Inhibition of human malignant glioma growth in vivo by human recombinant plasminogen kringles 1-3

Glioma Cells in the Tumor Periphery Have a Stem Cell Phenotype

Gliomas are highly infiltrative tumors incurable with surgery. Although surgery removes the bulk tumor, tumor cells in the periphery are left behind resulting in tumor relapses. The aim of the present study was to characterize the phenotype of tumor cells in the periphery focusing on tumor stemness, proliferation and chemo-resistance. This was investigated in situ in patient glioma tissue as well as in orthotopic glioblastoma xenografts. We identified 26 gliomas having the R132 mutation in Isocitrate DeHydrogenase 1 (mIDH1). A double immunofluorescence approach identifying mIDH1 positive tumor cells and a panel of markers was used. The panel comprised of six stem cell-related markers (CD133, Musashi-1, Bmi-1, Sox-2, Nestin and Glut-3), a proliferation marker (Ki-67) as well as a chemo-resistance marker (MGMT). Computer-based automated classifiers were designed to measure the mIDH1 positive nucleus area-fraction of the chosen markers. Moreover, orthotopic glioblastoma xenografts from five different patient-derived spheroid cultures were obtained and the tumor cells identified by human specific immunohistochemical markers. The results showed that tumor cells in the periphery of patient gliomas expressed stem cell markers, however for most markers at a significantly lower level than in the tumor core. The Ki-67 level was slightly reduced in the periphery, whereas the MGMT level was similar. In orthotopic glioblastoma xenografts all markers showed similar levels in the core and periphery. In conclusion tumor cells in the periphery of patient gliomas have a stem cell phenotype, although it is less pronounced than in the tumor core. Novel therapies aiming at preventing recurrence should therefore take tumor stemness into account. Migrating cells in orthotopic glioblastoma xenografts preserve expression and stem cell markers. The orthotopic model therefore has a promising translational potential.

Role of angiogenesis in the pathogenesis of cancer

It has been recognized for decades that angiogenesis is an important event in tumor growth and metastasis; the concept of the "angiogenic switch," whereby tumors acquire the ability to grow exponentially and disseminate beyond their primary site, is one of the central components in our understanding of cancer. A vast network of signaling molecules and receptors that are involved in the regulation of angiogenesis have been identified and characterized; most notably, the vascular endothelial growth factor (VEGF) family. Indeed, the VEGF family of growth factors and receptors has become a prototype for our understanding of angiogenesis during early development and in pathological conditions such as cancer. The specific inhibition of key regulatory molecules including VEGF-A (such as with bevacizumab treatment) has been recognized as a useful strategy to reduce tumor growth and progression in several tumor types. Nevertheless, the contribution of other members of the VEGF family, other signaling pathways, and also endogenous angiogenic inhibitors to tumor angiogenesis, is beginning to emerge. The diversity of pathways and molecules involved in the regulation of angiogenesis in both normal development and cancer will likely offer many more prospects for successful therapeutic intervention.

Effect of angiostatin on 1,2-dimethylhydrazine-induced colon cancer in mice

Antiangiogenic therapy is supposed to be an attractive approach for antitumor treatment. Human plasminogen-derived angiostatin K1-3 is one of the most potent antiangiogenic agents known currently. However, it is unclear whether angiostatin has got protective effects on colon cancer. So we investigated the protective effects of angiostatin on 1,2-dimethylhydrazine (DMH)-induced colon cancer in mice. Thirty Balb/C male mice, weighing 25-30 g and 8 weeks of age, were used. Twenty of the mice were treated with DMH subcutaneously (20 mg/kg) once a week for 12 weeks. Six mice died during the DMH injection and surviving mice were divided into two groups (7 mice in DMH and 7 mice in DMH + angiostatin groups). In the angiostatin group, 6 weeks after the last DMH injection the animals were first treated with angiostatin (20 μg/mouse) intraperitoneally and then subcutaneously every 48 h (5 μg/mouse) throughout a period of 12 weeks. The animals were killed after 30 weeks for histopathological examination. When we look at the distribution of lesions in the colon, they mainly occurred in the distal colon. The incidence of mean colonic lesions in a tumor-bearing mouse was 9.85 ± 4.91 in those treated with DMH and 8.71 ± 3.49 in those treated with angiostatin. The incidence of colon tumors was not significantly affected by low dose of angiostatin, and we noticed that the number of lesions decreased by 12% in DMH + angiostatin group compared to the number of the lesions in DMH group, but this decrease was not statistically significant (p > 0.05). The administration period of angiostatin corresponds to the precancerous period and the reduction in the number of lesions could be important for the protective function of angiostatin in DMH + angiostain group. We assume that therapeutic effects of angiostatin are related to its doses, route of administration, frequency and administration period. In addition, we believe that combination of high doses of angiostatin with radiation, gene therapy or chemotherapy might be successful in proper tumor model.

Antiangiogenic therapy and mechanisms of tumor resistance in malignant glioma

Despite advances in surgery, radiation therapy, and chemotherapeutics, patients with malignant glioma have a dismal prognosis. The formations of aberrant tumour vasculature and glioma cell invasion are major obstacles for effective treatment. Angiogenesis is a key event in the progression of malignant gliomas, a process involving endothelial cell proliferation, migration, reorganization of extracellular matrix and tube formation. Such processes are regulated by the homeostatic balance between proangiogenic and antiangiogenic factors, most notably vascular endothelial growth factors (VEGFs) produced by glioma cells. Current strategies targeting VEGF-VEGF receptor signal transduction pathways, though effective in normalizing abnormal tumor vasculature, eventually result in tumor resistance whereby a highly infiltrative and invasive phenotype may be adopted. Here we review recent anti-angiogenic therapy for malignant glioma and highlight implantable devices and nano/microparticles as next-generation methods for chemotherapeutic delivery. Intrinsic and adaptive modes of glioma resistance to anti-angiogenic therapy will be discussed with particular focus on the glioma stem cell paradigm.

"Buy one get one free": armed viruses for the treatment of cancer cells and their microenvironment

Oncolytic viral therapy is a promising biological therapy for the treatment of cancer. Recent advances in genetic engineering have facilitated the construction of custom-built oncolytic viruses that can be exquisitely targeted to tumors by exploiting each cancer's unique biology and their efficacy can be further enhanced by "arming" them with additional therapeutic genes. Such an approach allows the virus to unload its "therapeutic cargo" at the tumor site, thereby enhancing its anti-neoplastic properties. While several clever strategies have been recently described using genes that can induce cellular apoptosis/suicide and/or facilitate tumor/virus imaging, viruses armed with genes that also affect the tumor microenvironment present an exciting and promising approach to therapy. In this review we discuss recently developed oncolytic viruses armed with genes encoding for angiostatic factors, inflammatory cytokines, or proteases that modulate the extracellular matrix to regulate tumor vascularization, anti-tumor immune responses and viral spread throughout the solid tumor.

Biology of angiogenesis and invasion in glioma

Treatment of adult brain tumors, in particular glioblastoma, remains a significant clinical challenge, despite modest advances in surgical technique, radiation, and chemotherapeutics. The formation of abnormal, dysfunctional tumor vasculature and glioma cell invasion along white matter tracts are believed to be major components of the inability to treat these tumors effectively. Recent insight into the fundamental processes governing glioma angiogenesis and invasion provide a renewed hope for development of novel strategies aimed at reducing the morbidity of this uniformly fatal disease. In this review, we discuss background biology of the blood brain barrier and its pertinence to blood vessel formation and tumor invasion. We will then focus our attention on the biology of glioma angiogenesis and invasion, and the key mediators of these processes. Last, we will briefly discuss recent and ongoing clinical trials targeting mediators of angiogenesis or invasion in glioma patients. The findings provide a renewed hope for those endeavoring to improve treatment of patients with glioma by providing a novel set of rational targets for translational drug discovery.

Antimigratory effect of TK1-2 is mediated in part by interfering with integrin alpha2beta1

The recombinant two kringle domain of human tissue-type plasminogen activator (TK1-2) has been shown to inhibit endothelial cell proliferation, angiogenesis, and tumor cell growth despite of sharing a low amino acid sequence homology with angiostatin. Here, we explored a possible inhibitory mechanism of action of TK1-2 by focusing on antimigratory effect. TK1-2 effectively inhibited endothelial cell migration induced by basic fibroblast growth factor or vascular endothelial growth factor in a dose-dependent manner and tube formation on Matrigel. It blocked basic fibroblast growth factor-induced or vascular endothelial growth factor-induced phosphorylation of extracellular signal-regulated kinase 1/2 and formation of actin stress fibers and focal adhesions. Interestingly, TK1-2 alone induced the weak phosphorylation of focal adhesion kinase, whereas it inhibited focal adhesion kinase phosphorylation induced by growth factors. When immobilized, TK1-2 promoted adhesion and spreading of endothelial cells compared with bovine serum albumin. However, treatment with anti-alpha(2)beta(1) blocking antibody markedly diminished endothelial cell adhesion to immobilized TK1-2 compared with anti-alpha(v)beta(3) or anti-alpha(5)beta(1) antibody. Pretreatment of soluble TK1-2 also altered the binding level of anti-alpha(2)beta(1) antibody to endothelial cells in fluorescence-activated cell sorting analysis. Indeed, a blocking antibody against integrin alpha(2)beta(1) or knocking down of integrin alpha(2) expression prevented the inhibitory effect of TK1-2 in cell migration. Therefore, these results suggest that TK1-2 inhibits endothelial cell migration through inhibition of signaling and cytoskeleton rearrangement in part by interfering with integrin alpha(2)beta(1).

New molecular targets in angiogenic vessels of glioblastoma tumours

Antiangiogenesis approaches have the potential to be particularly effective in the treatment of glioblastoma tumours. These tumours exhibit extremely high levels of neovascularisation, which may contribute to their extremely aggressive behaviour, not only by providing oxygenation and nutrition, but also by establishing a leaky vasculature that lacks a blood-brain barrier. This leaky vasculature enables migration of tumour cells, as well as the build up of fluid, which exacerbates tissue damage due to increased intracranial pressure. Here, we discuss the considerable progress that has been made in the identification of the pro- and antiangiogenic factors produced by glioblastoma tumours and the effects of these molecules in animal models of the disease. The safety and efficacy of some of these approaches have now been demonstrated in clinical trials. However, the ability of tumours to overcome these therapies and to re-establish angiogenesis requires further clinical research regarding potential multimodality therapies, as well as basic research into the regulation of angiogenesis by as yet unidentified factors. Optimisation of noninvasive procedures for monitoring of angiogenesis would greatly facilitate such research.

Tumor angiogenesis promoted by ex vivo differentiated endothelial progenitor cells is effectively inhibited by an angiogenesis inhibitor, TK1-2

Neovascularization plays a critical role in the growth and metastatic spread of tumors and involves recruitment of circulating endothelial progenitor cells (EPC) from bone marrow as well as sprouting of preexisting endothelial cells. In this study, we examined if EPCs could promote tumor angiogenesis and would be an effective cellular target for an angiogenesis inhibitor, the recombinant kringle domain of tissue-type plasminogen activator (TK1-2). When TK1-2 was applied in the ex vivo culture of EPCs isolated from human cord blood, TK1-2 inhibited adhesive differentiation of mononuclear EPCs into endothelial-like cells. In addition, it inhibited the migration of ex vivo cultivated EPCs and also inhibited their adhesion to fibronectin matrix or endothelial cell monolayer. When A549 cancer cells were coimplanted along with ex vivo cultivated EPCs s.c. in nude mice, the tumor growth was increased. However, the tumor growth and the vascular density of tumor tissues increased by coimplanted EPCs were decreased upon TK1-2 treatment. Accordingly, TK1-2 treatment reduced the remaining number of EPCs in tumor tissues and their incorporation into the host vascular channels. In addition, overall expression levels of vascular endothelial growth factor (VEGF) and von Willebrand factor in tumor tissues were decreased upon TK1-2 treatment. Interestingly, strong VEGF expression by implanted EPCs was decreased by TK1-2. Finally, we confirmed in vitro that TK1-2 inhibited VEGF secretion of EPCs. TK1-2 also inhibited endothelial cell proliferation and migration induced by the conditioned medium of EPCs. Therefore, we concluded that EPCs, as well as mature endothelial cells, could be an important target of TK1-2.

The recombinant kringle domain of urokinase plasminogen activator inhibits in vivo malignant glioma growth

In a previous report, the recombinant kringle domain (UK1) of the urokinase type plasminogen activator (uPA) showed antiangiogenic activity. Here, we investigated in vivo antitumor effects of the UK1 of human uPA employing a brain tumor model. The systemic administration of UK1 purified from pichia expression (10 and 50 mg/kg/day intraperitoneally for 25 days) led to suppress the growth of a U87 human glioma xenograft, implanted into the brains of male BALB/cSlc nude mice, by 35% and 80%, respectively. In the immunohistochemical analysis, the tumors treated with UK1 showed decreased vascularity and expression of angiogenesis-related factors including vascular endothelial growth factor (VEGF), angiogenin, alpha-smooth muscle actin, von Willebrand's factor, and CD31 (PECAM-1 [Platelet endothelial cell adhesion molecule-1]), and increased apoptosis. UKl inhibited the in vitro proliferation and tube formation of VEGF-stimulated endothelial cells but not the proliferation of glioma cells. These results suggest that UK1 inhibits the malignant glioma growth by suppression of angiogenesis.

Direct binding of recombinant plasminogen kringle 1–3 to angiogenin inhibits angiogenin-induced angiogenesis in the chick embryo CAM

Angiogenin is one of the most potent angiogenesis-inducing proteins. Angiostatin is one of the most potent angiogenesis inhibitors, and it contains the first four kringle domains of plasminogen (K1-4). Recombinant human plasminogen kringle 1-3 (rK1-3) was expressed in Escherichia coli and purified to homogeneity. The binding of t-4-aminomethylcyclohexanecarboxylic acid with the purified kringle 1-3 was determined by changes in intrinsic fluorescence. rK1-3 exhibits comparable ligand-binding properties as native human plasminogen kringle 1-3. The purified rK1-3 inhibits neovascularization in the chick embryo chorioallantoic membrane (CAM) assay. Interaction of angiogenin with rK1-3 was examined by immunological binding assay and surface plasmon resonance kinetic analysis, and the equilibrium dissociation constants for the complex, Kd, are 0.89 and 0.18 microM, respectively. rK1-3 inhibits angiogenin-induced angiogenesis in the chick embryo CAM in a concentration-dependent manner. These results indicate that rK1-3 directly binds to angiogenin and thus rK1-3 inhibits the angiogenic activity of angiogenin.

Angiogenesis in gliomas: imaging and experimental therapeutics

Much of the interest in angiogenesis and hypoxia has led to investigating diagnostic imaging methodologies and developing efficacious agents against angiogenesis in gliomas. In many ways, because of the cytostatic effects of these agents on tumor growth and tumor-associated endothelial cells, the effects of therapy are not immediately evident. Hence finding clinically applicable imaging tools and pathologic surrogate markers is an important step in translating glioma biology to therapeutics. There are a variety of strategies in the approach to experimental therapeutics that target the hypoxia-inducible factor pathway, the endogenous antiangiogenic and proangiogenic factors and their receptors, adhesion molecules, matrix proteases and cytokines, and the existing vasculature. We discuss the rationale for antiangiogenesis as a treatment strategy, the preclinical and clinical assessment of antiangiogenic interventions and finally focus on the various treatment strategies, including combining antiangiogenic drugs with radiation and chemotherapy.

Anti-tumor effect of hematopoietic cells carrying the gene of ribonuclease inhibitor

Human ribonuclease inhibitor (hRI) is an acid protein with a molecular weight of 50 kDa. It can inhibit the activity of pancreatic RNase (RNase A). Angiogenin (Ang) is a member of the ribonuclease super family. It has 35% identity with RNase A and contains ribonucleolytic activity. The substrate specificity of angiogenin seems, however, to be more restricted than that of the pancreatic RNase. Since Ang is an important angiogenic factor and RI is a highly efficient inhibitor of Ang, it can be hypothesized that RI may be a latent antiangiogenic drug. This study focuses on the feasibility of transfecting the ri gene into mice hematopoietic cells and inducing the expression of the ri gene to block the angiogenesis of solid tumors. First, the cDNA gene of the ri from human placenta was cloned and inserted in a retroviral vector, pLNCX. The combined vector pLNCX-ri was transfected into retroviral packaging cells, PA317, and a clone producing a high titer of virus was obtained. Next, isolated hematopoietic cells from mice bone marrow were infected with viruses carrying the pLNCX-ri. The infected cells were then injected into lethally irradiated mice. The expression and the contribution of RI were assayed in vivo. After administration of hematopoietic cells carrying the ri gene, mice were implanted with B16 melanomas for 21 days. The results showed that tumors of control groups became large and well vascularized. In contrast, tumors from mice groups treated with hematopoietic cells carrying the ri gene were small and possessed a relatively low density of blood vessels. The inhibited growth rate of the tumors was 47%. This study demonstrated the potential utility of gene therapy for systemic delivery of a novel antiangiogenic agent--hRI.

Endogenous inhibitors of angiogenesis in malignant gliomas: nature's antiangiogenic therapy

Angiogenesis is necessary for tumor growth beyond a volume of approximately 2 mm(3). This observation, along with the accessibility of tumor vessels to therapeutic targeting, has resulted in a research focus on inhibitors of angiogenesis. A number of endogenous inhibitors of angiogenesis are found in the body. Some of these are synthesized by specific cells in different organs, and others are created by extracellular proteolytic cleavage of plasma-derived or extracellular matrix-localized proteins. In this review, we focus on angiostatin, endostatin, PEX, pigment epithelial-derived factor, and thrombospondin (TSP)-1 and -2, either because these molecules are expressed in malignant glioma biopsies or because animal studies in malignant glioma models have suggested that their therapeutic administration could be efficacious. We review the known mechanisms of action, potential receptors, expression in glioma biopsy samples, and studies testing their potential therapeutic efficacy in animal models of malignant glioma. Two conclusions can be made regarding the mechanisms of action of these inhibitors: (1) Several of these inhibitors appear to mediate their antiangiogenic effect through multiple protein-protein interactions that inhibit the function of proangiogenic molecules rather than through a specific receptor-mediated signaling event, and (2) TSP-1 and TSP-2 appear to mediate their antiangiogenic effect, at least in part, through a specific receptor, CD36, which initiates the antiangiogenic signal. Although not proven in gliomas, evidence suggests that expression of specific endogenous inhibitors of angiogenesis in certain organs may be part of a host antitumor response. The studies reviewed here suggest that new antiangiogenic therapies for malignant gliomas offer exciting promise as nontoxic, growth-inhibitory agents.

The kringle domain of tissue-type plasminogen activator inhibits in vivo tumor growth

The two-kringle domain of tissue-type plasminogen activator (t-PA) has previously been shown to contain anti-angiogenesis activity. In this study, we explored the potential in vivo anti-tumor effects of the recombinant kringle domain (TK1-2) of human t-PA. Anti-tumor effects of purified Pichia-driven TK1-2 were examined in nude mice models by subcutaneous implantation of human lung (A-549) and colon (DLD-1, HCT-116) cancer cell lines. Mice bearing the tumors were injected with PBS or purified TK1-2 (30 mg/kg) i.p. every day for 22 days. TK1-2 treatment suppressed the A-549, DLD-1, and HCT-116 tumor growth by 85.3%, 52.4%, and 62.5%, respectively. Immunohistological examination of the tumor tissues showed that TK1-2 treatment decreased the vessel density and also the expression of angiogenesis-related factors including angiogenin, VEGF, alpha-SMA, vWF, and TNF-alpha, and increased the apoptotic fraction of cells. TK1-2 neither inhibited in vitro growth of these cancer cells nor affected t-PA-mediated fibrin clot lysis. These results suggest that TK1-2 inhibits the tumor growth by suppression of angiogenesis without interfering with fibrinolysis.

Characterization and biological activities of recombinant human plasminogen kringle 1-3 produced in Escherichia coli

Angiogenesis, the formation of new capillaries from preexisting blood vessels, is involved in many pathological conditions, for example, tumorigenesis, diabetic retinopathy, and rheumatoid arthritis. Angiostatin, which contains the kringle 1-4 domains of plasminogen, is known to be a potent inhibitor of angiogenesis and a strong suppressor of various solid tumors. In this study, we expressed recombinant protein containing the kringle 1-3 domains of human plasminogen in Escherichia coli and investigated its biological activities. The protein was successfully refolded from inclusion bodies and purified at a 30% overall yield, as a single peak by HPLC. The purified recombinant protein had biochemical properties that were similar to those of the native form, which included molecular size, lysine-binding capacity, and immunoreactivity with a specific antibody. The recombinant protein was also found to strongly inhibit the proliferation of bovine capillary endothelial cells in vitro, and the formation of new capillaries on chick embryos. In addition, it suppressed the growth of primary Lewis lung carcinoma and B16 melanoma in an in vivo mouse model. Our findings suggest that the recombinant kringle 1-3 domains in a prokaryote expression system have anti-angiogenic activities, which may be useful in clinical and basic research in the field of angiogenesis.

Antiangiogenic therapy for primary and metastatic brain tumors

We first provide the theoretic foundation of antiangiogenic therapy by describing the biology of angiogenesis as it applies to brain tumors. We then outline experimental antiangiogenic therapies that are being applied preclinically to brain tumors, as well as published clinical trial data and ongoing clinical trials in patients. Primary and metastatic brain tumors are covered, although there is far less exploration in the literature of brain metastases.

Intramuscular delivery of antiangiogenic genes suppresses secondary metastases after removal of primary tumors

The success of surgery to remove primary tumors can be compromised by the subsequent outgrowth of metastases. It is recognized that primary tumors secrete antiangiogenic factors that suppress the outgrowth of their daughter metastases. In accord we show here that surgical removal of primary EL-4 lymphomas led to a marked decrease in the levels of circulating angiostatin and endostatin, and promoted the growth of distant nodular tumors. Expression vectors encoding angiostatin and endostatin, formulated with poly-N-vinyl pyrrolidone (PVP), were injected into the tibialis and gastrocnemia muscles, leading to expression of angiostatin and endostatin in muscle fibers. High levels of biologically active exogenous proteins were secreted into the circulation. Intramuscular gene therapy with angiostatin and endostatin plasmids significantly inhibited tumor vascularity and induced tumor cell apoptosis, and thereby suppressed the growth of secondary subcutaneous and disseminated metastatic tumors in the lung and liver. Simultaneous intramuscular delivery of both angiostatin and endostatin plasmids significantly prolonged the survival of mice after removal of primary tumors. These results suggest that intramuscular gene transfer of angiostatin and endostatin might serve as a prophylactic cancer-prevention strategy to combat the recurrence of cancer after surgical resection of primary tumors.

Identification and Characterization of a Novel Angiostatin-binding Protein by the Display Cloning Method

Angiostatin is a potent anti-angiogenic protein. To examine the angiostatin-interacting proteins, we used the display-cloning method with a T7 phage library presenting human cDNAs. The specific T7 phage clone that bound to the immobilized angiostatin was isolated, and a novel gene encoding the displayed polypeptide on the isolated T7 phage was identified. The displayed angiostatin-binding sequence was expressed in E. coli as a soluble protein and purified to homogeneity. This novel angiostatin-binding region interacted specifically to angiostatin with a dissociation constant of 3.4 x 10(-7) M. A sequence analysis showed that the identified sequence was a part of the large ORF of 1,998 amino acids, whose function has not yet been characterized. A Northern analysis indicated that the gene containing the angiostatin-binding sequence was expressed differentially in the developmental stages or cell types.

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.

Inhibition of angiogenesis and angiogenesis-dependent tumor growth by the cryptic kringle fragments of human apolipoprotein(a)

Apolipoprotein(a) (apo(a)) contains tandemly repeated kringle domains that are closely related to plasminogen kringle 4, followed by a single kringle 5-like domain and an inactive protease-like domain. Recently, the anti-angiogenic activities of apo(a) have been demonstrated both in vitro and in vivo. However, its effects on tumor angiogenesis and the underlying mechanisms involved have not been fully elucidated. To evaluate the anti-angiogenic and anti-tumor activities of the apo(a) kringle domains and to elucidate their mechanism of action, we expressed the last three kringle domains of apo(a), KIV-9, KIV-10, and KV, in Escherichia coli. The resultant recombinant protein, termed rhLK68, exhibited a dose-dependent inhibition of basic fibroblast growth factor-stimulated human umbilical vein endothelial cell proliferation and migration in vitro and inhibited the neovascularization in chick chorioallantoic membranes in vivo. The ability of rhLK68 to abrogate the activation of extracellular signal-regulated kinases appears to be responsible for rhLK68-mediated anti-angiogenesis. Furthermore, systemic administration of rhLK68 suppressed human lung (A549) and colon (HCT-15) tumor growth in nude mice. Immunohistochemical examination and in situ hybridization analysis of the tumors showed a significant decrease in the number of blood vessels and the reduced expression of vascular endothelial growth factor, basic fibroblast growth factor, and angiogenin, indicating that suppression of angiogenesis may have played a significant role in the inhibition of tumor growth. Collectively, these results suggest that a truncated apo(a), rhLK68, is a potent anti-angiogenic and anti-tumor molecule.

Angiogenesis factors in gliomas: a new key to tumour therapy?

Angiogenesis, the formation of new blood vessels, is required for the growth and expansion of tumours. Gliomas, the most common brain tumours, are particularly highly vascularized and, therefore, serve as a model to elucidate the process of tumour angiogenesis and to investigate new anti-angiogenic therapies. This review describes the role of angiogenic factors in glioma angiogenesis and new strategies to inhibit glioma growth by application of anti-angiogenic substances. We focus on vascular endothelial growth factor (VEGF), but also examine the role of angiopoietin and pleiotropic factors such as platelet-derived growth factor (PDGF), pleiotrophin and transforming growth factor-beta (TGF-beta). Strategies to inhibit glioma growth by reducing the action of angiogenic factors, by the application of anti-angiogenic substances such as angiostatin or endostatin, or inactivation of endothelial cells, are discussed. These new anti-angiogenic therapies appear to have a high potential not only for the treatment of gliomas, but also of other tumours.

Systemic administration of a recombinant adenovirus encoding a HSA-Angiostatin kringle 1-3 conjugate inhibits MDA-MB-231 tumor growth and metastasis in a transgenic model of spontaneous eye cancer

We previously reported that intratumoral injection of AdK3, a recombinant adenovirus encoding human angiostatin kringle (K) 1 to 3, inhibits tumor vascularization and tumor growth. To reduce the serum clearance of this factor, we constructed an adenovirus (AdK3-HSA) that carries a chimeric gene encoding a fusion protein between angiostatin K1-3 and human serum albumin (HSA). This conjugate inhibited endothelial cell proliferation as efficiently as K1-3. K3-HSA serum concentrations in immunodeficient mice systemically injected with AdK3-HSA were dramatically higher than in AdK3-injected mice. Furthermore, the growth of MDA-MB-231 tumors grafted into nude mice that had been injected intravenously with AdK3-HSA was inhibited by 79% (versus 17% with AdK3). In TRP-1/SV40 Tag transgenic mice, which spontaneously develop eye tumors with brain metastases, intravenous injections of AdK3-HSA in newborn mice blocked metastatic dissemination efficiently and significantly, and prolonged survival by 3 weeks. After 2 months, only 46% of AdK3-HSA-treated animals developed micrometastases, whereas 94% of the AdCO1-injected group displayed numerous macrometastases. Nevertheless, ocular tumor growth was not modified because of impaired diffusion of the conjugate in the eye compartment. Our results show that HSA genetic coupling is an efficient way to increase the pharmacokinetics of circulating angiogenic inhibitors and thus their antitumoral activity.

Angiostatin prolongs the survival of mice with leptomeningeal metastases

BACKGROUND

As a result of the more effective treatment of primary tumours, the incidence of leptomeningeal metastases (LM) is increasing. Current treatment modalities have little effect on the survival of patients with LM. We investigated whether antiangiogenic treatment inhibits the progression of leptomeningeal tumours.

MATERIALS AND METHODS

To assess the role of angiogenesis in leptomeningeal tumours, we inoculated melanoma cells in the subarachnoid space in balb/c mice. At different stages, the mice were sacrificed and the microvessel density was determined. Human specimens of LM were compared with the mouse model. For the intervention studies, the mice were treated with the angiogenesis inhibitor angiostatin. Survival was the endpoint in these studies.

RESULTS

Tumour seeding in the early disease stages was concentrated around the pre-existent arachnoid vasculature. In the more advanced stages, the tumour masses covered larger areas of the leptomeninges. Arachnoidal microvessel density in this advanced stage was increased compared with control mice. Systemic treatment of the mice with LM with angiostatin (100 mg kg-1 day-1) resulted in prolonged survival compared with mice treated with vehicle and with approximately one-fifth of the long-term survivors of the angiostatin-treated group.

CONCLUSIONS

This study shows that neovascularization is important in the growth of LM in mice. Systemic targeting of the vascular compartment may be a useful approach in novel therapeutic strategies for patients with LM.

Efficacy of BCNU and paclitaxel loaded subcutaneous implants in the interstitial chemotherapy of U-87 MG human glioblastoma xenografts

Nude mice were challenged with human U-87 MG glioblastoma tumors to assess the efficacy of different cytostatics and different application protocols. While the intraperitoneal application of BCNU solutions (3 times 20 mg BCNU/kg) had no effect on tumor growth, the application of polymer matrices made of a physical mixture of poly(1,3-bis[carboxyphenoxpropane]-co-sebacic acid) 20:80 with poly(D,L-lactic-co-glycolic acid) loaded with 0.25 mg BCNU, slowed down the growth of tumors significantly. When the animals were treated with implants carrying 0.25 mg BCNU they responded to the treatment whether the tumor had been inoculated recently (9 days ago) or whether it was fully established (after 20 days). After its sensitivity was proven, the xenograft model was used to further investigate the efficacy of anticancer drugs and some treatment regimens using polymer implants. Thus the tumor model allowed to discriminate between the efficacy of different doses of BCNU. Only implants loaded with 0.75 or 1 mg of BCNU led to a substantial suppression of tumor growth over approximately 2 months. While BCNU was only able to suppress the growth of the tumor, the combination of BCNU with paclitaxel led to a complete remission in some animals. These preliminary results suggest that combinations of cytostatics might improve local chemotherapy of malignant glioma substantially. Based on our data it will be worthwhile to investigate implants that release drugs such as BCNU and paclitaxel closer. Amongst other factors we will try to elucidate the effect of repetitive doses of drugs using programmable implants.

The X-ray crystallographic structure of the angiogenesis inhibitor angiostatin

Angiogenesis inhibitors have gained much public attention recently as anti-cancer agents and several are currently in clinical trials, including angiostatin (Phase I, Thomas Jefferson University Hospital, Philadelphia, PA). We report here the bowl-shaped structure of angiostatin kringles 1-3, the first multi-kringle structure to be determined. All three kringle lysine-binding sites contain a bound bicine molecule of crystallization while the former of kringle 2 and kringle 3 are cofacial. Moreover, the separation of the kringle 2 and kringle 3 lysiner binding sites is sufficient to accommodate the alpha-helix of the 30 residue peptide VEK-30 found in the kringle 2/VEK-30 complex. Together the three kringles produce a central cavity suggestive of a unique domain where they may function in concert.

Intratumoral gene therapy of malignant brain tumor in a rat model with angiostatin delivered by adeno-associated viral (AAV) vector

We have utilized a recombinant adeno-associated viral (AAV) vector carrying the angiostatin gene as an anti-angiogenesis strategy to treat the malignant brain tumor in a C6 glioma/Wistar rat model. Angiostatin, as a potent angiogenesis inhibitor, shows high promises as an anti-cancer drug through the inhibition of tumor neovessel formation. However, sustained in vivo protein delivery is required to achieve the therapeutic effects. The AAV vector has been proven to be able to deliver sustained and high-level gene expression in vivo, and therefore, is well suited to such a purpose. In this study, we implanted 5 x 10(5) C6 glioma cells into the rat brain 7 days before gene therapy. Intratumoral injection of a high-titer AAV-angiostatin vector has rendered efficacious tumor suppression and resulted in long-term survival in 40% of the treated rats, whereas the control AAV-GFP vector did not have any therapeutic benefits. In addition, we have investigated the combined gene therapy of an adenoviral vector carrying the suicidal thymidine kinase gene along with the AAV-angiostatin vector. The combined therapy offered the best tumor-suppressive effects and increased long-term survival to 55% in the treated rats. Our study has demonstrated the potential of using AAV as a safe and effective vector for anti-angiogenic gene therapy of brain tumors.

Angiostatin enhances B7.1-mediated cancer immunotherapy independently of effects on vascular endothelial growth factor expression

Tumors must develop an adequate vascular network to meet their increasing demands for nutrition and oxygen. Angiostatin, a multiple kringle (1-4)-containing fragment of plasminogen, is an effective natural inhibitor of tumor angiogenesis. Here we show that gene transfer of angiostatin into small (0.1 cm in diameter) solid EL-4 lymphomas established in syngeneic C57BL/6 mice led to reduced tumor angiogenesis and weak inhibition of tumor growth. In contrast, when angiostatin gene therapy was preceded by in situ gene transfer of the T-cell costimulator B7.1, large (0.4 cm in diameter) tumors were rapidly and completely eradicated, whereas B7.1 and angiostatin monotherapies were ineffective. Combined gene transfer of B7.1 and angiostatin generated potent systemic antitumor immunity that was effective in eradicating a systemic challenge of 10(7) EL-4 cells. Gene transfer of angiostatin expression plasmids led to overexpression of angiostatin in tumors, increased apoptosis of tumor cells, and decreased density of tumor blood vessels, which may allow the immune system to overcome tumor immune resistance. The latter effects were not the result of a decrease in vascular endothelial growth factor expression, as tumoral vascular endothelial growth factor expression increased slightly after angiostatin gene transfer, presumably in response to increasing hypoxia. These results suggest that combining immunogene therapy with a vascular attack by angiostatin is a particularly effective approach for eliciting antitumor immunity.

The hemostatic system and angiogenesis in malignancy

Coagulopathy and angiogenesis are among the most consistent host responses associated with cancer. These two respective processes, hitherto viewed as distinct, may in fact be functionally inseparable as blood coagulation and fibrinolysis, in their own right, influence tumor angiogenesis and thereby contribute to malignant growth. In addition, tumor angiogenesis appears to be controlled through both standard and non-standard functions of such elements of the hemostatic system as tissue factor, thrombin, fibrin, plasminogen activators, plasminogen, and platelets. "Cryptic" domains can be released from hemostatic proteins through proteolytic cleavage, and act systemically as angiogenesis inhibitors (e.g., angiostatin, antiangiogenic antithrombin III aaATIII). Various components of the hemostatic system either promote or inhibit angiogenesis and likely act by changing the net angiogenic balance. However, their complex influences are far from being fully understood. Targeted pharmacological and/or genetic inhibition of pro-angiogenic activities of the hemostatic system and exploitation of endogenous angiogenesis inhibitors of the angiostatin and aaATIII variety are under study as prospective anti-cancer treatments.

Application of advances in molecular biology to the treatment of brain tumors

Recent advances in molecular biology have substantially improved our understanding of the molecular genetics of primary brain neoplasms. Soon each histopathologic category of glioma will be further divided into subgroups according to similar genetic background, gene expression profile, and similarity of biologic responses to radiotherapy or chemotherapy. Identification of key molecules that are specifically altered in neoplastic cells will provide candidate molecular targets for tumor treatment. Novel therapeutic tools for targeting tumor cells, such as viral vectors for gene therapy, have been created. In the near future, the accumulation of new knowledge in brain tumor biology and genetics, combined with rational drug design, will revolutionize the treatment of malignant gliomas, which are among the most lethal human cancers.

Antiangiogenic therapy in brain tumor models

The prognosis of patients with malignant brain tumors remains poor despite new developments in neurosurgery, chemotherapy and radiotherapy. Malignant gliomas are highly vascularized, and there is ample evidence that their growth is angiogenesis-dependent. Therefore, new therapeutic approaches often include the inhibition of angiogenesis. In this review, experimental studies of antiangiogenic agents in brain tumor models are summarized. The results of these experiments as well as potential pitfalls in extrapolation to the clinic are discussed.

Combined effects of radiotherapy and angiostatin gene therapy in glioma tumor model

The objective of the present study was to evaluate the antitumor effect of a defective adenovirus expressing a secretable angiostatin-like molecule (AdK3) in combination with radiotherapy in rat C6 gliomas s.c. preestablished into athymic mice. In vitro, the combination regimen was significantly (P < 0.001) more cytotoxic for human microcapillary endothelial cells than either treatment alone, whereas survival of C6 glioma cells was not affected in the conditions used. Radiotherapy and AdK3 gene delivery was then studied on well established C6 xenografts (165 +/- 70 mm(3)). In these tumors, AdK3 intratumoral injections had only a marginal effect. Interestingly, when experimental radiotherapy was added, significantly higher (P < 0.005), and possibly synergistic, antitumoral effects were observed that tightly correlated a marked decrease of intratumoral vascularization. The combination of radiotherapy and AdK3 intratumoral injections also revealed a significant (P < 0.05) inhibition of tumor growth as compared with either treatment alone for larger tumors (467 +/- 120 mm(3)). Altogether, these data emphasize the potential of combining a destructive strategy directed against the tumor cells with an anti-angiogenic approach to fight cancer.

Disruption of interkringle disulfide bond of plasminogen kringle 1-3 changes the lysine binding capability of kringle 2, but not its antiangiogenic activity

Kringle 1-3 of human plasminogen is a potent inhibitor of endothelial cell proliferation. To understand a possible role for the unique cystine bridge between kringle 2 and kringle 3, we disrupted the interkringle disulfide bond by mutating Cys(169) and Cys(297) to serine residues. The yield of the mutant during the refolding process was decreased significantly. Anti-endothelial cell proliferative activity of the mutant was similar to that of the wild type. There was no significant difference in in vivo antiangiogenic activity between the wild type and the mutant in chorioallantoic membrane assay. However, in the mutant, the weak lysine binding capability of kringle 2 was not detected and its mobility in nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis is different from that of the wild type. These results support the notion that the overall antiangiogenic function of angiostatin is mediated by individual kringles, and suggest that the lysine binding capability of kringle 2 is likely not important for the antiangiogenic activity of kringle 1-3.