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 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.

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.