Disturbed intracellular folate homeostasis impairs autophagic flux and increases hepatocytic lipid accumulation.

BACKGROUND: Metabolic associated fatty liver disease (MAFLD), a prevalent liver disorder affecting one-third of the global population, encompasses a spectrum ranging from fatty liver to severe hepatic steatosis. Both genetic and lifestyle factors, particularly diet and nutrition, contribute to its etiology. Folate deficiency, a frequently encountered type of malnutrition, has been associated with the pathogenesis of MAFLD and shown to impact lipid deposition. However, the underlying mechanisms of this relationship remain incompletely understood. We investigated the impact of disturbed folate-mediated one-carbon metabolism (OCM) on hepatic lipid metabolism both in vitro using human hepatoma cells and in vivo using transgenic fluorescent zebrafish displaying extent-, stage-, and duration-controllable folate deficiency upon induction. RESULTS: Disturbed folate-mediated one-carbon metabolism, either by inducing folate deficiency or adding anti-folate drug, compromises autophagy and causes lipid accumulation in liver cells. Disturbed folate status down-regulates cathepsin L, a key enzyme involved in autophagy, through inhibiting mTOR signaling. Interfered mitochondrial biology, including mitochondria relocation and increased fusion-fission dynamics, also occurs in folate-deficient hepatocytes. Folate supplementation effectively mitigated the impaired autophagy and lipid accumulation caused by the inhibition of cathepsin L activity, even when the inhibition was not directly related to folate deficiency. CONCLUSIONS: Disruption of folate-mediated OCM diminishes cathepsin L expression and impedes autophagy via mTOR signaling, leading to lipid accumulation within hepatocytes. These findings underscore the crucial role of folate in modulating autophagic processes and regulating lipid metabolism in the liver.

SARS-CoV-2 Spike Protein Induces Time-Dependent CTSL Upregulation in HeLa Cells and Alveolarspheres.

Autophagy and lysosomal pathways are involved in the cell entry of SARS-CoV-2 virus. To infect the host cell, the spike protein of SARS-CoV-2 binds to the cell surface receptor angiotensin-converting enzyme 2 (ACE2). To allow the fusion of the viral envelope with the host cell membrane, the spike protein has to be cleaved. One possible mechanism is the endocytosis of the SARS-CoV-2-ACE2 complex and subsequent cleavage of the spike protein, mainly by the lysosomal protease cathepsin L. However, detailed molecular and dynamic insights into the role of cathepsin L in viral cell entry remain elusive. To address this, HeLa cells and iPSC-derived alveolarspheres were treated with recombinant SARS-CoV-2 spike protein, and the changes in mRNA and protein levels of cathepsins L, B, and D were monitored. Additionally, we studied the effect of cathepsin L deficiency on spike protein internalization and investigated the influence of the spike protein on cathepsin L promoters in vitro. Furthermore, we analyzed variants in the genes coding for cathepsin L, B, D, and ACE2 possibly associated with disease progression using data from Regeneron's COVID Results Browser and our own cohort of 173 patients with COVID-19, exhibiting a variant of ACE2 showing significant association with COVID-19 disease progression. Our in vitro studies revealed a significant increase in cathepsin L mRNA and protein levels following exposure to the SARS-CoV-2 spike protein in HeLa cells, accompanied by elevated mRNA levels of cathepsin B and D in alveolarspheres. Moreover, an increase in cathepsin L promoter activity was detected in vitro upon spike protein treatment. Notably, the knockout of cathepsin L resulted in reduced internalization of the spike protein. The study highlights the importance of cathepsin L and lysosomal proteases in the SARS-CoV-2 spike protein internalization and suggests the potential of lysosomal proteases as possible therapeutic targets against COVID-19 and other viral infections.

Studies on the Relationships between Growth and Gonad Development during First Sexual Maturation of Macrobrachium nipponense and Associated SNPs Screening.

In this study, we used full-sib families to investigate the association between growth and gonad development during first sexual maturation of M. nipponense. We found that male GSI was significantly negatively correlated with growth traits (p < 0.01) and there were no significant correlations between female GSI (Gonadosomatic index) and growth traits (p > 0.05). HSI (Hepatopancreas index) in both males and females showed no significant correlations with growth traits (p > 0.05). We furthermore investigated the association between the specific allele of Mn-CTS L1 polymorphism and gonad development and growth traits. In total, 35 mutation loci were screened and 16 high-quality single-nucleotide polymorphisms (SNPs) loci were obtained after validation. Four and two SNPs proved to be strongly associated with all growth traits in female and male M. nipponense separately, among which A+118T might be a candidate SNP positively associated with large growth traits. Two and one SNPs were screened, respectively, in males and females to associate with GSI, while three SNPs were detected to associate with female HSI, among which A+1379C may be applied as a potential molecular marker for gene-assisted selection to improve both reproduction speed and growth traits in M. nipponense.

Evaluation of Reproductive Histology Response of Adult Fasciola hepatica in Goats Vaccinated with Cathepsin L Phage-Exposed Mimotopes.

Fasciolosis, a globally re-emerging zoonotic disease, is mostly caused by the parasitic infection with Fasciola hepatica, often known as the liver fluke. This disease has a considerable impact on livestock productivity. This study aimed to evaluate the fluke burdens and faecal egg counts in goats that were administered phage clones of cathepsin L mimotopes and then infected with F. hepatica metacercariae. Additionally, the impact of vaccination on the histology of the reproductive system, specifically related to egg generation in adult parasites, was examined. A total of twenty-four goats, which were raised in sheds, were divided into four groups consisting of six animals each. These groups were randomly assigned. The goats were then subjected to two rounds of vaccination. Each vaccination involved the administration of 1 × 1013 phage particles containing specific mimotopes for cathepsin L2 (group 1: PPIRNGK), cathepsin L1 (group 2: DPWWLKQ), and cathepsin L1 (group 3: SGTFLFS). The immunisations were carried out on weeks 0 and 4, and the Quil A adjuvant was used in combination with the mimotopes. The control group was administered phosphate-buffered saline (PBS) (group 4). At week 6, all groups were orally infected with 200 metacercariae of F. hepatica. At week 22 following the initial immunisation, the subjects were euthanised, and adult F. hepatica specimens were retrieved from the bile ducts and liver tissue, and subsequently quantified. The specimens underwent whole-mount histology for the examination of the reproductive system, including the testis, ovary, vitellaria, Mehlis' gland, and uterus. The mean fluke burdens following the challenge were seen to decrease by 50.4%, 62.2%, and 75.3% (p < 0.05) in goats that received vaccinations containing cathepsin L2 PPIRNGK, cathepsin L1 DPWWLKQ, and cathepsin L1 SGTFLFS, respectively. Animals that received vaccination exhibited a significant reduction in the production of parasite eggs. The levels of IgG1 and IgG2 isotypes in vaccinated goats were significantly higher than in the control group, indicating that protection is associated with the induction of a mixed Th1/Th2 immune response. The administration of cathepsin L to goats exhibits a modest level of efficacy in inducing histological impairment in the reproductive organs of liver flukes, resulting in a reduction in egg output.

Effect of Zanthoxylum bungeanum extract on the quality and cathepsin L activity of Niuganba.

Niuganba (NGB) is a traditional fermented beef product. Protease activity typically significantly affects the quality of NGB. Some natural food extracts may markedly influence NGB's protease activity and performance. This study aims to investigate the effect of Zanthoxylum bungeanum extract (ZBE) on the quality and cathepsin L activity of NGB. Following ZBE treatment, the myofibril fragmentation index (MFI), the content of TCA-soluble peptides, surface hydrophobicity, disulfide bond content, and cathepsin L activity of NGB significantly decrease. The content of free thiol groups and ß-sheet significantly increases. Scanning electron microscopy (SEM) reveals that the arrangement of muscle fibers in the cross-section of NGB is more compact after ZBE treatment. The research results indicate that ZBE effectively inhibits cathepsin L activity, alleviates the degradation of myofibrillar proteins, improves the physicochemical characteristics of NGB, and enhances its structural stability.

Discovering novel Cathepsin L inhibitors from natural products using artificial intelligence.

Cathepsin L (CTSL) is a promising therapeutic target for metabolic disorders. Current pharmacological interventions targeting CTSL have demonstrated potential in reducing body weight gain, serum insulin levels, and improving glucose tolerance. However, the clinical application of CTSL inhibitors remains limited. In this study, we used a combination of artificial intelligence and experimental methods to identify new CTSL inhibitors from natural products. Through a robust deep learning model and molecular docking, we screened 150 molecules from natural products for experimental validation. At a concentration of 100 µM, we found that 36 of them exhibited more than 50 % inhibition of CTSL. Notably, 13 molecules displayed over 90 % inhibition and exhibiting concentration-dependent effects. The molecular dynamics simulation on the two most potent inhibitors, Plumbagin and Beta-Lapachone, demonstrated stable interaction at the CTSL active site. Enzyme kinetics studies have shown that these inhibitors exert an uncompetitive inhibitory effect on CTSL. In conclusion, our research identifies Plumbagin and Beta-Lapachone as potential CTSL inhibitors, offering promising candidates for the treatment of metabolic disorders and illustrating the effectiveness of artificial intelligence in drug discovery.

Molecular characterization of EcCLP1, a new putative cathepsin L protease from Echinococcus canadensis.

Echinococcus granulosus sensu lato is a platyhelminth parasite and the etiological cause of cystic echinococcosis (CE), a zoonotic and neglected disease that infects animals and humans worldwide. As a part of the biological arsenal of the parasite, cathepsin L proteases are a group of proteins that are believed to be essential for parasite penetration, immune evasion, and establishment in the tissues of the host. In this work, we have cloned and sequenced a new putative cathepsin L protease from Echinococcus canadensis (EcCLP1). The bioinformatic analysis suggests that EcCLP1 could be synthesized as a zymogen and activated after proteolytic cleavage. The multiple sequence alignment with other cathepsin proteases reveals important functional conserved features like a conserved active site, an N-linked glycosylation residue, a catalytic triad, an oxyanion hole, and three putative disulfide bonds. The phylogenetic analysis suggests that EcCLP1 could indeed be a cathepsin L cysteine protease from clade 1 as it grouped with cathepsins from other species in this clade. Modeling studies suggest that EcCLP1 has two domains forming a cleft where the active site is located and an occluding role for the propeptide. The transcriptomic analysis reveals different levels of cathepsin transcript expression along the different stages of the parasite life cycle. The whole-mount immunohistochemistry shows an interesting superficial punctate pattern of staining which suggests a secretory pattern of expression. The putative cathepsin L protease characterized here may represent an interesting tool for diagnostic purposes, vaccine design, or a new pharmacological target for antiparasitic intervention.

Title: Caractérisation moléculaire d'EcCLP1, une nouvelle protéase putative de type cathepsine L d'Echinococcus canadensis. Abstract: Echinococcus granulosus sensu lato est un Plathelminthe parasite et la cause étiologique de l'échinococcose kystique (EK), une maladie zoonotique et négligée qui infecte les animaux et les humains dans le monde entier. En tant que partie de l'arsenal biologique du parasite, les protéases de type cathepsine L sont un groupe de protéines considérées comme essentielles à la pénétration du parasite, l'évasion immunitaire et son établissement dans les tissus de l'hôte. Dans ce travail, nous avons cloné et séquencé une nouvelle protéase putative de type cathepsine L d'Echinococcus canadensis (EcCLP1). L'analyse bioinformatique suggère qu'EcCLP1 pourrait être synthétisée sous forme de zymogène et activée après clivage protéolytique. L'alignement de séquences multiples avec d'autres protéases de type cathepsine révèle d'importantes caractéristiques fonctionnelles conservées telles qu'un site actif conservé, un résidu de glycosylation lié à N, une triade catalytique, un trou oxyanion et trois liaisons disulfure putatives. L'analyse phylogénétique suggère qu'EcCLP1 pourrait en effet être une protéase de type cathepsine L du clade 1 car elle se regroupe avec les cathepsines d'autres espèces de ce clade. Les études de modélisation suggèrent qu'EcCLP1 possède deux domaines formant une fente où se trouve le site actif et un rôle d'occlusion pour le propeptide. L'analyse transcriptomique révèle différents niveaux d'expression du transcrit de la cathepsine au cours des différentes étapes du cycle de vie du parasite. L'immunohistochimie de montages entiers montre un intéressant motif de coloration ponctuée superficielle qui suggère un modèle d'expression sécrétoire. La protéase putative de type cathepsine L caractérisée ici peut représenter un outil intéressant à des fins de diagnostic, de conception de vaccins ou une nouvelle cible pharmacologique pour une intervention antiparasitaire.

Cathepsin L induces cellular senescence by upregulating CUX1 and p16INK4a.

Cathepsin L (CTSL) has been implicated in aging and age-related diseases, such as cardiovascular diseases, specifically atherosclerosis. However, the underlying mechanism(s) is not well documented. Recently, we demonstrated a role of CUT-like homeobox 1 (CUX1) in regulating the p16INK4a-dependent cellular senescence in human endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) via its binding to an atherosclerosis-associated functional SNP (fSNP) rs1537371 on the CDKN2A/B locus. In this study, to determine if CTSL, which was reported to proteolytically activate CUX1, regulates cellular senescence via CUX1, we measured the expression of CTSL, together with CUX1 and p16INK4a, in human ECs and VSMCs undergoing senescence. We discovered that CUX1 is not a substrate that is cleaved by CTSL. Instead, CTSL is an upstream regulator that activates CUX1 transcription indirectly in a process that requires the proteolytic activity of CTSL. Our findings suggest that there is a transcription factor in between CTSL and CUX1, and cleavage of this factor by CTSL can activate CUX1 transcription, inducing endothelial senescence. Thus, our findings provide new insights into the signal transduction pathway that leads to atherosclerosis-associated cellular senescence.

Cathepsin L promotes oesophageal squamous cell carcinoma development and may be associated with tumour-associated macrophages.

Background: Oesophageal squamous cell carcinoma (ESCC) is a leading cause of cancer-related deaths worldwide because existing treatments are often insufficient. Therefore, new, reliable biomarkers must be identified. CTSL overexpression is closely associated with tumour progression and poor prognosis. However, the role and mechanism of CTSL as an oncogene in ESCC remain unclear. Methods: Genome-wide association study (GWAS) data were used for Mendelian randomization analysis to investigate the possible relationships between CTSL and ESCC. The correlation between CTSL expression and prognosis was analysed using GEO, TCGA, and GEPIA data. We compared CTSL expression among the cell types using single-cell sequencing. Correlations between CTSL and the tumour microenvironment, immune cell infiltration, tumour mutational load, immunological checkpoints, and treatment sensitivity in patients with ESCC were investigated. Finally, using mouse models and cellular investigations, we assessed the effects of CTSL on the growth, apoptosis, and metastasis of ESCC tumour cells. Results: CTSL was overexpressed in ESCC and correlated with prognosis. We also discovered its close association with cell immunity, especially with tumour-associated macrophages and immune checkpoints in the tumour microenvironment. CTSL may play a key role in ESCC development by affecting M2 macrophage polarisation. CTSL and the M2 macrophage marker genes showed significant positive correlations. Mendelian randomization analysis confirmed a relationship between CTSL and ESCC. Finally, our in vitro and in vivo experiments demonstrated that CTSL promoted the proliferation and migration of ESCC cells, validating our bioinformatic analysis. Conclusion: CTSL emerged as a crucial gene in ESCC that influences patient prognosis and immunity, particularly in association with M2 macrophages. Therefore, targeting or modulating CTSL levels may provide new therapeutic strategies for patients with ESCC.

"Every Cloud Has a Silver Lining": How Three Rare Diseases Defend Themselves from COVID-19 and What We Have Learnt from It.

The process of SARS-CoV-2 infection, responsible for the COVID-19 pandemic, is carried out through different steps, with the interaction between ACE2 and Spike protein (S) being crucial. Besides of that, the acidic environment of endosomes seems to play a relevant role in the virus uptake into cells and its intracellular replication. Patients affected by two rare genetic tubulopathies, Gitelman's and Bartter's Syndromes, and a rare genetic metabolic disease, Fabry Disease, have shown intrinsic protection from SARS-CoV-2 infection and COVID-19 on account of specific intrinsic features that interfere with the virus uptake into cells and its intracellular replication, which will be reported and discussed in this paper, providing interesting insights for present and future research.

Increased Circulating CD14+ Monocytes in Patients with Psoriatic Arthritis Presenting Impaired Apoptosis Activity.

Psoriatic arthritis (PsA) is a chronic inflammatory arthritis primarily affecting peripheral and axial joints. The osteolytic effect in the damaged joint is mediated by osteoclast activation. We aimed to investigate differential gene expression in peripheral CD14+ monocytes between patients with psoriatic arthritis (n = 15) and healthy controls (HCs; n = 15). Circulating CD14+ monocytes were isolated from peripheral blood mononuclear cells using CD14+ magnetic beads. Cell apoptosis was measured via Annexin V using flow cytometry. The gene expression profiling was analyzed via microarray (available in the NCBI GEO database; accession number GSE261765), and the candidate genes were validated using PCR. The results showed a higher number of peripheral CD14+ monocytes in patients with PsA than in the HCs. By analyzing the microarray data, identifying the differentially expressed genes, and conducting pathway enrichment analysis, we found that the apoptosis signaling pathway in CD14+ cells was significantly impaired in patients with PsA compared to the HCs. Among the candidate genes in the apoptotic signaling pathway, the relative expression level of cathepsin L was confirmed to be significantly lower in the PsAs than in the HCs. We concluded that the numbers of peripheral CD14+ monocytes increased, and their apoptosis activity was impaired in patients with PsA, which could lead to enhanced macrophage maturation and osteoclast activation. The resistance of apoptotic death in peripheral CD14+ monocytes may contribute to active joint inflammation in PsA.

The SPRi determination of cathepsin L and S in plasma and peritoneal fluid of women with endometriosis.

PURPOSE: Endometriosis is a common disease with a complex pathomechanism and atypical symptoms, often leading to delayed diagnosis. Currently, the sole method for confirming the presence of the disease is through laparoscopy and histopathological examination of collected tissue. However, this invasive procedure carries potential risk and complications, necessitating the exploration of non-surgical diagnostic methods for endometriosis. This study aims to analyze peritoneal fluid and plasma samples for the expression of cathepsin L and cathepsin S to identify potential biomarkers for non-invasive diagnostic approaches to endometriosis. MATERIAL AND METHODS: In this cross-sectional study, plasma and peritoneal fluid samples were obtained during laparoscopy from 63 patients diagnosed with chronic pelvic pain or infertility. The study group consisted of women with confirmed endometriosis. The concentrations of cathepsins L and S were determined using an SPRi biosensor. RESULTS: The study did not reveal significant differences in the concentrations of cathepsin L and cathepsin S between the control group and the study group, both in peritoneal fluid and plasma. CONCLUSIONS: Based on the results of this study, it appears that cathepsins L and S are not suitable candidates as biomarkers for endometriosis.

Cytoskeletal ß-tubulin and cysteine cathepsin L deregulation by SARS-CoV-2 spike protein interaction with the neuronal model cell line SH-SY5Y.

SARS-CoV-2 mainly infects the respiratory tract but can also target other organs, including the central nervous system. While it was recently shown that cells of the blood-brain-barrier are permissive to SARS-CoV-2 infection in vitro, it remains debated whether neurons can be infected. In this study, we demonstrate that vesicular stomatitis virus particles pseudotyped with the spike protein of SARS-CoV-2 variants WT, Alpha, Delta and Omicron enter the neuronal model cell line SH-SY5Y. Cell biological analyses of the pseudo-virus treated cultures showed marked alterations in microtubules of SH-SY5Y cells. Because the changes in ß-tubulin occurred in most cells, but only few were infected, we further asked whether interaction of the cells with spike protein might be sufficient to cause molecular and structural changes. For this, SH-SY5Y cells were incubated with trimeric spike proteins for time intervals of up to 24 h. CellProfiler™-based image analyses revealed changes in the intensities of microtubule staining in spike protein-incubated cells. Furthermore, expression of the spike protein-processing protease cathepsin L was found to be up-regulated by wild type, Alpha and Delta spike protein pseudotypes and cathepsin L was found to be secreted from spike protein-treated cells. We conclude that the mere interaction of the SARS-CoV-2 with neuronal cells can affect cellular architecture and proteolytic capacities. The molecular mechanisms underlying SARS-CoV-2 spike protein induced cytoskeletal changes in neuronal cells remain elusive and require future studies.

Establishment, optimization and validation of a fluorescence polarization-based high-throughput screening assay targeting cathepsin L inhibitors.

Cathepsin L (CTSL), a lysosomal cysteine proteinase, is primarily dedicated to the metabolic turnover of intracellular proteins. It is involved in various physiological processes and contributes to pathological conditions such as viral infection, tumor invasion and metastasis, inflammatory status, atherosclerosis, renal disease, diabetes, bone diseases, and other ailments. The coronavirus disease 2019 (COVID-19), with its rapid global spread and significant mortality, has been a worldwide epidemic since the late 2019s. Notably, CTSL plays a role in the processing of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein, providing a potential avenue to block coronavirus host cell entry and thereby inhibit SARS-CoV-2 infection in humans. In this study, we have developed a novel method using fluorescence polarization (FP) for screening CTSL inhibitors in a high-throughput format. The optimized assay demonstrated its appropriateness for high-throughput screening (HTS) with a Z-factor of 0.9 in a 96-well format. Additionally, the IC50 of the known inhibitor, Z-Phe-Tyr-CHO, was determined to be 188.50 ± 46.88 nM. Upon screening over 2000 small molecules, we identified, for the first time, the anti-CTSL properties of a benzothiazoles derivative named IMB 8015. This work presents a novel high-throughput approach and its application in discovering and evaluating CTSL inhibitors.

Cathepsin L prevents the accumulation of alpha-synuclein fibrils in the cell.

The deposition of α-synuclein (α-Syn) fibrils in neuronal cells has been implicated as a causative factor in Parkinson's disease (PD) and dementia with Lewy Bodies (DLB). α-Syn can be degraded by autophagy, proteasome, and chaperone-mediated autophagy, and previous studies have suggested the potency of certain cathepsins, lysosomal proteases, for α-Syn degradation. However, no studies have comprehensively evaluated all cathepsins. Here, we evaluated the efficacy of all 15 cathepsins using a cell model of α-Syn fibril propagation and found that overexpression of cathepsin L (CTSL) was the most effective in preventing the accumulation of α-Syn aggregates. CTSL-mediated degradation of α-Syn aggregates was dependent on the autophagy machinery, and CTSL itself promoted autophagy flux. Interestingly, CTSL was effective in autophagic degradation of wild-type (WT) α-Syn, but not in the case of A53T and E46K missense mutations, which are causative for familial PD. These results suggest that CTSL is a potential therapeutic strategy for sporadic PD pathology in WT α-Syn.

SiteMine: Large-scale binding site similarity searching in protein structure databases.

Drug discovery and design challenges, such as drug repurposing, analyzing protein-ligand and protein-protein complexes, ligand promiscuity studies, or function prediction, can be addressed by protein binding site similarity analysis. Although numerous tools exist, they all have individual strengths and drawbacks with regard to run time, provision of structure superpositions, and applicability to diverse application domains. Here, we introduce SiteMine, an all-in-one database-driven, alignment-providing binding site similarity search tool to tackle the most pressing challenges of binding site comparison. The performance of SiteMine is evaluated on the ProSPECCTs benchmark, showing a promising performance on most of the data sets. The method performs convincingly regarding all quality criteria for reliable binding site comparison, offering a novel state-of-the-art approach for structure-based molecular design based on binding site comparisons. In a SiteMine showcase, we discuss the high structural similarity between cathepsin L and calpain 1 binding sites and give an outlook on the impact of this finding on structure-based drug design. SiteMine is available at https://uhh.de/naomi.

Unveiling the Antiviral Efficacy of Forskolin: A Multifaceted In Vitro and In Silico Approach.

Coleus forskohlii (Willd.) Briq. is a medicinal herb of the Lamiaceae family. It is native to India and widely present in the tropical and sub-tropical regions of Egypt, China, Ethiopia, and Pakistan. The roots of C. forskohlii are edible, rich with pharmaceutically bioactive compounds, and traditionally reported to treat a variety of diseases, including inflammation, respiratory disorders, obesity, and viral ailments. Notably, the emergence of viral diseases is expected to quickly spread; consequently, these data impose a need for various approaches to develop broad active therapeutics for utilization in the management of future viral infectious outbreaks. In this study, the naturally occurring labdane diterpenoid derivative, Forskolin, was obtained from Coleus forskohlii. Additionally, we evaluated the antiviral potential of Forskolin towards three viruses, namely the herpes simplex viruses 1 and 2 (HSV-1 and HSV-2), hepatitis A virus (HAV), and coxsackievirus B4 (COX-B4). We observed that Forskolin displayed antiviral activity against HAV, COX-B4, HSV-1, and HSV-2 with IC50 values of 62.9, 73.1, 99.0, and 106.0 µg/mL, respectively. Furthermore, we explored the Forskolin's potential antiviral target using PharmMapper, a pharmacophore-based virtual screening platform. Forskolin's modeled structure was analyzed to identify potential protein targets linked to its antiviral activity, with results ranked based on Fit scores. Cathepsin L (PDB ID: 3BC3) emerged as a top-scoring hit, prompting further exploration through molecular docking and MD simulations. Our analysis revealed that Forskolin's binding mode within Cathepsin L's active site, characterized by stable hydrogen bonding and hydrophobic interactions, mirrors that of a co-crystallized inhibitor. These findings, supported by consistent RMSD profiles and similar binding free energies, suggest Forskolin's potential in inhibiting Cathepsin L, highlighting its promise as an antiviral agent.

Expression, purification, and biological activity evaluation of cathepsin L in mammalian cells.

Cathepsin L (CTSL) could cleave and activate SARS-CoV-2 Spike protein to promote viral entry, making it a hopeful therapeutic target for COVID-19 prevention and treatment. So CTSL inhibitors are considered to be a promising strategy to SARS-CoV-2 infection. CTSL has previously been expressed in inclusion body in Escherichia coli. In order to prepare CTSL with high purity and activity in soluble active form, we transformed HEK-293T cells with a recombinant mammalian expression plasmid. CTSL was purified to a purity about 95%, found to migrate at approximately 43 kDa and exhibited substrate specificity against Z-Phe-Arg-AMC with specific activity of no less than 85 081 U/mg, characteristic of active CTSL. Although eukaryotic purified CTSL is commercially available, our study for the first time reported the details of the expression, purification, and characterization of active, recombinant CTSL in eukaryocyte system, which laid an experimental foundation for the establishment of high-throughput screening model for anti-coronavirus drugs targeting CTSL.

Nanoengineered Red Blood Cells Loaded with TMPRSS2 and Cathepsin L Inhibitors Block SARS-CoV-2 Pseudovirus Entry into Lung ACE2+ Cells.

The enzymatic activities of Furin, Transmembrane serine proteinase 2 (TMPRSS2), Cathepsin L (CTSL), and Angiotensin-converting enzyme 2 (ACE2) receptor binding are necessary for the entry of coronaviruses into host cells. Precise inhibition of these key proteases in ACE2+ lung cells during a viral infection cycle shall prevent viral Spike (S) protein activation and its fusion with a host cell membrane, consequently averting virus entry to the cells. In this study, dual-drug-combined (TMPRSS2 inhibitor Camostat and CTSL inhibitor E-64d) nanocarriers (NCs) are constructed conjugated with an anti-human ACE2 (hACE2) antibody and employ Red Blood Cell (RBC)-hitchhiking, termed "Nanoengineered RBCs," for targeting lung cells. The significant therapeutic efficacy of the dual-drug-loaded nanoengineered RBCs in pseudovirus-infected K18-hACE2 transgenic mice is reported. Notably, the modular nanoengineered RBCs (anti-receptor antibody+NCs+RBCs) precisely target key proteases of host cells in the lungs to block the entry of Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), regardless of virus variations. These findings are anticipated to benefit the development of a series of novel and safe host-cell-protecting antiviral therapies.

Olgotrelvir, a dual inhibitor of SARS-CoV-2 Mpro and cathepsin L, as a standalone antiviral oral intervention candidate for COVID-19.

BACKGROUND: Oral antiviral drugs with improved antiviral potency and safety are needed to address current challenges in clinical practice for treatment of COVID-19, including the risks of rebound, drug-drug interactions, and emerging resistance. METHODS: Olgotrelvir (STI-1558) is designed as a next-generation antiviral targeting the SARS-CoV-2 main protease (Mpro), an essential enzyme for SARS-CoV-2 replication, and human cathepsin L (CTSL), a key enzyme for SARS-CoV-2 entry into host cells. FINDINGS: Olgotrelvir is a highly bioavailable oral prodrug that is converted in plasma to its active form, AC1115. The dual mechanism of action of olgotrelvir and AC1115 was confirmed by enzyme activity inhibition assays and co-crystal structures of AC1115 with SARS-CoV-2 Mpro and human CTSL. AC1115 displayed antiviral activity by inhibiting replication of all tested SARS-CoV-2 variants in cell culture systems. Olgotrelvir also inhibited viral entry into cells using SARS-CoV-2 Spike-mediated pseudotypes by inhibition of host CTSL. In the K18-hACE2 transgenic mouse model of SARS-CoV-2-mediated disease, olgotrelvir significantly reduced the virus load in the lungs, prevented body weight loss, and reduced cytokine release and lung pathologies. Olgotrelvir demonstrated potent activity against the nirmatrelvir-resistant Mpro E166 mutants. Olgotrelvir showed enhanced oral bioavailability in animal models and in humans with significant plasma exposure without ritonavir. In phase I studies (ClinicalTrials.gov: NCT05364840 and NCT05523739), olgotrelvir demonstrated a favorable safety profile and antiviral activity. CONCLUSIONS: Olgotrelvir is an oral inhibitor targeting Mpro and CTSL with high antiviral activity and plasma exposure and is a standalone treatment candidate for COVID-19. FUNDING: Funded by Sorrento Therapeutics.