Anabaenopeptins: What We Know So Far.

Cyanobacteria are microorganisms with photosynthetic mechanisms capable of colonizing several distinct environments worldwide. They can produce a vast spectrum of bioactive compounds with different properties, resulting in an improved adaptative capacity. Their richness in secondary metabolites is related to their unique and diverse metabolic apparatus, such as Non-Ribosomal Peptide Synthetases (NRPSs). One important class of peptides produced by the non-ribosomal pathway is anabaenopeptins. These cyclic hexapeptides demonstrated inhibitory activity towards phosphatases and proteases, which could be related to their toxicity and adaptiveness against zooplankters and crustaceans. Thus, this review aims to identify key features related to anabaenopeptins, including the diversity of their structure, occurrence, the biosynthetic steps for their production, ecological roles, and biotechnological applications.

Discovery and In Vivo Anti-inflammatory Activity Evaluation of a Novel Non-peptidyl Non-covalent Cathepsin C Inhibitor.

Cathepsin C (Cat C) participates in inflammation and immune regulation by affecting the activation of neutrophil serine proteases (NSPs). Therefore, cathepsin C is an attractive target for treatment of NSP-related inflammatory diseases. Here, the complete discovery process of the first potent "non-peptidyl non-covalent cathepsin C inhibitor" was described with hit finding, structure optimization, and lead discovery. Starting with hit 14, structure-based optimization and structure-activity relationship study were comprehensively carried out, and lead compound 54 was discovered as a potent drug-like cathepsin C inhibitor both in vivo and in vitro. Also, compound 54 (with cathepsin C Enz IC50 = 57.4 nM) exhibited effective anti-inflammatory activity in an animal model of chronic obstructive pulmonary disease. These results confirmed that the non-peptidyl and non-covalent derivative could be used as an effective cathepsin C inhibitor and encouraged us to continue further drug discovery on the basis of this finding.

Molecular Initiating Events Associated with Drug-Induced Liver Malignant Tumors: An Integrated Study of the FDA Adverse Event Reporting System and Toxicity Predictions.

Liver malignant tumors (LMTs) represent a serious adverse drug event associated with drug-induced liver injury. Increases in endocrine-disrupting chemicals (EDCs) have attracted attention in recent years, due to their liver function-inhibiting abilities. Exposure to EDCs can induce nonalcoholic fatty liver disease and nonalcoholic steatohepatitis, which are major etiologies of LMTs, through interaction with nuclear receptors (NR) and stress response pathways (SRs). Therefore, exposure to potential EDC drugs could be associated with drug-induced LMTs. However, the drug classes associated with LMTs and the molecular initiating events (MIEs) that are specific to these drugs are not well understood. In this study, using the Food and Drug Administration Adverse Event Reporting System, we detected LMT-inducing drug signals based on adjusted odds ratios. Furthermore, based on the hypothesis that drug-induced LMTs are triggered by NR and SR modulation of potential EDCs, we used the quantitative structure-activity relationship platform for toxicity prediction to identify potential MIEs that are specific to LMT-inducing drug classes. Events related to cell proliferation and apoptosis, DNA damage, and lipid accumulation were identified as potential MIEs, and their relevance to LMTs was supported by the literature. The findings of this study may contribute to drug development and research, as well as regulatory decision making.

A cyclic peptide inhibitor of the SARS-CoV-2 main protease.

This paper presents the design and study of a first-in-class cyclic peptide inhibitor against the SARS-CoV-2 main protease (Mpro). The cyclic peptide inhibitor is designed to mimic the conformation of a substrate at a C-terminal autolytic cleavage site of Mpro. The cyclic peptide contains a [4-(2-aminoethyl)phenyl]-acetic acid (AEPA) linker that is designed to enforce a conformation that mimics a peptide substrate of Mpro. In vitro evaluation of the cyclic peptide inhibitor reveals that the inhibitor exhibits modest activity against Mpro and does not appear to be cleaved by the enzyme. Conformational searching predicts that the cyclic peptide inhibitor is fairly rigid, adopting a favorable conformation for binding to the active site of Mpro. Computational docking to the SARS-CoV-2 Mpro suggests that the cyclic peptide inhibitor can bind the active site of Mpro in the predicted manner. Molecular dynamics simulations provide further insights into how the cyclic peptide inhibitor may bind the active site of Mpro. Although the activity of the cyclic peptide inhibitor is modest, its design and study lays the groundwork for the development of additional cyclic peptide inhibitors against Mpro with improved activities.

USP7 limits CDK1 activity throughout the cell cycle.

Chemical inhibitors of the deubiquitinase USP7 are currently being developed as anticancer agents based on their capacity to stabilize P53. Regardless of this activity, USP7 inhibitors also generate DNA damage in a p53-independent manner. However, the mechanism of this genotoxicity and its contribution to the anticancer effects of USP7 inhibitors are still under debate. Here we show that, surprisingly, even if USP7 inhibitors stop DNA replication, they also induce a widespread activation of CDK1 throughout the cell cycle, which leads to DNA damage and is toxic for mammalian cells. In addition, USP7 interacts with the phosphatase PP2A and supports its active localization in the cytoplasm. Accordingly, inhibition of USP7 or PP2A triggers very similar changes of the phosphoproteome, including a widespread increase in the phosphorylation of CDK1 targets. Importantly, the toxicity of USP7 inhibitors is alleviated by lowering CDK1 activity or by chemical activation of PP2A. Our work reveals that USP7 limits CDK1 activity at all cell cycle stages, providing a novel mechanism that explains the toxicity of USP7 inhibitors through untimely activation of CDK1.

SARS-CoV-2 Papain-Like Protease Potential Inhibitors-In Silico Quantitative Assessment.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) encodes the papain-like protease (PLpro). The protein not only plays an essential role in viral replication but also cleaves ubiquitin and ubiquitin-like interferon-stimulated gene 15 protein (ISG15) from host proteins, making it an important target for developing new antiviral drugs. In this study, we searched for novel, noncovalent potential PLpro inhibitors by employing a multistep in silico screening of a 15 million compound library. The selectivity of the best-scored compounds was evaluated by checking their binding affinity to the human ubiquitin carboxy-terminal hydrolase L1 (UCH-L1), which, as a deubiquitylating enzyme, exhibits structural and functional similarities to the PLpro. As a result, we identified 387 potential, selective PLpro inhibitors, from which we retrieved the 20 best compounds according to their IC50 values toward PLpro estimated by a multiple linear regression model. The selected candidates display potential activity against the protein with IC50 values in the nanomolar range from approximately 159 to 505 nM and mostly adopt a similar binding mode to the known, noncovalent SARS-CoV-2 PLpro inhibitors. We further propose the six most promising compounds for future in vitro evaluation. The results for the top potential PLpro inhibitors are deposited in the database prepared to facilitate research on anti-SARS-CoV-2 drugs.

SARS-CoV-2 Mpro inhibitors with antiviral activity in a transgenic mouse model.

The COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continually poses serious threats to global public health. The main protease (Mpro) of SARS-CoV-2 plays a central role in viral replication. We designed and synthesized 32 new bicycloproline-containing Mpro inhibitors derived from either boceprevir or telaprevir, both of which are approved antivirals. All compounds inhibited SARS-CoV-2 Mpro activity in vitro, with 50% inhibitory concentration values ranging from 7.6 to 748.5 nM. The cocrystal structure of Mpro in complex with MI-23, one of the most potent compounds, revealed its interaction mode. Two compounds (MI-09 and MI-30) showed excellent antiviral activity in cell-based assays. In a transgenic mouse model of SARS-CoV-2 infection, oral or intraperitoneal treatment with MI-09 or MI-30 significantly reduced lung viral loads and lung lesions. Both also displayed good pharmacokinetic properties and safety in rats.

Extracellular neutral protease from Arthrospira platensis: Production, optimization and partial characterization.

Proteases are industrially important catalysts. They belong to a complex family of enzymes that perform highly focused proteolysis functions. Given their potential use, there has been renewed interest in the discovery of proteases with novel properties and a constant thrust to optimize the enzyme production. In the present study, a novel extracellular neutral protease produced from Arthrospira platensis was detected and characterized. Its proteolytic activity was strongly activated by ß-mercaptoethanol, 5,5-dithio-bis-(2-nitrobenzoic acid) and highly inhibited by Hg2+ and Zn2+ metal ions which support the fact that the studied protease belongs to the cysteine protease family. Using statistical modelling methodology, the logistic model has been selected to predict A. platensis growth-kinetic values. The optimal culture conditions for neutral protease production were found using Box-Behnken Design. The maximum experimental protease activities (159.79 U/mL) was achieved after 13 days of culture in an optimized Zarrouk medium containing 0.625 g/L NaCl, 0.625 g/L K2HPO4 and set on 9.5 initial pH. The extracellular protease of A. platensis can easily be used in the food industry for its important activity at neutral pH and its low production cost since it is a valuation of the residual culture medium after biomass recovery.

Biomimetic Macrocyclic Inhibitors of Human Cathepsin D: Structure-Activity Relationship and Binding Mode Analysis.

Human cathepsin D (CatD), a pepsin-family aspartic protease, plays an important role in tumor progression and metastasis. Here, we report the development of biomimetic inhibitors of CatD as novel tools for regulation of this therapeutic target. We designed a macrocyclic scaffold to mimic the spatial conformation of the minimal pseudo-dipeptide binding motif of pepstatin A, a microbial oligopeptide inhibitor, in the CatD active site. A library of more than 30 macrocyclic peptidomimetic inhibitors was employed for scaffold optimization, mapping of subsite interactions, and profiling of inhibitor selectivity. Furthermore, we solved high-resolution crystal structures of three macrocyclic inhibitors with low nanomolar or subnanomolar potency in complex with CatD and determined their binding mode using quantum chemical calculations. The study provides a new structural template and functional profile that can be exploited for design of potential chemotherapeutics that specifically inhibit CatD and related aspartic proteases.

Lead Molecule Prediction and Characterization for Designing MERS-CoV 3C-like Protease Inhibitors: An In silico Approach.

BACKGROUND: 3C-like protease also called the main protease is an essential enzyme for the completion of the life cycle of Middle East Respiratory Syndrome Coronavirus. In our study we predicted compounds which are capable of inhibiting 3C-like protease, and thus inhibit the lifecycle of Middle East Respiratory Syndrome Coronavirus using in silico methods. METHODS: Lead like compounds and drug molecules which are capable of inhibiting 3C-like protease was identified by structure-based virtual screening and ligand-based virtual screening method. Further, the compounds were validated through absorption, distribution, metabolism and excretion filtering. RESULTS: Based on binding energy, ADME properties, and toxicology analysis, we finally selected 3 compounds from structure-based virtual screening (ZINC ID: 75121653, 41131653, and 67266079) having binding energy -7.12, -7.1 and -7.08 Kcal/mol, respectively and 5 compounds from ligandbased virtual screening (ZINC ID: 05576502, 47654332, 04829153, 86434515 and 25626324) having binding energy -49.8, -54.9, -65.6, -61.1 and -66.7 Kcal/mol respectively. All these compounds have good ADME profile and reduced toxicity. Among eight compounds, one is soluble in water and remaining 7 compounds are highly soluble in water. All compounds have bioavailability 0.55 on the scale of 0 to 1. Among the 5 compounds from structure-based virtual screening, 2 compounds showed leadlikeness. All the compounds showed no inhibition of cytochrome P450 enzymes, no blood-brain barrier permeability and no toxic structure in medicinal chemistry profile. All the compounds are not a substrate of P-glycoprotein. CONCLUSION: Our predicted compounds may be capable of inhibiting 3C-like protease but need some further validation in wet lab.

Novel non-peptidic small molecule inhibitors of secreted aspartic protease 2 (SAP2) for the treatment of resistant fungal infections.

Targeting secreted aspartic protease 2 (SAP2), a kind of virulence factor, represents a new strategy for antifungal drug discovery. In this report, the first-generation of small molecule SAP2 inhibitors was rationally designed and optimized using a structure-based approach. In particular, inhibitor 23h was highly potent and selective and showed good antifungal potency for the treatment of resistant Candida albicans infections.

The aminopeptidase inhibitor, z-L-CMK, is toxic and induces cell death in Jurkat T cells through oxidative stress.

The leucine aminopeptidase inhibitor, benzyloxycarbonyl-leucine-chloromethylketone (z-L-CMK), was found to be toxic and readily induce cell death in Jurkat T cells. Dose-response studies show that lower concentration of z-L-CMK induced apoptosis in Jurkat T cells whereas higher concentration causes necrosis. In z-L-CMK-induced apoptosis, both the initiator caspases (-8 and -9) and effector caspases (-3 and -6) were processed to their respective subunits. However, the caspases remained intact in z-L-CMK-induced necrosis. The caspase inhibitor, z-VAD-FMK inhibited z-L-CMK-mediated apoptosis and caspase processing but has no effect on z-L-CMK-induced necrosis in Jurkat T cells. The high mobility group protein B1 (HMGB1) protein was found to be released into the culture medium by the necrotic cells and not the apoptotic cells. These results indicate that the necrotic cell death mediated by z-L-CMK at high concentrations is via classical necrosis rather than secondary necrosis. We also demonstrated that cell death mediated by z-L-CMK was associated with oxidative stress via the depletion of intracellular glutathione (GSH) and increase in reactive oxygen species (ROS), which was blocked by N-acetyl cysteine. Taken together, the results demonstrated that z-L-CMK is toxic to Jurkat T cells and induces apoptosis at low concentrations, while at higher concentrations the cells die of necrosis. The toxic side effects in Jurkat T cells mediated by z-L-CMK are associated with oxidative stress via the depletion of GSH and accumulation of ROS.

The effect of angiotensin receptor neprilysin inhibitor, sacubitril/valsartan, on central nervous system amyloid-ß concentrations and clearance in the cynomolgus monkey.

Sacubitril/valsartan (LCZ696) is the first angiotensin receptor neprilysin inhibitor approved to reduce cardiovascular mortality and hospitalization in patients with heart failure with reduced ejection fraction. As neprilysin (NEP) is one of several enzymes known to degrade amyloid-ß (Aß), there is a theoretical risk of Aß accumulation following long-term NEP inhibition. The primary objective of this study was to evaluate the potential effects of sacubitril/valsartan on central nervous system clearance of Aß isoforms in cynomolgus monkeys using the sensitive Stable Isotope Labeling Kinetics (SILK™)-Aß methodology. The in vitro selectivity of valsartan, sacubitril, and its active metabolite sacubitrilat was established; sacubitrilat did not inhibit other human Aß-degrading metalloproteases. In a 2-week study, sacubitril/valsartan (50mg/kg/day) or vehicle was orally administered to female cynomolgus monkeys in conjunction with SILK™-Aß. Despite low cerebrospinal fluid (CSF) and brain penetration, CSF exposure to sacubitril was sufficient to inhibit NEP and resulted in an increase in the elimination half-life of Aß1-42 (65.3%; p=0.026), Aß1-40 (35.2%; p=0.04) and Aßtotal (29.8%; p=0.04) acutely; this returned to normal as expected with repeated dosing for 15days. CSF concentrations of newly generated Aß (AUC(0-24h)) indicated elevations in the more aggregable form Aß1-42 on day 1 (20.4%; p=0.039) and day 15 (34.7%; p=0.0003) and in shorter forms Aß1-40 (23.4%; p=0.009), Aß1-38 (64.1%; p=0.0001) and Aßtotal (50.45%; p=0.00002) on day 15. However, there were no elevations in any Aß isoforms in the brains of these monkeys on day 16. In a second study cynomolgus monkeys were administered sacubitril/valsartan (300mg/kg) or vehicle control for 39weeks; no microscopic brain changes or Aß deposition, as assessed by immunohistochemical staining, were present. Further clinical studies are planned to address the relevance of these findings.

Aluminium sulfate exposure: A set of effects on hydrolases from brain, muscle and digestive tract of juvenile Nile tilapia (Oreochromis niloticus).

Aluminium is a major pollutant due to its constant disposal in aquatic environments through anthropogenic activities. The physiological effects of this metal in fish are still scarce in the literature. This study investigated the in vivo and in vitro effects of aluminium sulfate on the activity of enzymes from Nile tilapia (Oreochromis niloticus): brain acetylcholinesterase (AChE), muscle cholinesterases (AChE-like and BChE-like activities), pepsin, trypsin, chymotrypsin and amylase. Fish were in vivo exposed during 14days when the following experimental groups were assayed: control group (CG), exposure to Al2(SO4)3 at 1µg·mL-1 (G1) and 3µg·mL-1 (G3) (concentrations compatible with the use of aluminium sulfate as coagulant in water treatment). In vitro exposure was performed using animals of CG treatment. Both in vivo and in vitro exposure increased cholinesterase activity in relation to controls. The highest cholinesterase activity was observed for muscle BChE-like enzyme in G3. In contrast, the digestive enzymes showed decreased activity in both in vivo and in vitro exposures. The highest inhibitory effect was observed for pepsin activity. The inhibition of serine proteases was also quantitatively analyzed in zymograms using pixel optical densitometry as area under the peaks (AUP) and integrated density (ID). These results suggest that the inhibition of digestive enzymes in combination with activation of cholinesterases in O. niloticus is a set of biochemical effects that evidence the presence of aluminium in the aquatic environment. Moreover, these enzymatic alterations may support further studies on physiological changes in this species with implications for its neurological and digestive metabolisms.

Structure-based exploration and exploitation of the S4 subsite of norovirus 3CL protease in the design of potent and permeable inhibitors.

Human noroviruses are the primary cause of epidemic and sporadic acute gastroenteritis. The worldwide high morbidity and mortality associated with norovirus infections, particularly among the elderly, immunocompromised patients and children, constitute a serious public health concern. There are currently no approved human vaccines or norovirus-specific small-molecule therapeutics or prophylactics. Norovirus 3CL protease has recently emerged as a potential therapeutic target for the development of anti-norovirus agents. We hypothesized that the S4 subsite of the enzyme may provide an effective means of designing potent and cell permeable inhibitors of the enzyme. We report herein the structure-guided exploration and exploitation of the S4 subsite of norovirus 3CL protease in the design and synthesis of effective inhibitors of the protease.

Protease inhibitor in scorpion (Mesobuthus eupeus) venom prolongs the biological activities of the crude venom.

It is hypothesized that protease inhibitors play an essential role in survival of venomous animals through protecting peptide/protein toxins from degradation by proteases in their prey or predators. However, the biological function of protease inhibitors in scorpion venoms remains unknown. In the present study, a trypsin inhibitor was purified and characterized from the venom of scorpion Mesobuthus eupeus, which enhanced the biological activities of crude venom components in mice when injected in combination with crude venom. This protease inhibitor, named MeKTT-1, belonged to Kunitz-type toxins subfamily. Native MeKTT-1 selectively inhibited trypsin with a Kivalue of 130 nmol·L(-1). Furthermore, MeKTT-1 was shown to be a thermo-stable peptide. In animal behavioral tests, MeKTT-1 prolonged the pain behavior induced by scorpion crude venom, suggesting that protease inhibitors in scorpion venom inhibited proteases and protect the functionally important peptide/protein toxins from degradation, consequently keeping them active longer. In conclusion, this was the first experimental evidence about the natural existence of serine protease inhibitor in the venom of scorpion Mesobuthus eupeus, which preserved the activity of venom components, suggests that scorpions may use protease inhibitors for survival.

High-Throughput Screening Uncovers Novel Botulinum Neurotoxin Inhibitor Chemotypes.

Botulism is caused by potent and specific bacterial neurotoxins that infect host neurons and block neurotransmitter release. Treatment for botulism is limited to administration of an antitoxin within a short time window, before the toxin enters neurons. Alternatively, current botulism drug development targets the toxin light chain, which is a zinc-dependent metalloprotease that is delivered into neurons and mediates long-term pathology. Several groups have identified inhibitory small molecules, peptides, or aptamers, although no molecule has advanced to the clinic due to a lack of efficacy in advanced models. Here we used a homogeneous high-throughput enzyme assay to screen three libraries of drug-like small molecules for new chemotypes that modulate recombinant botulinum neurotoxin light chain activity. High-throughput screening of 97088 compounds identified numerous small molecules that activate or inhibit metalloprotease activity. We describe four major classes of inhibitory compounds identified, detail their structure-activity relationships, and assess their relative inhibitory potency. A previously unreported chemotype in any context of enzyme inhibition is described with potent submicromolar inhibition (Ki = 200-300 nM). Additional detailed kinetic analyses and cellular cytotoxicity assays indicate the best compound from this series is a competitive inhibitor with cytotoxicity values around 4-5 µM. Given the potency and drug-like character of these lead compounds, further studies, including cellular activity assays and DMPK analysis, are justified.

BACE1 Physiological Functions May Limit Its Use as Therapeutic Target for Alzheimer's Disease.

The protease ß-site amyloid precursor protein (APP)-cleaving enzyme 1 (BACE1) is required for the production of the amyloid-ß (Aß) peptide, which is central to the pathogenesis of Alzheimer's disease (AD). Chronic inhibition of this protease may temper amyloid production and cure or prevent AD. However, while BACE1 inhibitors are being pushed forward as drug candidates, a remarkable gap in knowledge on the physiological functions of BACE1 and its close homolog BACE2 becomes apparent. Here we discuss the major discoveries of the past 3 years concerning BACE1 biology and to what extent these could limit the use of BACE1 inhibitors in the clinic.

Mitigation of opioid off-target effects and identification of structural drivers of opioid receptor engagement for BACE-1 small molecule inhibitors.

Application of safety lead optimization screening strategies during the early stage of drug discovery led to the identification of a series of CNS-active small molecule inhibitors with opioid off-target effects, as evidenced by potent agonistic activity in functional cell-based assays for mu (MOP), kappa (KOP) and delta (DOP) opioid receptors. The translation of these effects was confirmed in vivo with the following observations: hypoactivity and decreased fecal production in rats (characteristic of MOP agonism); increased urine production in rats (characteristic of KOP agonism); and decreased intestinal transit time in mice, which was partially blocked by the MOP antagonist naloxone, demonstrating that the in vivo effects were specific for MOP. Based on the confirmation of in vitro-in vivo translatability, an in vitro screening strategy was implemented that resulted in the identification of an optimized backup molecule, devoid of in vivo off-target opioid effects. In addition, in silico modeling by docking of the various molecules to the opioid receptors allowed the identification of the structural drivers of these off-target effects, which can be applied to future chemical-design criteria. Thus, implementation of the safety lead optimization strategy described in this article demonstrates the utility and impact of such approaches on risk mitigation and identification of lead small molecules with improved safety profiles.

Antiviral activities of 15 dengue NS2B-NS3 protease inhibitors using a human cell-based viral quantification assay.

The dengue virus is a mosquito-borne pathogen responsible for an estimated 50-100 million human dengue infections annually. There are currently no approved drugs against this disease, resulting in a major unmet clinical need. The dengue viral NS2B-NS3 protease has been identified as a plausible drug target due to its involvement in viral replication in mammalian host cells. In the past decade, at least 20 dengue NS2B-NS3 protease inhibitors have been reported in the literature with a range of inhibitory activities in protease assays. However, such assays do not shed light on an inhibitor's ability to penetrate human cell membranes where the viral protease resides. In this study, we investigated the antiviral activities of 15 small-molecule and peptide-based NS2B-NS3 inhibitors on dengue serotype 2-infected HuH-7 human hepatocarcinoma cells. Experimental results revealed anthraquinone ARDP0006 (compound 5) to be the most potent inhibitor which reduced dengue viral titer by more than 1 log PFU/mL at 1 µM in our cell-based assays involving HuH-7 and K562 cell lines, suggesting that its scaffold could serve as a lead for further medicinal chemistry studies. Compound 5 was also found to be non-cytotoxic at 1 µM over 3 days incubation on HuH-7 cells using the Alamar Blue cellular toxicity assay.