Kringle 5 of plasminogen is a novel inhibitor of endothelial cell growth

Evaluation of biodistribution and antitumor effects of (188)Re-rhk5 in a mouse model of lung cancer

Targeting drugs to receptors involved in tumor angiogenesis is considered to be a novel and promising approach to improve cancer treatment. This study aimed to evaluate the anti-tumor efficacy of (188)Re-labeled recombinant human plasminogen kringle 5 ((188)Re‑rhk5) through [18F]-fluorodeoxyglucose (FDG) micro-positron emission tomography (PET). Radiolabeled rhk5 was obtained by conjugating the hystidine (6 x His) group at the carbon end of rhk5 with fac-[(188)Re(H(2)O)(3)(CO)(3)](+). The biodistribution study of (188)Re-rhk5 showed that (188)Re-rhk5 had a high initial tumor uptake and prolonged tumor retention. The highest tumor uptake of (188)Re-rhk5 (3.65±0.82% ID/g) was found 2 h after injection which decreased to 0.81±0.14% ID/g 12 h after injection. Following therapy, tumor size measurement indicated that (188)Re-rhk5-treated tumors were smaller than (188)Re-, rhk5- and saline-treated controls 6 days after the treatment. In vivo 18F-FDG micro-PET imaging showed significantly reduced tumor metabolism in the (188)Re-rhk5-treated mice vs. those treated with rhk5, (188)Re and saline control, 1 day after treatment. Moreover, the number of microvessels was significantly reduced after (188)Re-rhk5 treatment as determined by CD31 staining. Our results demonstrate that specific delivery of (188)Re-rhk5 allows preferential cytotoxicity to A549 lung cancer cells and tumor vasculature. (18)F-FDG micro-PET is a non-invasive imaging tool that can be utilized to assess early tumor responses to (188)Re-rhk5 therapy.

High efficacy and minimal peptide required for the anti-angiogenic and anti-hepatocarcinoma activities of plasminogen K5

Kringle 5(K5) is the fifth kringle domain of human plasminogen and its anti-angiogenic activity is more potent than angiostatin that includes the first four kringle fragment of plasminogen. Our recent study demonstrated that K5 suppressed hepatocarcinoma growth by anti-angiogenesis. To find high efficacy and minimal peptide sequence required for the anti-angiogenic and anti-tumour activities of K5, two deletion mutants of K5 were generated. The amino acid residues outside kringle domain of intact K5 (Pro452-Ala542) were deleted to form K5mut1(Cys462-Cys541). The residue Cys462 was deleted again to form K5mut2(Met463-Cys541). K5mut1 specifically inhibited proliferation, migration and induced apoptosis of endothelial cells, with an apparent two-fold enhanced activity than K5. Intraperitoneal injection of K5mut1 resulted in more potent tumour growth inhibition and microvessel density reduction than K5 both in HepA-grafted and Bel7402-xenografted hepatocarcinoma mouse models. These results suggested that K5mut1 has more potent anti-angiogenic activity than intact K5. K5mut2, which lacks only the amino terminal cysteine of K5mut1, completely lost the activity, suggesting that the kringle domain is essential for the activity of K5. The activity was enhanced to K5mut1 level when five acidic amino acids of K5 in NH₂ terminal outside kringle domain were replaced by five serine residues (K5mut3). The shielding effect of acidic amino acids may explain why K5mut1 has higher activity. K5, K5mut1 and K5mut3 held characteristic β-sheet spectrum while K5mut2 adopted random coil structure. These results suggest that K5mut1 with high efficacy is the minimal active peptide sequence of K5 and may have therapeutic potential in liver cancer.

The potential of nanomedicine therapies to treat neovascular disease in the retina

Neovascular disease in the retina is the leading cause of blindness in all age groups. Thus, there is a great need to develop effective therapeutic agents to inhibit and prevent neovascularization in the retina. Over the past decade, anti-VEGF therapeutic agents have entered the clinic for the treatment of neovascular retinal disease, and these agents have been effective for slowing and preventing the progression of neovascularization. However, the therapeutic benefits of anti-VEGF therapy can be diminished by the need for prolonged treatment regimens of repeated intravitreal injections, which can lead to complications such as endophthalmitis, retinal tears, and retinal detachment. Recent advances in nanoparticle-based drug delivery systems offer the opportunity to improve bioactivity and prolong bioavailability of drugs in the retina to reduce the risks associated with treating neovascular disease. This article reviews recent advances in the development of nanoparticle-based drug delivery systems which could be utilized to improve the treatment of neovascular disease in the retina.

Preparation and characterization of RGD tumour-homing-peptide-modified plasminogen K5

Plasminogen K5 (kringle 5) has strong inhibitory effects on endothelial-cell proliferation and migration. It was reported that K5 can reduce tumour neovascularization, resulting in clinically relevant antitumour effects. To determine whether addition of a tumour-targeting peptide could improve the tumour homing and antitumour activities of K5, we genetically modified K5 with an RGD (Arg-Gly-Asp) motif, which is a ligand with high affinity for αvβ₃ and αvβ₅ integrins. The fusion protein RGD-K5 was expressed in the Pichia pastoris system and the biological activity of RGD-K5 was assessed in vitro and in vivo. The results showed that the RGD-K5 exhibited a more potent effect of inhibiting endothelial cell proliferation and migration compared with that of traditional K5. RGD-K5 also displayed stronger anti-angiogenic activity in a CAM (chick chorioallantoic membrane) assay. Furthermore, RGD-K5 also showed stronger anti-angiogenic and antitumour effects in B16F10 melanoma-bearing mice compared with traditional K5. In conclusion, the biological activity of K5 can be further improved by the addition of a tumour-homing peptide, and the RGD-K5 may prove to be a promising novel candidate for cancer therapy.

The human alpha(2)-plasmin inhibitor: functional characterization of the unique plasmin(ogen)-binding region

The human alpha(2)-plasmin inhibitor (A2PI) possesses unique N- and C-terminal extensions that significantly influence its biological activities. The C-terminal segment, A2PIC (Asn(398)-Lys(452)), contains six lysines thought to be involved in the binding to lysine-binding sites in the kringle domains of human plasminogen, of which four (Lys(422), Lys(429), Lys(436), Lys(452)) are completely and two (Lys(406), Lys(415)) are partially conserved. Multiple Lys to Ala mutants of A2PIC were expressed in Escherichia coli and used in intrinsic fluorescence titrations with kringle domains K1, K4, K4 + 5, and K1 + 2 + 3 of human plasminogen. We were able to identify the C-terminal Lys(452) as the main binding partner in recombinant A2PIC (rA2PIC) constructs with isolated kringles. We could show a cooperative, zipper-like enhancement of the interaction between C-terminal Lys(452) and internal Lys(436) of rA2PIC and isolated K1 + 2 + 3, whereas the other internal lysine residues contribute only to a minor extent to the binding process. Sulfated Tyr(445) in the unique C-terminal segment revealed no influence on the binding affinity to kringle domains.

Plasminogen hydrolysis by cathepsin S and identification of derived peptides as selective substrate for cathepsin V and cathepsin L inhibitor

Plasminogen is a glycoprotein implicated in angiogenesis and fibrin clot degradation associated with the release of angiostatin and plasmin activation, respectively. We have recently reported that cathepsin V, but not cathepsins L, B, and K, can release angiostatin-like fragments from plasminogen. Here, we extended the investigation to cathepsin S which has been implicated in angiogenesis and tumor cell proliferation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of plasminogen hydrolysis by cathepsin S revealed generation of two fragments (60 and 38 kDa). Amino-terminal sequencing indicated that cleavage occurs at the Leu469-Leu470 peptide bond. In contrast to cathepsin V, which possesses antiangiogenic activity, cathepsin S plasminogen cleavage products were not capable of inhibiting angiogenesis on endothelial cells. Moreover, we explored the different selectivities presented by cathepsins V and S towards plasminogen and synthesized fluorescence resonance energy transfer peptides encompassing the hydrolyzed peptide bonds by both enzymes. The peptide Abz-VLFEKKQ-EDDnp (Abz=ortho-aminobenzoic acid; EDDnp= N-[2,4-dinitrophenyl]ethylenediamine), hydrolyzed by cath-epsin V at the Phe-Glu bond, is a selective substrate for the enzyme when compared with cathepsins B, L, and S, whereas Abz-VLFEKKVYLQ-EDDnp is an efficient cathepsin L inhibitor. The demonstrated importance of the S3′-P3′ interaction indicates the significance of the extended subsites for enzyme specificity and affinity.

Residues essential for plasminogen binding by the cation-independent mannose 6-phosphate receptor

The 300 kDa cation-independent mannose 6-phosphate receptor (CI-MPR) is a multifunctional protein that binds diverse intracellular and extracellular ligands with high affinity. The CI-MPR is a receptor for plasminogen, and this interaction can be inhibited by lysine analogues. To characterize the molecular basis for this interaction, surface plasmon resonance (SPR) analyses were performed using truncated forms of the CI-MPR and plasminogen. The results show that the N-terminal region of the CI-MPR containing domains 1 and 2, but not domain 1 alone, of the receptor's 15-domain extracytoplasmic region binds plasminogen (K(d) = 5 +/- 1 nM) with an affinity similar to that of the full-length receptor (K(d) = 20 +/- 6 nM). In addition to its C-terminal serine protease domain, plasminogen contains lysine binding sites (LBS), which are located within each of its five kringle domains, except kringle 3. We show that kringles 1-4, but not kringles 1-3, bind the CI-MPR, indicating an essential role for the LBS in kringle 4 of plasminogen. To identify the lysine residue(s) of the CI-MPR that serve(s) as an essential determinant for recognition by the LBS of plasminogen, site-directed mutagenesis studies were carried out using a construct encoding the N-terminal three domains of the CI-MPR (Dom1-3His) which contains both a mannose 6-phosphate (Man-6-P) and plasminogen binding site. The results demonstrate two lysine residues (Lys53 located in domain 1 and Lys125 located in the loop connecting domains 1 and 2) of the CI-MPR are key determinants for plasminogen binding but are not required for Man-6-P binding.

Adeno-associated virus-mediated delivery of kringle 5 of human plasminogen inhibits orthotopic growth of ovarian cancer

Kringle 5 (K5) of human plasminogen is a potent angiogenesis inhibitor. In this study, we investigated the effects of recombinant adeno-associated virus (AAV)-mediated delivery of K5 in mouse models of human ovarian cancer. A single intramuscular injection of AAV-K5 resulted in sustained expression of K5 reaching a maximum serum level of 800 ng ml(-1). Gene therapy inhibited both vascular endothelial growth factor (VEGF)-induced and tumor cell-induced angiogenesis in matrigel plug assays. Furthermore, a single injection of AAV-K5 significantly inhibited both subcutaneous and intraperitoneal growth of human ovarian cancer cells. Immunofluorescence studies of residual tumors surgically resected from the treated animals showed reduced tumor burden, which correlated with the inhibition of tumor neovascularization. In addition, AAV-K5 gene therapy differentially affected the nascent vessels more than mature vasculature and induced apoptotic death of tumor cells. These data show that AAV-K5 can be effectively used to inhibit ovarian cancer.

Recombinant kringle 5 from plasminogen antagonises hepatocyte growth factor-mediated signalling

The blood protein plasminogen is proteolytically cleaved to produce angiostatin and kringle 5 (K5), both of which are known angiogenesis inhibitors. A common structural element between K5, angiostatin and other endogenous angiogenesis inhibitors is the presence of the kringle protein-interacting domain. Another kringle domain-containing protein, hepatocyte growth factor (HGF), promotes angiogenesis by binding to and stimulating the tyrosine kinase receptor Met. HGF binding to Met is dependent on the kringle domains of HGF. Because both K5 and HGF contain kringle motifs and because these proteins have opposite effects on angiogenesis, we hypothesised that K5 can antagonise HGF-mediated signalling in a Met-dependent manner. We determined that K5 binding to H1299 cells is competed by HGF suggesting that these two proteins bind to the same protein. Purified K5 immunoprecipitates with Met and this interaction is abolished by increasing doses of HGF. Using proliferation, phosphorylation of Met and Akt as markers of HGF activity, we determined that K5 inhibits HGF-mediated signalling. Taken together, these data support a model by which K5 binds to Met and functions as a competitive antagonist of HGF signalling and presents a novel mechanism of action of K5.

Solution structure and functional characterization of human plasminogen kringle 5

The ligand binding properties of the kringle 5 (K5) domain of human plasminogen have been investigated via intrinsic tryptophan fluorescence. The oleic acid (OA) affinity for K5 was quantified, yielding an association constant K(a) approximately 2.08 x 10(4) mM(-1). Simultaneously, it was determined that OA and trans-4-(aminomethyl)cyclohexanecarboxylic acid (AMCHA) (K(a) approximately 50 mM(-1)) compete for binding to K5. The solution structure of K5 in the presence of 11 mM AMCHA was solved via NMR spectroscopy (protein heavy atom RMSD approximately 0.93 +/- 0.12 A). The AMCHA binding site was localized via (1)H/(15)N chemical shift perturbation mapping assisted by in silico docking. We have found that AMCHA binds at the canonical kringle lysine binding site (LBS), structured by the Pro54-Gly60 segment plus the neighboring Phe36, Thr37, Trp62, Leu71, and Tyr72 residues. The segment 30-42, encompassing LBS residues, appears to be endowed with a higher degree of structural flexibility as suggested by the relatively lower value of S(2), the generalized order parameter, consistent with a higher backbone heavy atom RMSD of approximately 1.22 A (vs 0.84 A overall) between the two monomeric units in the crystal unit cell, of potential significance for ligand binding. OA was found to perturb the same area of the protein, namely, the LBS, as well as Tyr74. Combined with previous studies, the observation of OA binding expands the range of ligands that interact with kringle 5 while it widens the scope of potential biological functions for kringle domains.

Nanoparticle-mediated expression of an angiogenic inhibitor ameliorates ischemia-induced retinal neovascularization and diabetes-induced retinal vascular leakage

OBJECTIVE

The aim of the study is to evaluate the effect of nanoparticle-mediated gene delivery of angiogenic inhibitors on retinal inflammation, vascular leakage, and neovascularization in diabetic retinopathy.

RESEARCH DESIGN AND METHODS

An expression plasmid of plasminogen kringle 5 (K5), a natural angiogenic inhibitor, was encapsulated with poly(lactide-coglycolide) to form K5 nanoparticles (K5-NP). Expression of K5 was determined by Western blot analysis and immunohistochemistry, and retinal vascular leakage was measured by permeability assay. Retinal neovascularization was evaluated using fluorescein-angiography and counting preretinal vascular cells in rats with oxygen-induced retinopathy. Effects of K5-NP on retinal inflammation were evaluated in streptozotocin-induced diabetic rats by leukostasis assay and Western blot analysis of intracellular adhesion molecule and vascular endothelial growth factor. Possible toxicities of K5-NP were evaluated using histology examination, retinal thickness measurement, and electroretinogram recording.

RESULTS

K5-NP mediated efficient expression of K5 and specifically inhibited growth of endothelial cells. An intravitreal injection of K5-NP resulted in high-level expression of K5 in the inner retina of rats during the 4 weeks they were analyzed. Injection of K5-NP significantly reduced retinal vascular leakage and attenuated retinal neovascularization, when compared with the contralateral eyes injected with Control-NP in oxygen-induced retinopathy rats. K5-NP attenuated vascular endothelial growth factor and intracellular adhesion molecule-1 overexpression and reduced leukostasis and vascular leakage for at least 4 weeks after a single injection in the retina of streptozotocin-induced diabetic rats. No toxicities of K5-NP were detected to retinal structure and function.

CONCLUSIONS

K5-NP mediates efficient and sustained K5 expression in the retina and has therapeutic potential for diabetic retinopathy.

Systemic and Periocular Deliveries of Plasminogen Kringle 5 Reduce Vascular Leakage in Rat Models of Oxygen-Induced Retinopathy and Diabetes

PURPOSE

Increased retinal vascular permeability is a common complication of diabetes and a major cause of vision loss in diabetic patients. The current study is to determine the effect of plasminogen kringle 5 (K5) on vascular leakage via systemic and periocular deliveries.

METHODS

Oxygen-induced retinopathy (OIR) was generated by exposing newborn rats to 75% oxygen. Diabetes was induced in adult rats by injection of streptozotocin (STZ). Retinal vascular permeability was measured by the Evans blue-albumin leakage method.

RESULTS

Subcutaneous, intraperitoneal, subconjunctival, and retrobulbar injections and topical eyedrop application of K5 significantly reduced retinal vascular permeability in both the OIR and STZ-diabetic rat models. Compared with the periocular deliveries, systemic administration requires higher doses of K5. K5 deliveries downregulated VEGF expression in the retina.

CONCLUSIONS

K5 can reduce retinal vascular permeability through systemic and periocular deliveries. These delivery routes of K5 have therapeutic potential in the treatment of vascular leakage.

Plasminogen kringle 5 induces apoptosis of brain microvessel endothelial cells: sensitization by radiation and requirement for GRP78 and LRP1

Recombinant plasminogen kringle 5 (rK5) has been shown to induce apoptosis of dermal microvessel endothelial cells (MvEC) in a manner that requires glucose-regulated protein 78 (GRP78). As we are interested in antiangiogenic therapy for glioblastoma tumors, and the effectiveness of antiangiogenic therapy can be enhanced when combined with radiation, we investigated the proapoptotic effects of rK5 combined with radiation on brain MvEC. We found that rK5 treatment of brain MvEC induced apoptosis in a dose- and time-dependent manner and that prior irradiation significantly sensitized (500-fold) the cells to rK5-induced apoptosis. The rK5-induced apoptosis of both unirradiated and irradiated MvEC required expression of GRP78 and the low-density lipoprotein receptor-related protein 1 (LRP1), a scavenger receptor, based on down-regulation studies with small interfering RNA, and blocking studies with either a GRP78 antibody or a competitive inhibitor of ligand binding to LRP1. Furthermore, p38 mitogen-activated protein kinase was found to be a necessary downstream effector for rK5-induced apoptosis. These data suggest that irradiation sensitizes brain MvEC to the rK5-induced apoptosis and that this signal requires LRP1 internalization of GRP78 and the activation of p38 mitogen-activated protein kinase. Our findings suggest that prior irradiation would have a dose-sparing effect on rK5 antiangiogenic therapy for brain tumors and further suggest that the effects of rK5 would be tumor specific, as the expression of GRP78 protein is up-regulated on the brain MvEC in glioblastoma tumor biopsies compared with the normal brain.

Reducing agent-mediated precipitation of high-abundance plasma proteins

Depletion of high-abundance proteins is regarded as a critical sample preparation step for most plasma proteomic analyses and profiling strategies. This report describes a process that rapidly and reproducibly precipitates high-abundance disulfide-rich proteins, including albumin and transferrin, from serum and plasma. A low volume of concentrated reducing agent, viz. dithiothreitol (DTT) or tris(2-carboxyethyl)phosphine (TCEP), was added directly to plasma followed by a brief incubation at ambient temperature. Removal of the precipitate via centrifugation and identification of the protein content revealed an albumin-enriched pellet. Direct analysis of the supernatant by MALDI-TOF-MS afforded peptidome and small protein profiles with enhanced features and minimal ionization of full-length albumin. The reproducible and quantitative nature of the method has been demonstrated by monitoring the plasma levels of an antiangiogenic protein biologic, rKringle5 (rK5). The 10.5-kDa analyte was only reliably detected in plasma after treatment with reducing agent, ionizing linearly from 150 to 1200 fmol (on-target) with a mean CV of 7%. This method distinguishes itself from immunoaffinity resin-based approaches since it can be scaled to large milliliter quantities and it is compatible with plasma from all species tested.

Molecular profile of endothelial invasion of three-dimensional collagen matrices: insights into angiogenic sprout induction in wound healing

Sprouting angiogenesis is a multistep process consisting of basement membrane degradation, endothelial cell (EC) activation, proliferation, invasion, lumen formation, and sprout stabilization. Such complexity is consistent with a requirement for orchestration of individual gene expression alongside multiple signaling pathways. To better understand the mechanisms that direct the transformation of adherent ECs on the surface of collagen matrices to develop multicellular invading sprouts, we analyzed differential gene expression with time using a defined in vitro model of EC invasion driven by the combination of sphingosine-1-phosphate, basic FGF, and VEGF. Gene expression changes were confirmed by real-time PCR and Western blot analyses. A cohort of cell adhesion molecule genes involved in adherens junction and cell-extracellular matrix (ECM) interactions were upregulated, whereas a set of genes associated with tight junctions were downregulated. Numerous genes encoding ECM proteins and proteases were induced, indicating that biosynthesis and remodeling of ECM is indispensable for sprouting angiogenesis. Knockdown of a highly upregulated gene, a disintegrin and metalloproteinase with thrombospondin-type repeats-1 (ADAMTS1), decreased invasion responses, confirming a role for ADAMTS1 in mediating EC invasion. Furthermore, differential expression of multiple members of the Wnt and Notch pathways was observed. Functional experiments indicated that inhibition and activation of the Notch signaling pathway stimulated and inhibited EC invasion responses, respectively. This study has enhanced the molecular road map of gene expression changes that occur during endothelial invasion and highlighted the utility of three-dimensional models to study EC morphogenesis.

A systematic methodology for proteome-wide identification of peptides inhibiting the proliferation and migration of endothelial cells

We introduce a systematic computational methodology based on bioinformatics that has enabled us to identify and classify >120 endogenous peptide inhibitors of endothelial cell proliferation and migration. These peptides are derived from members of the type IV collagen, thrombospondin, and CXC chemokine protein families, as well as somatotropin hormones, serpins, and various kringle-containing proteins. Their activity in suppressing the proliferation and migration of endothelial cells in vitro provides proof of principle for the validity of this computational method. Interestingly, some of the peptides are derived from proteins known to be proangiogenic. By performing receptor neutralization studies, we have identified receptors to which these peptides bind. On the basis of this receptor-binding information, we evaluated several examples of peptide-based combinatorial screening strategies. In some cases, this combinatorial screening identified strong synergism between peptides. The current work provides a guideline for a computational-based peptidomics approach for the discovery of endogenous bioactive peptides.

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

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

Intramuscular electroporation of a plasmid encoding human plasminogen kringle 5 induces growth inhibition of Lewis lung carcinoma in mice

Tumor growth and metastasis depend critically on blood vessel formation. Antiangiogenesis, therefore, represents a promising strategy for cancer therapy. The kringle 5 (K5) domain of human plasminogen is a potent angiogenesis inhibitor. To investigate whether intramuscular electroporation (EP) of K5 has antitumor activity in mouse tumor models, we constructed a plasmid encoding K5 (pVAX1-K5). Hela cells transfected with this plasmid produced and secreted K5 that inhibited the migration of human microvascular endothelial cells. Intramuscular EP treatment of pVAX1-K5 inhibited the growth of Lewis lung carcinoma and prolonged the survival time of tumor-bearing mice. Angiogenesis was obviously inhibited, and apoptosis was induced in tumor cells of mice that received intramuscular EP of pVAX1-K5. On the contrary, intramuscular injection of pVAX1-K5 without EP failed to show the same effects. The data indicate that intramuscular EP of plasmid DNA encoding the K5 domain is an effective strategy for the experimental treatment of cancer by expressing K5.

New molecular targets in angiogenic vessels of glioblastoma tumours

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

Asp-Tyr-Leu-Lys tetrapeptide inhibits airway inflammation in toluene-2,4-diisocyanate-induced asthma mice

BACKGROUND

Airway inflammation and remodelling contribute to chronic airway obstruction of asthma. Currently, no medication effectively controls airway remodelling and related vascular changes. Therefore, new strategies need to be developed. The kringle 5 domain has anti-angiogenic activity resulting from the tetrapeptide Lys-Leu-Tyr-Asp (KLYD).

OBJECTIVE

To investigate the therapeutic effect of KLYD and its inverse form Asp-Tyr-Leu-Lys (DYLK) on the inflammation and remodelling of toluene-2,4-diisocyanate (TDI)-sensitization/challenged mice.

METHODS

Cell numbers were measured in the presence of various concentrations of KLYD and DYLK using in vitro endothelial cell proliferation assay. The changes of cell number and the level of vascular endothelial growth factor (VEGF) in bronchoalveolar lavage (BAL) fluid and response to methacholine (MCh) were measured using the in vivo TDI-sensitized/challenged mice model. Muc5ac, smooth muscle actin (SMA) and proliferating cell nuclear antigen (PCNA) protein expression was analysed on trachea and intrapulmonary bronchi using immunohistochemical stain.

RESULTS

Compared with KLYD, DYLK had a greater inhibitory effect on endothelial cell proliferation (P<0.05). Pre-treatment of DYLK showed dose-dependent reduction in the response to MCh (P<0.05) and numbers of inflammatory cells in BAL fluids of TDI-sensitized/challenged mice. TDI induced increases in Muc5ac, SMA and PCNA protein expression and VEGF levels, which were also abolished by DYLK treatment.

CONCLUSIONS

Local administration of DYLK effectively inhibits the airway inflammation and airway remodelling of TDI-sensitized/challenged mice via down-regulation of VEGF. These findings suggest that anti-angiogenic peptide therapies, such as local administration of DYLK, are an effective strategy for the treatment of remodelling in asthma.

Increased suppression of oncolytic adenovirus carrying mutant k5 on colorectal tumor

Angiogenesis plays a key role in the development of a wide variety of malignant tumors. The approach of targeting antiangiogenesis has become an important field of cancer gene therapy. In this study, the antiangiogenesis protein K5 (the kringle 5 of human plasminogen) has been mutated by changing leucine71 to arginine to form mK5. Then the ZD55-mK5, which is an oncolytic adenovirus expressing mK5, was constructed. It showed stronger inhibition on proliferation of human umbilical vein endothelial cell. Moreover, in tube formation and embryonic chorioallantoic membrane assay, ZD55-mK5 exhibited more effective antiangiogenesis than ZD55-K5. In addition, ZD55-mK5 generated obvious suppression on the growth of colorectal tumor xenografts and prolonged the life span of nude mice. These results indicate that ZD55-mK5 is a potent agent for inhibiting the tumor angiogenesis and tumor growth.

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.

Plasminogen N-terminal activation peptide modulates the activity of angiostatin-related peptides on endothelial cell proliferation and migration

Angiostatin, a potent inhibitor of angiogenesis, is derived from the fibrinolytic proenzyme, plasminogen, by enzymatic processing. Plasminogen N-terminal activation peptide (PAP) is one of the products concomitantly released aside from angiostatin (kringles 1-4) and mini-plasminogen (kringle 5 plus the catalytic domain) when plasminogen is processed. To determine whether PAP alone or together with the angiostatin-related peptides derived from the processing of plasminogen modulate the proliferation and motility of endothelial cells, we have generated a recombinant PAP and used it to study its effects on endothelial cells in the presence and absence of the angiostatin-related peptides. Our results showed that PAP alone slightly increased the migration but not the proliferation of endothelial cells. However, in the presence of the angiostatin-related peptides, PAP attenuated the inhibitory activity of the angiostatin-related peptides on the proliferation and migration of endothelial cells. The inhibitory effect of PAP on the angiostatin-related peptides could be due to its binding to the kringle domains of the latter peptides.

Cathepsin V, but not cathepsins L, B and K, may release angiostatin-like fragments from plasminogen

Cathepsin V is a lysosomal cysteine peptidase highly expressed in corneal epithelium; however, its function in the eye is still unknown. Here, we describe the capability of cathepsin V to hydrolyze plasminogen, which is also expressed in human cornea at levels high enough to produce physiologically relevant amounts of angiostatin-related molecules. The co-localization of these two proteins suggests an important role for the enzyme in the maintenance of corneal avascularity, essential for optimal visual performance. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of plasminogen digestion by cathepsin V revealed the generation of three major products of 60, 50 and 40 kDa, which were electrotransferred to polyvinylidene difluoride membranes and excised for characterization. NH2-terminal amino acid sequencing of these fragments revealed the sequences EKKVYL, TEQLAP and LLPNVE, respectively. These data are compatible with cleavage sites at plasminogen F94–E95, S358–T359 and V468–L469 peptide bonds generating fragments of the five-kringle domains. In contrast, we did not detect any plasminogen degradation by cathepsins B, K and L. Using a Matrigel assay, we confirmed the angiogenesis inhibition activity on endothelial cells caused by plasminogen processing by cathepsin V. Our results suggest a novel physiological role for cathepsin V related to the control of neovascularization in cornea.

Combination of human plasminogen kringle 5 with ionizing radiation significantly enhances the efficacy of antitumor effect

Antiangiogenic therapy could destroy tumor vasculature and inhibit tumor growth. It might inhibit tumor growth significantly when used as a single treatment modality and its therapeutic benefit may even be greater when used in combination with established treatment modalities such as radiation therapy (RT). In the present report, we investigated the effect of recombinant human plasminogen kringle 5 domain (rhK5) in combination with ionizing radiation on angiogenesis, tumor growth and survival in a murine Lewis lung carcinoma (LLC) tumor model. Combined treatment using rhK5 and radiotherapy displayed obvious suppressive effect on LLC tumor growth as compared with single treatment with either modality (p < 0.05), and resulted in a more additive effect on tumor growth delay in this model. In addition, combined treatment significantly enhanced the survival of mice and no toxic effect, such as weight loss, was observed. The significant antitumor effect of rhK5 plus radiation was associated with a direct suppression effect on early neoangiogenesis and tumor cell apoptosis. Furthermore, the expression of VEGF and HIF-1alpha in tumor tissue correlated well with decreased vessel density. The results suggest that rhK5 significantly enhances the antitumor activity of RT and could be a potent adjuvant therapeutic approach to improve the efficacy of radiotherapy for lung cancer.

Plasminogen Kringle 5 blocks tumor progression by antiangiogenic and proinflammatory pathways

Proteolytic processing of human plasminogen generates potent antiangiogenic peptides such as angiostatin. The plasminogen kringle 5 (K5) domain, which is distinct from angiostatin, possesses potent antiangiogenic properties on its own, which can be exploited in cancer therapy. It has been recently observed that antiangiogenic agents promote leukocyte-vessel wall interaction as part of their antitumor effect. Although we have previously shown that K5 suppresses cancer growth in tumor xenograft models, its modulation of inflammation in experimental mice with intact immune systems is unknown. To determine whether K5 possesses immune proinflammatory properties, we investigated the effects of K5 in an immune competent model of breast cancer and observed that tumor rejection is substantially reduced in nonobese diabetic/severe combined immunodeficient and BALB/c nude when compared with wild-type BALB/c mice, suggesting an important role for T-lymphoid cells in the antitumor effect of K5. Tumor explant analysis shows that K5 enhances tumor recruitment of CD3(+) lymphoid cells, in particular, the NKT phenotype. We also observed a significant decrease in tumor-associated microvessel length and density consistent with antiangiogenic activity. Histologic analysis of K5 tumors also revealed a robust neutrophilic infiltrate, which may be explained by the neutrophil chemotactic activity of K5 as well as its ability to promote CD64 up-regulation within the CD11b(+) adhesive neutrophil population. In sum, our findings confirm that the K5 protein acts as a potent angiostatic agent and possesses a novel proinflammatory role via its ability to recruit tumor-associated neutrophils and NKT lymphocytes, leading to a potent antitumor response.

Angiogenesis inhibitors and the need for anti-angiogenic therapeutics

Angiogenesis is the formation of new blood vessels from pre-existing vessels to form capillary networks, which, among other diseases, such as diabetic retinopathy and macular degeneration, is particularly important for tumor growth and metastasis. Thus, depriving a tumor of its vascular supply by means of anti-angiogenic agents has been of great interest since its proposal in the 1970s. This review looks at the common angiogenic inhibitors (angiostatin, endostatin, maspin, pigment epithelium-derived factor, bevacizumab and other monoclonal antibodies, and zoledronic acid) and their current status in clinical trials.

Increased sFlt-1 to PlGF ratio in women who subsequently develop preeclampsia

The purpose of this study was to determine whether the levels of soluble fms-like tyrosine kinase-1 (sFlt-1) and placenta growth factor (PlGF) are altered during the second trimester in the plasma of women who subsequently develop preeclampsia. We performed a case-control study to compare the levels of sFlt-1 and PlGF in the preeclamptic (n=46) and normal pregnant women (n=100). The maternal plasma levels of sFlt-1 and PlGF were measured by enzyme-linked immunosorbent assay. The sFlt-1 levels were significantly higher in the preeclamptic women than in normal controls (p<0.001), while the PlGF levels were significantly lower (p<0.001). In normal controls, sFlt-1 levels were positively correlated (r=0.27, p=0.008), whereas, in the preeclamptic women, those were negatively correlated with the PlGF levels (r=-0.423, p=0.005). Furthermore, the log[sFlt-1/PlGF] ratio was significantly higher in the preeclamptic women than in normal controls (p<0.001). The receiver operating characteristic curve revealed a specificity of 78% with a diagnostic sensitivity of 80.4%; the optimal cut-off value of the log[sFlt-1/PlGF] ratio was 1.4 (95% CI 0.756-0.910, p<0.001). Preeclampsia showed a strong association with increased levels of sFlt-1 and decreased levels of PlGF in the second trimester maternal plasma. Accordingly, the sFlt-1/PlGF ratio may provide early prediction of subsequent development of preeclampsia.

Targeting matrix metalloproteinases and endothelial cells with a fusion peptide against tumor

Development of novel therapy for patients with tumor is still a challenge at the present time. We designed a fusion peptide (RK5) with two targets as a novel agent against tumor. The fusion peptide RK5 containing the kringle 5 fragment of human plasminogen and a decapeptide (CTTHWGFTLC) was constructed and expressed in yeast. Matrix metalloproteinase (MMP) activity, proliferation, and migration of endothelial cells were examined in vitro, respectively. Angiogenesis, tumor growth, metastasis, and survival time were evaluated in in vivo models. Administration of RK5 was delivered by both protein and gene approach. The results showed that RK5 inhibited the activity of MMP-9 and exhibited more inhibitory effects on proliferation and migration of endothelial cells than that of kringle 5 fragment and decapeptide individually. RK5 also inhibited angiogenesis, tumor growth, and metastasis and increased survival time of mice bearing tumor. In addition, the effectiveness of RK5 could be achieved by both protein and gene delivery. In conclusion, RK5 has potential to inhibit tumor growth and metastasis and to prolong survival time of animals bearing tumor. Therefore, fusion peptide RK5 with two targets provides a new design for the development of antitumor drugs and has potential for clinical application.

Plasminogen structural domains exhibit different functions when associated with cell surface GRP78 or the voltage-dependent anion channel

Both the voltage-dependent anion channel and the glucose-regulated protein 78 have been identified as plasminogen kringle 5 receptors on endothelial cells. In this study, we demonstrate that kringle 5 binds to a region localized in the N-terminal domain of the glucose-regulated protein 78, whereas microplasminogen does so through the C-terminal domain of the glucose-regulated protein 78. Both plasminogen fragments induce Ca(2+) signaling cascades; however, kringle 5 acts through voltage-dependent anion channel and microplasminogen does so via the glucose-regulated protein 78. Because trafficking of voltage-dependent anion channel to the cell surface is associated with heat shock proteins, we investigated a possible association between voltage-dependent anion channel and glucose-regulated protein 78 on the surface of 1-LN human prostate tumor cells. We demonstrate that these proteins co-localize, and changes in the expression of the glucoseregulated protein 78 affect the expression of voltage-dependent anion channel. To differentiate the functions of these receptor proteins, either when acting singly or as a complex, we employed human hexokinase I as a specific ligand for voltage-dependent anion channel, in addition to kringle 5. We show that kringle 5 inhibits 1-LN cell proliferation and promotes caspase-7 activity by a mechanism that requires binding to cell surface voltage-dependent anion channel and is inhibited by human hexokinase I.

Angiogenesis and antiangiogenic therapy in endometriosis

Endometriosis, the presence of endometrium-like tissue outside of the uterine cavity, is a common disease among women of reproductive age. Typical symptoms include abdominal pain and painful menstruation. In addition, endometriosis is associated with reduced fertility. Current treatment modalities, the surgical removal of endometriotic lesions and the hormonal suppression of estrogen are associated with significant morbidity, side-effects and recurrence rates. Despite uncertainties about the pathophysiology of the disease it has recently become apparent that angiogenesis plays a pivotal role in endometriosis. This review focuses on a multitude of factors involved in the angiogenic phenotype of endometriosis demonstrating that many biological systems such as the immune system and steroid hormones are closely connected to angiogenic pathways in this disease. In addition, experimental and clinical data are discussed that concentrate on the inhibition of angiogenesis as a novel therapeutic approach for endometriosis.

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.

Angiostatin inhibits monocyte/macrophage migration via disruption of actin cytoskeleton

In light of the involvement of tumor-associated macrophages (TAM) in the promotion of tumor growth and metastasis, strategies to prevent TAM recruitment within the tumor microenvironment are currently under investigation. The recent observation that angiostatin reduces macrophage infiltration in an atherosclerosis model prompted our laboratory to further explore the use of human plasminogen angiostatin (hK1-3) protein as a macrophage modulatory agent. We demonstrate that hK1-3 blocks migration of murine peritoneal macrophages (91% decrease, P<0.00005) and human monocytes (85% decrease, P<0.05) in vitro. Cell viability of hK1-3-treated cells is not affected, as determined by fluorochrome-labeled inhibitors of caspase-propidium iodide (FLICA/PI) flow cytometry analysis. Furthermore, confocal microscopy of phalloidin-stained cells reveals that hK1-3 leads to disruption of actin filopodia/lamellipodia in human monocytes and induces distinct podosome accumulation in mature differentiated macrophages. Paradoxically, we observed a 3.5-fold increase in secretion and a 3- to 5.5-fold increase in gelatinolytic activity of macrophage-produced matrix metalloproteinase-9, which we suggest is a cellular response to compensate for the dominant static effect of hK1-3 on actin. We also demonstrate that hK1-3 induces the phosphorylation of extracellular signal-regulated kinase (ERK1/2) in human monocytes. hK1-3-mediated macrophage immobilization has the potential to be exploited therapeutically in pathological conditions associated with cellular hypoxia, such as cancer and atherosclerosis.

Antitumor effects of non-replicative herpes simplex vectors expressing antiangiogenic proteins and thymidine kinase on Lewis lung carcinoma establishment and growth

There is growing evidence that combinations of antiangiogenic proteins with other antineoplastic treatments such as chemo- or radiotherapy and suicide genes-mediated tumor cytotoxicity lead to synergistic effects. In the present work, we tested the activity of two non-replicative herpes simplex virus (HSV)-1-based vectors, encoding human endostatin::angiostatin or endostatin::kringle5 fusion proteins in combination with HSV-1 thymidine kinase (TK) molecule, on endothelial cells (ECs) and Lewis lung carcinoma (LLC) cells. We observed a significant reduction of the in vitro growth, migration and tube formation by primary ECs upon direct infection with the two recombinant vectors or cultivation with conditioned media obtained from the vector-infected LLC cells. Moreover, direct cytotoxic effect of HSV-1 TK on both LLC and ECs was demonstrated. We then tested the vectors in vivo in two experimental settings, that is, LLC tumor growth or establishment, in C57BL/6 mice. The treatment of pre-established subcutaneous tumors with the recombinant vectors with ganciclovir (GCV) induced a significant reduction of tumor growth rate, while the in vitro infection of LLC cells with the antiangiogenic vectors before their implantation in mice flanks, either in presence or absence of GCV, completely abolished the tumor establishment.

Kringle 5 of human plasminogen, an angiogenesis inhibitor, induces both autophagy and apoptotic death in endothelial cells

Inhibition of endothelial cell proliferation and angiogenesis is emerging as an important strategy in cancer therapeutics. Kringle 5 (K5) of human plasminogen is a potent angiogenesis inhibitor. Previous studies have shown K5 exposure promotes caspase activity and apoptosis in endothelial cells. Here we report that K5 treatment evokes an autophagic response in endothelial cells that is specific and initiated even in the absence of nutritional stress. Endothelial cells exposed to K5 up-regulated Beclin 1 levels within a few hours. Furthermore, progressively increasing amounts of antiapoptotic Bcl-2 were found to be complexed with Beclin 1, although total levels of Bcl-2 remained unchanged. Prolonged exposure to K5 ultimately led to apoptosis via mitochondrial membrane depolarization and caspase activation in endothelial cells. Knocking down Beclin 1 levels by RNA interference decreased K5 induced autophagy but accelerated K5-induced apoptosis. These studies suggest that interfering with the autophagic survival response can potentiate the antiangiogenic effects of Kringle 5 in endothelial cells.

Refolding, purification, and activation of miniplasminogen and microplasminogen isolated from E. coli inclusion bodies

Two des-kringle derivatives of human plasminogen, microplasminogen and miniplasminogen, have been expressed at high levels as inclusion bodies in Escherichia coli using a T7 expression system. In each case, the isolated inclusion bodies were refolded and purified. A final yield of approximately 10% of total refolded protein was observed in each case. Both refolded molecules were successfully activated to their functional forms, microplasmin and miniplasmin, by the plasminogen activator urokinase. The kinetic properties of the refolded microplasmin and miniplasmin were comparable to full length, native plasmin.

Ocular neovascularization: Implication of endogenous angiogenic inhibitors and potential therapy

Ocular neovascularization (NV) is the primary cause of blindness in a wide range of ocular diseases, such as diabetic retinopathy (DR) and age-related macular degeneration (AMD). The exact mechanism underlying the pathogenesis of ocular NV is not yet well understood, and as a consequence, there is no satisfactory therapy for ocular NV. In the last 10 years, a number of studies provided increasing evidence demonstrating that the imbalance between angiogenic stimulating factors and angiogenic inhibitors is a major contributor to the angiogenesis induced by various insults, such as hypoxia or ischemia, inflammation and tumor. The angiogenic inhibitors alone or in combination with other existing therapies are, therefore, believed to be promising in the treatment of ocular NV in the near future. This article reviews recent progress in studies on the mechanisms and treatment of ocular NV, focusing on the implication and therapeutic potential of endogenous angiogenic inhibitors in ocular NV.

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.

Liposome-mediated gene transfer of K1-5 suppresses tumor development and improves the prognosis of hepatocellular carcinoma in mice

It has been reported that kringle 1-5 (K1-5) has a potent and specific antiangiogenic activity. In the present study, we investigated the antitumor effect of gene transfer of K1-5 for hepatocellular carcinoma in mice. Inhibitory effect by the media of Cos-1 cells containing K1-5 on bovine capillary endothelial (BCE) cell proliferation was evaluated by a tetrazolium-based assay. For tumor growth, intrahepatic metastasis, and survival studies, intravenous injection of liposome-K1-5 cDNA complexes was performed to nude mice implanted with three hepatoma cell lines into the liver. Production of K1-5 was investigated by immunohistochemistry and Western blotting. The number of vessels in the tumor was counted in 0.125 mm2 fields. Expression of vascular endothelial growth factor (VEGF) and angiopoietin (Ang)-1 and -2 in tumors was investigated by Western blotting. Serum ALT levels and body weight of the mice were measured. Proliferation of BCE cells was inhibited by 44% in the media containing K1-5. Gene transfer of K1-5 suppressed tumor growth of the three hepatoma cell lines, respectively. In the K1-5-treated group, survival period was prolonged and the number of intrahepatic metastases was reduced. Expression of K1-5 protein was detected on hepatoma cells and hepatocytes. The number of vessels in tumor tissues was decreased by K1-5 transfection. Expression of angiopoietin-2 in tumor tissues was suppressed by K1-5 transfection. Serum ALT levels and body weight of mice were not influenced by K1-5 transfection. These findings suggest that antiangiogenic gene therapy with K1-5 cDNA will be a safe and effective strategy to suppress the growth of hepatocellular carcinoma.

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

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

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.

Gene transfer of kringle 1-5 suppresses tumor development and improves prognosis of mice with hepatocellular carcinoma

BACKGROUND & AIMS

Recent studies indicate that kringle 1-5 has a potent and specific antiangiogenic activity. Here, we investigated the antitumor effect of kringle 1-5 gene transfer on hepatocellular carcinoma in mice.

METHODS

The inhibitory effect of kringle 1-5 protein on proliferation of bovine capillary endothelial cells was evaluated by a tetrazolium-based assay. To study tumor growth, intrahepatic metastasis, and survival, liposome/kringle 1-5 complementary DNA complexes were injected intravenously in nude mice preimplanted with 1 of 3 hepatoma cell lines into the liver. Production of kringle 1-5 was tested by immunohistochemistry and Western blotting. Intratumoral vessel density was quantified. Expression of vascular endothelial growth factor, angiopoietin-1, and angiopoietin-2 in tumors was examined by Western blotting. Serum alanine aminotransferase and alpha-fetoprotein levels and body weights were measured.

RESULTS

Proliferation of bovine capillary endothelial cells was inhibited by purified kringle 1-5 in a dose-dependent manner. Gene transfer of kringle 1-5 caused a significant reduction in vessel density with suppression of tumor growth of the 3 hepatoma cell lines and serum alpha-fetoprotein levels, prolonged the survival period, and reduced the number of intrahepatic metastases. Among the analyzed angiogenic factors, kringle 1-5 reduced angiopoietin-2 expression levels. Expression of kringle 1-5 protein was detected on hepatoma cells and hepatocytes in the liver. However, it did not alter serum alanine aminotransferase levels and body weights, suggesting kringle 1-5 lacks severe side effects.

CONCLUSIONS

Antiangiogenic gene therapy with kringle 1-5 complementary DNA is a promising safe and effective strategy for suppression of growth of hepatocellular carcinoma.

Expression of recombinant kringle 1-5 domains of human plasminogen by a prokaryote expression system

Kringle1-5 (K1-5), a proteolytic fragment containing five kringle domains of human plasminogen generated by plasmin-mediated proteolysis, has been already identified by Cao et al. with relation to anti-angiogenesis and proliferation of endothelial cells. To investigate anti-angiogenesis activity of recombinant human K1-5 (rhK1-5) expressed in Escherichia coli BL21, the cDNA of human K1-5 obtained from cloning vector pUC57-K1-5 by PCR, was inserted into an expression vector pET30(+) to construct a prokaryotic expression vector pET-K1-5. Recombinant K1-5 efficiently expressed in E. coli BL21 after IPTG induction was monitored by SDS-PAGE and Western blotting with an anti-angiostatin monoclonal antibody and an anti-hexahistidine tag antibody. The expressed K1-5 accounted for approximately 32% of the total bacterial proteins as estimated by densitometry, and existed mainly as inclusion bodies. The inclusion bodies were washed, lysed, purified, and refolded to a purity of 96% as estimated by capillary electrophoresis and the final purification yield of K1-5 in E. coli system was approximately 5.8 mg/L. Purified K1-5 protein was tested on chicken embryo chorioallantoic membranes (CAMs), and a large number of newly formed blood vessels were significantly regressed. In the present study, we demonstrated that bacterial-expressed K1-5 effectively inhibited angiogenesis of the chicken embryo in a dose-dependent manner through CAM assay. In addition, the rhK1-5 potently inhibited endothelial cell proliferation but not non-endothelial cells. For the first time, these findings demonstrate that the rhK1-5 produced by a prokaryote expression system effectively inhibited angiogenesis of the chicken embryo in a dose-dependent manner and specially suppressed in vitro the proliferation of human umbilical vein endothelial cells. This fact derived from the present study further suggests the rhK1-5 can be used for anti-angiogenesis therapy of cancer.

Pericellular proteases in angiogenesis and vasculogenesis

Pericellular proteases play an important role in angiogenesis and vasculogenesis. They comprise (membrane-type) matrix metalloproteinases [(MT-)MMPs], serine proteases, cysteine cathepsins, and membrane-bound aminopeptidases. Specific inhibitors regulate them. Major roles in initiating angiogenesis have been attributed to MT1-matrix metalloproteinase (MMP), MMP-2, and MMP-9. Whereas MT-MMPs are membrane-bound by nature, MMP-2 and MMP-9 can localize to the membrane by binding to alphavbeta3-integrin and CD44, respectively. Proteases switch on neovascularization by activation, liberation, and modification of angiogenic growth factors and degradation of the endothelial and interstitial matrix. They also modify the properties of angiogenic growth factors and cytokines. Neovascularization requires cell migration, which depends on the assembly of protease-protein complexes at the migrating cell front. MT1-MMP and urokinase (u-PA) form multiprotein complexes in the lamellipodia and focal adhesions of migrating cells, facilitating proteolysis and sufficient support for endothelial cell migration and survival. Excessive proteolysis causes loss of endothelial cell-matrix interaction and impairs angiogenesis. MMP-9 and cathepsin L stimulate the recruitment and action of blood- or bone-marrow-derived accessory cells that enhance angiogenesis. Proteases also generate fragments of extracellular matrix and hemostasis factors that have anti-angiogenic properties. Understanding the complexity of protease activities in angiogenesis contributes to recognizing new targets for stimulation or inhibition of neovascularization in disease.

Enhanced anti-angiogenic effect of a deletion mutant of plasminogen kringle 5 on neovascularization

Kringle 5 (K5), a proteolytic fragment of plasminogen, has been proved to be an angiogenic inhibitor. Previously, we have evaluated the effect of K5 on the vascular leakage and neovascularization in a rat model of oxygen-induced retinopathy. In this study, we expressed K5 and a deletion mutant of K5 (K5 mutant) in a prokaryocyte expression system and purified them by affinity chromatography. K5 mutant was generated by deleting 11 amino acids from K5 while retaining the three disulfide bonds. The anti-angiogenic activity of intact K5 and K5 mutant were compared in endothelial cells and retinal neovascularization rat model. K5 mutant inhibited the proliferation of primary human retinal capillary endothelial cells (HRCEC) in a concentration-dependent manner, with an apparent EC50 of approximate 35 nmol/L, which is twofold more potent than intact K5. In the even higher concentration range, K5 mutant did not inhibit pericytes from the same origin of HRCEC, which suggested an endothelial cell-specific inhibition. K5 mutant had no effect on normal liver cells and Bel7402 hepatoma cells even at high concentration range either. Intravitreal injection of the K5 and mutant in the oxygen-induced retinopathy rat model both resulted in significantly fewer neovascular tufts and nonperfusion area than controls with PBS injection, as shown by fluorescein angiography. Furthermore, K5 mutant exhibited more strong inhibition effect on neovascularization than intact K5 by quantification of vascular cells. These results suggest that this K5 deletion mutant is a more potent angiogenic inhibitor than intact K5 and may have therapeutic potential in the treatment of those disorders with neovascularization, such as solid tumor, diabetic retinopathy, age-related macular degeneration, rheumatoid arthritis, and hyperplasia of prostate.

Plasminogen kringle 5-engineered glioma cells block migration of tumor-associated macrophages and suppress tumor vascularization and progression

Angiostatin, a well-characterized angiostatic agent, is a proteolytic cleavage product of human plasminogen encompassing the first four kringle structures. The fifth kringle domain (K5) of human plasminogen is distinct from angiostatin and has been shown, on its own, to act as a potent endothelial cell inhibitor. We propose that tumor-targeted K5 cDNA expression may act as an effective therapeutic intervention as part of a cancer gene therapy strategy. In this study, we provide evidence that eukaryotically expressed His-tagged human K5 cDNA (hK5His) is exported extracellularly and maintains predicted disulfide bridging conformation in solution. Functionally, hK5His protein produced by retrovirally engineered human U87MG glioma cells suppresses in vitro migration of both human umbilical vein endothelial cells and human macrophages. Subcutaneous implantation of Matrigel-embedded hK5His-producing glioma cells in nonobese diabetic/severe combined immunodeficient mice reveals that hK5His induces a marked reduction in blood vessel formation and significantly suppresses the recruitment of tumor-infiltrating CD45+ Mac3+ Gr1- macrophages. Therapeutically, we show in a nude mouse orthotopic brain cancer model that tumor-targeted K5 expression is capable of effectively suppressing glioma growth and promotes significant long-term survival (>120 days) of test animals. These data suggest that plasminogen K5 acts as a novel two-pronged anticancer agent, mediating its inhibitory effect via its action on host-derived endothelial cells and tumor-associated macrophages, resulting in a potent, clinically relevant antitumor effect.

In vivo generation of angiostatin isoforms by administration of a plasminogen activator and a free sulfhydryl donor: a phase I study of an angiostatic cocktail of tissue plasminogen activator and mesna

PURPOSE

Angiostatin4.5 (AS4.5), the endogenous human angiostatin, is derived from plasminogen in a two-step process. A plasminogen activator converts plasminogen to plasmin, then plasmin undergoes autoproteolysis to AS4.5. A free sulfhydryl donor can mediate plasmin autoproteolysis. To translate this process to human cancer therapy, we conducted a phase I trial of administration of a tissue plasminogen activator (tPA) with a free sulfhydryl donor (mesna).

PATIENTS AND METHODS

Fifteen patients with advanced solid tumors were treated. The dose of tPA was escalated (cohorts; 1, 2, 3, 5, and 7.5 mg/h for 6 hours). Mesna was administered as a 240 mg/m2 bolus followed by an infusion of 50 mg/h, concurrent with tPA. Both tPA and mesna were administered 3 consecutive days every 14 days.

RESULTS

No dose-limiting toxicity was observed. Two AS4.5 isoforms were generated, Lys-AS4.5 and Glu-AS4.5. Mean baseline Lys-AS4.5 level was 20.4 nmol/L (SE, 2.9). In the 5 mg/h tPA cohort, Lys-AS4.5 levels increased by an average of 143% or 24 nmol/L (SE, 4.9) above baseline. Glu-AS4.5 (M(r) approximately 62,000) was also generated (additional 77 amino acids at amino terminus compared with Lys-AS4.5). Glu-AS4.5 level at baseline was undetectable in four of five patients in the 5 mg/h tPA cohort, but at end of infusion, was approximately 67 nmol/L (SE, 20). Two patients in the 5 mg/h tPA cohort experienced decreases in tumor markers with treatment, although no clinical objective responses were observed.

CONCLUSION

This study shows that in vivo generation of AS4.5 is safe in humans and may provide a practical approach to achieve antiangiogenic therapy.

TGF-β-induced apoptosis in endothelial cells mediated by M6P/IGFII-R and mini-plasminogen

Transforming growth factor-β (TGF-β), a key modulator of endothelial cell apoptosis, must be activated from the latent form (LTGF-β) to induce biological responses. In the present study, we report activation of TGF-β by functional and physical co-operation of the mannose-6-phosphate/insulin-like-growth-factor-II receptor (CD222) and the urokinase-type plasminogen activator receptor (CD87). We show that endothelial cells express CD222 and CD87 in a membrane complex and demonstrate that the association of these two receptors is essential for the release of active TGF-β in the transduced mouse fibroblast used as model cells. By contrast, smooth-muscle cells, which express CD222 and CD87 at similar density to endothelial cells but not in complexed form, do not activate TGF-β. We also have found that mini-plasminogen is a high-affinity ligand for CD222 and is essential for the activation of TGF-β by the CD87-CD222 complex to induce apoptosis in endothelial cells. This specific mechanism of TGF-β-mediated apoptosis in endothelial cells is thus a potential novel target to be considered for treatment of pathological vascular disorders (e.g. tumor angiogenesis).