic chordoma that metastasized to a prior laparoscopic radical nephrectomy port-site.

METHODS

A 62-year-old woman underwent laparoscopic radical nephrectomy (LRN) for a pT1b grade 3 renal cell carcinoma, followed 6 weeks later by resection of a sacral chordoma. The incisions and areas of dissection for the two procedures were discontinuous.

RESULTS

Eight months following the LRN she developed a nodule in one of the laparoscopic port-sites. The port-site metastasis was treated with wide surgical resection, which was confirmed as metastatic chordoma on histologic examination.

CONCLUSION

Based on the chronological sequence and physical distance between surgical sites, only biological factors could have contributed to this port-site metastasis. This unusual case highlights the important role that tumor and host biologic mechanisms play in the development of port-site metastasis.

Integrins and angiogenesis

The growth of new blood vessels is a dynamic yet highly regulated process that depends on coordinated signaling by growth factor and cell adhesion receptors. As part of the molecular program regulating angiogenesis, endothelial cells acquire a proliferative and invasive phenotype but also show increased susceptibility to apoptotic stimuli. Integrins are the principle adhesion receptors used by endothelial cells to interact with their extracellular microenvironment, and integrin-mediated interactions play a critical role in regulating cell proliferation, migration, and survival. Alterations in the repertoire and?or activity of integrins, as well as the availability and structural property of their ligands, regulate the vascular cell during the growth or repair of blood vessels.

Regulated angiogenesis and vascular regression in mice overexpressing vascular endothelial growth factor in airways

Angiogenesis and vascular remodeling occurs in many inflammatory diseases, including asthma. In this study, we determined the time course and reversibility of the angiogenesis and vascular remodeling produced by vascular endothelial growth factor (VEGF) in a tet-on inducible transgenic system driven by the CC10 promoter in airway epithelium. One day after switching on VEGF expression, endothelial sprouts arose from venules, grew toward the epithelium, and were abundant by 3 to 5 days. Vessel density reached twice baseline by 7 days. Many new vessels were significantly larger than normal, were fenestrated, and penetrated the epithelium. Despite their mature appearance at 7 days suggested by their pericyte coat and basement membrane, the new vessels started to regress within 3 days when VEGF was switched off, showing stasis and luminal occlusion, influx of inflammatory cells, and retraction and apoptosis of endothelial cells and pericytes. Vessel density returned to normal within 28 days after VEGF withdrawal. Our study showed the dynamic nature of airway angiogenesis and regression. Blood vessels can respond to VEGF by sprouting angiogenesis within a few days, but regress more slowly after VEGF withdrawal, and leave a historical record of their previous extent in the form of empty basement membrane sleeves.

Friends or foes - bipolar effects of the tumour stroma in cancer

The restricted view of tumour progression as a multistep process defined by the accumulation of mutations in cancer cells has largely ignored the substantial contribution of the tumour microenvironment to malignancy. Even though the seed and soil hypothesis of Paget dates to 1889, it has been less than two decades since researchers have included the tumour microenvironment in their analyses of tumour progression. What have we recently learned from studying tumour-stroma interactions, and will this help to define new targets for therapy?

Effect of Anti-Cancer Drugs on the Binding of 125I-Fibrinogen to Two Leukaemia Cell Lines In Vitro

Anti-cancer drugs may be able to inhibit tumour growth and metastasis by blocking fibrinogen- and/or fibrin-related pathways. To test this hypothesis, the effect of various anti-neoplastic drugs on the binding of 125I-Fibrinogen to two leukaemia cell lines, HL60 and P388, was investigated. All the drugs tested inhibited the binding of fibrinogen to leukaemia cells. This effect was particularly marked for drugs that act as inhibitors of protein synthesis. Since these anti-neoplastic drugs do not have anti-coagulant actions, these results provide evidence for the potential of targeting tumour fibrinogen as a new form of cancer chemotherapy.

The role of fibrinogen and related fragments in tumour angiogenesis and metastasis

Angiogenesis, the development of new blood vessels from existing vasculature, involves the migration, proliferation and differentiation of endothelial cells and is crucial for the growth and mestastasis of tumours. A specific association between cancer and the haemostatic system has long been recognised. Haemostatic mechanisms regulate blood flow by controlling platelet adhesion and fibrin deposition, and a number of haemostatic proteins have been shown to regulate angiogenesis, either directly, by interacting with endothelial cells themselves, or indirectly, by interacting with other regulators of angiogenesis. The polypeptide fibrinogen is the central protein in the haemostasis pathway and is found deposited in the majority of human and experimental animal tumours. In this review, the evidence for the ability of fibrinogen and various protein/peptide fragment derivatives to modulate angiogenic mechanisms in vitro and to affect tumour growth and metastasis in vivo is discussed.

Tumor growth and metastasis are not affected in thrombin-activatable fibrinolysis inhibitor-deficient mice

Many studies have indicated that the plasminogen activation system may have a prominent role in cancer. Activation of the zymogen plasminogen into the serine protease plasmin by plasminogen activator is mediated by carboxyterminal basic amino acids in fibrin, including lysines and arginines. Thrombin-activatable fibrinolysis inhibitor (TAFI) is a circulating carboxypeptidase B-type proenzyme that, after activation, removes carboxyterminal lysine or arginine residues in fibrin, resulting in decreased plasminogen activation and attenuated fibrinolysis. To determine directly whether TAFI is involved in primary tumor growth and metastasis formation, we examined the effects of TAFI deficiency on subcutaneous growth and experimentally or spontaneously induced pulmonary metastasis formation of different tumor cell types in mice. In all tumor models TAFI deficiency did not affect the formation and growth of primary and metastasized tumors.

Adult respiratory distress syndrome: do selective anticoagulants help?

The adult respiratory distress syndrome (ARDS) is a form of acute lung injury that is characterized by florid extravascular fibrin deposition. Thrombosis in the pulmonary vasculature and disseminated intravascular coagulation have also been observed in association with ARDS. Fibrin deposition does not occur in the normal lung but is virtually universal in acute lung injury induced by disparate insults. A large body of basic and preclinical evidence further implicates abnormalities of pathways of fibrin turnover in the pathogenesis of acute inflammation and fibrotic repair. Coagulation is locally upregulated in the injured lung, while fibrinolytic activity is depressed. These abnormalities occur concurrently and favor alveolar fibrin deposition. The systemic derangements of fibrin turnover in sepsis are similar to those that occur in the injured lung. Recent clinical trials demonstrate that interventions using selective anticoagulation can provide a mortality advantage and that selective anticoagulants differ in their ability to provide clinical benefit. Preclinical trials in primates with sepsis-induced ARDS now indicate that anticoagulant interventions that block the extrinsic coagulation pathway can protect against the development of pulmonary fibrin deposition as well as lung dysfunction and acute inflammation. These observations provide proof of principle that key steps in the coagulation cascade are appropriate therapeutic targets to prevent the development of acute lung injury in ARDS. Ongoing studies and prior publications also support the hypothesis that reversal of the fibrinolytic defect in ARDS could protect against the development of acute lung injury. In all, these studies suggest that fibrin deposition in the injured lung as well as abnormalities of coagulation and fibrinolysis are integral to the pathogenesis of ARDS. The ability of selective anticoagulants to effectively and safely alter clinical outcome in ARDS remains to be determined.

Regulation of urokinase receptor expression by phosphoglycerate kinase

Post-transcriptional regulation represents a major mechanism by which eukaryotic gene expression is regulated through cis-trans interactions that serve as signals for rapid alterations of messenger RNA (mRNA) stability. Regulation of urokinase-type plasminogen activator receptor (uPAR) mRNA involves the interaction of a uPAR mRNA coding region sequence with a 50 kD uPAR mRNA binding protein. We purified this protein from human bronchial epithelial (Beas2B) cells and identified it as phosphoglycerate kinase (PGK). We cloned PGK cDNA by polymerase chain reaction and expressed the recombinant PGK protein, which specifically bound the uPAR mRNA coding region by gel mobility shift and Northwestern blotting. We also confirmed a direct interaction of PGK protein with uPAR mRNA by immunoprecipitation. Overexpression of PGK in uPAR-overproducing H157 lung carcinoma cells resulted in decreased cytoplasmic uPAR mRNA and cell surface uPAR protein expression. Reduced uPAR mRNA expression involved decreased stability of the uPAR mRNA. Decline in 3H-thymidine incorporation and migration occurred in H157 cells transfected with PGK cDNA. These results demonstrate that PGK regulates uPAR expression at the post-transcriptional level.

Urokinase receptor mRNA stability involves tyrosine phosphorylation in lung epithelial cells

Interaction between urokinase-type plasminogen activator (uPA) and its receptor (uPAR) localizes cellular proteolysis and promotes cellular proliferation and migration, effects that may contribute to the pathogenesis of lung inflammation and neoplasia. Enhanced uPAR expression as well as stabilization of uPAR mRNA by transforming growth factor-beta and phorbol myristate acetate (PMA) shares a common mechanism involving phosphorylation and dephosphorylation of a uPAR mRNA-binding protein (uPAR mRNABp). PMA-induced tyrosine phosphorylation of the uPAR mRNABp inhibited the uPAR mRNA-uPAR mRNABp interaction, stabilized uPAR mRNA and enhanced uPAR protein expression. Downregulation of the uPAR mRNA and uPAR mRNABp interaction by PMA and transforming growth factor-beta can be reversed by pretreatment of cells with herbimycin which in turn inhibits expression of uPAR protein via a decrease in uPAR mRNA stability. Our experiments indicate that post-transcriptional regulation of uPAR expression requires activation of tyrosine kinases. Cytokines can regulate uPAR expression of lung-derived epithelial cells at the post-transcriptional level by tyrosine phosphorylation of the uPAR mRNA binding protein and may thereby influence tissue remodeling in lung injury or neoplasia.

Tissue factor, thrombin, and cancer

In addition to its primary role in hemostasis and blood coagulation, thrombin is a potent mitogen capable of inducing cellular functions. Therefore, it should come as no surprise that thrombin has proved to be of importance in the behavior of cancer. In this review, we focus on the ability of tissue factor (TF) and thrombin to influence tumor angiogenesis. Both exert their influence on angiogenesis through clotting-dependent and clotting-independent mechanisms: (1). directly affecting signaling pathways that mediate cell functions, and (2). mediating clot formation, thereby providing a growth media for tumor cells. Therefore, anticoagulant drugs may prove efficacious in cancer treatment due to their ability to reduce the characteristic hypercoagulability of cancer and alter the fundamental biology of cancer.

Port site metastases in urological laparoscopic surgery

PURPOSE

Laparoscopic surgery is rapidly gaining widespread acceptance among urologists, including extensive application in malignant conditions. However, untoward occurrences of port site metastases have not eluded to urological applications. This up-to-date review on port site metastases in urology delineates possible contributing factors and describes techniques to prevent it.

MATERIALS AND METHODS

We comprehensively reviewed published experimental and clinical studies with special emphasis on the incidence, pathophysiology and prevention of port site metastases.

RESULTS

Nine cases of port site metastases after urological laparoscopy have been described in clinical and experimental studies. Etiological factors include natural malignant disease behavior, host immune status, local wound factors, laparoscopy related factors such as aerosolization of tumor cells (the use of gas, type of gas, insufflation and desufflation, and pneumoperitoneum) and sufficient technical experience of the surgeons and operating team (adequate laparoscopic equipment, skill, minimal handling of the tumor, surgical manipulation and wound contamination during instruments change, organ morcellation and specimen removal).

CONCLUSIONS

Port site metastases is a multifactorial phenomenon with an as yet undetermined incidence. The problem is influenced to some extent by surgeon and operating team experience and, therefore, it could be partially prevented. The suggested preventive steps are avoiding laparoscopic surgery when there are ascites, trocar fixation to prevent dislodgment, avoiding gas leakage along and around the trocar, sufficient technical readiness of the operating team (adequate laparoscopic equipment and technique, minimal handling and avoiding tumor boundary violation of the tumor), using a bag for specimen removal, placing drainage when needed before desufflation, povidone-iodine irrigation of instruments, trocars and port site wounds, and suturing 10 mm. and larger trocar wounds.

Platelet-CD40 ligand interaction with melanoma cell and monocyte CD40 enhances cellular procoagulant activity

Platelet-tumor cell interactions are believed to be important in tumor metastasis. Tumor cell tissue factor (TF) expression enhances metastasis and angiogenesis, and is primarily responsible for tumor-induced thrombin generation and the formation of tumor cell-platelet aggregates. Activated platelets express and release CD40 ligand (CD40L), which induces endothelial TF expression by ligation to CD40. We investigated the effect of platelet-derived CD40L on the TF activity of human CD40-positive melanoma cells and monocytes by incubating supernatants from activated or resting platelets with tumor cells or monocytes, and by bringing resting or activated platelets into close apposition with tumor cell monolayers. CD40L was present on the surface of activated (but not resting) platelets and was also released following platelet activation. Both recombinant soluble CD40L (rsCD40L) and activated platelet supernatants increased procoagulant activity (PCA) and TF antigen in tumor cells and monocytes. The increase in TF activity induced by both rsCD40L and activated platelet supernatants was inhibited by anti-CD40L antibody. Furthermore, contact of activated platelets with tumor cells increased cellular PCA, and this effect was also inhibited by anti-CD40L. In malignancy, the increase in cellular TF activity via CD40 (tumor cell)-CD40L (platelet) interaction may possibly enhance intravascular coagulation and hematogenous metastasis.

Endothelium and disordered fibrin turnover in the injured lung: newly recognized pathways

OBJECTIVES

To review derangements of pathways of fibrin turnover that promote pathologic fibrin deposition in the acute respiratory distress syndrome and to review the contribution of the endothelium and parenchymal lung cells to the derangements. In addition, to review how these pathways can be exploited in specific clinical circumstances, including sepsis and acute lung injury. Lastly, to review newly recognized posttranscriptional and urokinase-dependent pathways by which the fibrinolytic system is regulated in the lung.

DATA SOURCES

Medical literature published in English from 1966 to present.

DATA SUMMARY

Local abnormalities of fibrin turnover in the injured lung recapitulate the systemic changes observed in sepsis. In both circumstances, the procoagulant response is increased, whereas fibrinolytic activity is concurrently depressed. The increased procoagulant activity is related to tissue factor associated with factor VII/VIIa. Fibrinolytic activity in the vasculature is mainly attributable to tissue plasminogen activator, whereas extravascular fibrinolytic activity in the lung is mainly attributable to urokinase plasminogen activator (uPA). Depressed fibrinolytic activity is in large part attributable to plasminogen activator inhibitor-1. In sepsis, activated protein C is also deficient, potentiating the inflammatory response, coagulopathy, and depressed fibrinolysis. Recombinant human activated protein C (drotrecogin alfa [activated]) was successful as an intervention for sepsis in a recent phase 3 clinical trial (PROWESS). Recently, novel posttranscriptional pathways that regulate expression of uPA, its receptor (uPAR), and plasminogen activator inhibitor-1 have been identified. The responsible mechanisms involve cis-trans interactions between newly recognized messenger RNA (mRNA) binding sequences and mRNA binding proteins. A 51 nucleotide mRNA binding sequence within the coding region of uPAR mRNA interacts with a novel 50-kDa mRNA binding protein to destabilize the message. Sequences within the 3' untranslated region of uPA or plasminogen activator inhibitor-1 mRNA interact with 30- and 60-kDa proteins, respectively, to regulate message stability. All of these pathways operate in lung epithelial cells, and endothelial cells regulate uPA expression through a similar pathway. In addition, uPA itself is capable of inducing expression of other components of the fibrinolytic system, including uPAR. This observation defines another feedback loop that could amplify local fibrinolysis and other uPA- or uPAR-mediated cellular responses, including cellular proteolysis, proliferation, and directed cellular migration.

CONCLUSIONS

Novel posttranscriptional pathways regulate expression of uPA, uPAR, and plasminogen activator inhibitor-1. uPA itself is capable of inducing other components of the fibrinolytic system. Some or all of these newly recognized pathways are operative in endothelial and parenchymal lung cells and may influence disordered fibrin turnover in the injured lung.

Anticoagulants in thrombosis and cancer: the missing link

Many cancer patients reportedly have hypercoaguable state, with recurrent thrombosis due to the impact of cancer cells and chemotherapy on the coagulation cascade. A number of retrospective studies showed that cancer patients are at higher risk of developing venous thromboembolism. In addition to the pathological mechanisms associated with tumor-mediated increase in thrombotic events, cancer therapies including chemotherapy, immobilization, cancer surgery and the use of central venous catheters contribute toward a hypercoaguable state and are therefore independent risk factors of venous thromboembolism in cancer patients. Studies have demonstrated that unfractionated heparin or low molecular weight heparin (LMWH) interferes with various processes involved in tumor growth and metastasis. These processes might include fibrin formation, binding of heparin to angiogenic growth factors--such as basic fibroblast growth factor and VEGF--modulation of tissue factor, release of tissue factor pathway inhibitor and other mechanisms. Clinical trials have suggested an improved efficacy of LMWH, as compared with UFH on the survival of cancer patients with deep vein thrombosis. Similarly, the impact of warfarin on the survival of cancer patients with thromboembolic disorders was demonstrated. Recent studies from our laboratory defined the role of the LMWH (tinzaparin), warfarin, antifactor VIIa and recombinant tissue factor pathway inhibitor in the modulation of angiogenesis, tumor growth and tumor metastasis.

Roles of bradykinin in vascular permeability and angiogenesis in solid tumor

Bradykinin (BK) is involved in tumor angiogenesis. To elucidate the mechanism underlying BK-induced angiogenesis, we evaluated the roles of BK in tumor-associated vascular permeability and angiogenesis in the different phases of tumor development in mice bearing sarcoma 180 cells. The vascular permeability was significantly enhanced in the early growth phase (which peaked at day 5), and was thereafter markedly reduced. By contrast, tumor angiogenesis increased gradually over a 20-day experimental period. Oral administration of a B2 receptor antagonist, FR173657 (30 mg/kg/day), significantly suppressed the vascular permeability, but a B1 antagonist, desArg10-Hoe140 (1 mg/kg/day) did not. An immunohistochemical study revealed the presence of immunoreactive B2 receptor in the endothelial cells in the early phase, whereas B2 receptors were also observed in the stromal fibroblasts in the late phase. We also found that VEGF was detected exclusively in the stromal fibroblasts only in the late phase. Furthermore, VEGF immunoreactivity was attenuated by the treatment with FR173657. Tumor angiogenesis was significantly reduced by treating the tumor tissues with FR173657 both in the early phase (days 1-6, 30 mg/kg/day, oral administration) and in the late phase (days 7-12, 30 mg/kg/day, oral administration), whereas it was inhibited by neutralization with anti-VEGF antibody (1 microg/site/day, local injection) only in the late phase. These results suggest that BK would promote angiogenesis by increasing vascular permeability in the early phase via B2 receptor in the endothelial cells and by promoting up-regulation of VEGF via B2 receptor in the stromal fibroblasts in the late phase.

Targeting tissue factor on tumor vascular endothelial cells and tumor cells for immunotherapy in mouse models of prostatic cancer

The efficacy and safety of an immunoconjugate (icon) molecule, composed of a mutated mouse factor VII (mfVII) targeting domain and the Fc effector domain of an IgG1 Ig (mfVII/Fc icon), was tested with a severe combined immunodeficient (SCID) mouse model of human prostatic cancer and an immunocompetent mouse model of mouse prostatic cancer. The SCID mice were first injected s.c. with a human prostatic tumor line, forming a skin tumor that produces a high blood titer of prostate-specific antigen and metastasizes to bone. The icon was encoded in a replication-incompetent adenoviral vector that was injected directly into the skin tumor. The tumor cells infected by the vector synthesize and secrete the icon into the blood, and the blood-borne icon binds with high affinity and specificity to mouse tissue factor expressed on endothelial cells lining the lumen of the tumor vasculature and to human tissue factor expressed on the tumor cells. The Fc domain of the icon activates a cytolytic immune attack against cells that bind the icon. The immunotherapy tests in SCID mice demonstrated that intratumoral injections of the adenoviral vector encoding the mfVII/human Fc icon resulted in long-term regression of the injected human prostatic tumor and also of a distant uninjected tumor, without associated toxicity to the mice. Comparable results were obtained with a SCID mouse model of human melanoma. At the end of the experiments the mice appeared to be free of viable tumor cells. This protocol also could be efficacious for treating cancer patients who have vascularized tumors.

Tumors and fibrinogen. The role of fibrinogen as an extracellular matrix protein

The progression of a tumor from benign and localized to invasive and metastatic growth is the major cause of poor clinical outcome in cancer patients. Much like in a healing wound, the deposition of fibrin(ogen), along with other adhesive glycoproteins, into the extracellular matrix (ECM) serves as a scaffold to support binding of growth factors and to promote the cellular responses of adhesion, proliferation, and migration during angiogenesis and tumor cell growth. Inappropriate synthesis and deposition of ECM constituents is linked to altered regulation of cell proliferation, leading to tumor cell growth and malignant transformation. Fibrin deposition occurs within the stroma of a majority of tumor types. In contrast, abundant FBG, not fibrin, is present within the stroma of breast cancers. It is thought to originate from exudation of plasma FBG and subsequent deposition into the tumor stroma and not endogenous synthesis and secretion of FBG by breast tumor cells. However, we show that MCF-7 human breast cancer cells synthesize and secrete FBG polypeptides, suggesting that the origin of FBG in the stroma of breast carcinoma may be due to endogenous synthesis and deposition. Moreover, FBG assembles into ECM as conformationally altered FBG, not as fibrin. Studies in our laboratory demonstrate that FBG alters the ability of breast cancer cells to migrate. Together, the results of studies from our laboratory, as well as the laboratories of others, indicate that the presence of fibrin(ogen) within the tumor stroma likely affects the progression of tumor cell growth and metastasis. This review focuses on FBG within tumors and its relationship with other tumor constituents, ultimately focusing on the role of FBG in breast cancer.

Urokinase induces expression of its own receptor in Beas2B lung epithelial cells

Interaction between the urokinase-type plasminogen activator (uPA) and its receptor (uPAR) localizes cellular proteolysis and promotes cellular proliferation and migration. The interaction between uPA and uPAR at the surface of epithelial cells thereby contributes to the pathogenesis of lung inflammation and neoplasia. In this study, we sought to determine if uPA itself alters uPAR expression by lung epithelial cells. uPA enhanced uPAR expression as well as (125)I-uPA binding in Beas2B lung epithelial cells in a time- and concentration-dependent manner. The uPA-mediated induction of uPAR is not accomplished through its receptor and requires enzymatic activity. The low molecular weight fragment of uPA, lacking the receptor binding domain, was as potent as intact two-chain uPA in inducing expression of uPAR at the cell surface. Plasmin, the end product of plasminogen activation, did not alter uPA-mediated uPAR expression. Induction of uPAR by uPA represents a novel pathway by which epithelial cells can regulate uPAR-dependent cellular responses that may contribute to stromal remodeling in lung injury or neoplasia.

Effects of cancer chemotherapy on the blood fibrinogen concentrations of cancer patients

Blood fibrinogen concentrations and glutamic-pyruvic transaminase activities of 66 adult cancer inpatients (aged 22 - 70 years) were determined both before and after one or two chemotherapy regimens. The percentage of hepatoma patients with abnormal blood fibrinogen levels (< 1.5 or > 6.0 g/l) was higher (64.3% of 14 patients) than that in other cancer categories (19.2% of 52 patients). The mean blood fibrinogen concentrations of male (3.5 g/l) and female (4.5 g/l) cancer patients were higher than those previously reported for healthy humans (2.8 and 2.9 g/l, respectively). After chemotherapy, blood fibrinogen concentrations decreased in patients whose primary tumours were surgically removed (from 4.8 to 3.2 g/l) but increased (from 3.0 to 4.8 g/l) in those who did not undergo surgery. Glutamic-pyruvic transaminase activities did not appear to be related to blood fibrinogen levels. We conclude that the increase in mean blood fibrinogen levels of cancer patients is probably related to tumour growth. Different mechanisms may operate in patients with hepatoma.

No grip, no growth: the conceptual basis of excessive proteolysis in the treatment of cancer

The formation of new bloodvessels, called angiogenesis, is critical for a tumour to grow beyond a few mm(3) in size. A provisional matrix promotes endothelial cell adhesion, migration, proliferation and survival. Synthesis and degradation of this matrix closely resemble processes that occur during coagulation and fibrinolysis. Degradation of the matrix and fibrinolysis are tightly controlled and balanced by stimulators and inhibitors of the plasminogen activation system. Here we give an overview of these processes during tumour progression. We postulate a novel way to inhibit angiogenesis by removal of the matrix through specific and localised overstimulation of the plasminogen activation system.

Urinary tissue factor levels in neoplastic diseases

BACKGROUND

Abnormalities in laboratory coagulation and fibrinolysis parameters can be detected in cancer patients, and tissue factor (TF) is implicated. TF is produced by certain tumors and is increased in both tumor associated macrophages and blood monocytes (mTF). TF is also found in urine (uTF), and its levels may be clinically important.

MATERIALS AND METHODS

Using a simple and highly standardized kinetic chromogenic assay (KCA), we measured uTF levels in controls (normal, n=57; patients with renal stones, n=30), patients with benign and malignant conditions of the bladder (n=75), prostate (n=106), breast (n=94), and colorectum (n=62). Each benign disease group was subdivided into inflammatory and noninflammatory categories.

RESULTS

The controls and benign noninflammatory groups gave similar results and were, therefore, unified for further analysis. The malignant and inflammatory groups showed higher uTF levels than the controls (P<0.001 for bladder, P<0.01 prostate, P<0.001 breast, and P<0.001 for colorectum). The difference between malignant and benign inflammatory disease was significant for the bladder group (P<0.05). Cancer patients showed uTF activity above the upper quartile range of the normal control group--74.4% for bladder, 68.0% for prostate, 77.3% for breast and 73.0% for colorectal disease. uTF levels were related to tumor progression, patients survival time, serum prostate specific antigen (PSA), and static bone scan images (SBSI). Levels were also higher in patients with bladder cancer recurrence and those who subsequently died.

CONCLUSION

uTF levels are raised in malignant and inflammatory disease compared to controls and patients with noninflammatory conditions, and are related to tumor grade or stage, patients survival and to markers of tumor progression.

Resistance of cancer cells to immune recognition and killing

It is well recognized that, in order for a wound to heal, the fibrin clot must be eliminated by fibrinolytic enzymes. In certain instances, however, fibrin is ineffectively degraded or even not degraded. For example, in pregnancy, the placenta contains a layer of fibrin (Nitabuck's layer) which presents as 'self' to the immune system. Similar situations have been observed in many solid tumors. A hypothesis is presented according to which tumor cells can escape detection and attack by the immune system in most cancer patients. The tumor dons a 'coat' of the host's own protein on its cell surface. The coat is composed of fibrin and of a polymeric form of human serum albumin (HSA) which, by contrast to pure fibrin, is resistant to fibrinolytic degradation. Such a coated tumor appears as 'self' to the immune system, and thus is not detected as a tumor by the immune system (i.e. natural killer cells). When tumors are prepared for in vitro assays against drugs, they are routinely treated with proteolytic enzymes (e.g. pepsin, or chymotrypsin, etc.) which dissolve the protein coat, exposing the tumor cell surface to the drug. Thus, the in vivo existence of a coat on the tumor surface may explain why some drugs have little or no effect in vivo, while the same drugs are active in vitro.

Cytotoxic and antitumor effect of fibrinogen-methotrexate conjugate

In this paper we describe the chemical procedure of fibrinogen-methotrexate (F-MTX) conjugate preparation and its in vitro and in vivo antitumor activity. F-MTX conjugates were synthesized in reaction of fibrinogen with MTX N-hydroxysuccynimide ester. The conjugates were not cross-linked and were soluble in water. The results of the in vitro and in vivo studies have shown: (1) a lower in vitro cytotoxicity of the F-MTX conjugate as compared with MTX alone; (2) a significantly higher in vivo antitumor activity of the F-MTX conjugate in mice with P388 leukemia as compared with MTX alone; (3) a significantly increased in vivo lethal toxicity of F-MTX as compared with MTX. The results suggest the therapeutic utility of the fibrinogen-methotrexate conjugate and the usefulness of fibrinogen as a chemotherapeutic drug carrier. However, a new effort in the preparation of F-MTX conjugate should be made to decrease its in vivo toxicity.

Vascular permeability factor/vascular endothelial growth factor and the significance of microvascular hyperpermeability in angiogenesis

This Chapter has reviewed the literature concerning VPF/VEGF as a potent vascular permeabilizing cytokine. In accord with this important role, microvessels have been found to be hyperpermeable to plasma proteins and other circulating macromolecules at sites where VPF/VEGF and its receptors are overexpressed, i.e., in tumors, healing wounds, retinopathies, many important inflammatory conditions and in certain physiological processes, such as ovulation and corpus luteum formation. Moreover, microvascular hyperpermeability to plasma proteins was shown to have an important consequence: the laying down of a fibrin-rich extracellular matrix. This provisional matrix, in turn, favors and supports the ingrowth of fibroblasts and endothelial cells which, together, transform the provisional matrix into the mature stroma characteristic of tumors and healed wounds. Finally, we have considered the pathways by which these and other circulating macromolecules cross the endothelium of normal and VPF/VEGF-permeabilized microvessels. These pathways include VVOs and trans-endothelial openings that have been variously interpreted as inter-endothelial cell gaps or trans-endothelial cell pores. At least some trans-endothelial cell pores may arise from VVOs. In conclusion, these data provide new insights into the mechanisms of angiogenesis and stroma formation, insights which are potentially applicable to a wide variety of disease states and which may lead to identification of new targets for therapeutic intervention.

Inhibition of metastases by anticoagulants

Metastasis involves several distinct steps, including one in which the tumor cell, after entry into the bloodstream, comes to rest in a capillary located at the distant site where a metastatic tumor will ultimately form. Components of the blood-clotting pathway may contribute to metastasis by trapping cells in capillaries or by facilitating adherence of cells to capillary walls. Conceivably, anticoagulants could interfere with this step in the metastatic process. In this review, we have summarized current knowledge on the interaction of malignant cells, clotting factors, and anticoagulants. We used computerized (MEDLINE) and manual searches to identify studies done in humans, in animals, and in in vitro systems that were published in English between 1952 and 1998. We found many reports that the formation of metastatic tumors could be inhibited by heparin, a vitamin K antagonist (warfarin), and inhibitors of platelet aggregation (prostacyclin and dipyridamole). Despite these encouraging preliminary results and a compelling biochemical rationale, only limited information exists on the clinical use of anticoagulants for the prevention or treatment of metastatic cancer because there have been so few controlled and prospectively randomized studies on this topic. In view of the preliminary results, anticoagulants may hold promise for the prevention and treatment of metastases. We believe that larger controlled investigations are strongly warranted to evaluate the clinical potential of anticoagulants for the prevention and treatment of metastases in humans.

Binding of latent matrix metalloproteinase 9 to fibrin: activation via a plasmin-dependent pathway

The binding of two matrix metalloproteinases (MMP) to fibrin was evaluated. MMP-2 (72-kDa) and MMP-9 (92-, 130-, and 225-kDa) were selected since both contain a fibronectin-like region and fibronectin binds fibrin. Gelatin zymography indicated selective and dose dependent binding of MMP-9 to fibrin. No MMP-2 binding to fibrin occurred. Densitometry revealed that the 130- and 225-kDa forms demonstrated similar sigmoidal binding profiles whereas 92-kDa uptake was hyperbolic. Fibronectin and TIMP-1 competition studies indicated that the fibronectin and C-terminal MMP-9 domains, respectively, were not involved with fibrin binding. The MMP-9 collagen-like region may be of regulatory significance since type I and II fibrillar and type IV basement membrane collagens demonstrated fibrin binding. During fibrinolysis, latent fibrin-bound MMP-9 was processed to lower molecular weight forms consistent with proteolytic activation. This process was inhibited by epsilon-aminocaproic acid, indicating a plasmin-dependent pathway. The significance of these findings to procoagulant activity and MMP-mediated extracellular matrix destruction during inflammation and tumor invasion and metastasis is discussed.

Laparoscopic staging of bladder tumor: concerns about port site metastases

Since the first laparoscopic pelvic lymph node dissection (LPLND) was performed for prostate cancer, only one case of port site metastasis has been reported, an incidence of 0.1%. On the other hand, three cases of port site metastasis have been reported after laparoscopic staging of transitional-cell carcinoma (TCC) of the bladder, a reported incidence of almost 4%. Herein, we review the circumstances of these three cases and address the potential risk factors and possible preventive measures regarding LPLND and port site metastasis in patients with TCC of the bladder.

The in vivo activity of vascular endothelial growth factor isoforms in the avian embryo

The activity of the different isoforms of quail vascular endothelial growth factor (VEGF; 122, 146, 166 and 190 amino acids) were quantitatively examined in vivo by overexpression in the chicken embryo using the retroviral expression vector RCAS. All isoforms were potent inducers of vascularization and permeability. A linear relationship between expression of their mRNA and induction of vascularization and permeability was observed for all isoforms. Pattern formation and morphogenesis was otherwise not altered. Overexpression of qVEGF122 and 146 in the eye of chicken embryos did not induce vascularization of either the cornea or retina-which are avascular tissues in birds. We conclude that all isoforms of VEGF are potent inducers of angiogenesis dependent on a permissive environment.

Growth and Dissemination of Lewis Lung Carcinoma in Plasminogen-Deficient Mice

Plasminogen activation has been proposed to play a critical role in cancer invasion and metastasis. The effects of complete ablation of plasminogen activation in cancer was studied by inoculation of a metastatic Lewis lung carcinoma expressing high levels of plasminogen activator into plasminogen-deficient (Plg−/−) mice and matched control mice. Primary tumors developed in all mice with no difference in the rate of appearance between Plg−/− and control mice. However, the primary tumors in Plg−/− mice were smaller and less hemorrhagic and displayed reduced skin ulceration. In addition, dissemination of the tumor to regional lymph nodes was delayed in Plg−/− mice. Surprisingly, no quantitative differences were observed in lung metastasis between Plg−/− and control mice. In addition, Plg deficiency was compatible with metastasis of the primary tumor to a variety of other organs. Nevertheless, Plg−/− mice displayed a moderately increased survival after primary tumor resection. These findings suggest that plasmin-mediated proteolysis contributes to the morbidity and mortality of Lewis lung carcinoma in mice, but sufficient proteolytic activity is generated in Plg−/− mice for efficient tumor development and metastasis.