A synthetic heparin-mimicking polyanionic compound binds to the LDL receptor-related protein and inhibits vascular smooth muscle cell proliferation

Heparin-Mimicking Polymers: Synthesis and Biological Applications

Heparin is a naturally occurring, highly sulfated polysaccharide that plays a critical role in a range of different biological processes. Therapeutically, it is mostly commonly used as an injectable solution as an anticoagulant for a variety of indications, although it has also been employed in other forms such as coatings on various biomedical devices. Due to the diverse functions of this polysaccharide in the body, including anticoagulation, tissue regeneration, anti-inflammation, and protein stabilization, and drawbacks of its use, analogous heparin-mimicking materials are also widely studied for therapeutic applications. This review focuses on one type of these materials, namely, synthetic heparin-mimicking polymers. Utilization of these polymers provides significant benefits compared to heparin, including enhancing therapeutic efficacy and reducing side effects as a result of fine-tuning heparin-binding motifs and other molecular characteristics. The major types of the various polymers are summarized, as well as their applications. Because development of a broader range of heparin-mimicking materials would further expand the impact of these polymers in the treatment of various diseases, future directions are also discussed.

Kallistatin antagonizes Wnt/β-catenin signaling and cancer cell motility via binding to low-density lipoprotein receptor-related protein 6

Kallistatin, a plasma protein, exerts pleiotropic effects in inhibiting angiogenesis, inflammation and tumor growth. Canonical Wnt signaling is the primary pathway for oncogenesis in the mammary gland. In this study, we demonstrate that kallistatin bound to the Wnt coreceptor low-density lipoprotein receptor-related protein 6 (LRP6), thus, blocking Wnt/β-catenin signaling and Wnt-mediated growth and migration in MDA-MB-231 breast cancer cells. Kallistatin inhibited Wnt3a-induced proliferation, migration, and invasion of cultured breast cancer cells. Moreover, kallistatin was bound to LRP6 in breast cancer cells, as identified by immunoprecipitation followed by western blot. Kallistatin suppressed Wnt3a-mediated phosphorylation of LRP6 and glycogen synthase kinase-3β, and the elevation of cytosolic β-catenin levels. Furthermore, kallistatin antagonized Wnt3a-induced expression of c-Myc, cyclin D1, and vascular endothelial growth factor. These findings indicate a novel role of kallistatin in preventing breast tumor growth and mobility by direct interaction with LRP6, leading to blockade of the canonical Wnt signaling pathway.

Nanoscale growth factor patterns by immobilization on a heparin-mimicking polymer

In this study, electrostatic interactions between sulfonate groups of an immobilized polymer and the heparin binding domains of growth factors important in cell signaling were exploited to nanopattern the proteins. Poly(sodium 4-styrenesulfonate-co-poly(ethylene glycol) methacrylate) (pSS-co-pPEGMA) was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization using ethyl S-thiobenzoyl-2-thiopropionate as a chain transfer agent and 2,2'-azoisobutyronitrile (AIBN) as the initiator. The resulting polymer (1) was characterized by 1H NMR, GPC, FT-IR, and UV-vis and had a number average molecular weight (Mn) of 24,000 and a polydispersity index (PDI) of 1.17. The dithioester end group of 1 was reduced to the thiol, and the polymer was subsequently immobilized on a gold substrate. Binding of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) to the polymer via the heparin binding domains was then confirmed by surface plasmon resonance (SPR). The interactions were stable at physiological salt concentrations. Polymer 1 was cross-linked onto silicon wafers using an electron beam writer forming micro- and nanopatterns. Resolutions of 100 nm and arbitrary nanoscale features such as concentric circles and contiguous squares and triangles were achieved. Fluorescence microscopy confirmed that bFGF and VEGF were subsequently immobilized to the polymer micro- and nanopatterns.

A Network-based Analysis of Polyanion-binding Proteins Utilizing Yeast Protein Arrays

The high affinity of certain cellular polyanions for many proteins (polyanion-binding proteins (PABPs)) has been demonstrated previously. It has been hypothesized that such polyanions may be involved in protein structure stabilization, stimulation of folding through chaperone-like activity, and intra- and extracellular protein transport as well as intracellular organization. The purpose of the proteomics studies reported here was to seek evidence for the idea that the nonspecific but high affinity interactions of PABPs with polyanions have a functional role in intracellular processes. Utilizing yeast protein arrays and five biotinylated cellular polyanion probes (actin, tubulin, heparin, heparan sulfate, and DNA), we identified proteins that interact with these probes and analyzed their structural and amino acid sequence requirements as well as their predicted functions in the yeast proteome. We also provide evidence for the existence of a network-like system for PABPs and their potential roles as critical hubs in intracellular behavior. This investigation takes a first step toward achieving a better understanding of the nature of polyanion-protein interactions within cells and introduces an alternative way of thinking about intracellular organization.

Regulation, function and clinical significance of heparanase in cancer metastasis and angiogenesis

Heparanase is an endoglycosidase which cleaves heparan sulfate (HS) and hence participates in degradation and remodeling of the extracellular matrix (ECM). Heparanase is preferentially expressed in human tumors and its over-expression in tumor cells confers an invasive phenotype in experimental animals. The enzyme also releases angiogenic factors from the ECM and thereby induces an angiogenic response in vivo. Heparanase upregulation correlates with increased tumor vascularity and poor post-operative survival of cancer patients. Heparanase is synthesized as a 65 kDa inactive precursor that undergoes proteolytic cleavage, yielding 8 and 50 kDa protein subunits that heterodimerize to form an active enzyme. Human heparanase is localized primarily within late endosomes and lysosomes and occasionally on the cell surface and within the cell nucleus. Transcriptional activity of the heparanase promoter is stimulated by demethylation, early growth response 1 (EGR1) transcription factor, estrogen, inflammatory cytokines and inactivation of p53. N-acetylated glycol-split species of heparin as well as siRNA heparanase gene silencing inhibit tumor metastasis and angiogenesis in experimental models. These observations and the unexpected identification of a single functional heparanase, suggest that the enzyme is a promising target for anti-cancer and anti-inflammatory drug development. Heparanase exhibits also non-enzymatic activities, independent of its involvement in ECM degradation and changes in the extracellular microenvironment. For example, cell surface expression of heparanase elicits a firm cell adhesion, reflecting an involvement in cell-ECM interaction. Heparanase enhances Akt signaling and stimulates PI3K- and p38-dependent endothelial cell migration and invasion. It also promotes VEGF expression via the Src pathway. The enzyme may thus activate endothelial cells and elicits angiogenic and survival responses. Studies with heparanase over-expressing transgenic mice revealed that the enzyme functions in normal processes involving cell mobilization, HS turnover, tissue vascularization and remodeling. In this review, we summarize the current status of heparanase research, emphasizing molecular and cellular aspects of the enzyme, including its mode of processing and activation, control of heparanase gene expression, enzymatic and non-enzymatic functions, and causal involvement in cancer metastasis and angiogenesis. We also discuss clinical aspects and strategies for the development of heparanase inhibitors.

Paradoxical effects of aurintricarboxylic acid and RG-13577: acute thrombosis and in-stent stenosis in a passive-coated stent

PURPOSE

To investigate if a platelet inhibitor (aurintricarboxylic acid [ATA]) and a heparin-mimicking antagonist (RG-13577) of basic fibroblast growth factor 2 (bFGF2) could be combined as a stable compound and attached to conventional bare metal stents to hinder thrombus formation and inflammatory reactions of stenting.

METHODS

Fifteen domestic pigs were stented with RG-13577/ATA-coated (n=6), ATA-coated (n=12), and bare metal stents (n=12) in the left anterior descending (LAD) and left circumflex (LCX) coronary arteries. All surviving pigs were evaluated with contrast angiography and intravascular ultrasonography (IVUS) after 4 weeks. Histological analysis of the stented arteries was performed after hematoxylin-eosin staining. Tissue factor (TF) staining and scanning electron microscopy (SEM) were performed in animals with acute stent thrombosis.

RESULTS

Five of the 6 animals receiving an RG-13577/ATA-coated stent experienced acute stent thrombosis, while no adverse events occurred in the animals of the other 2 groups. Follow-up angiography did not show significant in-stent stenosis in either bare or ATA-coated stents. However, histomorphometry revealed larger neointimal area (3.54+/-0.69 mm2 versus 1.82+/-0.27 mm2, p<0.05) and outward plaque area (1.56+/-0.34 mm2 versus 0.61+/-0.12 mm2, p<0.05) in ATA-coated stents. Three-dimensional IVUS analysis showed analogous results, with significantly larger neointimal volume and outward plaque volume in ATA-coated stents. There was a slight increase in TF staining around the stent struts, while SEM showed increased platelet adhesion and activity in RG-13577/ATA-coated stents versus the ATA-coated and bare metal stents.

CONCLUSION

RG-13577/ATA-coated stents lead to acute stent thrombosis. The ATA coating alone did not lead to acute events, but resulted in higher neointimal hyperplasia and expansive remodeling. These results underline the importance of preclinical studies before using new coated stents in human arteries.

Inhibition of rat smooth muscle cell adhesion and proliferation by non-anticoagulant heparins

Heparin is a well established growth inhibitor of arterial smooth muscle cells (SMCs) both in animal models and in vitro. Even though the cellular mechanisms involved in the anti-proliferative properties of heparin are being resolved, the structural requirements for the biological effects of heparin are not known in detail. Here, we have studied the effect of chemically modified heparins of different molecular weights and anticoagulant activities on proliferation and adhesion of rat aortic SMCs in vitro. The effects of native heparin (NH) and chemically modified heparins were examined after stimulation with fetal calf serum (FCS), platelet-derived growth factor BB (PDGF BB), basic fibroblast growth factor (bFGF), and heparin-binding epidermal growth factor (hbEGF) with respect to DNA synthesis and expression of phosphorylated and activated mitogen-activated protein kinase (pERK1 and 2). In a similar manner as NH, the modified heparins were capable of inhibiting activation of ERK1 and 2 and DNA synthesis induced by FCS and hbEGF whereas the modified heparins potentiated the mitogenic effect of bFGF and no compound affected PDGF BB-induced ERK activity and SMC growth. In contrast, cell adhesion to fibronectin was inhibited by NH and modified heparins in a size-dependent manner with the lowest effect by the smallest compound. The results show that heparins with varying anticoagulant activities and molecular weights but with similar sulfate content can retain anti-proliferative properties while the effect on some other biological processes such as cell adhesion is lost. Possibly, such chemical alterations may yield useful substances for the prevention of SMC proliferation after arterial injury.

Structure-activity relationships of heparin-mimicking compounds in induction of bFGF release from extracellular matrix and inhibition of smooth muscle cell proliferation and heparanase activity

A series of nine synthetic polyaromatic compounds were synthesized by polymerization of aromatic ring monomers with formaldehyde, which yield substantially ordered backbones with different functional anionic groups (hydroxyl and carboxyl) on the phenol ring. These compounds were tested for their heparin-mimicking activity: (1) inhibition of heparanase activity; (2) inhibition of SMC proliferation; and (3) release of bFGF from the ECM. We demonstrate that compounds that have two hydroxyl groups para and ortho to the carboxylic group and a carboxylic group at a distance of two carbons from the phenol ring inhibit heparanase activity and SMC proliferation, as well as induced an almost complete release of bFGF from ECM. Addition of a methyl group next to the carboxylic group led to a preferential inhibition of heparanase activity. Similar results were obtained with a compound that contains one hydroxyl group para to the carboxylic group and an ether group near the carboxylic group on the phenol ring. Preferential inhibition of SMC proliferation was best achieved when the position of the hydroxyl group is para and ortho to the carboxylic group and the carboxylic group is at a distance of one carbon from the phenol ring. On the other hand, for maximal release of bFGF from ECM, the position of the carboxylic group should be three carbons away from the phenol ring. These new heparin-mimicking compounds may have a potential use in inhibition of tumor metastasis, arteriosclerosis, and inflammation.

A chemically modified dextran inhibits smooth muscle cell growth in vitro and intimal in stent hyperplasia in vivo

PURPOSE

Intimal smooth muscle cell (SMC) hyperplasia is a main component of the arterial wall response to injury. We have investigated the capacity of a water-soluble nonanticoagulant functionalized dextran (E9) in inhibition of SMC growth in vitro and in vivo.

METHODS

E9 was obtained with chemical substitutions with anionic and hydrophobic groups on the dextran backbone. SMC proliferation (cell counting, thymidine uptake, cell cycle analysis) was followed in culture in the presence of E9. Western blot analysis against phosphorylated mitogen-activated protein kinase (MAPK), extracellular signal-regulated protein kinase 1/2, and assessment of MAPK activity on serum-stimulated SMCs also were investigated. Binding/displacement experiments, electron microscopy, and cell fractionations were used to follow the binding and internalization of radiolabeled and fluorescentlabeled E9. New Zealand white rabbit iliac arteries were injured with balloon dilatation and stent deployment. Animals were treated for 14 days with saline solution or E9 (5 mg/kg injected subcutaneously, twice daily). Morphometric analyses were carried out in each group (n = 6 arteries, 18 sections).

RESULTS

Nonanticoagulant E9 inhibited SMC proliferation in vitro. Tyrosine phosphorylation of MAPK 1/2 and MAPK activity were inhibited with E9 within 5 minutes of incubation. The binding and rapid cytoplasmic internalization of the synthetic compound was evidenced, but, in contrast to heparin, we did not detect any nuclear localization of the antiproliferative E9. In the in vivo model, qualitative modifications of neointimal structure with a thinner fibrocellular neointima were noticed after E9 treatment. Morphometric analyses of stented arteries in E9-treated animals indicated an important reduction (P <.01) of intimal growth: 33% and 45% for intimal area and intima/media ratio, respectively.

CONCLUSION

Cytoplasmic internalization of the synthetic polysaccharide correlated to the SMC growth inhibition that involved the MAPK pathway. In vivo inhibition of intimal instent hyperplasia with this nonanticoagulant derived dextran is shown providing a new candidate for a potential selective treatment of SMC proliferation.

Differential expression of mRNA coding for the alpha-2-macroglobulin family and the LRP receptor system in C57BL/6J and C3H/HeJ male mice

Expression of mouse A2M (MAM), murinoglobulin (MUG), the A2M receptor or LDL-Receptor related protein (A2MR/LRP) and the Receptor Associated Protein (RAP) were measured by northern blotting of mRNA isolated from liver, heart and peritoneal macrophages from C3H/HeJ and C57BL/6J (B6) mice. Marked differences between males of the two mouse strains were observed for MAM and MUG mRNA levels in liver, which were reflected in plasma levels of both proteinase inhibitors, as confirmed by immune-electrophoresis. C3H/HeJ mice had higher levels of the MAM and MUG mRNA and their corresponding plasma proteins than B6 mice. B6 mice expressed higher levels of LRP mRNA relative to C3H/HeJ mice but had lower levels of RAP mRNA. LRP receptor activity, assayed by fluoresceinated-A2M binding, was higher in B6 cells. The present data contribute to the knowledge of genetic background characteristics among male mouse of these two strains, which can take part in many biological events such as lipid metabolism, inflammation and immune response to different infectious agents.