The therapeutic efficacy of angiostatin against weakly- and highly-immunogenic 3LL tumors

BACKGROUND

Antiagiogenesis represents a promising approach to cancer therapy. We have previously demonstrated that the antitumor effects of endostatin, one of the most potent angiostatic agents, could be enhanced when combined with immunotherapy. Our current study evaluated whether anti-tumor immune response could also potentiate the therapuetic efficacy of another antiangiogenic drug, angiostatin.

METHODS AND RESULTS

Using Matrigel assay, we showed that our preparation of recombinant angiostatin possessed potent anti-angiogenic activity in vivo. The antitumor effects of recombinant angiostatin were tested against weakly-immunogenic 3LL Lewis lung carcinoma versus its highly immunogenic variant 3LL-C75. We showed that angiostatin inhibited the growth of 3LL-C75 more potently than that of 3LL tumor, suggesting that the host's immune response potentiates the antitumor effects of angiostatin. This conclusion was further supported by the finding that the antitumor activity of angiostatin against 3LL-C75 tumor was lower in immunodeficient nude mice in comparison with immunocompetent mice. Immunization of C57BL/6 mice with 3LL-C75 cells stimulated the antitumor immunity and inhibited the growth of parental 3LL tumor. Angiostatin treatment of immunized mice further enhanced the antitumor effect of tumor vaccination.

CONCLUSION

Antitumor immune response could complement the therapeutic efficacy of angiostatin.

Therapeutic effect of angiostatin gene transfer in a murine model of endometriosis

Endometriosis, the growth of ectopic endometrial tissue, is a chronic recurrent disease affecting 10% of the female population causing dyspareunia, pelvic pain, dysmenorrhea, and infertility. Suppression of ovarian activity is the cornerstone of medical therapy with limited benefit and severe adverse effects. Angiogenesis plays a major role in the development of endometriosis suggesting that anti-angiogenic therapy would offer a new therapeutic approach. We report successful treatment of endometriosis in estrogen-supplemented ovariectomized mice by transient overexpression (6 to 10 days of duration) of the gene for a natural angiogenesis inhibitor angiostatin, delivered to the peritoneum by a replication-deficient adenovirus vector (AdAngiostatin). Established endometriosis was eradicated in 14 of 14 AdAngiostatin-treated animals, whereas 11 of 13 control animals showed full disease development. Administered to normal cycling mice for the same transient period, AdAngiostatin caused impaired ovarian function with suppressed corpus luteum development, decreased production of estradiol and progesterone, decreased ovarian and uterine weight, and increased body weight. AdAngiostatin treatment lowered the levels of sex steroids but did not induce total castration. Gene therapy with angiogenic inhibitors is a highly effective treatment for endometriosis, even in a host with preserved estrogen levels. However, local or targeted delivery of the gene must be considered to avoid prolonged systemic effects and impaired ovarian function.

Angiostatin inhibits and regresses corneal neovascularization

OBJECTIVE

To determine the ability of angiostatin and the angiostatin-producing low-metastatic (LM) clone of Lewis lung carcinoma (LLC) to inhibit and regress corneal neovascularization, as compared with the non-angiostatin-producing high-metastatic (HM) clone.

METHODS

Three groups of C57BL6/J mice underwent chemical and mechanical denudation of corneal and limbal epithelium. One group remained tumor free while the other 2 were implanted with LLC cells (either the HM or LM clones) subcutaneously the day before, 2 weeks after, or 4 weeks after denudation. Corneas were harvested 2 weeks after tumor implantation (at 2, 4, and 6 weeks after denudation for tumor-free mice). Neovascularization was quantified by CD31 immunostaining. In a second experiment, recombinant angiostatin was delivered continuously for 2 weeks via an osmotic pump in mice with established corneal neovascularization.

RESULTS

The mean percentages of neovascularized corneal area in mice 2 weeks after LM-LLC implantation were 4.6%, 3.7%, and 37.0%, at 2, 4, and 6 weeks after scraping, respectively. In contrast, in the mice implanted with HM-LLC, the corresponding values were 45.4% (P =.01), 90.1% (P =.03), and 80.3% (P =.005). For tumor-free mice, the corresponding values were 62.0% (P =.003), 68.9% (P =.03), and 59.3% (P =.06). Mice implanted with angiostatin pumps had a 37.7% neovascularized corneal area 2 weeks after implantation and 4 weeks after scraping while mice implanted with sham pumps had 60.5% (P =.007).

CONCLUSION

Angiostatin inhibits and regresses corneal neovascularization induced by mechanical and alkali corneal injury.

CLINICAL RELEVANCE

This appears to be the first evidence of biologically induced regression of corneal neovascularization, and the first direct demonstration of angiostatin-induced regression of neovascularization in any tissue.

Effective treatment of ligneous conjunctivitis with topical plasminogen

PURPOSE

The etiology of ligneous conjunctivitis is now known to be due to an underlying type 1 plasminogen deficiency. We hereby report the clinical features of three cases and their response to topically administered plasminogen.

DESIGN

Observational case series.

METHODS

Two Caucasian females aged 5 years and an 18-month male of north African descent presented with a membranous conjunctivitis, which recurred after surgical excision. Case 1 presented before the association with plasminogen deficiency was known with a bilateral chronic membranous mucopurulent conjunctivitis from the age of 14 months associated with bronchiolitis and gingival hyperplasia. A diagnosis of ligneous conjunctivitis was entertained and a number of drops were instituted. At the age of 4 years plasminogen levels were ordered. Case 2 presented at the age of 4 years with a unilateral chronic membranous conjunctivitis. Plasminogen levels were requested as soon as a diagnosis of ligneous conjunctivitis was suspected. Case 3 was born with congenital hydrocephalus. Conjunctivitis was treated with antibiotics from the age of 1 month. He presented to the eye clinic at the age of 5 months when a clinical diagnosis of ligneous conjunctivitis was entertained and treated with a number of medications. Plasminogen levels were available at 9 months of age.

RESULTS

The two female patients returned plasminogen levels of 0.25 U/ml and 0.3 U/ml, well below the normal level of 0.7-1.0 U/ml. Functional plasminogen levels in the male infant were not recordable with plasminogen antigen levels of 0.125 U/ml (normal range, 0.52-1.82). All cases have responded well to excision of the membranes and institution of topical plasminogen drops. There has been no recurrence with more than 12 months' follow-up.

CONCLUSIONS

With the knowledge of the etiology of ligneous conjunctivitis, efforts are underway to identify the best method of delivery of plasminogen. Topical plasminogen concentrate from fresh frozen plasma holds promise as the definitive treatment for this chronic membranous conjunctivitis

[Information about cancer treatment and the media]

A 'hopeful' development in cancer treatment (angiostatin) was reported in the Dutch press, which led to considerable disquiet amongst patients. There were no scientific articles that warranted this press publication. It has previously been stated that it is unethical for medical researchers to inform the press about treatments which have not been scrutinized by the medical community. The press on the other hand, should maintain a more responsible attitude toward medical claims and double-check medical information, even when it comes from renowned medical researchers. The main distinction between mainstream medicine and medical quackery is that the former is based on the results of controlled published research. When physicians propagate results in the popular press that have not been critically evaluated by the medical community, the distinction between quackery and mainstream medicine is undermined.

Angiogenesis in ovarian cancer: molecular pathology and therapeutic strategies

Ovarian cancer claims the lives of more women in North America each year than all other gynecologic malignancies combined. Despite the high initial response rates of patients with advanced ovarian cancer to aggressive primary surgical debulking followed by combination chemotherapy, the majority of patients will ultimately develop disease recurrence. The high risk of relapse and nearly guaranteed incurability after relapse is due to genetic instability and a high mutation rate of neoplastic cells that together allow for a high risk of selection for drug resistance. Given the seemingly insurmountable obstacle that acquired drug resistance presents in a setting of minimal, often undetectable, residual tumor burden in women with ovarian cancer, antiangiogenic-targeted therapies offer an attractive strategy for enhanced long-term disease-free survival. The past decade has witnessed a substantial proliferation in our knowledge regarding tumor angiogenesis, which has spurred interest in antiangiogenesis drug development. Current clinical trials are evaluating these agents in a variety of solid tumors, including ovarian cancer. Preliminary work has provided hope that the addition of antiangiogenic therapies may be incorporated into the treatment of women afflicted with ovarian cancer and may translate into enhanced survival.

Antiangiogenic and antifibrotic gene therapy in a chronic infusion model of peritoneal dialysis in rats

To identify the relative importance of peritoneal fibrosis and angiogenesis in peritoneal membrane dysfunction, adenoviral mediated gene transfer of angiostatin, a recognized angiogenesis inhibitor, and decorin, a transforming growth factor-beta-inhibiting proteoglycan, were used in a daily infusion model of peritoneal dialysis. A peritoneal catheter and subcutaneous port were inserted in rats. Five and fourteen d after insertion, adenovirus-expressing angiostatin, decorin, or AdDL70, a null control virus, were administered. Daily infusion of 4.25% Baxter Dianeal was initiated 7 d after catheter insertion and continued until day 35. Three initial doses of lipopolysaccharide were administered on days 8, 10, and 12 to promote an inflammatory response. Net ultrafiltration was used as a measure of membrane function, and peritoneum-associated vasculature and mesenteric collagen content was quantified. Ultrafiltration dysfunction, angiogenesis, and fibrosis were observed in daily infusion control animals. Animals treated with AdAngiostatin demonstrated an improvement in net ultrafiltration (-3.1 versus -7.8 ml for control animals; P = 0.0004) with a significant reduction in vessel density. AdDecorin-treated animals showed a reduction in mesenteric collagen content (1.8 versus 2.9 microg/mg; P = 0.04); however, AdDecorin treatment had no effect on net ultrafiltration. In a rodent model of peritoneal membrane failure, net ultrafiltration was significantly improved and peritoneal-associated blood vessels were significantly reduced by using adenovirus-mediated gene transfer of angiostatin. Decorin, a transforming growth factor-beta-inhibiting proteoglycan, reduced collagen content but did not affect net ultrafiltration. Improvement in the function of the peritoneum as a dialysis membrane after treatment with angiostatin has implications for treatment of peritoneal membrane dysfunction seen in patients on long-term dialysis.

Recurrent venous thrombosis in Behçet's disease: successful endovascular treatment with thrombolysis and stent

We report the case of a patient with Behçet's disease (BD) and recurrent venous thrombosis in the right subclavian vein, successfully treated with balloon dilatation and the insertion of a Wallstent. Subsequent follow up at 6 months showed no evidence of reocclusion. Endovascular stents should be considered as a possible interventional modality in BD patients with aneurysms or recurrent venous or arterial thrombosis.

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.

[Anti-angiogenesis - a therapy concept in the treatment of head and neck carcinomas? A review]

BACKGROUND

Head and neck squamous cell carcinoma (HNSCC) is an aggressive malignancy that is now the sixth most common neoplasm in the world. Despite numerous advances in treatment, the long-term survival has remained the same for the last 25 years. Angiogenesis has been shown to be important for HNSCC tumour growth and metastasis. Therefore, inhibitors of angiogenesis are a new class of anti-neoplastic substances that might be a powerful complement to conventional therapy in HNSCC.

MATERIAL AND METHODS

The role of angiogenesis in HNSCC as well as preclinical and clinical trials concerning inhibitors of tumor-angiogenesis are discussed here.

RESULTS

Many of the investigated angiogenesis inhibitors demonstrated anti-tumor effects in preclinical and clinical trials. In a few cases, partial remission was observed.

CONCLUSIONS

Anti-angiogenic therapy will undoubtly have the potential to change standard tumor therapies. Some anti-angiogenic substances appear to be promising candidates for a clinical use in the therapy of HNSCC.

Angiostatin gene therapy inhibits the growth of murine squamous cell carcinoma in vivo

Tumor growth is an angiogenesis-dependent process and therapeutic strategies aimed at inhibiting angiogenesis are theoretically attractive. Angiostatin has been shown to potently inhibit endothelial proliferation in vitro and tumor growth in vivo. We now show that a shift in the balance of tumor angiogenesis by gene transfer of a cDNA coding for mouse angiostatin into mouse squamous cell carcinoma NRS-1 and SCC-VII cells suppresses tumor growth in vivo. The inhibition of an angiostatin-transfected tumor was accompanied by a marked reduction in vascularity and the presence of many apoptotic tumor cells. However, transfected-angiostatin cDNA does not affect the expression of the vascular endothelial growth factor (VEGF) and VEGF-R2 in the vascular endothelium. The inhibition mechanisms of neovascularization may be mediated independent of VEGF:VEGF-R2 complex. Our data may provide a useful approach for human oral cancer therapy by gene therapy with angiostatin.

[Tumor angiogenesis and tumor angiogenesis inhibitors]

It is important to survey the molecular targets which are involved in tumor angiogenesis for the development of antiangiogenic agents as one of the cancer therapy. This article is meant to review the recent molecular targets of tumor angiogenesis and the molecular mechanism of antiangiogenic agents in human clinical trials.

Recombinant angiostatin prevents retinal neovascularization in a murine proliferative retinopathy model

Retinal neovascularization is central to the pathogenesis of proliferative diabetic retinopathy, the leading cause of blindness among the middle-aged population. Angiostatin, a proteolytic fragment of plasminogen is one of the most promising inhibitors of angiogenesis currently in clinical trials. Here we show that recombinant angiostatin can inhibit retinal neovascularization in a mouse model of proliferative retinopathy. Because proliferative diabetic retinopathy is a recurrent disease, effective therapy will need to be sustained. Recombinant adeno-associated viruses permit long-term expression of transfected genes; however, they can only accommodate a small insert sequence. Thus, we engineered and tested a shortened recombinant angiostatin derivative containing a signal sequence to permit secretion. Recombinant protein was purified from the medium of transfected HEK293 cells and injected subcutaneously into treated animals. The retinal vasculature was analyzed in retinal flat mounts and using immunohistochemically stained sections. Both methods demonstrate that this short, secreted form of angiostatin is effective in reducing the development of blood vessels in a nontumor environment and has therapeutic potential for neovascular retinopathies such as diabetic retinopathy, retinopathy of prematurity, retinal vein occlusion and, possibly, age-related macular degeneration.

Angiostatin and angiostatin-related proteins

The study of angiogenesis, and the promise of angiogenesis inhibition as a means of cancer therapy, has dramatically accelerated in the last several years. The discovery and publication of angiostatin by O'Reilly and colleagues in Judah Folkman's lab in 1994 has greatly contributed to this progress. Angiostatin is a kringle-containing fragment of plasminogen, which is a potent inhibitor of angiogenesis in vivo, and selectively inhibits endothelial cell proliferation and migration in vitro. There have been a number of proposed proteolytic mechanisms by which plasminogen is cleaved to form angiostatin, and the resulting cleavage products contain different NH2 and COOH termini of the angiostatin. Therefore, it is possible that there are more than one angiostatin isoforms (or angiostatin-related proteins) which occur in one or more normal or pathophysiological situations. It is also possible that some of the proteolytic processes which can convert plasminogen to angiostatin-like proteins are simply laboratory artifacts. Angiostatin-related proteins exert potent endothelial cell inhibitory activity, including the induction of apoptosis, and inhibition of migration, and the intact kringle structures are believed to be necessary for the antiangiogenic activity. Efforts are now underway to translate the understanding of the biology of angiostatin to clinical practice, which includes phase 1 clinical trials with recombinant angiostatin K1-3 (kringles 1-3) as well as phase 1 trials of an Angiostatin Cocktail, which induces the direct in vivo conversion of plasminogen to angiostatin 4.5 (kringles 1-4, plus most of kringle 5). The translation of the basic science of angiostatin and angiostatin-related proteins to clinical trial promises to provide an important new tool in the treatment of cancer by inhibition of angiogenesis.

Angiostatin and endostatin: endogenous inhibitors of tumor growth

Considerable progress has been made in the understanding of the molecular structure and mechanistic aspects of Angiostatin and Endostatin, endogenous angiogenesis inhibitors that have been shown to regress tumors in murine models. The growing body of literature surrounding these molecules and on the efficacy of these proteins is in part due to the ability to generate these proteins in recombinant systems as well characterized molecules. Recombinant human Angiostatin and Endostatin are in Phase I trials, following the manufacture of clinical grade material at large scale. This review highlights the recent advances made on understanding the structure and function of Angiostatin and Endostatin.

Purification, refolding of hybrid hIFNgamma-kringle 5 expressed in Escherichia coli

The DNA sequence coding for plasminogen kringle 5 (pK5), an inhibitor of angiogenesis, was fused with that coding for interferon gamma and over-produced in the form of inactive inclusion bodies in E. coli. The amount of fusion protein was about 40% of total protein produced. The fusion protein contained in the inclusion bodies was solubilized in 8 M urea and purified by anion-exchange chromatography. We employed the orthogonal experimental design L16(4(5)) (5 factors, 4 levels, 16 experiments) procedure for researching the influence of denaturant, aggregation suppressor L-arginine, NaCl, pH, and glycine on the refolding procedure. Our results suggest that the presence of appropriate L-arginine, NaCl, and denaturant in the refolding buffer inhibits the aggregation of the fusion protein and increases the yield of renatured protein with biological activity. The refolded fusion protein, gammaIFN/pk5, has in vitro anti-endothelial cell proliferation activity.

Combination angiostatin and endostatin gene transfer induces synergistic antiangiogenic activity in vitro and antitumor efficacy in leukemia and solid tumors in mice

Angiostatin and endostatin are potent endothelial cell growth inhibitors that have been shown to inhibit angiogenesis in vivo and tumor growth in mice. However, tumor shrinkage requires chronic delivery of large doses of these proteins. Here we report synergistic antitumor activity and survival of animals when these factors are delivered in combination to tumors by retroviral gene transfer. We have demonstrated this efficacy in both murine leukemia and melanoma models. Complete loss of tumorigenicity was seen in 40% of the animals receiving tumors transduced by the combination of angiostatin and endostatin in the leukemia model. The synergy was also demonstrated in vitro on human umbilical vein endothelial cell differentiation and this antiangiogenic activity may suggest a mechanism for the antitumor activity in vivo. These findings imply separate pathways by which angiostatin and endostatin mediate their antiangiogenic effects. Together, these data suggest that a combination of antiangiogenic factors delivered by retroviral gene transfer may produce synergistic antitumor effects in both leukemia and solid tumors, thus avoiding long-term administration of recombinant proteins. The data also suggest that novel combinations of antiangiogenic factors delivered into tumors require further investigation as therapeutic modalities.

Molecular mechanisms of tumor angiogenesis and tumor progression

The formation of new blood vessels (angiogenesis) is crucial for the growth and persistence of primary solid tumors and their metastases. Furthermore, angiogenesis is also required for metastatic dissemination, since an increase in vascular density will allow easier access of tumor cells to the circulation. Induction of angiogenesis precedes the formation of malignant tumors, and increased vascularization seems to correlate with the invasive properties of tumors and thus with the malignant tumor phenotype. In the last few years, the discovery and characterization of tumor-derived angiogenesis modulators greatly contributed to our understanding of how tumors regulate angiogenesis. However, although angiogenesis appears to be a rate-limiting event in tumor growth and metastatic dissemination, a direct connection between the induction of angiogenesis and the progression to tumor malignancy is less well understood. In this review, we discuss the most recent observations concerning the modulation of angiogenesis and their implications in tumor progression, as well as their potential impact on cancer therapy.

Plasminogen did not affect lung function in surfactant-treated preterm lambs

Preterm infants with respiratory distress syndrome develop fibrin-rich hyaline membranes within the alveoli and have depressed fibrinolytic activity, which is thought to be due to a relative deficiency of plasminogen. Local fibrin deposition inhibits surfactant function and amplifies inflammation. We hypothesized that plasminogen administration to surfactant-treated preterm lambs would prevent fibrin-rich hyaline membrane formation, resulting in the amelioration of lung pathology and improved lung function. We randomly treated preterm lambs (gestational age 127-129 days) with either 16 mg of lysine-plasminogen (n = 10) or saline (n = 10), and ventilated them for 5 h. There were no significant differences in physiologic measurements of lung function (ventilation efficiency index, oxygenation index, dynamic compliance, quasi-static pressure volume curve), measures of lung injury (alveolar wash protein content and (125)I-albumin recovery) or surfactant pool size. The degree and extent of bronchiolar erosion and hyaline membrane formation were similar in the two groups. Plasminogen administration did not improve lung function or prevent hyaline membrane formation in surfactant-treated lambs.

Anti-angiogenic treatment strategies for malignant brain tumors

The use of angiogenesis inhibitors may offer novel strategies in brain tumor therapy. In contrast to traditional cancer treatments that attack tumor cells directly, angiogenesis inhibitors target at the formation of tumor-feeding blood vessels that provide continuous supply of nutrients and oxygen. With respect to brain tumor therapy, inhibitors of angiogenesis display unique features that are unknown to conventional chemotherapeutic agents. The most important features are independence of the blood-brain barrier, cell type specificity, and reduced resistance. Malignant brain tumors, especially malignant gliomas, are among the most vascularized tumors known. Despite multimodal therapeutic approaches, the prognosis remains dismal. Thus, angiogenesis inhibitors may be highly effective drugs against these tumors. In a clinical setting, they could be applied in the treatment of multiple tumors or postsurgically as an adjuvant therapy to prevent recurrence. This article provides an overview of current anti-angiogenic treatment strategies with emphasis on substances already in clinical trials or candidate substances for clinical trials. The cellular and molecular basis of these substances is reviewed.

Antiangiogenesis -- therapeutic strategies and clinical implications for brain tumors

The poor prognosis of patients with malignant brain tumors in spite of aggressive multimodality therapy has led to the search for novel therapeutic strategies. Among the targets for such treatment approaches, tumor angiogenesis has captured the attention of not only the medical field but also of the lay public because of its conceptual departure from traditional methods of cancer therapy. Angiogenesis and vascular proliferation are particularly important in the growth and progression of malignant gliomas and are used as indicators of the degree of malignancy. Recent studies have helped us gain a better understanding of the molecular mediators of this process. It is now evident that after the initial formation of malignancy the continued growth of a glioma is critically dependent on its angiogenic potential. Hence, several approaches to control angiogenesis are being developed and tested. In the present review, we examine some of these approaches from a therapeutic perspective and summarize the findings from early human trials of such agents.