Cathepsin B: Active site mapping with peptidic substrates and inhibitors

Synthesis and Evaluation of a Cathepsin B-Recognizing Trifunctional Chelating Agent to Improve Tumor Retention of Radioimmunoconjugates

Cathepsin B (CTSB) is a lysosomal protease that is overexpressed in tumor cells. Radioimmunoconjugates (RICs) composed of CTSB-recognizing chelating agents are expected to increase the molecular weights of their radiometabolites by forming conjugates with CTSB in cells, resulting in their improved retention in tumor cells. We designed a novel CTSB-recognizing trifunctional chelating agent, azide-[111In]In-DOTA-CTSB-substrate ([111In]In-ADCS), to synthesize a RIC, trastuzumab-[111In]In-ADCS ([111In]In-TADCS), and evaluated its utility to improve tumor retention of the RIC. [111In]In-ADCS and [111In]In-TADCS were synthesized with satisfactory yield and purity. [111In]In-ADCS was markedly stable in murine plasma until 96 h postincubation. [111In]In-ADCS showed binding to CTSB in vitro, and the conjugation was blocked by the addition of CTSB inhibitor. In the internalization assay, [111In]In-TADCS exhibited high-level retention in SK-OV-3 cells, indicating the in vitro utility of the CTSB-recognizing unit. In the biodistribution assay, [111In]In-TADCS showed high-level tumor accumulation, but the retention was hardly improved. In the first attempt to combine a CTSB-recognizing unit and RIC, these findings show the fundamental properties of the CTSB-recognizing trifunctional chelating agent to improve tumor retention of RICs.

Coordination chemistry suggests that independently observed benefits of metformin and Zn2+ against COVID-19 are not independent

Independent trials indicate that either oral Zn2+ or metformin can separately improve COVID-19 outcomes by approximately 40%. Coordination chemistry predicts a mechanistic relationship and therapeutic synergy. Zn2+ deficit is a known risk factor for both COVID-19 and non-infectious inflammation. Most dietary Zn2+ is not absorbed. Metformin is a naked ligand that presumably increases intestinal Zn2+ bioavailability and active absorption by cation transporters known to transport metformin. Intracellular Zn2+ provides a natural buffer of many protease reactions; the variable "set point" is determined by Zn2+ regulation or availability. A Zn2+-interactive protease network is suggested here. The two viral cysteine proteases are therapeutic targets against COVID-19. Viral and many host proteases are submaximally inhibited by exchangeable cell Zn2+. Inhibition of cysteine proteases can improve COVID-19 outcomes and non-infectious inflammation. Metformin reportedly enhances the natural moderating effect of Zn2+ on bioassayed proteome degradation. Firstly, the dissociable metformin-Zn2+ complex could be actively transported by intestinal cation transporters; thereby creating artificial pathways of absorption and increased body Zn2+ content. Secondly, metformin Zn2+ coordination can create a non-natural protease inhibitor independent of cell Zn2+ content. Moderation of peptidolytic reactions by either or both mechanisms could slow (a) viral multiplication (b) viral invasion and (c) the pathogenic host inflammatory response. These combined actions could allow development of acquired immunity to clear the infection before life-threatening inflammation. Nirmatrelvir (Paxlovid®) opposes COVID-19 by selective inhibition the viral main protease by a Zn2+-independent mechanism. Pending safety evaluation, predictable synergistic benefits of metformin and Zn2+, and perhaps metformin/Zn2+/Paxlovid® co-administration should be investigated.

Role of Cathepsin B Expression in Oral Squamous Cell Carcinoma: A Comprehensive Review

This comprehensive review delves into the intricate landscape of oral squamous cell carcinoma (OSCC) by examining the role of cathepsin B expression in its pathogenesis. OSCC, a prevalent and clinically significant oral malignancy, poses a considerable global health burden, necessitating a thorough exploration of its underlying molecular mechanisms. Cathepsin B, a lysosomal cysteine protease, emerges as a critical player in OSCC, influencing tumour initiation, invasion, and metastasis. The review begins with a brief overview of OSCC, emphasizing its epidemiological and clinical features, followed by exploring the significance of studying cathepsin B expression in this context. In the manuscript, the structure and function of cathepsin B are elucidated, providing a foundation for understanding its aberrant expression in OSCC. Clinical studies revealing correlations with tumour grade and stage, along with prognostic significance, are scrutinized, offering insights into the potential diagnostic and prognostic utility of cathepsin B. The biological functions of cathepsin B in OSCC, including its impact on tumour invasion and modulation of apoptosis, are comprehensively discussed. The Therapeutic Implications section explores targeting cathepsin B as a potential strategy, emphasizing the need for future research to overcome associated challenges. In the Conclusion section, the review synthesizes key findings, delineates implications for future research, and highlights the potential impact of cathepsin B on OSCC diagnosis and treatment, contributing to the ongoing efforts to advance our understanding of this complex malignancy, which is associated with a high mortality rate and improve clinical outcomes.

Structure-based discovery of dual pathway inhibitors for SARS-CoV-2 entry

Since 2019, SARS-CoV-2 has evolved rapidly and gained resistance to multiple therapeutics targeting the virus. Development of host-directed antivirals offers broad-spectrum intervention against different variants of concern. Host proteases, TMPRSS2 and CTSL/CTSB cleave the SARS-CoV-2 spike to play a crucial role in the two alternative pathways of viral entry and are characterized as promising pharmacological targets. Here, we identify compounds that show potent inhibition of these proteases and determine their complex structures with their respective targets. Furthermore, we show that applying inhibitors simultaneously that block both entry pathways has a synergistic antiviral effect. Notably, we devise a bispecific compound, 212-148, exhibiting the dual-inhibition ability of both TMPRSS2 and CTSL/CTSB, and demonstrate antiviral activity against various SARS-CoV-2 variants with different viral entry profiles. Our findings offer an alternative approach for the discovery of SARS-CoV-2 antivirals, as well as application for broad-spectrum treatment of viral pathogenic infections with similar entry pathways.

4-Cyanamido-substituted benzenesulfonamides act as dual carbonic anhydrase and cathepsin inhibitors

A set of novel N-cyano-N-substituted 4-aminobenzenesulfonamide derivatives were synthesized and investigated for their inhibitory activity against four cytosolic carbonic anhydrase (CA, EC 4.2.1.1) isoforms (hCA I, II, VII and XIII) and two cathepsins (S and B). N-alkyl/benzyl-substituted derivatives were revealed to be very potent inhibitors against brain-associated hCA VII, but inactive against both cathepsins. On the other hand, N-acyl-substituted derivatives displayed significant inhibitory activities against cathepsin S, but only moderate to poor inhibitory potency against hCA VII. Both hCA VII and cathepsin S have recently been validated as therapeutic targets in neuropathic pain. This study provided an excellent starting point for further structural optimization of this class of bifunctional compounds to enhance their inhibitory activity and selectivity against hCA VII and cathepsin S and to achieve new compounds with an attractive dual mechanism of action as anti-neuropathic agents.

E-64c-Hydrazide Based Cathepsin C Inhibitors: Optimizing the Interactions with the S1'-S2' Area

The zymogens of the neutrophil serine proteases elastase, proteinase 3, and cathepsin G are converted proteolytically into their pro-inflammatory active forms by the action of cathepsin C. The inhibition of this cysteine protease therefore is an interesting therapeutic approach for the treatment of inflammatory disorders with a high neutrophil burden such as COPD. Based on E-64c-hydrazide as lead structure, we have recently developed a covalently acting cathepsin C inhibitor using a n-butyl residue attached at the amine nitrogen of the hydrazide moiety to efficiently address the deep hydrophobic S2 pocket. To further optimize the affinity and selectivity profile of this inhibitor, the S1'-S2' area was now investigated by a combinatorial approach, showing that Nle-tryptamide is a ligand superior to the initially used Leu-isoamylamide. Using the neutrophil precursor line U937 as a cell culture model, this optimized inhibitor blocks the intracellular cathepsin C activity and thereby suppresses the activation of neutrophil elastase.

Synthetic Approaches of Epoxysuccinate Chemical Probes

Synthetic chemical probes are powerful tools for investigating biological processes. They are particularly useful for proteomic studies such as activity-based protein profiling (ABPP). These chemical methods initially used mimics of natural substrates. As the techniques gained prominence, more and more elaborate chemical probes with increased specificity towards given enzyme/protein families and amenability to various reaction conditions were used. Among the chemical probes, peptidyl-epoxysuccinates represent one of the first types of compounds used to investigate the activity of the cysteine protease papain-like family of enzymes. Structurally derived from the natural substrate, a wide body of inhibitors and activity- or affinity-based probes bearing the electrophilic oxirane unit for covalent labeling of active enzymes now exists. Herein, we review the literature regarding the synthetic approaches to epoxysuccinate-based chemical probes together with their reported applications, from biological chemistry and inhibition studies to supramolecular chemistry and the formation of protein arrays.

The Relationship Between Exercise, Cathepsin B, and Cognitive Functions: Systematic Review

Exercise has been shown repeatedly to improve cognitive functions. Many investigators have reported that peripheral signal molecules play an important role in regulating exercise-induced cognitive improvement. In this review we aimed to evaluate and clarify the literature to date that has focused on the relationship between Cathepsin B, cognitive functions, and exercise. We conducted a systematic review of the following databases from their inception until 10 April 2022: Pubmed, Web of Science, Scopus, Cochrane Library, Physiotherapy Evidence Database. The search strategy was comprised of ("cathepsin b") AND (exercise OR "physical activity") AND (cognit*). We followed three different quality appraisal tools to ensure the quality of the included studies. Eight studies assessing the effects of exercise on peripheral Cathepsin B levels and cognitive outcomes were included. Half of these studies indicated that exercise increased peripheral Cathepsin B levels and improved cognitive function. Further carefully designed studies focusing on the effects of exercise on peripheral Cathepsin B levels and cognitive performance are needed to better comprehend the underlying mechanisms of these relationships.

Smart Delivery Systems Responsive to Cathepsin B Activity for Cancer Treatment

Cathepsin B is a lysosomal cysteine protease, contributing to vital cellular homeostatic processes including protein turnover, macroautophagy of damaged organelles, antigen presentation, and in the extracellular space, it takes part in tissue remodeling, prohormone processing, and activation. However, aberrant overexpression of cathepsin B and its enzymatic activity is associated with different pathological conditions, including cancer. Cathepsin B overexpression in tumor tissues makes this enzyme an important target for smart delivery systems, responsive to the activity of this enzyme. The generation of technologies which therapeutic effect is activated as a result of cathepsin B cleavage provides an opportunity for tumor-targeted therapy and controlled drug release. In this review, we summarized different technologies designed to improve current cancer treatments responsive to the activity of this enzyme that were shown to play a key role in disease progression and response to the treatment.

Falcipains: Biochemistry, target validation and structure-activity relationship studies of inhibitors as antimalarials

Malaria is a tropical disease with significant morbidity and mortality burden caused by Plasmodium species in Africa, the Middle East, Asia, and South America. Pathogenic Plasmodium species have lately become increasingly resistant to approved chemotherapeutics and combination therapies. Therefore, there is an emergent need for identifying new druggable targets and novel chemical classes against the parasite. Falcipains, cysteine proteases required for heme metabolism in the erythrocytic stage, have emerged as promising drug targets against Plasmodium species that infect humans. This perspective discusses the biology, biochemistry, structural features, and genetics of falcipains. The efforts to identify selective or dual inhibitors and their structure-activity relationships are reviewed to give a perspective on the design of novel compounds targeting falcipains for antimalarial activity evaluating reasons for hits and misses for this important target.

Dipeptide-Derived Alkynes as Potent and Selective Irreversible Inhibitors of Cysteine Cathepsins

The potential of designing irreversible alkyne-based inhibitors of cysteine cathepsins by isoelectronic replacement in reversibly acting potent peptide nitriles was explored. The synthesis of the dipeptide alkynes was developed with special emphasis on stereochemically homogeneous products obtained in the Gilbert-Seyferth homologation for C≡C bond formation. Twenty-three dipeptide alkynes and 12 analogous nitriles were synthesized and investigated for their inhibition of cathepsins B, L, S, and K. Numerous combinations of residues at positions P1 and P2 as well as terminal acyl groups allowed for the derivation of extensive structure-activity relationships, which were rationalized by computational covalent docking for selected examples. The determined inactivation constants of the alkynes at the target enzymes span a range of >3 orders of magnitude (3-10 133 M^-1 s^-1). Notably, the selectivity profiles of alkynes do not necessarily reflect those of the nitriles. Inhibitory activity at the cellular level was demonstrated for selected compounds.

Cysteine Cathepsins in Breast Cancer: Promising Targets for Fluorescence-Guided Surgery

The majority of breast cancer patients is treated with breast-conserving surgery (BCS) combined with adjuvant radiation therapy. Up to 40% of patients has a tumor-positive resection margin after BCS, which necessitates re-resection or additional boost radiation. Cathepsin-targeted near-infrared fluorescence imaging during BCS could be used to detect residual cancer in the surgical cavity and guide additional resection, thereby preventing tumor-positive resection margins and associated mutilating treatments. The cysteine cathepsins are a family of proteases that play a major role in normal cellular physiology and neoplastic transformation. In breast cancer, the increased enzymatic activity and aberrant localization of many of the cysteine cathepsins drive tumor progression, proliferation, invasion, and metastasis. The upregulation of cysteine cathepsins in breast cancer cells indicates their potential as a target for intraoperative fluorescence imaging. This review provides a summary of the current knowledge on the role and expression of the most important cysteine cathepsins in breast cancer to better understand their potential as a target for fluorescence-guided surgery (FGS). In addition, it gives an overview of the cathepsin-targeted fluorescent probes that have been investigated preclinically and in breast cancer patients. The current review underscores that cysteine cathepsins are highly suitable molecular targets for FGS because of favorable expression and activity patterns in virtually all breast cancer subtypes. This is confirmed by cathepsin-targeted fluorescent probes that have been shown to facilitate in vivo breast cancer visualization and tumor resection in mouse models and breast cancer patients. These findings indicate that cathepsin-targeted FGS has potential to improve treatment outcomes in breast cancer patients.

Engineered, Scalable Production of Optically Pure l-Phenylalanines Using Phenylalanine Ammonia-Lyase from Arabidopsis thaliana

An efficient preparative-scale synthetic procedure of l-phenylalanine derivatives has been developed using mutant variants of phenylalanine ammonia-lyase from Arabidopsis thaliana (AtPAL). After rigorous reaction engineering, the AtPAL-catalyzed hydroamination reaction of cinnamic acids provided several unnatural amino acids of high synthetic value, such as (S)-m- and (S)-p-methoxyphenylalanine; (S)-o- and (S)-m-methylphenylalanine; and (S)-o- and (S)-p-bromophenylalanine at preparative scale, significantly surpassing the catalytic efficiency in terms of conversions and yields of the previously reported PcPAL-based biotransformations. The AtPAL variants tolerated high substrate and product concentrations, representing an important extension of the PAL-toolbox, while the engineered biocatalytic procedures of improved E-factor and space-time yields fulfill the requirements of sustainable and green chemistry, providing facile access to valuable amino acid building blocks.

Interaction of Epigallocatechin Gallate and Quercetin with Spike Glycoprotein (S-Glycoprotein) of SARS-CoV-2: In Silico Study

Severe acute respiratory syndrome (SARS)-CoV-2 from the family Coronaviridae is the cause of the outbreak of severe pneumonia, known as coronavirus disease 2019 (COVID-19), which was first recognized in 2019. Various potential antiviral drugs have been presented to hinder SARS-CoV-2 or treat COVID-19 disease. Side effects of these drugs are among the main complicated issues for patients. Natural compounds, specifically primary and secondary herbal metabolites, may be considered as alternative options to provide therapeutic activity and reduce cytotoxicity. Phenolic materials such as epigallocatechin gallate (EGCG, polyphenol) and quercetin have shown antibacterial, antifungal, antiviral, anticancer, and anti-inflammatory effects in vitro and in vivo. Therefore, in this study, molecular docking was applied to measure the docking property of epigallocatechin gallate and quercetin towards the transmembrane spike (S) glycoprotein of SARS-CoV-2. Results of the present study showed Vina scores of -9.9 and -8.3 obtained for EGCG and quercetin by CB-Dock. In the case of EGCG, four hydrogen bonds of OG1, OD2, O3, and O13 atoms interacted with the Threonine (THR778) and Aspartic acid (ASP867) amino acids of the spike glycoprotein (6VSB). According to these results, epigallocatechin gallate and quercetin can be considered potent therapeutic compounds for addressing viral diseases.

Beyond basic research: the contribution of cathepsin B to cancer development, diagnosis and therapy

INTRODUCTION

In view of other candidate proteins from the cathepsin family of proteases holding great potential in being targeted during cancer therapy, the importance of Cathepsin B (CtsB) stands out as being truly exceptional. Based on its contribution to oncogenesis, its intimate connection with regulating apoptosis and modulating extracellular and intracellular functions through its secretion or compartmentalized subcellular localization, collectively highlight its complex molecular involvement with a myriad of normal and pathological regulatory processes. Despite its complex functional nature, CtsB is emerging as one of the few cathepsin proteases that has been extensively researched to yield tangible outcomes for cancer therapy.

AREAS COVERED

In this article, we review the scientific literature that has justified or shaped the importance of CtsB expression in cancer progression, from the perspective of highlighting a paradigm that is rapidly changing from basic research toward a broader clinical and translational context.

EXPERT OPINION

In doing so, we detail its maturation as a diagnostic marker through describing the development of CtsB-specific Activity-Based Probes, the rapid evolution of these toward a new generation of Prodrugs, and the evaluation of these in model systems for their therapeutic potential as anti-cancer agents in the clinic.

Cathepsin B/HSP70 complex induced by Ilexsaponin I suppresses NLRP3 inflammasome activation in myocardial ischemia/reperfusion injury

BACKGROUND

Myocardial ischemia/reperfusion injury (MI/RI) is a clinical issue in MI therapy that requires effective intervention. Cathepsin B (CTSB) plays an essential role in regulating cell death, inflammatory response and angiogenesis. Ilexsaponin I (ISI), a triterpenoid saponin obtained from Ilex pubescens Hook. et Arn, has anti-inflammatory and cardioprotective effects. However, the effect of ISI on MI/RI is unclear.

PURPOSE

The study aims to disclose the mechanism of ISI as a potent therapeutic agent for MI/RI.

METHODS

Left anterior descending (LAD) coronary artery ligation and oxygen-glucose deprivation and reperfusion (OGD/R) were used to establish MI/RI model in vivo and in vitro. ELISA, western blot and immunofluorescence were carried out to detect CTSB activity and NLRP3 inflammasome activation. Coimmunoprecipitation (Co-IP), molecular docking and surface plasmon resonance (SPR) analysis were used to detect the interaction of CTSB/HSP70 complex. Infarct area determination, echocardiography and hematoxylin and eosin (HE) staining were performed to assess the cardioprotection of ISI in vivo.

RESULTS

Plasma CTSB was elevated in patients after percutaneous coronary intervention (PCI), and was positively correlated with the level of cTnI in plasma, which was also found in MI/RI rat model. ISI significantly suppressed the overexpression and activity of CTSB after MI/RI or OGD/R. ISI remarkably suppressed CTSB triggered-NLRP3 inflammasome activation and reduced the maturation of IL-1β and IL-18. Importantly, we firstly found that ISI promoted CTSB/HSP70 complex formation to disrupt CTSB/NLRP3 complex, leading to NLRP3 inflammasome inactivation. ISI could also limit infarct size, improve cardiac function and reduce inflammatory infiltrates in vivo and protected H9c2 cells against OGD/R insult in vitro. Interrupting the HSP70 and CTSB interaction with HSP70 siRNA blocked the effect of ISI on CTSB, NLRP3 inflammasome activation and the cardioprotective effect.

CONCLUSION

ISI probably exerts cardioprotective effect against MI/RI by modulating HSP70 competitively bind to CTSB to suppress the activation of the NLRP3 inflammasome.

Mussel-inspired monomer - A new selective protease inhibitor against dentine collagen degradation

OBJECTIVES

To evaluate the inhibitory effect of a novel mussel-inspired monomer (N-(3,4-dihydroxyphenethyl)methacrylamide (DMA) on the soluble and matrix-bound proteases.

METHODS

The inhibitory effect of DMA (0, 1, 5, and 10 mM) and 1 mM chlorhexidine (CHX) dissolved in 50% ethanol/water on soluble recombinant human matrix metalloproteinases (rhMMP-2, -8, and -9), as well as cysteine cathepsins (B and K) were evaluated using both fluorometric assay kits and molecular docking. The effect of CHX and DMA on matrix-bound proteases was examined by in situ zymography, and the fluorescence intensity and relative area were calculated by Image J software. All data obtained were analyzed by one-way ANOVA followed by Tukey test (α = 0.05).

RESULTS

The anti-proteolytic ability of DMA increased in a dose-dependent manner except that of rhMMP-9. Inhibitory effect of 1 mM DMA against rhMMP-2, - 8, - 9, as well as cathepsin B and K was all significantly lower than 1 mM CHX (p < 0.05). The molecular docking analysis was in good agreement with the experimental results, that the binding energy of DMA was lower than CHX for all proteases. In situ zymography revealed that all DMA- and CHX-treated groups significantly inactivated the matrix-bound proteases, with a dramatic reduction of the fluorescence intensity and relative area compared with the control group (p < 0.05).

SIGNIFICANCE

Under the prerequisite condition that the overall inhibitory performance on matrix-bound proteases was comparable by DMA and CHX, the more selective property of DMA could avoid inducing potential negative effects by suppressing MMP-9 when applied in dental treatment compared with CHX.

Recruitment of lysosomal cathepsins B, L and D as digestive enzymes in Coleoptera

The recruitment of the lysosomal cathepsins B (CAB), L (CAL) and D (CAD) as luminal digestive enzymes was investigated in 3 species of beetles. Gene expression was determined by RNA-seq in different regions of the midgut and in the carcasses from the transcriptomes of Dermestes maculatus, Tenebrio molitor and Zabrotes subfasciatus. These data together with phylogenetic analyses, allowed us to identify the sequences of the gene coding for digestive and lysosomal CABs, CADs and CALs in T. molitor and Z. subfasciatus and observe the absence of digestive cathepsins in D. maculatus. Comparisons of structures based on the overall similarity of modelled structures were performed and subsite residues in the lysosomal and digestive CALs were identified by molecular docking. The data showed that S2 subsites are very variable, probably as an adaption to a luminal digestive role. The survey of sequences of the gene coding for cathepsins in the genomes of 13 beetle species from different phylogenetic groups showed that expansion of CAL and CAB genes occurred only in the Cucujiformia clade. Several digestive CABs have a reduced occluding loop, probably to act as digestive enzymes. Pollen-feeding was proposed to be the selective pressure to recruit cathepsins as digestive enzymes in Cucujiformia beetles.

Clickable, selective, and cell-permeable activity-based probe of human cathepsin B - Minimalistic approach for enhanced selectivity

Human cathepsin B is a cysteine-dependent protease whose roles in both normal and diseased cellular states remain yet to be fully delineated. This is primarily due to overlapping substrate specificities and lack of unambiguously annotated physiological functions. In this work, a selective, cell-permeable, clickable and tagless small molecule cathepsin B probe, KDA-1, is developed and kinetically characterized. KDA-1 selectively targets active site Cys25 residue of cathepsin B for labeling and can detect active cellular cathepsin B in proteomes derived from live human MDA-MB-231 breast cancer cells and HEK293 cells. It is anticipated that KDA-1 probe will find suitable applications in functional proteomics involving human cathepsin B enzyme.

FITC characterization of a cathepsin B-responsive nanoprobe for report of differentiation of HL60 cells into macrophages

A cathepsin B (Cat B)-responsive optical nanoprobe is designed and prepared for report of HL60 differentiation into macrophage. A peptide sequence FRFK is linked to fluorescein (FITC) via the distant amino group of its lysine and N-terminated with acrylic acid (AA) to yield a molecular fluorescent probe AA-FRFK (FITC). The molecular probe is further embedded in poly(lactic-co-glycolic acid) (PLGA) to form a fluorescent nanoprobe AA-FRFK (FITC)@PLGA. The resultant optical nanoprobe is degradable by lysosomal Cat B, which is expressed in macrophages with a level of 5-10 times of that in HL60 cells. As a result, a significant decrease in fluorescence intensity is associated with the differentiation process of HL60 to macrophage and can be used as an indication of the differentiation process. The findings may pave a way toward the development of a universal in vitro labeling strategy of exogenous stem cells for report of in vivo cell differentiation by a dual-mode imaging modality involving optical imaging and magnetic resonance imaging.

Functional characterization of cathepsin B and its role in the antimicrobial immune responses in golden pompano (Trachinotus ovatus)

Cathepsin B (CTSB) is one of the typical representatives of cysteine protease family. It has the activity of both exopeptidase and endopeptidase. It plays an important role in antigen presentation, degradation, apoptosis, inflammatory response and physiological process of many diseases. In this study, CTSB of Trachinotus ovatus (TroCTSB) was cloned, and its structure and function were analyzed. The results showed that the coding region of TroCTSB was 993 bp, encoding 330 amino acid residues. The homology analysis showed that the amino acid sequence of TroCTSB was similar to that in other teleosts and mammals (68.69%-88.48%). Under normal physiological conditions, TroCTSB was widely distributed in various tissues with the highest expression level in stomach, followed by liver, and the lowest expression level in blood. The optimal pH and temperature of purified recombinant protein rTroCTSB were 5.5 and 40 °C, respectively. The toxicity test of metal ions showed that Fe²⁺, Cu²⁺, Ca²⁺ and Zn²⁺ could all inhibit the activity of TroCTSB, with Zn²⁺ ranking the first. In addition, after Edwardsiella tarda infection, the expression of TroCTSB was significantly up-regulated in liver, spleen and head kidney. The overexpression of TroCTSB significantly inhibited the infection of E. tarda in golden pompano tissues, and the knockdown of TroCTSB remarkably promoted the reproduction of E. tarda in golden pompano tissues in vivo. This study suggests that TroCTSB was involved in the antibacterial immune response of T. ovatus, and provided a reference for further research in elucidating the resistance mechanism of TroCTSB.

An Activity-Based Probe for Cathepsin K Imaging with Excellent Potency and Selectivity

The cysteine protease cathepsin K is a target for the treatment of diseases associated with high bone turnover. Cathepsin K is mainly expressed in osteoclasts and responsible for the destruction of the proteinaceous components of the bone matrix. We designed various fluorescent activity-based probes (ABPs) and their precursors that bind to and inactivate cathepsin K. ABP 25 exhibited extraordinary potency (k_inac/K_i = 35,300 M^-1s^-1) and selectivity for human cathepsin K. Crystal structures of cathepsin K in complex with ABP 25 and its nonfluorescent precursor 21 were determined to characterize the binding mode of this new type of acrylamide-based Michael acceptor with the particular orientation of the dibenzylamine moiety to the primed subsite region. The cyanine-5 containing probe 25 allowed for sensitive detection of cathepsin K, selective visualization in complex proteomes, and live cell imaging of a human osteosarcoma cell line, underlining its applicability in a pathophysiological environment.

Flavan-3-ol Microbial Metabolites Modulate Proteolysis in Neuronal Cells Reducing Amyloid-beta (1-42) Levels

Introduction

Alzheimer's disease (AD) is a progressive neurodegeneration characterized by extensive protein aggregation and deposition in the brain, associated with defective proteasomal and autophagic‐lysosomal proteolytic pathways. Since current drugs can only reduce specific symptoms, the identification of novel treatments is a major concern in AD research. Among natural compounds, (poly)phenols and their derivatives/metabolites are emerging as candidates in AD prevention due to their multiple beneficial effects. This study aims to investigate the ability of a selection of phenyl‐γ‐valerolactones, gut microbiota‐derived metabolites of flavan‐3‐ols, to modulate the functionality of cellular proteolytic pathways.

Methods and Results

Neuronal SH‐SY5Y cells transfected with either the wild‐type or the 717 valine‐to‐glycine amyloid precursor protein mutated gene are used as an AD model and treated with 5‐(4ʹ‐hydroxyphenyl)‐γ‐valerolactone, 5‐(3ʹ,4ʹ‐dihydroxyphenyl)‐γ‐valerolactone and 5‐(3ʹ‐hydroxyphenyl)‐γ‐valerolactone‐4ʹ‐sulfate. Combining in vitro and in silico studies, it is observed that the phenyl‐γ‐valerolactones of interest modulated cellular proteolysis via proteasome inhibition and consequent autophagy upregulation and inhibited cathepsin B activity, eventually reducing the amount of intra‐ and extracellular amyloid‐beta (1‐42) peptides.

Conclusion

The findings of this study establish, for the first time, that these metabolites exert a neuroprotective activity by regulating intracellular proteolysis and confirm the role of autophagy and cathepsin B as possible targets of AD preventive/therapeutic strategies.

Recombinant sugarcane cystatin CaneCPI-5 down regulates inflammation and promotes angiogenesis and collagen deposition in a mouse subcutaneous sponge model

Cystatins are natural inhibitors of cysteine peptidases that are found practically in all living organisms. CaneCPI-5 is a sugarcane cystatin with inhibitory activity against human cathepsins B, K and L, which are cysteine proteases highly expressed in a variety of pathological conditions, usually marked by persistent inflammation and processing of the extracellular matrix. This work evaluated the effects of daily administration of the recombinant cystatin CaneCPI-5 [0.01, 0.1 or 1.0 μg in 10 μL of Phosphate-Buffered Saline (PBS)] on the inflammatory, angiogenic and fibrogenic components during chronic inflammatory response induced by subcutaneous sponge implants. The anti-inflammatory effect of treatment with CaneCPI-5 was confirmed by reduction of the levels of the pro-inflammatory mediators TNF-α, CXCL1 and CCL2/JE/MCP-1, as well as the activity of the myeloperoxidase and n-acetyl-β-D-glucosaminidase. Treatment with CaneCPI-5 promoted angiogenesis in the implants, increasing the production of cytokines VEGF and FGF and the formation of new blood vessels. Finally, the administration of the recombinant cystatin favored the production of the pro-fibrogenic cytokine TGF-β1 and collagen deposition next to the implants. Together, these results show the potential therapeutic application of CaneCPI-5 as an anti-inflammatory agent, capable of favoring angiogenesis and fibrogenesis processes, necessary for tissue repair.

New Insights into the Chemical Reactivity of Dry-Cured Fermented Sausages: Focus on Nitrosation, Nitrosylation and Oxidation

Nitrite and nitrate are added to cured meat for their bacteriological, technological and sensorial properties. However, they are suspected to be involved in the formation of nitroso compounds (NOCs), such as potentially mutagenic nitrosamines, nitrosylheme and nitrosothiols. Controlling the sanitary and sensorial qualities of cured meat products by reducing these additives requires elucidating the mechanisms involved in the formation of NOCs. To this end, we studied the dose-response relationship of added sodium nitrite and/or sodium nitrate (0/0, 80/80, 0/200, and 120/120 ppm) on the formation of NOCs in dry cured fermented sausages. The results showed a basal heme iron nitrosylation in the absence of NaNO2/NaNO3 due to starter cultures. This reaction was promoted by the addition of NaNO2/NaNO3 in the other conditions. Reducing the dose to 80/80 ppm still limits lipid oxidation without the formation of non-volatile nitrosamines. Conversely, the addition of NO2/NO3 slightly increases protein oxidation through higher carbonyl content. The use of 80/80 ppm could be a means of reducing these additives in dry-cured fermented meat products.

Cysteine Cathepsins and Their Prognostic and Therapeutic Relevance in Leukemia

Cysteine cathepsins are lysosomal proteases that require Cys-His ion pair in their catalytic site for enzymatic activity. While their aberrant expression and oncogenic functions have been widely reported in solid tumors, recent findings suggest that these proteases also play an important role in the pathogenesis of hematological malignancies. In this review, we summarize the potential clinical implications of cysteine cathepsins as diagnostic and prognostic markers in leukemia, and present evidences which supports the utility of these proteases as potential therapeutic targets in hematological malignancies. We also highlight the available information on the expression patterns, regulation, and potential functions of cysteine cathepsins in normal hematopoiesis and hematological malignancies. In hematopoiesis, cysteine cathepsins play a variety of physiological roles including regulation of hematopoietic stem cell adhesion in the bone marrow, trafficking, and maturation. They are also involved in several functions of immune cells which include the selection of lymphocytes in the thymus, antigen processing, and presentation. However, the expression of cysteine cathepsins is dysregulated in hematological malignancies where they have been shown to play diverse functions. Interestingly, several pieces of evidence over the past few years have demonstrated overexpression of cathepsins in leukemia and their association with worst survival outcomes in patients. Strategies aimed at altering the expression, activity, and subcellular localization of these cathepsins are emerging as potential therapeutic modalaties in the management of hematological malignancies. Recent findings also suggest the involvement of these proteases in modulating the immune response in leukemia and lymphomas.

Azanitrile Inhibitors of the SmCB1 Protease Target Are Lethal to Schistosoma mansoni: Structural and Mechanistic Insights into Chemotype Reactivity

Azapeptide nitriles are postulated to reversibly covalently react with the active-site cysteine residue of cysteine proteases and form isothiosemicarbazide adducts. We investigated the interaction of azadipeptide nitriles with the cathepsin B1 drug target (SmCB1) from Schistosoma mansoni, a pathogen that causes the global neglected disease schistosomiasis. Azadipeptide nitriles were superior inhibitors of SmCB1 over their parent carba analogs. We determined the crystal structure of SmCB1 in complex with an azadipeptide nitrile and analyzed the reaction mechanism using quantum chemical calculations. The data demonstrate that azadipeptide nitriles, in contrast to their carba counterparts, undergo a change from E- to Z-configuration upon binding, which gives rise to a highly favorable energy profile of noncovalent and covalent complex formation. Finally, azadipeptide nitriles were considerably more lethal than their carba analogs against the schistosome pathogen in culture, supporting the further development of this chemotype as a treatment for schistosomiasis.

Design, synthesis and stepwise optimization of nitrile-based inhibitors of cathepsins B and L

Human cathepsin B (CatB) is an important biological target in cancer therapy. In this work, we performed a knowledge-based design approach and the synthesis of a new set of 19 peptide-like nitrile-based cathepsin inhibitors. Reported compounds were assayed against a panel of human cysteine proteases: CatB, CatL, CatK, and CatS. Three compounds (7h, 7i, and 7j) displayed nanomolar inhibition of CatB and selectivity over CatK and CatL. The selectivity was achieved by using the combination of a para biphenyl ring at P3, halogenated phenylalanine in P2 and Thr-O-Bz group at P1. Likewise, compounds 7i and 7j showed selective CatB inhibition among the panel of enzymes studied. We have also described a successful example of bioisosteric replacement of the amide bond for a sulfonamide one [7e → 6b], where we observed an increase in affinity and selectivity for CatB while lowering the compound lipophilicity (ilogP). Our knowledge-based design approach and the respective structure-activity relationships provide insights into the specific ligand-target interactions for therapeutically relevant cathepsins.

IQF characterization of a cathepsin B-responsive nanoprobe for report of differentiation of HL60 cells into macrophages

Tracking of in vivo fates of exogenous cell transplants in terms of viability, migration, directional differentiation and function delivery by a suitable method of medical imaging is of great significance in the development and application of various cell therapies. In this contribution directional differentiation of HL60 cells into macrophages and granulocytes, and a difference in the associated expression level of cathepsin B (Cat B) among the parent and daughter cells is used as a model to guide and evaluate the development of a Cat B-responsive Abz-FRFK-Dnp@PLGA nanoprobe for an optical report of the differentiation process. A well-documented internally quenched fluorescence (IQF) pair coupled with a peptide substrate FRFK of Cat B was synthesized and imbedded in PLGA to form the nanoprobe. The nanoprobe is resistant to leakage when dispersed in water for 10 days. Degradation of the nanoprobe is dominated by Cat B. HL60 cells were then labelled with the Abz-FRFK-Dnp@PLGA nanoprobe to track the differentiation process. Differentiation of labelled HL60 cells into macrophages exhibited a significantly higher fluorescence relative to the granulocytes or the labelled parent cells. The fluorescence difference allows the differentiation process to be followed. The established characterization and assessment procedure is to be used for the development and evaluation of nanoprobes for other imaging modalities.

A Cat B-responsive Abz-FRFK-Dnp@PLGA nanoprobe for an optical report of the differentiation of HL60 cells into macrophages.

Cathepsin B inhibition blocks neurite outgrowth in cultured neurons by regulating lysosomal trafficking and remodeling

Lysosomes are known to mediate neurite outgrowth in neurons. However, the principal lysosomal molecule controlling that outgrowth is unclear. We studied primary mouse neurons in vitro and found that they naturally develop neurite outgrowths over time and as they did so the lysosomal cysteine protease cathepsin B (CTSB) mRNA levels dramatically increased. Surprisingly, we found that treating those neurons with CA-074Me, which inhibits CTSB, prevented neurites. As that compound also inhibits another protease, we evaluated a N2a neuronal cell line in which the CTSB gene was deleted (CTSB knockout, KO) using CRISPR technology and induced their neurite outgrowth by treatment with retinoic acid. We found that CTSB KO N2a cells failed to produce neurite outgrowths but the wild-type (WT) did. CA-074Me is a cell permeable prodrug of CA-074, which is cell impermeable and a specific CTSB inhibitor. Neurite outgrowth was and was not suppressed in WT N2a cells treated with CA-074Me and CA-074, respectively. Lysosome-associated membrane glycoprotein 2-positive lysosomes traffic to the plasma cell membrane in WT but not in CTSB KO N2 a cells. Interestingly, no obvious differences between WT and CTSB KO N2a cells were found in neurite outgrowth regulatory proteins, PI3K/AKT, ERK/MAPK, cJUN, and CREB. These findings show that intracellular CTSB controls neurite outgrowth and that it does so through regulation of lysosomal trafficking and remodeling in neurons. This adds valuable information regarding the physiological function of CTSB in neural development.

A highly potential cleavable linker for tumor targeting antibody-chemokines

Chemokines are the large family of chemotactic cytokines that play an important role in leukocyte movement and migration stimulation. Until now, several antibody-cytokine (chemokine) fusion proteins have been investigated in clinical trials because of their ability to evoke the circulating leukocytes far from the tumor site. In this case, creating the concentration gradient regarding the chemokine is very important to recruit the circulating leukocytes with maximum performance to the tumor environment. To achieve a proper gradient, the chemokine separation from the tumor antigen-bounded antibody can be very crucial. Thus, we designed a novel linker that can be cleaved by enzymes presented around the tumor site including cathepsin B, urokinase-type plasminogen activator (uPA) and matrix metalloproteinases (MMPs). Also, it can inhibit tumor progression by competing with the native substrate of key proteases in the tumor microenvironment. The proposed linker was evaluated using some bioinformatics approaches. In silico results showed that the linker is structurally stable and could be detected and cleaved using the mentioned enzymes.Communicated by Ramaswamy H. Sarma.

Lysosomal quality control of cell fate: a novel therapeutic target for human diseases

In eukaryotic cells, lysosomes are digestive centers where biological macromolecules are degraded by phagocytosis and autophagy, thereby maintaining cellular self-renewal capacity and energy supply. Lysosomes also serve as signaling hubs to monitor the intracellular levels of nutrients and energy by acting as platforms for the assembly of multiple signaling pathways, such as mammalian target of rapamycin complex 1 (mTORC1) and adenosine 5′-monophosphate (AMP)-activated protein kinase (AMPK). The structural integrity and functional balance of lysosomes are essential for cell function and viability. In fact, lysosomal damage not only disrupts intracellular clearance but also results in the leakage of multiple contents, which pose great threats to the cell by triggering cell death pathways, including apoptosis, necroptosis, pyroptosis, and ferroptosis. The collapse of lysosomal homeostasis is reportedly critical for the pathogenesis and development of various diseases, such as tumors, neurodegenerative diseases, cardiovascular diseases, and inflammatory diseases. Lysosomal quality control (LQC), comprising lysosomal repair, lysophagy, and lysosomal regeneration, is rapidly initiated in response to lysosomal damage to maintain lysosomal structural integrity and functional homeostasis. LQC may be a novel but pivotal target for disease treatment because of its indispensable role in maintaining intracellular homeostasis and cell fate.

Nucleus distribution of cathepsin B in senescent microglia promotes brain aging through degradation of sirtuins

Cathepsin B (CatB) leakage from the lysosome into the cytosol in senescent microglia is associated with cognitive impairment. However, whether cellular compartmental translocation of CatB is associated with brain aging remains unclear. In the present study, increased CatB was found in the nucleus of CatB-overexpressed microglia followed by L-leucyl-L-leucine methyl ester, a lysosome-destabilizing reagent, and in the nuclear fraction of the cortex and hippocampus from aged mice. Moreover, CatB enzymatic activity examination showed the nuclear CatB exhibited the proteolytic activity to cleave its specific substrates. The amount of sirtuin1 (Sirt1), Sirt6, Sirt7, and p-Sirt1 was decreased in the cortical lysates from aged mice, in parallel with increased expression of proinflammatory mediators, which were diminished by CatB deficiency. Furthermore, intralateral ventricle administration of microglia overexpressed CatB, and treatment with L-leucyl-L-leucine methyl ester induced cognitive impairment in middle-aged mice. These observations suggest that the increase and nucleus translocation of CatB in senescent microglia were involved in the degradation of nuclear Sirts, which induced proinflammatory responses, resulting in cognition impairment.

Palmoplantar keratoderma caused by a missense variant in CTSB encoding cathepsin B

BACKGROUND

Palmoplantar keratoderma (PPK) refers to a large group of disorders characterized by extensive genetic and phenotypic heterogeneity. PPK diagnosis therefore increasingly relies upon genetic analysis.

AIM

To delineate the genetic defect underlying a case of diffuse erythematous PPK associated with peeling of the skin.

METHODS

Whole exome and direct sequencing, real-time quantitative PCR, protein modelling and a cathepsin B enzymatic assay were used.

RESULTS

The patient studied had severe diffuse erythematous PPK transgrediens. Pedigree analysis suggested an autosomal dominant mode of inheritance. Whole exome sequencing revealed a heterozygous missense mutation in the CTSB gene, encoding the cysteine protease cathepsin B. Genomic duplications in a noncoding region, which regulates the expression of CTSB, were recently found to cause erythrokeratolysis hiemalis, a rare autosomal dominant disorder of cornification. This mutation affects a highly conserved residue, and is predicted to be pathogenic. Protein modelling indicated that the mutation is likely to lead to increased endopeptidase cathepsin B activity. Accordingly, the CTSB variant was found to result in increased cathepsin B proteolytic activity.

CONCLUSION

In summary, we report the identification of the first gain-of-function missense mutation in CTSB, which was found to be associated in one individual with a dominant form of diffuse PPK.

Coumarin as a structural component of substrates and probes for serine and cysteine proteases

Coumarins represent well-established structures to introduce fluorescence into tool compounds for biochemical investigations. They are valued for their small size, chemical stability and accessibility as well as their tunable photochemical properties. As components of fluorophore/quencher pairs or FRET donor/acceptor pairs, coumarins have frequently been applied in substrate mapping approaches for serine and cysteine proteases. This review also focuses on the incorporation of coumarins into the side chain of amino acids and the exploitation of the resulting fluorescent amino acids for the positional profiling of protease substrates. The protease-inhibiting properties of certain coumarin derivatives and the utilization of coumarin moieties to assemble activity-based probes for serine and cysteine proteases are discussed as well.

•

Coumarins represent well-established structures to introduce fluorescence into tool compounds for biochemical investigations.

•

They are valued for their small size, chemical stability and accessibility as well as their tunable photochemical properties.

•

Coumarins are components of fluorophore/quencher pairs or FRET donor/acceptor pairs in substrate mapping of proteases.

•

Coumarins have been incorporated into amino acids side chains to be used for the positional profiling of protease substrates.

•

Coumarins have protease-inhibiting properties and are used for activity-based probes for serine and cysteine proteases.

Structure-activity relationships of triazole-benzodioxine inhibitors of cathepsin X

Cathepsin X is a cysteine carboxypeptidase that is involved in various physiological and pathological processes. In particular, highly elevated expression and activity of cathepsin X has been observed in cancers and neurodegenerative diseases. Previously, we identified compound Z9 (1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-2-((4-isopropyl-4H-1,2,4-triazol-3-yl)thio)ethan-1-one) as a potent and specific reversible cathepsin X inhibitor. Here, we have explored the effects of chemical variations to Z9 of either benzodioxine or triazol moieties, and the importance of the central ketomethylenethio linker. The ketomethylenethio linker was crucial for cathepsin X inhibition, whereas changes of the triazole heterocycle did not alter the inhibitory potencies to a greater extent. Replacement of benzodioxine moiety with substituted benzenes reduced cathepsin X inhibition. Overall, several synthesized compounds showed similar or improved inhibitory potencies against cathepsin X compared to Z9, with IC₅₀ values of 7.1 μM-13.6 μM. Additionally, 25 inhibited prostate cancer cell migration by 21%, which is under the control of cathepsin X.

Mapping the S1 and S1' subsites of cysteine proteases with new dipeptidyl nitrile inhibitors as trypanocidal agents

The cysteine protease cruzipain is considered to be a validated target for therapeutic intervention in the treatment of Chagas disease. A series of 26 new compounds were designed, synthesized, and tested against the recombinant cruzain (Cz) to map its S1/S1´ subsites. The same series was evaluated on a panel of four human cysteine proteases (CatB, CatK, CatL, CatS) and Leishmania mexicana CPB, which is a potential target for the treatment of cutaneous leishmaniasis. The synthesized compounds are dipeptidyl nitriles designed based on the most promising combinations of different moieties in P1 (ten), P2 (six), and P3 (four different building blocks). Eight compounds exhibited a Ki smaller than 20.0 nM for Cz, whereas three compounds met these criteria for LmCPB. Three inhibitors had an EC50 value of ca. 4.0 μM, thus being equipotent to benznidazole according to the antitrypanosomal effects. Our mapping approach and the respective structure-activity relationships provide insights into the specific ligand-target interactions for therapeutically relevant cysteine proteases.

Organoruthenated Nitroxoline Derivatives Impair Tumor Cell Invasion through Inhibition of Cathepsin B Activity

Lysosomal cysteine peptidase cathepsin B (catB) is an important tumor-promoting factor involved in tumor progression and metastasis representing a relevant target for the development of new antitumor agents. In the present study, we synthesized 11 ruthenium compounds bearing either the clinical agent nitroxoline that was previously identified as potent selective reversible inhibitor of catB activity or its derivatives. We demonstrated that organoruthenation is a viable strategy for obtaining highly effective and specific inhibitors of catB endo- and exopeptidase activity, as shown using enzyme kinetics and microscale thermophoresis. Furthermore, we showed that the novel metallodrugs by catB inhibition significantly impair processes of tumor progression in in vitro cell based functional assays at low noncytotoxic concentrations. Generally, by using metallodrugs we observed an improvement in catB inhibition, a reduction of extracellular matrix degradation and tumor cell invasion in comparison to free ligands, and a correlation with the reactivity of the monodentate halide leaving ligand.

Eleven ruthenium compounds bearing either the clinical agent nitroxoline or its potent cathepsin B (catB) inhibiting derivatives were evaluated as antimetastatic agents. We demonstrated that organoruthenation is a viable strategy for obtaining highly effective and specific inhibitors of catB activities, as shown using enzyme kinetics and microscale thermophoresis. Furthermore, we showed that the novel metallodrugs significantly impair processes of tumor progression in in vitro cell based functional assays at low noncytotoxic concentrations.

Cysteine Cathepsin Protease Inhibition: An update on its Diagnostic, Prognostic and Therapeutic Potential in Cancer

In keeping with recent developments in basic research; the importance of the Cathepsins as targets in cancer therapy have taken on increasing importance and given rise to a number of key areas of interest in the clinical setting. In keeping with driving basic research in this area in a translational direction; recent findings have given rise to a number of exciting developments in the areas of cancer diagnosis; prognosis and therapeutic development. As a fast-moving area of research; the focus of this review brings together the latest findings and highlights the translational significance of these developments.