Background: Fibroblast activation protein (FAP) is a proline selective serine protease that is overexpressed in tumor stroma and in lesions of many other diseases that are characterized by tissue remodeling. In 2014, a most potent FAP-inhibitor (referred to as UAMC1110) with low nanomolar FAP-affinity and high selectivity toward related enzymes such as prolyl oligopeptidase (PREP) and the dipeptidyl-peptidases (DPPs): DPP4, DPP8/9 and DPP2 were developed. This inhibitor has been adopted recently by other groups to create radiopharmaceuticals by coupling bifunctional chelatorlinker systems. Here, we report squaric acid (SA) containing bifunctional DATA 5m and DOTA chelators based on UAMC1110 as pharmacophor. The novel radiopharmaceuticals DOTA.SA.FAPi and DATA 5m .SA.FAPi with their non-radioactive derivatives were characterized for in vitro inhibitory efficiency to FAP and PREP, respectively and radiochemical investigated with gallium-68. Further, first proof-ofconcept in vivo animal study followed by ex vivo biodistribution were determined with [ 68 Ga]Ga-DOTA.SA.FAPi. Results: [ 68 Ga]Ga-DOTA.SA.FAPi and [ 68 Ga]Ga-DATA 5m .SA.FAPi showed high complexation > 97% radiochemical yields after already 10 min and high stability over a period of 2 h. Affinity to FAP of DOTA.SA.FAPi and DATA 5m .SA.FAPi and its nat Ga and nat Lu-labeled derivatives were excellent resulting in low nanomolar IC 50 values of 0.7-1.4 nM. Additionally, all five compounds showed low affinity for the related protease PREP (high IC 50 with 1.7-8.7 μM). First proof-of-principle in vivo PET-imaging animal studies of the [ 68 Ga]Ga-DOTA.SA.FAPi precursor in a HT-29 human colorectal cancer xenograft mouse model indicated promising results with high accumulation in tumor (SUV mean of 0.75) and low background signal. Ex vivo biodistribution showed highest uptake in tumor (5.2%ID/g) at 60 min post injection with overall low uptake in healthy tissues.

The caseinolytic protease proteolytic subunit (ClpP) is a serine protease playing an important role in proteostasis of eukaryotic organelles and prokaryotic cells. Alteration of ClpP function has been proved to affect the virulence and infectivity of a number of pathogens. Increased bacterial resistance to antibiotics has become a global problem and new classes of antibiotics with novel mechanisms of action are needed. In this regard, ClpP has emerged as an attractive and potentially viable option to tackle pathogen fitness without suffering cross-resistance to established antibiotic classes and, when not an essential target, without causing an evolutionary selection pressure. This opens a greater window of opportunity for the host immune system to clear the infection by itself or by co-administration with commonly prescribed antibiotics. A comprehensive overview of the function, regulation and structure of ClpP across the different organisms is given. Discussion about mechanism of action of this protease in bacterial pathogenesis and human diseases are outlined, focusing on the compounds developed in order to target the activation or inhibition of ClpP.

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Withaferin A (WA), a natural phytochemical derived from the plant Withania somnifera, is a well-studied bioactive compound exerting a broad spectrum of health promoting effects. To gain better insight in the potential therapeutic capacity of WA, we evaluated the transcriptional effects of WA on primary human umbilical vein endothelial cells (HUVECs) and an endothelial cell line (EA.hy926). RNA microarray analysis of WA treated HUVEC cells demonstrated increased expression of the antioxidant gene heme oxygenase (HO-1). Transcriptional regulation of this gene is strongly dependent on the transcription factor NF-E2-related factor 2 (Nrf2), which senses chemical changes in the cell and coordinates transcriptional responses to maintain chemical homeostasis via expression of antioxidant genes and cytoprotective Phase II detoxifying enzymes. Under normal conditions, Nrf2 is kept in the cytoplasm by Kelch-like ECH-associated protein 1 (Keap1), an adaptor protein controlling the half-life of Nrf2 via constant proteasomal degradation. In this study we demonstrate that WA time- and concentration-dependently induces HO-1 expression in endothelial cells via upregulation and increased nuclear translocation of Nrf2. According to the crucial negative regulatory role of Keap1 in Nrf2 expression levels, a direct interaction of WA with Keap1 could be demonstrated. In vitro and in silico evaluations suggest that specific cysteine residues in Keap1 might be involved in the interaction with WA.

This study shows that caspase-1 autocleavage, ASC speck assembly, and mature IL-1β and IL-18 secretion accompany rapid DPP8/DPP9-regulated pyroptosis induction in macrophages expressing a LeTx-responsive Nlrp1b allele.