Cathepsin B Dipeptidyl Carboxypeptidase and Endopeptidase Activities Demonstrated across a Broad pH Range

Identification of functional biomarkers for personalized nanomedicine in advanced breast cancer in vitro models

Nanomedicines represent promising advanced therapeutics for the enhanced treatment of breast cancer, the primary cause of cancer-related deaths in women; however, the clinical translation of nanomedicines remains challenging. Advanced in vitro models of breast cancer may improve preclinical evaluations and the identification of biomarkers that aid the stratification of patients who would benefit from a given nanomedicine. In this study, we first developed a matrix-embedded breast cancer cell spheroid model representing the extracellular matrix and confirmed the faithful recapitulation of disease aggressiveness in vitro. We then characterized factors influencing nanomedicine drug release (i.e., cathepsin B levels/activity, reactive oxygen species levels, glutathione levels, and cytoplasmic pH values) and evaluated nanomedicine internalization and cytotoxicity evaluation in our spheroid model. We confirmed the reduced-to-oxidized glutathione ratio as a functional biomarker of disulfide linker-containing polypeptide-drug conjugate effectiveness. We then established a biobank of patient-derived breast cancer organoids that recapitulate clinical intra-tumor and inter-tumor heterogeneity as a more advanced model. Analysis in organoids revealed that patient-specific responses to a polypeptide-based nanomedicine correlated with cathepsin B levels, supporting the potential of the functional biomarker for patient-tailored nanomedicine selection. Our findings highlight that exhaustively characterized advanced in vitro models support the evaluation of nanomedicines and the identification of functional biomarkers.

Cathepsin B in urological tumors: unraveling its role and therapeutic potential

Cathepsin B(CTSB) is a key protease within the lysosomal protease family and is recognized as a tumor-promoting factor that exerts a substantial impact on cancer progression. It plays a critical role in the initiation, proliferation, metastasis, and angiogenesis of cancer, significantly advancing the disease. This review offers a concise overview of the structure and biological functions of CTSB, clarifying its relationship with cancer and the role it plays in the disease's progression. Additionally, we discuss the association between CTSB and several common malignant tumors of the urinary system, highlighting its potential role and clinical significance within these tumors, as well as the challenges that remain.

Cathepsin B inhibition blocks amyloidogenesis in the mouse models of neurological lysosomal diseases MPS IIIC and sialidosis

Neuronal accumulation of amyloid aggregates is a hallmark of brain pathology in neurological lysosomal storage diseases (LSDs), including mucopolysaccharidoses (MPS); however, the molecular mechanism underlying this pathology has not been understood. We demonstrate that elevated lysosomal cathepsin B (CTSB) levels and CTSB leakage to the cytoplasm triggers amyloidogenesis in two neurological LSDs. CTSB levels were elevated 3- to 5-fold in the cortices of mouse models of MPS IIIC (Hgsnat-Geo and Hgsnat P304L ) and sialidosis (Neu1 ΔEx3 ), as well as in cortical samples of MPS I, IIIA, IIIC, and IIID patients. CTSB was found in the cytoplasm of pyramidal layer IV-V cortical neurons containing thioflavin-S+, β-amyloid+ aggregates consistent with a pro-senile phenotype. In contrast, CTSB-deficient MPS IIIC (Hgsnat P304L /Ctsb -/- ) mice as well as Hgsnat P304L and Neu1 ΔEx3 mice chronically treated with irreversible brain-penetrable CTSB inhibitor E64 showed a drastic reduction in neuronal thioflavin-S+/APP+ deposits. Neurons of Hgsnat P304L /Ctsb -/- mice and E64-treated Hgsnat P304L mice also showed reduced levels of P62+, LC3+ puncta, GM2 ganglioside, and misfolded subunit C of mitochondrial ATP synthase, consistent with restored autophagy. E64 treatment also rescued hyperactivity and reduced anxiety in Hgsnat P304L mice, implying that CTSB may become a novel pharmacological target for MPS III and similar LSDs.

Muscle-brain crosstalk mediated by exercise-induced myokines - insights from experimental studies

Over the past couple of decades, it has become apparent that skeletal muscles might be engaged in endocrine signaling, mostly as a result of exercise or physical activity in general. The importance of this phenomenon is currently studied in terms of the impact that exercise- or physical activity -induced signaling factors have, in the interaction of the "muscle-brain crosstalk." So far, skeletal muscle-derived myokines were demonstrated to intercede in the connection between muscles and a plethora of various organs such as adipose tissue, liver, or pancreas. However, the exact mechanism of muscle-brain communication is yet to be determined. It is speculated that, in particular, brain-derived neurotrophic factor (BDNF), irisin, cathepsin B (CTSB), interleukin 6 (IL-6), and insulin-like growth factor-1 (IGF-1) partake in this crosstalk by promoting neuronal proliferation and synaptic plasticity, also resulting in improved cognition and ameliorated behavioral alterations. Researchers suggest that myokines might act directly on the brain parenchyma via crossing the blood-brain barrier (BBB). The following article reviews the information available regarding rodent studies on main myokines determined to cross the BBB, specifically addressing the association between exercise-induced myokine release and central nervous system (CNS) impairments. Although the hypothesis of skeletal muscles being critical sources of myokines seems promising, it should not be forgotten that the origin of these factors might vary, depending on the cell types engaged in their synthesis. Limited amount of research providing information on alterations in myokines expression in various organs at the same time, results in taking them only as circumstantial evidence on the way to determine the actual involvement of skeletal muscles in the overall state of homeostasis. The following article reviews the information available regarding rodent studies on main myokines determined to cross the BBB, specifically addressing the association between exercise-induced myokine release and CNS impairments.

Phenoxy-1,2-dioxetane-based activatable chemiluminescent probes: tuning of photophysical properties for tracing enzymatic activities in living cells

The use of chemiluminophores for tracing enzymatic activities in live-cell imaging has gained significant attention, making them valuable tools for diagnostic applications. Among various chemiluminophores, the phenoxy-1,2-dioxetane scaffold exhibits significant structural versatility and its activation is governed by the chemically initiated electron exchange luminescence (CIEEL) mechanism. This mechanism can be initiated by enzymatic activity, changes in pH, or other chemical stimuli. The photophysical properties of phenoxy-1,2-dioxetanes can be fine-tuned through the incorporation of different substituents on the phenolic ring and by anchoring them with specific triggers. This review discusses the variations in physicochemical properties, including emission maxima, quantum yield, aqueous solubility, and pKa, as influenced by structural modifications, thereby establishing a comprehensive structure-activity relationship. Furthermore, it categorises the probes based on different enzyme classes, such as hydrolase-sensitive probes, oxidoreductase-responsive probes, and transferase-activatable phenoxy-1,2-dioxetanes, offering a promising platform technology for the early diagnosis of diseases and disorders. The summary section highlights key opportunities and limitations associated with applying phenoxy-1,2-dioxetanes in achieving precise and effective enzyme assays.

Optimization of a pendant-shaped PEGylated linker for antibody-drug conjugates

In this work, we conceived and developed antibody-drug conjugates (ADCs) that could efficiently release the drug after enzymatic cleavage of the linker moiety by tumoral proteases. The antibody-drug linkers we used are the result of a rational optimization of a previously reported PEGylated linker, PUREBRIGHT® MA-P12-PS, which showed excellent drug loading capacities but lacked an inbuilt drug discharge mechanism, thus limiting the potency of the resulting ADCs. To address this limitation, we chose to incorporate a protease-sensitive trigger into the linker to favor the release of a "PEGless" drug inside the tumor cells and, therefore, obtain potent ADCs. Currently, most marketed ADCs are based on the Val-Cit dipeptide followed by a self-immolative spacer for releasing the drug in its unmodified form. Here, we selected two untraditional peptide sequences, a Phe-Gly dipeptide and a Val-Ala-Gly tripeptide and placed one or the other in between the drug on one side (N-terminus) and the rest of the linker, including the PEG moiety, on the other side (C-terminus), without a self-immolative group. We found that both linkers responded to cathepsin B, a reference lysosomal enzyme, and liberated a PEG-free drug catabolite, as desired. We then used the two linkers to generate ADCs based on trastuzumab (a HER2-targeting antibody) and DM1 (a microtubule-targeted cytotoxic agent) with an average drug-to-antibody ratio (DAR) of 4 or 8. The ADCs showed restored cytotoxicity in vitro, which was proportional to the DM1 loading and generally higher for the ADCs bearing Val-Ala-Gly in their structure. In an ovarian cancer mouse model, the DAR 8 ADC based on Val-Ala-Gly behaved better than Kadcyla® (an approved ADC of DAR 3.5 used as control throughout this study), leading to a higher tumor volume reduction and more prolonged median survival. Taken together, our results depict a successful linker optimization process and encourage the application of the Val-Ala-Gly tripeptide as an alternative to other existing protease-sensitive triggers for ADCs.

Expanding the Library of Covalent Cysteine Cathepsin Probes Featuring Sulfoxonium Ylide Electrophiles

Covalent activity-based probes are invaluable tools to monitor protease activity in vitro and in vivo. We recently discovered that dimethyl sulfoxonium ylides (SYs) bind selectively to cysteine cathepsin proteases in a mechanism-dependent manner. Herein, we present the synthetic routes and characterization of an expanded library of SY probes with a greater diversity in recognition sequences. The probes exhibit a range of potency and selectivity for the cathepsin family members. We also investigated the impact of fluorophore positioning on probes bearing P1 lysine. When sulfonated cyanine 5 was attached via the lysine side chain, the resulting probe was selective for cathepsin S. When attached to the α-amine, with the side chain amine either free or Boc-protected, the probes reacted with both cathepsin S and X. Bulk in the P1 position is thus well tolerated by cathepsin S but not cathepsin X. We examined the impact of Cy5 sulfonation on probe properties, demonstrating that unsulfonated probes exhibit greater cellular uptake, which affects their relative selectivity. Finally, we demonstrated that SY probes exhibit minimal labeling of cathepsin S in freshly prepared lysates, but this increases during the prolonged incubation of lysates. This work extends our understanding of SY probes and informs future probe development.

Application of a crude digestive proteases preparation to improve the ripening of marinated fillets from low-technological value Baltic herring (Clupea harengus membras L.)

BACKGROUND

As a result of climate change (reduced the oxygen content and food available in the waters) and overfishing, ever larger batches of the herring catch are classified as low-value fish and used for feedstuff or canned food production. Fast and complete ripening of marinated fillets, especially from low-value Baltic herring, poses a problem because of the low muscle protease activity and changes in muscle tissue proteins.

RESULTS

For the first time, a crude digestive proteases preparation (CDPP) was obtained from herring viscera using a two-stage method consisting of ethanol extraction and then salt precipitation. CDPP had a reduced hemoglobin content, with optimum activity at pH 7.5-8.8 or 60-120 g kg-1 NaCl. At pH 4-5, it still exhibited 24-68% of proteolytic activity. CDPP was used for 4-24 h of brining of fresh and frozen-thawed fillets or injection of fresh fillets before marinating. CDPP-brining increased especially cathepsin D and carboxypeptidase A activities, whereas it decreased cathepsin B and L activities in the marinades. CDPP-brining mitigated the negative effect of freezing-thawing on mass-yield, protease activity, protein hydrolysis, texture profile, colour and sensory quality of the marinated fillets. CDPP-injection was found to be the best method because it increased mass-yield and ripeness of the marinated fillets to a greater extent than CDPP-brining did. The marinades from the CDPP-treated fillets had no bitter taste as a result of the presence of hemoglobin or chymotrypsin, and there were no results indicating lipid oxidation.

CONCLUSION

The application of CDPP in marinating technology is a viable approach to enable the use of low-value herring in food production, shorten the marinating time, and improve the ripeness and sensory quality of meat. © 2024 Society of Chemical Industry.

Beyond Nanoparticle-Based Intracellular Drug Delivery: Cytosol/Organelle-Targeted Drug Release and Therapeutic Synergism

Nanoparticle (NP)-based drug delivery systems are conceived to solve poor water-solubility and chemical/physical instability, and their purpose expanded to target specific sites for maximizing therapeutic effects and minimizing unwanted events of payloads. Targeted sites are also narrowed from organs/tissues and cells to cytosol/organelles. Beyond specific site targeting, the particular release of payloads at the target sites is growing in importance. This review overviews various issues and their general strategies during multiple steps, from the preparation of drug-loaded NPs to their drug release at the target cytosol/organelles. In particular, this review focuses on current strategies for "first" delivery and "later" release of drugs to the cytosol or organelles of interest using specific stimuli in the target sites. Recognizing or distinguishing the presence/absence of stimuli or their differences in concentration/level/activity in one place from those in another is applied to stimuli-triggered release via bond cleavage or nanostructural transition. In addition, future directions on understanding the intracellular balance of stimuli and their counter-stimuli are demonstrated to synergize the therapeutic effects of payloads released from stimuli-sensitive NPs.

Cathepsin X deficiency alters the processing and localisation of cathepsin L and impairs cleavage of a nuclear cathepsin L substrate

Proteases function within sophisticated networks. Altering the activity of one protease can have sweeping effects on other proteases, leading to changes in their activity, structure, specificity, localisation, stability, and expression. Using a suite of chemical tools, we investigated the impact of cathepsin X, a lysosomal cysteine protease, on the activity and expression of other cysteine proteases and their inhibitors in dendritic cells. Among all proteases examined, cathepsin X gene deletion specifically altered cathepsin L levels; pro-cathepsin L and its single chain accumulated while the two-chain form was unchanged. This effect was recapitulated by chemical inhibition of cathepsin X, suggesting a dependence on its catalytic activity. We demonstrated that accumulation of pro- and single chain cathepsin L was not due to a lack of direct cleavage by cathepsin X or altered glycosylation, secretion, or mRNA expression but may result from changes in lysosomal oxidative stress or pH. In the absence of active cathepsin X, nuclear cathepsin L and cleavage of the known nuclear cathepsin L substrate, Lamin B1, were diminished. Thus, cathepsin X activity selectively regulates cathepsin L, which has the potential to impact the degree of cathepsin L proteolysis, the nature of substrates that it cleaves, and the location of cleavage.

Cellular depletion of major cathepsin proteases reveals their concerted activities for lysosomal proteolysis

Proteins delivered by endocytosis or autophagy to lysosomes are degraded by exo- and endoproteases. In humans 15 lysosomal cathepsins (CTS) act as important physiological regulators. The cysteine proteases CTSB and CTSL and the aspartic protease CTSD are the most abundant and functional important lysosomal proteinases. Whereas their general functions in proteolysis in the lysosome, their individual substrate, cleavage specificity, and their possible sequential action on substrate proteins have been previously studied, their functional redundancy is still poorly understood. To address a possible common role of highly expressed and functional important CTS proteases, we generated CTSB-, CTSD-, CTSL-, and CTSBDL-triple deficient (KO) human neuroblastoma-derived SH-SY5Y cells and CTSB-, CTSD-, CTSL-, CTSZ and CTSBDLZ-quadruple deficient (KO) HeLa cells. These cells with a combined cathepsin deficiency exhibited enlarged lysosomes and accumulated lipofuscin-like storage material. The lack of the three (SH-SY5Y) or four (HeLa) major CTSs caused an impaired autophagic flux and reduced degradation of endocytosed albumin. Proteome analyses of parental and CTS-depleted cells revealed an enrichment of cleaved peptides, lysosome/autophagy-associated proteins, and potentially endocytosed membrane proteins like the amyloid precursor protein (APP), which can be subject to endocytic degradation. Amino- and carboxyterminal APP fragments accumulated in the multiple CTS-deficient cells, suggesting that multiple CTS-mediated cleavage events regularly process APP. In summary, our analyses support the idea that different lysosomal cathepsins act in concert, have at least partially and functionally redundant substrates, regulate protein degradation in autophagy, and control cellular proteostasis, as exemplified by their involvement in the degradation of APP fragments.

Ion Mobility-Based Enrichment-Free N-Terminomics Analysis Reveals Novel Legumain Substrates in Murine Spleen

Aberrant levels of the asparaginyl endopeptidase legumain have been linked to inflammation, neurodegeneration, and cancer, yet our understanding of this protease is incomplete. Systematic attempts to identify legumain substrates have been previously confined to in vitro studies, which fail to mirror physiological conditions and obscure biologically relevant cleavage events. Using high-field asymmetric waveform ion mobility spectrometry (FAIMS), we developed a streamlined approach for proteome and N-terminome analyses without the need for N-termini enrichment. Compared to unfractionated proteomic analysis, we demonstrate FAIMS fractionation improves N-termini identification by >2.5 fold, resulting in the identification of >2882 unique N-termini from limited sample amounts. In murine spleens, this approach identifies 6366 proteins and 2528 unique N-termini, with 235 cleavage events enriched in WT compared to legumain-deficient spleens. Among these, 119 neo-N-termini arose from asparaginyl endopeptidase activities, representing novel putative physiological legumain substrates. The direct cleavage of selected substrates by legumain was confirmed using in vitro assays, providing support for the existence of physiologically relevant extra-lysosomal legumain activity. Combined, these data shed critical light on the functions of legumain and demonstrate the utility of FAIMS as an accessible method to improve depth and quality of N-terminomics studies.

Atg4B and Cathepsin B-Triggered in Situ Luciferin Formation for Precise Cancer Autophagy Bioluminescence Imaging

Autophagy plays a crucial role in tumorigenesis and progression, but current approaches to visualize it in vivo show limited precision due to their single-analyte-responsive mode. Hence, by simultaneously employing dual autophagy enzymes Atg4B and cathepsin B to trigger the in situ formation of luciferin, we herein propose a strategy for precise autophagy bioluminescence imaging. An Atg4B-responsive peptide Ac-Thr-Phe-Gly-d-Cys (TFGC) and a cathepsin B-activatable compound Ac-Lys-Gly-Arg-Arg-CBT (KGRR-CBT) were rationally designed. During tumor autophagy, these two compounds were uptaken by cancer cells and cleaved by their corresponding enzymes to yield d-cysteine and 2-cyano-6-aminobenzothiazole, respectively, which underwent a CBT-Cys click reaction to yield d-aminoluciferin, turning the bioluminescence "on". The responsiveness of these two compounds toward the two enzymes was tested in vitro, and the ability to turn bioluminescence "on" was validated in living cancer cells and in vivo. We anticipate that our precise autophagy imaging strategy could be further applied for the diagnosis of autophagy-related diseases in the near future.

The Role of Cysteine Protease Cathepsins B, H, C, and X/Z in Neurodegenerative Diseases and Cancer

Papain-like cysteine proteases are composed of 11 human cysteine cathepsins, originally located in the lysosomes. They exhibit broad specificity and act as endopeptidases and/or exopeptidases. Among them, only cathepsins B, H, C, and X/Z exhibit exopeptidase activity. Recently, cysteine cathepsins have been found to be present outside the lysosomes and often participate in various pathological processes. Hence, they have been considered key signalling molecules. Their potentially hazardous proteolytic activities are tightly regulated. This review aims to discuss recent advances in understanding the structural aspects of these four cathepsins, mechanisms of their zymogen activation, regulation of their activities, and functional aspects of these enzymes in neurodegeneration and cancer. Neurodegenerative effects have been evaluated, particularly in Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, multiple sclerosis, and neuropsychiatric disorders. Cysteine cathepsins also participate in tumour progression and metastasis through the overexpression and secretion of proteases, which trigger extracellular matrix degradation. To our knowledge, this is the first review to provide an in-depth analysis regarding the roles of cysteine cathepsins B, H, C, and X in neurodegenerative diseases and cancer. Further advances in understanding the functions of cysteine cathepsins in these conditions will result in the development of novel, targeted therapeutic strategies.

Zeolitic Imidazolate Framework-8 (ZIF-8) as a Drug Delivery Vehicle for the Transport and Release of Telomerase Inhibitor BIBR 1532

Telomerase is constitutively overexpressed in the majority of human cancers and telomerase inhibition provides a promising broad-spectrum anticancer therapeutic strategy. BIBR 1532 is a well-known synthetic telomerase inhibitor that blocks the enzymatic activity of hTERT, the catalytic subunit of telomerase. However, water insolubility of BIBR 1532 leads to low cellular uptake and inadequate delivery and thus, limits its anti-tumor effects. Zeolitic imidazolate framework-8 (ZIF-8) is considered as an attractive drug delivery vehicle for improved transport, release and anti-tumor effects of BIBR 1532. Herein, ZIF-8 and BIBR 1532@ZIF-8 were synthesized, respectively, and the physicochemical characterizations confirmed the successful encapsulation of BIBR 1532 in ZIF-8 coupled with an improved stability of BIBR 1532. ZIF-8 could alter the permeability of lysosomal membrane probably by the imidazole ring-dependent protonation. Moreover, ZIF-8 encapsulation facilitated the cellular uptake and release of BIBR 1532 with more accumulation in the nucleus. BIBR 1532 encapsulation with ZIF-8 triggered a more obvious growth inhibition of cancer cells as compared with free BIBR 1532. A more potent inhibition on hTERT mRNA expression, aggravated G0/G1 arrest accompanied with an increased cellular senescence were detected in BIBR 1532@ZIF-8-treated cancer cells. Our work has provided preliminary information on improving the transport, release and efficacy of water-insoluble small molecule drugs by using ZIF-8 as a delivery vehicle.

The endo-lysosomal system in Parkinson's disease: expanding the horizon

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease, and its prevalence is increasing with age. A wealth of genetic evidence indicates that the endo-lysosomal system is a major pathway driving PD pathogenesis with a growing number of genes encoding endo-lysosomal proteins identified as risk factors for PD, making it a promising target for therapeutic intervention. However, detailed knowledge and understanding of the molecular mechanisms linking these genes to the disease are available for only a handful of them (e.g. LRRK2, GBA1, VPS35). Taking on the challenge of studying poorly characterized genes and proteins can be daunting, due to the limited availability of tools and knowledge from previous literature. This review aims at providing a valuable source of molecular and cellular insights into the biology of lesser-studied PD-linked endo-lysosomal genes, to help and encourage researchers in filling the knowledge gap around these less popular genetic players. Specific endo-lysosomal pathways discussed range from endocytosis, sorting, and vesicular trafficking to the regulation of membrane lipids of these membrane-bound organelles and the specific enzymatic activities they contain. We also provide perspectives on future challenges that the community needs to tackle and propose approaches to move forward in our understanding of these poorly studied endo-lysosomal genes. This will help harness their potential in designing innovative and efficient treatments to ultimately re-establish neuronal homeostasis in PD but also other diseases involving endo-lysosomal dysfunction.