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

Matrix metalloproteinases and matrikines in angiogenesis

Neoangiogenesis, the formation of new blood capillaries from pre-existing vessels, plays an important role in a number of physiological and pathological processes, particularly in tumor growth and metastasis. Extracellular proteolysis by matrix metalloproteinases or other neutral proteinases is an absolute requirement for initiating tumor invasion and angiogenesis. Cryptic segments or pre-existing domains within larger proteins, most of them belonging to the extracellular matrix, can be exposed by conformational changes and/or generated by partial enzymatic hydrolysis. They can positively or negatively regulate important functions of endothelial cells including adhesion, migration, proliferation, cell survival and cell-cell interactions. Such regulations by cryptic segments and proteolytic fragments led to the concept of matricryptins and matrikines, respectively. Matrix metalloproteinases and matrikines in conjunction with other pro- or anti-angiogenic factors might act in concert at any step of the angiogenesis process. A number of matrikines have been identified as potent anti-angiogenic factors, which could provide a new alternative to anti-proteolytic strategies for the development of anti-angiogenic therapeutic molecules aimed at inhibiting tumor growth and metastasis. Some of them are currently being investigated in clinical trials.

Aerosolized granulocyte macrophage colony-stimulating factor (GM-CSF) therapy in metastatic cancer

A recent phase I study of aerosolized granulocyte macrophage colony-stimulating factor (GM-CSF) in patients with malignant metastases to the lungs demonstrated excellent tolerance and possible efficacy. This therapy was offered to other patients who refused "standard" treatment or when no effective therapy was available. Forty-five patients were treated; 40 had pulmonary metastases. Aerosolized GM-CSF (250 microg/dose) was administered twice a day using a 1 week on, 1 week off schedule. The mean interval between diagnosis and therapy was 32 months. Twenty-four patients had disease stabilization or partial regression. The mean duration of benefit was 10 months. This benefit was noted in 8 of 13 with a sarcoma, 6 of 14 with melanoma, and 5 of 12 with renal cell carcinoma. Eighteen patients reported mostly self-limiting toxicities. The frequency of certain melanoma-specific T lymphocytes in 1 patient with stable disease was found to have increased 10-fold after therapy. Aerosolized GM-CSF appears to have limited but promising efficacy in treatment of pulmonary metastatic disease. In one patient, we have evidence of upregulation of melanoma-specific cytotoxic T-cells. Further study is warranted to understand the impact of this therapy on the natural history of metastatic cancer.

Elements regulating angiogenesis and correlative microvessel density in benign hyperplastic and malignant prostate tissue

PURPOSE

To quantify the ex vivo production of proangiogenic proteins (vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), urokinase-type plasminogen activator (u-PA), tissue-type plasminogen activator (tPA)) and angiogenesis inhibitors (plasminogen activator inhibitor type-1 (PAI-1) and angiostatin) from epithelial and stromal components of primary prostate cancer (CaP) and benign prostatic hyperplasia (BPH) cultures. To perform microvessel density (MVD) counts on sections of BPH and CaP from the same prostatectomy specimens.

SCOPE

Angiogenic cytokine expression was measured by immunoassays and in vitro angiostatin generating capacities assessed using immunoblotting. CaP and BPH tissue was immunostained using factor VIII antibody to determine MVD.

CONCLUSIONS

Elements regulating angiogenesis are present in both primary cultures of CaP and BPH, suggesting that angiogenic ability is well established in the absence of carcinoma.

Matrix metalloproteinases and tumor progression

The matrix metalloproteinases (MMPs) are a family of more than 20 distinct enzymes that are frequently overexpressed in human tumors. Functional studies have shown that MMPs play an important role in the proteolytic destruction of extracellular matrix and basement membranes, thereby facilitating tumor invasion and metastasis. In addition, these enzymes may also be important in other steps of tumor evolution including neoplastic cell proliferation and angiogenesis stimulation. On the basis of the relevance of MMPs in tumor progression, a number of different strategies aimed to block the unwanted activity of these enzymes in cancer have been developed. Unfortunately, most clinical trials with the first series of MMP inhibitors have failed to show clear benefit in patients with advanced cancer. Explanations for this lack of success include the failure to recognize the role of these enzymes in early stages of the disease as well as inadequacy of either the employed inhibitors or the proteases to be targeted. The introduction of novel concepts such as tumor degradome, and global approaches to protease analysis, may facilitate the identification of the relevant MMPs that must be targeted in each individual cancer patient. On the other hand, the finding that MMPs are enzymes whose effects on biologically active substrates can have profound consequences on cell behaviour, suggests that selective inhibition of a limited set of MMPs at early stages of tumor evolution might be much more effective than using wide-spectrum inhibitors active against most family members, and administered to patients at late stages of the disease. Further studies directed to elucidate these questions will be necessary to clarify whether any of the multiple strategies of MMP inhibition may be part of future therapeutic approaches to control tumor progression.

Cell Surface-Dependent Generation of Angiostatin4.5

Angiostatin4.5 (AS4.5) is a naturally occurring human angiostatin isoform, consisting of plasminogen kringles 1-4 plus 85% of kringle 5 (amino acids Lys78 to Arg529). Prior studies indicate that plasminogen is converted to AS4.5 in a two-step reaction. First, plasminogen is activated to plasmin. Then plasmin undergoes autoproteolysis within the inner loop of kringle 5, which can be induced by a free sulfhydryl donor or an alkaline pH. We now demonstrate that plasminogen can be converted to AS4.5 in a cell membrane-dependent reaction. Actin was shown previously to be a surface receptor for plasmin(ogen). We now show that beta-actin is present on the extracellular membranes of cancer cells (PC-3, HT1080, and MDA-MB231), and beta-actin can mediate plasmin binding to the cell surface and autoproteolysis to AS4.5. In the presence of beta-actin, no small molecule-free sulfhydryl donor is needed for generation of AS4.5. Antibodies to actin reduced membrane-dependent generation of AS4.5 by 70%. In a cell-free system, addition of actin to in vitro-generated plasmin resulted in stoichiometric conversion to AS4.5. Annexin II and alpha-enolase have been reported to be plasminogen receptors, but we did not demonstrate a role for these proteins in conversion of plasminogen to AS4.5. Our data indicate that membrane-associated beta-actin, documented previously as a plasminogen receptor, is a key cell membrane receptor capable of mediating conversion of plasmin to AS4.5. This conversion may serve an important role in regulating tumor angiogenesis, invasion, and metastasis, and surface beta-actin may also serve as a prognostic marker to predict tumor behavior.

Human kallikrein 6 activity is regulated via an autoproteolytic mechanism of activation/inactivation

Human kallikrein 6 (protease M/zyme/neurosin) is a serine protease that has been suggested to be a serum biomarker for ovarian cancer and may also be involved in pathologies of the CNS. The precursor form of human kallikrein 6 (pro-hK6) was overexpressed in Pichia pastoris and found to be autoprocessed to an active but unstable mature enzyme that subsequently yielded the inactive, self-cleavage product, hK6 (D81-K244). Site-directed mutagenesis was used to investigate the basis for the intrinsic catalytic activity and the activation mechanism of pro-hK6. A single substitution R80 --> Q stabilized the activity of the mature enzyme, while substitution of the active site serine (S197 --> A) resulted in complete loss of hK6 proteolytic activity and facilitated protein production. Our data suggest that the enzymatic activity of hK6 is regulated by an autoactivation/autoinactivation mechanism. Mature hK6 displayed a trypsin-like activity against synthetic substrates and human plasminogen was identified as a putative physiological substrate for hK6, as specific cleavage at the plasminogen internal bond S460-V461 resulted in the generation of angiostatin, an endogenous inhibitor of angiogenesis and metastatic growth.

Matrix metalloproteinase-12 (MMP-12) in osteoclasts: new lesson on the involvement of MMPs in bone resorption

Osteoclasts require matrix metalloproteinase (MMP) activity and cathepsin K to resorb bone, but the critical MMP has not been identified. Osteoclasts express MMP-9 and MMP-14, which do not appear limiting for resorption, and the expression of additional MMPs is not clear. MMP-12, also called metalloelastase, is reported only in a few cells, including tissue macrophages and hypertrophic chondrocytes. MMP-12 is critical for invasion and destruction in pathologies such as aneurysm and emphysema. In the present study, we demonstrate that osteoclasts express MMP-12, although only in some situations. Northern blots show that highly purified rabbit osteoclasts in culture express MMP-12 at the same level as macrophages, whereas in situ hybridizations performed on rabbit bone do not show any MMP-12 expression in osteoclasts whatever the bone type. In contrast, in situ hybridizations performed on mouse bone show MMP-12 expression in osteoclasts in calvariae and long bones. We also demonstrate that recombinant MMP-12 cleaves the putative functional domains of osteopontin and bone sialoprotein, two bone matrix proteins that strongly influence osteoclast activities, such as attachment, spreading and resorption. Furthermore, we investigated the role of MMP-12 in bone resorption and osteoclast recruitment by comparing MMP-12 knockout and wild-type mice in specialized culture models known to depend on MMP activity, as well as in the ovariectomy model, and we did not find any indication for a limiting role of MMP-12 in these processes. In conclusion, we found that osteoclasts are able to express MMP-12, but MMP-12 did not appear critical for osteoclast recruitment or resorption. The fact that none of the MMPs identified so far in osteoclasts appears limiting for resorption, gives strength to the hypothesis that the critical MMP for bone solubilization is produced by non-osteoclastic cells.

Metastasis and angiogenesis

Angiogenesis and the development of metastases are intrinsically connected. Experimental data suggest that establishment and growth of metastases are influenced by soluble factors secreted from the originating solid tumor. Among these factors are so-called endogenous inhibitors of angiogenesis which keep metastasis in a non-proliferating quiescent state. For a number of tumors it has been shown that this dormant state is mediated through inhibition of angiogenesis. This dormant state is characterized by normal proliferation, increased apoptosis, and insufficient neovascularization. Removal of inhibiting antiangiogenic factors leads to growth of dormant metastases. Several endogenous inhibitors have been identified so far and some of them have already been successfully applied in experimental therapeutic trials. This might be of special interest for the treatment of cerebral metastases which are the most common type of malignant brain tumors. Similar to the spread of metastases, it is known that single glioma cells can be found in distant parts of the brain. While local recurrence is a common phenomenon in glioma, formation of clinical apparent distant metastasis occurs rarely. Several lines of evidence suggest that growth inhibition of remote glioma cells may be mediated by an endogenous inhibitory mechanism.

Anti-tumor activity of a combination of plasminogen activator and captopril in a human melanoma xenograft model

Angiostatin, a proteolytic fragment of plasminogen consisting of the first 3 or 4 kringle domains, reduces tumor growth by specifically inhibiting tumor angiogenesis. Angiostatin is generated in vitro in a 2-step process. First, plasminogen is converted to plasmin by plasminogen activators. Next, plasmin excises the angiostatin fragment from plasminogen, a process requiring molecules that are able to donate a free sulfhydryl group. In this study, we investigated whether stimulation of in vivo angiostatin generation by administration of plasminogen activator and a free sulfhydryl group donor (FSD) has anti-tumor activity. First, we determined the optimal conditions for in vitro angiostatin generation by incubating murine plasma with different concentrations of plasminogen activator and/or the FSD captopril. Angiostatin generation was monitored by western blot analysis. Our results were extrapolated to the in vivo situation by administering the optimal dose of tissue-type plasminogen activator (tPA, i.v. injection 3 times/week) and captopril (in drinking water) to mice and analyzing the presence of angiostatin in the circulation. Angiostatin was readily detectable in mice receiving both tPA and captopril, but not in mice receiving either one of the agents. Finally, the anti-tumor activity of the tPA/captopril treatment was tested in a human melanoma xenograft model. Administration of tPA alone had only a marginal effect on tumor growth. Captopril alone reduced tumor growth by about 60%, whereas treatment with both captopril and tPA resulted in 83% inhibition of tumor growth.

What the structure of angiostatin may tell us about its mechanism of action

Originally discovered in 1994 by Folkman and coworkers, angiostatin was identified through its antitumor effects in mice and later shown to be a potent inhibitor of angiogenesis. An internal fragment of plasminogen, angiostatin consists of kringle domains that are known to be lysine-binding. The crystal structure of angiostatin was the first multikringle domain-containing structure to be published. This review will focus on what is known about the structure of angiostatin and its implications in function from the current literature.

Sequence-specific silencing of MT1-MMP expression suppresses tumor cell migration and invasion: importance of MT1-MMP as a therapeutic target for invasive tumors

Membrane-type 1 matrix metalloproteinase (MT1-MMP/MMP-14) has been believed a key enzyme in tumor invasion, because it is expressed in a variety of malignant human tumors, and overexpression of the enzyme enhances the ability of cellular invasiveness. However, it has not necessarily been clarified whether the endogenously expressed MT1-MMP in human tumors plays a critical role in their invasiveness. We used RNA silencing technology to downregulate the endogenous MT1-MMP expression in human tumor cells (fibrosarcoma HT1080 and gastric carcinoma MKN-28 cell lines), and evaluated the effect on the invasion of a reconstituted basement membrane (Matrigel). Transfection of a double-stranded RNA targeted to the MT1-MMP gene decreased the level of the enzyme to less than 10-20% without affecting production of other MMPs. According to the degree of silencing, activation of proMMP-2 was inhibited. CD44 shedding was also inhibited, but only in part. Decreased MT1-MMP levels were also reflected in reduced cell motility on hyaluronan (HA) and invasion in Matrigel. Thus, specific downregulation of MT1-MMP expression was sufficient to cause significant inhibition of the migration and invasion of tumor cells, even though other MMPs continued to be expressed.

Cyclooxygenase-2 overexpression inhibits cathepsin D-mediated cleavage of plasminogen to the potent antiangiogenic factor angiostatin

Overexpression of cyclooxygenase (COX)-2 and enhanced synthesis of prostaglandin E2 (PGE2) have been implicated in human endometrial pathologies. To investigate the molecular role of COX-2, the Ishikawa human endometrial epithelial cell line was stably transfected with the pIRES2 vector containing COX-2 cDNA in either the sense or antisense directions. PGE2 concentrations were significantly elevated in the cells transfected with the COX-2 sense compared with wild-type cells or cells transfected with the antisense cDNA (P < 0.01). Elevated PGE2 synthesis was associated with enhanced expression and signaling of PGE2 receptors (EP). cDNA array analysis revealed differential expression of cathepsin D between the COX-2 sense and antisense cells. Cathepsin D RNA and protein expression was 6.7- and 2.1-fold lower in the COX-2 sense compared with COX-2 antisense cells respectively. Cathepsin D is known to cleave plasminogen to the potent antiangiogenic factor angiostatin. To investigate differential angiostatin generation, conditioned media from COX-2 sense, COX-2 antisense and wild-type cells were incubated with plasminogen and subsequently subjected to Western blot analysis. In comparison to wild-type cells, the cleavage of plasminogen to angiostatin was abolished when incubated in COX-2 sense cells conditioned media and elevated when incubated in COX-2 antisense cells conditioned media. Coincubation of plasminogen with the cathepsin D inhibitor pepstatin A inhibited the cleavage of plasminogen to angiostatin in the COX-2 antisense conditioned media. These data demonstrate that COX-2 exerts a negative feedback on the expression of cathepsin D. This in turn reduces the generation of the antiangiogenic factor angiostatin, hence promoting a proangiogenic environment.

Generation and role of angiostatin in human platelets

Platelets regulate new blood vessel growth, because they contain a number of angiogenesis promoters and inhibitors. Additionally, platelets contain matrix metalloproteinases (MMPs), which when released mediate platelet adhesion and aggregation, and plasminogen, a fibrinolytic system enzyme that serves to limit blood clot formation. Enzymatic cleavage of plasminogen by MMPs generates angiostatin, an angiogenesis inhibitor. Therefore, we examined whether platelets generate angiostatin during aggregation in vitro. Platelets were isolated from healthy human donors and then aggregated with collagen, thrombin, or HT-1080 fibrosarcoma cells. Angiostatin was detected by Western blot analysis in the platelet releasates of all blood donors irrespective of the aggregating agent used. Platelet pellet homogenates showed the presence of angiostatin in all donors, which was released upon aggregation. Furthermore, platelet-derived angiostatin was isolated and purified by lysine-Sepharose affinity chromatography from collagen-aggregated platelet releasates. Bioassay of platelet-derived angiostatin showed that it inhibited the formation of capillary structures by human umbilical vein endothelial cells (HUV-EC-Cs) in an in vitro angiogenesis model. Inhibition of angiostatin in platelet releasates promoted the formation of capillary structures by HUV-EC-Cs. We conclude that healthy human platelets contain angiostatin, which is released in active form during platelet aggregation, and platelet-derived angiostatin has the capacity to inhibit angiogenesis.

Increased expression of MMP-2 and MMP-9 in esophageal squamous cell carcinoma

PURPOSE

Matrix metalloproteinases (MMPs) are known to play an important role in extracellular matrix remodeling during the process of tumor invasion and metastasis. However, little is known about their role in preinvasive lesions and early esophageal carcinomas.

METHOD

Immunohistochemical analysis of matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9) expression was carried out in paraffin-embedded sections of surgically resected esophageal squamous cell carcinoma (ESCC) (58 cases) and paired distal normal esophageal tissues (44 cases) and correlated with clinicopathological parameters.

RESULT

Overexpression of MMP-2 and MMP-9 proteins was observed in 39 (67%) and 32 (55%) of the 58 ESCCs, respectively localized in tumor cell cytoplasm and stromal elements. Histological evaluation of hematoxylin- and eosin-stained 44 matched distal normal esophageal tissue sections revealed that 26 comprised of normal epithelium, while 15 tissues showed evidence of dysplasia and three tissues showed hyperplasia. Interestingly, 12 (80%) and 13 (87%) of these 15 dysplasias showed immunostaining for MMP-2 and MMP-9 proteins, respectively. Low levels of MMP-2 and MMP-9 were observed in 10 (38%) and 6 (23%) of 26 matched histologically normal esophageal tissues, respectively. Higher MMP-2 immunopositivity was observed in well and moderately differentiated SCCs in comparison with poorly differentiated tumors. The expression of MMP-2 was significantly reduced with the progressive de-differentiation of esophageal SCCs ( P =0.03). Overexpression of MMP-2 and MMP-9 in dysplasia as well as SCC suggests that these alterations occur in early stages of esophageal tumorigenesis.

CONCLUSION

Increased levels of MMP-2 and MMP-9 proteins in ESCCs as compared to normal esophageal tissues suggest their association with esophageal tumorigenesis. Increased levels of these MMPs are observed in majority of dysplasias analyzed herein, indicating that these alterations may be early events in esophageal tumorigenesis. In-depth studies are warranted to determine their role in development and progression of esophageal cancer.

MMP-2 and MMP-9 synergize in promoting choroidal neovascularization

Matrix metalloproteinase 2 (MMP-2) and MMP-9 are increased in human choroidal neovascularization (CNV) occurring during the exudative most aggressive form of age-related macular degeneration (AMD), but their precise role and potential interactions remain unclear. To address the question of MMP-2 and MMP-9 functions, mice deficient in the expression of MMP-2 (MMP-2 KO), MMP-9 (MMP-9 KO), and both MMP-2 and MMP-9 (MMP-2,9 KO) with their corresponding wild-type mice (WT) underwent CNV induction by laser-induced rupture of the Bruch's membrane. Both the incidence and the severity of CNV were strongly attenuated in double deficient compared with single gene deficient mice or corresponding WT controls. The reduced neovascularization was accompanied by fibrinogen/fibrin accumulation. Furthermore, overexpression of the endogenous MMP inhibitors TIMP-1 or TIMP-2 (delivered by adenoviral vectors) in WT mice or daily injection of a synthetic and gelatinase selective MMP inhibitor (Ro 26-2853) significantly decreased the pathological reaction. These findings suggest that MMP-2 and MMP-9 may cooperate in the development of AMD and that their selective inhibition represents an alternative strategy for the treatment of choroidal neovascularization.

Inhibition of tumor angiogenesis by angiostatin: from recombinant protein to gene therapy

Tumor growth, local invasion, and metastatic dissemination are dependent on the formation of new microvessels. The process of angiogenesis is regulated by a balance between pro-angiogenic and anti-angiogenic factors, and the shift to an angiogenic phenotype (the "angiogenic switch") is a key event in tumor progression. The use of anti-angiogenic agents to restore this balance represents a promising approach to cancer treatment. Known physiological inhibitors include trombospondin, several interleukins, and the proteolytic break-down products of several proteins. Angiostatin, an internal fragment of plasminogen, is one of the more potent of this latter class of angiogenesis inhibitors. Like endostatin, another anti-angiogenic peptide derived from collagen XVIII, angiostatin can induce tumor vasculature regression, leading to a complete cessation of tumor growth. Inhibitors of angiogenesis target normal endothelial cells, therefore the development of resistance to these drugs is unlikely. The efficacy of angiostatin has been demonstrated in animal models for many different types of solid tumors. Anti-angiogenic cancer therapy with angiostatin requires prolonged administration of the peptide. The production of the functional polypeptides is expensive and technical problems related to physical properties and purity are frequently encountered. Gene transfer represents an alternative method to deliver angiostatin. Gene therapy has the potential to produce the therapeutic agent in high concentrations in a local area for a sustained period, thereby avoiding the problems encountered with long-term administration of recombinant proteins, monoclonal antibodies, or anti-angiogenic drugs. In this review we compare the different gene therapy strategies that have been applied to angiostatin, with special regard to their ability to provide sufficient angiostatin at the target site.

Molecular targets in the inhibition of angiogenesis

Angiogenesis, the process of blood vessel formation, is crucial for malignant tumour growth and metastases; therefore, it has become an attractive target for anticancer therapy. Theoretically applicable to most solid tumours, this therapy may be advantageous over existing cytotoxic therapy, since it is directed at genetically stable endothelium growing within tumours rather than at malignant cells, which acquire resistance to treatment. Many promising angiogenesis inhibitors have been developed, although their activity has yet to be demonstrated in human clinical trials. To improve therapeutic benefit, this may require further insight into tumour angiogenesis, development of appropriate surrogate markers of activity, treatment of early stage neoplastic disease and probably a combination of different classes of antiangiogenesis agents to overcome redundant mechanisms of angiogenesis control.

Extracellular matrix remodelling: the role of matrix metalloproteinases

Matrix metalloproteinases (MMPs) are a growing family of metalloendopeptidases that cleave the protein components of the extracellular matrix and thereby play a central role in tissue remodelling. For many years following their discovery, MMPs were believed to function primarily as regulators of ECM composition and to facilitate cell migration simply by removing barriers such as collagen. It is becoming increasingly clear, however, that MMPs are implicated in the functional regulation of a host of non-ECM molecules that include growth factors and their receptors, cytokines and chemokines, adhesion receptors and cell surface proteoglycans, and a variety of enzymes. MMPs therefore play an important role in the control of cellular interactions with and response to their environment in conditions that promote tissue turnover, be they physiological, such as normal development, or pathological, such as inflammation and cancer. This review summarizes some of the recent discoveries that have shed new light on the role of MMPs in physiology and disease.

Matrix metalloproteinases in tumor progression: focus on basal and squamous cell skin cancer

Many normal biological processes, such as reproduction, fetal development and wound healing, are critically dependent on controlled degradation of extracellular matrix (ECM) macromolecules. However, excessive degradation of matrix components occurs in pathologic tissue destruction, e.g. in atherosclerosis, rheumatoid arthritis, and cancer. Matrix metalloproteinases (MMPs) are degradative enzymes that play an important role in all aspects of tumor progression by enhancing tumor-induced angiogenesis and destroying local tissue architecture and basement membranes to allow tumor invasion and metastasis. Efficient breakdown of the ECM surrounding invasive cancer islands involves interplay between tumor cells, stromal cells, and inflammatory cells, all of which express a distinct set of MMPs. Besides the classical role of MMPs in degradation of ECM, MMPs may also indirectly influence the tumor microenvironment through the release of growth factors, cryptic sites or angiogenic factors, or through the generation of matrix fragments that inhibit tumor cell proliferation, migration and angiogenesis. This makes the contribution of MMPs to tumorigenesis much more complex than initially thought. Currently, a number of clinical studies have focused on testing MMP inhibitors as potential antineoplastic agents. In this review we discuss the present role of MMPs in the development and progression of cancer, focusing on non-melanoma skin cancers basal (BCC) and squamous (SCC) cell carcinoma, and the possible influence of MMPs in their differences.

Macrophage metalloelastase as a major factor for glomerular injury in anti-glomerular basement membrane nephritis

Rat anti-glomerular basement membrane (GBM) nephritis is a model of crescentic glomerulonephritis induced by injection of anti-GBM antiserum. To elucidate the mechanism of glomerular injury, we analyzed the gene expression patterns in the kidneys of anti-GBM nephritis rats using DNA arrays, and found that macrophage metalloelastase/matrix metalloproteinase (MMP)-12 was one of the highly expressed genes in the kidneys on days 3 and 7 after the injection of anti-GBM antiserum. Enhancement of MMP-12 mRNA expression was confirmed by Northern blot analysis, and in situ hybridization revealed that MMP-12 mRNA was expressed in ED-1-positive macrophages and multinuclear giant cells in the glomeruli with crescent. Moreover, these cells were positive with anti-rat rMMP-12 Ab on the section of the kidneys of anti-GBM nephritis rats on day 7. To clarify the role of MMP-12, we conducted a neutralization experiment using anti-rat rMMP-12 Ab, which had an ability to inhibit rMMP-12 activity of degrading natural substrate such as bovine elastin or human fibronectin in vitro. Anti-rat rMMP-12 Ab or control Ig was injected in each of six rats on days 0, 2, 4, and 6 after the injection of anti-GBM antiserum. Consequently, crescent formation and macrophage infiltration in the glomeruli were significantly reduced in the rats treated with anti-rat rMMP-12 Ab, and the amount of urine protein was also decreased. These results disclosed that MMP-12 played an important role in glomerular injury in a crescentic glomerulonephritis model, and inhibition of MMP-12 may lead to a new therapeutic strategy for this disease.

Angiogenesis: vascular remodeling of the extracellular matrix involves metalloproteinases

Endothelial cell invasion is an essential event during angiogenesis (the formation of new blood vessels). This process involves the degradation of the extracellular matrix, the basement membrane, and interstitial stroma, and is governed by the activation of matrix metalloproteinases. However, the contribution of matrix metalloproteinases in angiogenesis is much more complicated. Tumor growth above a certain size is dependent on new vessels. A number of studies have demonstrated that treating tumors with matrix metalloproteinase inhibitors results in tumor reduction and a decrease in tumor angiogenesis. Matrix metalloproteinases as sole matrix eaters or degraders is a matter of the past. Not only tumor cells but more importantly bystander cells such as stromal cells produce matrix metalloproteinases. Matrix metalloproteinases therefore are also part of the pathologic microenvironment in different diseases. This enzymatic microenvironment dictates the endothelial cell fate, the angiogenic switch, and finally angiogenesis. During recent years, the role of matrix metalloproteinases has expanded, and their function as modulators of biologically active signaling molecules has drawn much attention. Depending on their substrate (growth factors or their receptors, extracellular matrix components, and angiogenic factors), matrix metalloproteinase activation results in the generation of proangiogenic or antiangiogenic factors. These data challenge the old concept that matrix metalloproteinases are simply proangiogenic. The knowledge of the local enzymatic profile and what, where, and how matrix metalloproteinases are involved in angiogenesis of tumors or other diseases will help design future therapeutic strategies better reflecting the complexity of the underlying biologic process of angiogenesis.

Antiangiogenic gene therapy for hepatocellular carcinoma using angiostatin gene

Recent studies have reported that antiangiogenic gene delivery into cancer cells inhibits growth of certain tumors in vivo. Hepatocellular carcinoma (HCC) is a hypervascular cancer, and antiangiogenic gene therapy might be suitable for HCC. In the present study, we investigated the antiangiogenic effects of angiostatin gene transduction into HCC both in vitro and in vivo. Angiostatin gene was cloned into a pSecTag2B mammalian expression vector to construct pSecTag2B-ANG. pSecTag2B or pSecTag2B-ANG were transfected into an HCC cell line, PLC/PRF/5, and then stable transfectants were obtained by Zeocin selection. pSecTag2B or pSecTag2B-ANG transfection did not alter the expression of vascular endothelial growth factor (VEGF), a potent angiogenic stimulator, or pigment epithelium-derived factor (PEDF), an angiogenic inhibitor, in PLC/PRF/5 cells. However, conditioned media (CM) derived from pSecTag2B-ANG-transfected PLC/PRF/5 cells (CM-ANG) suppressed the proliferation and migration of human umbilical vein endothelial cells (HUVEC) by 35% and 50%, respectively, relative to their effects on nontransfected cells. In in vivo experiments, pSecTag2B-ANG stable transfected (CM-Mock) and nontransfected cells (CM-N) were mixed at various proportions and the mixed cells were subcutaneously implanted into athymic mice. Suppression of tumor growth was noted in mice implanted with angiostatin gene-transfected cells, and such suppression was proportional with the percentage of transfected cells. Analysis of the vascular density in these tumors showed that the tumor growth suppression effect of angiostatin gene correlated with suppression of tumor vascularity. In conclusion, antiangiogenic gene therapy using angiostatin gene is potentially suitable for the treatment of patients with HCC.

Interleukin-2 and cancer: critical analysis of results, problems and expectations

The cancer process in a combination of two kinds of events: a multistep cellular genetic defects giving cells independent growth and great adaptation capability, a multistep interactions profiles with what is called the stromal reaction from the original in situ tumor to the invasive metastatic and angiogenic tumor. The immune system plays an important role in the control of the cancer process but always must be seen as a part integrated in the stromal reaction. In order to boost the immune system capability to treat a cancer we must never forget these cellular and tissular dimensions. Interleukins, growth factors and monoclonal antibodies are new agents are able to bring immunotherapy of cancer to reality. Interleukin 2 did not match our dreams of the ideal factor which can stimulate the defective immune system and bring the cancer evolution to an end. The little but real remissions obtained with the IL-2 high dose protocols still sustains our trust of the immune system as a critical barrier to cancer evolution but the numerous side effects reminds us that cytokines are not to be used as antibiotics and hormones. IL-2 is a regulator of the immune system at the microenvironment level, therefore flooding the blood circulation with high IL-2 doses is not appropriate. We have also to understand that IL-2 can interact directly with cancer cells and also with stromal cells (endothelial and fibroblastic cells), the outcome of IL-2 immunotherapy is not restricted to the interactions with immune cells.

Imidazole ring-opened DNA purines and their biological significance

Fragmentation of purine imidazole ring and production of formamidopyrimidines in deoxynucleosides (Fapy lesions) occurs upon DNA oxidation as well as upon spontaneous or alkali-triggered rearrangement of certain alkylated bases. Many chemotherapeutic agents such as cyclophosphamide or thiotepa produce such lesions in DNA. Unsubstituted FapyA and FapyG, formed upon DNA oxidation cause moderate inhibition of DNA synthesis, which is DNA polymerase and sequence dependent. Fapy-7MeG, a methylated counterpart of FapyG-, a efficiently inhibits DNA replication in vitro and in E.coli, however its mutagenic potency is low. This is probably due to preferential incorporation of cytosine opposite Fapy-7MeG and preferential extension of Fapy-7MeG:C pair. In contrast, FapyA and Fapy-7MeA possess miscoding potential. Both lesions in SOS induced E.coli preferentially mispair with cytosine giving rise to A-->G transitions. Fapy lesions substituted with longer chain alkyl groups also show simult aneous lethal and mutagenic properties. Fapy lesions are actively eliminated from DNA by repair glycosylases specific for oxidized purines and pyrimidines both in bacteria and eukaryotic cells. Bacterial enzymes include E.coli formamidopyrimidine-DNA-glycosylase (Fpg protein), endonuclease III (Nth protein) and endonuclease VIII (Nei protein).

Roles of matrix metalloproteinases in tumor metastasis and angiogenesis

Matrix metalloproteinases (MMPs), zinc dependent proteolytic enzymes, cleave extracellular matrix (ECM: collagen, laminin, firbronectin, etc) as well as non-matrix substrates (growth factors, cell surface receptors, etc). The deregulation of MMPs is involved in many diseases, such as tumor metastasis, rheumatoid arthritis, and periodontal disease. Metastasis is the major cause of death among cancer patients. In this review, we will focus on the roles of MMPs in tumor metastasis. The process of metastasis involves a cascade of linked, sequential steps that involve multiple host-tumor interactions. Specifically, MMPs are involved in many steps of tumor metastasis. These include tumor invasion, migration, host immune escape, extravasation, angiogenesis, and tumor growth. Therefore, without MMPs, the tumor cell cannot perform successful metastasis. The activities of MMPs are tightly regulated at the gene transcription levels, zymogen activation by proteolysis, and inhibition of active forms by endogenous inhibitors, tissue inhibitor of metalloproteinase (TIMP), and RECK. The detailed regulations of MMPs are described in this review.

A critical evaluation of DNA adducts as biological markers for human exposure to polycyclic aromatic compounds

The causative role of polycyclic aromatic hydrocarbons (PAH) in human carcinogenesis is undisputed. Measurements of PAH-DNA adduct levels in easily accessible white blood cells therefore represent useful early endpoints in exposure intervention or chemoprevention studies. The successful applicability of DNA adducts as early endpoints depends on several criteria: i. adduct levels in easily accessible surrogate tissues should reflect adduct levels in target-tissues, ii. toxicokinetics and the temporal relevance should be properly defined. iii. sources of interand intra-individual variability must be known and controllable, and finally iv. adduct analyses must have advantages as compared to other markers of PAHexposure. In general, higher DNA adduct levels or a higher proportion of subjects with detectable DNA adduct levels were found in exposed individuals as compared with nonexposed subjects, but saturation may occur at high exposures. Furthermore, DNA adduct levels varied according to changes in exposure, for example smoking cessation resulted in lower DNA adduct levels and adduct levels paralleled seasonal variations of air-pollution. Intraindividual variation during continuous exposure was low over a short period of time (weeks), but varied significantly when longer time periods (months) were investigated. Inter-individual variation is currently only partly explained by genetic polymorphisms in genes involved in PAH-metabolism and deserves further investigation. DNA adduct measurements may have three advantages over traditional exposure assessment: i. they can smooth the extreme variability in exposure which is typical for environmental toxicants and may integrate exposure over a longer period of time. Therefore, DNA adduct assessment may reduce the monitoring effort. ii. biological monitoring of DNA adducts accounts for all exposure routes. iii. DNA adducts may account for inter-individual differences in uptake, elimination, distribution, metabolism and repair amongst exposed individuals. In conclusion, there is now a sufficiently large scientific basis to justify the application of DNA adduct measurements as biomarkers in exposure assessment and intervention studies. Their use in risk-assessment, however, requires further investigation.

Different inhibitors of plasmin differentially affect angiostatin production and angiogenesis

Plasmin is a broad-spectrum serine proteinase, which is presumed to cleave many extracellular proteins and affect angiogenesis. In the present work, we studied the effect of two different inhibitors of plasmin (epsilon-aminocaproic and alpha(2)-antiplasmin) on angiogenesis in vivo using the chicken embryo chorioallantoic membrane assay, and in vitro using human umbilical vein endothelial cells. Epsilon-aminocaproic acid inhibited, while alpha(2)-antiplasmin induced, angiogenesis, as well as human umbilical vein endothelial cell proliferation, migration and tube formation on matrigel in a dose-dependent manner. Since plasmin has been implicated in the production of angiostatin, we studied the effect of the two plasmin inhibitors on angiostatin protein amounts in the chicken embryo chorioallantoic membrane. In this tissue, the 38- and 45-kDa isoforms of angiostatin are differentially affected by the two inhibitors: epsilon-aminocaproic acid increased, while alpha(2)-antiplasmin decreased the amounts of both isoforms. These data suggest that plasmin may have an antiangiogenic role in vivo through generation of angiostatin. Moreover, plasmin inhibitors differentially affect in vivo angiogenesis, depending on the mechanism by which they inhibit plasmin activity.

Host microenvironment in breast cancer development: inflammatory and immune cells in tumour angiogenesis and arteriogenesis

Breast cancer progression is associated with and dependent upon robust neovascularization. It is becoming clear that tumour-associated 'normal' cells, such as immune/inflammatory cells, endothelial cells and stromal cells, conspire with cancer cells in promoting this process. In particular, infiltrating immune/inflammatory cells secrete a diverse repertoire of growth factors and proteases that enable them to enhance tumour growth by stimulating angiogenesis and, as we suggest here, by promoting 'tumour arteriogenesis' - enlargement of feeding vessels supplying the expanding tumour capillary bed. Macrophages and their chemoattractants (e.g. macrophage chemoattractant protein-1) are critical for the arteriogenic process in ischaemia, and probably also in breast neoplasia. A better understanding of these various cellular and molecular constituents of breast cancer neovascularization may be useful in designing more effective therapies.

A novel strategy for the generation of angiostatic kringle regions from a precursor derived from plasminogen

In this study we have explored the feasibility of generating angiostatin by incorporating an endoproteolytic furin cleavage site into plasminogen to allow conversion of the precursor molecule into an angiostatic active K1-3 fragment. We show that secretable angiostatin can be successfully generated from cells infected with adenovirus carrying the furin-mutated plasminogen (AdmuthPlgK3). Supernatant from cells transduced with AdmuthPlagK3 inhibits tube formation and proliferation and migration of human umbilical vein endothelial cells with an efficiency similar to that of supernatant from cells infected with adenovirus expressing kringle 1-3 of plasminogen (AdK1-3). Administration of AdmuthPlgK3 and AdK1-3 in mice results in significantly decreased endothelial cell infiltration in VEGF-embedded Matrigel plugs. Treatment with AdmuthPlgK3 and AdK1-3 exerts strong antitumoral effect in models of hepatocellular carcinoma and Lewis lung cancer. This antitumor effect was associated with decreased microvessel density in the tumors. Taken together, our data demonstrate that angiostatin endowed with strong antiangiogenic and antitumor effects can be released from a furin-mutated plasminogen acting as a precursor. This strategy may have potential to develop angiostatic anti-cancer therapies.

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

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

A potential role of macrophage activation in the treatment of cancer

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

Prospective pilot study of recombinant granulocyte-macrophage colony-stimulating factor and interferon-gamma in patients with inoperable hepatocellular carcinoma

Interferon (IFN)-gamma and Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) enhance tumor immunogenicity. The authors assessed tolerability and effectiveness of a combination therapy of these recombinant human (rh) cytokines in patients with inoperable hepatocellular carcinoma (HCC). In a monocentric, open, nonrandomized pilot study, rhGM-CSF (5 microg/kg qd, Monday and Tuesday) and rhIFN-gamma (100 microg qd, Wednesday and Thursday) were subcutaneously administered in 9-week cycles. Primary objective was survival, as secondary outcomes volumetric changes of tumor mass and biologic parameters reflecting systemic immunologic or local tumor responses were measured. Only patients with complete response (CR), partial response (PR), or stable disease (SD) proceeded to new treatment cycles. Fifteen patients (median 63 years, range 46-74 years, all men) were enrolled. Survival after the first cycle was 80% with SD in 9 of 15 patients (60%). PR was detected in one patient after the second cycle. Two patients finished five treatment cycles. Overall survival at 26 and 52 weeks was 40% and 20%, respectively. Median survival in patients with inducible HLA-DR on hepatoma cells (40%) was increased (42 weeks, 27-100) as compared with HLA-DR negative cases (60%; 13 weeks, 8-23; p < 0.0001), and a control group (p = 0.01). Parameters reflecting systemic immunomodulatory activities were not associated with clinical outcome. In 13 of 15 patients (87%), adverse events were reported, all less than grade 2 and none requiring therapy discontinuation. Immunotherapeutic approaches hold promise to prolong survival in selected patients with advanced HCC who respond by enhanced tumor immunogenicity.

The antitumoral effect of endostatin and angiostatin is associated with a down-regulation of vascular endothelial growth factor expression in tumor cells

Endostatin and angiostatin are known as tumor-derived angiogenesis inhibitors, but their mechanisms of action are not yet completely defined. We report here that endostatin and angiostatin, delivered by adenoviral vectors, reduced in vitro the neovessel formation in the mouse aortic ring assay by 85 and 40%, respectively. We also demonstrated in vivo that both endostatin and angiostatin inhibited local invasion and tumor vascularization of transplanted murine malignant keratinocytes, and reduced by 50 and 90% the development of highly vascularized murine mammary tumors. This inhibition of tumor growth was associated with a reduction of tumor vascularization. Expression analysis of vascular endothelial growth factor (VEGF) carried out in the mouse aortic ring model revealed a 3- to 10-fold down-regulation of VEGF mRNA expression in endostatin-treated rings. A similar down-regulation of VEGF expression at both mRNA and protein levels was also observed in the two in vivo cancer models after treatment with each angiogenesis inhibitor. This suggests that endostatin and angiostatin effects may be mediated, at least in part, by their ability to down-regulate VEGF expression within the tumor. This work provides evidence that endostatin and angiostatin act on tumor cells themselves.

Matrix metalloproteinase-9 contributes to choroidal neovascularization

Age-related macular degeneration (AMD) is the primary cause of irreversible photoreceptors loss in adult patients and current therapies are limited. Increased levels of matrix metalloproteinases (MMPs) have been documented in neovascularization of severe ocular pathologies such as AMD and proliferative diabetic retinopathy. We report here that MMP-9 (gelatinase B) expression is induced and temporally regulated in the course of experimental choroidal neovascularization. We used transgenic mice expressing beta-galactosidase reporter gene under the dependence of MMP-9 promoter and RT-PCR analysis on choroidal neovascular structures microdissected from serial sections by laser pressure catapulting to show that MMP-9 expression is up-regulated concomitantly with the appearance of inflammatory cells in the subretinal lesion. In mice deficient in MMP-9 expression the development of choroidal neovascularization induced by laser photocoagulation still occurred, but at a reduced level.

Angiogenesis as a target for cancer therapy

Antiangiogenic drugs are unique for having highly specific targets while carrying the potential to be effective against a wide variety of tumors. Moreover, some of the major limitations of cytotoxic therapies likely will be avoided by this entirely new class of anticancer weapons. After the realization of the potential advantages of antiangiogenic therapy, the field of angiogenesis research is growing exponentially. Still, there is much to learn about the machinery that tumors use to recruit new blood vessels, and the results of the clinical trials will show the best way to apply that knowledge for cancer therapy.

Metalloelastase (MMP-12) expression by tumour cells in squamous cell carcinoma of the vulva correlates with invasiveness, while that by macrophages predicts better outcome

Human metalloelastase (MMP-12) has been implicated in elastin degradation and macrophage migration in many pathological conditions. It also generates angiostatin, thus having a potential to prevent tumour angiogenesis. It has previously been shown that transformed epithelial cells express MMP-12 in skin cancer. The aim of this study was further to elucidate the role of metalloelastase in squamous cell cancer (SCC) progression. By in situ hybridization, expression of MMP-12 mRNA was detected in 28/33 vulvar SCC samples in CD-68-positive macrophages, while 10 samples had positive cancer cells. By immunohistochemistry, MMP-12 protein was seen in the same area as the mRNA. MMP-12 mRNA expression in tumour cells correlated with more aggressive histology (p = 0.0099). In contrast, macrophage-derived MMP-12 mRNA was more abundant in well-differentiated grade I than grade III tumours (p = 0.01). However, the level of MMP-12 mRNA, regardless of its origin, did not correlate with metastasis or patient survival. No significant correlation was found between macrophage-derived MMP-12 mRNA and a low amount of blood vessels, as quantitated after von Willebrand staining. In agreement with vulvar SCCs in vivo, MMP-12 was expressed in cultured SCC cells by northern and western blot analysis. In HaCaTs and epithelial MCF-10f cells, MMP-12 mRNA was induced by transforming growth factor-beta1 (TGF-beta1) and tumour necrosis factor-alpha (TNF-alpha) as measured by quantitative RT-PCR (TaqMan). Two MMPs capable of generating angiostatin in vivo, matrilysin (MMP-7) and gelatinase B (MMP-9), were also examined in these tumours. MMP-7 mRNA was mainly expressed by epithelial tumour cells, particularly in less differentiated tumours. MMP-9 was usually expressed by neutrophils and macrophages; epithelial protein was predominantly found in grade II/III tumours. These results suggest a dual role for MMP-12 in tumour progression.

Persistent parity-induced changes in growth factors, TGF-beta3, and differentiation in the rodent mammary gland

Epidemiological studies have repeatedly demonstrated that women who undergo an early first full-term pregnancy have a significantly reduced lifetime risk of breast cancer. Similarly, rodents that have previously undergone a full-term pregnancy are highly resistant to carcinogen-induced breast cancer compared with age-matched nulliparous controls. Little progress has been made, however, toward understanding the biological basis of this phenomenon. We have used DNA microarrays to identify a panel of 38 differentially expressed genes that reproducibly distinguishes, in a blinded manner, between the nulliparous and parous states of the mammary gland in multiple strains of mice and rats. We find that parity results in the persistent down-regulation of multiple genes encoding growth factors, such as amphiregulin, pleiotrophin, and IGF-1, as well as the persistent up-regulation of the growth-inhibitory molecule, TGF-beta3, and several of its transcriptional targets. Our studies further indicate that parity results in a persistent increase in the differentiated state of the mammary gland as well as lifelong changes in the hematopoietic cell types resident within the gland. These findings define a developmental state of the mammary gland that is refractory to carcinogenesis and suggest novel hypotheses for the mechanisms by which parity may modulate breast cancer risk.

Stromelysin-2 overexpression in human esophageal squamous cell carcinoma: potential clinical implications

The degradation of the extracellular matrix (ECM) is a major step in the process of tumor invasion and metastasis, mediated by matrix metalloproteinases (MMPs). Knowledge of alterations in the expression of stromelysin-2 (ST-2) or MMP-10 in human esophageal squamous cell carcinoma (ESCC) is meager. Immunohistochemical analysis of ST-2 expression was carried out in surgically resected ESCCs (50 cases) and paired distal histologically normal esophageal tissues (50 cases), correlated with clinicopathological parameters. Overexpression of ST-2 protein, in tumor cell cytoplasm and stromal elements, was observed in 37 of the 50 (74%) ESCCs localized in tumor cell cytoplasm and stromal elements. Low levels of ST-2 were observed in 8 of the 50 (16%) matched histologically normal esophageal tissues. Significant associations were observed between ST-2 overexpression and tumor size (r = 0.02, P = 0.04), local invasiveness of the tumor (r = -0.30, P = 0.002) and distant organ metastasis (r = -0.227, P = 0.02), suggestive of its involvement in development and progression of ESCCs. The data underscore the significance of ST-2 expression in context to the aggressive tumor characteristics observed in ESCCs in the Indian population, wherein extremely poor prognosis has been ascribed to extensive local invasion and metastasis.

Differential production of angiostatin by concomitant antitumoral resistance-inducing cancer cells

The phenomenon by which tumor-bearing hosts are capable of inhibiting secondary tumor implants or metastases, known as concomitant antitumoral resistance (CAR), is presumably due to antiangiogenesis at places distant from the primary tumor. Although angiostatin, a potent inhibitor of angiogenesis, has been reported to be one of the factors responsible for suppressing the growth of secondary tumors in mice bearing previous tumors, it has not been definitively proven yet. With the aim of investigating whether CAR-inducing cancer cells display a differential angiostatin production and to support the role ascribed to that molecule concerning the inhibition of secondary tumor implants, 5 tumor models with different CAR-inducing capacities were studied herein. One of the 2 human lung cancer cell lines analyzed revealed a strong CAR against secondary s.c. tumor implants in nude mice, and 2 of 3 of the murine mammary tumors used exhibited inhibitory effect on secondary s.c. and i.v. tumor inoculations in syngeneic hosts. Since angiostatin is a proteolytic fragment from plasminogen, we examined by Western blot the ability of all conditioned media collected from the tumor cells studied to convert plasminogen to angiostatin. An association between in vivo generation of CAR and in vitro conversion of plasminogen into angiostatin was found. Since different enzymatic mechanisms were described to explain the generation of angiostatin, we also studied gelatinase and urokinase-type plasminogen activator secretion in conditioned media by zymography. The conversion of plasminogen into angiostatin by conditioned media was mainly inhibited by broad-spectrum serine proteinase inhibitors, suggesting a possible role for 1 or more enzymes of that group in the process. These findings suggest the existence of a differential angiostatin generation by CAR-inducing cancer cells, providing additional support to previous data obtained by other authors.

Angiogenesis inhibitors and radiotherapy of primary tumours

The modern approach to cancer therapy involves combinations of surgery, radiation and drugs targeted against malignant tumour cells. However, expanding knowledge in the fields of angiogenesis and vascular biology over the last several years has led to the investigation of therapeutic strategies targeted to the vasculature (proliferating and non-proliferating endothelial cells) in combination with standard therapy. It is the objective of this review to describe the potential use of antiangiogenic therapy, targeted to the proliferating endothelium, from the point of view of the radiation oncologist. This review will describe the concept of a two-cell compartment model for tumours, with both the endothelial cells as well as the tumour cells being potential targets for radiotherapy. This review will then explore the promising evidence and rationale for combining antiangiogenic drugs and radiotherapy to enhance local control.

Generation of biologically active angiostatin kringle 1-3 by activated human neutrophils

The contribution of polymorphonuclear neutrophils (PMN) to host defense and natural immunity extends well beyond their traditional role as professional phagocytes. In this study, we demonstrate that upon stimulation with proinflammatory stimuli, human PMN release enzymatic activities that, in vitro, generate bioactive angiostatin fragments from purified plasminogen. We also provide evidence that these angiostatin-like fragments, comprising kringle domain 1 to kringle domain 3 (kringle 1-3) of plasminogen, are generated as a byproduct of the selective proteolytic activity of neutrophil-secreted elastase. Remarkably, affinity-purified angiostatin kringle 1-3 fragments generated by neutrophils inhibited basic fibroblast growth factor plus vascular endothelial growth factor-induced endothelial cell proliferation in vitro, and both vascular endothelial growth factor-induced angiogenesis in the matrigel plug assay and fibroblast growth factor-induced angiogenesis in the chick embryo chorioallantoic membrane assay, in vivo. These results represent the first demonstration that biologically active angiostatin-like fragments can be generated by inflammatory human neutrophils. Because angiostatin is a potent inhibitor of angiogenesis, tumor growth, and metastasis, the data suggest that activated PMN not only act as potent effectors of inflammation, but might also play a critical role in the inhibition of angiogenesis in inflammatory diseases and tumors, by generation of a potent anti-angiogenic molecule.

Regulation of endothelial cell survival and apoptosis during angiogenesis

The process of angiogenesis plays an important role in many physiological and pathological conditions. Inhibition of endothelial cell (EC) apoptosis providing EC survival is thought to be an essential mechanism during angiogenesis. Many of the angiogenic growth factors inhibit EC apoptosis. In addition, the adhesion of ECs to the extracellular matrix or intercellular adhesion promotes EC survival. In contrast, increasing evidence suggests that the induction of EC apoptosis may counteract angiogenesis. In this review, we focus on the regulation of EC survival and apoptosis during angiogenesis and especially on the effects and intracellular signaling promoted by angiogenic growth factors, endogenous angiogenic inhibitors (such as angiostatin, endostatin, and thrombospondin-1), and the adhesion to the extracellular matrix. Furthermore, we discuss the effects of cross talk between adhesion molecules and growth factors. Understanding the molecular mechanisms involved in the regulation of EC survival and apoptosis may provide new targets for the development of new therapies to enhance angiogenesis in the case of tissue-ischemia (eg, the neovascularization of myocardium) or to inhibit angiogenesis in the case of neovascularization-dependent disease (eg, tumor, diabetic retinopathy).

Matrix metalloproteinases in cancer: prognostic markers and therapeutic targets

Degradation of extracellular matrix is crucial for malignant tumour growth, invasion, metastasis and angiogenesis. Matrix metalloproteinases (MMPs) are a family of zinc-dependent neutral endopeptidases collectively capable of degrading essentially all matrix components. Elevated levels of distinct MMPs can be detected in tumour tissue or serum of patients with advanced cancer and their role as prognostic indicators in cancer is studied. In addition, therapeutic intervention of tumour growth and invasion based on inhibition of MMP activity is under intensive investigation and several MMP inhibitors are in clinical trials in cancer. In this review, we discuss the current view on the feasibility of MMPs as prognostic markers and as targets for therapeutic intervention in cancer.

Angiostatin inhibits coronary angiogenesis during impaired production of nitric oxide

BACKGROUND

The in vivo mechanism by which inhibition of NO synthase impairs ischemia-induced coronary vascular growth is unknown. We hypothesized that production of the growth inhibitor angiostatin increases during decreased NO production, blunting angiogenesis and collateral growth.

METHODS AND RESULTS

Measurements were made in myocardial tissue or interstitial fluid (MIF) from dogs undergoing repetitive coronary occlusions under control conditions or during antagonism of NO synthase (N(G)-nitro-L-arginine methyl ester [L-NAME]) for 7, 14, or 21 days. A sham group was instrumented identically but received no occlusions. In controls, capillary density in the ischemic zone increased initially but returned to baseline at the later times. In the L-NAME group, capillary density was lower at 7 days compared with that of controls. MIF from control dogs induced in vitro endothelial tube formation and cell proliferation, significantly greater than that from the L-NAME group. MIF from shams did not stimulate tube formation. In controls or shams, tube formation or cell proliferation did not change after administration of antiangiostatin, but this antibody restored the responses to control levels in the L-NAME group. Angiostatin expression in MIF was increased in the L-NAME group compared with controls and shams. The activities of tissue matrix metalloproteinases (MMPs) MMP-2 and MMP-9, which generate angiostatin, were increased in the L-NAME group.

CONCLUSIONS

Inhibition of NO synthase increased expression of angiostatin and activities of MMP-2 and MMP-9. Our findings indicate that angiostatin inhibits coronary angiogenesis during compromised NO production and may underscore the impairment of coronary angiogenesis during endothelial dysfunction.

Thymidine phosphorylase expression in normal, hyperplastic and neoplastic prostates: correlation with tumour associated macrophages, infiltrating lymphocytes, and angiogenesis

Thymidine phosphorylase is an angiogenic factor primarily expressed by cancer cells, stromal cells and tumour-associated macrophages in many human malignancies. These different types of thymidine phosphorylase-expressing cells, however, may have a distinct place in the angiogenic process, and this question was addressed in the present study. A series of 20 normal/hyperplastic prostate glands and 60 prostate carcinomas was investigated by immunohistochemistry, using specific antibodies for thymidine phosphorylase (P-GF.44C), tumour-associated macrophages (CD68), endothelium (CD31) and prostate specific antigen (ER-PR8). Thymidine phosphorylase expression by normal and hyperplastic epithelial or stromal cells occurred almost exclusively in the context of an intense lymphocytic infiltrate. High thymidine phosphorylase cancer cells and thymidine phosphorylase stromal cells expression was associated with high angiogenesis in prostate carcinomas, and this significant association was extended to include both tumour-associated macrophages and tumour-infiltrating lymphocytes. Thymidine phosphorylase expression and tumour-infiltrating lymphocytes were related inversely with prostate specific antigen reactivity. In conclusion, thymidine phosphorylase is a major angiogenic factor in prostate carcinomas and its up-regulation is likely to occur in the context of a host immune response.

Angiostatin II is the predominant glycoform in pleural effusates of rabbit VX-2 lung tumors

Angiostatin (AST), a polypeptide with potent antiangiogenic properties, is released proteolytically from plasminogen in vivo. Plasminogen exists naturally in plasma as two glycoforms (PLGs), I and II. Recently it was shown with the use of a chick-embryo chorioallantoic membrane (CAM) assay that rabbit PLG-I and -II yield distinct ASTs-AST-I and -II, respectively-with different antiangiogenic activities. AST glycoforms were of similar molecular weight, approximately 30 to 32,000 kD, and probably consisted of kringles 1 to 3 only. AST has now been identified in the interpleural effusate released from VX-2 lung tumors in rabbits. Effusate was collected from six rabbits with high tumor burdens and fractionated by means of lysine-Sepharose chromatography. The epsilon-aminohexanoic acid-eluted protein of all effusates contained AST (kringles 1-3) at a mean concentration of 1.2 microg/mL of effusate; with regard to AST content, 97% was AST-II. A CAM assay revealed that the lysine-Sepharose-bound fraction from all interpleural effusates contained potent antiangiogenic activity. Blood and urine from rabbits with high burdens of VX-2 contained essentially only AST-II, at mean concentrations of 145 and 4 ng/mL, respectively. AST was absent from the blood of control rabbits. In an attempt to compare their uptake by VX-2, iodine 125-labeled AST-I and iodine 131-labeled AST-II were injected intravenously into tumor-bearing rabbits. AST-I entered the tumor 1.6 times faster than AST-II. As a means of accounting for the preponderance of AST-II in the interpleural effusate, we postulate that VX-2 cells release proteolytic activity to activate plasminogen but that of the two PLGs, PLG-II may be the preferred substrate for AST formation in vivo.