Identification of clinically viable quinolinol inhibitors of botulinum neurotoxin A light chain

A Superior Corrosion Protection of Mg Alloy via Smart Nontoxic Hybrid Inhibitor-Containing Coatings

The increase of corrosion resistance of magnesium and its alloys by forming the smart self-healing hybrid coatings was achieved in this work in two steps. In the first step, using the plasma electrolytic oxidation (PEO) treatment, a ceramic-like bioactive coating was synthesized on the surface of biodegradable MA8 magnesium alloy. During the second step, the formed porous PEO layer was impregnated with a corrosion inhibitor 8-hydroxyquinoline (8-HQ) and bioresorbable polymer polycaprolactone (PCL) in different variations to enhance the protective properties of the coating. The composition, anticorrosion, and antifriction properties of the formed coatings were studied. 8-HQ allows controlling the rate of material degradation due to the self-healing effect of the smart coating. PCL treatment of the inhibitor-containing layer significantly improves the corrosion and wear resistance and retains an inhibitor in the pores of the PEO layer. It was revealed that the corrosion inhibitor incorporation method (including the number of steps, impregnation, and the type of solvent) significantly matters to the self-healing mechanism. The hybrid coatings obtained by a 1-step treatment in a dichloromethane solution containing 6 wt.% polycaprolactone and 15 g/L of 8-HQ are characterized by the best corrosion resistance. This coating demonstrates the lowest value of corrosion current density (3.02 × 10−7 A cm−2). The formation of the hybrid coating results in the corrosion rate decrease by 18 times (0.007 mm year−1) as compared to the blank PEO layer (0.128 mm year−1). An inhibitor efficiency was established to be 83.9%. The mechanism of corrosion protection of Mg alloy via smart hybrid coating was revealed.

Fragment-Based Lead Discovery Strategies in Antimicrobial Drug Discovery

Fragment-based lead discovery (FBLD) is a powerful application for developing ligands as modulators of disease targets. This approach strategy involves identification of interactions between low-molecular weight compounds (100-300 Da) and their putative targets, often with low affinity (K_D ~0.1-1 mM) interactions. The focus of this screening methodology is to optimize and streamline identification of fragments with higher ligand efficiency (LE) than typical high-throughput screening. The focus of this review is on the last half decade of fragment-based drug discovery strategies that have been used for antimicrobial drug discovery.

Designing, synthesis and evaluation of derived analogues of selected small molecule non-peptidic inhibitors against serotype BoNT/ F

Botulinum neurotoxins are lethal Biowarfare categorized in group A of selected agents, by CDC USA. The unavailability of counter-measures against these neurotoxins has been a matter of extensive research. The 8-hydroxyquinoline (8-HQ) scaffold is established privileged compound and its potential as drug candidate against BoNTs is recently being explored. We have reported 8-HQ compounds NSC1014 and NSC1011 as potential small molecule inhibitors against BoNT/F. In the present study, analogues of NSC84087 and NSC1014 were designed, synthesized and studied for their inhibitory role against BoNT/F intoxication through in silico study, in vitro and in-vivo assays. ∼25 in-house synthesized small molecule inhibitors were evaluated against rBoNT/F light chain through fluorescence thermal shift (FTS) assay and then further assessed through endopeptidase assay. The binding affinity analysis was done through surface plasmon resonance (SPR) based Proteon™ XPR 36 system. Finally, the in-vivo efficacy of these compounds was evaluated in mice model. Analogues C87.9, C87.10 and C87.12 of compound NSC84087 and C14.10, C14.11 and C14.13 of NSC1014 showed promising results through FTS assay and endopeptidase assay. SPR based protein-small molecule interaction studies showed KD values in sub-micromolar range signifying high affinity interaction. The IC₅₀ of C14.10 was found to be the lowest of 3.016 ± 0.798 μM as determined through endopeptidase assay. Finally, efficacy of selected molecules was evaluated in mice, C14.10 and C14.13 protected 40% animals against 4X LD₅₀ and extended survival time up to 200% at 10X LD₅₀. The present study thus proposes the emergence of NSC84087 and NSC1014 analogues as lead compound against BoNT/F.

Identification of Slow-Binding Inhibitors of the BoNT/A Protease

Botulinum neurotoxin A (BoNT/A) is a lethal toxin, which causes botulism, and is categorized as a bioterrorism threat, which causes flaccid paralysis and death. Botulinum A neurotoxicity is governed through its light chain (LC), a zinc metalloprotease. Pharmacological investigations aimed at negating BoNT/A's LC have typically looked to inhibitors that have been shown to inhibit the light chain's activity by reversible zinc chelation within its active site. This report outlines the first examples of nonpeptidic inhibitors of the BoNT/A LC that possess slow-binding kinetics, a needed logic to counteract the longevity of BoNT/A. Cyclopropane, alkyl, and alkenyl derivatives of 2,4-dichlorocinamic hydroxamic acid (DCHA) were shown to possess both one-step and two-step slow-binding kinetics. Structure-kinetic relationships (SKRs) were observed and were rationalized with the aid of docking models that predicted improved interactions with residues within a hydrophobic cleft adjacent to the active site.

Toxicology and pharmacology of botulinum and tetanus neurotoxins: an update

Tetanus and botulinum neurotoxins cause the neuroparalytic syndromes of tetanus and botulism, respectively, by delivering inside different types of neurons, metalloproteases specifically cleaving the SNARE proteins that are essential for the release of neurotransmitters. Research on their mechanism of action is intensively carried out in order to devise improved therapies based on antibodies and chemical drugs. Recently, major results have been obtained with human monoclonal antibodies and with single chain antibodies that have allowed one to neutralize the metalloprotease activity of botulinum neurotoxin type A1 inside neurons. In addition, a method has been devised to induce a rapid molecular evolution of the metalloprotease domain of botulinum neurotoxin followed by selection driven to re-target the metalloprotease activity versus novel targets with respect to the SNARE proteins. At the same time, an intense and wide spectrum clinical research on novel therapeutics based on botulinum neurotoxins is carried out, which are also reviewed here.

2-(2-(4-Methoxyphenyl)furo[3,2-h]quinolin-3-yl)acetic Acid

A simple and efficient protocol for the synthesis of the previously unknown 2-(2-(4-methoxyphenyl)furo[3,2-h]quinolin-3-yl)acetic acid was elaborated. The suggested method is based on the telescoped multicomponent reaction of 8-hydroxyquinoline, 4-methylglyoxal, and Meldrum’s acid. The studied process includes the initial interaction of the starting compounds in MeCN followed by intramolecular cyclization to the target product in refluxing acetic acid. The advantage of this approach is the application of readily available starting materials, atom economy, and a simple work-up procedure. The structure of the synthesized furylacetic acid derivative was proven by 1H, 13C, 2D-NMR, IR spectroscopy, and high-resolution mass spectrometry.

Novel Antimicrobial 8-Hydroxyquinoline-Based Agents: Current Development, Structure-Activity Relationships, and Perspectives

The search for new antimicrobials is imperative due to the emergent resistance of new microorganism strains. In this context, revisiting known classes like 8-hydroxyquinolines could be an interesting strategy to discover new agents. The 8-hydroxyquinoline derivatives nitroxoline and clioquinol are used to treat microbial infections; however, these drugs are underused, being available in few countries or limited to topical use. After years of few advances, in the last two decades, the potent activity of clioquinol and nitroxoline against several targets and the privileged structure of 8-hydroxyquinoline nucleus have prompted an increased interest in the design of novel antimicrobial, anticancer, and anti-Alzheimer agents based on this class. Herein, we discuss the current development and antimicrobial structure-activity relationships of this class in the perspective of using the 8-hydroxyquinoline nucleus for the search for novel antimicrobial agents. Furthermore, the most investigated molecular targets concerning 8-hydroxyquinoline derivatives are explored in the final section.

Precise Introduction of the -CHnX3-n (X = F, Cl, Br, I) Moiety to Target Molecules by a Radical Strategy: A Theoretical and Experimental Study

Addition of halomethyl radicals to form bioactive molecules has recently become an efficient strategy. The reaction has a bottleneck, however, which is the effective and selective generation of the proper halomethyl ^•CH_nX_3-n radical by combining CH_nX_4-n with a carbon radical. Understanding the reactivity and selectivity of carbon radicals in the hydrogen atom transfer (HAT) and halogen atom transfer (XAT) reactions of CH_nX_4-n is key to the development of such an attractive method. With the help of the emerging data-driven strategy, DFT calculations were used to explore various correlations. For selectivity, the relative energy barriers between HAT and XAT reactions (ΔG^⧧_H - ΔG^⧧_X) correlate reasonably well with the three parameters ΔG_H, ΔG_X, and IP, and the correlation studies reveal that the calculated IP_inver and the experimental ΔBDE can be used to conveniently predict the selectivity. Predicted selectivities are consistent with experimental determinations. This work not only provides a possibility for selecting carbon radicals with the known or easily obtained physicochemical data but also demonstrates that the informatic workflow such as generating data and identifying correlations has potential applications in mining reaction rules.

An 8-Hydroxy-Quinoline Derivative Protects Against Lipopolysaccharide-Induced Lethality in Endotoxemia by Inhibiting HMGB1-Mediated Caspase-11 Signaling

Sepsis, an inflammatory syndrome secondary to infection, is the leading cause of in-hospital lethality. It is evidenced that LPS, the major pathological component of the Gram-negative bacteria membrane, predominantly contributes to the pathogenesis of sepsis. Cytoplasmic lipopolysaccharide (LPS) can be sensed by the noncanonical inflammasome and triggers the oligomerization of caspase-11, resulting in pyroptosis and lethal immune responses in sepsis. A previous study has shown that hepatocyte-released high mobility group box 1 (HMGB1) mediates caspase-11–dependent lethality in sepsis by delivering extracellular LPS into the cytosol. Here, we established a phenotypic screening system using recombinant HMGB1 plus LPS in mouse peritoneal macrophages, identifying a novel 8-hydroxyquinoline derivative named 7-[phenyl (pyridin-2-ylamino) methyl] quinolin-8-ol (8-ol, NSC84094) that can specifically inhibit HMGB1-mediated caspase-11 signaling. 8-ol targets directly to HMGB1 and changes the secondary conformation, consequently disrupting the interaction between LPS and HMGB1 and inhibiting the HMGB1-mediated delivery of LPS into the cytosol. Intervention of 8-ol significantly reduced the release of IL-1α and IL-1β and protected against caspase-11–mediated organ injury and lethality in endotoxemic mice. Thus, this study clearly suggests that the HMGB1–caspase-11 pathway is a potential drug target in lethal immune disorders and might open a new avenue in the treatment of sepsis.

Drug screening to identify compounds to act as co-therapies for the treatment of Burkholderia species

Burkholderia pseudomallei is a soil-dwelling organism present throughout the tropics. It is the causative agent of melioidosis, a disease that is believed to kill 89,000 people per year. It is naturally resistant to many antibiotics, requiring at least two weeks of intravenous treatment with ceftazidime, imipenem or meropenem followed by 6 months of orally delivered co-trimoxazole. This places a large treatment burden on the predominantly middle-income nations where the majority of disease occurs. We have established a high-throughput assay for compounds that could be used as a co-therapy to potentiate the effect of ceftazidime, using the related non-pathogenic bacterium Burkholderia thailandensis as a surrogate. Optimization of the assay gave a Z’ factor of 0.68. We screened a library of 61,250 compounds and identified 29 compounds with a pIC₅₀ (-log₁₀(IC₅₀)) greater than five. Detailed investigation allowed us to down select to six “best in class” compounds, which included the licensed drug chloroxine. Co-treatment of B. thailandensis with ceftazidime and chloroxine reduced culturable cell numbers by two orders of magnitude over 48 hours, compared to treatment with ceftazidime alone. Hit expansion around chloroxine was performed using commercially available compounds. Minor modifications to the structure abolished activity, suggesting that chloroxine likely acts against a specific target. Finally, an initial study demonstrates the utility of chloroxine to act as a co-therapy to potentiate the effect of ceftazidime against B. pseudomallei. This approach successfully identified potential co-therapies for a recalcitrant Gram-negative bacterial species. Our assay could be used more widely to aid in chemotherapy to treat infections caused by these bacteria.

Botulinum toxin as an ultrasensitive reporter for bacterial and SARS-CoV-2 nucleic acid diagnostics

The rapid identification of pathogenic microorganisms plays a crucial role in the timely diagnosis and treatment strategies during a global pandemic, especially in resource-limited area. Herein, we present a sensitive biosensor strategy depended on botulinum neurotoxin type A light chain (BoNT/A LC) activated complex assay (BACA). BoNT/A LC, the surrogate of BoNT/A which embodying the most potent biological poisons, could serve as an ultrasensitive signal reporter with high signal-to-noise ratio to avoid common strong background response, poor stability and low intensity of current biosensor methods. A nanoparticle hybridization system, involving specific binding probes that recognize pathogenic 16S rRNAs or SARS-CoV-2 gene site, was developed to measure double-stranded biotinylated target DNA containing a single-stranded overhang using Fluorescence Resonance Energy Transfer (FRET)-based assay and colorimetric method. The method is validated widely by six different bacteria strains and severe acute respiratory related coronavirus 2 (SARS-CoV-2) nucleic acid, demonstrating a single cell or 1 aM nucleic acid detecting sensitivity. This detection strategy offers a solution for general applications and has a great prospect to be a simple instrument-free colorimetric tool, especially when facing public health emergency.

Identification of 3-hydroxy-1,2-dimethylpyridine-4(1H)-thione as a metal-binding motif for the inhibition of botulinum neurotoxin A

Botulinum neurotoxin serotype A (BoNT/A) is an important therapeutic target owing to its extremely potent nature, but also has potential use as a biowarfare agent. Currently, no therapeutic exists to reverse the long-lasting paralysis caused by BoNT/A. Herein, we describe the identification of 3-hydroxy-1,2-dimethylpyridine-4(1H)-thione (3,4-HOPTO) as a metal binding warhead for the inhibition of BoNT/A1. An initial screen of 96 metal binding fragments identified three derivatives containing the 3,4-HOPTO scaffold to inhibit the BoNT/A1 light chain (LC) at >95% at 1 mM. Additional screening of a 3,4-HOPTO sub-library identified structure-activity relationships (SARs) between N-substituted 3,4-HOPTO derivatives and the BoNT/A1 LC. Subsequent synthesis was conducted to improve on inhibitory potency - achieving low μM biochemical IC50 values. Representative compounds were evaluated in a cellular-based assay and showed promising μM activity.

Catch and Anchor Approach To Combat Both Toxicity and Longevity of Botulinum Toxin A

Botulinum neurotoxins have remarkable persistence (∼weeks to months in cells), outlasting the small-molecule inhibitors designed to target them. To address this disconnect, inhibitors bearing two pharmacophores-a zinc binding group and a Cys-reactive warhead-were designed to leverage both affinity and reactivity. A series of first-generation bifunctional inhibitors was achieved through structure-based inhibitor design. Through X-ray crystallography, engagement of both the catalytic Zn2+ and Cys165 was confirmed. A second-generation series improved on affinity by incorporating known reversible inhibitor pharmacophores; the mechanism was confirmed by exhaustive dialysis, mass spectrometry, and in vitro evaluation against the C165S mutant. Finally, a third-generation inhibitor was shown to have good cellular activity and low toxicity. In addition to our findings, an alternative method of modeling time-dependent inhibition that simplifies assay setup and allows comparison of inhibition models is discussed.

Alkyl gallium(III) quinolinolates: A new class of highly selective anti-leishmanial agents

A series of eight alkyl gallium complexes of general formulae [GaMe₂(L)] and [Ga(Me)₂L] have been synthesised, characterised and their antimicrobial activity against bacteria, cancer cells and Leishmania assessed. All eight complexes are novel, with the solid-state structures of all complexes successfully authenticated by single crystal X-ray diffraction. The dimethyl complexes all adopt a four-coordinate tetrahedral confirmation, while the monomethyl complexes are five-coordinate trigonal bipyramidal. All complexes were screened for their anti-bacterial activity either by solution state diffusion, or a solid-state stab test. The five soluble complexes underwent testing against two differing mammalian cell controls, with excellent selectivity observed against COS-7 cells, with an IC₅₀ range of 88.5 μM to ≥100 μM. Each soluble complex was also tested for their anti-cancer capabilities, with no significant activity observed. Excellent activity was exhibited against the protozoan parasite Leishmania major (strain: V121) in both the promastigote and amastigote forms, with IC₅₀ values ranging from 1.11 μM-13.4 μM for their anti-promastigote activity and % infection values of 3.5% ± 0.65-11.5% ± 0.65 for the more clinically relevant amastigote. Selectivity indices for each were found to be in the ranges of 6.61-64.7, with significant selectivity noted for two of the complexes. At minimum, the gallium complexes show a 3-fold enhancement in activity towards the Leishmaniaamastigotes over the parent quinolinols alone.

Targeted 8-hydroxyquinoline fragment based small molecule drug discovery against neglected botulinum neurotoxin type F

OBJECTIVES

Botulinum neurotoxins are highly potent biological warfare agents. The unavailability of countermeasures against these neurotoxins has been a matter of extensive research. However, no clinical therapeutics has come to existence till date. The 8-hydroxyquinoline (8-HQ) scaffold is established privileged compound and its potential as drug candidate against BoNTs is recently being explored.

METHODS

In present work, three course studies were performed involving in silico, in vitro and in vivo cascade to screen 8-HQ small molecule inhibitors against BoNT/F intoxication. ~800 molecules obtained from open repositories were screened in silico and commercially obtained twenty-four 8-HQ derived small molecule inhibitors were evaluated against rBoNT/F light chain through fluorescence thermal shift (FTS) assay. Selected compounds were further evaluated through endopeptidase assay. Further binding affinity analysis was done through surface plasmon resonance (SPR) based Proteon™ XPR 36 system. Finally, the in vivo efficacy of these compounds was evaluated in mice model.

RESULTS

Three compounds NSC1011, NSC1014 and NSC84094 were found to be highly inhibitory after screening of 8-HQ compounds through FTS assay and endopeptidase assay. SPR based protein-small molecule interaction studies showed highest affinity binding of NSC1014 (K_D: 5.58E-06) with BoNT/F-LC. NSC1011, NSC1014, and NSC84094 displayed IC₅₀ of 30.47 ± 6.24, 14.91 ± 2.49 and 17.39 ± 2.74 μM, respectively, in endopeptidase assay. NSC1011 and NSC1014 displayed marked extension of survival time in mice model.

CONCLUSION

NSC1011 and NSC1014 have emerged as promising drug candidate against BoNT/F intoxication displaying higher potential than previously reported compounds.

Identification of Inhibitors against Botulinum Neurotoxins: 8-Hydroxyquinolines Hold Promise

Botulinum neurotoxins (BoNTs) are the most toxic category A biological warfare agents. There is no therapeutics available for BoNT intoxication yet, necessitating the development of a medical countermeasure against these neurotoxins. The discovery of small molecule-based drugs has revolutionized in the last two decades resulting in the identification of several small molecule inhibitors of BoNTs. However, none progressed to clinical trials. 8-Hydroxyquinolines scaffold-based molecules are important 'privileged structures' that can be exploited as inhibitors of a diverse range of targets. In this review, our study of recent reports suggests the development of 8-hydroxyquinoline derived molecules as a potential drug may be on the horizon.

Strategies to Counteract Botulinum Neurotoxin A: Nature's Deadliest Biomolecule

Botulinum neurotoxin serotype A (BoNT/A), marketed commercially as Botox, is the most toxic substance known to man with an estimated intravenous lethal dose (LD₅₀) of 1-2 ng/kg in humans. Despite its widespread use in cosmetic and medicinal applications, no postexposure therapeutics are available for the reversal of intoxication in the event of medical malpractice or bioterrorism. Accordingly, the Centers for Disease Control and Prevention categorizes BoNT/A as a Category A pathogen, posing the highest risk to national security and public health as a result of the ease with which BoNT/A can be weaponized and disseminated. BoNT/A-mediated lethality results from neurons impeded from releasing acetylcholine, which ultimately causes muscle paralysis and possible death by asphyxiation with the loss of diaphragm function. Currently, the only available respite for BoNT/A poisoning is antibody-based therapy; however, this intervention is only effective within 12-24 h postexposure. Small molecule therapeutics remain the only opportunity to reverse BoNT/A intoxication after neuronal poisoning and are urgently needed. Nevertheless, no small molecule BoNT/A inhibitors have reached the clinic or even advanced to clinical trials. This Account highlights the accomplishments and existing challenges facing BoNT/A drug discovery today. Using the comprehensive body of work from our laboratory, we illustrate our nearly two-decade endeavor to discover a clinically relevant BoNT/A inhibitor. Specifically, a discussion on the identification and characterization of new chemical leads, the development of in vitro and in vivo assays, and pertinent discoveries in BoNT/A structural biology related to small molecule inhibition is presented. Lead discovery efforts in our laboratory have leveraged both in vitro high-throughput screening and rational design, and an array of mechanistic strategies for inhibiting BoNT/A has been discovered, including noncovalent inhibition, metal-binding active site inhibition, covalent inhibition, and α- and β-exosite inhibition. We contrast the strengths and weaknesses of each of these mechanistic strategies and propose the most favorable approach for success. Finally, we discuss multiple serendipitous discoveries of antibotulism small molecules with alternative mechanisms of action. Remaining challenges facing clinically relevant BoNT/A inhibition are presented and analyzed, including the current inability to reconcile toxin half-life (months to greater than one year) in neurons with in vivo pharmaceutical lifetimes and reoccurring inconsistencies between in vitro, cellular, and in vivo translation. Our Account of BoNT/A chemical research emphasizes the present accomplishments and critically analyzes the remaining obstacles for drug discovery. Importantly, we call for an increased focus on the discovery of safe and effective covalent inhibitors of BoNT/A that compete with the inherent half-life of the toxin.

Protein-Catalyzed Capture Agents

Protein-catalyzed capture agents (PCCs) are synthetic and modular peptide-based affinity agents that are developed through the use of single-generation in situ click chemistry screens against large peptide libraries. In such screens, the target protein, or a synthetic epitope fragment of that protein, provides a template for selectively promoting the noncopper catalyzed azide-alkyne dipolar cycloaddition click reaction between either a library peptide and a known ligand or a library peptide and the synthetic epitope. The development of epitope-targeted PCCs was motivated by the desire to fully generalize pioneering work from the Sharpless and Finn groups in which in situ click screens were used to develop potent, divalent enzymatic inhibitors. In fact, a large degree of generality has now been achieved. Various PCCs have demonstrated utility for selective protein detection, as allosteric or direct inhibitors, as modulators of protein folding, and as tools for in vivo tumor imaging. We provide a historical context for PCCs and place them within the broader scope of biological and synthetic aptamers. The development of PCCs is presented as (i) Generation I PCCs, which are branched ligands engineered through an iterative, nonepitope-targeted process, and (ii) Generation II PCCs, which are typically developed from macrocyclic peptide libraries and are precisely epitope-targeted. We provide statistical comparisons of Generation II PCCs relative to monoclonal antibodies in which the protein target is the same. Finally, we discuss current challenges and future opportunities of PCCs.

Targeting Metalloenzymes for Therapeutic Intervention

Metalloenzymes are central to a wide range of essential biological activities, including nucleic acid modification, protein degradation, and many others. The role of metalloenzymes in these processes also makes them central for the progression of many diseases and, as such, makes metalloenzymes attractive targets for therapeutic intervention. Increasing awareness of the role metalloenzymes play in disease and their importance as a class of targets has amplified interest in the development of new strategies to develop inhibitors and ultimately useful drugs. In this Review, we provide a broad overview of several drug discovery efforts focused on metalloenzymes and attempt to map out the current landscape of high-value metalloenzyme targets.

Natural Compounds and Their Analogues as Potent Antidotes against the Most Poisonous Bacterial Toxin

Botulinum neurotoxins (BoNTs), the most poisonous proteins known to humankind, are a family of seven (serotype A to G) immunologically distinct proteins synthesized primarily by different strains of the anaerobic bacterium Clostridium botulinum Being the causative agents of botulism, the toxins block neurotransmitter release by specifically cleaving one of the three soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE) proteins, thereby inducing flaccid paralysis. The development of countermeasures and therapeutics against BoNTs is a high-priority research area for public health because of their extreme toxicity and potential for use as biowarfare agents. Extensive research has focused on designing antagonists that block the catalytic activity of BoNTs. In this study, we screened 300 small natural compounds and their analogues extracted from Indian plants for their activity against BoNT serotype A (BoNT/A) as well as its light chain (LCA) using biochemical and cellular assays. One natural compound, a nitrophenyl psoralen (NPP), was identified to be a specific inhibitor of LCA with an in vitro 50% inhibitory concentration (IC₅₀) value of 4.74 ± 0.03 µM. NPP was able to rescue endogenous synaptosome-associated protein 25 (SNAP-25) from cleavage by BoNT/A in human neuroblastoma cells with an IC₅₀ of 12.2 ± 1.7 µM, as well as to prolong the time to the blocking of neutrally elicited twitch tensions in isolated mouse phrenic nerve-hemidiaphragm preparations.IMPORTANCE The long-lasting endopeptidase activity of BoNT is a critical biological activity inside the nerve cell, as it prompts proteolysis of the SNARE proteins, involved in the exocytosis of the neurotransmitter acetylcholine. Thus, the BoNT endopeptidase activity is an appropriate clinical target for designing new small-molecule antidotes against BoNT with the potential to reverse the paralysis syndrome of botulism. In principle, small-molecule inhibitors (SMIs) can gain entry into BoNT-intoxicated cells if they have a suitable octanol-water partition coefficient (log P) value and other favorable characteristics (P. Leeson, Nature 481:455-456, 2012, https://doi.org/10.1038/481455a). Several efforts have been made in the past to develop SMIs, but inhibitors effective under in vitro conditions have not in general been effective in vivo or in cellular models (L. M. Eubanks, M. S. Hixon, W. Jin, S. Hong, et al., Proc Natl Acad Sci U S A 104:2602-2607, 2007, https://doi.org/10.1073/pnas.0611213104). The difference between the in vitro and cellular efficacy presumably results from difficulties experienced by the compounds in crossing the cell membrane, in conjunction with poor bioavailability and high cytotoxicity. The screened nitrophenyl psoralen (NPP) effectively antagonized BoNT/A in both in vitro and ex vivo assays. Importantly, NPP inhibited the BoNT/A light chain but not other general zinc endopeptidases, such as thermolysin, suggesting high selectivity for its target. Small-molecule (nonpeptidic) inhibitors have better oral bioavailability, better stability, and better tissue and cell permeation than antitoxins or peptide inhibitors.

A facile and general acid-catalyzed deuteration at methyl groups of N-heteroarylmethanes

A facile and general Brønsted acid-catalyzed deuteration at the methyl group of N-heteroarylmethanes was achieved through a dearomatic enamine intermediate under relatively mild reaction conditions. Both 2-methyl and 4-methyl groups in quinolines were deuterated with high deuterium incorporation. Pyridines, benzo[d]thiazoles, indoles and imines including these clinical drugs were also deuterated efficiently at the methyl groups. This reaction could be conducted on a large scale (500 mmol), showing its good potential for use in large-scale synthesis.

Metal Ions Effectively Ablate the Action of Botulinum Neurotoxin A

Botulinum neurotoxin serotype A (BoNT/A) causes a debilitating and potentially fatal illness known as botulism. The toxin is also a bioterrorism threat, yet no pharmacological antagonist to counteract its effects has reached clinical approval. Existing strategies to negate BoNT/A intoxication have looked to antibodies, peptides, or organic small molecules as potential therapeutics. In this work, a departure from the traditional drug discovery mindset was pursued, in which the enzyme's susceptibility to metal ions was exploited. A screen of a series of metal salts showed marked inhibitory activity of group 11 and 12 metals against the BoNT/A light chain (LC) protease. Enzyme kinetics revealed that copper (I) and (II) cations displayed noncompetitive inhibition of the LC (Ki ≈ 1 μM), while mercury (II) cations were 10-fold more potent. Crystallographic and mutagenesis studies elucidated a key binding interaction between Cys165 on BoNT/A LC and the inhibitory metals. As potential copper prodrugs, ligand-copper complexes were examined in a cell-based model and were found to prevent BoNT/A cleavage of the endogenous protein substrate, SNAP-25, even at low μM concentrations of complexes. Further investigation of the complexes suggested a bioreductive mechanism causing intracellular release of copper, which directly inhibited the BoNT/A protease. In vivo experiments demonstrated that copper (II) dithiocarbamate and bis(thiosemicarbazone) complexes could delay BoNT/A-mediated lethality in a rodent model, indicating their potential for treating the harmful effects of BoNT/A intoxication. Our studies illustrate that metals can be therapeutically viable enzyme inhibitors; moreover, enzymes that share homology with BoNT LCs may be similarly targeted with metals.

Utilizing Ayurvedic literature for the identification of novel phytochemical inhibitors of botulinum neurotoxin A

ETHNOPHARMACOLOGICAL RELEVANCE

Ayurveda, an ancient holistic system of health care practiced on the Indian subcontinent, utilizes a number of multi-plant formulations and is considered by many as a potential source for novel treatments, as well as the identification of new drugs. Our aim is to identify novel phytochemicals for the inhibition of bacterial exotoxin, botulinum neurotoxin A (BoNT/A) based on Ayurvedic literature. BoNT/A is released by Clostridium species, which when ingested, inhibits the release of acetylcholine by concentrating at the neuromuscular junction and causes flaccid paralysis, resulting in a condition termed as botulism, and may also lead to death due to respiratory arrest.

METHODS

Fifteen plants were selected from the book 'Diagnosis and treatment of diseases in Ayurveda' by Vaidya Bhagwan Dash and Lalitesh Kashyap, based on their frequency of use in the formulations used for the treatment of six diseases with neuromuscular symptoms similar to botulism. Phytochemicals from these plants were screened using in silico, and in vitro methods. Structures of 570 reported phytochemicals from 14 plants were docked inside six reported BoNT/A light chain crystal structures using ensemble docking module in Maestro (Schrödinger, LLE).

RESULTS

From the docking scores and structural diversity, nine compounds including acoric acid 1, three flavonoids, three coumarins derivatives, one kava lactone were selected and screened using an in vitro HPLC-based protease assay. The bioassay results showed that several compounds possess BoNT/A LC inhibition of 50-60% when compared to positive controls NSC 84094 and CB7967495 (80-95%).

CONCLUSION

Further testing of the active compounds identified from Ayurvedic literature and structure-activity studies of acoric acid 1 using more sensitive bioassays is under way. The identification of acoric acid 1, a novel scaffold against BoNT/A, exemplifies the utility of Ayurvedic literature for the discovery of novel drug leads.

Newly Designed Quinolinol Inhibitors Mitigate the Effects of Botulinum Neurotoxin A in Enzymatic, Cell-Based, and ex Vivo Assays

Botulinum neurotoxin A (BoNT/A) is one of the most deadly toxins and is the etiological agent of the potentially fatal condition, botulism. Herein, we investigated 8-hydroxyquinoline (quinolin-8-ol) as a potential inhibitor scaffold for preventing the deadly neurochemical effects of the toxin. Quinolinols are known chelators that can disrupt the BoNT/A metalloprotease zinc-containing active site, thus impeding its proteolysis of the endogenous protein substrate, synaptosomal-associated protein 25 (SNAP-25). By use of this information, the structure-activity relationship (SAR) of the quinolinol-5-sulfonamide scaffold was explored through preparation of a crude sulfonamide library and evaluation of the library in a BoNT/A LC enzymatic assay. Potency optimization of the sulfonamide hit compounds was undertaken as informed by docking studies, granting a lead compound with a submicromolar K_i. These quinolinol analogues demonstrated inhibitory activity in a cell-based model for SNAP-25 cleavage and an ex vivo assay for BoNT/A-mediated muscle paralysis.

A matrix-focused structure-activity and binding site flexibility study of quinolinol inhibitors of botulinum neurotoxin serotype A

Our initial discovery of 8-hydroxyquinoline inhibitors of BoNT/A and separation/testing of enantiomers of one of the more active leads indicated considerable flexibility in the binding site. We designed a limited study to investigate this flexibility and probe structure-activity relationships; utilizing the Betti reaction, a 36 compound matrix of quinolinol BoNT/A LC inhibitors was developed using three 8-hydroxyquinolines, three heteroaromatic amines, and four substituted benzaldehydes. This study has revealed some of the most effective quinolinol-based BoNT/A inhibitors to date, with 7 compounds displaying IC₅₀ values ⩽1μM and 11 effective at ⩽2μM in an ex vivo assay.

Picolinic acids as β-exosite inhibitors of botulinum neurotoxin A light chain

In developing small-molecule inhibitors of botulinum neurotoxin serotype A light chain (BoNT/A LC), substituted picolinic acids were identified. Extensive investigation into the SAR of the picolinic acid scaffold revealed 5-(1-butyl-4-chloro-1H-indol-2-yl)picolinic acid (CBIP), which possessed low micromolar activity against BoNT/A. Kinetic and docking studies demonstrated binding of CBIP to the β-exosite: a largely unexplored site on the LC that holds therapeutic relevance for botulism treatment.

Small molecule non-peptide inhibitors of botulinum neurotoxin serotype E: Structure-activity relationship and a pharmacophore model

Botulinum neurotoxins (BoNTs) are the most poisonous biological substance known to humans. They cause flaccid paralysis by blocking the release of acetylcholine at the neuromuscular junction. Here, we report a number of small molecule non-peptide inhibitors of BoNT serotype E. The structure-activity relationship and a pharmacophore model are presented. Although non-peptidic in nature, these inhibitors mimic key features of the uncleavable substrate peptide Arg-Ile-Met-Glu (RIME) of the SNAP-25 protein. Among the compounds tested, most of the potent inhibitors bear a zinc-chelating moiety connected to a hydrophobic and aromatic moiety through a carboxyl or amide linker. All of them show low micromolar IC50 values.

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.

Identification of small molecule inhibitors of botulinum neurotoxin serotype E via footprint similarity

Botulinum neurotoxins (BoNT) are among the most poisonous substances known, and of the 7 serotypes (A-G) identified thus far at least 4 can cause death in humans. The goal of this work was identification of inhibitors that specifically target the light chain catalytic site of the highly pathogenic but lesser-studied E serotype (BoNT/E). Large-scale computational screening, employing the program DOCK, was used to perform atomic-level docking of 1.4 million small molecules to prioritize those making favorable interactions with the BoNT/E site. In particular, 'footprint similarity' (FPS) scoring was used to identify compounds that could potentially mimic features on the known substrate tetrapeptide RIME. Among 92 compounds purchased and experimentally tested, compound C562-1101 emerged as the most promising hit with an apparent IC₅₀ value three-fold more potent than that of the first reported BoNT/E small molecule inhibitor NSC-77053. Additional analysis showed the predicted binding pose of C562-1101 was geometrically and energetically stable over an ensemble of structures generated by molecular dynamic simulations and that many of the intended interactions seen with RIME were maintained. Several analogs were also computationally designed and predicted to have further molecular mimicry thereby demonstrating the potential utility of footprint-based scoring protocols to help guide hit refinement.

Targeting RING domains of Mdm2-MdmX E3 complex activates apoptotic arm of the p53 pathway in leukemia/lymphoma cells

Reactivation of tumor-suppressor p53 for targeted cancer therapy is an attractive strategy for cancers bearing wild-type (WT) p53. Targeting the Mdm2–p53 interface or MdmX ((MDM4), mouse double minute 4)–p53 interface or both has been a focus in the field. However, targeting the E3 ligase activity of Mdm2–MdmX really interesting new gene (RING)–RING interaction as a novel anticancer strategy has never been explored. In this report, we describe the identification and characterization of small molecule inhibitors targeting Mdm2–MdmX RING–RING interaction as a new class of E3 ligase inhibitors. With a fluorescence resonance energy transfer-based E3 activity assay in high-throughput screening of a chemical library, we identified inhibitors (designated as MMRis (Mdm2–MdmX RING domain inhibitors)) that specifically inhibit Mdm2–MdmX E3 ligase activity toward Mdm2 and p53 substrates. MMRi6 and its analog MMRi64 are capable of disrupting Mdm2–MdmX interactions in vitro and activating p53 in cells. In leukemia cells, MMRi64 potently induces downregulation of Mdm2 and MdmX. In contrast to Nutlin3a, MMRi64 only induces the expression of pro-apoptotic gene PUMA (p53 upregulated modulator of apoptosis) with minimal induction of growth-arresting gene p21. Consequently, MMRi64 selectively induces the apoptotic arm of the p53 pathway in leukemia/lymphoma cells. Owing to the distinct mechanisms of action of MMRi64 and Nutlin3a, their combination synergistically induces p53 and apoptosis. Taken together, this study reveals that Mdm2–MdmX has a critical role in apoptotic response of the p53 pathway and MMRi64 may serve as a new pharmacological tool for p53 studies and a platform for cancer drug development.

8-Hydroxyquinoline: a privileged structure with a broad-ranging pharmacological potential

An overview of the broad-ranging pharmacological applications of 8-HQ derivatives.

New targets in the search for preventive and therapeutic agents for botulism

Botulism is a severe neuroparalytic disease resulting from exposure to one of the most poisonous toxins to humans. Because of this high potency and the use of toxins as biological weapons, botulism is a public health concern and each case represents an emergency. Current therapy involves respiratory supportive care and anti-toxins administration. As a preventive measure, vaccination against toxins represents an effective strategy but is undesirable due the rarity of botulism and the effectiveness of toxins in treating several neuromuscular disorders. This paper summarizes the current issues in botulism treatment and prevention, highlighting the challenge for future researches.

Discovery and SAR study of a sulfonamide hydroxamic acid inhibitor for the botulinum neurotoxin serotype A light chain

Through the use of chemical synthesis and high throughput screening, we discovered a sulfonamide hydroxamic acid inhibitor for the botulinum neurotoxin serotype A light chain. A structure activity relationship study of the parent inhibitor resulted in the synthesis of a new inhibitor with an IC₅₀of 0.95 ± 0.60 μM for the BoNT/A LC.