Macrophage-derived metalloelastase is responsible for the generation of angiostatin in Lewis lung carcinoma

Matrix metalloproteinases and their inhibitors in tumour growth and invasion

Controlled degradation of the extracellular matrix (ECM) is crucial for the growth, invasive capacity, metastasis and angiogenesis of tumours. Matrix metalloproteinases (MMPs), a family of zinc-dependent neutral endopeptidases that are collectively capable of degrading essentially all ECM components, apparently play an important role in all of these aspects of tumour development. In addition, there is recent evidence that MMPs are also important for tumour cell survival. At present, therapeutic intervention on tumour growth and invasion based on the inhibition of MMP activity is under intensive investigation, and several MMP inhibitors are already being used on malignant tumours of various organs in clinical trials. In this review we discuss the role of MMPs and their inhibitors in tumour invasion as a basis for prognostic purposes and for targeted therapeutic intervention in cancer.

Prolonged neoadjuvant treatment in locally advanced tumours: a novel concept based on biological considerations

BACKGROUND

Neoadjuvant chemotherapy is increasingly applied in patients with locally advanced cancers of many tumour types. Usually three cycles of chemotherapy are administered to reduce the tumour size prior to local therapy, and another three cycles thereafter. The chemotherapy certainly contributes to the improved outcome of this approach. However, biological factors within the primary tumour have been neglected, while they might also contribute to the eradication of micrometastases. We believe that the neoadjuvant strategy can be improved by optimally exploiting certain biological factors inherent to the primary tumour. In a group of patients with locally advanced breast cancer (LABC) we studied this concept. Recently we described the clinical results of this phase II study in patients with LABC treated with neoadjuvant chemotherapy plus granulocyte-macrophage colony-stimulating factor (GM-CSF). A remarkable good response and survival was seen. In contrast to other studies we applied six cycles of neoadjuvant treatment in stead of a sandwich approach consisting of three cycles before and three cycles after local therapy, leaving the primary tumour and draining lymph nodes in situ for a prolonged period. In addition, GM-CSF was administered as a haematopoietic growth factor in stead of granulocyte colony-stimulating factor (G-CSF) as GM-CSF has also immuno-stimulating properties. Our findings definitely warrant further exploration of prolonged neoadjuvant systemic treatment in combination with GM-CSF in other high risk primary tumours.

HYPOTHESES

The promising results of our study may be attributable to two potential biological phenomena. Firstly, the conservation of the tumour and its draining lymph nodes may prove to be an essential part of this approach, with particular emphasis on the activation of tumour specific cytotoxic T cells. Secondly, circulating angiogenesis inhibitors originating from the primary tumour may enhance the effect of chemotherapy on micrometastases.

Role of endothelial cell survival and death signals in angiogenesis

Angiogenesis, the process of new microvessel development, is encountered in a select number of physiological processes and is central to the pathogenesis of a wide variety of diseases. There is now convincing evidence that regulated patterns of endothelial cell survival and death, a process known as apoptosis, play a central role in the periodic remodeling of the vasculature, and in the timely evolution and regression of angiogenic responses. In this review we discuss the current evidence suggesting a role for inducers and inhibitors of angiogenesis as well as other mediators that modify endothelial cells functions in the survival and death of endothelial cells. We also discuss how dysregulation of apoptosis can lead to aberrant angiogenesis as demonstrated in the pathogenesis of retinopathy of prematurity and cancer.

Perspective: tumour spread--the problems of latency

Tumour latency, or dormancy, is a well-recognized clinical phenomenon and induction or maintenance of this state would appear to offer a novel therapeutic approach to limiting the effects of neoplastic disease. Current interest has focused on the role that neovascularization plays in this process and the consequences of shifts in the balance between angiogenic and anti-angiogenic peptides. Targeting tumour vasculature by the administration or induction of such anti-angiogenic peptides is close to clinical evaluation.

Matrix Metalloproteinases Generate Angiostatin: Effects on Neovascularization

Angiostatin, a cleavage product of plasminogen, has been shown to inhibit endothelial cell proliferation and metastatic tumor cell growth. Recently, the production of angiostatin has been correlated with tumor-associated macrophage production of elastolytic metalloproteinases in a murine model of Lewis lung cell carcinoma. In this report we demonstrate that purified murine and human matrix metalloproteinases generate biologically functional angiostatin from plasminogen. Macrophage elastase (MMP-12 or MME) proved to be the most efficient angiostatin-producing MMP. MME was followed by gelatinases and then the stomelysins in catalytic efficiency; interstitial collagenases had little capacity to generate angiostatin. Both recombinant angiostatin and angiostatin generated from recombinant MME-treated plasminogen inhibited human microvascular endothelial cell proliferation and differentiation in vitro. Finally, employing macrophages isolated from MME-deficient mice and their wild-type littermates, we demonstrate that MME is required for the generation of angiostatin that inhibits the proliferation of human microvascular endothelial cells.

Wound fluid from venous leg ulcers degrades plasminogen and reduces plasmin generation by keratinocytes

Plasminogen, the pro-enzyme of plasmin, aids various processes essential for normal, acute wound healing, such as fibrinolysis and cell migration. We have investigated if plasminogen is available to perform these functions in chronic wounds such as venous leg ulcers. We report that plasminogen is degraded by fluid from venous leg ulcers to a number of fragments, including kringle domains 1-3, an angiostatin-related protein. The enzyme responsible was inhibited by the serine protease inhibitor phenyl-methylsulfonyl fluoride, but was not inhibited by alpha1-anti-trypsin, an inhibitor of neutrophil elastase, by alpha2-anti-plasmin, an inhibitor of plasmin, or by the matrix metalloprotease inhibitor 1,10 phenanthroline. Plasminogen degraded by wound fluid was a weaker substrate than intact plasminogen for plasmin generation by the keratinocyte cell line HaCaT. These results suggest that serine protease activity in leg ulcer fluid degrades plasminogen and support the hypothesis that keratinocyte migration may be impaired in leg ulcers because of a reduced availability of intact plasminogen for plasmin generation.

Characterization of kringle domains of angiostatin as antagonists of endothelial cell migration, an important process in angiogenesis

Angiogenesis is a complex process that involves endothelial cell proliferation, migration, basement membrane degradation, and neovessel organization. Angiostatin, consisting of four homologous triple-disulfide bridged kringle domains, has previously been shown to exhibit profound inhibition of endothelial cell proliferation in vitro and angiogenesis in vivo. It was also demonstrated that angiostatin could suppress the growth of a variety of tumors via the blocking of angiogenesis. The primary aim of our study was to characterize the kringle domains of angiostatin for their inhibitory activities of endothelial cell migration in order to elucidate their contributions to the anti-angiogenic function of angiostatin. In this report, we demonstrate for the first time that the kringles of angiostatin play different roles in inhibiting endothelial cell migration, a crucial process in angiogenesis. Kringle 4, which has only marginal anti-proliferative activity, is among the most potent fragments in inhibiting endothelial cell migration (IC50 of approximately 500 nM). In contrast, kringle 1-3, which is equivalent to angiostatin in inhibiting endothelial cell proliferation, manifests only a modest anti-migratory effect. The combination of kringle 1-3 and kringle 4 results in an anti-migratory activity comparable to that of angiostatin. When kringle 1 is removed from kringle 1-3, the resulting kringle 2-3 becomes more potent than kringle 1-3. This implies that kringle 1, although virtually ineffective in inhibiting endothelial cell migration, may influence the conformation of kringle 1-3 to alter its anti-migratory activity. We also show that disruption of the kringle structure by reducing/alkylating agents markedly attenuates the anti-migratory activity of angiostatin, demonstrating the significance of kringle conformation in maintaining the anti-angiogenic activity of angiostatin. Our data suggest that different kringle domains may contribute to the overall anti-angiogenic function of angiostatin by their distinct anti-migratory activities.

Macrophage formation of angiostatin during inflammation. A byproduct of the activation of plasminogen

Angiostatin is a potent inhibitor of tumor angiogenesis and the growth of metastatic foci. Recent studies have indicated that neoplastic cells can generate angiostatin directly or in cooperation with tumor-associated macrophages. In studies reported here, we determined whether angiostatin is generated in mice under non-neoplastic settings. Utilizing murine RAW264.7 macrophages and thioglycollate-elicited peritoneal macrophages, we demonstrate that angiostatin-like fragments are generated as a byproduct of the proteolytic regulation of membrane-bound plasmin. Plasmin proteolysis and subsequent loss in membrane-bound plasmin activity requires active plasmin but was unaffected by inhibitors of metalloproteinases. Lysine binding fragments of plasmin, isolated from macrophage-conditioned media utilizing affinity chromatography, appeared as a major (48 kDa) and two minor bands (42 and 50 kDa) in SDS-polyacrylamide gel electrophoresis and were immunoreactive with anti-kringle 1-3 IgG. Each peptide begins with Lys77 and contains the entire sequence of angiostatin. The affinity isolated plasmin fragments inhibited bFGF-induced endothelial cell proliferation. Lavage fluid recovered from the peritoneal cavities of mice previously injected with thioglycollate contained angiostatin-like plasmin fragments similar to those generated in vitro. This is the first demonstration that angiostatin-like plasmin fragments are generated in a non-neoplastic inflammatory setting. Thus, in addition to regulating pericellular plasmin activity, proteolysis of plasmin generates inactive kringle-containing fragments expressing angiostatic properties.

Prothrombin kringle-2 domain has a growth inhibitory activity against basic fibroblast growth factor-stimulated capillary endothelial cells

Recently, O'Reilly et al. (O'Reilly, M. S., Holmgren, L., Shing, Y., Chen, C., Rosenthal, R. A., Moses, M., Lane, W. S., Cao, Y., Sage, E. H., and Folkman, J. (1994) Cell 79, 315-328; O'Reilly, M. S., Boehm, T., Shing, Y., Fukai, N., Vasios, G., Lane, W. S., Flynn, E., Birkhead, J. R., Olsen, B. R., and Folkman, J. (1997) Cell 88, 277-285) developed a simple in vitro angiogenesis assay system using bovine capillary endothelial cell proliferation and purified potent angiogenic inhibitors, including angiostatin and endostatin. Using a simple in vitro assay for angiogenesis, we purified a protein molecule that showed anti-endothelial cell proliferative activity from the serum of New Zealand White rabbits, which was stimulated by lipopolysaccharide. The purified protein showed only bovine capillary endothelial cell growth inhibition and not any cytotoxicity. This molecule was identified as a prothrombin kringle-2 domain (fragment-2) using Edman degradation and the amino acid sequence deduced from the cloned cDNA. Both the prothrombin kringle-2 domain released from prothrombin by factor Xa cleavage and the angiogenic inhibitor purified from rabbit sera exhibited anti-endothelial cell proliferative activity. The recombinant rabbit prothrombin kringle-2 domain showed potent inhibitory activity with half-maximal concentrations (ED50) of 2 microg/ml media. As in angiostatin, the recombinant rabbit prothrombin kringle-2 domain also inhibited angiogenesis in the chorioallantoic membrane of chick embryos.

Activated Endothelial Cells Induce Apoptosis in Leukemic Cells by Endothelial Interleukin-8

Tumor cells are eradicated by several systems, including Fas ligand-Fas and tumor necrosis factor (TNF)-tumor necrosis factor receptor (TNFR). In the previous study, we purified an apoptosis-inducing factor (AIF) to homogeneity from a medium conditioned by PDBu-treated HL-60 cells. N-terminal sequence analysis showed that AIF is identical to endothelial interleukin-8 (IL-8). A novel apoptosis system, in which endothelial cells participate via endothelial IL-8 release, is identified here. Human umbilical vein cells (VE cells) produce and secrete IL-8 by stimulation of IL-1 and TNF-. Endothelial IL-8, which is secreted from VE cells by stimulation of IL-1 and TNF- , induces apoptosis in myelogenous leukemia cell line K562 cells. Monocyte-derived IL-8 could not induce apoptosis in K562 cells. Moreover, interaction between VE cells and K562 cells induces the release of endothelial IL-8 from VE cells, and the attached K562 cells undergo apoptosis. Moreover, interactions between VE cell and other cell lines, such as HL-60, U937, Jurkat, and Daudi, induce the secretion of endothelial IL-8 and the induction of apoptosis in cell lines. Endothelial IL-8 significantly inhibits tumor growth of intraperitoneal and subcutaneous tumor mass of K562 cells and induces apoptosis in their cells in vivo. Endothelial IL-8 plays an important role in apoptosis involving endothelial cells, which may provide us with a new therapy for hematological malignancies.

© 1998 by The American Society of Hematology.

Activated Endothelial Cells Induce Apoptosis in Leukemic Cells by Endothelial Interleukin-8

Tumor cells are eradicated by several systems, including Fas ligand-Fas and tumor necrosis factor (TNF)-tumor necrosis factor receptor (TNFR). In the previous study, we purified an apoptosis-inducing factor (AIF) to homogeneity from a medium conditioned by PDBu-treated HL-60 cells. N-terminal sequence analysis showed that AIF is identical to endothelial interleukin-8 (IL-8). A novel apoptosis system, in which endothelial cells participate via endothelial IL-8 release, is identified here. Human umbilical vein cells (VE cells) produce and secrete IL-8 by stimulation of IL-1 and TNF-. Endothelial IL-8, which is secreted from VE cells by stimulation of IL-1 and TNF- , induces apoptosis in myelogenous leukemia cell line K562 cells. Monocyte-derived IL-8 could not induce apoptosis in K562 cells. Moreover, interaction between VE cells and K562 cells induces the release of endothelial IL-8 from VE cells, and the attached K562 cells undergo apoptosis. Moreover, interactions between VE cell and other cell lines, such as HL-60, U937, Jurkat, and Daudi, induce the secretion of endothelial IL-8 and the induction of apoptosis in cell lines. Endothelial IL-8 significantly inhibits tumor growth of intraperitoneal and subcutaneous tumor mass of K562 cells and induces apoptosis in their cells in vivo. Endothelial IL-8 plays an important role in apoptosis involving endothelial cells, which may provide us with a new therapy for hematological malignancies.

© 1998 by The American Society of Hematology.

Tissue inhibitors of metalloproteinases and metalloproteinases in atherosclerosis

The ability of the metalloproteinases to degrade extracellular matrix proteins is essential for the matrix remodelling that occurs during infiltration of inflammatory cells, intimal thickening, angiogenesis and plaque rupture which are a result of atherosclerosis. Increased metalloproteinase activity therefore requires stimulation of metalloproteinase expression by cytokines and growth factors, activation of metalloproteinases, and downregulation of tissue inhibitors of metalloproteinases. In addition, metalloproteinases may influence atherosclerosis by processing of proteins involved in inflammation and cell growth and death and the tissue inhibitors of metalloproteinases may also play a less inhibitory role by influencing cell growth and apoptosis.

Expression of human macrophage metalloelastase gene in hepatocellular carcinoma: correlation with angiostatin generation and its clinical significance

Macrophage metalloelastase, a member of the human matrix metalloproteinase family, is believed to play an important role in angiostatin generation, which, in experimental studies, has an antiangiogenic function and is a key molecule in tumor dormancy. However, no clinical studies have been reported regarding the correlation between human macrophage metalloelastase (HME) gene expression and angiostatin production. Therefore, the present study was designed to evaluate the HME messenger RNA (mRNA) expression and angiostatin generation in hepatocellular carcinoma (HCC). Tumorous and contiguous nontumorous tissues were obtained from 40 HCC patients who underwent curative partial hepatectomy. By using Northern blot hybridization, HME mRNA was detected in 25 of the 40 HCC samples and, in all of these cases, the expression in tumorous tissues was stronger than in the nontumorous tissues. In situ hybridization identified the HCC cells as mainly responsible for the signals shown in Northern blot. Angiostatin was detected by Western blot mainly in tumors and showed significant association with HME mRNA expression in tumorous tissues (P = .0008). The patients whose tumors did not express HME mRNA and, thus, did not produce angiostatin, demonstrated poorer survival than those whose tumors showed high expression of HME mRNA and angiostatin generation (P = . 002). The univariate and multivariate analyses revealed that HME mRNA expression is a new and independent variable affecting overall survival (P = .001 and P = .03, respectively). These findings show that the HME gene is expressed in HCC being significantly associated with angiostatin generation by such tumors and that HME mRNA expression may serve as a new molecular prognostic marker in HCC patients after partial hepatectomy.

Matrix metalloproteinase degradation of extracellular matrix: biological consequences

Targeted mutagenesis has allowed investigators to perform controlled experiments in mammals and determine the contribution of individual proteins to physiologic and pathologic processes. Recent lessons learned from matrix metalloproteinase gene targeted mice and other in vivo observations have given new life to old concepts regarding the role of proteolytic fragments of extracellular matrix proteins in regulating a variety of critical processes in cell biology.

Clinical evaluation of biologically targeted drugs: obstacles and opportunities

Recent insights into the molecular mechanisms of cancer have indicated that a variety of fundamental cellular processes are dysregulated in malignant cells. These processes include cell cycle control, signal transduction pathways, apoptosis, telomere stability, angiogenesis, and interactions with the extracellular matrix. Remarkable advances in molecular genetics, enzymology, and medicinal chemistry have permitted the design of compounds that modulate some of these processes with specificity that was unimaginable a decade ago. As these novel, biologically targeted compounds enter the clinic, they will require a strategy for clinical evaluation and development different from that used commonly for cytotoxic antineoplastic agents. This review examines the development of cancer drugs directed against angiogenesis, metastasis, signal transduction, telomerase, and molecular message (antisense), outlines strategies for the clinical testing of agents directed at these processes, and contrasts these efforts with traditional approaches to cancer drug testing.

Complex role of matrix metalloproteinases in angiogenesis

Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) play a significant role in regulating angiogenesis, the process of new blood vessel formation. Interstitial collagenase (MMP-1), 72 kDa gelatinase A/type IV collagenase (MMP-2), and 92 kDa gelatinase B/type IV collagenase (MMP-9) dissolve extracellular matrix (ECM) and may initiate and promote angiogenesis. TIMP-1, TIMP-2, TIMP-3, and possibly, TIMP-4 inhibit neovascularization. A new paradigm is emerging that matrilysin (MMP-7), MMP-9, and metalloelastase (MMP-12) may block angiogenesis by converting plasminogen to angiostatin, which is one of the most potent angiogenesis antagonists. MMPs and TIMPs play a complex role in regulating angiogenesis. An understanding of the biochemical and cellular pathways and mechanisms of angiogenesis will provide important information to allow the control of angiogenesis, e.g. the stimulation of angiogenesis for coronary collateral circulation formation; while the inhibition for treating arthritis and cancer.

Transforming growth factor-beta 1 inhibits generation of angiostatin by human pancreatic cancer cells

BACKGROUND

Angiostatin, a proteolytic fragment of plasminogen, is a potent inhibitor of angiogenesis. We have previously shown that the human pancreatic cancer cell line ASPC-1 produces enzymatic activity capable of generating angiostatin. In this study we sought to determine whether angiostatin production by ASPC-1 cells was regulated by the growth factor transforming growth factor-beta 1 (TGF-beta 1), a key mediator of tumor angiogenesis.

METHODS

ASPC-1 cells were grown to 70% to 80% confluence in 20% fetal calf serum-RPMI. Medium was changed to serum free. TGF-beta 1 was added at concentrations of 0, 1, 5, and 10 ng/mL with or without plasminogen activator inhibitor type-1 (PAI-1) at concentrations of 0, 5, 10, 50, and 100 micrograms/mL. Cells were then cultured for an additional 24 hours. The serum-free conditioned medium was obtained. Angiostatin generation was determined by incubating 20 micrograms of plasminogen with 100 microL of serum-free conditioned medium for 0, 1, 2, 3, 6, 12, and 24 hours. Samples were run on 12% sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transferred. The membrane was probed with a monoclonal antibody to the kringle 1-3 fragment of plasminogen and developed using enhanced chemiluminescence.

RESULTS

TGF-beta 1 and PAI-1 inhibited the conversion of plasminogen into angiostatin in a time- and dose-dependent manner. Antibody to PAI-1 completely blocks TGF-beta 1 mediated angiostatin inhibition.

CONCLUSIONS

TGF-beta 1 inhibits the generation of the antiangiogenic molecule angiostatin by human pancreatic cancer cells in a time- and dose-dependent manner. This effect is mediated through modulation of the plasminogen/plasmin system.

Angiostatin-mediated suppression of cancer metastases by primary neoplasms engineered to produce granulocyte/macrophage colony-stimulating factor

We determined whether tumor cells consistently generating granulocyte/macrophage colony- stimulating factor (GM-CSF) can recruit and activate macrophages to generate angiostatin and, hence, inhibit the growth of distant metastasis. Two murine melanoma lines, B16-F10 (syngeneic to C57BL/6 mice) and K-1735 (syngeneic to C3H/HeN mice), were engineered to produce GM-CSF. High GM-CSF (>1 ng/10(6) cells)- and low GM-CSF (<10 pg/10(6) cells)-producing clones were identified. Parental, low, and high GM-CSF-producing cells were injected subcutaneously into syngeneic and into nude mice. Parental and low-producing cells produced rapidly growing tumors, whereas the high-producing cells produced slow-growing tumors. Macrophage density inversely correlated with tumorigenicity and directly correlated with steady state levels of macrophage metalloelastase (MME) mRNA. B16 and K-1735 subcutaneous (s.c.) tumors producing high levels of GM-CSF significantly suppressed lung metastasis of 3LL, UV-2237 fibrosarcoma, K-1735 M2, and B16-F10 cells, but parental or low-producing tumors did not. The level of angiostatin in the serum directly correlated with the production of GM-CSF by the s.c. tumors. Macrophages incubated with medium conditioned by GM-CSF- producing B16 or K-1735 cells had higher MME activity and generated fourfold more angiostatin than control counterparts. These data provide direct evidence that GM-CSF released from a primary tumor can upregulate angiostatin production and suppress growth of metastases.

Matrix metalloproteinases (MMPs) and their physiological inhibitors (TIMPs) are differentially expressed during excisional skin wound repair

During cutaneous wound healing a number of migratory and remodeling events occur that require the action of matrix metalloproteinases (MMPs) and their natural inhibitors (TIMPs). In this study, we analyzed the temporal and spatial expression patterns of these molecules during the healing of murine excisional skin wounds. Our data imply that defined phases of repair rely on distinct repertoires of MMP activity and TIMP counterregulation. Reepithelialization was found to be associated with active production of collagenase, 92-kDa gelatinase, and stromelysins-1 and -2 by distinct subpopulations of keratinocytes at the migrating border. Notably, no TIMP transcripts were expressed in the epidermis, but TIMP-1 expression in the wound colocalized with expression of collagenase, 92-kDa gelatinase, and stromelysin-1, albeit in distinct cells. Concomitant with the formation of an extensive hyperproliferative epithelium, TIMP-1 transcripts accumulated at the mesenchymal/epidermal border of the granulation tissue. During later phases of wound repair, we observed an increase in 72-kDa gelatinase and MT1-MMP expression, whereby the transcripts of these colocalizing MMPs were detected exclusively and at high levels in the granulation tissue. At completion of reepithelialization, the expression levels of the MMPs and TIMP-1 seen in epidermal and dermal compartments declined to near-basal levels, whereas the macrophage-specific metalloelastase (MME) reached maximum expression. In reepithelialized wound tissue, MME transcripts were detected in deep layers of reconstituted dermis and seemed to cluster around vascular structures. Systemic glucocorticoid treatment, which is known to result in impaired wound healing, led to a nearly complete shut-off of MME expression. These observations imply an additional role of macrophage-related proteolysis, independent of its classical roles during earlier, inflammatory phases of cutaneous wound repair.

Angiostatin generation by human pancreatic cancer

BACKGROUND

Angiostatin, a proteolytic fragment of plasminogen, is a potent inhibitor of angiogenesis. In vitro, angiostatin can be generated by pancreatic elastase proteolysis of plasminogen; however, in vivo, the enzymes responsible for angiostatin production are not known. A recent study demonstrates the involvement of a serine protease in angiostatin generation. In this study we sought to determine if the human pancreatic carcinoma cell line ASPC1 produced enzymatic activity capable of converting plasminogen to angiostatin and to determine if urokinase plasminogen activator (uPA) is involved in this system. Methods. ASPC1 cells were grown to near confluence in 20% FBS-RPMI. Media were changed to serum free and cells cultured for an additional 24 h. The serum free conditioned media (SFCM) was obtained. Angiostatin generation was determined by incubating 20 microg of human plasminogen with 100 microl of SFCM for 0, 3, 8, 12, 24, and 48 h. Plasminogen cleavage was assessed in the presence of the following protease inhibitors: pefabloc, aprotinin, phosphoramidon, leupeptin, and EDTA. The effect of uPA on angiostatin generation was determined by incubating plasminogen with antibody to uPA. Angiostatin generation was determined by Western blot.

RESULTS

Incubation of plasminogen with SFCM resulted in the generation of immunoreactive bands at 48 kDa corresponding to human angiostatin. Angiostatin generation by ASPC1 SFCM was time dependent; there was a significant decrease in the plasminogen substrate beginning at 3 h with complete conversion to angiostatin by 48 h. Enzymatic activity leading to angiostatin production was found to be due to a serine protease. Antibody to uPA effectively blocked angiostatin production by ASPC1 SFCM in a dose-dependent manner.

CONCLUSION

Human pancreatic cancer cells express enzymatic activity which leads to the generation of angiostatin. Conversion of plasminogen to angiostatin is due to a serine protease. This serine protease is most likely uPA.

Angiostatin gene transfer: inhibition of tumor growth in vivo by blockage of endothelial cell proliferation associated with a mitosis arrest

The antitumoral effects that follow the local delivery of the N-terminal fragment of human plasminogen (angiostatin K3) have been studied in two xenograft murine models. Angiostatin delivery was achieved by a defective adenovirus expressing a secretable angiostatin K3 molecule from the cytomegalovirus promoter (AdK3). In in vitro studies, AdK3 selectively inhibited endothelial cell proliferation and disrupted the G2/M transition induced by M-phase-promoting factors. AdK3-infected endothelial cells showed a marked mitosis arrest that correlated with the down-regulation of the M-phase phosphoproteins. A single intratumoral injection of AdK3 into preestablished rat C6 glioma or human MDA-MB-231 breast carcinoma grown in athymic mice was followed by a significant arrest of tumor growth, which was associated with a suppression of neovascularization within and at the vicinity of the tumors. AdK3 therapy also induced a 10-fold increase in apoptotic tumor cells as compared with a control adenovirus. Furthermore, we showed that systemic injection of AdK3 delayed C6 tumor establishment and growth, confirming that angiostatin can function in a paracrin manner. Our data support the concept that targeted antiangiogenesis, using adenovirus-mediated gene transfer, represents a promising alternative strategy for delivering antiangiogenic factors as their bolus injections present unsolved pharmacological problems.

A human fibrosarcoma inhibits systemic angiogenesis and the growth of experimental metastases via thrombospondin-1

Concomitant tumor resistance refers to the ability of some large primary tumors to hold smaller tumors in check, preventing their progressive growth. Here, we demonstrate this phenomenon with a human tumor growing in a nude mouse and show that it is caused by secretion by the tumor of the inhibitor of angiogenesis, thrombospondin-1. When growing subcutaneously, the human fibrosarcoma line HT1080 induced concomitant tumor resistance, preventing the growth of experimental B16/F10 melanoma metastases in the lung. Resistance was due to the production by the tumor cells themselves of high levels of thrombospondin-1, which was present at inhibitory levels in the plasma of tumor-bearing animals who become unable to mount an angiogenic response in their corneas. Animals carrying tumors formed by antisense-derived subclones of HT1080 that secreted low or no thrombospondin had weak or no ability to control the growth of lung metastases. Although purified human platelet thrombospondin-1 had no effect on the growth of melanoma cells in vitro, when injected into mice it was able to halt the growth of their experimental metastases, providing clear evidence of the efficacy of thrombospondin-1 as an anti-tumor agent.

Different patterns of stromal and cancer cell thymidine phosphorylase reactivity in non-small-cell lung cancer: impact on tumour neoangiogenesis and survival

Angiogenesis is recognized as an important step in tumour pathogenesis that is related to invasion and metastatic spread and which consequently results in poor clinical outcome. In this study, we have examined the role of tumour stroma-activated fibroblasts and macrophage infiltration in the development of the angiogenic and metastatic phenotype in non-small-cell lung cancer (NSCLC). A total of 141 cases of early stage I-II NSCLC treated with surgery alone were analysed. The JC-70 (anti-CD31) MAb was used for the assessment of vascular grade. The P-GF.44C MAb was used to assess thymidine phosphorylase (TP) reactivity in cancer cells, stromal fibroblasts and macrophages. Cancer cell TP overexpression related to high vascular grade and to advanced T stage (P = 0.0004 and P = 0.02). Expression of TP in stromal fibroblasts also correlated with high angiogenesis (P = 0.01), but was independent of cancer cell expression. Fibroblast TP overexpression was related to abundant stroma (P = 0.003), suggesting that TP may be a marker of active stroma. Moreover, intense macrophage infiltration was associated with fibroblast TP reactivity, regardless of the amount of stroma, suggesting that macrophages may be a major contributor to TP expression in stroma. Survival analysis showed that cancer cell TP overexpression was related to poor prognosis (P = 0.005). Although stroma TP is related to angiogenesis, in the low vascular grade group it defined a group of patients with better prognosis (P = 0.02). It may be that fibroblast TP reactivity is an indirect marker of tumour infiltration by functional macrophages, which have an antitumour effect. We conclude that stromal macrophage and fibroblast TP reactivity may have an important role in non-small-cell lung cancer behaviour. Understanding the role of stromal fibroblasts and inflammatory cells and their interaction with oncoprotein expression is essential for the elucidation of lung cancer pathogenesis.

Role of HGF/SF and c-Met in morphogenesis and metastasis of epithelial cells

We have analysed the role of hepatocyte growth factor/scatter factor (HGF/SF) in the process of morphogenesis and metastasis of epithelial (carcinoma) cells. HGF/SF induces various morphogenic responses in epithelial cells that derive from different tissues when these are grown in three-dimensional gels, e.g. branching tubules in kidney, breast, and prostate epithelial cells, crypt-like structures with brush border in colon epithelial cells, and alveolar-like aggregates in lung and pancreas cells. Epithelial cells are thus able to form complex structures in vitro which resemble the structures formed in the organ they originate from. We also examined the response of human breast carcinoma cells to HGF/SF in vivo. MDA MB 435 cells transfected with HGF/SF were injected into the mammary fat pad of nude mice, where they form tumours which spontaneously metastasize to the lungs. We found that expression of HGF/SF promoted metastasis whereas expression of the cell adhesion molecule E-cadherin was inhibitory. Moreover, expression of E-cadherin reconstituted the ability of the cells to form complex structures in response to HGF/SF in vitro. These data demonstrate that the different responses to HGF/SF depend on the state of the epithelial cells: morphogenesis requires epithelial differentiation and cell polarity, whereas metastasis is observed when the cells have lost their epithelial characteristics. Moreover, we have recently identified Gab-1 as a direct-binding substrate of the c-Met receptor. Gab-1 binds to c-Met phosphorylated on tyrosine residues, but not to a number of other tyrosine kinases from different subfamilies. A newly identified proline-rich domain of Gab-1 is responsible for the binding to the bidentate docking site in c-Met. Expression of Gab-1 in epithelial cells is sufficient to induce c-Met-specific cellular responses which include the formation of branching tubules. Thus, Gab-1 seem to correspond to the substrate of the c-Met receptor tyrosine kinase that mediates the epithelial morphogenesis.

Expression of angiostatin cDNA in a murine fibrosarcoma suppresses primary tumor growth and produces long-term dormancy of metastases

Tumor growth and metastasis are angiogenesis dependent. Previously, we reported that angiostatin, a potent angiogenesis inhibitor, produced by a primary Lewis lung carcinoma suppressed its growth of lung metastases (O'Reilly, M.S., L. Holmgren, Y. Shing, C. Chen, R.A. Rosenthal, M. Moses, W.S. Lane, Y. Cao, E.H. Sage, and J. Folkman. 1994. Cell. 79:315-328). Now we show that a shift of balance of tumor angiogenesis by gene transfer of a cDNA coding for mouse angiostatin into murine T241 fibrosarcoma cells suppresses primary and metastatic tumor growth in vivo. Implantation of stable clones expressing mouse angiostatin in C57Bl6/J mice inhibits primary tumor growth by an average of 77%. After removal of primary tumors, the pulmonary micrometastases in approximately 70% of mice remain in a microscopic dormant and avascular state for the duration of the experiments, e.g., 2-5 mo. The tumor cells in the dormant micrometastases exhibit a high rate of apoptosis balanced by a high proliferation rate. Our study, to our knowledge, for the first time shows the diminished growth of lung metastases after removal of the primary tumor, suggesting that metastases are self-inhibitory by halting angiogenesis. Our data may also provide a novel approach for cancer therapy by antiangiogenic gene therapy with a specific angiogenesis inhibitor.

Angiostatin-converting enzyme activities of human matrilysin (MMP-7) and gelatinase B/type IV collagenase (MMP-9)

Angiostatin is one of the most potent inhibitors of angiogenesis. Reports have shown that metalloelastase, pancreas elastase, plasmin reductase, and plasmin convert plasminogen to angiostatin. However, the cleavage sites of plasminogen by those enzymes have not been determined. Here we demonstrate that two members of the human matrix metalloproteinase (MMP) family, matrilysin (MMP-7) and gelatinase B/type IV collagenase (MMP-9), hydrolyze human plasminogen to generate angiostatin fragments. The cleavage sites have been determined. The 58-kDa bands derived from plasminogen by MMP-7 and MMP-9 both have the N-terminal sequence KVYLSEXKTG, which corresponds to that of angiostatin. This N terminus is identical to that of the starting plasminogen itself and corresponds to residues 97-106 of prepro-plasminogen. The 42- and 38-kDa bands generated by MMP-7 both have the N-terminal sequence VVLLPNVETP, which corresponds to the amino acid sequence 467-476 of prepro-plasminogen, between kringle domain 4 and 5. MMP-9 cleaves plasminogen to generate a 42-kDa fragment with the N-terminal sequence PVVLLPNVE, 1 residue upstream of the MMP-7 cleavage site. These results indicate that MMP-7 and MMP-9 may regulate new blood vessel formation by cleaving plasminogen and generating angiostatin molecules.

Matrix metalloproteinases in skin

Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases collectively capable of degrading essentially all extracellular matrix components. These enzymes can be produced by several different types of cells in skin such as fibroblasts, keratinocytes, macrophages, endothelial cells, mast cells, and eosinophils and their activity can be specifically inhibited by TIMPs (tissue inhibitors of metalloproteinases), which bind to active MMPs with 1:1 stoichiometry. In general, MMPs are not constitutively expressed in skin but are induced temporarily in response to exogenous signals such as various cytokines, growth factors, cell matrix interactions and altered cell-cell contacts. At present, more evidence is accumulating that MMPs play an important role in proteolytic remodeling of extracellular matrix in various physiologic situations, including developmental tissue morphogenesis, tissue repair, and angiogenesis. On the other hand, MMPs play an important pathogenetic role in excessive breakdown of connective tissue components, e.g. in rheumatoid arthritis, osteoarthritis, chronic ulcers, dermal photoageing, and periodontitis, as well as in tumor cell invasion and metastasis. In this review we discuss the role of MMPs and TIMPs in human skin based on new observations on the regulation of the expression of MMPs, on their substrate specificity, and MMP expression in physiologic and pathologic conditions of skin involving matrix remodeling. Furthermore, therapeutic modalities based on regulating MMP activity will be reviewed.

Factors controlling ocular angiogenesis

PURPOSE

To provide an overview of the cellular and molecular factors involved in ocular angiogenesis.

METHODS

A literature search and review encompassing a broad range of medical and basic science disciplines was undertaken to survey contemporary insights into the mechanisms of angiogenic stimulation and inhibition.

RESULTS

Ocular angiogenesis is a complex pathophysiologic process. Factors have been isolated that play key roles in the regulation of angiogenesis. The influence of stimulating growth factors is counterbalanced by a number of antiproliferative agents. The net result of these opposing factors on the vascular endothelial cell determines the outcome of angiogenesis homeostasis. Both endogenous and synthetic molecules can regulate ocular angiogenesis.

CONCLUSIONS

The isolation and synthesis of molecular regulators of angiogenesis has enhanced our understanding of this process. Clinical trials are underway to determine the efficacy of these agents in controlling pathologic angiogenesis, including that in ocular disease.

The mechanism of cancer-mediated conversion of plasminogen to the angiogenesis inhibitor angiostatin

Angiostatin, a potent naturally occurring inhibitor of angiogenesis and growth of tumor metastases, is generated by cancer-mediated proteolysis of plasminogen. Human prostate carcinoma cells (PC-3) release enzymatic activity that converts plasminogen to angiostatin. We have now identified two components released by PC-3 cells, urokinase (uPA) and free sulfhydryl donors (FSDs), that are sufficient for angiostatin generation. Furthermore, in a defined cell-free system, plasminogen activators [uPA, tissue-type plasminogen activator (tPA), or streptokinase], in combination with one of a series of FSDs (N-acetyl-L-cysteine, D-penicillamine, captopril, L-cysteine, or reduced glutathione] generate angiostatin from plasminogen. An essential role of plasmin catalytic activity for angiostatin generation was identified by using recombinant mutant plasminogens as substrates. The wild-type recombinant plasminogen was converted to angiostatin in the setting of uPA/FSD; however, a plasminogen activation site mutant and a catalytically inactive mutant failed to generate angiostatin. Cell-free derived angiostatin inhibited angiogenesis in vitro and in vivo and suppressed the growth of Lewis lung carcinoma metastases. These findings define a direct mechanism for cancer-cell-mediated angiostatin generation and permit large-scale production of bioactive angiostatin for investigation and potential therapeutic application.

Kringle 5 of plasminogen is a novel inhibitor of endothelial cell growth

Angiostatin is a potent angiogenesis inhibitor which has been identified as an internal fragment of plasminogen that includes its first four kringle modules. We have recently demonstrated that the anti-endothelial cell proliferative activity of angiostatin is also displayed by the first three kringle structures of plasminogen and marginally so by kringle 4 (Cao, Y., Ji, R.-W., Davidson, D., Schaller, J., Marti, D., Sohndel, S., McCance, S. G., O'Reilly, M. S. , Llinás, M., and Folkman, J. (1996) J. Biol. Chem. 271, 29461-29467). We now report that the kringle 5 fragment of human plasminogen is a specific inhibitor for endothelial cell proliferation. Kringle 5 obtained as a proteolytic fragment of human plasminogen displays potent inhibitory effect on bovine capillary endothelial cells with a half-maximal concentration (ED50) of approximately 50 nM. Thus, kringle 5 would appear to be more potent than angiostatin on inhibition of basic fibroblast growth factor-stimulated capillary endothelial cell proliferation. Appropriately folded recombinant mouse kringle 5 protein, expressed in Escherichia coli, exhibits a comparable inhibitory effect as the proteolytic kringle 5 fragment. Thus, kringle 5 domain of human plasminogen is a novel endothelial inhibitor that is sufficiently potent to block the growth factor-stimulated endothelial cell growth.

Generation of angiostatin by reduction and proteolysis of plasmin. Catalysis by a plasmin reductase secreted by cultured cells

Extracellular manipulation of protein disulfide bonds has been implied in diverse biological processes, including penetration of viruses and endotoxin into cells and activation of certain cytokine receptors. We now demonstrate reduction of one or more disulfide bonds in the serine proteinase, plasmin, by a reductase secreted by Chinese hamster ovary or HT1080 cells. Reduction of plasmin disulfide bond(s) triggered proteolysis of the enzyme, generating fragments with the domain structure of the angiogenesis inhibitor, angiostatin. Two of the known reductases secreted by cultured cells are protein disulfide isomerase and thioredoxin, and incubation of plasmin with these purified reductases resulted in angiostatin fragments comparable with those generated from plasmin in cell culture. Thioredoxin-derived angiostatin inhibited proliferation of human dermal microvascular endothelial cells with half-maximal effect at approximately 0.2 microg/ml. Angiostatin made by cells and by purified reductases contained free sulfhydryl group(s), and S-carbamidomethylation of these thiol group(s) ablated biological activity. Neither protein disulfide isomerase nor thioredoxin were the reductases used by cultured cells, because immunodepletion of conditioned medium of these proteins did not affect angiostatin generating activity. The plasmin reductase secreted by HT1080 cells required a small cofactor for activity, and physiologically relevant concentrations of reduced glutathione fulfilled this role. These results have consequences for plasmin activity and angiogenesis, particularly in the context of tumor growth and metastasis. Moreover, this is the first demonstration of extracellular reduction of a protein disulfide bond, which has general implications for cell biology.

Suppression of tumor growth with recombinant murine angiostatin

Angiostatin, a 38 kDa internal fragment of plasminogen, is an antiangiogenic endothelial cell inhibitor. It regresses several primary and metastatic tumors in mice. To produce recombinant angiostatin for further structural and functional studies, the mouse angiostatin gene preceded by a sequence including a signal peptide of plasminogen was introduced into baculovirus. Recombinant murine angiostatin was purified from the culture medium of angiostatin baculovirus-infected insect cells (yield = 1 mg/liter) with a single-step of lysine-Sepharose chromatography. The angiostatin baculovirus-infected insect cells expressed and secreted a 52 kDa polypeptide that demonstrated all of the biological activities of angiostatin. A partial amino acid sequence of the NH2-terminus of the secreted protein revealed that the signal peptide was recognized and properly cleaved in insect cells. The recombinant murine angiostatin potently inhibited the proliferation of bovine capillary endothelial cells in vitro (half maximal inhibition = 50 ng/ml) and suppressed the growth of primary Lewis lung carcinoma in vivo (6 mg/kg/day, T/C = 0.08).