Radiolabeled heparan sulfate immobilized on microplate as substrate for the detection of heparanase activity

Chemical toolbox to interrogate Heparanase-1 activity

The development of a robust chemical toolbox to interrogate the activity of heparanase-1 (HPSE-1), an endo-β-d-glucuronidase and the only known enzyme that cleaves heparan sulfate (HS), has become critically important. The primary function of HPSE-1, cleaving HS side chains from heparan sulfate proteoglycans (HSPGs), regulates the integrity of the extracellular matrix (ECM) and the bioavailability of active, heparan sulfate-binding partners such as enzymes, growth factors, chemokines, and cytokines. HPSE-1 enzymatic activity is strictly regulated and has been found to play fundamental roles in pathophysiological processes. HPSE-1 is significantly overexpressed under various conditions including cancer, metastasis, angiogenesis, and inflammation, making HPSE-1 a promising therapeutic and diagnostic target. Chemical tools that can detect and image HPSE-1 activity in vitro and/or in vivo can help drive the discovery of novel and efficacious anti-HPSE-1 drugs, investigate the basic biology of HPSE-1, and help serve as a diagnostic tool in clinical applications. Here, we will give an overview of the common chemical tools to detect HPSE-1 activity and highlight the novel heparanase probes recently developed in our lab.

Discovery and development of small-molecule heparanase inhibitors

Heparanase-1 (HPSE) is a promising yet challenging therapeutic target. It is the only known enzyme that is responsible for cleavage of heparan sulfate (HS) side chains from heparan sulfate proteoglycans (HSPGs), and is the key enzyme involved in the remodeling and degradation of the extracellular matrix (ECM). Overexpression of HPSE is found in various types of diseases, including cancers, inflammations, diabetes, and viral infections. Inhibiting HPSE can restore ECM functions and integrity, making the development of HPSE inhibitors a highly sought-after topic. So far, all HPSE inhibitors that have entered clinical trials belong to the category of HS mimetics, and no small-molecule or drug-like HPSE inhibitors have made similar progress. None of the HS mimetics have been approved as drugs, with some clinical trials discontinued due to poor bioavailability, side effects, and unfavorable pharmacokinetics characteristics. Small-molecule HPSE inhibitors are, therefore, particularly appealing due to their drug-like characteristics. Advances in the chemical spaces and drug design technologies, including the increasing use of in vitro and in silico screening methods, have provided new opportunities in drug discovery. This article aims to review the discovery and development of small-molecule HPSE inhibitors via screening strategies to shed light on the future endeavors in the development of novel HPSE inhibitors.

Ultrasensitive small molecule fluorogenic probe for human heparanase

Heparanase (HPA) is a critical enzyme involved in the remodeling of the extracellular matrix (ECM), and its elevated expression has been linked with diseases such as various types of cancer and inflammation. The detection of heparanase enzymatic activity holds tremendous value in the study of the cellular microenvironment, and search of molecular therapeutics targeting heparanase, however, no structurally defined probes are available for the detection of heparanase activity. Here we present the development of the first ultrasensitive fluorogenic small-molecule probe for heparanase enzymatic activity via tuning the electronic effect of the substrate. The probe exhibits a 756-fold fluorescence turn-on response in the presence of human heparanase, allowing one-step detection of heparanase activity in real-time with a picomolar detection limit. The high sensitivity and robustness of the probe are exemplified in a high-throughput screening assay for heparanase inhibitors.

The Development of Assays for Heparanase Enzymatic Activity: Towards a Gold Standard

The enzyme heparanase, an endo-β-glucuronidase, degrades heparan sulfate (HS) chains on the cell surface and in the extracellular matrix. Heparanase regulates numerous biological processes that drive tumour growth, metastasis and angiogenesis. In addition to its key role in cancer progression, it has also been implicated in an ever-growing number of other diseases, particularly those associated with inflammation. The importance of heparanase in biology has led to numerous efforts over the years to develop assays to monitor its activity and to screen for new inhibitors as potential drug candidates. Despite these efforts and the commercialization of a few kits, most heparanase assays are still complex, labour intensive, costly or have limited application. Herein we review the various methods for assaying heparanase enzymatic activity, focusing on recent developments towards new assays that hold the promise of accelerating research into this important enzyme.

Polymeric fluorescent heparin as one-step FRET substrate of human heparanase

Heparanase, an endo-β-D-glucuronidase, cleaves cell surface and extracellular matrix heparan sulfate (HS) chains and plays important roles in cellular growth and metastasis. Heparanase assays reported to-date are labor intensive, complex and/or expensive. A simpler assay is critically needed to understand the myriad roles of heparanase. We reasoned that fluorescent heparin could serve as an effective probe of heparanase levels. Following synthesis and screening, a heparin preparation labeled with DABCYL and EDANS was identified, which exhibited a characteristic increase in signal following cleavage by human heparanase. This work describes the synthesis of this heparin substrate, its kinetic and spectrofluorometric properties, optimization of the heparanase assay, use of the assay in inhibitor screening, and elucidation of the state of heparanase in different cell lines. Our FRET-based assay is much simpler and more robust than all assays reported in the literature as well as a commercially available kit.

Development of new methods for determining the heparanase enzymatic activity

INTRODUCTION

Heparanase is a mammalian endo-β-glucuronidase. Notwithstanding its importance in various pathological and non-pathological events few straightforward methods for heparanase enzymatic activity has been stated. The aim of this study was to develop two heparanase activity assays to cover a whole range of applications. First, a fast and easy method based on commercial homogenous substrate, fondaparinux, was described. The other method is a quantitative assay based on biotinylated heparan sulfate that uses an easier technique to immobilize the substrate in a 96-well plate.

METHODS

1): The heparanase recombinant enzyme and fondaparinux were incubated overnight. After incubation, a fluorescent redox marker, resazurin, was added. The reduction of resazurin depends on the amount of glucuronic acid released by heparanase digestion. Fluorescence measurements were done using excitation and emission wavelengths of 560 nm and 590 nm, respectively.

METHODS

2): The 96-well plate was incubated with protamine sulfate. Subsequently, biotinylated heparan sulfate was immobilized. The enzymatic assay was performed using chimeric recombinant heparanase at different concentrations. In sequence, the immobilized biotinylated heparan sulfate that was not digested by recombinant heparanase was bound to streptavidin conjugated with europium. Fluorescence was measured using a time-resolved fluorometer.

CONCLUSION

Both methods have high sensitivity and can be used to detect heparanase activity. Fondaparinux assay is a quick and easy method for screening of heparanase inhibitors using recombinant enzyme or bacterial crude extract. Biotinylated heparan sulfate assay can be used for quantitative analysis in biological samples and protamine sulfate showed been capable to immobilized heparan sulfate.

Synthesis of heparan sulfate tetrasaccharide as a substrate for human heparanase

Regiospecifically sulfated heparan sulfate tetrasaccharide, GlcAβ-GlcN(NS6S)α-GlcAβ-GlcN(NS6S)α was first synthesized as an octyl glycoside. Total synthesis was achieved effectively by coupling the corresponding disaccharide units in short steps.

Plasma heparanase as a significant marker of treatment response in children with Hodgkin lymphoma: pilot study

INTRODUCTION

The aim of this pilot study was to determine heparanase plasma levels (HP) at diagnosis and at restaging in children diagnosed with Hodgkin lymphoma and to investigate whether this parameter provides prognostic information for response to treatment after induction therapy.

PATIENTS AND METHODS

HP levels of 19 pediatric patients (mean age: 10.3 years (y) (range, 4-18 y), 9 girls, 10 boys) with Hodgkin lymphoma were assayed at diagnosis and at restaging. HP levels were determined using an ELISA anti-human heparanase immunoassay kit. According to diagnosis, CAT scan and/or FDG/ PET-CT fusion were performed to assess response to treatment after 2-3 courses of chemotherapy. Two patients received VAMP protocol (1 stage IA, 1 stage IIA), 1 received AV-PC (nonbulky stage IIA), 4 received COPP/ABV (3 stage IIA bulky, 1 stage IIIA nonbulky), 4 received ABVE-PC (2 stage IIB, 1 stage IIA bulky, 1 stage IIIA bulky), 2 received ABVD (1 stage IIA bulky, 1 stage IIIA), and 6 received escalated BEACOPP (1 stage IIIB, 3 stage IVA, 2 stage IVB).

RESULTS

Changes in HP levels were found to correlate with response to treatment for most of the children. At diagnosis, average HP level was 1019 pg/mL (range, 141-5733 pg/mL), decreasing at restaging to 588 pg/mL (range, 62-3267 pg/mL) (p = .034). At diagnosis, the average HP of the 16 patients in CR or VGPR was 1104 pg/mL; it had decreased at restaging to 586 pg/mL (p = .032). At diagnosis, the average HP level for the 3 patients with TP or PR was 1704 pg/mL; it had increased to 1938 pg/mL at restaging (p = .166). Due to the small number of patients, no correlation was observed between HP levels at diagnosis, staging, or any other clinical prognostic factor.

CONCLUSIONS

Changes in plasma HP levels correlated with response to treatment for children diagnosed with Hodgkin lymphoma. This provides a rationale for exploring clinical interest in plasma heparanase measurements of a larger group, using the test for clinical trials of antiangiogenic therapies.

Heparan sulfate regulates fibrillin-1 N- and C-terminal interactions

Fibrillin-1 N- and C-terminal heparin binding sites have been characterized. An unprocessed monomeric N-terminal fragment (PF1) induced a very high heparin binding response, indicating heparin-mediated multimerization. Using PF1 deletion and short fragments, a heparin binding site was localized within the domain encoded by exon 7 after the first hybrid domain. Rodent embryonic fibroblasts adhered to PF1 and deletion fragments, and, when cells were plated on fibrillin-1 or fibronectin Arg-Gly-Asp cell-binding fragments, cells showed heparin-dependent spreading and focal contact formation in response to soluble PF1. Within domains encoded by exons 59-62 near the fibrillin-1 C terminus are novel conformation-dependent high affinity heparin and tropoelastin binding sites. Heparin disrupted tropoelastin binding but did not disrupt N- and C-terminal fibrillin-1 interactions. Thus, fibrillin-1 N-terminal interactions with heparin/heparan sulfate directly influence cell behavior, whereas C-terminal interactions with heparin/heparan sulfate regulate elastin deposition. These data highlight how heparin/heparan sulfate controls fibrillin-1 interactions.

Development of an enzyme-linked immunosorbent assay (ELISA)-like fluorescence assay to investigate the interactions of glycosaminoglycans to cells

Sulfated glycosaminoglycans were labeled with biotin to study their interaction with cells in culture. Thus, heparin, heparan sulfate, chondroitin 4-sulfate, chondroitin 6-sulfate and dermatan sulfate were labeled using biotin-hydrazide, under different conditions. The structural characteristics of the biotinylated products were determined by chemical (molar ratios of hexosamine, uronic acid, sulfate and biotin) and enzymatic methods (susceptibility to degradation by chondroitinases and heparitinases). The binding of biotinylated glycosaminoglycans was investigated both in endothelial and smooth muscle cells in culture, using a novel time resolved fluorometric method based on interaction of europium-labeled streptavidin with the biotin covalently linked to the compounds. The interactions of glycosaminoglycans were saturable and number of binding sites could be obtained for each individual compound. The apparent dissociation constant varied among the different glycosaminoglycans and between the two cell lines. The interactions of the biotinylated glycosaminoglycans with the cells were also evaluated using confocal microscopy. We propose a convenient and reliable method for the preparation of biotinylated glycosaminoglycans, as well as a sensitive non-competitive fluorescence-based assay for studies of the interactions and binding of these compounds to cells in culture.

Synthesis and heparanase inhibitory activity of sulfated mannooligosaccharides related to the antiangiogenic agent PI-88

A stepwise synthetic route to the mannooligosaccharides from the neutral fraction of Pichia holstii phosphomannan hydrolysate, including a tetrasaccharylamine component, was developed using only two or three readily available d-mannose building blocks. These compounds were sulfonated to give the corresponding sulfated oligosaccharides which are closely related to the constituents of the anticancer agent PI-88. The synthetic approach is well suited to the preparation of analogues as demonstrated by the synthesis of a series of (1-->3)-linked mannooligosaccharides. The inhibitory activity of the sulfated oligosaccharides against heparanase was determined using a Microcon ultrafiltration assay. The tetra- and pentasaccharides were potent competitive inhibitors of heparanase (K(i)=200-280nM) whilst the shorter di- and trisaccharides were partial competitive inhibitors and did not completely inhibit the enzyme even at very high concentrations.

Enzyme-mediated individual nanoparticle release assay

Numerous methods have been developed to measure the presence of macromolecular species in a sample; however, the number of methods that detect functional activity or modulators of that activity is more limited. To address this limitation, an approach was developed that uses the optical detection of nanoparticles as a measure of enzyme activity. Nanoparticles are increasingly being used as biological labels in static binding assays; here, we describe their use in a release assay format, where the enzyme-mediated liberation of individual nanoparticles from a surface is measured. A double-stranded fragment of DNA is used as the initial tether to bind the nanoparticles to a solid surface. The nanoparticle spatial distribution and number are determined using dark-field optical microscopy and digital image capture. Site-specific cleavage of the DNA tether results in nanoparticle release. The methodology and validation of this approach for measuring enzyme-mediated, individual DNA cleavage events, rapidly, with high specificity, and in real-time are described. This approach was used to detect and discriminate between nonmethylated and methylated DNA, and demonstrates a novel platform for high-throughput screening of modulators of enzyme activity.

An ELISA method for the detection and quantification of human heparanase

Heparanase is a mammalian endo-beta-D-glucuronidase that cleaves heparan sulfate side chains at a limited number of sites. Heparanase enzymatic activity is thought to participate in degradation and remodeling of the extracellular matrix and to facilitate cell invasion associated with tumor metastasis, angiogenesis, and inflammation. Traditionally, heparanase activity was well correlated with the metastatic potential of a large number of tumor-derived cell types. More recently, heparanase upregulation was detected in an increasing number of primary human tumors, correlating, in some cases, with poor postoperative survival and increased tumor vascularity. The present study was undertaken to develop a highly sensitive ELISA suitable for the determination and quantification of human heparanase in tissue extracts and body fluids. The assay preferentially detects the 8+50 kDa active heparanase heterodimer vs. the latent 65 kDa proenzyme and correlates with immunoblot analysis of heparanase containing samples. It detects heparanase at concentrations as low as 200 pg/ml and is suitable for quantification of heparanase in tissue extracts and urine.

Fibrillin-1 interactions with heparin. Implications for microfibril and elastic fiber assembly

Fibrillin-1 assembly into microfibrils and elastic fiber formation involves interactions with glycosaminoglycans. We have used BIAcore technology to investigate fibrillin-1 interactions with heparin and with heparin saccharides that are analogous to S-domains of heparan sulfate. We have identified four high affinity heparin-binding sites on fibrillin-1, localized three of these sites, and defined their binding kinetics. Heparin binding to the fibrillin-1 N terminus has particularly rapid kinetics. Hyaluronan and chondroitin sulfate did not interact significantly with fibrillin-1. Heparin saccharides with more than 12 monosaccharide units bound strongly to all four fibrillin-1 sites. Heparin did not inhibit fibrillin-1 N- and C-terminal interactions or RGD-dependent cell attachment, but heparin and MAGP-1 competed for binding to the fibrillin-1 N terminus, and heparin and tropoelastin competed for binding to a central fibrillin-1 sequence. By regulating these key interactions, heparin can profoundly influence microfibril and elastic fiber assembly.