High-throughput methods for measuring heparanase activity and screening potential antimetastatic and anti-inflammatory agents

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.

A Fluorogenic Green Merocyanine-Based Probe to Detect Heparanase-1 Activity

Heparanase-1 (HPSE-1), an endo-β-D-glucuronidase, is an extracellular matrix (ECM) remodeling enzyme that degrades heparan sulfate (HS) chains of heparan sulfate proteoglycans (HSPGs). HPSE-1 functions to remodel the ECM and thereby disseminate cells, liberate HS-bound bioactive molecules, and release biologically active HS fragments. Being the only known enzyme for the cleavage of HS, HPSE-1 regulates a number of fundamental cellular processes including cell migration, cytokine regulation, angiogenesis, and wound healing. Overexpression of HPSE-1 has been discovered in most cancers, inflammatory diseases, viral infections, among others. As an emerging therapeutic target, the biological role of HPSE-1 remains to be explored but is hampered by a lack of research tools. To expand the chemical tool-kit of fluorogenic probes to interrogate HPSE-1 activity, we design and synthesized a fluorogenic green disaccharide-based HPSE-1 probe using our design strategy of tuning the electronic effect of the aryl aglycon. The novel probe exhibits a highly sensitive 278-fold fluorescence turn-on response in the presence of recombinant human HPSE-1, while emitting green light at 560 nm, enabling the fluorescence imaging of HPSE-1 activity in cells.

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.

An Enzymatic Activity Assay for Heparanase That Is Useful for Evaluating Clinically Relevant Inhibitors and Studying Kinetics

The enzyme heparanase cleaves heparan sulfate and is involved in a range of human diseases including cancer, inflammation, diabetes, and viral infection. There is a need for a simple and reliable enzymatic assay to allow for the screening of compounds to find inhibitors of heparanase. We have developed an assay that uses the heparinoid fondaparinux as enzyme substrate and detects one of the products of catalysis, which contains a newly formed reducing terminus, with the tetrazolium salt WST-1. Due to the homogenous substrate and single point of cleavage therein, this assay allows for more systematic kinetic analysis of heparanase inhibitors. Here, we provide a detailed method for conducting this assay and also provide information to assist researchers in evaluating whether the assay is performing properly in their laboratories.

A Cell-Based Renilla Luminescence Reporter Plasmid Assay for High-Throughput Screening to Identify Novel FDA-Approved Drug Inhibitors of HPV-16 Infection

Like cervical cancer, anal cancer is caused by human papillomavirus (HPV). HPV is the most common sexually transmitted agent and is found in the anal canal of almost all HIV-positive men who have sex with men (MSM). Rates of HPV anal cancer are disproportionately higher in this population. Although the nanovalent HPV vaccine is efficacious in protecting against oncogenic HPV types, a substantial proportion of MSM remains unvaccinated and anal HPV infection continues to be an important public health burden. Therefore, it is important to identify strategies to prevent HPV infection. We report on two promising and interlinked strategies: (1) the development of a cell-based Renilla luminescence reporter assay using HPV-16 pseudovirions that encapsidate SV40-driven Renilla luminescence reporter expression plasmid and (2) use of this assay for high-throughput screening (HTS) of FDA- and internationally approved drugs to identify those that could be repurposed to prevent HPV infection. We conducted a screen of 1906 drugs. The assay was valid with a Z' of 0.67 ± 0.04, percent coefficient of variance of 10.0, and signal-to-background noise window of 424.0 ± 8.0. Five drugs were chosen for further analyses based on selection parameters of ≥77.0% infection of HPV-16 pseudovirion-driven Renilla expression with <20.0% cytotoxicity. Of these, the antifungal pentamidine and a gamma-amino butyric acid receptor agonist securinine exhibited ≥90.0% infection with <10.0% cytotoxicity. This luminescent cell-based reporter expression plasmid assay for HTS is a valid method to identify FDA- and internationally approved drugs with the potential to be repurposed into prevention modalities for HPV infection.

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.

Cloning and bacterial expression systems for recombinant human heparanase production: Substrate specificity investigation by docking of a putative heparanase substrate

Human heparanase (HPSE) is an enzyme that degrades the extracellular matrix. It is implicated in a multiplicity of physiological and pathological processes encouraging angiogenesis and tumor metastasis. The protein is a heterodimer composed of a subunit of 8 kDa and another of 50 kDa. The two protein subunits are noncovalently associated. The cloning and expression of the two protein subunits in Escherichia coli and their subsequent purification to homogeneity under native conditions result in the production of an active HPSE enzyme. The substrate specificity of the HPSE was studied by docking of a putative substrate that is a designed oligosaccharide with the minimum recognition backbone, with the additional 2-N-sulfate and 6-O-sulfate groups at the nonreducing GlcN and a fluorogenic tag at the reducing extremity GlcN. To develop a quantitative fluorescence assay with this substrate would be extremely useful in studies on HPSE, as the HPSE cleavage of fluorogenic tag would result in a measurable response.

Heparanase: a rainbow pharmacological target associated to multiple pathologies including rare diseases

In recent years, heparanase has attracted considerable attention as a promising target for innovative pharmacological applications. Heparanase is a multifaceted protein endowed with enzymatic activity, as an endo-β-D-glucuronidase, and nonenzymatic functions. It is responsible for the cleavage of heparan sulfate side chains of proteoglycans, resulting in structural alterations of the extracellular matrix. Heparanase appears to be involved in major human diseases, from the most studied tumors to chronic inflammation, diabetic nephropathy, bone osteolysis, thrombosis and atherosclerosis, in addition to more recent investigation in various rare diseases. The present review provides an overview on heparanase, its biological role, inhibitors and possible clinical applications, covering the latest findings in these areas.

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.

Development of a colorimetric assay for heparanase activity suitable for kinetic analysis and inhibitor screening

The role that heparanase plays during metastasis and angiogenesis in tumors makes it an attractive target for cancer therapeutics. Despite this enzyme's significance, most of the assays developed to measure its activity are complex. Moreover, they usually rely on labeling variable preparations of the natural substrate heparan sulfate, making comparisons across studies precarious. To overcome these problems, we have developed a convenient assay based on the cleavage of the synthetic heparin oligosaccharide fondaparinux. The assay measures the appearance of the disaccharide product of heparanase-catalyzed fondaparinux cleavage colorimetrically using the tetrazolium salt WST-1. Because this assay has a homogeneous substrate with a single point of cleavage, the kinetics of the enzyme can be reliably characterized, giving a K(m) of 46 microM and a k(cat) of 3.5 s(-1) with fondaparinux as substrate. The inhibition of heparanase by the published inhibitor, PI-88, was also studied, and a K(i) of 7.9 nM was determined. The simplicity and robustness of this method, should, not only greatly assist routine assay of heparanase activity but also could be adapted for high-throughput screening of compound libraries, with the data generated being directly comparable across studies.

Oligomannurarate sulfate, a novel heparanase inhibitor simultaneously targeting basic fibroblast growth factor, combats tumor angiogenesis and metastasis

Inhibitors of tumor angiogenesis and metastasis are increasingly emerging as promising agents for cancer therapy. Recently, heparanase inhibitors have offered a new avenue for such work because heparanase is thought to be critically involved in the metastatic and angiogenic potentials of tumor cells. Here, we report that oligomannurarate sulfate (JG3), a novel marine-derived oligosaccharide, acts as a heparanase inhibitor. Our results revealed that JG3 significantly inhibited tumor angiogenesis and metastasis, both in vitro and in vivo, by combating heparanase activity via binding to the KKDC and QPLK domains of the heparanase molecule. The JG3-heparanase interaction was competitively inhibited by low molecular weight heparin (4,000 Da) but not by other glycosaminoglycans. In addition, JG3 abolished heparanase-driven invasion, inhibited the release of heparan sulfate-sequestered basic fibroblast growth factor (bFGF) from the extracellular matrix, and repressed subsequent angiogenesis. Moreover, JG3 inactivated bFGF-induced bFGF receptor and extracellular signal-regulated kinase 1/2 phosphorylation and blocked bFGF-triggered angiogenic events by directly binding to bFGF. Thus, JG3 seems to inhibit both major heparanase activities by simultaneously acting as a substrate mimetic and as a competitive inhibitor of heparan sulfate. These findings suggest that JG3 should be considered as a promising candidate agent for cancer therapy.

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.

High-throughput measurements of biochemical responses using the plate::vision multimode 96 minilens array reader

The plate::vision is a high-throughput multimode reader capable of reading absorbance, fluorescence, fluorescence polarization, time-resolved fluorescence, and luminescence. Its performance has been shown to be quite comparable with other readers. When the reader is integrated into the plate::explorer, an ultrahigh-throughput screening system with event-driven software and parallel plate-handling devices, it becomes possible to run complicated assays with kinetic readouts in high-density microtiter plate formats for high-throughput screening. For the past 5 years, we have used the plate::vision and the plate::explorer to run screens and have generated more than 30 million data points. Their throughput, performance, and robustness have speeded up our drug discovery process greatly.

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.