The evolving field of biodefence: therapeutic developments and diagnostics

Understanding the Structure-Activity Relationship through Density Functional Theory: A Simple Method Predicts Relative Binding Free Energies of Metalloenzyme Fragment-like Inhibitors

Despite being involved in several human diseases, metalloenzymes are targeted by a small percentage of FDA-approved drugs. Development of novel and efficient inhibitors is required, as the chemical space of metal binding groups (MBGs) is currently limited to four main classes. The use of computational chemistry methods in drug discovery has gained momentum thanks to accurate estimates of binding modes and binding free energies of ligands to receptors. However, exact predictions of binding free energies in metalloenzymes are challenging due to the occurrence of nonclassical phenomena and interactions that common force field-based methods are unable to correctly describe. In this regard, we applied density functional theory (DFT) to predict the binding free energies and to understand the structure-activity relationship of metalloenzyme fragment-like inhibitors. We tested this method on a set of small-molecule inhibitors with different electronic properties and coordinating two Mn²⁺ ions in the binding site of the influenza RNA polymerase PA_N endonuclease. We modeled the binding site using only atoms from the first coordination shell, hence reducing the computational cost. Thanks to the explicit treatment of electrons by DFT, we highlighted the main contributions to the binding free energies and the electronic features differentiating strong and weak inhibitors, achieving good qualitative correlation with the experimentally determined affinities. By introducing automated docking, we explored alternative ways to coordinate the metal centers and we identified 70% of the highest affinity inhibitors. This methodology provides a fast and predictive tool for the identification of key features of metalloenzyme MBGs, which can be useful for the design of new and efficient drugs targeting these ubiquitous proteins.

Design of abiotic polymer ligand-decorated lipid nanoparticles for effective neutralization of target toxins in the blood

Macromolecular toxins often induce inflammatory cytokine production, multiple-organ dysfunction, and cell death. Synthetic polymer ligands (PLs) prepared with several functional monomers have the potential of neutralizing target toxins after binding to them; therefore, they are of significant interest as abiotic antidotes. Although PLs show little toxin neutralization effect in the bloodstream because of immediate elimination from there, the toxin neutralization effect is significantly improved by the direct decoration of PLs onto lipid nanoparticles (PL-LNPs). However, this direct decoration decreases PL mobility, induces LNP aggregation after capturing the target, and decreases LNP blood circulation time. We designed novel PL-LNPs to improve PL mobility, inhibit the aggregation tendency after capturing the target, and increase LNP blood circulation time in order to achieve highly effective toxin neutralization in vivo. Specifically, LNPs were modified with PLs-conjugated polyethylene glycol (PEG), and additional PEG was used to modify the PL-decorated LNPs (PL-PEG-LNPs). Histones were used as target toxins, and N-isopropylacrylamide-based PLs were used for histone capture. PEGylation increased the plasma LNP level 24 h after intravenous injection by ∼90 times and inhibited LNP aggregation after histone capture. The dissociation constant (K_d) of PL-PEG-LNPs against histone was two times smaller compared to that of PL-LNPs. Although PL-LNPs inhibited histone-platelet interaction in the bloodstream, a large amount of histone-PL-LNP complexes accumulated in the lungs because of aggregation. However, PL-PEG-LNPs inhibited both histone-platelet interaction and histone accumulation in the lungs. Importantly, PL-PEG-LNP treatment increased the survival rate of histone-treated mice compared to PL-LNPs. These results provide a platform for the development of abiotic antidote nanoparticles in vivo.

Strategy for the enrichment of protein biomarkers from diverse bacterial select agents

BACKGROUND

Some pathogenic bacteria can be potentially used for nefarious applications in the event of bioterrorism or biowarfare. Accurate identification of biological agent from clinical and diverse environmental matrices is of paramount importance for implementation of medical countermeasures and biothreat mitigation.

OBJECTIVE

A novel methodology is reported here for the development of a novel enrichment strategy for the generally conserved abundant bacterial proteins for an accurate downstream species identification using tandem MS analysis in biothreat scenario.

METHODS

Conserved regions in the common bacterial protein markers were analyzed using bioinformatic tools and stitched for a possible generic immuno-capture for an intended downstream MS/MS analysis. Phylogenetic analysis of selected proteins was carried out and synthetic constructs were generated for the expression of conserved stitched regions of 60 kDa chaperonin GroEL. Hyper-immune serum was raised against recombinant synthetic GroEL protein.

RESULTS

The conserved regions of common bacterial proteins were stitched for a possible generic immuno-capture and subsequent specific identification by tandem MS using variable regions of the molecule. Phylogenetic analysis of selected proteins was carried out and synthetic constructs were generated for the expression of conserved stitched regions of GroEL. In a proof-of-concept study, hyper-immune serum raised against recombinant synthetic GroEL protein exhibited reactivity with ~60 KDa proteins from the cell lysates of three bacterial species tested.

CONCLUSION

The envisaged methodology can lead to the development of a novel enrichment strategy for the abundant bacterial proteins from complex environmental matrices for the downstream species identification with increased sensitivity and substantially reduce the time-to-result.

Protein biomarker elucidation for the verification of biological agents in the taxonomic group of Gammaproteobacteria using tandem mass spectrometry

Some pathogenic microbes can be used for nefarious applications and instigate population-based fear. In a bio-threat scenario, rapid and accurate methods to detect biological agents in a wide range of complex environmental and clinical matrices, is of paramount importance for the implementation of mitigation protocols and medical countermeasures. This study describes targeted and shot-gun tandem MS based approaches for the verification of biological agents from the environmental samples. The marker proteins and peptides were elucidated by an exhaustive literature mining, in silico analysis of prioritized proteins, and MS/MS analysis of abundant proteins from selected bacterial species. For the shot-gun methodology, tandem MS analysis of abundant peptides was carried from spiked samples. The validation experiments employing a combination of shot-gun tandem MS analysis and a targeted search reported here is a proof of concept to show the applicability of the methodology for the unambiguous verification of biological agents at sub-species level, even with limited fractionation of crude protein extracts from environmental samples.

Oral administration of recombinant Bacillus subtilis spores expressing mutant staphylococcal enterotoxin B provides potent protection against lethal enterotoxin challenge

Pathogenicity of Staphylococcus aureus is induced by staphylococcal enterotoxin B (SEB). A mutant form of SEB (mSEB) is immunogenic as well as less toxic. Recombinant mSEB and SEB were expressed in pET28a prokaryotic plasmids. Tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) levels in mSEB-stimulated macrophages were lower than those in SEB-stimulated macrophages (p < 0.001, p < 0.01 respectively). Using CotC as a fusion protein, we constructed recombinant Bacillus subtilis spores expressing mSEB on the spore surface and evaluated their safety and protective efficacy via mouse models. Oral administration of mSEB-expressing spores increased SEB-specific IgA in feces and SEB-specific IgG1 and IgG2a in the sera, compared with mice in naïve and CotC spore-treated groups (p < 0.001, p < 0.01, p < 0.001 respectively). Six weeks following oral dosing of recombinant spores, significant differences were not found in the serum biochemical indices between the mSEB group and the naïve and CotC groups. Furthermore, oral administration of mSEB spores increased the survival rate by 33.3% in mice intraperitoneally injected with 5 µg of wild-type SEB plus 25 µg lipopolysaccharide (LPS). In summation, recombinant spores stably expressing mSEB were developed, and oral administration of such recombinant spores induced a humoral immune response and provided protection against SEB challenge in mice.

Multiplex Immunoassay Techniques for On-Site Detection of Security Sensitive Toxins

Biological toxins are a heterogeneous group of high molecular as well as low molecular weight toxins produced by living organisms. Due to their physical and logistical properties, biological toxins are very attractive to terrorists for use in acts of bioterrorism. Therefore, among the group of biological toxins, several are categorized as security relevant, e.g., botulinum neurotoxins, staphylococcal enterotoxins, abrin, ricin or saxitoxin. Additionally, several security sensitive toxins also play a major role in natural food poisoning outbreaks. For a prompt response to a potential bioterrorist attack using biological toxins, first responders need reliable, easy-to-use and highly sensitive methodologies for on-site detection of the causative agent. Therefore, the aim of this review is to present on-site immunoassay platforms for multiplex detection of biological toxins. Furthermore, we introduce several commercially available detection technologies specialized for mobile or on-site identification of security sensitive toxins.

Rapid protocol of dot-immunnoassay for orthopoxviruses detection

The aim of the work was to create a sensitive and fast immunochemical test for the detection of orthopoxviruses (OPXV) in the "point of care" format. This work presents the results of the comparative evaluation of a single-stage (rapid version) and two-stage protocol of dot-immunoassay based on plane protein array for detection of vaccinia virus (VACV), cowpoxvirus (CPXV) and ectromelia virus (ECTV) in viral culture materials with different degrees of purification. It has been established that rabbit polyclonal VACV-antibodies can be used in a one-stage dot-analysis, both as a capture agent immobilized on a substrate and as a detection reagent bound with colloidal gold particles. It is shown that the sensitivity of detection of OPXV is inversely related to the degree of purification of viruses. The one-stage variant of the dot-immunoassay allows reducing the analysis time to 39 min and increasing the detection sensitivity of all the studied orthopoxviruses in crude viral samples to a range of 10⁴-10³ PFU/mL. The increase in sensitivity in the rapid version of the analysis, presumably, occurs due to binding of capture antibodies to subviral structures that form large aggregates of gold particles. Ultrasonic treatment of culture virus reduces the detection sensitivity, presumably due to both the destruction of conformational epitopes located on the surface of subvirus structures, as well as the increase in the dispersion of cell debris, which limits diffusion and contacts of viral antigens with capture antibodies on the substrate. Both versions of the analysis are specific and do not detect interactions both with preparations of non-infected cell culture and with heterogeneous controls of the causative agents of erythematous infections. The rapid protocol of dot-immunnoassay described above can be used to detect, or help to exclude, the presence of threat viruses in samples and could be useful in a variety of biodefense applications. Ready-to-use setup, ease of analysis and the ability to visually accounting for results allow the test to be used outside of laboratories.

Elucidation of protein biomarkers for verification of selected biological warfare agents using tandem mass spectrometry

Some pathogens and toxins have the potential to be used as weapons of mass destruction and instigate population-based fear. Efforts to mitigate biothreat require development of efficient countermeasures which in turn relies on fast and accurate methods to detect the biological agents in a range of complex matrices including environmental and clinical samples. We report here an mass spectrometry (MS) based methodology, employing both targeted and shot-gun approaches for the verification of biological agents from the environmental samples. Our shot-gun methodology relied on tandem MS analysis of abundant peptides from the spiked samples, whereas, the targeted method was based on an extensive elucidation of marker proteins and unique peptides resulting in the generation of an inclusion list of masses reflecting relevant peptides for the unambiguous identification of nine bacterial species [listed as priority agents of bioterrorism by Centre for Disease Control and Prevention (CDC)] belonging to phylogenetically diverse genera. The marker peptides were elucidated by extensive literature mining, in silico analysis, and tandem MS (MS/MS) analysis of abundant proteins of the cultivated bacterial species in our laboratory. A combination of shot-gun MS/MS analysis and the targeted search using a panel of unique peptides is likely to provide unambiguous verification of biological agents at sub-species level, even with limited fractionation of crude protein extracts from environmental samples. The comprehensive list of peptides reflected in the inclusion list, makes a valuable resource for the multiplex analysis of select biothreat agents and further development of targeted MS/MS assays.

Sepsis: mechanisms of bacterial injury to the patient

In bacteremia the majority of bacterial species are killed by oxidation on the surface of erythrocytes and digested by local phagocytes in the liver and the spleen. Sepsis-causing bacteria overcome this mechanism of human innate immunity by versatile respiration, production of antioxidant enzymes, hemolysins, exo- and endotoxins, exopolymers and other factors that suppress host defense and provide bacterial survival. Entering the bloodstream in different forms (planktonic, encapsulated, L-form, biofilm fragments), they cause different types of sepsis (fulminant, acute, subacute, chronic, etc.). Sepsis treatment includes antibacterial therapy, support of host vital functions and restore of homeostasis. A bacterium killing is only one of numerous aspects of antibacterial therapy. The latter should inhibit the production of bacterial antioxidant enzymes and hemolysins, neutralize bacterial toxins, modulate bacterial respiration, increase host tolerance to bacterial products, facilitate host bactericidal mechanism and disperse bacterial capsule and biofilm.

Structural and biochemical characterization of the protease domain of the mosaic botulinum neurotoxin type HA

The extreme toxicity of botulinum neurotoxins (BoNTs) relies on their specific cleavage of SNARE proteins, which eventually leads to muscle paralysis. One newly identified mosaic toxin, BoNT/HA (aka H or FA), cleaves VAMP-2 at a unique position between residues L54 and E55, but the molecular basis underlying VAMP-2 recognition of BoNT/HA remains poorly characterized. Here, we report a ∼2.09 Å resolution crystal structure of the light chain protease domain of BoNT/HA (LC/HA). Structural comparison between LC/HA and LC of BoNT/F1 (LC/F1) reveals distinctive hydrophobic and electrostatic features near the active sites, which may explain their different VAMP-2 cleavage sites. When compared to BoNT/F5 that cleaves VAMP-2 at the same site as BoNT/HA, LC/HA displays higher affinity for VAMP-2, which could be caused by their different surface charge properties surrounding a VAMP-2 exosite-binding cleft. Furthermore, systematic mutagenesis studies on VAMP-2 and structural modeling demonstrate that residues R47 to K59 spanning the cleavage site in VAMP-2 may adopt a novel extended conformation when interacting with LC/HA and LC/F5. Taken together, our structure provides new insights into substrate recognition of BoNT/HA and paves the way for rational design of small molecule or peptide inhibitors against LC/HA.

A review on the antagonist Ebola: A prophylactic approach

Ebola virus (EBOV), a member of Filoviridae virus family under the genus Ebolavirus, has emerged as a dangerous and potential threat to human health globally. It causes a severe and deadly hemorrhagic fever in humans and other mammals, called Ebola Virus Disease (EVD). In recent outbreaks of EVD, there has been loss of large numbers of individual’s life. Therefore, EBOV has attracted researchers and increased interests in developing new models for virus evolution, and therapies. The EBOV interacts with the immune system of the host which led to understand how the virus functions and effects immune system behaviour. This article presents an exhaustive review on Ebola research which includes EVD illness, symptoms, transmission patterns, patho-physiology conditions, development of antiviral agents and vaccines, resilient health system, dynamics and mathematical model of EBOV, challenges and prospects for future studies.

Rational designing of an antidote nanoparticle decorated with abiotic polymer ligands for capturing and neutralizing target toxins

Many of macromolecular toxins induce cell death by directly interacting with cells or induction of inflammatory cytokines. Abiotic polymer ligands (PLs) composed of functional monomers are able to bind and neutralize toxins in vivo and are of great interest for efficient antidotes. However, little has been reported about recognition and neutralization of target molecules in the bloodstream because of readily elimination from the bloodstream. Here, we report a rational design of PLs-decorated lipid nanoparticles (PL-NPs) for neutralizing a target toxin in vivo. PL that decorated on the NPs would cooperatively interacts with target biomacromolecules since the lipid molecules in NPs have a high degree of freedom. In the present study, N-isopropylacrylamide based PLs interacting with histones, major mediators of sepsis, were synthesized. Affinity between PL-NPs and histones depends on monomer composition and polymer length. The optimized PL-NP showed little affinity for plasma proteins. The PL-NPs inhibited the toxicity of histones both in vitro and in vivo, suggesting that PLs on the NPs cooperatively bound to histones and neutralized their toxicity. In addition, circulation time of optimized PL was significantly prolonged by the modification onto NPs. These results provide a platform for designing antidote nanoparticles neutralizing toxic biomacromolecules.

Prevalence of Staphylococcal Enterotoxins in Ready-to-Eat Foods Sold in Istanbul

The aim of this study was to investigate the prevalence of staphylococcal enterotoxins (SEs) in ready-to-eat (RTE) foods sold in Istanbul, Turkey. A total of 5,241 samples were randomly collected from various caterers, hotels, and restaurants from 2014 to 2016. The samples were classified into four groups: (i) various cooked RTE meat and vegetable meals, (ii) various RTE salads, charcuterie, and cold appetizers, (iii) various cooked RTE bakery products (pasta, pastries, pizza, pita, ravioli, etc.), and (iv) any cooked RTE sweets and desserts (pudding, custard, cream, ashura, etc.). The samples were examined for the presence of SEs by 3M Tecra Staph Enterotoxin Visual Immunoassay method, which is a manual enzyme-linked immunosorbent assay method. Among all samples, only 1 (0.019%) RTE meal (vegetable meal with meat) was found to be contaminated with SEs, a good result in terms of staphylococcal food poisoning risk and public health.

Anthrax lethal toxin (LeTx) neutralization by PA domain specific antisera

Anthrax associated causalities in humans and animals are implicated mainly due to the action of two exotoxins that are secreted by the bacterium Bacillus antharcis during the infection. These exotoxins comprise of three protein components namely protective antigen (PA), lethal factor (LF) and edema factor (EF). The protective antigen is the common toxin component required to form both lethal toxin (LeTx) and edema toxin (EdTx). The LeTx is formed, when PA combines with LF and EdTx is formed when PA combines with EF. Therapeutic interventions aiming to neutralize these key effectors of anthrax pathology would therefore, provide an effective means to counter the toxicity imposed by the anthrax toxins on the host. The present work describes the lethal toxin neutralization potential of polyclonal antisera developed against the individual domains of the protective antigen component of the anthrax toxin. The individual domains were produced as recombinant proteins in E. coli and validated with peptide mass fingerprinting by MALDI-TOF analysis and corresponding mice polyclonal antisera by western blotting. Each domain specific antibody titre and isotype was ascertained by ELISA. The isotyping revealed the predominance of IgG1 isotype. The toxin neutralizing potential of these domain specific antisera were evaluated by in-vitro cell viability MTT assay, employing J774.1 mouse macrophage cell line against LeTx (0.25 μg ml^-1 PA and 0.125 μg ml^-1 LF concentrations). Among the four domain specific antisera, the antiserum against PA domain IV could neutralize LeTx with high efficiency. No significant neutralization of LeTx was observed with other domain specific antibodies. Results indicate that antibodies to r-PA domain IV could be explored further as therapeutic anti toxin molecule along with appropriate antibiotic regimens against anthrax.

Network Experiences from a Cross-Sector Biosafety Level-3 Laboratory Collaboration: A Swedish Forum for Biopreparedness Diagnostics

The Swedish Forum for Biopreparedness Diagnostics (FBD) is a network that fosters collaboration among the 4 agencies with responsibility for the laboratory diagnostics of high-consequence pathogens, covering animal health and feed safety, food safety, public health and biodefense, and security. The aim of the network is to strengthen capabilities and capacities for diagnostics at the national biosafety level-3 (BSL-3) laboratories to improve Sweden's biopreparedness, in line with recommendations from the EU and WHO. Since forming in 2007, the FBD network has contributed to the harmonization of diagnostic methods, equipment, quality assurance protocols, and biosafety practices among the national BSL-3 laboratories. Lessons learned from the network include: (1) conducting joint projects with activities such as method development and validation, ring trials, exercises, and audits has helped to build trust and improve communication among participating agencies; (2) rotating the presidency of the network steering committee has fostered trust and commitment from all agencies involved; and (3) planning for the implementation of project outcomes is important to maintain gained competencies in the agencies over time. Contacts have now been established with national agencies of the other Nordic countries, with an aim to expanding the collaboration, broadening the network, finding synergies in new areas, strengthening the ability to share resources, and consolidating long-term financing in the context of harmonized European biopreparedness.

The Swedish Forum for Biopreparedness Diagnostics (FBD) is a network that fosters collaboration among the 4 agencies with responsibility for the laboratory diagnostics of high-consequence pathogens, covering animal health and feed safety, food safety, public health and biodefense, and security.

A novel staphylococcal enterotoxin B subunit vaccine candidate elicits protective immune response in a mouse model

Staphylococcal enterotoxin B (SEB), produced by the gram-positive bacterium Staphylococcus aureus, is responsible for food poisoning and toxic shock syndrome, and is considered a potential bioterrorism agent. Unfortunately, still now no approved vaccines are available against SEB. In this study, we constructed a series of nontoxic SEB mutants (mSEBs) and examined whether these mSEBs provide protective immunity against SEB challenge. These mSEB vaccine candidates did not demonstrate superantigen activity in mouse splenocyte cultures. Immunization with the vaccine candidates triggered the production of IgG-antibodies with neutralizing activity. In addition, increased production of IgG1 and IgG3 was observed after immunization, which signifies both Th1- and Th2-induced immune responses. Among the vaccine candidates tested, S9, a double mutant (N23A and Y90A) and S19, a quadruple mutant (N23A, Y90A, R110A, and F177A), demonstrated complete protection against a lethal SEB challenge. Altogether, our results strongly suggest that these mSEBs could be an effective recombinant SEB vaccine candidates for further/future preclinical and clinical studies.

Cellular Protection of SNAP-25 against Botulinum Neurotoxin/A: Inhibition of Thioredoxin Reductase through a Suicide Substrate Mechanism

Botulium neurotoxins (BoNTs) are among the most lethal toxins known to man. They are comprised of seven serotypes with BoNT/A being the most deadly; yet, there is no approved therapeutic for their intoxication or one that has even advanced to clinical trials. Botulinum neurotoxicity is ultimately governed through light chain (LC) protease SNARE protein cleavage leading to a loss of neurotransmitter release. Pharmacological attempts to ablate BoNT/A intoxication have sought to either nullify cellular toxin entry or critical biochemical junctions found within its intricate mechanism of action. In these regards, reports have surfaced of nonpeptidic small molecule inhibitors, but few have demonstrated efficacy in neutralizing cellular toxicity, a key prerequisite before rodent lethality studies can be initiated. On the basis of a lead discovered in our BoNT/A cellular assay campaign, we investigated a family of N-hydroxysuccinimide inhibitors grounded upon structure activity relationship (SAR) fundamentals. Molecules stemming from this SAR exercise were theorized to be protease inhibitors. However, this proposition was overturned on the basis of extensive kinetic analysis. Unexpectedly, inhibitor data pointed to thioredoxin reductase (TrxR), an essential component required for BoNT protease translocation. Also unforeseen was the inhibitors' mechanism of action against TrxR, which was found to be brokered through a suicide-mechanism utilizing quinone methide as the inactivating element. This new series of TrxR inhibitors provides an alternative means to negate the etiological agent responsible for BoNT intoxication, the LC protease.

Mass spectrometry for the detection of bioterrorism agents: from environmental to clinical applications

In the current context of international conflicts and localized terrorist actions, there is unfortunately a permanent threat of attacks with unconventional warfare agents. Among these, biological agents such as toxins, microorganisms, and viruses deserve particular attention owing to their ease of production and dissemination. Mass spectrometry (MS)-based techniques for the detection and quantification of biological agents have a decisive role to play for countermeasures in a scenario of biological attacks. The application of MS to every field of both organic and macromolecular species has in recent years been revolutionized by the development of soft ionization techniques (MALDI and ESI), and by the continuous development of MS technologies (high resolution, accurate mass HR/AM instruments, novel analyzers, hybrid configurations). New possibilities have emerged for exquisite specific and sensitive detection of biological warfare agents. MS-based strategies for clinical application can now address a wide range of analytical questions mainly including issues related to the complexity of biological samples and their available volume. Multiplexed toxin detection, discovery of new markers through omics approaches, and identification of untargeted microbiological or of novel molecular targets are examples of applications. In this paper, we will present these technological advances along with the novel perspectives offered by omics approaches to clinical detection and follow-up.

Development of a Genus-Specific Antigen Capture ELISA for Orthopoxviruses - Target Selection and Optimized Screening

Orthopoxvirus species like cowpox, vaccinia and monkeypox virus cause zoonotic infections in humans worldwide. Infections often occur in rural areas lacking proper diagnostic infrastructure as exemplified by monkeypox, which is endemic in Western and Central Africa. While PCR detection requires demanding equipment and is restricted to genome detection, the evidence of virus particles can complement or replace PCR. Therefore, an easily distributable and manageable antigen capture enzyme-linked immunosorbent assay (ELISA) for the detection of orthopoxviruses was developed to facilitate particle detection. By comparing the virus particle binding properties of polyclonal antibodies developed against surface-exposed attachment or fusion proteins, the surface protein A27 was found to be a well-bound, highly immunogenic and exposed target for antibodies aiming at virus particle detection. Subsequently, eight monoclonal anti-A27 antibodies were generated and characterized by peptide epitope mapping and surface plasmon resonance measurements. All antibodies were found to bind with high affinity to two epitopes at the heparin binding site of A27, toward either the N- or C-terminal of the crucial KKEP-segment of A27. Two antibodies recognizing different epitopes were implemented in an antigen capture ELISA. Validation showed robust detection of virus particles from 11 different orthopoxvirus isolates pathogenic to humans, with the exception of MVA, which is apathogenic to humans. Most orthopoxviruses could be detected reliably for viral loads above 1 × 103 PFU/mL. To our knowledge, this is the first solely monoclonal and therefore reproducible antibody-based antigen capture ELISA able to detect all human pathogenic orthopoxviruses including monkeypox virus, except variola virus which was not included. Therefore, the newly developed antibody-based assay represents important progress towards feasible particle detection of this important genus of viruses.

Rapid Microfluidic Assay for the Detection of Botulinum Neurotoxin in Animal Sera

Potent Botulinum neurotoxins (BoNTs) represent a threat to public health and safety. Botulism is a disease caused by BoNT intoxication that results in muscle paralysis that can be fatal. Sensitive assays capable of detecting BoNTs from different substrates and settings are essential to limit foodborne contamination and morbidity. In this report, we describe a rapid 96-well microfluidic double sandwich immunoassay for the sensitive detection of BoNT-A from animal sera. This BoNT microfluidic assay requires only 5 μL of serum, provides results in 75 min using a standard fluorescence microplate reader and generates minimal hazardous waste. The assay has a <30 pg·mL⁻¹ limit of detection (LOD) of BoNT-A from spiked human serum. This sensitive microfluidic BoNT-A assay offers a fast and simplified workflow suitable for the detection of BoNT-A from serum samples of limited volume in most laboratory settings.

Plant-Derived Monoclonal Antibodies for Prevention and Treatment of Infectious Disease

Numerous monoclonal antibodies (MAbs) that recognize and neutralize infectious pathogens have been isolated and developed over the years. The fact that infectious diseases can involve large populations of infected individuals is an important factor that has motivated the search for both cost-effective and scalable methods of antibody production. The current technologies for production of antibodies in plants allow for very rapid expression and evaluation that can also be readily scaled for multikilogram production runs. In addition, recent progress in manipulating glycosylation in plant production systems has allowed for the evaluation of antibodies containing glycans that are nearly homogeneous, are mammalian in structure, and have enhanced neutralizing capabilities. Among the anti-infectious disease antibodies that have been produced in plants are included those intended for prevention or treatment of anthrax, Clostridium perfringens, Ebola virus, human immunodeficiency virus, herpes simplex virus, rabies, respiratory syncytial virus, staphylococcal enterotoxin, West Nile virus, and tooth decay. Animal and human efficacy data for these MAbs are discussed.

Toward the discovery of dual inhibitors for botulinum neurotoxin A: concomitant targeting of endocytosis and light chain protease activity

Dyngo-4a™ has been found to be an endocytic inhibitor of BoNT/A neurotoxicity through dynamin inhibition. Herein, we demonstrate this molecule to have a previously unrecognized dual activity against BoNT/A, dynamin-protease inhibition. To establish the importance of this dual activity, detailed kinetic analysis of Dyngo-4a's inhibition of BoNT/A metalloprotease as well as cellular and animal toxicity studies have been described. The research presented is the first polypharmacological approach to counteract BoNT/A intoxication.

A monoclonal antibody to an abrin chimera recognizing a unique epitope on abrin A chain confers protection from abrin-induced lethality

Abrin, obtained from the seeds of Abrus precatorius plant, is a potent toxin belonging to the family of type II ribosome-inactivating proteins. Recently, a recombinant vaccine consisting of the A subunits of abrin and its homolog Abrus precatorius agglutinin (APA) was demonstrated to protect mice from abrin lethality. Toward identifying neutralizing epitopes recognized during this response, we generated monoclonal antibodies against the proposed vaccine candidate. One antibody, namely A7C4, the corresponding epitope of which was found to be distal to the active site of the enzymatic A chain, prevented abrin-mediated toxicity on cells and abrin-induced lethality in mice but did not inhibit the catalytic activity of the A chain. The in vivo protection conferred by monoclonal antibody A7C4 highlights the potential use of this antibody as a promising immunotherapeutic.

Monoclonal antibody, mAb 4C13, an effective detoxicant antibody against ricin poisoning

Ricin is a glycoprotein produced in castor seeds and consists of two polypeptide chains named Ricin Toxin A Chain (RTA) and Ricin Toxin B Chain (RTB), linked via a disulfide bridge. Due to its high toxicity, ricin is regarded as a high terrorist risk for the public. However, antibodies can play a pivotal role in neutralizing the toxin. In this research, the anti-toxicant effect of mAb 4C13, a monoclonal antibody (mAb) established using detoxicated ricin as the immunized antigen, was evaluated. Compared with mAb 4F2 and mAb 5G6, the effective mechanism of mAb 4C13 was analyzed by experiments relating to its cytotoxicity, epitope on ricin, binding kinetics with the toxin, its blockage on the protein synthesis inhibition induced by ricin and the intracelluar tracing of its complex with ricin. Our result indicated that mAb 4C13 could recognize and bind to RTA, RTB and exert its high affinity to the holotoxin. Both cytotoxicity and animal toxicity of ricin were well blocked by pre-incubating the toxin with mAb 4C13. By intravenous injection, mAb 4C13 could rescue the mouse intraperitoneally (ip) injected with a lethal dose of ricin (20μg/kg) even at 6h after the intoxication and its efficacy was dependent on its dosage. This research indicated that mAb 4C13 could be an excellent candidate for therapeutic antibodies. Its potent antitoxic efficiency was related to its recognition on the specific epitope with very high affinity and its blockage of protein synthesis inhibition in cytoplasm followed by cellular internalization with ricin.

Biochemical and structural analysis of an Eis family aminoglycoside acetyltransferase from bacillus anthracis

Proteins from the enhanced intracellular survival (Eis) family are versatile acetyltransferases that acetylate amines at multiple positions of several aminoglycosides (AGs). Their upregulation confers drug resistance. Homologues of Eis are present in diverse bacteria, including many pathogens. Eis from Mycobacterium tuberculosis (Eis_Mtb) has been well characterized. In this study, we explored the AG specificity and catalytic efficiency of the Eis family protein from Bacillus anthracis (Eis_Ban). Kinetic analysis of specificity and catalytic efficiency of acetylation of six AGs indicates that Eis_Ban displays significant differences from Eis_Mtb in both substrate binding and catalytic efficiency. The number of acetylated amines was also different for several AGs, indicating a distinct regiospecificity of Eis_Ban. Furthermore, most recently identified inhibitors of Eis_Mtb did not inhibit Eis_Ban, underscoring the differences between these two enzymes. To explain these differences, we determined an Eis_Ban crystal structure. The comparison of the crystal structures of Eis_Ban and Eis_Mtb demonstrates that critical residues lining their respective substrate binding pockets differ substantially, explaining their distinct specificities. Our results suggest that acetyltransferases of the Eis family evolved divergently to garner distinct specificities while conserving catalytic efficiency, possibly to counter distinct chemical challenges. The unique specificity features of these enzymes can be utilized as tools for developing AGs with novel modifications and help guide specific AG treatments to avoid Eis-mediated resistance.

Epitope targeting of tertiary protein structure enables target-guided synthesis of a potent in-cell inhibitor of botulinum neurotoxin

Botulinum neurotoxin (BoNT) serotype A is the most lethal known toxin and has an occluded structure, which prevents direct inhibition of its active site before it enters the cytosol. Target-guided synthesis by in situ click chemistry is combined with synthetic epitope targeting to exploit the tertiary structure of the BoNT protein as a landscape for assembling a competitive inhibitor. A substrate-mimicking peptide macrocycle is used as a direct inhibitor of BoNT. An epitope-targeting in situ click screen is utilized to identify a second peptide macrocycle ligand that binds to an epitope that, in the folded BoNT structure, is active-site-adjacent. A second in situ click screen identifies a molecular bridge between the two macrocycles. The resulting divalent inhibitor exhibits an in vitro inhibition constant of 165 pM against the BoNT/A catalytic chain. The inhibitor is carried into cells by the intact holotoxin, and demonstrates protection and rescue of BoNT intoxication in a human neuron model.

Probing BoNT/A protease exosites: implications for inhibitor design and light chain longevity

Botulinum neurotoxin serotype A (BoNT/A) is one of the most lethal toxins known. Its extreme toxicity is due to its light chain (LC), a zinc protease that cleaves SNAP-25, a synaptosome-associated protein, leading to the inhibition of neuronal activity. Studies on BoNT/A LC have revealed that two regions, termed exosites, can play an important role in BoNT catalytic activity. A clear understanding of how these exosites influence neurotoxin catalytic activity would provide a critical framework for deciphering the mechanism of SNAP-25 cleavage and the design of inhibitors. Herein, based on the crystallographic structure of BoNT/A LC complexed with its substrate, we designed an α-exosite binding probe. Experiments with this unique probe demonstrated that α-exosite binding enhanced both catalytic activity and stability of the LC. These data help delineate why α-exosite binding is needed for SNAP-25 cleavage and also provide new insights into the extended lifetime observed for BoNT/A LC in vivo.

Structural basis for the neutralization and specificity of Staphylococcal enterotoxin B against its MHC Class II binding site

Staphylococcal enterotoxin (SE) B is among the potent toxins produced by Staphylococcus aureus that cause toxic shock syndrome (TSS), which can result in multi-organ failure and death. Currently, neutralizing antibodies have been shown to be effective immunotherapeutic agents against this toxin, but the structural basis of the neutralizing mechanism is still unknown. In this study, we generated a neutralizing monoclonal antibody, 3E2, against SEB, and analyzed the crystal structure of the SEB-3E2 Fab complex. Crystallographic analysis suggested that the neutralizing epitope overlapped with the MHC II molecule binding site on SEB, and thus 3E2 could inhibit SEB function by preventing interaction with the MHC II molecule. Mutagenesis studies were done on SEB, as well as the related Staphylococcus aureus toxins SEA and SEC. These studies revealed that tyrosine (Y)46 and lysine (K)71 residues of SEB are essential to specific antibody-antigen recognition and neutralization. Substitution of Y at SEA glutamine (Q)49, which corresponds to SEB Y46, increased both 3E2's binding to SEA in vitro and the neutralization of SEA in vivo. These results suggested that SEB Y46 is responsible for distinguishing SEB from SEA. These findings may be helpful for the development of antibody-based therapy for SEB-induced TSS.

Structural insight into exosite binding and discovery of novel exosite inhibitors of botulinum neurotoxin serotype A through in silico screening

Botulinum neurotoxin serotype A (BoNT/A) is the most lethal toxin among the Tier 1 Select Agents. Development of potent and selective small molecule inhibitors against BoNT/A zinc metalloprotease remains a challenging problem due to its exceptionally large substrate binding surface and conformational plasticity. The exosites of the catalytic domain of BoNT/A are intriguing alternative sites for small molecule intervention, but their suitability for inhibitor design remains largely unexplored. In this study, we employed two recently identified exosite inhibitors, D-chicoric acid and lomofungin, to probe the structural features of the exosites and molecular mechanisms of synergistic inhibition. The results showed that D-chicoric acid favors binding at the α-exosite, whereas lomofungin preferentially binds at the β-exosite by mimicking the substrate β-sheet binding interaction. Molecular dynamics simulations and binding interaction analysis of the exosite inhibitors with BoNT/A revealed key elements and hotspots that likely contribute to the inhibitor binding and synergistic inhibition. Finally, we performed database virtual screening for novel inhibitors of BoNT/A targeting the exosites. Hits C1 and C2 showed non-competitive inhibition and likely target the α- and β-exosites, respectively. The identified exosite inhibitors may provide novel candidates for structure-based development of therapeutics against BoNT/A intoxication.

Second generation steroidal 4-aminoquinolines are potent, dual-target inhibitors of the botulinum neurotoxin serotype A metalloprotease and P. falciparum malaria

Significantly more potent second generation 4-amino-7-chloroquinoline (4,7-ACQ) based inhibitors of the botulinum neurotoxin serotype A (BoNT/A) light chain were synthesized. Introducing an amino group at the C(3) position of the cholate component markedly increased potency (IC50 values for such derivatives ranged from 0.81 to 2.27 μM). Two additional subclasses were prepared: bis(steroidal)-4,7-ACQ derivatives and bis(4,7-ACQ)cholate derivatives; both classes provided inhibitors with nanomolar-range potencies (e.g., the Ki of compound 67 is 0.10 μM). During BoNT/A challenge using primary neurons, select derivatives protected SNAP-25 by up to 89%. Docking simulations were performed to rationalize the compounds' in vitro potencies. In addition to specific residue contacts, coordination of the enzyme's catalytic zinc and expulsion of the enzyme's catalytic water were a consistent theme. With respect to antimalarial activity, the compounds provided better IC90 activities against chloroquine resistant (CQR) malaria than CQ, and seven compounds were more active than mefloquine against CQR strain W2.

Induced IL-10 splice altering approach to antiviral drug discovery

Ebola virus causes an acute hemorrhagic fever lethal in primates and rodents. The contribution of host immune factors to pathogenesis has yet to be determined and may reveal efficacious targets for potential treatment. In this study, we show that the interleukin (IL)-10 signaling pathway modulates Ebola pathogenesis. IL-10(-/-) mice and wild-type mice receiving antisense targeting IL-10 signaling via disrupting expression through aberrant splice altering were resistant to ebola virus infection. IL-10(-/-) mice exhibited reduced viral titers, pathology, and levels of IL-2, IL-6, keratinocyte-derived chemokine (KC), and macrophage inflammatory protein-1 α and increased interferon (IFN)-γ relative to infected wild-type mice. Furthermore, antibody depletion studies in IL-10(-/-) mice suggest a requirement for natural killer cells and IFN-γ for protection. Together, these data demonstrate that resistance to ebola infection is regulated by IL-10 and can be targeted in a prophylactic manner to protect against lethal hemorrhagic virus challenge.

Identification of exosite-targeting inhibitors of anthrax lethal factor by high-throughput screening

Protease inhibitor discovery has focused almost exclusively on compounds that bind to the active site. Inhibitors targeting protease exosites, regions outside of the active site that influence catalysis, offer potential advantages of increased specificity but are difficult to systematically discover. Here, we describe an assay suitable for detecting exosite-targeting inhibitors of the metalloproteinase anthrax lethal factor (LF) based on cleavage of a full-length mitogen-activated protein kinase kinase (MKK) substrate. We used this assay to screen a small-molecule library and then subjected hits to a secondary screen to exclude compounds that efficiently blocked cleavage of a peptide substrate. We identified a compound that preferentially inhibited cleavage of MKKs compared with peptide substrates and could suppress LF-induced macrophage cytolysis. This approach should be generally applicable to the discovery of exosite-targeting inhibitors of many additional proteases.

Recent developments in cell-based assays and stem cell technologies for botulinum neurotoxin research and drug discovery

Botulinum neurotoxins (BoNTs) are exceptionally potent inhibitors of neurotransmission, causing muscle paralysis and respiratory failure associated with the disease botulism. Currently, no drugs are available to counter intracellular BoNT poisoning. To develop effective medical treatments, cell-based assays provide a valuable system to identify novel inhibitors in a time- and cost-efficient manner. Consequently, cell-based systems including immortalized cells, primary neurons and stem cell-derived neurons have been established. Stem cell-derived neurons are highly sensitive to BoNT intoxication and represent an ideal model to study the biological effects of BoNTs. Robust immunoassays are used to quantify BoNT activity and play a central role during inhibitor screening. In this review, we examine recent progress in physiologically relevant cell-based assays and high-throughput screening approaches for the identification of both direct and indirect BoNT inhibitors.

Filovirus-like particles as vaccines and discovery tools

Ebola and Marburg viruses are members of the family Filoviridae, which cause severe hemorrhagic fevers in humans. Filovirus outbreaks have been sporadic, with mortality rates currently ranging from 30 to 90%. Unfortunately, there is no efficacious human therapy or vaccine available to treat disease caused by either Ebola or Marburg virus infection. Expression of the filovirus matrix protein, VP40, is sufficient to drive spontaneous production and release of virus-like particles (VLPs) that resemble the distinctively filamentous infectious virions. The addition of other filovirus proteins, including virion proteins (VP)24, 30 and 35 and glycoprotein, increases the efficiency of VLP production and results in particles containing multiple filovirus antigens. Vaccination with Ebola or Marburg VLPs containing glycoprotein and VP40 completely protects rodents from lethal challenge with the homologous virus. These candidate vaccines are currently being tested for immunogenicity and efficacy in nonhuman primates. Furthermore, the Ebola and Marburg VLPs are being used as a surrogate model to further understand the filovirus life cycle, with the goal of developing rationally designed vaccines and therapeutics. Thus, in addition to their use as a vaccine, VLPs are currently being used as tools to learn lessons about filovirus pathogenesis, immunology, replication and assembly requirements.

Synthesis/biological evaluation of hydroxamic acids and their prodrugs as inhibitors for Botulinum neurotoxin A light chain

Botulinum neurotoxin A (BoNT/A) is the most potent toxin known. Unfortunately, it is also a potential bioweapon in terrorism, which is without an approved therapeutic treatment once cellular intoxication takes place. Previously, we reported how hydroxamic acid prodrug carbamates increased cellular uptake, which translated to successful inhibition of this neurotoxin. Building upon this research, we detail BoNT/A protease molecular modeling studies accompanied by the construction of small library of hydroxamic acids based on 2,4-dichlorocinnamic hydroxamic acid scaffold and their carbamate prodrug derivatization along with the evaluation of these molecules in both enzymatic and cellular models.

Mechanistic insights into the neutralization of cytotoxic abrin by the monoclonal antibody D6F10

Abrin, an A/B toxin obtained from the Abrus precatorius plant is extremely toxic and a potential bio-warfare agent. Till date there is no antidote or vaccine available against this toxin. The only known neutralizing monoclonal antibody against abrin, namely D6F10, has been shown to rescue the toxicity of abrin in cells as well as in mice. The present study focuses on mapping the epitopic region to understand the mechanism of neutralization of abrin by the antibody D6F10. Truncation and mutational analysis of abrin A chain revealed that the amino acids 74-123 of abrin A chain contain the core epitope and the residues Thr112, Gly114 and Arg118 are crucial for binding of the antibody. In silico analysis of the position of the mapped epitope indicated that it is present close to the active site cleft of abrin A chain. Thus, binding of the antibody near the active site blocks the enzymatic activity of abrin A chain, thereby rescuing inhibition of protein synthesis by the toxin in vitro. At 1∶10 molar concentration of abrin:antibody, the antibody D6F10 rescued cells from abrin-mediated inhibition of protein synthesis but did not prevent cell attachment of abrin. Further, internalization of the antibody bound to abrin was observed in cells by confocal microscopy. This is a novel finding which suggests that the antibody might function intracellularly and possibly explains the rescue of abrin's toxicity by the antibody in whole cells and animals. To our knowledge, this study is the first report on a neutralizing epitope for abrin and provides mechanistic insights into the poorly understood mode of action of anti-A chain antibodies against several toxins including ricin.

Mapping the epitopes of a neutralizing antibody fragment directed against the lethal factor of Bacillus anthracis and cross-reacting with the homologous edema factor

The lethal toxin (LT) of Bacillus anthracis, composed of the protective antigen (PA) and the lethal factor (LF), plays an essential role in anthrax pathogenesis. PA also interacts with the edema factor (EF, 20% identity with LF) to form the edema toxin (ET), which has a lesser role in anthrax pathogenesis. The first recombinant antibody fragment directed against LF was scFv 2LF; it neutralizes LT by blocking the interaction between PA and LF. Here, we report that scFv 2LF cross-reacts with EF and cross-neutralizes ET, and we present an in silico method taking advantage of this cross-reactivity to map the epitope of scFv 2LF on both LF and EF. This method identified five epitope candidates on LF, constituted of a total of 32 residues, which were tested experimentally by mutating the residues to alanine. This combined approach precisely identified the epitope of scFv 2LF on LF as five residues (H229, R230, Q234, L235 and Y236), of which three were missed by the consensus epitope candidate identified by pre-existing in silico methods. The homolog of this epitope on EF (H253, R254, E258, L259 and Y260) was experimentally confirmed to constitute the epitope of scFv 2LF on EF. Other inhibitors, including synthetic molecules, could be used to target these epitopes for therapeutic purposes. The in silico method presented here may be of more general interest.

Virtual medicinal chemistry: in silico pre-docking functional group transformation for discovery of novel inhibitors of botulinum toxin serotype A light chain

A novel method for applying high-throughput docking to challenging metalloenzyme targets is described. The method utilizes information-based virtual transformation of library carboxylates to hydroxamic acids prior to docking, followed by compound acquisition, one-pot (two steps) chemical synthesis and in vitro screening. In two experiments targeting the botulinum neurotoxin serotype A metalloprotease light chain, hit rates of 32% and 18% were observed.

Conformation-dependent high-affinity potent ricin-neutralizing monoclonal antibodies

Ricin is a potential biothreat agent with no approved antidote available for ricin poisoning. The aim of this study was to develop potent antibody-based antiricin antidotes. Four strong ricin resistant hybridoma clones secreting antiricin monoclonal antibodies (mAbs) were developed. All four mAbs are bound to conformational epitopes of ricin toxin B (RTB) with high affinity (KD values from 2.55 to 36.27 nM). RTB not only triggers cellular uptake of ricin, but also facilitates transport of the ricin toxin A (RTA) from the endoplasmic reticulum to the cytosol, where RTA exerts its toxic activity. The four mAbs were found to have potent ricin-neutralizing capacities and synergistic effects among them as determined by an in vitro neutralization assay. In vivo protection assay demonstrated that all four mAbs had strong efficacy against ricin challenges. D9 was found to be exceptionally effective. Intraperitoneal (i.p.) administration of D9, at a dose of 5 μ g, 6 weeks before or 6 hours after an i.p. challenge with 5 × LD50 of ricin was able to protect or rescue 100% of the mice, indicating that mAb D9 is an excellent candidate to be developed as a potent antidote against ricin poisoning for both prophylactic and therapeutic purposes.

Evaluation of adamantane hydroxamates as botulinum neurotoxin inhibitors: synthesis, crystallography, modeling, kinetic and cellular based studies

Botulinum neurotoxins (BoNTs) are the most lethal biotoxins known to mankind and are responsible for the neuroparalytic disease botulism. Current treatments for botulinum poisoning are all protein based and thus have a limited window of treatment opportunity. Inhibition of the BoNT light chain protease (LC) has emerged as a therapeutic strategy for the treatment of botulism as it may provide an effective post exposure remedy. Using a combination of crystallographic and modeling studies a series of hydroxamates derived from 1-adamantylacetohydroxamic acid (3a) were prepared. From this group of compounds, an improved potency of about 17-fold was observed for two derivatives. Detailed mechanistic studies on these structures revealed a competitive inhibition model, with a K(i)=27 nM, which makes these compounds some of the most potent small molecule, non-peptidic BoNT/A LC inhibitors reported to date.

Synthetic human monoclonal antibodies toward staphylococcal enterotoxin B (SEB) protective against toxic shock syndrome

Staphylococcal enterotoxin B (SEB) is a potent toxin that can cause toxic shock syndrome and act as a lethal and incapacitating agent when used as a bioweapon. There are currently no vaccines or immunotherapeutics available against this toxin. Using phage display technology, human antigen-binding fragments (Fabs) were selected against SEB, and proteins were produced in Escherichia coli cells and characterized for their binding affinity and their toxin neutralizing activity in vitro and in vivo. Highly protective Fabs were converted into full-length IgGs and produced in mammalian cells. Additionally, the production of anti-SEB antibodies was explored in the Nicotiana benthamiana plant expression system. Affinity maturation was performed to produce optimized lead anti-SEB antibody candidates with subnanomolar affinities. IgGs produced in N. benthamiana showed characteristics comparable with those of counterparts produced in mammalian cells. IgGs were tested for their therapeutic efficacy in the mouse toxic shock model using different challenge doses of SEB and a treatment with 200 μg of IgGs 1 h after SEB challenge. The lead candidates displayed full protection from lethal challenge over a wide range of SEB challenge doses. Furthermore, mice that were treated with anti-SEB IgG had significantly lower IFNγ and IL-2 levels in serum compared with mock-treated mice. In summary, these anti-SEB monoclonal antibodies represent excellent therapeutic candidates for further preclinical and clinical development.

Targeting bacterial toxins

Protein toxins constitute the main virulence factors of several species of bacteria and have proven to be attractive targets for drug development. Lead candidates that target bacterial toxins range from small molecules to polymeric binders, and act at each of the multiple steps in the process of toxin-mediated pathogenicity. Despite recent and significant advances in the field, a rationally designed drug that targets toxins has yet to reach the market. This Review presents the state of the art in bacterial toxin targeted drug development with a critical consideration of achieved breakthroughs and withstanding challenges. The discussion focuses on A-B-type protein toxins secreted by four species of bacteria, namely Clostridium difficile (toxins A and B), Vibrio cholerae (cholera toxin), enterohemorrhagic Escherichia coli (Shiga toxin), and Bacillus anthracis (anthrax toxin), which are the causative agents of diseases for which treatments need to be improved.

Time-dependent botulinum neurotoxin serotype A metalloprotease inhibitors

Botulinum neurotoxins (BoNTs) are the most lethal of biological substances, and are categorized as class A biothreat agents by the Centers for Disease Control and Prevention. There are currently no drugs to treat the deadly flaccid paralysis resulting from BoNT intoxication. Among the seven BoNT serotypes, the development of therapeutics to counter BoNT/A is a priority (due to its long half-life in the neuronal cytosol and its ease of production). In this regard, the BoNT/A enzyme light chain (LC) component, a zinc metalloprotease responsible for the intracellular cleavage of synaptosomal-associated protein of 25 kDa, is a desirable target for developing post-BoNT/A intoxication rescue therapeutics. In an earlier study, we reported the high throughput screening of a library containing 70,000 compounds, and uncovered a novel class of benzimidazole acrylonitrile-based BoNT/A LC inhibitors. Herein, we present both structure-activity relationships and a proposed mechanism of action for this novel inhibitor chemotype.