Evaluation of novel cathepsin-X inhibitors in vitro and in vivo and their ability to improve cathepsin-B-directed antitumor therapy

Cathepsin X is a conserved cell death protein involved in algal response to environmental stress

Phytoplankton are responsible for half of the global photosynthesis and form vast blooms in aquatic ecosystems. Bloom demise fuels marine microbial life and is suggested to be mediated by programmed cell death (PCD) induced by diverse environmental stressors. Despite its importance, the molecular basis for algal PCD remains elusive. Here, we reveal novel PCD genes conserved across distant algal lineages using cell-to-cell heterogeneity in the response of the diatom Phaeodactylum tricornutum to oxidative stress. Comparative transcriptomics of sorted sensitive and resilient subpopulations following oxidative stress revealed genes directly linked to their contrasting fates of cell death and survival. Comparing these genes with those found in a large-scale mutant screen in the green alga Chlamydomonas reinhardtii identified functionally relevant conserved PCD gene candidates, including the cysteine protease cathepsin X/Z (CPX). CPX mutants in P. tricornutum CPX1 and C. reinhardtii CYSTEINE ENDOPEPTIDASE 12 (CEP12) exhibited resilience to oxidative stress and infochemicals that induce PCD, supporting a conserved function of these genes in algal PCD. Phylogenetic and predictive structural analyses show that CPX is highly conserved in eukaryotes, and algae exhibit strong structural similarity to human Cathepsin X/Z (CTSZ), a protein linked to various diseases. CPX is expressed by diverse algae across the oceans and correlates with upcoming demise events during toxic Pseudo-nitzschia blooms, providing support for its ecological significance. Elucidating PCD components in algae sheds light on the evolutionary origin of PCD in unicellular organisms and on the cellular strategies employed by the population to cope with stressful conditions.

Characterization and kinetics of a cathepsin B-inhibiting protein from Musa acuminata Colla peel

Hyperexpression of cathepsin B caused by an imbalance of endogenous inhibitors is involved in multiple pathologies, hence making it a key therapeutic target. Protease inhibitors are effective biomolecules that regulate protease activities and are considered potential therapeutic agents in various diseases. Plant protease inhibitors have been reported as an effective complementary alternative drug. A proteinaceous cathepsin B inhibitor (CBI-BP) has been isolated from Musa acuminata Colla (banana) peel with a molecular weight of 27.9 kDa on SDS-PAGE. The purity of the CBI-BP was confirmed on the native- PAGE. The isolated CBI-BP showed an IC50 value of 8.14 μg and a Ki value of 10.59 μg (0.19 μM). Cathepsin B inhibition kinetics indicated that CBI-BP follows a mixed-type of cathepsin B inhibition. Its inhibition activity was also confirmed by reverse zymography. The inhibitor was stable from pH 2.6-10.0 with maximum activity at pH 7.2, temperature 25-100 °C and exhibited thermostability for 60 min at 70 °C. MALDI/TOF/MS analysis of CBI-BP showed 40 % similarity to the GH18 domain-containing protein (A0A4S8JRM9) from Musa balbisiana. Although in-silico docking studies showed binding of A0A4S8JRM9 to cathepsin B affects the binding energy of the substrate to cathepsin B but is not reported for any anti-cathepsin B activity. This suggests that isolated CBI-BP might be a novel protein with anti-cathepsin B activity. Thus the isolated CBI-BP may be further explored as possible anti-cathepsin B drug.

The novel quinoline derivative SKA-346 as a KCa3.1 channel selective activator

The calcium-activated KCa3.1 channel plays a crucial role in T-cell immune response. Genetic manipulation of T-cells to upregulate the expression of K+ channels has been shown to boost T-cell cytotoxicity in cancer. Here, we aimed to identify and characterize an activator that would augment KCa3.1 currents without affecting other channels. We synthesized five quinoline derivatives and used electrophysiology to screen them on KCa3.1 and a panel of 14 other ion channels. One quinoline derivative, SKA-346, activated KCa3.1 with an EC50 of 1.9 μM and showed selectivity against the other channels. In silico analysis using RosettaLigand and GLIDE demonstrated a well-converged pose of SKA-346 in a binding pocket at the interface between the calmodulin N-lobe and the S45A helix in the S4-S5 linker of the KCa3.1 channel. SKA-346 (30 mg kg-1), tolerated by mice after intra-peritoneal administration, exhibited a peak plasma concentration of 6.29 μg mL-1 (29.2 μM) at 15 min and a circulating half-life (t 1/2) of 2.8 h. SKA-346 could serve as a template for the development of more potent KCa3.1 activators to enhance T-cell cytotoxicity in cancer.

Compensational role between cathepsins

Cathepsins, a family of lysosomal peptidases, play a crucial role in maintaining cellular homeostasis by regulating protein turnover and degradation as well as many specific regulatory actions that are important for proper cell function and human health. Alterations in the activity and expression of cathepsins have been observed in many diseases such as cancer, inflammation, neurodegenerative disorders, bone remodelling-related conditions and others. These changes are not exclusively harmful, but rather appear to be a compensatory response on the lack of one cathepsin in order to maintain tissue integrity. The upregulation of specific cathepsins in response to the inhibition or dysfunction of other cathepsins suggests a fine-tuned system of proteolytic balance and understanding the compensatory role of cathepsins may improve therapeutic potential of cathepsin's inhibitors. Selectively targeting one cathepsin or modulating their activity could offer new treatment strategies for a number of diseases. This review emphasises the need for comprehensive research into cathepsin biology in the context of disease. The identification of the specific cathepsins involved in compensatory responses, the elucidation of the underlying molecular mechanisms and the development of targeted interventions could lead to innovative therapeutic approaches.

Upconversion nanoparticle-based fluorescence resonance energy transfer sensing platform for the detection of cathepsin B activity in vitro and in vivo

A simple fluorescence resonance energy transfer (FRET) sensing platform (termed as USP), comprised of upconversion nanoparticles (UCNPs) as the energy donor and Cy5 as the energy acceptor, has been synthesized for cathepsin B (CTSB) activity detection in vitro and in vivo. When Cy5-modified peptide substrate (peptide-Cy5) of CTSB is covalently linked on the surface of UCNPs, the FRET between the UCNPs (excitation: 980 nm; emission: 541 nm/655 nm) and Cy5 (excitation: 645 nm) leads to a reduction in the red upconversion luminescence (UCL) signal intensity of UCNPs. Cy5 can be liberated from UCNPs in the presence of CTSB through the cleavage of peptide-Cy5 by CTSB, leading to the recovery of the red UCL signal of UCNPs. Because the green UCL signal of UCNPs remains constant during the CTSB digestion, it can be considered as an internal reference. The findings demonstrate the ability of USP to detect CTSB with the linear detection ranges of 1 to 100 ng·mL^-1 in buffer and 2 × 10³ to 1 × 10⁵ cells in 0.2 mL cell lysates. The limits of detection (LODs) are 0.30 ng·mL^-1 in buffer and 887 cells in 0.2 mL of cell lysates (S/N = 3). The viability of USP to detect CTSB activity in tumor-bearing mice is has further been investigated using in vivo fluorescent imaging.

Cathepsin B in programmed cell death machinery: mechanisms of execution and regulatory pathways

Cathepsin B (CatB), a cysteine protease, is primarily localized within subcellular endosomal and lysosomal compartments. It is involved in the turnover of intracellular and extracellular proteins. Interest is growing in CatB due to its diverse roles in physiological and pathological processes. In functional defective tissues, programmed cell death (PCD) is one of the regulable fundamental mechanisms mediated by CatB, including apoptosis, pyroptosis, ferroptosis, necroptosis, and autophagic cell death. However, CatB-mediated PCD is responsible for disease progression under pathological conditions. In this review, we provide an overview of the critical roles and regulatory pathways of CatB in different types of PCD, and discuss the possibility of CatB as an attractive target in multiple diseases. We also summarize current gaps in the understanding of the involvement of CatB in PCD to highlight future avenues for research.

Melatonin attenuates chronic stress-induced hippocampal inflammatory response and apoptosis by inhibiting ADAM17/TNF-α axis

Melatonin, as a dietary supplement, has a potent neuroprotective effect and exerts a certain antidepressant effect. This study explored the molecular mechanisms and targets of melatonin on chronic stress-induced hippocampal damage from the perspective of inhibiting inflammatory cytokines release. Our results indicated that melatonin alleviated chronic restraint stress (CRS)-induced inflammatory response and apoptosis, thus improving hippocampal structural damage and subsequent depression-like behaviors in rats. The radar map displayed that the change of TNF-α content was the most significant. Meanwhile, correlation analysis showed that TNF-α content was highly positively correlated with apoptosis. Molecular autodocking studies suggested that TNF-α converting enzyme ADAM17 as a potential target has a priority in docking with melatonin. Molecular mechanism studies indicated that melatonin inhibited CRS-induced activation of the ADAM17/TNF-α axis and its downstream proteins p38 and p53 phosphorylation in the hippocampus. Analogously, Both ADAM17 inhibitor TMI-1 and TNF-α inhibitor thalidomide relieved the effects of CRS on ADAM17/TNF-α axis and its downstream proteins phosphorylation, hippocampal apoptosis, hippocampal inflammatory response, and depression-like behaviors in rats. Altogether, these findings reveal that melatonin relieves CRS-induced inflammatory response and apoptosis, and subsequent depression-like behaviors by inhibiting ADAM17/TNF-α axis.

All Roads Lead to Cathepsins: The Role of Cathepsins in Non-Alcoholic Steatohepatitis-Induced Hepatocellular Carcinoma

Cathepsins are lysosomal proteases that are essential to maintain cellular physiological homeostasis and are involved in multiple processes, such as immune and energy regulation. Predominantly, cathepsins reside in the lysosomal compartment; however, they can also be secreted by cells and enter the extracellular space. Extracellular cathepsins have been linked to several pathologies, including non-alcoholic steatohepatitis (NASH) and hepatocellular carcinoma (HCC). NASH is an increasingly important risk factor for the development of HCC, which is the third leading cause of cancer-related deaths and poses a great medical and economic burden. While information regarding the involvement of cathepsins in NASH-induced HCC (NASH-HCC) is limited, data to support the role of cathepsins in either NASH or HCC is accumulating. Since cathepsins play a role in both NASH and HCC, it is likely that the role of cathepsins is more significant in NASH-HCC compared to HCC derived from other etiologies. In the current review, we provide an overview on the available data regarding cathepsins in NASH and HCC, argue that cathepsins play a key role in the transition from NASH to HCC, and shed light on therapeutic options in this context.