Differential binding of plasminogen, plasmin, and angiostatin4.5 to cell surface beta-actin: implications for cancer-mediated angiogenesis

Angiostatin4.5 (AS4.5) is the product of plasmin autoproteolysis and consists of kringles 1 to 4 and approximately 85% of kringle 5. In culture, cancer cell surface globular beta-actin mediates plasmin autoproteolysis to AS4.5. We now show that plasminogen binds to prostate cancer cells and that the binding colocalizes with surface beta-actin, but AS4.5 does not bind to the cell surface. Plasminogen and plasmin bind to immobilized beta-actin similarly, with a Kd of approximately 140 nmol/L. The binding is inhibited by epsilon-aminocaproic acid (epsilonACA), indicating the requirement for a lysine-kringle domain interaction. Using a series of peptides derived from beta-actin in competitive binding studies, we show that the domain necessary for plasminogen binding is within amino acids 55 to 69 (GDEAQSKRGILTLKY). Substitution of Lys61 or Lys68 with arginine results in the loss of the ability of the peptide to block plasminogen binding, indicating that Lys61 and Lys68 are essential for plasminogen binding. Other actin peptides, including peptides with lysine, did not inhibit the plasminogen-actin interaction. AS4.5 did not bind actin at concentrations up to 40 micromol/L. Plasminogen, plasmin, and AS4.5 all contain kringles 1 to 4; however, kringle 5 is truncated in AS4.5. Isolated kringle 5 binds to actin, suggesting intact kringle 5 is necessary for plasminogen and plasmin to bind to cell surface beta-actin, and the truncated kringle 5 in AS4.5 results in its release from beta-actin. These data may explain the mechanism by which AS4.5 is formed locally on cancer cell surfaces and yet acts on distant sites.     

血管抑素和内皮抑素的研究进展

近年来,越来越多的学者对血管抑素和内皮抑素的结构、作用机制以及抗肿瘤作用做了深入的研究,认为它们极有可能成为未来抗肿瘤的主要药物,为肿瘤治疗提供新的有效手段.     

A novel strategy for the tumor angiogenesis-targeted gene therapy: generation of angiostatin from endogenous plasminogen by protease gene transfer

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.     

Endothelial progenitor cells as putative targets for angiostatin

Angiostatin, a product of the proteolytic cleavage of plasminogen, possesses potent antitumor and antiangiogenic properties in vivo. Studies with cultured endothelial cells suggest that under certain conditions, angiostatin inhibits the migration and proliferation of these cells or, alternatively, increases their rate of apoptosis. In general, the effects of angiostatin have been considerably less potent in vitro than in vivo. One potential explanation for this disparity is that the in vivo target of angiostatin is not the mature endothelial cell. Recently, evidence has accumulated to show that circulating endothelial progenitor cells (EPCs) contribute to neovascularization. In this study, we have isolated EPCs from human subjects and demonstrated that, in contrast to that of mature endothelial cells, the growth of EPCs is exquisitely sensitive to angiostatin. These results suggest that angiostatin and related compounds may exert their biological effects by inhibiting the contribution of EPCs to angiogenesis and not by altering the growth of mature endothelial cells.     

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

HCC is a common cancer and HBV and AFB(1) are well-documented, major risk factors. Epidemiologic studies have documented that cigarette smoking also contributes to the development of HCC. PAHs are ubiquitous environmental pollutants and products of incomplete combustion. They are present in both mainstream and sidestream cigarette smoke. PAHs are metabolically activated by phase I enzymes, including CYP1A1, into electrophilic reactants (diol epoxides), which covalently bind to DNA to form adducts. Diol epoxides are also substrates for phase II detoxifying enzymes, including GSTM and GSTP. To examine the association between PAH-DNA adducts and HCC, adduct levels were determined in liver tissue by relative staining intensity with an immunoperoxidase method using a polyclonal antiserum against BPDE-modified DNA. Subjects were also genotyped for polymorphism in several genes involved in the metabolism of PAH, including GSTM1 and GSTP1. Liver tissue was collected from patients with histologically confirmed HCC (n = 105) and from non-HCC controls (n = 37). There was a significant positive correlation (r = 0.3, p < 0.01) between adducts in tumor and adjacent nontumor tissues among HCC cases. The risk of HCC was higher after adjustment for age, sex and HBsAg in the group with the highest tertile tissue levels of PAH-DNA adducts (mean relative nuclear staining intensity of tumor and nontumor tissue > 344) than in the group with the lowest tertile (staining < 241, OR = 3.9, 95% CI = 1.0-14.9). Among non-HCC controls, there were no significant associations between adduct levels and cigarette smoking, GSTM1 null genotype and HBsAg positivity. A strikingly increased HCC risk was observed (OR = 20.3, 95% CI = 5.0-81.8) among HBsAg-positive subjects whose PAH-DNA adduct levels were high (mean relative nuclear staining intensity of tumor and nontumor tissue > 301, median of control tissues) compared to HBsAg-negative subjects who had low PAH-DNA adduct levels. 4-ABP- and AFB(1)-DNA adducts had been measured previously in these same tissues. Subjects with elevated DNA adduct levels of PAH, 4-ABP and AFB(1) had a significantly higher HCC risk with an OR of 36.7 (95% CI 7.2-187.2) compared to those who had low DNA adduct levels. These results suggest that PAHs may play a role in human hepatocarcinogenesis in conjunction with HBsAg carrier status, GSTM1 and GSTP1 genotypes and exposure to 4-ABP and AFB(1).     

血管抑素基因转染抑制胆囊癌细胞的实验研究

目的：观察血管抑素基因转染对体外人胆囊癌细胞系GBC—SD细胞株增殖及血管抑素表达和裸鼠致瘤体积的影响，初步探讨血管抑素基因转染抑制胆囊癌细胞生长的可能性。方法：应用pcDNA3．1（＋）-angiostatin基因转染GBC—SD胆囊癌细胞。观察细胞生长情况，制作细胞生长曲线；Western—blot法分析血管抑素的表达情况；裸鼠种植瘤模型观察肿瘤的体积和质量。结果：pcDNA3．1（＋）-angiostatin基因转染的GBC—SD胆囊癌细胞生长明显受到抑制，血管抑素的蛋白表达也明显增加。转染的肿瘤细胞在裸鼠种植瘤明显小于阴性组和空白组。结论：血管抑素基因转染可能具有抑制胆囊癌细胞增殖及生长的作用。     

血管抑素基因转染抑制胆囊癌细胞的实验研究

目的:观察血管抑素基因转染对体外人胆囊癌细胞系GBC-SD细胞株增殖及血管抑素表达和裸鼠致瘤体积的影响,初步探讨血管抑素基因转染抑制胆囊癌细胞生长的可能性.方法:应用pcDNA3.1( )-angiostatin 基因转染GBC-SD胆囊癌细胞.观察细胞生长情况,制作细胞生长曲线;Western-blot法分析血管抑素的表达情况;裸鼠种植瘤模型观察肿瘤的体积和质量.结果:pcDNA3.1( )-angiostatin 基因转染的GBC-SD胆囊癌细胞生长明显受到抑制,血管抑素的蛋白表达也明显增加.转染的肿瘤细胞在裸鼠种植瘤明显小于阴性组和空白组.结论:血管抑素基因转染可能具有抑制胆囊癌细胞增殖及生长的作用.     

Elevated levels of angiostatin in effusions from patients with malignant disease

The aim of this study was to determine the presence of angiostatin in ascitic and pleural effusions from cancer patients, as well as of metalloproteinases (MMPs) and urokinase-type plasminogen activator (uPA), both involved in angiostatin generation in in vitro models. Ascitic fluids, pleural exudates, and sera from 21 cancer patients were analyzed for the presence of angiostatin by western blot, whereas gelatinases MMP-2 and MMP-9, and uPA were evaluated by zymography. Our study revealed elevated levels of angiostatin in effusions of cancer patients, contrasting with mostly intermediate levels in less than half of their sera, and undetectable levels in normal sera. Despite the observation of enhanced levels of HMW-uPA and MMP-2 in malignant effusions from cancer patients, their analysis in individual samples showed no association between angiostatin presence and the enzymes, suggesting that the latter would not play an unimportant role, if any, in in vivo generation of angiostatin.     

Tumor production of angiostatin is enhanced after exposure to TNF-alpha.

Infection of tumors with an adenoviral vector expressing a chimeric gene composed of the CArG elements of the Egr-1 promoter and a cDNA encoding TNF-alpha (Ad.Egr-TNF) has previously been shown to result in the production of high intratumoral levels of TNF-alpha and thereby tumor regression. The antitumor effects of TNF-alpha were ascribed to vascular thrombosis. We and others, have reported that inhibition of tumor vessel thrombosis using anticoagulation therapy does not abrogate the antitumor effects after TNF-alpha treatment. To investigate the potential antiangiogenic effects of TNF-alpha, we studied the generation of angiostatin after intratumoral injection of Ad.Egr-TNF. We report an increase in plasma angiostatin levels both during and after treatment with Ad.Egr-TNF that parallel tumor regression. We also report that TNF-alpha enhances angiostatin production by inducing the activity of plasminogen activator and the release of MMP-9 by tumor cells. These studies support a model in which the antiangiogenic effects of TNF-alpha on the tumor microvasculature are mediated by generation of angiostatin.     

Synergy between angiostatin and endostatin: inhibition of ovarian cancer growth

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.     

Prolonged treatment with angiostatin reduces metastatic burden during radiation therapy

Ionizing radiation (IR) and concomitant angiostatin (AS) produce greater than additive local antitumor effects. We examined whether prolonged AS treatment added to IR reduces proliferation of lung metastases from LLC primary tumors. Flank tumors were treated with 40 Gy with or without AS (25 mg/kg/day). IR plus a 14-day course of AS improved local tumor control and blocked the increase in lung weights observed in the group receiving IR plus a 2-day course of AS group. Animals treated with prolonged AS exhibited no increase in lung weight and no macrometastases. These findings suggest that long-term treatment with antiangiogenic compounds may be effective in preventing metastases from IR-treated tumors as well as increasing the local antitumor effects of radiotherapy.     

Growth of human melanoma xenografts is suppressed by systemic angiostatin gene therapy

The effect of local and systemic delivery of the angiostatin gene on human melanoma growth was studied in nude mice. Liposome-coated plasmids carrying the cDNA coding for murine and human angiostatin (CMVang and BSHang) were injected weekly, locally or systemically, in mice transplanted with melanoma cells. The treatment reduced melanoma growth by 50% to 90% compared to that occurring in control animals treated with liposome-coated plasmid carrying the lacZ gene or in untreated controls. The growth of both locally injected and controlateral uninjected tumors in mice bearing two melanoma grafts was significantly suppressed after intratumoral treatment. Tumor growth inhibition was also observed in mice treated by intraperitoneal delivery, suggesting that angiostatin gene therapy acts through a systemic effect. Both melanoma growth suppression and delay in the onset of tumor growth were observed in treated mice. PCR performed on tumors and normal tissues showed that the lipofected DNA was present in tissues from treated mice, and angiostatin expression was demonstrated by RT-PCR. Histopathological analysis of melanoma nodules revealed an increase in apoptotic cells and a reduction in vessel density in tumors from treated mice. Our results suggest that systemic, liposome-mediated administration of genes coding for antiangiogenic factors represents a promising strategy for melanoma treatment in humans.     

Effect of angiostatin on liver metastasis of pancreatic cancer in hamsters.

The liver is the most common site of metastasis in pancreatic cancer, and there are no promising strategies to treat it. Angiostatin, a kringle-containing fragment of plasminogen, is a potent inhibitor of angiogenesis. The effect of angiostatin on liver metastasis in pancreatic cancer was investigated by using our established hamster model of liver metastasis. Pancreatic cancer cells (PGHAM-1, 1 x 10(6)) derived from N-nitrosobis(2-oxopropyl)amine (BOP)-induced pancreatic tumor in Syrian golden hamsters were transplanted into the spleen of female hamsters, and the animals were subcutaneously injected with angiostatin and saline. Subsequently, the macroscopic appearance of liver surface metastases was evaluated. In addition, histological sections of the liver metastases were analyzed for neovascularization, proliferation, and apoptosis on the basis of von Willebrand factor, argyrophilic nucleolar organizer region (Ag-NOR), and TdT-mediated dUTP-biotin nick end labeling (TUNEL) staining, respectively. The results showed significant tumor growth retardation and inhibition of angiogenesis in metastatic liver tumors in response to treatment with angiostatin. Moreover, the metastases remained in a nearly dormant state due to a balance between apoptosis and proliferation of the tumor, with no detectable side effects. This is the first experimental trial of angiostatin on pancreatic cancer and liver metastasis. The results suggest that angiostatin therapy could be effective against liver metastases of pancreatic cancer.     

血管抑制素对血管内皮细胞系ECV-304的抑制作用

 目的　观察血管抑制素 (Angiostatin)对血管内皮细胞系ECV 3 0 4的抑制作用。 方法　利用MTT法分析结果 ,实验分为 :1 .将血管抑制素与细胞同时加入 ;2 .先接种细胞 ,培养 2 4h后再加血管抑制素。结果　血管抑制素对ECV 3 0 4的抑制作用呈典型的量效关系。结论　血管抑制素对血管内皮细胞有显著的抑制作用。     

血管生长抑制因子angiostatin在昆虫细胞中的表达及活性研究

背景与目的:抑制新生血管的形成,有助于抑制肿瘤的生长,减少和预防肿瘤转移的发生。血管抑素(angiostatin)是一种重要的内源性新生血管生成抑制剂,对血管内皮细胞增殖有较强的抑制作用。为获得具有高活性的Angiostatin表达,本研究通过杆状病毒表达系统表达重组的angiostatin,分析其在昆虫细胞中表达和生物活性。方法:用带有angiostatin的杆状病毒转移载体pBlueBacHis2B和病毒DNA共同转染Sf9细胞,构建重组病毒,蚀斑实验筛选,PCR分析确定后扩增产生大量高滴度的病毒贮存液;用SDS-PAGE电泳和Westernblot对感染不同时间后分泌的重组蛋白做时间表达分析;用ProBondTM纯化系统对表达的重组angiostatin进行纯化,分光光度计确定蛋白含量,SDS-PAGE电泳确定蛋白纯度;采用MTT法测定重组蛋白angiostatin对原代培养的人脐静脉内皮细胞(HUVEC)的抑制作用而后通过鸡胚尿囊膜实验进一步证实其抗血管形成作用。结果:成功构建了滴度为2×108pfu/ml的angiostatin重组杆状病毒,并在昆虫细胞Sf9中高效表达了分子量为53ku的angiostatin重组蛋白,纯度约为90%,重组angiostatin蛋白不仅在体外显著抑制内皮细胞的生长(IC50为2.3μg/ml),而且显著抑制鸡胚尿囊膜血管的生长。结论:此系统可制备高滴度angiostatin重组杆状病毒贮存液,并在Sf9昆虫细胞中高效表达该重组蛋白,经在体和离体细胞学实验验证其对内皮细胞的增殖具有抑制作用。     

Growth Inhibition of Breast Cancer in Rat by AAV Mediated Angiostatin Gene

Objective： To observe growth inhibition effect of adeno-associated viral vectors （AAV） mediated angiostatin （ANG） gene on implanted breast cancer in rat and its mechanism. Methods： Gene transfer technique was used to transfer AAV-ANG to the tumor. Growth curves were drawn to observe the growth of breast cancer implanted in rat, and immunohistochemical method was used to detect the effects of angiostatin on microvesel density （MVD） of breast cancer implanted in rat. Results： Angiostatin inhibited the growth of breast cancer implanted in rat and decreased the microvessel density of tumor. Conclusion： Expression of an angiostatin transgene can suppress the growth of breast cancer implanted in rat through the inhibition of the growth of microvessels, surggesting that angiostatin gene transfer technique may be effective against breast cancer.     

血管抑素联合顺铂治疗Lewis肺癌

目的探讨血管抑素联合顺铂对内皮细胞增殖和Lewis肺癌生长抑制作用.方法将内皮细胞接种到96孔板中,加入不同试药72 h后,作MTT检测每孔中的细胞数.将Lewis肺癌细胞接种到C57小鼠右腋下,随机分为4组,分别用不同试药处理.每2日测量瘤体积,20天后处死动物,称取瘤重,常规病理和免疫组织化学染色检查,观察微血管密度和血管内皮细胞生长因子表达情况.结果顺铂与血管抑素在抑制血管内皮细胞增殖方面具有协同作用.顺铂组和顺铂 血管抑素组瘤体积、瘤重和血管密度均明显＜对照组.其中以顺铂与血管抑素在同时应用时瘤体积与瘤重又明显低于顺铂组.结论血管抑素与顺铂同时使用对lewis肺癌生长的抑制作用优于先后使用.     

Continuous administration of angiostatin inhibits accelerated growth of colorectal liver metastases after partial hepatectomy

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.     

重组人血管抑素抑制人鼻咽癌生长的实验研究

目的：观察重组人血管抑素（ｒｅｃｏｍｂｉｎａｎｔ ｈｕｍａｎ ａｎｇｉｏｓｔａｔｉｎ,ｒｈＡＧＮ）对鼻咽癌皮下移植瘤生长的抑制作用,探讨其应用价值。方法：应用ＭＴＴ法观察ｒｈＡＧＮ对ＣＮＥ－１鼻咽癌细胞和ＨＤＭＥＣ血管内皮细胞增殖的影响;建立ＣＮＥ－１鼻咽癌裸鼠皮下移植瘤模型,皮下注射不同剂量ｒｈＡＧＮ,治疗期为３０天,观察肿瘤体积和重量变化。结果：（１）在０．５μｇ／ｍｌ、１．０μｇ／ｍｌ和２．     

Linoleic acid enhances angiogenesis through suppression of angiostatin induced by plasminogen activator inhibitor 1

Background:

The intake of dietary fatty acids is highly correlated with the risk of various cancers. Linoleic acid (LA) is the most abundant polyunsaturated fat in the western diet, but the mechanism(s) by fatty acids such as LA modulate cancer cells is unclear. In this study, we examined the role of LA in various steps in gastric cancer progression.

Methods:

The difference in gene expression between LA-treated and untreated OCUM-2MD3 gastric carcinoma cells was examined by mRNA differential display. The involvement of candidate genes was examined by oligo- and plasmid-mediated RNA interference. Biological functions of several of these genes were examined using in vitro assays for invasion, angiogenesis, apoptosis, cell viability, and matrix digestion. Angiogenesis in vivo was measured by CD-31 immunohistochemistry and microvessel density scoring.

Results:

LA enhanced the plasminogen activator inhibitor 1 (PAI-1) mRNA and protein expression, which are controlled by PAI-1 mRNA-binding protein. LA-stimulated invasion depended on PAI-1. LA also enhanced angiogenesis by suppression of angiostatin, also through PAI-1. LA did not alter cell growth in culture, but increased dietary LA-enhanced tumour growth in an animal model.

Conclusion:

Our findings suggest that dietary LA impacts multiple steps in cancer invasion and angiogenesis, and that reducing LA in the diet may help slow cancer progression.