Design and Synthesis of 1,3-Diarylpyrazoles and Investigation of Their Cytotoxicity and Antiparasitic Profile.

Herein, we report a series of 1,3-diarylpyrazoles that are analogues of compound 26/HIT 8. We previously identified this molecule as a 'hit' during a high-throughput screening campaign for autophagy inducers. A variety of synthetic strategies were utilized to modify the 1,3-diarylpyrazole core at its 1-, 3-, and 4-position. Compounds were assessed in vitro to identify their cytotoxicity properties. Of note, several compounds in the series displayed relevant cytotoxicity, which warrants scrutiny while interpreting biological activities that have been reported for structurally related molecules. In addition, antiparasitic activities were recorded against a range of human-infective protozoa, including Trypanosoma cruzi, T. brucei rhodesiense, and Leishmania infantum. The most interesting compounds displayed low micromolar whole-cell potencies against individual or several parasitic species, while lacking cytotoxicity against human cells.

Partial Inhibition of Glycolysis Reduces Atherogenesis Independent of Intraplaque Neovascularization in Mice.

OBJECTIVE: Intraplaque neovascularization is an important feature of unstable human atherosclerotic plaques. However, its impact on plaque formation and stability is poorly studied. Because proliferating endothelial cells generate up to 85% of their ATP from glycolysis, we investigated whether pharmacological inhibition of glycolytic flux by the small-molecule 3PO (3-[3-pyridinyl]-1-[4-pyridinyl]-2-propen-1-one) could have beneficial effects on plaque formation and composition. Approach and Results: ApoE-/- (apolipoprotein E deficient) mice treated with 3PO (50 µg/g, ip; 4×/wk, 4 weeks) showed a metabolic switch toward ketone body formation. Treatment of ApoE-/-Fbn1C1039G+/- mice with 3PO (50 µg/g, ip) either after 4 (preventive, twice/wk, 10 weeks) or 16 weeks of Western diet (curative, 4×/wk, 4 weeks) inhibited intraplaque neovascularization by 50% and 38%, respectively. Plaque formation was significantly reduced in all 3PO-treated animals. This effect was independent of intraplaque neovascularization. In vitro experiments showed that 3PO favors an anti-inflammatory M2 macrophage subtype and suppresses an M1 proinflammatory phenotype. Moreover, 3PO induced autophagy, which in turn impaired NF-κB (nuclear factor-kappa B) signaling and inhibited TNF-α (tumor necrosis factor-alpha)-mediated VCAM-1 (vascular cell adhesion molecule-1) and ICAM-1 (intercellular adhesion molecule-1) upregulation. Consistently, a preventive 3PO regimen reduced endothelial VCAM-1 expression in vivo. Furthermore, 3PO improved cardiac function in ApoE-/-Fbn1C1039G+/- mice after 10 weeks of treatment. CONCLUSIONS: Partial inhibition of glycolysis restrained intraplaque angiogenesis without affecting plaque composition. However, less plaques were formed, which was accompanied by downregulation of endothelial adhesion molecules-an event that depends on autophagy induction. Inhibition of coronary plaque formation by 3PO resulted in an overall improved cardiac function.

Molecular Imaging of Apoptosis: The Case of Caspase-3 Radiotracers.

The molecular imaging of apoptosis remains an important method for the diagnosis and monitoring of the progression of certain diseases and the evaluation of the efficacy of anticancer apoptosis-inducing therapies. Among the multiple biomarkers involved in apoptosis, activated caspase-3 is an attractive target, as it is the most abundant of the executioner caspases. Nuclear imaging is a good candidate, as it combines a high depth of tissue penetration and high sensitivity, features necessary to detect small changes in levels of apoptosis. However, designing a caspase-3 radiotracer comes with challenges, such as selectivity, cell permeability and transient caspase-3 activation. In this review, we discuss the different caspase-3 radiotracers for the imaging of apoptosis together with the challenges of the translation of various apoptosis-imaging strategies in clinical trials.

Prolyl Carboxypeptidase Mediates the C-Terminal Cleavage of (Pyr)-Apelin-13 in Human Umbilical Vein and Aortic Endothelial Cells.

The aim of this study was to investigate the C-terminal cleavage of (pyr)-apelin-13 in human endothelial cells with respect to the role and subcellular location of prolyl carboxypeptidase (PRCP). Human umbilical vein and aortic endothelial cells, pre-treated with prolyl carboxypeptidase-inhibitor compound 8o and/or angiotensin converting enzyme 2 (ACE2)-inhibitor DX600, were incubated with (pyr)-apelin-13 for different time periods. Cleavage products of (pyr)-apelin-13 in the supernatant were identified by mass spectrometry. The subcellular location of PRCP was examined via immunocytochemistry. In addition, PRCP activity was measured in supernatants and cell lysates of LPS-, TNFα-, and IL-1ß-stimulated cells. PRCP cleaved (pyr)-apelin-13 in human umbilical vein and aortic endothelial cells, while ACE2 only contributed to this cleavage in aortic endothelial cells. PRCP was found in endothelial cell lysosomes. Pro-inflammatory stimulation induced the secretion of PRCP in the extracellular environment of endothelial cells, while its intracellular level remained intact. In conclusion, PRCP, observed in endothelial lysosomes, is responsible for the C-terminal cleavage of (pyr)-apelin-13 in human umbilical vein endothelial cells, while in aortic endothelial cells ACE2 also contributes to this cleavage. These results pave the way to further elucidate the relevance of the C-terminal Phe of (pyr)-apelin-13.

In Vitro Evaluation of the Squaramide-Conjugated Fibroblast Activation Protein Inhibitor-Based Agents AAZTA5.SA.FAPi and DOTA.SA.FAPi.

Recently, the first squaramide-(SA) containing FAP inhibitor-derived radiotracers were introduced. DATA5m.SA.FAPi and DOTA.SA.FAPi with their non-radioactive complexes showed high affinity and selectivity for FAP. After a successful preclinical study with [68Ga]Ga-DOTA.SA.FAPi, the first patient studies were realized for both compounds. Here, we present a new squaramide-containing compound targeting FAP, based on the AAZTA5 chelator 1,4-bis-(carboxylmethyl)-6-[bis-(carboxymethyl)-amino-6-pentanoic-acid]-perhydro-1,4-diazepine. For this molecule (AAZTA5.SA.FAPi), complexation with radionuclides such as gallium-68, scandium-44, and lutetium-177 was investigated, and the in vitro properties of the complexes were characterized and compared with those of DOTA.SA.FAPi. AAZTA5.SA.FAPi and its derivatives labelled with non-radioactive isotopes demonstrated similar excellent inhibitory potencies compared to the previously published SA.FAPi ligands, i.e., sub-nanomolar IC50 values for FAP and high selectivity indices over the serine proteases PREP and DPPs. Labeling with all three radiometals was easier and faster with AAZTA5.SA.FAPi compared to the corresponding DOTA analogue at ambient temperature. Especially, scandium-44 labeling with the AAZTA derivative resulted in higher specific activities. Both DOTA.SA.FAPi and AAZTA5.SA.FAPi showed sufficiently high stability in different media. Therefore, these FAP inhibitor agents could be promising for theranostic approaches targeting FAP.

Efforts towards an On-Target Version of the Groebke-Blackburn-Bienaymé (GBB) Reaction for Discovery of Druglike Urokinase (uPA) Inhibitors.

Target-guided synthesis (TGS) has emerged as a promising strategy in drug discovery. Although reported examples of TGS generally involve two-component reactions, there is a strong case for developing target-guided versions of three-component reactions (3CRs) because of their potential to deliver highly diversified druglike molecules. To this end, the Groebke-Blackburn-Bienaymé reaction was selected as a model 3CR. We recently reported a series of druglike urokinase inhibitors, and these serve as reference compounds in the present study. Due to the limited number of literature reports on target-guided 3CRs, multiple experimental parameters were optimized here. Most challenging was the formation of imine intermediates under near-physiological conditions. This aspect was addressed by exploring chemical imine stabilization strategies. Notably, imines are also crucial intermediates of other 3CRs. Such systematic studies are strongly required for further development of the TGS domain but are largely absent in the literature. Hence, this work is intended as a reference for future multicomponent-based TGS studies.

Caspase-3 probes for PET imaging of apoptotic tumor response to anticancer therapy.

Apoptosis is a highly regulated process involved in the normal organism development and homeostasis. In the context of anticancer therapy, apoptosis is also studied intensively in an attempt to induce cell death in cancer cells. Caspase activation is a known key event in the apoptotic process. In particular, active caspase-3 and -7 are the common effectors in several apoptotic pathways, therefore effector caspase activation may be a promising biomarker for response evaluation to anticancer therapy. Quantitative imaging of apoptosis in vivo could provide early assessment of therapeutic effectiveness and could also be used in drug development to evaluate the efficacy as well as potential toxicity of novel treatments. Positron Emission Tomography (PET) is a highly sensitive molecular imaging modality that allows non-invasive in vivo imaging of biological processes such as apoptosis by using radiolabeled probes. Here we describe the development and evaluation of fluorine-18-labeled caspase-3 activity-based probes (ABPs) for PET imaging of apoptosis. ABPs were selected by screening of a small library of fluorine-19-labeled DEVD peptides containing different electrophilic warhead groups. An acyloxymethyl ketone was identified with low nanomolar affinity for caspase-3 and was radiolabeled with fluorine-18. The resulting radiotracer, [18F]MICA-302, showed good labeling of active caspase-3 in vitro and favorable pharmacokinetic properties. A µPET imaging experiment in colorectal tumor xenografts demonstrated an increased tumor accumulation of [18F]MICA-302 in drug-treated versus control animals. Therefore, our data suggest this radiotracer may be useful for clinical PET imaging of response to anticancer therapy.

Synthesis and evaluation of novel benzotropolones as Atg4B inhibiting autophagy blockers.

Autophagy is an intracellular degradation/recycling pathway that provides nutrients and building blocks to cellular metabolism and keeps the cytoplasm clear of obsolete proteins and organelles. During recent years, dysregulated autophagy activity has been reported to be a characteristic of many different disease types, including cancer and neurodegenerative disorders. This has created a strong case for development of autophagy modulating compounds as potential treatments for these diseases. Inhibitors of autophagy have been proposed as a therapeutic intervention in, e.g., advanced cancer, and inhibiting the cysteine protease Atg4B has been put forward as a main strategy to block autophagy. We recently identified and demonstrated -both in vitro and in vivo - that compounds with a benzotropolone basic structure targeting Atg4B, can significantly slow down tumor growth and potentiate the effect of classical chemotherapy. In this study we report the synthesis and inhibition profile of new benzotropolone derivatives with additional structural modifications at 6 different positions. To obtain a solid inhibition profile, all compounds were evaluated on three levels, including two cell-based assays to confirm autophagy and intracellular Atg4B inhibition and an SDS-PAGE-based experiment to assess in vitro Atg4B affinity. Several molecules with a promising profile were identified.

ClpP Protease, a Promising Antimicrobial Target.

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.

Evaluation of [18 F]BR420 and [18 F]BR351 as radiotracers for MMP-9 imaging in colorectal cancer.

MMP-9 is a zinc-dependent endopeptidase that is involved in the proteolytic degradation of the extracellular matrix and plays an important role in cancer migration, invasion, and metastasis. The aim of this study was to evaluate the potential of MMP-tracers [18 F]BR420 and [18 F]BR351 for MMP-9 imaging in a colorectal cancer xenograft model. [18 F]BR420 and [18 F]BR351 were synthesized using an automated synthesis module. For [18 F]BR420, a novel and improved radiosynthesis was developed. Plasma stability and MMP-9-targeting capacity of both radiotracers was compared in the Colo205 colorectal cancer model. MMP-9 and MMP-2 expression levels in the tumors were evaluated by immunohistochemistry and in situ zymography. µPET imaging as well as ex vivo biodistribution revealed a higher tumor uptake for [18 F]BR420 (3.15% ± 0.03% ID/g vs 0.94% ± 0.18% ID/g for [18 F]BR351 at 2 hours pi) but slower blood clearance compared with [18 F]BR351. [18 F]BR351 was quickly metabolized in plasma with 20.28% ± 5.41% of intact tracer remaining at 15 minutes postinjection (PI). By contrast, [18 F]BR420 displayed a higher metabolic stability with >86% intact tracer remaining at 2 hours PI. Immunohistochemistry revealed the presence of MMP-9 and MMP-2 in the tumor tissue, which was confirmed by in situ zymography. However, an autoradiography analysis of tracer distribution in the tumors did not correlate with MMP-9 expression. [18 F]BR420 displayed a higher tumor uptake and higher stability compared with [18 F]BR351 but a low tumor-to-blood ratio and discrepancy between tracer distribution and MMP-9 immunohistochemistry. Therefore, both tracers will not be usefulness for MMP-9 imaging in colorectal cancer.

Resistance and cross-resistance profile of the diaryltriazine NNRTI and candidate microbicide UAMC01398.

OBJECTIVES: The resistance development, cross-resistance to other NNRTIs and the impact of resistance on viral replicative fitness were studied for the new and potent NNRTI UAMC01398. METHODS: Resistance was selected by dose escalation and by single high-dose selection against a comprehensive panel of NNRTIs used as therapeutics and NNRTIs under investigation for pre-exposure prophylaxis of sexual HIV transmission. A panel of 27 site-directed mutants with single mutations or combinations of mutations involved in reverse transcriptase (RT) inhibitor-mediated resistance was developed and used to confirm resistance to UAMC01398. Cross-resistance to other NNRTIs was assessed, as well as susceptibility of UAMC01398-resistant HIV to diarylpyrimidine-resistant viruses. Finally, the impact of UAMC01398 resistance on HIV replicative fitness was studied. RESULTS: We showed that UAMC01398 has potent activity against dapivirine-resistant HIV, that at least four mutations in the RT are required in concert for resistance and that the resistance profile is similar to rilpivirine, both genotypically and phenotypically. Resistance development to UAMC01398 is associated with a severe fitness cost. CONCLUSIONS: These data, together with the enhanced safety profile and good solubility in aqueous gels, make UAMC01398 an excellent candidate for HIV topical prevention.

Increased tissue and circulating levels of dipeptidyl peptidase-IV enzymatic activity in patients with pancreatic ductal adenocarcinoma.

BACKGROUND/OBJECTIVES: Pancreatic ductal adenocarcinoma (PDAC) is frequently heralded by an impairment of glucose homeostasis. Dipeptidyl peptidase-IV (DPP-IV) and fibroblast activation protein alpha (FAP) are aminopeptidases that regulate several bioactive peptides involved in glucoregulation, and are frequently dysregulated in cancer. The present study analyzes blood plasma levels and the quantity and localization of DPP-IV and FAP in PDAC tissues. METHODS: DPP-IV and FAP concentration and enzymatic activity were evaluated in the plasma from 93 PDAC, 39 type 2 diabetes mellitus (T2DM) and 29 control subjects, and in matched paired non-tumorous and tumor tissues from 48 PDAC patients. The localization of DPP-IV and FAP was determined using immunohistochemistry and catalytic histochemistry. RESULTS: The enzymatic activity and concentration of DPP-IV was higher in PDAC tumor tissues compared to non-tumorous pancreas. DPP-IV was expressed in cancer cells and in the fibrotic stroma by activated (myo)fibroblasts including DPP-IV(+)FAP(+) cells. FAP was expressed in stromal cells and in some cancer cells and its expression was increased in the tumors. Plasmatic DPP-IV enzymatic activity, and in particular the ratio between DPP-IV enzymatic activity and concentration in PDAC with recent onset DM was higher compared to T2DM. In contrast, the plasmatic FAP enzymatic activity was lower in PDAC compared to T2DM and controls and rose after tumor removal. CONCLUSIONS: DPP-IV-like enzymatic activity is upregulated in PDAC tissues. PDAC patients with recent onset diabetes or prediabetes have increased plasmatic DPP-IV enzymatic activity. These changes may contribute to the frequently observed association of PDAC and recent onset impairment of glucoregulation.

Novel selective glucocorticoid receptor agonists (SEGRAs) with a covalent warhead for long-lasting inhibition.

The synthesis and in vitro properties of six analogues of the selective glucocorticoid receptor (GR) agonist GSK866, bearing a warhead for covalent linkage to the glucocorticoid receptor, is described.

Development of a novel antibody-tetrazine conjugate for bioorthogonal pretargeting.

Recently, bioorthogonal chemistry based on the Inverse Electron-Demand Diels-Alder (IEDDA) cycloaddition between 1,2,4,5-tetrazines and trans-cyclooctene (TCO) analogues added an interesting dimension to molecular imaging. Until now, antibodies (Abs) were tagged with TCO and after pretargeting they were reacted with tetrazines substituted with reporters. However, TCO tags have the tendency to degrade under physiological conditions, and due to their hydrophobic nature are buried within the protein. This results in loss of reactivity and a low Ab functional loading. To circumvent these problems, we report for the first time an approach in which tetrazines are used as tags for antibody (Ab) modification, and TCO as the imaging agent. We developed a new Ab-tetrazine conjugate, which displays a high functional loading, good stability and reactivity. We utilized this immunoconjugate for live-cell imaging together with novel TCO probes, resulting in selective and rapid labeling of SKOV-3 cells. Our approach may be useful for in vivo pretargeted imaging.

Repositioning the substrate activity screening (SAS) approach as a fragment-based method for identification of weak binders.

Fragment-based drug discovery (FBDD) has evolved into an established approach for "hit" identification. Typically, most applications of FBDD depend on specialised cost- and time-intensive biophysical techniques. The substrate activity screening (SAS) approach has been proposed as a relatively cheap and straightforward alternative for identification of fragments for enzyme inhibitors. We have investigated SAS for the discovery of inhibitors of oncology target urokinase (uPA). Although our results support the key hypotheses of SAS, we also encountered a number of unreported limitations. In response, we propose an efficient modified methodology: "MSAS" (modified substrate activity screening). MSAS circumvents the limitations of SAS and broadens its scope by providing additional fragments and more coherent SAR data. As well as presenting and validating MSAS, this study expands existing SAR knowledge for the S1 pocket of uPA and reports new reversible and irreversible uPA inhibitor scaffolds.

From human immunodeficiency virus non-nucleoside reverse transcriptase inhibitors to potent and selective antitrypanosomal compounds.

The presence of a structural recognition motif for the nucleoside P2 transporter in a library of pyrimidine and triazine non-nucleoside HIV-1 reverse transcriptase inhibitors, prompted for the evaluation of antitrypanosomal activity. It was demonstrated that the structure-activity relationship for anti-HIV and antitrypanosomal activity was different. Optimization in the diaryl triazine series led to 6-(mesityloxy)-N2-phenyl-1,3,5-triazine-2,4-diamine (69), a compound with potent in vitro and moderate in vivo antitrypanosomal activity.

UPLC-TQD-MS/MS Method Validation for Quality Control of Alkaloid Content in Lepidium meyenii (Maca)-Containing Food and Dietary Supplements.

Lepidium meyenii Walp. (Brassicaceae), also known as Maca or Peruvian ginseng, is a common ingredient in food supplements with many claimed health benefits, such as improved endurance, increased energy level, and enhanced sexual properties. Due to potential toxicity of its chemicals, including alkaloids, some regulatory authorities, e.g., in Belgium, Germany, the United States, expressed concerns about the safe consumption of Maca root. However, due to the lack of commercial standards, no established analytical method currently exists for this purpose. The current project focuses on the quantitative determination of potentially toxic alkaloids from Maca. The current study presents the first analytical method for quality control of alkaloid content in Maca-containing food and dietary supplements, assessing the presence of 11 major compounds belonging to three different classes, i.e., imidazole, ß-carboline, and pyrrole alkaloids. An accurate, rapid, and sensitive UPLC-TQD-MS/MS method is reported, which was fully validated according to the International Council for Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) and SANTE/11312/2021 guidelines. To ensure the method's applicability and practicability in the absence of primary standards, validation of secondary standards (SSs) alongside primary standards (PSs) was also conducted for imidazole alkaloids. As a result, in Maca raw powder, total alkaloid content was found to vary from 418 to 554 ppm (mg/kg). Furthermore, all quantified imidazole alkaloids were ascertained to be the major alkaloids with the total content from 323 to 470 ppm in Maca raw powder, followed by the ß-carboline and pyrrole alkaloids. It was also observed that the commercial preparation of finished products affects the total alkaloid content, evidenced by the large variation from 56 to 598 ppm. Ultimately, from a regulatory point of view, it seems advisible not to request the complete absence of the alkaloids but to impose a maximum level based on safety considerations. In addition to the analytical method, a low-cost, simple, and scalable synthetic scheme of macapyrrolins A, C, and G was reported for the first time.

Study of the Conformational Dynamics of Prolyl Oligopeptidase by Mass Spectrometry: Lessons Learned.

Ion mobility mass spectrometry (IM-MS) can be used to analyze native proteins according to their size and shape. By sampling individual molecules, it allows us to study mixtures of conformations, as long as they have different collision cross sections and maintain their native conformation after dehydration and vaporization in the mass spectrometer. Even though conformational heterogeneity of prolyl oligopeptidase has been demonstrated in solution, it is not detectable in IM-MS. Factors that affect the conformation in solution, binding of an active site ligand, the stabilizing Ser554Ala mutation, and acidification do not qualitatively affect the collision-induced unfolding pattern. However, measuring the protection of accessible cysteines upon ligand binding provides a principle for the development of MS-based ligand screening methods.

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.

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.