Structural recognition by recombinant human heparanase that plays critical roles in tumor metastasis. Hierarchical sulfate groups with different effects and the essential target disulfated trisaccharide sequence

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.

Synthetic Heparanase Inhibitors Can Prevent Herpes Simplex Viral Spread

Herpes simplex virus (HSV-1) employs heparan sulfate (HS) as receptor for cell attachment and entry. During late-stage infection, the virus induces the upregulation of human heparanase (Hpse) to remove cell surface HS allowing viral spread. We hypothesized that inhibition of Hpse will prevent viral release thereby representing a new therapeutic strategy for HSV-1. A range of HS-oligosaccharides was prepared to examine the importance of chain length and 2-O-sulfation of iduronic moieties for Hpse inhibition. It was found that hexa- and octasaccharides potently inhibited the enzyme and that 2-O-sulfation of iduronic acid is tolerated. Computational studies provided a rationale for the observed structure-activity relationship. Treatment of human corneal epithelial cells (HCEs) infected with HSV-1 with the hexa- and octasaccharide blocked viral induced shedding of HS which significantly reduced spread of virions. The compounds also inhibited migration and proliferation of immortalized HCEs thereby providing additional therapeutic properties.

A Universal and Modular Scaffold for Heparanase Activatable Probes and Drugs

Heparanase (HPSE) is an endo-β-glucuronidase involved in extracellular matrix remodeling in rapidly healing tissues, most cancers and inflammation, and viral infection. Its importance as a therapeutic target warrants further study, but such is hampered by a lack of research tools. To expand the toolkits for probing HPSE enzymatic activity, we report the design of a substrate scaffold for HPSE comprised of a disaccharide substrate appended with a linker, capable of carrying cargo until being cleaved by HPSE. Here exemplified as a fluorogenic, coumarin-based imaging probe, this scaffold can potentially expand the availability of HPSE-responsive imaging or drug delivery tools using a variety of imaging moieties or other cargo. We show that electronic tuning of the scaffold provides a robust response to HPSE while simplifying the structural requirements of the attached cargo. Molecular docking and modeling suggest a productive probe/HPSE binding mode. These results further support the hypothesis that the reactivity of these HPSE-responsive probes is predominantly influenced by the electron density of the aglycone. This universal HPSE-activatable scaffold will greatly facilitate future development of HPSE-responsive probes and drugs.

Intracerebroventricular dosing of N-sulfoglucosamine sulfohydrolase in mucopolysaccharidosis IIIA mice reduces markers of brain lysosomal dysfunction

Mucopolysaccharidosis type IIIA (MPS IIIA) is a lysosomal storage disorder caused by N-sulfoglucosamine sulfohydrolase (SGSH) deficiency. SGSH removes the sulfate from N-sulfoglucosamine residues on the nonreducing end of heparan sulfate (HS-NRE) within lysosomes. Enzyme deficiency results in accumulation of partially degraded HS within lysosomes throughout the body, leading to a progressive severe neurological disease. Enzyme replacement therapy has been proposed, but further evaluation of the treatment strategy is needed. Here, we used Chinese hamster ovary cells to produce a highly soluble and fully active recombinant human sulfamidase (rhSGSH). We discovered that rhSGSH utilizes both the CI-MPR and LRP1 receptors for uptake into patient fibroblasts. A single intracerebroventricular (ICV) injection of rhSGSH in MPS IIIA mice resulted in a tissue half-life of 9 days and widespread distribution throughout the brain. Following a single ICV dose, both total HS and the MPS IIIA disease-specific HS-NRE were dramatically reduced, reaching a nadir 2 weeks post dose. The durability of effect for reduction of both substrate and protein markers of lysosomal dysfunction and a neuroimmune response lasted through the 56 days tested. Furthermore, seven weekly 148 μg doses ICV reduced those markers to near normal and produced a 99.5% reduction in HS-NRE levels. A pilot study utilizing every other week dosing in two animals supports further evaluation of less frequent dosing. Finally, our dose-response study also suggests lower doses may be efficacious. Our findings show that rhSGSH can normalize lysosomal HS storage and markers of a neuroimmune response when delivered ICV.

More than a Leaving Group: N-Phenyltrifluoroacetimidate as a Remote Directing Group for Highly α-Selective 1,2-cis Glycosylation

The anomeric configuration can greatly affect the biological functions and activities of carbohydrates. Herein, we report that N-phenyltrifluoroacetimidoyl (PTFAI), a well-known leaving group for catalytic glycosylation, can act as a stereodirecting group for the challenging 1,2-cis α-glycosylation. Utilizing rapidly accessible 1,6-di-OPTFAI glycosyl donors, TMSOTf-catalyzed glycosylation occurred with excellent α-selectivity and broad substrate scope, and the remaining 6-OPTFAI group can be cleaved chemoselectively. The remote participation of 6-OPTFAI is supported by the first characterization of the crucial 1,6-bridged bicyclic oxazepinium ion intermediates by low-temperature NMR spectroscopy. These cations were found to be relatively stable and mainly responsible for the present stereoselectivities. Further application is highlighted in glycosylation reactions toward trisaccharide heparins as well as the convergent synthesis of chacotriose derivatives using a bulky 2,4-di-O-glycosylated donor.

Structure and cleavage pattern of a hyaluronate 3-glycanohydrolase in the glycoside hydrolase 79 family

Hyaluronidases have attracted a great deal of interest in the field of medicine due to their fundamental roles in the breakdown of hyaluronan. However, little is known about the catalytic mechanism of the hyaluronate 3-glycanohydrolases. Here, we report the crystal structure and cleavage pattern of a leech hyaluronidase (LHyal), which hydrolyzes the β-1,3-glycosidic bonds of hyaluronan. LHyal exhibits the typical structural features of glycoside hydrolase 79 family but contains a variable 'exo-pocket' loop where basic residues R102 and K103 are the structural determinants of hyaluronan binding. Through analysis of the hydrolysis of even- and odd-numbered hyaluronan oligosaccharides, we demonstrate that hexasaccharide is the shortest natural substrate, which can be cleaved from both the reducing and non-reducing ends to release disaccharides, and pentasaccharides are the smallest fragments for recognition and hydrolysis. These observations provide new insights into the degradation of hyaluronan and the evolutionary relationships of the GH79 family enzymes.

Saturated tetrasaccharide profile of enoxaparin. An additional piece to the heparin biosynthesis puzzle

Enoxaparin, widely used antithrombotic drug, is a polydisperse glycosaminoglycan with highly microheterogeneous structure dictated by both parent heparin heterogeneity and depolymerization conditions. While the process-related modifications of internal and terminal sequences of enoxaparin have been extensively studied, very little is known about the authentic non-reducing ends (NRE). In the present study a multi-step isolation and thorough structural elucidation by NMR and LC/MS allowed to identify 16 saturated tetramers along with 23 unsaturated ones in the complex enoxaparin tetrasaccharide fraction. Altogether the elucidated structures represent a unique enoxaparin signature, whereas the composition of saturated tetramers provides a structural readout strictly related to the biosynthesis of parent heparin NRE. In particular, both glucuronic and iduronic acids were detected at the NRE of macromolecular heparin. The tetrasaccharides bearing glucosamine at the NRE are most likely associated with the heparanase hydrolytic action. High sulfation degree and 3-O-sulfation are characteristic for both types of NRE.

A quantitative method to detect non-antithrombin-binding 3-O-sulfated units in heparan sulfate

Heparan sulfate is synthesized by most animal cells and interacts with numerous proteins via specific sulfation motifs to regulate various physiological processes. Various 3-O-sulfated motifs are considered to be key in controlling the binding specificities to the functional proteins. One such motif synthesized by 3-O-sulfotransferase-1 (3OST-1) serves as a binding site for antithrombin (AT) and has been thoroughly studied because of its pharmacological importance. However, the physiological roles of 3-O-sulfates produced by other 3OST isoforms, which do not bind AT, remain obscure, in part due to the lack of a standard method to analyze this rare modification. This study aims to establish a method for quantifying 3-O-sulfated components of heparan sulfate, focusing on non-AT-binding units. We previously examined the reaction products of human 3OST isoforms and identified five 3-O-sulfated components, including three non-AT-binding disaccharides and two AT-binding tetrasaccharides, as digestion products of heparin lyases. In this study, we prepared these five components as a standard saccharide for HPLC analysis. Together with eight non-3-O-sulfated disaccharides, a standard mixture of 13 units was prepared. Using reverse-phase ion-pair HPLC with a postcolumn fluorescent labeling system, the separation conditions were optimized to quantify the 13 units. Finally, we analyzed the compositional changes of 3-O-sulfated units in heparan sulfate from P19 cells before and after neuronal differentiation. We successfully detected the 3-O-sulfated units specifically expressed in the differentiated neurons. This is the first report that shows the quantification of three non-AT-binding 3-O-sulfated units and establishes a new approach to explore the physiological functions of 3-O-sulfate.

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.

Heparanase: Cloning, Function and Regulation

In 2019, we mark the 20th anniversary of the cloning of the human heparanase gene. Heparanase remains the only known enzyme to cleave heparan sulfate, which is an abundant component of the extracellular matrix. Thus, elucidating the mechanisms underlying heparanase expression and activity is critical to understanding its role in healthy and pathological settings. This chapter provides a historical account of the race to clone the human heparanase gene, describes the intracellular and extracellular function of the enzyme, and explores the various mechanisms regulating heparanase expression and activity at the gene, transcript, and protein level.

Modulating Heparanase Activity: Tuning Sulfation Pattern and Glycosidic Linkage of Oligosaccharides

Heparanase cleaves polymeric heparan sulfate (HS) molecules into smaller oligosaccharides, allowing for release of angiogenic growth factors promoting tumor development and autoreactive immune cells to reach the insulin-producing β cells. Interaction of heparanase with HS chains is regulated by specific substrate sulfation sequences. We have synthesized 11 trisaccharides that are highly tunable in structure and sulfation pattern, allowing us to determine how heparanase recognizes HS substrate and selects a favorable cleavage site. Our study shows that (1) N-SO₃^- at +1 subsite and 6-O-SO₃^- at -2 subsite of trisaccharides are critical for heparanase recognition, (2) addition of 2-O-SO₃^- at the -1 subsite and of 3-O-SO₃^- to GlcN unit is not advantageous, and (3) the anomeric configuration (α or β) at the reducing end is crucial in controlling heparanase activity. Our study also illustrates that the α-trisaccharide having N- and 6-O-SO₃^- at -2 and +1 subsites inhibited heparanase and was resistant toward hydrolysis.

Molecular Aspects of Heparanase Interaction with Heparan Sulfate, Heparin and Glycol Split Heparin

Heparanase is the principal enzyme that degrades heparan sulfate (HS) in both physiological (HS turnover) and pathological (tumor metastasis, inflammation) cell conditions, catalysing the hydrolysis of the β-1-4 glycosidic bond in -GlcUA-β(1-4)-GlcNX-. Despite efforts to define the minimum trisaccharide sequence that allows glycans to be recognized by heparanase, a rigorous "molecular code" by which the enzyme reads and degrades HS chains has not been identified. The X-ray diffraction model of heparanase, resolved by Wu et al (2015), revealed a complex between the trisaccharide GlcNS6S-GlcUA-GlcNS6S and heparanase. Efforts are ongoing to better understand how HS mimetics longer than three residues are recognized by heparanase before being hydrolyzed or inhibit the enzyme. It is also important to consider the flexibility of the enzyme active site, a feature that opens up the development of heparanase inhibitors with structures significantly different from HS or heparin. This chapter reviews the state-of-the-art knowledge about structural aspects of heparanase activities in terms of substrate recognition, mechanism of hydrolysis, and inhibition.

Non-Anticoagulant Heparins as Heparanase Inhibitors

The chapter will review early and more recent seminal contributions to the discovery and characterization of heparanase and non-anticoagulant heparins inhibiting its peculiar enzymatic activity. Indeed, heparanase displays a unique versatility in degrading heparan sulfate chains of several proteoglycans expressed in all mammalian cells. This endo-β-D-glucuronidase is overexpressed in cancer, inflammation, diabetes, atherosclerosis, nephropathies and other pathologies. Starting from known low- or non-anticoagulant heparins, the search for heparanase inhibitors evolved focusing on structure-activity relationship studies and taking advantage of new chemical-physical analytical methods which have allowed characterization and sequencing of polysaccharide chains. New methods to screen heparanase inhibitors and to evaluate their mechanism of action and in vivo activity in experimental models prompted their development. New non-anticoagulant heparin derivatives endowed with anti-heparanase activity are reported. Some leads are under clinical evaluation in the oncology field (e.g., acute myeloid leukemia, multiple myeloma, pancreatic carcinoma) and in other pathological conditions (e.g., sickle cell disease, malaria, labor arrest).

Flipping the Molecular Switch: Influence of Perlecan and Its Modifiers in the Tumor Microenvironment

The tumor microenvironment (TME) is rich in matrix components, growth factors, cytokines, and enzymatic modifiers that respond to changing conditions, to alter the fundamental properties of the tumor bed. Perlecan/HSPG2, a large, multi-domain heparan sulfate proteoglycan, is concentrated in the reactive stroma that surrounds tumors. Depending on its state in the TME, perlecan can either prevent or promote the progression of cancers to metastatic disease. Breast, prostate, lung, and renal cancers all preferentially metastasize to bone, a dense, perlecan-rich environment that is initially a "hostile" niche for cancer cells. Driven by inflammation, production of perlecan and its enzyme modifiers, which include matrix metalloproteinases (MMPs), sulfatases (SULFs), and heparanase (HPSE), increases in the reactive stroma surrounding growing and invading tumors. MMPs act upon the perlecan core protein, releasing bioactive fragments of the protein, primarily from C-terminal domains IV and V. These fragments influence cell adhesion, invasion, and angiogenesis. Sulfatases and heparanases act directly upon the heparan sulfate chains, releasing growth factors from reservoirs to reach receptors on the cancer cell surface. We propose that perlecan modifiers, by promoting the degradation of the perlecan-rich stroma, "flip the molecular switch" and convert the "hostile" stroma into a welcoming one that supports cancer dissemination and metastasis. Targeted therapies that prevent this molecular conversion of the TME should be considered as potential new therapeutics to limit metastasis.

Heparanase Inhibition by Pixatimod (PG545): Basic Aspects and Future Perspectives

Pixatimod is an inhibitor of heparanase, a protein which promotes cancer via its regulation of the extracellular environment by enzymatic cleavage of heparan sulfate (HS) and non-enzymatic signaling. Through its inhibition of heparanase and other HS-binding signaling proteins, pixatimod blocks a number of pro-cancerous processes including cell proliferation, invasion, metastasis, angiogenesis and epithelial-mesenchymal transition. Several laboratories have found that these activities have translated into potent activity using a range of different mouse cancer models, including approximately 30 xenograft and 20 syngeneic models. Analyses of biological samples from these studies have confirmed the heparanase targeting of this agent in vivo and the broad spectrum of anti-cancer effects that heparanase blockade achieves. Pixatimod has been tested in combination with a number of approved anti-cancer drugs demonstrating its clinical potential, including with gemcitabine, paclitaxel, sorafenib, platinum agents and an anti-PD-1 antibody. Clinical testing has shown pixatimod to be well tolerated as a monotherapy, and it is currently being investigated in combination with the anti-PD-1 drug nivolumab in a pancreatic cancer phase I trial.

An Overview of the Structure, Mechanism and Specificity of Human Heparanase

The retaining endo-β-D-glucuronidase Heparanase (HPSE) is the primary mammalian enzyme responsible for breakdown of the glycosaminoglycan heparan sulfate (HS). HPSE activity is essential for regulation and turnover of HS in the extracellular matrix, and its activity affects diverse processes such as inflammation, angiogenesis and cell migration. Aberrant heparanase activity is strongly linked to cancer metastasis, due to structural breakdown of extracellular HS networks and concomitant release of sequestered HS-binding growth factors. A full appreciation of HPSE activity in health and disease requires a structural understanding of the enzyme, and how it engages with its HS substrates. This chapter summarizes key findings from the recent crystal structures of human HPSE and its proenzyme. We present details regarding the 3-dimensional protein structure of HPSE and the molecular basis for its interaction with HS substrates of varying sulfation states. We also examine HPSE in a wider context against related β-D-glucuronidases from other species, highlighting the structural features that control exo/endo - glycosidase selectivity in this family of enzymes.

Heparanase as an Additional Tool for Detecting Structural Peculiarities of Heparin Oligosaccharides

Due to the biological properties of heparin and low-molecular-weight heparin (LMWH), continuous advances in elucidation of their microheterogeneous structure and discovery of novel structural peculiarities are crucial. Effective strategies for monitoring manufacturing processes and assessment of more restrictive specifications, as imposed by the current regulatory agencies, need to be developed. Hereby, we apply an efficient heparanase-based strategy to assert the structure of two major isomeric octasaccharides of dalteparin and investigate the tetrasaccharides arising from antithrombin binding region (ATBR) of bovine mucosal heparin. Heparanase, especially when combined with other sample preparation methods (e.g., size exclusion, affinity chromatography, heparinase depolymerization), was shown to be a powerful tool providing relevant information about heparin structural peculiarities. The applied approach provided direct evidence that oligomers bearing glucuronic acid–glucosamine-3-O-sulfate at their nonreducing end represent an important structural signature of dalteparin. When extended to ATBR-related tetramers of bovine heparin, the heparanase-based approach allowed for elucidation of the structure of minor sequences that have not been reported yet. The obtained results are of high importance in the view of the growing interest of regulatory agencies and manufacturers in the development of low-molecular-weight heparin generics as well as bovine heparin as alternative source.

Chondroitin sulfate E blocks enzymatic action of heparanase and heparanase-induced cellular responses

We examined whether chondroitin sulfates (CSs) exert inhibitory effects on heparanase (Hpse), the sole endoglycosidase that cleaves heparan sulfate (HS) and heparin, which also stimulates chemokine production. Hpse-mediated degradation of HS was suppressed in the presence of glycosaminoglycans derived from a squid cartilage and mouse bone marrow-derived mast cells, including the E unit of CS. Pretreatment of the chondroitin sulfate E (CS-E) with chondroitinase ABC abolished the inhibitory effect. Recombinant proteins that mimic pro-form and mature-form Hpse bound to the immobilized CS-E. Cellular responses as a result of Hpse-mediated binding, namely, uptake of Hpse by mast cells and Hpse-induced release of chemokine CCL2 from colon carcinoma cells, were also blocked by the CS-E. CS-E may regulate endogenous Hpse-mediated cellular functions by inhibiting enzymatic activity and binding to the cell surface.

Specificity and action pattern of heparanase Bp, a β-glucuronidase from Burkholderia pseudomallei

The specificity and action pattern of a β-glucuronidase derived from the pathogenic bacteria Burkholderia pseudomallei and expressed in Escherichia coli as a recombinant protein has been evaluated. While this enzyme shows activity on a number of glycosaminoglycans, our study has focused on its action on heparin, heparan sulfate and their biosynthetic intermediates as well as chemoenzymatically synthesized, structurally defined heparan sulfate oligosaccharides. These heparin/heparan sulfate (HP/HS) substrates examined varied in size and structure, but all contained an uronic acid (UA) residue β-(1→4) linked to a glucosamine residue. On the substrates tested, this enzyme (heparanase Bp) acted only on a glucuronic acid residue β-(1→4) linked to an N-acetylglucosamine, N-sulfoglucosamine or N-acetyl-6-O-sulfoglucosamine residue. A substrate was required to have a length of pentasaccharide or longer and heparanase Bp acted with a random endolytic action pattern on HP/HS. The specificity and glycohydrolase mechanism of action of heparanase Bp resembles mammalian heparanase and is complementary to the bacterial heparin lyases, which act through an eliminase mechanism on a glucosamine residue (1→4) linked to a UA residue, suggesting its utility as a tool for the structural determination of HP/HS as well as representing a possible model for the medically relevant mammalian heparanase. The utility heparanase Bp was demonstrated by the oligosaccharide mapping of heparin, which afforded resistant intact highly sulfated domains ranging from tetrasaccharide to >28-mer with a molecular weight >9000.

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.

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.

Epigenetic Regulation of the Biosynthesis & Enzymatic Modification of Heparan Sulfate Proteoglycans: Implications for Tumorigenesis and Cancer Biomarkers

Emerging evidence suggests that the enzymes in the biosynthetic pathway for the synthesis of heparan sulfate moieties of heparan sulfate proteoglycans (HSPGs) are epigenetically regulated at many levels. As the exact composition of the heparan sulfate portion of the resulting HSPG molecules is critical to the broad spectrum of biological processes involved in oncogenesis, the epigenetic regulation of heparan sulfate biosynthesis has far-reaching effects on many cellular activities related to cancer progression. Given the current focus on developing new anti-cancer therapeutics focused on epigenetic targets, it is important to understand the effects that these emerging therapeutics may have on the synthesis of HSPGs as alterations in HSPG composition may have profound and unanticipated effects. As an introduction, this review will briefly summarize the variety of important roles which HSPGs play in a wide-spectrum of cancer-related cellular and physiological functions and then describe the biosynthesis of the heparan sulfate chains of HSPGs, including how alterations observed in cancer cells serve as potential biomarkers. This review will then focus on detailing the multiple levels of epigenetic regulation of the enzymes in the heparan sulfate synthesis pathway with a particular focus on regulation by miRNA and effects of epigenetic therapies on HSPGs. We will also explore the use of lectins to detect differences in heparan sulfate composition and preview their potential diagnostic and prognostic use in the clinic.

Heparanase: roles in cell survival, extracellular matrix remodelling and the development of kidney disease

Heparanase has regulatory roles in various processes, including cell communication, gene transcription and autophagy. In addition, it is the only known mammalian endoglycosidase that is capable of degrading heparan sulfate (HS). HS chains are important constituents and organizers of the extracellular matrix (ECM), and have a key role in maintaining the integrity and function of the glomerular filtration barrier. In addition, HS chains regulate the activity of numerous bioactive molecules, such as cytokines and growth factors, at the cell surface and in the ECM. Given the functional diversity of HS, its degradation by heparanase profoundly affects important pathophysiological processes, including tumour development, neovascularization and inflammation, as well as progression of kidney disease. Heparanase-mediated degradation and subsequent remodelling of HS in the ECM of the glomerulus is a key mechanism in the development of glomerular disease, as exemplified by the complete resistance of heparanase-deficient animals to diabetes and immune-mediated kidney disease. This Review summarizes the role of heparanase in the development of kidney disease, and its potential as a therapeutic target.

Investigating Glycol-Split-Heparin-Derived Inhibitors of Heparanase: A Study of Synthetic Trisaccharides

Heparanase is the only known endoglycosidase able to cleave heparan sulfate. Roneparstat and necuparanib, heparanase inhibitors obtained from heparin and currently being tested in man as a potential drugs against cancer, contain in their structure glycol-split uronic acid moieties probably responsible for their strong inhibitory activity. We describe here the total chemical synthesis of the trisaccharide GlcNS6S-GlcA-1,6anGlcNS (1) and its glycol-split (gs) counterpart GlcNS6S-gsGlcA-1,6anGlcNS (2) from glucose. As expected, in a heparanase inhibition assay, compound 2 is one order of magnitude more potent than 1. Using molecular modeling techniques we have created a 3D model of 1 and 2 that has been validated by NOESY NMR experiments. The pure synthetic oligosaccharides have allowed the first in depth study of the conformation of a glycol-split glucuronic acid. Introducing a glycol-split unit in the structure of 1 increases the conformational flexibility and shortens the distance between the two glucosamine motives, thus promoting interaction with heparanase. However, comparing the relative activities of 2 and roneparstat, we can conclude that the glycol-split motive is not the only determinant of the strong inhibitory effect of roneparstat.

Heparanase: From basic research to therapeutic applications in cancer and inflammation

Heparanase, the sole heparan sulfate degrading endoglycosidase, regulates multiple biological activities that enhance tumor growth, angiogenesis and metastasis. Heparanase expression is enhanced in almost all cancers examined including various carcinomas, sarcomas and hematological malignancies. Numerous clinical association studies have consistently demonstrated that upregulation of heparanase expression correlates with increased tumor size, tumor angiogenesis, enhanced metastasis and poor prognosis. In contrast, knockdown of heparanase or treatments of tumor-bearing mice with heparanase-inhibiting compounds, markedly attenuate tumor progression further underscoring the potential of anti-heparanase therapy for multiple types of cancer. Heparanase neutralizing monoclonal antibodies block myeloma and lymphoma tumor growth and dissemination; this is attributable to a combined effect on the tumor cells and/or cells of the tumor microenvironment. In fact, much of the impact of heparanase on tumor progression is related to its function in mediating tumor-host crosstalk, priming the tumor microenvironment to better support tumor growth, metastasis and chemoresistance. The repertoire of the physio-pathological activities of heparanase is expanding. Specifically, heparanase regulates gene expression, activates cells of the innate immune system, promotes the formation of exosomes and autophagosomes, and stimulates signal transduction pathways via enzymatic and non-enzymatic activities. These effects dynamically impact multiple regulatory pathways that together drive inflammatory responses, tumor survival, growth, dissemination and drug resistance; but in the same time, may fulfill some normal functions associated, for example, with vesicular traffic, lysosomal-based secretion, stress response, and heparan sulfate turnover. Heparanase is upregulated in response to chemotherapy in cancer patients and the surviving cells acquire chemoresistance, attributed, at least in part, to autophagy. Consequently, heparanase inhibitors used in tandem with chemotherapeutic drugs overcome initial chemoresistance, providing a strong rationale for applying anti-heparanase therapy in combination with conventional anti-cancer drugs. Heparin-like compounds that inhibit heparanase activity are being evaluated in clinical trials for various types of cancer. Heparanase neutralizing monoclonal antibodies are being evaluated in pre-clinical studies, and heparanase-inhibiting small molecules are being developed based on the recently resolved crystal structure of the heparanase protein. Collectively, the emerging premise is that heparanase expressed by tumor cells, innate immune cells, activated endothelial cells as well as other cells of the tumor microenvironment is a master regulator of the aggressive phenotype of cancer, an important contributor to the poor outcome of cancer patients and a prime target for therapy.

Kinetic analysis and molecular modeling of the inhibition mechanism of roneparstat (SST0001) on human heparanase

Heparanase is a β-d-glucuronidase which cleaves heparan sulfate chains in the extracellular matrix and on cellular membranes. A dysregulated heparanase activity is intimately associated with cell invasion, tumor metastasis and angiogenesis, making heparanase an attractive target for the development of anticancer therapies. SST0001 (roneparstat; Sigma-Tau Research Switzerland S.A.) is a non-anticoagulant 100% N-acetylated and glycol-split heparin acting as a potent heparanase inhibitor, currently in phase I in advanced multiple myeloma. Herein, the kinetics of heparanase inhibition by roneparstat is reported. The analysis of dose-inhibition curves confirmed the high potency of roneparstat (IC₅₀ ≈ 3 nM) and showed, at higher concentrations, a Hill coefficient consistent with the engagement of two molecules of inhibitor. A homology model of human heparanase GS3 construct was built and used for docking experiments with inhibitor fragments. The model has high structural similarity with the recently reported crystal structure of human heparanase. Different interaction schemes are proposed, which support the hypothesis of a complex binding mechanism involving the recruitment of one or multiple roneparstat chains, depending on its concentration. In particular, docking solutions were obtained in which (i) a single roneparstat molecule interacts with both heparin-binding domains (HBDs) of heparanase or (ii) two fragments of roneparstat interact with either HBD-1 or HBD-2, consistent with the possibility of different inhibitor:enzyme binding stoichiometries. This study provides unique insights into the mode of action of roneparstat as well as clues of its interaction with heparanase at a molecular level, which could be exploited to design novel potential inhibitor molecules.

Microwave-assisted simultaneous O,N-sulfonation in the synthesis of heparin-like oligosaccharides

Simultaneous O,N-sulfonation of heparin-like saccharides was achieved in short reaction times and excellent yields (>90%) under microwave irradiation.

Structural characterization of human heparanase reveals insights into substrate recognition

Heparan sulfate (HS) is a glycosaminoglycan that forms a key component of the extracellular matrix (ECM). Breakdown of HS is carried out by heparanase (HPSE), an endo-β-glucuronidase of the glycoside hydrolase 79 (GH79) family. Overexpression of HPSE results in breakdown of extracellular HS and release of stored growth factors and hence is strongly linked to cancer metastasis. Here we present crystal structures of human HPSE at 1.6-Å to 1.9-Å resolution that reveal how an endo-acting binding cleft is exposed by proteolytic activation of latent proHPSE. We used oligosaccharide complexes to map the substrate-binding and sulfate-recognition motifs. These data shed light on the structure and interactions of a key enzyme involved in ECM maintenance and provide a starting point for the design of HPSE inhibitors for use as biochemical tools and anticancer therapeutics.

The Responses of Hyperglycemic Dividing Mesangial Cells to Heparin Are Mediated by the Non-reducing Terminal Trisaccharide

Our previous studies showed: (i) that growth-arrested G0/G1 rat mesangial cells stimulated to divide in hyperglycemic medium initiate intracellular hyaluronan synthesis that induces autophagy and the cyclin D3-induced formation of a monocyte-adhesive extracellular hyaluronan matrix after completing cell division; and (ii) that heparin inhibits the intracellular hyaluronan and autophagy responses, but after completing division, induces hyaluronan synthesis at the plasma membrane with the formation of a larger monocyte-adhesive hyaluronan matrix. This study shows: (i) that the non-terminal trisaccharide of heparin is sufficient to initiate the same responses as intact heparin, (ii) that a fully sulfated tetrasaccharide isolated from bacterial heparin lyase 1 digests of heparin that contains a Δ-2S-iduronate on the non-reducing end does not initiate the same responses as intact heparin, and (iii) that removal of the Δ-2S-iduronate to expose the fully sulfated trisaccharide (GlcNS(6S)-IdoUA(2S)-GlcNS(6S)) does initiate the same responses as intact heparin. These results provide evidence that mammalian heparanase digestion of heparin and heparan sulfate exposes a cryptic motif on the non-reducing termini that is recognized by a receptor on dividing cells.

Distribution of Heparan Sulfate Oligosaccharides in Murine Mucopolysaccharidosis Type IIIA

Heparan sulfate (HS) catabolism begins with endo-degradation of the polysaccharide to smaller HS oligosaccharides, followed by the sequential action of exo-enzymes to reduce these oligosaccharides to monosaccharides and inorganic sulfate. In mucopolysaccharidosis type IIIA (MPS IIIA) the exo-enzyme, N-sulfoglucosamine sulfohydrolase, is deficient resulting in an inability to hydrolyze non-reducing end glucosamine N-sulfate esters. Consequently, partially degraded HS oligosaccharides with non-reducing end glucosamine sulfate esters accumulate. We investigated the distribution of these HS oligosaccharides in tissues of a mouse model of MPS IIIA using high performance liquid chromatography electrospray ionization-tandem mass spectrometry. Oligosaccharide levels were compared to total uronic acid (UA), which was used as a measure of total glycosaminoglycan. Ten oligosaccharides, ranging in size from di- to hexasaccharides, were present in all the tissues examined including brain, spleen, lung, heart, liver, kidney and urine. However, the relative levels varied up to 10-fold, suggesting different levels of HS turnover and storage. The relationship between the di- and tetrasaccharides and total UA was tissue specific with spleen and kidney showing a different disaccharide:total UA ratio than the other tissues. The hexasaccharides showed a stronger correlation with total UA in all tissue types suggesting that hexasaccharides may more accurately reflect the storage burden in these tissues.

A liquid chromatography-mass spectrometry-based approach to characterize the substrate specificity of mammalian heparanase

Extracellular heparanase activity releases growth factors and angiogenic factors from heparan sulfate (HS) storage sites and alters the integrity of the extracellular matrix. These activities lead to a loss of normal cell matrix adherent junctions and correlate with invasive cellular phenotypes. Elevated expression of heparanase is associated with several human cancers and with vascular remodeling. Heparanase cleaves only a limited fraction of glucuronidic linkages in HS. There have been few investigations of the functional consequences of heparanase activity, largely due to the heterogeneity and complexity of HS. Here, we report a liquid chromatography-mass spectrometry (LC-MS)-based approach to profile the terminal structures created by heparanase digestion and reconstruct the heparanase cleavage sites from the products. Using this method, we demonstrate that heparanase cleaves at the non-reducing side of highly sulfated HS domains, exposing cryptic growth factor binding sites. This cleavage pattern is observed in HS from several tissue sources, regardless of overall sulfation degree, indicating a common recognition pattern. We further demonstrate that heparanase cleavage of HS chains leads to increased ability to support FGF2-dependent cell proliferation. These results suggest a new mechanism to explain how heparanase might potentiate the uncontrolled cell proliferation associated with cancer through its ability to activate nascent growth factor-promoting domains within HS.

The mechanisms and physiological relevance of glycocalyx degradation in hepatic ischemia/reperfusion injury

SIGNIFICANCE

Hepatic ischemia/reperfusion (I/R) injury is an inevitable side effect of major liver surgery that can culminate in liver failure. The bulk of I/R-induced liver injury results from an overproduction of reactive oxygen and nitrogen species (ROS/RNS), which inflict both parenchymal and microcirculatory damage. A structure that is particularly prone to oxidative attack and modification is the glycocalyx (GCX), a meshwork of proteoglycans and glycosaminoglycans (GAGs) that covers the lumenal endothelial surface and safeguards microvascular homeostasis. ROS/RNS-mediated degradation of the GCX may exacerbate I/R injury by, for example, inducing vasoconstriction, facilitating leukocyte adherence, and directly activating innate immune cells.

RECENT ADVANCES

Preliminary experiments revealed that hepatic sinusoids contain a functional GCX that is damaged during murine hepatic I/R and major liver surgery in patients. There are three ROS that mediate GCX degradation: hydroxyl radicals, carbonate radical anions, and hypochlorous acid (HOCl). HOCl converts GAGs in the GCX to GAG chloramides that become site-specific targets for oxidizing and reducing species and are more efficiently fragmented than the parent molecules. In addition to ROS/RNS, the GAG-degrading enzyme heparanase acts at the endothelial surface to shed the GCX.

CRITICAL ISSUES

The GCX seems to be degraded during major liver surgery, but the underlying cause remains ill-defined.

FUTURE DIRECTIONS

The relative contribution of the different ROS and RNS intermediates to GCX degradation in vivo, the immunogenic potential of the shed GCX fragments, and the role of heparanase in liver I/R injury all warrant further investigation.

The Role of Heparanase and Sulfatases in the Modification of Heparan Sulfate Proteoglycans within the Tumor Microenvironment and Opportunities for Novel Cancer Therapeutics

Heparan sulfate proteoglycans (HSPGs) are an integral and dynamic part of normal tissue architecture at the cell surface and within the extracellular matrix. The modification of HSPGs in the tumor microenvironment is known to result not just in structural but also functional consequences, which significantly impact cancer progression. As substrates for the key enzymes sulfatases and heparanase, the modification of HSPGs is typically characterized by the degradation of heparan sulfate (HS) chains/sulfation patterns via the endo-6-O-sulfatases (Sulf1 and Sulf2) or by heparanase, an endo-glycosidase that cleaves the HS polymers releasing smaller fragments from HSPG complexes. Numerous studies have demonstrated how these enzymes actively influence cancer cell proliferation, signaling, invasion, and metastasis. The activity or expression of these enzymes has been reported to be modified in a variety of cancers. Such observations are consistent with the degradation of normal architecture and basement membranes, which are typically compromised in metastatic disease. Moreover, recent studies elucidating the requirements for these proteins in tumor initiation and progression exemplify their importance in the development and progression of cancer. Thus, as the influence of the tumor microenvironment in cancer progression becomes more apparent, the focus on targeting enzymes that degrade HSPGs highlights one approach to maintain normal tissue architecture, inhibit tumor progression, and block metastasis. This review discusses the role of these enzymes in the context of the tumor microenvironment and their promise as therapeutic targets for the treatment of cancer.

Modulation of heparan sulfate in the glomerular endothelial glycocalyx decreases leukocyte influx during experimental glomerulonephritis

The glomerular endothelial glycocalyx is postulated to be an important modulator of permeability and inflammation. The glycocalyx consists of complex polysaccharides, the main functional constituent of which, heparan sulfate (HS), is synthesized and modified by multiple enzymes. The N-deacetylase-N-sulfotransferase (Ndst) enzymes initiate and dictate the modification process. Here we evaluated the effects of modulation of HS in the endothelial glycocalyx on albuminuria and glomerular leukocyte influx using mice deficient in endothelial and leukocyte Ndst1 (TEKCre+/Ndst1flox/flox). In these mice, glomerular expression of a specific HS domain was significantly decreased, whereas the expression of other HS domains was normal. In the endothelial glycocalyx, this specific HS structure was not associated with albuminuria or with changes in renal function. However, glomerular leukocyte influx was significantly reduced during antiglomerular basement membrane nephritis, which was associated with less glomerular injury and better renal function. In vitro decreased adhesion of wild-type and Ndst1-deficient granulocytes to Ndst1-silenced glomerular endothelial cells was found, accompanied by a decreased binding of chemokines and L-selectin. Thus, modulation of HS in the glomerular endothelial glycocalyx significantly reduced the inflammatory response in antiglomerular basement membrane nephritis.

Heparan sulfate glycosaminoglycans modulate migration and survival in zebrafish primordial germ cells

Early in embryonic development, primordial germ cells (PGCs) are specified and migrate from the site of their origin to where the gonad develops, following a specific route. Heparan sulfate glycosaminoglycans (HS-GAGs) are ubiquitous in extracellular matrix and the cell surface and have long been speculated to play a role during the migration of PGCs. In line with this speculation, whole-mount immunohistochemistry revealed the existence of HS-GAGs in the vicinity of migrating PGCs in early zebrafish embryos. To examine the roles of HS-GAGs during PGC migration, zebrafish heparanase 1 (hpse1), which degrades HS-GAGs, was cloned and overexpressed specifically in PGCs. The guidance signal for the migration of PGCs was disrupted with the overexpression of hpse1, as cluster formation and marginal localization at the blastoderm were significantly perturbed at 6 hours postfertilization. Furthermore, the number of PGCs was significantly decreased with the lack of vicinal HS-GAGs, as observed in the whole-mount in situ hybridization and quantitative PCR of the PGC marker gene vasa. Terminal deoxynucleotidyl transferase dUTP nick-end labeling indicated significantly increased apoptosis in PGCs overexpressing hpse1, suggesting that HS-GAGs contribute to the maintenance of PGC survival. In conclusion, HS-GAGs play multifaceted roles in PGCs during migration and are required both for guidance signals and multiplication of PGCs.

Efficient synthesis of a library of heparin tri- and tetrasaccharides relevant to the substrate of heparanase

A robust glycosylation protocol was fixed to construct the GlcN–(1α→4)-GlcA/IdoA linkagesen routeto heparin oligosaccharides.

Synthesis of a pseudo-disaccharide library and its application to the characterisation of the heparanase catalytic site

A novel methodology is described for the efficient and divergent synthesis of pseudodisaccharides, molecules comprising of amino carbasugar analogues linked to natural sugars. The methodology is general and enables the introduction of diversity both at the carbasugar and the natural sugar components of the pseudodisaccharides. Using this approach, a series of pseudodisaccharides are synthesised that mimic the repeating backbone unit of heparan sulfate, and are tested for inhibition of heparanase, a disease-relevant enzyme that hydrolyses heparan sulfate. A new homology model of human heparanase is described based on a family 79 β-glucuronidase. This model is used to postulate a computational rationale for the observed activity of the different pseudodisaccharides and provide valuable information that informs the design of potential inhibitors of this enzyme.

Mechanisms of heparanase inhibition by the heparan sulfate mimetic PG545 and three structural analogues

The tetrasaccharide heparan sulfate (HS) mimetic PG545, a clinical anti-cancer candidate, is an inhibitor of the HS-degrading enzyme heparanase. The kinetics of heparanase inhibition by PG545 and three structural analogues were investigated to understand their modes of inhibition. The cholestanol aglycon of PG545 significantly increased affinity for heparanase and also modified the inhibition mode. For the tetrasaccharides, competitive inhibition was modified to parabolic competition by the addition of the cholestanol aglycon. For the trisaccharides, partial competitive inhibition was modified to parabolic competition. A schematic model to explain these findings is presented.

Method development and analysis of free HS and HS in proteoglycans from pre- and postmenopausal women: evidence for biosynthetic pathway changes in sulfotransferase and sulfatase enzymes

Heparan sulfate (HS) is one of the most complex and informative biopolymers found on the cell surface or in the extracellular matrix as either free HS fragments or constituents of HS proteoglycans (HSPGs). Analysis of free HS and HSPG sugar chains in human serum at the disaccharide level has great potential for early disease diagnosis and prognosis; however, the low concentration of HS in human serum, together with the complexity of the serum matrix, limits the information on HS. In this study, we present and validate the development of a new sensitive method for in-depth compositional analysis of free HS and HSPG sugar chains. This protocol involved several steps including weak anion exchange chromatography, ultrafiltration, and solid-phase extraction for enhanced detection prior to LC-MS/MS analysis. Using this protocol, a total of 51 serum samples from 26 premenopausal and 25 postmenopausal women were analyzed. Statistically significant differences in heparin/HS disaccharide profiles were observed. The proportion of N-acetylation and N-sulfation in both free HS and HSPG sugar chains were significantly different between pre- and postmenopausal women, indicating changes in N-deacetylase/N-sulfotransferases (NDSTs), the enzymes involved in the initial step of the biosynthetic pathway. Differences in the proportion of 6-O-sulfation suggest that 6-O-sulfotransferase and/or 6-O-sulfatase enzymes may also be implicated.

Involvement of heparanase in atherosclerosis and other vessel wall pathologies

Heparanase, the sole mammalian endoglycosidase degrading heparan sulfate, is causally involved in cancer metastasis, angiogenesis, inflammation and kidney dysfunction. Despite the wide occurrence and impact of heparan sulfate proteoglycans in vascular biology, the significance of heparanase in vessel wall disorders is underestimated. Blood vessels are highly active structures whose morphology rapidly adapts to maintain vascular function under altered systemic and local conditions. In some pathologies (restenosis, thrombosis, atherosclerosis) this normally beneficial adaptation may be detrimental to overall function. Enzymatic dependent and independent effects of heparanase on arterial structure mechanics and repair closely regulate arterial compliance and neointimal proliferation following endovascular stenting. Additionally, heparanase promotes thrombosis after vascular injury and contributes to a pro-coagulant state in human carotid atherosclerosis. Importantly, heparanase is closely associated with development and progression of atherosclerotic plaques, including stable to unstable plaque transition. Consequently, heparanase levels are markedly increased in the plasma of patients with acute myocardial infarction. Noteworthy, heparanase activates macrophages, resulting in marked induction of cytokine expression associated with plaque progression towards vulnerability. Together, heparanase emerges as a regulator of vulnerable lesion development and potential target for therapeutic intervention in atherosclerosis and related vessel wall complications.