Furin-targeting activity-based probes with phosphonate and phosphinate esters as warheads

Granzyme-targeting quenched activity-based probes for assessing tumor response to immunotherapy

Molecular imaging of immune activation holds tremendous potential for the development of novel immunotherapy. In particular, chemical probes capable of detecting immune responses before changes in tumor size occur can guide early therapeutic strategies. Here, we present quenched activity-based probes targeting granzymes as a biomarker of antitumor immunity. Through optimization of peptide recognition element and functional chemical warhead, we have developed an optical imaging probe Cy5-IEPCyaPhP-QSY21, which rapidly reacts with GzmB at substoichiometric concentrations and enables efficient, selective labeling of the active enzyme in a complex proteome. With high specificity and minimal background signal, this probe produces GzmB-induced near-infrared fluorescence signals in the tumors of living mice shortly after injection. Both in vivo and ex vivo fluorescence signals correlate with GzmB expression and activity, and the population of CD8+ cells in tumor tissues. Moreover, it demonstrates the potential to track tumor response to immunotherapy. Thus, this study offers a chemical tool for assessing immune-mediated anticancer activity using noninvasive optical imaging.

Covalent activity-based probes for imaging of serine proteases

Serine proteases are one of the largest mechanistic classes of proteases. They regulate a plethora of biochemical pathways inside and outside the cell. Aberrant serine protease activity leads to a wide variety of human diseases. Reagents to visualize these activities can be used to gain insight into the biological roles of serine proteases. Moreover, they may find future use for the detection of serine proteases as biomarkers. In this review, we discuss small molecule tools to image serine protease activity. Specifically, we outline different covalent activity-based probes and their selectivity against various serine protease targets. We also describe their application in several imaging methods.