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...

Cysteine cathepsins are proteases critical in physiopathological processes and show potential as targets or biomarkers for diseases and medical conditions. The 11 members of the cathepsin family are redundant in...

Fluorophores experience altered emission lifetimes when incorporated into and liberated from macromolecules or molecular aggregates; this trend suggests the potential for a fluorescent, responsive probe capable of undergoing self‐assembly and aggregation and consequently altering the lifetime of its fluorescent moiety to provide contrast between the active and inactive probes. We developed a cyanobenzothioazole‐fluorescein conjugate (1), and spectroscopically examined the lifetime changes caused by its reduction‐induced aggregation in vitro. A decrease in lifetime was observed for compound 1 in a buffered system activated by the biological reducing agent glutathione, thus suggesting a possible approach for designing responsive self‐aggregating lifetime imaging probes.

Heparanase is a critical enzyme involved in the remodeling of the extracellular matrix (ECM), and its elevated expression has been linked with diseases such as 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, assays developed for this enzyme so far have suffered prohibitive drawbacks. Here we present an ultrasensitive fluorogenic small-molecule probe for heparanase enzymatic activity. 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, an endo-β-glucuronidase of the glycoside hydrolase 79 (GH79) family 1,2 , is responsible for the cleavage of heparan sulfate (HS) chains of heparan sulfate proteoglycans (HSPG) 3 . These protein-polysaccharide conjugated macromolecules, abundantly expressed in the extracellular matrix (ECM), play an essential structural role in maintaining the ECM integrity.Moreover, the HS side chains bind to an array of biological effector molecules, such as growth factors, chemokines, and cytokines, thereby serving as their reservoir that can liberate the desired signaling molecules when needed.

Fluorophores are greatly influenced by their environment. In their full paper, L. Cui et al. show that triggering the aggregation of a self‐condensing scaffold labeled with a fluorophore induces changes in the emission spectrum, polarization, and lifetime. The aggregates exhibited a shorter lifetime detectable in cells by fluorescence lifetime imaging microscopy, thus suggesting that triggered aggregation strategies can be used in the probes for various biological events through lifetime imaging.

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.

Fluorophores experience altered emission lifetimes when incorporated into and liberated from macromolecules or molecular aggregates; this trend suggests the potential for a fluorescent, responsive probe capable of undergoing self-assembly and aggregation and consequently altering the lifetime of its fluorescent moiety to provide contrast between the active and inactive probes. We developed a cyanobenzothioazole-fluorescein conjugate (1), and spectroscopically examined the lifetime changes caused by its reduction-induced aggregation in vitro. A decrease in lifetime was observed for compound 1 in a buffered system activated using the biological reducing agent glutathione, suggesting a possible approach for designing responsive self-aggregating lifetime imaging probes.

Substrate-based probes utilize known substrate specificity parameters to create a probe that can be activated by a target enzyme. In developing probes for heparanase, an endo-beta-glucuronidase, we previously reported that small, inactive substrate-based probes could be electronically tuned by incorporating electron-withdrawing atoms on the aromatic aglycone fluorophore, ortho- to the cleaved glycosidic bond. However, the installation of electron-withdrawing groups directly onto established fluorophores or other reporters complicates the synthesis of new heparanase probes. In this work we report a new design strategy to expand the toolkit of heparanase imaging probes, in which the installation of an electronically tuned benzyl alcohol linker restored the activity of a previously inactive heparanase probe using 4-methylumbelliferone as the fluorescent reporter, suggesting such a linker can provide a scaffold for facile development of activatable heparanase probes bearing a variety of imaging moieties.