Dendrimer Heparan Sulfate Glycomimetics: Potent Heparanase Inhibitors for Anticancer Therapy

Rational synthesis of a heparan sulfate saccharide that promotes the activity of BMP2

Heparan sulfate (HS) is a glycosaminoglycan (GAG) found throughout nature and is involved in a wide range of functions including modulation of cell signalling via sequestration of growth factors. Current consensus is that the specificity of HS motifs for protein binding are individual for each protein. Given the structural complexity of HS the synthesis of libraries of these compounds to probe this is not trivial. Herein we present the synthesis of an HS decamer, the design of which was undertaken rationally from previously published data for HS binding to the growth factor BMP-2. The biological activity of this HS decamer was assessed in vitro, showing that it had the ability to both bind BMP-2 and increase its thermal stability as well as enhancing the bioactivity of BMP-2 in vitro in C2C12 cells. At the same time no undesired anticoagulant effect was observed. This decamer was then analysed in vivo in a rabbit model where higher bone formation, bone mineral density (BMD) and trabecular thickness were observed over an empty defect or collagen implant alone. This indicated that the HS decamer was effective in promoting bone regeneration in vivo.

Synthesis and Detection of BODIPY-, Biotin-, and 19 F- Labeled Single-Entity Dendritic Heparan Sulfate Mimetics

Heparin and heparan sulfate (HS) are naturally occurring mammalian glycosaminoglycans, and their synthetic and semi-synthetic mimetics have attracted significant interest as potential therapeutics. However, understanding the mechanism of action by which HS, heparin, and HS mimetics have a biological effect is difficult due to their highly charged nature, broad protein interactomes, and variable structures. To address this, a library of novel single-entity dendritic mimetics conjugated to BODIPY, Fluorine-19 (19 F), and biotin was synthesized for imaging and localization studies. The novel dendritic scaffold allowed for the conjugation of labeling moieties without reducing the number of sulfated capping groups, thereby better mimicking the multivalent nature of HS-protein interactions. The 19 F labeled mimetics were assessed in phantom studies and were detected at concentrations as low as 5 mM. Flow cytometric studies using a fluorescently labeled mimetic showed that the compound associated with immune cells from tumors more readily than splenic counterparts and was directed to endosomal-lysosomal compartments within immune cells and cancer cells. Furthermore, the fluorescently labeled mimetic entered the central nervous system and was detectable in brain-infiltrating immune cells 24 hours after treatment. Here, we report the enabling methodology for rapidly preparing various labeled HS mimetics and molecular probes with diverse potential therapeutic applications.

Heparanase inhibition as a systemic approach to protect the endothelial glycocalyx and prevent microvascular complications in diabetes

BACKGROUND

Diabetes mellitus is a chronic disease which is detrimental to cardiovascular health, often leading to secondary microvascular complications, with huge global health implications. Therapeutic interventions that can be applied to multiple vascular beds are urgently needed. Diabetic retinopathy (DR) and diabetic kidney disease (DKD) are characterised by early microvascular permeability changes which, if left untreated, lead to visual impairment and renal failure, respectively. The heparan sulphate cleaving enzyme, heparanase, has previously been shown to contribute to diabetic microvascular complications, but the common underlying mechanism which results in microvascular dysfunction in conditions such as DR and DKD has not been determined.

METHODS

In this study, two mouse models of heparan sulphate depletion (enzymatic removal and genetic ablation by endothelial specific Exotosin-1 knock down) were utilized to investigate the impact of endothelial cell surface (i.e., endothelial glycocalyx) heparan sulphate loss on microvascular barrier function. Endothelial glycocalyx changes were measured using fluorescence microscopy or transmission electron microscopy. To measure the impact on barrier function, we used sodium fluorescein angiography in the eye and a glomerular albumin permeability assay in the kidney. A type 2 diabetic (T2D, db/db) mouse model was used to determine the therapeutic potential of preventing heparan sulphate damage using treatment with a novel heparanase inhibitor, OVZ/HS-1638. Endothelial glycocalyx changes were measured as above, and microvascular barrier function assessed by albumin extravasation in the eye and a glomerular permeability assay in the kidney.

RESULTS

In both models of heparan sulphate depletion, endothelial glycocalyx depth was reduced and retinal solute flux and glomerular albumin permeability was increased. T2D mice treated with OVZ/HS-1638 had improved endothelial glycocalyx measurements compared to vehicle treated T2D mice and were simultaneously protected from microvascular permeability changes associated with DR and DKD.

CONCLUSION

We demonstrate that endothelial glycocalyx heparan sulphate plays a common mechanistic role in microvascular barrier function in the eye and kidney. Protecting the endothelial glycocalyx damage in diabetes, using the novel heparanase inhibitor OVZ/HS-1638, effectively prevents microvascular permeability changes associated with DR and DKD, demonstrating a novel systemic approach to address diabetic microvascular complications.

Molecular Basis for Inhibition of Heparanases and β-Glucuronidases by Siastatin B

Siastatin B is a potent and effective iminosugar inhibitor of three diverse glycosidase classes, namely, sialidases, β-d-glucuronidases, and N-acetyl-glucosaminidases. The mode of inhibition of glucuronidases, in contrast to sialidases, has long been enigmatic as siastatin B appears too bulky and incorrectly substituted to be accommodated within a β-d-glucuronidase active site pocket. Herein, we show through crystallographic analysis of protein-inhibitor complexes that siastatin B generates both a hemiaminal and a 3-geminal diol iminosugar (3-GDI) that are, rather than the parent compound, directly responsible for enzyme inhibition. The hemiaminal product is the first observation of a natural product that belongs to the noeuromycin class of inhibitors. Additionally, the 3-GDI represents a new and potent class of the iminosugar glycosidase inhibitor. To substantiate our findings, we synthesized both the gluco- and galacto-configured 3-GDIs and characterized their binding both structurally and kinetically to exo-β-d-glucuronidases and the anticancer target human heparanase. This revealed submicromolar inhibition of exo-β-d-glucuronidases and an unprecedented binding mode by this new class of inhibitor. Our results reveal the mechanism by which siastatin B acts as a broad-spectrum glycosidase inhibitor, identify a new class of glycosidase inhibitor, and suggest new functionalities that can be incorporated into future generations of glycosidase inhibitors.

The novel HS-mimetic, Tet-29, regulates immune cell trafficking across barriers of the CNS during inflammation

BACKGROUND

Disruption of the extracellular matrix at the blood-brain barrier (BBB) underpins neuroinflammation in multiple sclerosis (MS). The degradation of extracellular matrix components, such as heparan sulfate (HS) proteoglycans, can be prevented by treatment with HS-mimetics through their ability to inhibit the enzyme heparanase. The heparanase-inhibiting ability of our small dendrimer HS-mimetics has been investigated in various cancers but their efficacy in neuroinflammatory models has not been evaluated. This study investigates the use of a novel HS-mimetic, Tet-29, in an animal model of MS.

METHODS

Neuroinflammation was induced in mice by experimental autoimmune encephalomyelitis, a murine model of MS. In addition, the BBB and choroid plexus were modelled in vitro using transmigration assays, and migration of immune cells in vivo and in vitro was quantified by flow cytometry.

RESULTS

We found that Tet-29 significantly reduced lymphocyte accumulation in the central nervous system which, in turn, decreased disease severity in experimental autoimmune encephalomyelitis. The disease-modifying effect of Tet-29 was associated with a rescue of BBB integrity, as well as inhibition of activated lymphocyte migration across the BBB and choroid plexus in transwell models. In contrast, Tet-29 did not significantly impair in vivo or in vitro steady state-trafficking under homeostatic conditions.

CONCLUSIONS

Together these results suggest that Tet-29 modulates, rather than abolishes, trafficking across central nervous system barriers.

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.

Mechanism-based heparanase inhibitors reduce cancer metastasis in vivo

Cancer growth is accompanied by changes to the extracellular environment of tumors, which aids the proliferation and spread of cancer cells. Cancer-associated extracellular matrix changes include excessive degradation of heparan sulfate carbohydrates, promoting metastatic spread by multiple mechanisms. Heparanase is the main human enzyme responsible for extracellular heparan sulfate breakdown and strongly drives metastasis when overexpressed. Few effective heparanase inhibitors are known, and the most effective molecules to date possess nondrug-like structures with multiple off-target effects. We have carried out structure-guided development of heparanase inhibitors, which covalently bind to the enzyme active site to cause irreversible inhibition. These inhibitors are heparanase specific and reduce metastasis in animal models with comparable efficacy to current “best-in-class” compounds.

Heparan sulfate proteoglycans (HSPGs) mediate essential interactions throughout the extracellular matrix (ECM), providing signals that regulate cellular growth and development. Altered HSPG composition during tumorigenesis strongly aids cancer progression. Heparanase (HPSE) is the principal enzyme responsible for extracellular heparan sulfate catabolism and is markedly up-regulated in aggressive cancers. HPSE overactivity degrades HSPGs within the ECM, facilitating metastatic dissemination and releasing mitogens that drive cellular proliferation. Reducing extracellular HPSE activity reduces cancer growth, but few effective inhibitors are known, and none are clinically approved. Inspired by the natural glycosidase inhibitor cyclophellitol, we developed nanomolar mechanism-based, irreversible HPSE inhibitors that are effective within physiological environments. Application of cyclophellitol-derived HPSE inhibitors reduces cancer aggression in cellulo and significantly ameliorates murine metastasis. Mechanism-based irreversible HPSE inhibition is an unexplored anticancer strategy. We demonstrate the feasibility of such compounds to control pathological HPSE-driven malignancies.

Synthesis of novel S- and O-disaccharide analogs of heparan sulfate for heparanase inhibition

Heparan sulfate (HS), a glycosaminoglycan related to heparin, is a linear polysaccharide, consisting of repeating disaccharide units. This compound is involved in multiple biological processes such as inflammation, coagulation, angiogenesis and viral infections. Our work focuses on the synthesis of simple HS analogs for the study of structure-activity relationships, with the aim of modulating these biological activities. Thioglycoside analogs, in which the interglycosidic oxygen is replaced by a sulfur atom, are very interesting compounds in terms of therapeutic applications. Indeed, the thioglycosidic bond leads to an improvement of their stability and can allow the inhibition of enzymes involved in physiological and pathological processes. In our previous work, we developed a synthetic sequence which led to a non-sulfated thiodisaccharide analog of HS. In this paper, we report our results of the development of a new synthetic method allowing access to the novel sulfated S-disaccharide, as well as to their oxygenated analogues (O-disaccharide and sulfated O-disaccharide). These 4 compounds were also tested for the inhibition of heparanase, an enzyme involved in biological processes like tumor growth and inflammation. The obtained IC₅₀ values in the micromolar range showed the impact of the interglycosidic sulfur atom and the 6-sulfate group.

Recovery of Post-Stroke Spatial Memory and Thalamocortical Connectivity Following Novel Glycomimetic and rhBDNF Treatment

Stroke-induced cognitive impairments remain of significant concern, with very few treatment options available. The involvement of glycosaminoglycans in neuroregenerative processes is becoming better understood and recent advancements in technology have allowed for cost-effective synthesis of novel glycomimetics. The current study evaluated the therapeutic potential of two novel glycomimetics, compound A and G, when administered systemically five-days post-photothrombotic stroke to the PFC. As glycosaminoglycans are thought to facilitate growth factor function, we also investigated the combination of our glycomimetics with intracerebral, recombinant human brain-derived neurotrophic factor (rhBDNF). C56BL/6J mice received sham or stroke surgery and experimental treatment (day-5), before undergoing the object location recognition task (OLRT). Four-weeks post-surgery, animals received prelimbic injections of the retrograde tracer cholera toxin B (CTB), before tissue was collected for quantification of thalamo-PFC connectivity and reactive astrogliosis. Compound A or G treatment alone modulated a degree of reactive astrogliosis yet did not influence spatial memory performance. Contrastingly, compound G+rhBDNF treatment significantly improved spatial memory, dampened reactive astrogliosis and limited stroke-induced loss of connectivity between the PFC and midline thalamus. As rhBDNF treatment had negligible effects, these findings support compound A acted synergistically to enhance rhBDNF to restrict secondary degeneration and facilitate functional recovery after PFC stroke.

Synthesis of novel glycolipid mimetics of heparan sulfate and their application in colorectal cancer treatment in a mouse model

Heparan sulfate (HS) is a highly sulfated natural carbohydrate that plays crucial roles in cancer, inflammation, and angiogenesis. Heparanase (HPSE) is the sole HS degrading endoglycosidase that cleaves HS at structure‐dependent sites along the polysaccharide chain. Overexpression of HPSE by cancer cells correlates with increased tumor size and enhanced metastasis. Previously we have shown that a tetramer HS mimetic is a potent HPSE inhibitor displaying remarkable anticancer activity in vivo. Building on that work, we report the synthesis and testing of a novel library of single entity trimer glycolipid mimetics that effectively inhibit HPSE at low nanomolar concentrations. A lipophilic arm was introduced to assess whether an improvement of pharmacokinetics and plasma residence time would offset the reduction in charge and multivalency. Preclinical tests in a mouse syngeneic model showed effective tumor growth inhibition by the tetramer but not the trimer glycomimetic.

Development of Improved Synthetic Routes to Pixatimod (PG545), a Sulfated Oligosaccharide-Steroid Conjugate

The heparan sulfate (HS) mimetic pixatimod (PG545) is a highly potent inhibitor of angiogenesis, tumor growth, and metastasis currently in clinical trials for cancer. PG545 has also demonstrated potent antiviral activity against numerous HS-dependent viruses, including SARS-CoV-2, and shows promise as an antiviral drug for the treatment of COVID-19. Structurally, PG545 consists of a fully sulfated tetrasaccharide conjugated to the steroid 5α-cholestan-3β-ol. The reported synthesis of PG545 suffers from a low yield and poor selectivity in the critical glycosylation step. Given its clinical importance, new efficient routes for the synthesis of PG545 and analogues were developed. Particular attention was given to improving the key glycosylation step by using more stable protecting groups and optimized glycosyl donors.

GAG Multivalent Systems to interact with Langerin

Langerin is a C-type Lectin expressed at the surface of Langerhans cells, which play a pivotal role in protecting organisms against pathogen infections. To address this aim, Langerin presents at least two recognition sites, one Ca2+-dependent and another one independent, capable of recognizing a variety of carbohydrate ligands. In contrast to other lectins, Langerin recognizes sulfated glycosaminoglycans (GAGs), a family of complex and heterogeneous polysaccharides present in the cell membrane and the extracellular matrix at the interphase generated in the trimeric form of Langerin but absent in the monomeric form. The complexity of these oligosaccharides has impeded the development of well-defined monodisperse structures to study these interaction processes. However, in the last few decades, an improvement of synthetic developments to achieve the preparation of carbohydrate multivalent systems mimicking the GAGs has been described. Despite all these contributions, very few examples are reported where the GAG multivalent structures are used to evaluate the interaction with Langerin. These molecules should pave the way to explore these GAG-Langerin interactions.

Inhibition of Tumor-Host Cell Interactions Using Synthetic Heparin Mimetics

Low-molecular-weight heparin (LMWH) is the guideline-based drug for antithrombotic treatment of cancer patients, while its direct antitumor effects are a matter of ongoing debate. Although therapeutically established for decades, LMWH has several drawbacks mainly associated with its origin from animal sources. Aiming to overcome these limitations, a library of synthetic heparin mimetic polymers consisting of homo- and copolymers of sulfonated and carboxylated noncarbohydrate monomers has recently been synthesized via reversible addition-fragmentation chain transfer polymerization. These heparin mimetics were investigated for their capacities to interfere with simulated steps of tumor cell metastasis. Among them, homo- and copolymers from sodium 4-styrenesulfonate (poly(SSS)) with acrylic acid (poly(SSS-co-AA)) with an MW between 5 and 50 kDa efficiently attenuated cancer cell-induced coagulation and thus platelet activation and degranulation similar to or even better than LMWH. Furthermore, independent of anticoagulant activities, these polymers affected other metastasis-relevant targets with impressive affinities. Hence, they blocked heparanase enzymatic activity outmatching commercial heparins or a glycosidic drug candidate. Furthermore, these polymers bind P-selectin and the integrin VLA-4 similar to or even better than heparin, indicated by a biosensor approach and thus efficiently blocked melanoma cell binding to endothelium under blood flow conditions. This is the first report on the prospects of synthetic heparin mimetics as promising nontoxic compounds in oncology to potentially substitute heparin as an anticoagulant and to better understand its role as an antimetastatic drug.

Cell-surface heparan sulfate proteoglycans as multifunctional integrators of signaling in cancer

Proteoglycans (PGs) represent a large proportion of the components that constitute the extracellular matrix (ECM). They are a diverse group of glycoproteins characterized by a covalent link to a specific glycosaminoglycan type. As part of the ECM, heparan sulfate (HS)PGs participate in both physiological and pathological processes including cell recruitment during inflammation and the promotion of cell proliferation, adhesion and motility during development, angiogenesis, wound repair and tumor progression. A key function of HSPGs is their ability to modulate the expression and function of cytokines, chemokines, growth factors, morphogens, and adhesion molecules. This is due to their capacity to act as ligands or co-receptors for various signal-transducing receptors, affecting pathways such as FGF, VEGF, chemokines, integrins, Wnt, notch, IL-6/JAK-STAT3, and NF-κB. The activation of those pathways has been implicated in the induction, progression, and malignancy of a tumor. For many years, the study of signaling has allowed for designing specific drugs targeting these pathways for cancer treatment, with very positive results. Likewise, HSPGs have become the subject of cancer research and are increasingly recognized as important therapeutic targets. Although they have been studied in a variety of preclinical and experimental models, their mechanism of action in malignancy still needs to be more clearly defined. In this review, we discuss the role of cell-surface HSPGs as pleiotropic modulators of signaling in cancer and identify them as promising markers and targets for cancer treatment.

The Heparan Sulfate Sulfotransferases HS2ST1 and HS3ST2 Are Novel Regulators of Breast Cancer Stem-Cell Properties

Heparan sulfate (HS) is a glycosaminoglycan found mainly in its protein-conjugated form at the cell surface and the extracellular matrix. Its high sulfation degree mediates functional interactions with positively charged amino acids in proteins. 2-O sulfation of iduronic acid and 3-O sulfation of glucosamine in HS are mediated by the sulfotransferases HS2ST and HS3ST, respectively, which are dysregulated in several cancers. Both sulfotransferases regulate breast cancer cell viability and invasion, but their role in cancer stem cells (CSCs) is unknown. Breast CSCs express characteristic markers such as CD44⁺/CD24^−/low, CD133 and ALDH1 and are involved in tumor initiation, formation, and recurrence. We studied the influence of HS2ST1 and HS3ST2 overexpression on the CSC phenotype in breast cancer cell lines representative of the triple-negative (MDA-MB-231) and hormone-receptor positive subtype (MCF-7). The CD44⁺/CD24^−/low phenotype was significantly reduced in MDA-MB-231 cells after overexpression of both enzymes, remaining unaltered in MCF-7 cells. ALDH1 activity was increased after HS2ST1 and HS3ST2 overexpression in MDA-MB-231 cells and reduced after HS2ST1 overexpression in MCF-7 cells. Colony and spheroid formation were increased after HS2ST1 and HS3ST2 overexpression in MCF-7 cells. Moreover, MDA-MB-231 cells overexpressing HS2ST1 formed more colonies and could not generate spheres. The phenotypic changes were associated with complex changes in the expression of the stemness-associated notch and Wnt-signaling pathways constituents, syndecans, heparanase and Sulf1. The results improve our understanding of breast CSC function and mark a subtype-specific impact of HS modifications on the CSC phenotype of triple-negative and hormone receptor positive breast cancer model cell lines.

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.

The Good and Bad Sides of Heparanase-1 and Heparanase-2

In this chapter, we will emphasize the importance of heparan sulfate proteoglycans (HSPG) in controlling various physiological and pathological molecular mechanisms and discuss how the heparanase enzyme can modulate the effects triggered by HSPG. Additionally, we will also navigate about the existing knowledge of the possible role of heparanase-2 in biological events. Heparan sulfate is widely distributed and evolutionarily conserved, evidencing its vital importance in cell development and functions such as cell proliferation, migration, adhesion, differentiation, and angiogenesis. During remodeling of the extracellular matrix, the breakdown of heparan sulfate by heparanase results in the release of molecules containing anchored glycosaminoglycan chains of great interest in heparanase-mediated cell signaling pathways in various physiological states, tumor development, inflammation, and other diseases. Taken together, it appears that heparanase plays a key role in the maintenance of the pathology of cancer and inflammatory diseases and is a potential target for anti-cancer therapies. Therefore, heparanase inhibitors are currently being examined in clinical trials as novel cancer therapeutics. Heparanase-2 has no enzymatic activity, displays higher affinity for heparan sulfate and the coding region alignment shows 40% identity with the heparanase gene. Heparanase-2 plays an important role in embryogenic development however its mode of action and biological function remain to be elucidated. Heparanase-2 functions as an inhibitor of the heparanase-1 enzyme and also inhibits neovascularization mediated by VEGF. The HPSE2 gene is repressed by the Polycomb complex, together suggesting a role as a tumor suppressor.

Nanomedicine - a promising therapy for hematological malignancies

Hematological tumors are a group of diseases defined as the clonal proliferation of blood-forming cells. In recent years, incidences of hematological malignancies have increased. Traditional methods of diagnosing hematological tumors are primarily based on observing morphological features under light microscopy, and molecular diagnostics and immunological indicators are powerful auxiliary diagnostic methods. However, traditional methods cannot efficiently identify tumor markers and limit the efficiency and accuracy of diagnosis. Although treatment methods have been improved continuously, chemotherapy remains a primary technique for the treatment of hematological tumors. Traditional chemotherapy exhibits poor drug selectivity and lacks good biocompatibility and pharmacokinetic properties. The therapeutic effect is not ideal and the risk of toxic side effects is high. The nanosize and surface charge properties of nanodrugs are effective in improving drug delivery efficiency. The high load and rich surface modification methods of nanomaterials provide various possibilities for improving the biocompatibility and pharmacokinetics of drugs, as well as the targeting of drugs. In addition, a nanomedicine loading platform can load multiple drugs simultaneously and design the optimal proportion of combined drug schemes, which can improve the efficacy of drugs and reduce the occurrence of drug resistance. With their unique physical and chemical properties and biological characteristics, the application of nanoparticles in the diagnosis and treatment of hematological tumors has received considerable attention. In this review, we summarize recent advances in the application of various types of nanostructures for the diagnosis and treatment of hematological malignancies, investigate the advantages of nanomedicine compared with the traditional diagnosis and treatment of hematological tumors, and discuss their biological security and application prospects.

Antitumor activity and structure-activity relationship of heparanase inhibitors: Recent advances

Heparanase (HPSE)-directed tumor progression plays a crucial role in mediating tumor-host crosstalk and priming the tumor microenvironment, leading to tumor growth, metastasis and chemo-resistance. HPSE-mediated breakdown of structural heparan sulfate (HS) networks in the extracellular matrix (ECM) and basement membranes (BM) directly facilitates tumor growth and metastasis. Lysosome HPSE also induces multi-drug resistance via enhanced autophagy. Therefore, HPSE inhibitors development has become an attractive topic to block tumor growth and metastasis or eliminate drug resistance. In this review, we summarize HPSE inhibitors applied experimentally and clinically according to interaction with the binding sites of HPSE and participation of growth factors. The antitumor activity and structure-activity relationship (SAR) are also emphasized.

Heparanase: A Challenging Cancer Drug Target

Heparanase has been viewed as a promising anti-cancer drug target for almost two decades, but no anti-heparanase therapy has yet reached the clinic. This endoglycosidase is highly expressed in a variety of malignancies, and its high expression is associated with greater tumor size, more metastases, and a poor prognosis. It was first described as an enzyme cleaving heparan sulfate chains of proteoglycans located in extracellular matrices and on cell surfaces, but this is not its only function. It is a multi-functional protein with activities that are enzymatic and non-enzymatic and which take place both outside of the cell and intracellularly. Knowledge of the crystal structure of heparanase has assisted the interpretation of earlier structure-function studies as well as in the design of potential anti-heparanase agents. This review re-examines the various functions of heparanase in light of the structural data. The functions of the heparanase variant, T5, and structure and functions of heparanase-2 are also examined as these heparanase related, but non-enzymatic, proteins are likely to influence the in vivo efficacy of anti-heparanase drugs. The anti-heparanase drugs currently under development predominately focus on inhibiting the enzymatic activity of heparanase, which, in the absence of inhibitors with high clinical efficacy, prompts a discussion of whether this is the best approach. The diversity of outcomes attributed to heparanase and the difficulties of unequivocally determining which of these are due to its enzymatic activity is also discussed and leads us to the conclusion that heparanase is a valid, but challenging drug target for cancer.

Bringing Heparan Sulfate Glycomics Together with Proteomics for the Design of Novel Therapeutics: A Historical Perspective

Increasing knowledge of how peptides bind saccharides, and of how saccharides bind peptides, is starting to revolutionize understanding of cell-extracellular matrix relationships. Here, a historical perspective is taken of the relationship between heparan sulfate glycosaminoglycans and how they interact with peptide growth factors in order to both drive and modulate signaling through the appropriate cognate receptors. Such knowledge is guiding the preparation of targeted sugar mimetics that will impact the treatment of many different kinds of diseases, including cancer.