Active site-directed probes targeting dipeptidyl peptidases 8 and 9.

Dipeptidyl peptidases (DPP) 8 and 9 are intracellular serine proteases that play key roles in various biological processes and recent findings highlight DPP8 and DPP9 as potential therapeutic targets for hematological and inflammasome-related diseases. Despite the substantial progress, the precise biological functions of these proteases remain elusive, and the lack of selective chemical tools hampers ongoing research. In this paper, we describe the synthesis and biochemical evaluation of the first active site-directed DPP8/9 probes which are derived from DPP8/9 inhibitors developed in-house. Specifically, we synthesized fluorescent inhibitors containing nitrobenzoxadiazole (NBD), dansyl (DNS) and cyanine-3 (Cy3) reporters to visualize intracellular DPP8/9. We demonstrate that the fluorescent inhibitors have high affinity and selectivity towards DPP8/9 over related S9 family members. The NBD-labeled DPP8/9 inhibitors were nominated as the best in class compounds to visualize DPP8/9 in human cells. Furthermore, a method has been developed for selective labeling and visualization of active DPP8/9 in vitro by fluorescence microscopy. A collection of potent and selective biotinylated DPP8/9-targeting probes was also prepared by replacing the fluorescent reporter with a biotin group. The present work provides the first DPP8/9-targeting fluorescent compounds as useful chemical tools for the study of DPP8 and DPP9's biological functions.

Druglike, 18F-labeled PET Tracers Targeting Fibroblast Activation Protein.

Fibroblast activation protein (FAP) is a very reliable biomarker for tissue remodeling. FAP has so far mainly been studied in oncology, but there is growing interest in the enzyme in other diseases like fibrosis. Recently, FAP-targeting diagnostics and therapeutics have emerged, of which the so-called FAPIs are among the most promising representatives. FAPIs typically have a relatively high molecular weight and contain very polar, multicharged chelator moieties. While this is not limiting the application of FAPIs in oncology, more druglike FAPIs could be required to optimally study diseases characterized by denser, less permeable tissue. In response, we designed the first druglike 18F-labeled FAPIs. We report target potencies, biodistribution, and pharmacokinetics and demonstrate FAP-dependent uptake in murine tumor xenografts. Finally, this paper puts forward compound 10 as a highly promising, druglike FAPI for 18F-PET imaging. This molecule is fit for additional studies in fibrosis and its preclinical profile warrants clinical investigation.

Highly Selective Inhibitors of Dipeptidyl Peptidase 9 (DPP9) Derived from the Clinically Used DPP4-Inhibitor Vildagliptin.

Dipeptidyl peptidase 9 (DPP9) is a proline-selective serine protease that plays a key role in NLRP1- and CARD8-mediated inflammatory cell death (pyroptosis). No selective inhibitors have hitherto been reported for the enzyme: all published molecules have grossly comparable affinities for DPP8 and 9 because of the highly similar architecture of these enzymes' active sites. Selective DPP9 inhibitors would be highly instrumental to address unanswered research questions on the enzyme's role in pyroptosis, and they could also be investigated as therapeutics for acute myeloid leukemias. Compounds presented in this manuscript (42 and 47) combine low nanomolar DPP9 affinities with unprecedented DPP9-to-DPP8 selectivity indices up to 175 and selectivity indices >1000 toward all other proline-selective proteases. To rationalize experimentally obtained data, a molecular dynamics study was performed. We also provide in vivo pharmacokinetics data for compound 42.