Continuous administration of angiostatin inhibits accelerated growth of colorectal liver metastases after partial hepatectomy.
(17/210)
Human plasminogen-derived angiostatin is one of the most potent antiangiogenic agents currently known. However, it is unclear whether angiostatin is also effective against accelerated tumor growth induced by local up-regulation of growth factors, including angiogenesis stimulators, such as in regenerating liver. Prior to addressing this question, we tested, in mice, whether continuous administration of angiostatin could improve its biological effects. This assumption was based on the relatively short half-life of angiostatin in mice, as well as on the theoretical necessity to suppress tumor-induced angiogenesis continually. The findings presented here clearly indicate continuous administration to be superior to the conventional twice-daily bolus injections. Using the maximally effective regimen of 100 mg/kg/day via s.c. pump infusion, we found angiostatin to not only suppress s.c. primary tumors but also to significantly inhibit the outgrowth of colorectal hepatic metastases in resting liver and even to inhibit accelerated tumor growth in regenerating liver after 70% partial hepatectomy. In conclusion, angiostatin could play an important role in patients subjected to partial hepatectomy to prevent outgrowth of residual micrometastases, provided it is administered continuously to obtain maximal biological effects. (+info)
Synergy between angiostatin and endostatin: inhibition of ovarian cancer growth.
(18/210)
Ovarian cancer is the leading cause of fatality among gynecological malignancies. Ovarian cancer growth is angiogenesis-dependent, and an increased production of angiogenic growth factors such as vascular endothelial growth factor is prognostically significant even during early stages of the disease. Therefore, we investigated whether antiangiogenic treatment can be used to inhibit the growth of ovarian cancer in an experimental model system. Mouse angiostatin (kringle 1-4) and endostatin were expressed in yeast. Purified angiostatin and endostatin were then used to treat established ovarian cancers in athymic mice. These studies showed that both angiostatin and endostatin inhibited tumor growth. However, angiostatin treatment was more effective in inhibiting ovarian cancer growth when compared with endostatin in parallel experiments. Residual tumors obtained from angiostatin- and endostatin-treated animals showed decreased number of blood vessels and, as a consequence, increased apoptosis of tumor cells. Subsequently, the efficacy of a combined treatment with angiostatin and endostatin was investigated. In the presence of both angiostatic proteins, endothelial cell proliferation was synergistically inhibited. Similarly, a combination regimen using equal amounts of angiostatin and endostatin showed more than additive effect in tumor growth inhibition when compared with treatment with individual angiostatic protein. These studies demonstrate synergism between two angiostatic molecules and that antiangiogenic therapy can be used to inhibit ovarian cancer growth. (+info)
A novel strategy for the tumor angiogenesis-targeted gene therapy: generation of angiostatin from endogenous plasminogen by protease gene transfer.
(19/210)
When NIH 3T3 fibroblasts were transduced with a retroviral vector containing a cDNA for porcine pancreatic elastase 1 and cultured in the presence of affinity-purified human plasminogen, the exogenously added plasminogen was digested to generate the kringle 1-3 segment known as angiostatin, a potent angiogenesis inhibitor. This was evidenced by immunoblot analysis of the plasminogen digests using a monoclonal antibody specifically reacting with the kringle 1-3 segment, and by efficient inhibition of proliferation of human umbilical vein endothelial cells by the plasminogen digests isolated from the culture medium of 3T3 fibroblasts. However, when Lewis lung carcinoma cells were transduced with the same vector and injected subcutaneously into mice in their back or via the tail vein, their growth at the injection sites or in the lungs was markedly suppressed compared with the growth of similarly treated nontransduced Lewis lung carcinoma cells. Nevertheless, the transduced cells were able to grow as avidly as the control cells in vitro. Assuming that the elastase 1 secreted from the transduced cells is likely to be exempt from rapid inhibition by its physiological inhibitor, alpha1-protease inhibitor, as shown in the inflammatory tissues, the elastase 1 secreted from the tumor cells may effectively digest the plasminogen that is abundantly present in the extravascular spaces and generate the kringle 1-3 segment in the vicinity of implanted tumor cell clusters. Although the selection of more profitable virus vectors and cells to be transduced awaits further studies, such a protease gene transfer strategy may provide us with a new approach to anti-angiogenesis gene therapy for malignant tumors and their metastasis in vivo. (+info)
Mouse macrophage metalloelastase gene transfer into a murine melanoma suppresses primary tumor growth by halting angiogenesis.
(20/210)
Mouse macrophage metalloelastase (MME) has been associated with the generation of angiostatin, an internal fragment of plasminogen, which inhibits angiogenesis. To clarify whether tumor cells that consistently generate MME can suppress angiogenesis and, therefore, inhibit the growth of primary tumors in vivo, we transfected a cDNA coding for MME into murine B16-BL6 melanoma cells that grow rapidly and are MME deficient. The generation of active MME in MME-transfected clones was confirmed by immunoprecipitation followed by in vitro cleavage of plasminogen. Subcutaneous implantation of these stable clones in C57BL/6 mice inhibited primary tumor growth by an average of 73% (P = 0.00002), which directly correlated with a significant reduction of blood vessel formation (approximately 76%) in such tumors. Microangiography revealed massive angiogenesis in control tumors (mock and vector); however, in MME-transfected primary tumors it demonstrated a decreased and disrupted vascular network. Western blot analysis using a specific anti-mouse angiostatin antibody demonstrated a strong 38-kDa immunoreactive band in MME-transfected tumors and in the serum of mice bearing those tumor cells. These results show that placing MME gene directly into B16-BL6 melanoma cells is an effective approach to suppress primary tumor growth in vivo because it halts angiogenesis. Our data provide a feasible and promising strategy for gene therapy of cancer by targeting tumor vasculature. (+info)
Combined effects of radiotherapy and angiostatin gene therapy in glioma tumor model.
(21/210)
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. (+info)
Liposome-delivered angiostatin strongly inhibits tumor growth and metastatization in a transgenic model of spontaneous breast cancer.
(22/210)
The possibility to inhibit tumor growth by interfering with the formation of new vessels, which most neoplasias depend on, has recently raised considerable interest. An angiogenic switch, in which proliferating cells acquire the ability to direct new vessel formation, is thought to be an early step in the natural history of solid tumors. Using a transgenic model of breast cancer, which shows many similarities to its human counterpart, including ability to metastasize, we targeted angiostatin production to an early stage of tumor formation. Liposome-delivered angiostatin considerably delayed primary tumor growth and, more importantly, inhibited the appearance of lung metastases. These findings can be relevant to the design of therapeutic intervention in humans. (+info)
Binding of the NG2 proteoglycan to kringle domains modulates the functional properties of angiostatin and plasmin(ogen).
(23/210)
Interactions of the developmentally regulated chondroitin sulfate proteoglycan NG2 with human plasminogen and kringle domain-containing plasminogen fragments have been analyzed by solid-phase immunoassays and by surface plasmon resonance. In immunoassays, the core protein of NG2 binds specifically and saturably to plasminogen, which consists of five kringle domains and a serine protease domain, and to angiostatin, which contains plasminogen kringle domains 1-3. Apparent dissociation constants for these interactions range from 12 to 75 nm. Additional evidence for NG2 interaction with kringle domains comes from its binding to plasminogen kringle domain 4 and to miniplasminogen (kringle domain 5 plus the protease domain) with apparent dissociation constants in the 18-71 nm range. Inhibition of plasminogen and angiostatin binding to NG2 by 6-aminohexanoic acid suggests that lysine binding sites are involved in kringle interaction with NG2. The interaction of NG2 with plasminogen and angiostatin has very interesting functional consequences. 1) Soluble NG2 significantly enhances the activation of plasminogen by urokinase type plasminogen activator. 2) The antagonistic effect of angiostatin on endothelial cell proliferation is inhibited by soluble NG2. Both of these effects of NG2 should make the proteoglycan a positive regulator of the cell migration and proliferation required for angiogenesis. (+info)
Angiostatin expression in non-small cell lung cancer.
(24/210)
Angiostatin, a potent inhibitor of angiogenesis, tumor growth, and metastasis, was examined in a panel of human lung cancer cell lines with Western blot analysis and in 143 primary non-small cell lung carcinomas with immunohistochemistry. Thirty-four of 143 cases (24%) stained positively. Patients with angiostatin-positive tumors survived longer (146 weeks) than patients with angiostatin-negative tumors (77 weeks; log-rank test: P = 0.07; rank-sum test: P = 0.02). To determine whether combining stimulating and inhibiting factors might improve the prognostic capability, both angiostatin and vascular endothelial growth factor (VEGF) were analyzed together with respect to patient survival. The median survival time of patients with angiostatin-positive/VEGF-negative carcinomas was 184 weeks, whereas the median survival time of patients with angiostatin-negative/VEGF-positive tumors was only 52 weeks. The angiostatin-positive tumors exhibited an increased incidence of apoptosis and a reduced capability to be transplanted into nude mice, but these differences did not reach or were only of borderline statistical significance. (+info)