Human apolipoprotein(a) kringle V inhibits angiogenesis in vitro and in vivo by interfering with the activation of focal adhesion kinases

O-glycan structures in apo(a) subunit of human lipoprotein(a) suppresses the pro-angiogenic activity of galectin-1 on human umbilical vein endothelial cells

Apolipoprotein(a) [apo(a)] is a highly polymorphic O-glycoprotein circulating in human plasma as lipoprotein(a) [Lp(a)]. The O-glycan structures of apo(a) subunit of Lp(a) serve as strong ligands of galectin-1, an O-glycan binding pro-angiogenic lectin abundantly expressed in placental vascular tissues. But the pathophysiological significance of apo(a)-galectin-1 binding is not yet been revealed. Carbohydrate-dependent binding of galectin-1 to another O-glycoprotein, neuropilin-1 (NRP-1) on endothelial cells activates vascular endothelial growth factor receptor 2 (VEGFR2) and mitogen-activated protein kinase (MAPK) signaling. Using apo(a), isolated from human plasma, we demonstrated the potential of the O-glycan structures of apo(a) in Lp(a) to inhibit angiogenic properties such as proliferation, migration, and tube-formation in human umbilical vein endothelial cells (HUVECs) as well as neovascularization in chick chorioallantoic membrane. Further, in vitro protein-protein interaction studies have confirmed apo(a) as a superior ligand to NRP-1 for galectin-1 binding. We also demonstrated that the protein levels of galectin-1, NRP-1, VEGFR2, and downstream proteins in MAPK signaling were reduced in HUVECs in the presence of apo(a) with intact O-glycan structures compared to that of de-O-glycosylated apo(a). In conclusion, our study shows that apo(a)-linked O-glycans prevent the binding of galectin-1 to NRP-1 leading to the inhibition of galectin-1/neuropilin-1/VEGFR2/MAPK-mediated angiogenic signaling pathway in endothelial cells. As higher plasma Lp(a) level in women is an independent risk factor for pre-eclamsia, a pregnancy-associated vascular complication, we propose that apo(a) O-glycans-mediated inhibition of the pro-angiogenic activity of galectin-1 may be one of the underlying molecular mechanism of pathogenesis of Lp(a) in pre-eclampsia.

Apolipoprotein(a), an enigmatic anti-angiogenic glycoprotein in human plasma: A curse or cure?

Angiogenesis is a finely co-ordinated, multi-step developmental process of the new vascular structure. Even though angiogenesis is regularly occurring in physiological events such as embryogenesis, in adults, it is restricted to specific tissue sites where rapid cell-turnover and membrane synthesis occurs. Both excessive and insufficient angiogenesis lead to vascular disorders such as cancer, ocular diseases, diabetic retinopathy, atherosclerosis, intra-uterine growth restriction, ischemic heart disease, stroke etc. Occurrence of altered lipid profile and vascular lipid deposition along with vascular disorders is a hallmark of impaired angiogenesis. Among lipoproteins, lipoprotein(a) needs special attention due to the presence of a multi-kringle protein subunit, apolipoprotein(a) [apo(a)], which is structurally homologous to many naturally occurring anti-angiogenic proteins such as plasminogen and angiostatin. Researchers have constructed different recombinant forms of apo(a) (rhLK68, rhLK8, RHACK2, KV-11, and AU-6) and successfully exploited its potential to inhibit unwanted angiogenesis during tumor metastasis and retinal neovascularization. Similar to naturally occurring anti-angiogenic proteins, apo(a) can directly interfere with angiogenic signaling pathways. Besides this, apo(a) can also exert its anti-angiogenic effect indirectly by inducing endothelial cell apoptosis, by inhibiting endothelial progenitor cell functions or by upregulating nuclear factors in endothelial cells via apo(a)-bound oxPLs. However, the impact of the anti-angiogenic potential of native apo(a) during physiological angiogenesis in embryos and wounded tissues is not yet explored. In this context, we review the studies so far done to demonstrate the anti-angiogenic activity of apo(a) and the recent developments in using apo(a) as a therapeutic agent to treat impaired angiogenesis during vascular disorders, with emphasis on the gaps in the literature.

Inhibition of Pathological Retinal Neovascularization by a Small Peptide Derived from Human Tissue-Type Plasminogen Kringle 2

Retinal neovascularization is a hallmark pathological process of numerous ocular diseases which comprise the most common causes of blindness and affect millions of people from infants to the elderly. Compared to large proteins, small peptides have advantages for therapeutic application in ocular diseases, especially for retinal diseases. In this study, we investigated a small peptide derived from human tissue-type plasminogen kringle 2 (t-PA kringle 2), named TKII-12, and investigated the effect of TKII-12 on various aspects of vascular endothelial growth factor (VEGF)-induced angiogenesis in vitro and in vivo. Our results showed that TKII-12 effectively inhibited VEGF-induced human retinal microvascular endothelial cell proliferation, migration and tube formation on Matrigel dose-dependently as well as sequence-dependently. TKII-12 inhibited VEGF-induced formation of actin stress fibers and focal adhesions in vascular endothelial cells. Moreover, TKII-12 effectively inhibited retinal neovascularization in a mouse oxygen-induced retinopathy (OIR) model. Our study demonstrated that TKII-12 could effectively inhibit retinal angiogenesis in vitro and in vivo by eliminating the formation of focal adhesion complexes and the organization of actin stress fibers. TKII-12 can serve as a prototype for retinal angiogenesis inhibitory drug development.

An oral 2-hydroxypropyl-β-cyclodextrin-loaded spirooxindole-pyrrolizidine derivative restores p53 activity via targeting MDM2 and JNK1/2 in hepatocellular carcinoma

Validation of a small molecular compound targeting the oncogenic pathways is the primary approach for the development of the anti-cancer drugs. In the present study, we employed the computational mimic drug targets prediction software to foresee the molecular targets of a series of spirooxindole-pyrrolizidine derivatives, which were synthesized by our laboratory viatargeted combinational chemistry. We found that CPHSP, a novel spirooxindole-pyrrolizidine derivative, can target the MDM2/p53 signaling that is essential for the tumorigenesis of hepatocellular carcinoma (HCC). To validate its anti-tumoral function, we firstly established the soluble receipt of CPHSP through 2-hydroxypropyl-β-cyclodextrin (HBC) loading and showed that oral administration of HBC-loaded CPHSP significantly inhibited the tumor growth and prolonged the survival time of tumor-bearing mice in the subcutaneously human hepatoma cells-xenografted nude mouse model of HCC. Immunohistochemistry staining showed that HBC-loaded CPHSP treatment suppressed the proliferation and induced apoptosis of tumor cells in this model. Our mechanistic studies showed that CPHSP treatment inhibited MDM2 protein expression and up-regulated p53 activity and activated MKK4/MKK7/JNK1/2/C-Jun signaling pathway, which resulted in cell cycle arrest and apoptosis of HepG2 cells in vitro. Moreover, we showed that JNK1/2 activation could also up-regulate p53 expression in CPHSP-treated HepG2 cells. Finally, we documented the antitumor activities of oral administration of the HBC-loaded CPHSP in the ML-1 bearing orthotopic mouse model. In summary, this study suggests that oral administration of HBC-loaded CPHSP is a safe and effective treatment for HCC, of which the clinical potency for patients with HCC warrants further studies.

Correlation between chronic venous ulcer exudate proteins and clinical profile: A cross-sectional study

Chronic venous ulcers affect the quality of life of patients around the world. The aims of this study were to identify the proteins expressed in chronic venous ulcer exudates, to categorize them according to their roles and to correlate them with the clinical and epidemiological aspects of the disease. The study population consisted of 37 ulcers from 28 patients, and the inflammatory exudates of these thirty-seven ulcers were subjected to tryptic digestion and mass spectrometry analysis. Twenty-three patients were female (62.2%), and five (37.8%) were male. The patients had a mean age of 70 (±10.1) years. Of the patients, 73% adhered to compression and rest, 81.1% reported a history of primary varices, 54.1% reported a history of systemic arterial hypertension, 54.1% reported a history of devitalized tissue in the wound bed and 64.9% reported ulcers with more than ten years of evolution. Seventy-six proteins were identified, and they were grouped according to their primary role in the healing process. Eight correlations between clinical and epidemiological data and protein expression were noteworthy: diabetes mellitus vs. Ig gamma-2 and apolipoprotein-A1 and albumin; congestive heart failure vs. Ig lambda-2; colonization vs. actin; compressive therapy vs. Ig kappa; systemic arterial hypertension vs. alpha-2-macroglobulin and apolipoprotein-A1; area of ulcer vs. apolipoprotein-A1; race vs. heavy chain Ig and Ig γ-1 chain; age and race vs. Ig γ-1 chain. These associations may help to elucidate the prognosis and chronicity of chronic venous ulcers based on secreted proteins.

Anti-angiogenesis through noninvasive to minimally invasive intraocular delivery of the peptide CC12 identified by in vivo-directed evolution

Anti-vascular endothelial growth factor (VEGF) therapies are widely used for the treatment of neovascular fundus diseases such as diabetic retinopathy. However, these agents need to be injected intravitreally, because their strong hydrophilicity and high molecular weight prevent them from penetrating cell membranes and complex tissue barriers. Moreover, the repeated injections that are required can cause infection and tissue injury. In this study, we used in vivo-directed evolution phage display technology to identify a novel dodecapeptide, named CC12, with the ability to penetrate the ocular barrier in a noninvasive (via conjunctival sac instillation) or minimally invasive (via retrobulbar injection) manner. KV11, an antiangiogenesis peptide previously demonstrated to inhibit pathological neovascularization in the retina, was then used as a model antiangiogenesis cargo for CC12. We found that conjugation of KV11 peptide with CC12 peptide facilitated the delivery of KV11 to the retina, resulting in significant inhibition of retinal neovascularization development via topical application without tissue toxicity. Collectively, our data of multilevel evaluations demonstrate that CC12 may enable the noninvasive to minimally invasive intraocular delivery of antiangiogenic therapeutics.

Inhibition of pathological corneal neovascularization by a small peptide derived from human apolipoprotein (a) Kringle V

PURPOSE

The aim of this study was to evaluate the antiangiogenic activity of AU6, a novel 6-amino acid peptide derived from Kringle V of human apolipoprotein (a).

METHODS

RF/6A rhesus macaque choroid endothelial cells were used for in vitro studies. MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt] assays and modified Boyden chamber and Matrigel assays were used to evaluate the inhibitory effect of AU6 on vascular endothelial growth factor (VEGF)-stimulated endothelial cell functions, including cell proliferation, migration, and tube formation. The chick chorioallantoic membrane model, micropocket corneal neovascularization (CNV) model, and alkali burn CNV model were evaluated in vivo. Bevacizumab (Avastin), the VEGF-neutralizing antibody, and a scrambled peptide (AU6s) were used as positive and negative controls, respectively.

RESULTS

AU6 inhibited VEGF-induced RF/6A cell migration, proliferation, and tube formation. It also reduced pathological neovascularization in the chorioallantoic membrane model and in the 2 CNV models, that is, the mouse corneal micropocket model and the rat cornea alkali burn model.

CONCLUSIONS

AU6 effectively inhibited pathogenic CNV. This novel peptide shows potential as a new treatment for ocular neovascularization.

Antiangiogenic Therapy with Human Apolipoprotein(a) Kringle V and Paclitaxel in a Human Ovarian Cancer Mouse Model

INTRODUCTION: The present study compared the effect of combination therapy using human apolipoprotein(a) kringle V (rhLK8) to conventional chemotherapy with paclitaxel for human ovarian carcinoma producing high or low levels of vascular endothelial growth factor (VEGF). MATERIALS AND METHODS: Human ovarian carcinoma cells producing high (SKOV3ip1) or low (HeyA8) levels of VEGF were implanted into the peritoneal cavity of female nude mice. Seven days later, mice were randomized into four groups: control (vehicle), paclitaxel [5 mg/kg, weekly intraperitoneal (i.p.) injection], rhLK8 (50 mg/kg, daily i.p. injection), or the combination of paclitaxel and rhLK8. Mice were treated for 4 weeks and examined by necropsy. RESULTS: In mice implanted with SKOV3ip1 cells, rhLK8 treatment had no significant effect on tumor incidence or the volume of ascites but induced a significant decrease in tumor weight compared with control mice. Paclitaxel significantly reduced tumor weight and ascites volume, and combination treatment with paclitaxel and rhLK8 had an additive therapeutic effect. Similarly, in HeyA8 mice, the effect of combination treatment on tumor weight and tumor incidence was statistically significantly greater than that of paclitaxel or rhLK8 alone. Immunohistochemical analysis showed a significant decrease in microvessel density and a marked increase of apoptosis in tumor and tumor-associated endothelial cells in response to combination treatment with paclitaxel and rhLK8. CONCLUSION: Collectively, these results suggest that antiangiogenic therapy with rhLK8 in combination with taxane-based conventional chemotherapy could be effective for the treatment of ovarian carcinomas, regardless of VEGF status.

Suppression of colorectal cancer liver metastasis by apolipoprotein(a) kringle V in a nude mouse model through the induction of apoptosis in tumor-associated endothelial cells

The formation of liver metastases in colorectal cancer patients is the primary cause of patient death. Current therapies directed at liver metastasis from colorectal cancer have had minimal impact on patient outcomes. Therefore, the development of alternative treatment strategies for liver metastasis is needed. In the present study, we demonstrated that recombinant human apolipoprotein(a) kringle V, also known as rhLK8, induced the apoptotic turnover of endothelial cells in vitro through the mitochondrial apoptosis pathway. The interaction of rhLK8 with glucose-regulated protein 78 (GRP78) may be involved in the induction of apoptosis because the inhibition of GRP78 by GRP78-specific antibodies or siRNA knockdown inhibited the rhLK8-mediated apoptosis of human umbilical vein endothelial cells in vitro. Next, to evaluate the effects of rhLK8 on angiogenesis and metastasis, an experimental model of liver metastasis was established by injecting a human colorectal cancer cell line, LS174T, into the spleens of BALB/c nude mice. The systemic administration of rhLK8 significantly suppressed liver metastasis from human colorectal cancer cells and improved host survival compared with controls. The combination of rhLK8 and 5-fluorouracil substantially increased these survival benefits compared with either therapy alone. Histological observation showed significant induction of apoptosis among tumor-associated endothelial cells in liver metastases from rhLK8-treated mice compared with control mice. Collectively, these results suggest that the combination of rhLK8 with conventional chemotherapy may be a promising approach for the treatment of patients with life-threatening colorectal cancer liver metastases.

Immunoglobulin Fc domain fusion to apolipoprotein(a) kringle V significantly prolongs plasma half-life without affecting its anti-angiogenic activity

Angiogenesis is crucial for tumor growth and metastasis. Blocking this process is, therefore, a potentially powerful approach for the treatment of cancer. Human apolipoprotein(a) kringle V (rhLK8) is an angiogenesis inhibitor and is currently under development as an anti-cancer therapeutic. However, a relatively short in vivo half-life limits its widespread clinical use. This study was performed to evaluate whether fusion of an Fc domain to rhLK8 can extend plasma half-life. RhLK8-Fc fusion protein was expressed in CHO DG44 cells as a dimer and was readily purified by protein G affinity chromatography. The anti-angiogenic activity of rhLK8-Fc was similar to that of rhLK8, as determined by migration and tube formation assays with endothelial cells in vitro and a chorioallantoic membrane assay in vivo. Pharmacokinetic profiles in mice after single intravenous administration of rhLK8 or rhLK8-Fc showed that Fc fusion significantly increased the elimination half-life (t(½)) and the systemic exposure (AUC(inf)) of the protein, in parallel with a significant decrease in total clearance (CL). These data suggest that Fc fusion to rhLK8 is a powerful strategy for extending the plasma half-life of rhLK8 without affecting its anti-angiogenic activity, and could thus improve the clinical applicability of rhLK8.

Apolipoprotein(a) inhibits in vitro tube formation in endothelial cells: identification of roles for Kringle V and the plasminogen activation system

Elevated plasma concentrations of lipoprotein(a) are associated with increased risk for atherothrombotic diseases. Apolipoprotein(a), the unique glycoprotein component of lipoprotein(a), is characterized by the presence of multiple kringle domains, and shares a high degree of sequence homology with the serine protease zymogen plasminogen. It has been shown that angiostatin, a proteolytic fragment of plasminogen containing kringles 1–4, can effectively inhibit angiogenesis. Moreover, proteolytic fragments of plasminogen containing kringle 5 are even more potent inhibitors of angiogenesis than angiostatin. Despite its strong similarity with plasminogen, the role of apolipoprotein(a) in angiogenesis remains controversial, with both pro- and anti-angiogenic effects reported. In the current study, we evaluated the ability of apolipoprotein(a) to inhibit VEGF- and angiopoietin-induced tube formation in human umbilical cord endothelial cells. A 17 kringle-containing form of recombinant apo(a) (17K), corresponding to a well-characterized, physiologically-relevant form of the molecule, effectively inhibited tube formation induced by either VEGF or angiopoietin-1. Using additional recombinant apolipoprotein(a) (r-apo(a)) variants, we demonstrated that this effect was dependent on the presence of an intact lysine-binding site in kringle V domain of apo(a), but not on the presence of the functional lysine-binding site in apo(a) kringle IV type 10; sequences within in the amino-terminal half of the molecule were also not required for the inhibitory effects of apo(a). We also showed that the apo(a)-mediated inhibition tube formation could be reversed, in part by the addition of plasmin or urokinase plasminogen activator, or by removal of plasminogen from the system. Further, we demonstrated that apo(a) treated with glycosidases to remove sialic acid was significantly less effective in inhibiting tube formation. This is the first report of a functional role for the glycosylation of apo(a) although the mechanisms underlying this observation remain to be determined in the context of angiogenesis.

Targeted antivascular therapy with the apolipoprotein(a) kringle V, rhLK8, inhibits the growth and metastasis of human prostate cancer in an orthotopic nude mouse model

Antivascular therapy has emerged as a rational strategy to improve the treatment of androgen-independent prostate cancer owing to the necessity of establishing a vascular network for the growth and progression of the primary and metastatic tumor. We determined whether recombinant human apolipoprotein(a) kringle V, rhLK8, produces therapeutic efficacy in an orthotopic human prostate cancer animal model. Fifty thousand androgen-independent human prostate cancer cells (PC-3MM2) were injected into the prostate of nude mice. After 3 days, these mice were randomized to receive the vehicle solution (intraperitoneally [i.p.], daily), paclitaxel (8 mg/kg i.p., weekly), rhLK8 (50 mg/kg i.p., daily), or a combination of paclitaxel and rhLK8 for 4 weeks. Treatment with paclitaxel or rhLK8 alone did not show significant therapeutic effects on tumor incidence or on tumor size compared with the control group. The combination of rhLK8 and paclitaxel significantly reduced tumor size and incidence of lymph node metastasis. Significant reduction in microvessel density and cellular proliferation and induction of apoptosis of tumor cells, and tumor-associated endothelial cells, were also achieved. Similarly, PC-3MM2 tumors growing in the tibia showed significant suppression of tumor growth and lymph node metastasis by the combination treatment with rhLK8 and paclitaxel. The integrity of the bone was significantly preserved, and apoptosis of tumor cells and tumor-associated endothelial cells was increased. In conclusion, these results suggest that targeting the tumor microenvironment with the antivascular effect of rhLK8 combined with conventional cytotoxic chemotherapy could be a new and effective approach in the treatment of androgen-independent prostate cancer and their metastases.

Human apolipoprotein(a) kringle V inhibits ischemia-induced retinal neovascularization via suppression of fibronectin-mediated angiogenesis

Retinal neovascularization is observed in progression of diabetic retinopathy. New vessels grow into the vitreous cavity in proliferative diabetic retinopathy, resulting in traction retinal detachment and vitreous hemorrhage. To overcome the catastrophic visual loss due to these complications, efforts have been focused on the treatment of retinal neovascularization. In this study, we demonstrated the inhibitory effect of recombinant human apolipoprotein(a) kringle V (rhLK8) in an animal model of ischemia-induced retinal neovascularization. rhLK8 induced no definite toxicity on endothelial cells and retinal tissues at the therapeutic dosage. Interestingly, rhLK8 showed antiangiogenic effect, particularly on fibronectin-mediated migration of endothelial cells. Further experiments demonstrated high binding affinity of rhLK8 to α3β1 integrin, and suppression of it might be the mechanism of antiangiogenic effect of rhLK8. Furthermore, rhLK8 inhibited phosphorylation of focal adhesion kinase, resulting in suppression of activation of consequent p130CAS-Jun NH(2)-terminal kinase. Taken together, our data suggested the possible application of rhLK8 in the treatment of retinal neovascularization by suppression of fibronectin-mediated angiogenesis.

Protocadherin-10 is involved in angiogenesis and methylation correlated with multiple myeloma

Protocadherin-10 (PCDH10) which is located at 4q28.3, is a member of the cadherin superfamily of cell adhesion molecules. PCDH10 is broadly expressed in normal adult, but nearly undetectable in multiple myeloma (MM) tissues and cell lines. Its promoter methylation was detected in virtually all the silenced or downregulated cell lines. The silencing of PCDH10 could be reversed by pharmacological demethylation, indicating a methylation-mediated mechanism. In the current study, we investigated 44 patients (23 females, 21 males), 77.27% (34/44) of whom presented high methylation of PCDH10. We found no associations between promoter hypermethylation and gender or age at the time of initial diagnosis. We also examined the role of PCDH10 as a mediator of MM cell proliferation, cell cycle progression, and its involvement in angiogenesis. Our results demonstrate that the PCDH10 gene is a target for epigenetic silencing in MM and provide a link between the dysregulation of angiogenesis and DNA methylation.

Generation of bivalent and bispecific kringle single domains by loop grafting as potent agonists against death receptors 4 and 5

Bivalent or bispecific binding activity of proteins has been mainly achieved by assembling two or more domains in a single molecule. Here we report bivalent/bispecific single-domain proteins based on the kringle domain (KD), which has a cystine knot structural motif and is highly tolerant of sequence modifications. KD has seven loops protruding from the core fold into two largely opposite directions, dubbed loop cluster regions (LCRs) 1 and 2. Mutational analysis of previously isolated agonistic KD variants against human death receptors (DRs) 4 and 5 revealed that they can simultaneously recognize two target molecules of DR4 and/or DR5 via the two independent binding sites of LCR1 and LCR2. Binding loop mapping of yeast-surface-displayed KD mutants identified high-affinity target binding loops in LCR2, which were then grafted into conformationally compatible loops located on the opposite side of LCR1 within the same or different KD variants to generate bivalent/bispecific KD variants against DR4 and/or DR5 with improved affinity. The loop-grafted bivalent/bispecific KD variants showed enhanced cell-death-inducing activity of tumor cells compared with their monovalent/monospecific and bivalent/monospecific counterparts, demonstrating an advantage of bispecific targeting to both DR4 and DR5 over the targeting of only one of the two pro-apoptotic receptors. Our results suggest that the KD with the two independent binding surfaces for target recognition is an appropriate scaffold for the development of bivalency and/or bispecificity by loop grafting on the single domain, which offers a distinct advantage over other protein scaffolds with a single binding surface.

Antiangiogenic kringles derived from human plasminogen and apolipoprotein(a) inhibit fibrinolysis through a mechanism that requires a functional lysine-binding site

Many proteins in the fibrinolysis pathway contain antiangiogenic kringle domains. Owing to the high degree of homology between kringle domains, there has been a safety concern that antiangiogenic kringles could interact with common kringle proteins during fibrinolysis leading to adverse effects in vivo. To address this issue, we investigated the effects of several antiangiogenic kringle proteins including angiostatin, apolipoprotein(a) kringles IV(9)-IV(10)-V (LK68), apolipoprotein(a) kringle V (rhLK8) and a derivative of rhLK8 mutated to produce a functional lysine-binding site (Lys-rhLK8) on the entire fibrinolytic process in vitro and analyzed the role of lysine binding. Angiostatin, LK68 and Lys-rhLK8 increased clot lysis time in a dose-dependent manner, inhibited tissue-type plasminogen activator-mediated plasminogen activation on a thrombin-modified fibrinogen (TMF) surface, showed binding to TMF and significantly decreased the amount of plasminogen bound to TMF. The inhibition of fibrinolysis by these proteins appears to be dependent on their functional lysine-binding sites. However, rhLK8 had no effect on these processes owing to an inability to bind lysine. Collectively, these results indicate that antiangiogenic kringles without lysine binding sites might be safer with respect to physiological fibrinolysis than lysine-binding antiangiogenic kringles. However, the clinical significance of these findings will require further validation in vivo.

The Chick Embryo Chorioallantoic Membrane as an In Vivo Assay to Study Antiangiogenesis

Antiangiogenesis, e.g., inhibition of blood vessel growth, is being investigated as a way to prevent the growth of tumors and other angiogenesis-dependent diseases. Pharmacological inhibition interferes with the angiogenic cascade or the immature neovasculature with synthetic or semi-synthetic substances, endogenous inhibitors or biological antagonists.The chick embryo chorioallantoic membrane (CAM) is an extraembryonic membrane, which serves as a gas exchange surface and its function is supported by a dense capillary network. Because its extensive vascularization and easy accessibility, CAM has been used to study morphofunctional aspects of the angiogenesis process in vivo and to study the efficacy and mechanism of action of pro- and anti-angiogenic molecules. The fields of application of CAM in the study of antiangiogenesis, including our personal experience, are illustrated in this review article.

Apolipoprotein(a) stimulates vascular endothelial cell growth and migration and signals through integrin alphaVbeta3

Elevated plasma concentrations of Lp(a) [lipoprotein(a)] are an emerging risk factor for atherothrombotic disease. Apo(a) [apolipoprotein(a)], the unique glycoprotein component of Lp(a), contains tandem repeats of a plasminogen kringle (K) IV-like domain. In the light of recent studies suggesting that apo(a)/Lp(a) affects endothelial function, we evaluated the effects of apo(a)/Lp(a) on growth and migration of cultured HUVECs (human umbilical-vein endothelial cells). Two full-length r-apo(a) [recombinant apo(a)] variants (12K and 17K), as well as Lp(a), were able to stimulate HUVEC growth and migration to a comparable extent; 17K r-apo(a) also decreased the levels of total and active transforming growth factor-beta secreted by these cells. Using additional r-apo(a) variants corresponding to deletions and/or site-directed mutants of various kringle domains in the molecule, we were able to determine that the observed effects of full-length r-apo(a) on HUVECs were dependent on the presence of a functional lysine-binding site(s) in the apo(a) molecule. With respect to signalling events elicited by apo(a) in HUVECs, we found that 17K treatment of the cells increased the phosphorylation level of FAK (focal adhesion kinase) and MAPKs (mitogen-activated protein kinases), including ERK (extracellular-signal-regulated kinase), p38 and JNK (c-Jun N-terminal kinase). In addition, we showed that LM609, the function-blocking antibody to integrin alphaVbeta3, abrogated the effects of 17K r-apo(a) and Lp(a) on HUVECs. Taken together, the results of the present study suggest that the apo(a) component of Lp(a) signals through integrin alphaVbeta3 to activate endothelial cells.

A novel peptide from human apolipoprotein(a) inhibits angiogenesis and tumor growth by targeting c-Src phosphorylation in VEGF-induced human umbilical endothelial cells

Many angiogenesis inhibitors are derived from large plasma proteins. Previous studies showed that the Kringle5-like domain (termed KV) in human apolipoprotein (a) is a potential antiangiogenic factor. However, its active region and the underling molecular mechanism remain elusive. Here, we identified an 11-amino acid peptide (named KV11) as the key region for the antiangiogenic function of the KV domain of apolipoprotein (a). We demonstrate that KV11 inhibits angiogenesis in vitro by suppressing human umbilical vein endothelial cell migration and microtubule formation. KV11 inhibits angiogenesis in chicken chorioallantoic membrane assays and mouse corneal micropocket angiogenesis assays in vivo. KV11 peptide shows no effect on tumor cell growth or proliferation, but significantly inhibits tumor growth in SCID mouse xenograft tumor model (p < 0.01) by preventing tumor angiogenesis. We elucidate that KV11 peptide suppresses angiogenesis and tumor progression by targeting the c-Src/ERK signaling pathways. Together, these studies provide the first evidence that KV11 from apolipoprotein KV domain has anti-angiogenesis functions and may be an anti-tumor drug candidate.

Secreted human apolipoprotein(a) kringle IV-10 and kringle V inhibit angiogenesis and xenografted tumor growth

Abstract Angiogenesis plays an important role in normal physiology of blood vessel growth, but can contribute to the pathogenesis of diseases, such as cancer. A new anti-angiogenic recombinant kringle protein, composed of the fused domains of human apolipoprotein(a) carboxyl-terminal kringle IV-10 and kringle V, was expressed in Pichia pastoris and human colorectal carcinoma (HCT 116) cells to investigate its influence on angiogenesis and tumor growth. The mature recombinant protein exhibited the characteristic features of kringle-containing proteins (glycosylation and disulfide bond formation) and, when added to cultures of human umbilical vein endothelial cell, resulted in a 31% decrease in proliferation relative to untreated controls (p<0.05). The neo-angiogenesis was diminished by 63% in chick embryos treated with 10 mug recombinant protein compared with 7% for phosphate buffer solution-treated embryos (p<0.01). Transfection of a kringle IV-10-kringle V fusion protein construct into HCT 116 cells decreased tumorigenesis and inhibited tumor growth in vivo without affecting tumor cell proliferation. HCT 116 cells that expressed recombinant protein displayed a much lower relative growth ratio of 8% (p<0.01) against the control tumor cells. From these results, we conclude that human apolipoprotein(a) carboxyl-terminal kringle IV-10-kringle V fusion protein is an effective inhibitor of angiogenesis and angiogenesis-dependent tumor growth.

Plasmin-cleaved beta-2-glycoprotein 1 is an inhibitor of angiogenesis

beta-2-Glycoprotein 1, an abundant plasma glycoprotein, binds anionic cell surfaces and functions as a regulator of thrombosis. Here, we show that cleavage of the kringle domain at Lys317/Thr318 switches its function to a regulator of angiogenesis. In vitro, the cleaved protein specifically inhibited the proliferation and migration of endothelial cells. The protein was without effect on preformed endothelial cell tubes. In vivo, the cleaved protein inhibited neovascularization into subcutaneously implanted Matrigel and Gelfoam sponge implants and the growth of orthotopically injected tumors. Collectively, these data indicate that plasmin-cleaved beta-2-glycoprotein 1 is a potent antiangiogenic and antitumor molecule of potential therapeutic significance.

Lipoprotein[a] and cancer: Anti-neoplastic effect besides its cardiovascular potency

While the death rate from cancer has substantially decreased over the past decade, the search for effective and tolerable therapies is a great challenge as yet. The evidence that malignant cells cannot grow to a clinically detectable tumor mass and spread in the absence of an adequate vascular support, has opened a new area of research towards the selective inhibition or even destruction of tumor vessels. Angiostatin and angiostatin-related proteins are a family of specific angiogenesis inhibitors produced by tumors from a family of naturally occurring proteins, which also includes plasminogen and lipoprotein[a]. The anti-angiogenic activity of these proteins resides in cryptic and highly-repetitive molecular domains hidden within the protein moiety, called kringles. Lipoprotein[a] is an intriguing molecule consisting of a low-density lipoprotein core in addition to the covalently bound apolipoprotein[a]. Apolipoprotein[a] is characterized by an inactive protease domain, a single copy of the plasminogen kringle V and multiple repeats of domains homologous to the plasminogen kringle IV. Reliable studies on animal models indicate that the proteolytic break-down products of apolipoprotein[a] would posses anti-angiogenic and anti-tumoral properties both in vitro and in vivo, a premise to develop novel therapeutic modalities which may efficiently suppress tumor growth and metastasis. This review is focused on the biochemical structure, metabolism and the anti-angiogenic activity of this unique and elusive kringle-containing lipoprotein.

Disruption of hexokinase II (HXK2) partly relieves glucose repression to enhance production of human kringle fragment in gratuitous recombinant Saccharomyces cerevisiae

The GAL1 gene encoding galactokinase was disrupted in a recombinant Saccharomyces cerevisiae strain in which production of LK8 protein, a kringle fragment of human apolipoprotein, is under the control of GAL1 promoter. Null mutation of the HXK2 gene was introduced further in the gal1Delta strain to relieve glucose repression. A pattern for LK8 expression was compared for the two recombinant S. cerevisiae systems in continuous and fed-batch cultivations. A critical dilution rate in continuous cultivation that repressed LK8 expression was significantly higher for the gal1Deltahxk2Delta strain than that for the gal1Delta strain to sustain the LK8 production even at high glucose consumption rate. Expressed LK8 for the gal1Delta strain was not detectable when the dilution rate exceeded 0.05 h(-1). Maximum LK8 concentration of 57 mgl(-1) was obtained in glucose-limited fed-batch cultivation of the gal1Deltahxk2Delta strain, corresponding to a 13.8-fold enhancement compared with the gal1Delta strain grown under the same conditions.

Adeno-associated virus-mediated expression of apolipoprotein (a) kringles suppresses hepatocellular carcinoma growth in mice

Hepatocellular carcinoma (HCC) constitutes more than 90% of all primary liver cancers. HCC is a hypervascular tumor that develops from dedifferentiation of small avascular HCC and is therefore a good target for anti-angiogenic gene therapy. Recent studies have identified apolipoprotein(a) [apo(a)] kringles LK68 and LK8 (LKs) as having a potential antiangiogenic and anti-tumor activity, and the current study evaluates the therapeutic potential of gene therapy with recombinant adeno-associated virus carrying genes encoding LKs (rAAV-LK) in the treatment of hypervascular HCC. We generated rAAV-LK to obtain persistent transgene expression in vivo, which is essential for anti-angiogenic therapy. The rAAV-produced LKs substantially inhibited proliferation and migration of human umbilical vein endothelial cells (HUVECs) in vitro, validating their anti-angiogenic potential. Intramuscular administration of rAAV-LK gave 60% to 84% suppression (P < .05) of tumor growth in mice bearing subcutaneously transplanted HCC derived from Huh-7 and Hep3B cells, respectively. Histological and immunohistochemical analyses of HCC tumor sections showed that a single administration of rAAV-LK gave rise to persistent expression of LKs that inhibited tumor angiogenesis and triggered tumor apoptosis, and, thus, significantly suppressed tumor growth. The administration of rAAV-LK provided a significant survival benefit (P < .05), and 3 of 10 rAAV-LK-treated mice were still alive without visible tumors and without clinical symptoms 188 days after treatment. In conclusion, rAAV-LK is a potential candidate for anti-angiogenic gene therapy in the treatment of HCC.

Elements in the C terminus of apolipoprotein [a] responsible for the binding to the tenth type III module of human fibronectin

In previous studies, we showed that the C-terminal domain, F2, but not the N-terminal domain, F1, is responsible for the binding of apolipoprotein [a] (apo[a]) to human fibronectin (Fn). To pursue those observations, we prepared, by both elastase digestion and recombinant technology, subsets of F2 of a different length containing either kringle (K) V or the protease domain (PD). We also studied rhesus monkey apo[a], which is known to contain PD but not KV. In the case of Fn, we used both an intact product and its tenth type III module (10FN-III) expressed in Escherichia coli. The binding studies carried out on microtiter plates showed that the affinity of F2 for immobilized 10FN-III was approximately 6-fold higher than that for Fn (dissociation constants = 1.75 +/- 0.31 nM and 10.25 +/- 1.62 nM, respectively). The binding was also exhibited by rhesus apo[a] and by an F2 subset containing the PD linked to an upstream microdomain comprising KIV-8 to KIV-10 and KV, inactive by itself. Competition experiments on microtiter plates showed that both Fn and 10FN-III, when in solution, are incompetent to bind F2. Together, our results indicate that F2 binds to immobilized 10FN-III more efficiently than whole Fn and that the binding can be sustained by truncated forms of F2 that contain the catalytically inactive PD linked to an upstream four K microdomain.

Mechanisms and significance of bifunctional NK4 in cancer treatment

Based on the background that hepatocyte growth factor (HGF) and c-Met/HGF receptor tyrosine kinase play a definite role in tumor invasion and metastasis, NK4, four-kringles containing intramolecular fragment of HGF, was isolated as a competitive antagonist for the HGF-c-Met system. Independent of its HGF-antagonist action, NK4 inhibited angiogenesis induced by vascular endothelial cell growth factor and basic fibroblast growth factor, as well as HGF, indicating that NK4 is a bifunctional molecule that acts as an HGF-antagonist and angiogenesis inhibitor. Interestingly, kringle domains in distinct types of proteins, e.g., plasminogen, prothrombin, plasminogen activators, apolipoprotein(a), and HGF, share angioinhibitory actions. In experimental models of distinct types of cancers, NK4 protein administration or NK4 gene therapy inhibited tumor invasion, metastasis, and angiogenesis-dependent tumor growth. Cancer treatment with NK4 may prove to suppress malignant tumors to be 'static' in both tumor growth and spreading, as based on biological characteristics of malignant tumors.

Dermal wound healing is subject to redox control

Previously we have reported in vitro evidence suggesting that that H2O2 may support wound healing by inducing VEGF expression in human keratinocytes (C. K. Sen et al., 2002, J. Biol. Chem.277, 33284-33290). Here, we test the significance of H2O2 in regulating wound healing in vivo. Using the Hunt-Schilling cylinder approach we present the first evidence that the wound site contains micromolar concentrations of H2O2. At the wound site, low concentrations of H2O2 supported the healing process, especially in p47(phox)- and MCP-1-deficient mice in which endogenous H2O2 generation is impaired. Higher doses of H2O2 adversely influenced healing. At low concentrations, H2O2 facilitated wound angiogenesis in vivo. H2O2 induced FAK phosphorylation both in wound-edge tissue in vivo and in human dermal microvascular endothelial cells. H2O2 induced site-specific (Tyr-925 and Tyr-861) phosphorylation of FAK. Other sites, including the Tyr-397 autophosphorylation site, were insensitive to H2O2. Adenoviral gene delivery of catalase impaired wound angiogenesis and closure. Catalase overexpression slowed tissue remodeling as evidenced by a more incomplete narrowing of the hyperproliferative epithelium region and incomplete eschar formation. Taken together, this work presents the first in vivo evidence indicating that strategies to influence the redox environment of the wound site may have a bearing on healing outcomes.