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Faculty & Staff


B.S. Biology, University of Heidelberg, Heidelberg, Germany 1995
M.A. Biology, Portland State University, Portland, OR 1997
PhD. Env. & Mol. Toxicology, University of Wisconsin-Madison 2004       
Postdoctoral Research: Food Microbiology & Toxicology, University of Wisconsin-Madison

Areas of Study

Clostridium botulinum
Clostridial Neurotoxins in Health and Disease
Neuronal Toxin Detection and Analysis Systems
Food and Industrial Microbiology

Research Overview

Our lab’s research focuses on Clostridium botulinum (C. botulinum) and its neurotoxins as pathogens and agents of serious foodborne illness and as important and unique pharmaceuticals that are widely used for many clinical applications around the world.  We are a state-of-the-art lab continuing a long-term botulinum neurotoxins (BoNTs) research program with a rich history at UW-Madison, starting with Ed Schantz’s production of first crystalline BoNTs, Ed Schantz and Eric Johnson’s production of the first batches of pharmaceutically used BoNTs, and many novel discoveries.

Ongoing research in our lab examines toxin production by C. botulinum, purification and characterization of BoNTs and related homologs, lateral transfer of BoNT genes within Clostridium, structure function studies of novel BoNTs, investigations of countermeasures for botulism including vaccines and small molecule inhibitors, development of novel BoNT based pharmaceuticals, tetanus vaccines, and food safety studies.


Member of International Neurotoxin Association: 2012 – current
Member of American Society of Microbiologists (ASM): 2013-current
Consultant for Merz Pharma (Germany): 2013 – ongoing
Expert consultant for UW-Madison Institutional Biosafety Committee: 2017-current

Lab Personnel

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Marite Bradshaw
Senior Scientist
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Brieana Gregg
Research Specialist
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Sonal Gupta
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Becky Kaufman
Research Specialist
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Molly Sneller
Research Specialist
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Bill Tepp
Sr Research Specialist
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Travis Wentz
Grad Student

Research Papers

  • Inzalaco HN, Tepp WH, Fredrick C, Bradshaw M, Johnson EA, Pellett S (2021) Posttranslational Regulation of Botulinum Neurotoxin Production in Clostridium botulinum Hall A- hyper . mSphere 6((4)):e0032821 PMC8386421 · Pubmed · DOI

    No abstract available.

  • Turner LD, Nielsen AL, Lin L, Pellett S, Sugane T, Olson ME, Johnson EA, Janda KD (2021) Irreversible inhibition of BoNT/A protease: proximity-driven reactivity contingent upon a bifunctional approach. RSC medicinal chemistry 12((6)):960-969 PMC8221255 · Pubmed · DOI

    No abstract available.

  • Turner LD, Nielsen AL, Lin L, Pellett S, Sugane T, Olson ME, Janda KD (2021) COVALENT INHIBITION OF BOTULINUM NEUROTOXIN A - EXPLORATION OF WARHEAD REACTIVITY AND FUNCTION USING A BIFUNCTIONAL APPROACH. Toxicon : official journal of the International Society on Toxinology 190((Suupl 1)):S72-S73 PMC8183569 · Pubmed

    No abstract available.

  • Lin L, Turner LD, Šilhár P, Pellett S, Johnson EA, Janda KD (2021) Identification of 3-hydroxy-1,2-dimethylpyridine-4(1 H )-thione as a metal-binding motif for the inhibition of botulinum neurotoxin A. RSC medicinal chemistry 12((1)):137-143 PMC8130615 · Pubmed · DOI

    No abstract available.

  • Lin L, Olson ME, Sugane T, Turner LD, Tararina MA, Nielsen AL, Kurbanov EK, Pellett S, Johnson EA, Cohen SM, Allen KN, Janda KD (2020) Catch and Anchor Approach To Combat Both Toxicity and Longevity of Botulinum Toxin A. Journal of medicinal chemistry 63((19)):11100-11120 PMC7581224 · Pubmed · DOI

    No abstract available.

  • Przedpelski A, Tepp WH, Pellett S, Johnson EA, Barbieri JT (2020) A Novel High-Potency Tetanus Vaccine. mBio 11((4)): PMC7439469 · Pubmed · DOI

    No abstract available.

  • Pellett S, Tepp WH, Johnson EA (2019) Critical Analysis of Neuronal Cell and the Mouse Bioassay for Detection of Botulinum Neurotoxins. Toxins 11((12)): PMC6950160 · Pubmed · DOI

    Botulinum Neurotoxins (BoNTs) are a large protein family that includes the most potent neurotoxins known to humankind. BoNTs delivered locally in humans at low doses are widely used pharmaceuticals. Reliable and quantitative detection of BoNTs is of paramount importance for the clinical diagnosis of botulism, basic research, drug development, potency determination, and detection in clinical, environmental, and food samples. Ideally, a definitive assay for BoNT should reflect the activity of each of the four steps in nerve intoxication. The in vivo mouse bioassay (MBA) is the 'gold standard' for the detection of BoNTs. The MBA is sensitive, robust, semi-quantitative, and reliable within its sensitivity limits. Potential drawbacks with the MBA include assay-to-assay potency variations, especially between laboratories, and false positives or negatives. These limitations can be largely avoided by careful planning and performance. Another detection method that has gained importance in recent years for research and potency determination of pharmaceutical BoNTs is cell-based assays, as these assays can be highly sensitive, quantitative, human-specific, and detect fully functional holotoxins at physiologically relevant concentrations. A myriad of other in vitro BoNT detection methods exist. This review focuses on critical factors and assay limitations of the mouse bioassay and cell-based assays for BoNT detection.

  • Pellett S, Tepp WH, Johnson EA (2019) Botulinum neurotoxins A, B, C, E, and F preferentially enter cultured human motor neurons compared to other cultured human neuronal populations. FEBS letters 593((18)):2675-2685 PMC7751886 · Pubmed · DOI

    Human-induced pluripotent stem cell (hiPSC)-derived neurons can be exquisitely sensitive to botulinum neurotoxins (BoNTs), exceeding sensitivity of the traditionally used mouse bioassay. In this report, four defined hiPSC-derived neuronal populations including primarily GABAergic, glutamatergic, dopaminergic, and motor neurons were examined for BoNT/A, B, C, D, E, and F sensitivity. The data indicate that sensitivity varies markedly for the BoNTs tested. Motor neurons are significantly more sensitive than other neuron types for all BoNTs except BoNT/D. Examination of SNARE protein levels and BoNT-specific cell surface protein receptors reveals few differences between the cell types except greater expression levels of the receptor protein SV2C and synapsin-IIa in motor neurons. This indicates that differential toxicity of BoNTs for motor neurons compared to other neuronal cell types involves multiple mechanisms.

  • Moritz MS, Tepp WH, Inzalaco HN, Johnson EA, Pellett S (2019) Comparative functional analysis of mice after local injection with botulinum neurotoxin A1, A2, A6, and B1 by catwalk analysis. Toxicon : official journal of the International Society on Toxinology 167:20-28 PMC6688953 · Pubmed · DOI

    Botulinum neurotoxins (BoNTs) are potent neurotoxins and are the causative agent of botulism, as well as valuable pharmaceuticals. BoNTs are divided into seven serotypes that comprise over 40 reported subtypes. BoNT/A1 and BoNT/B1 are currently the only subtypes approved for pharmaceutical use in the USA. While several other BoNT subtypes including BoNT/A2 and/A6 have been proposed as promising pharmaceuticals, detailed characterization using in vivo assays are essential to determine their pharmaceutical characteristics compared to the currently used BoNT/A1 and/B1. Several methods for studying BoNTs in mice are being used, but no objective and quantitative assay for assessment of functional outcomes after injection has been described. Here we describe the use of CatWalk XT as a new analytical tool for the objective and quantitative analysis of the paralytic effect after local intramuscular injection of BoNT subtypes A1, A2, A6, and B1. Catwalk is a sophisticated gait and locomotion analysis system that quantitatively analyzes a rodent's paw print dimensions and footfall patterns while traversing a glass plate during unforced walk. Significant changes were observed in several gait parameters in mice after local intramuscular injection of all tested BoNT subtypes, however, no changes were observed in mice injected intraperitoneally with the same BoNTs. While a clear difference in time to peak paralysis was observed between BoNT/A1 and/B1, injection of all four toxins resulted in a deficit in the injected limb with the other limbs functionally compensating and with no qualitative differences between the four BoNT subtypes. The presented data demonstrate the utility of CatWalk as a tool for functional outcomes after local BoNT injection through its ability to collect large amounts of quantitative data and objectively analyze sensitive changes in static and dynamic gait parameters.

  • Moritz MS, Tepp WH, Bradshaw M, Johnson EA, Pellett S (2018) Isolation and Characterization of the Novel Botulinum Neurotoxin A Subtype 6. mSphere 3((5)): PMC6200982 · Pubmed · DOI

    Botulinum neurotoxins (BoNTs), the most potent toxins known to humans and the causative agent of botulism, exert their effect by entering motor neurons and cleaving and inactivating SNARE proteins, which are essential for neurotransmitter release. BoNTs are proven, valuable pharmaceuticals used to treat more than 200 neuronal disorders. BoNTs comprise 7 serotypes and more than 40 isoforms (subtypes). BoNT/A1 is the only A-subtype used clinically due to its high potency and long duration of action. While other BoNT/A subtypes have been purified and described, only BoNT/A2 is being investigated as an alternative to BoNT/A1. Here we describe subtype BoNT/A6 with improved pharmacological properties compared to BoNT/A1. It was isolated from CDC41370, which produces both BoNT/B2 and BoNT/A6. The gene encoding BoNT/B2 was genetically inactivated, and A6 was isolated to greater than 95% purity. A6 was highly potent in cultured primary rodent neuronal cultures and in human induced pluripotent stem cell-derived neurons, requiring 20-fold less toxin to cause 50% SNAP-25 cleavage than A1. Second, A6 entered hiPSCs faster and more efficiently than A1 and yet had a long duration of action similar to BoNT/A1. Third, BoNT/A6 had similar LD as BoNT/A1 after intraperitoneal injection in mice; however, local intramuscular injection resulted in less systemic toxicity than BoNT/A1 and a higher (i.m.) LD, indicating its potential as a safer pharmaceutical. These data suggest novel characteristics of BoNT/A6 and its potential as an improved pharmaceutical due to more efficient neuronal cell entry, greater ability to remain localized at the injection site, and a long duration. Botulinum neurotoxins (BoNTs) have proved to be an effective treatment for a large number of neuropathic conditions. BoNTs comprise a large family of zinc metalloproteases, but BoNT/A1 is used nearly exclusively for pharmaceutical purposes. The genetic inactivation of a second BoNT gene in the native strain enabled expression and isolation of a single BoNT/A6 from cultures. Its characterization indicated that BoNT/A subtype A6 has a long duration of action comparable to A1, while it enters neurons faster and more efficiently and remains more localized after intramuscular injection. These characteristics of BoNT/A6 are of interest for potential use of BoNT/A6 as a novel BoNT-based therapeutic that is effective and has a fast onset, an improved safety profile, and a long duration of action. Use of BoNT/A6 as a pharmaceutical also has the potential to reveal novel treatment motifs compared to currently used treatments.

  • Pellett S, Bradshaw M, Tepp WH, Pier CL, Whitemarsh RCM, Chen C, Barbieri JT, Johnson EA (2018) The Light Chain Defines the Duration of Action of Botulinum Toxin Serotype A Subtypes. mBio 9((2)): PMC5874905 · Pubmed · DOI

    Botulinum neurotoxin (BoNT) is the causative agent of botulism and a widely used pharmaceutical to treat a variety of neurological diseases. BoNTs are 150-kDa protein toxins organized into heavy chain (HC) and light chain (LC) domains linked by a disulfide bond. The HC selectively binds to neurons and aids cell entry of the enzymatically active LC. There are seven immunological BoNT serotypes (A to G); each serotype includes genetic variants, termed subtypes. Only two subtypes, BoNT/A1 and BoNT/B1, are currently used as therapeutics. BoNT serotype A (BoNT/A) subtypes A2 to A8 show distinct potency, duration of action, and pathology relative to BoNT/A1. Specifically, BoNT/A3 possesses shorter duration of action and elicits distinct symptoms in mice at high toxin doses. In this report, we analyzed the roles of LC and HC of BoNT/A3 for duration of action, neuronal cell entry, and mouse pathology by using clostridium-derived recombinant hybrid BoNTs consisting of reciprocal LC and HC (BoNTA1/A3 and BoNTA3/A1). Hybrid toxins were processed in their expression host to a dichain BoNT consisting of LC and HC linked via a disulfide bond. The LC and HC defined BoNT potency in mice and BoNT toxicity for cultured neuronal cells, while the LC defined the duration of BoNT action in cell and mouse models. Protein alignment identified a previously unrecognized region within the LC subtype A3 (LC/A3) relative to the other LC serotype A (LC/A) subtypes (low primary acid homology [LPH]) that correlated to intracellular LC localization. This study shows the utility of recombinant hybrid BoNTs with new therapeutic potential, while remaining sensitive to antitoxins and therapies to native BoNT. Botulinum neurotoxins are the most potent protein toxins for humans and potential bioterrorism threats, but they are also widely used as pharmaceuticals. Within the large family of BoNTs, only two subtypes are currently used as pharmaceuticals, with a large number of BoNT subtypes remaining as untapped potential sources for unique pharmaceuticals. Here, two recombinant hybrid toxins were engineered, consisting of domains from two BoNT subtypes that possess distinct duration of action and activity in human neurons and mice. We define the functional domains responsible for BoNT action and demonstrate creation of functional hybrid BoNTs with new therapeutic potential, while remaining sensitive to antitoxins and therapies to native BoNT.

  • Ramachandran R, Marino MJ, Paul S, Wang Z, Mascarenhas NL, Pellett S, Johnson EA, DiNardo A, Yaksh TL (2018) A Study and Review of Effects of Botulinum Toxins on Mast Cell Dependent and Independent Pruritus. Toxins 10((4)): PMC5923300 · Pubmed · DOI

    Pruriceptive itch originates following activation of peripheral sensory nerve terminals when pruritogens come in contact with the skin. The ability of botulinum neurotoxins (BoNTs) to attenuate transmitter release from afferent terminals provides a rationale for studying its effect on pruritus. This study investigated the effects of BoNT/A1 and BoNT/B1 on mast cell dependent (Compound 48/80:48/80) and independent (Chloroquine:CQ) scratching. C57Bl/6 male mice received intradermal injection of 1.5 U of BoNT/A1, BoNT/B1 or saline 2, 7, 14 and 21 days prior to ipsilateral 48/80 or CQ at the nape of the neck. Ipsilateral hind paw scratching was determined using an automated recording device. The effect of BoNTs on 48/80 mediated mast cell degranulation was analyzed in human and murine mast cells and the presence of SNAREs was determined using qPCR, immunostaining and Western blot. Pre-treatment with BoNT/A1 and BoNT/B1 reduced 48/80 and CQ induced scratching behavior starting on day 2 with reversal by day 21. Both serotypes inhibited 48/80 induced mast cell degranulation. qPCR and immunostaining detected SNAP-25 mRNA and protein, respectively, in mast cells, however, Western blots did not. This study demonstrates the long-lasting anti-pruritic effects of two BoNT serotypes, in a murine pruritus model using two different mechanistically driven pruritogens. These data also indicate that BoNTs may have a direct effect upon mast cell degranulation.

  • Pellett S, Tepp WH, Lin G, Johnson EA (2017) Substrate cleavage and duration of action of botulinum neurotoxin type FA ("H, HA"). Toxicon : official journal of the International Society on Toxinology 147:38-46 PMC5911199 · Pubmed · DOI

    Botulinum neurotoxin (BoNT) type FA is the only known naturally occurring chimeric BoNT of domains of BoNT/A and BoNT/F. BoNT/FA consists of an F5-like light chain (LC), a unique heavy chain (HC) translocation domain, and a HC receptor binding domain similar to BoNT/A1. Previous analyses of purified BoNT/FA have indicated a 5-10-fold greater potency in cultured human or rat neurons as compared to BoNT/A1 and a 400-500-fold greater potency compared to BoNT/B1. However, in vivo potency in mice was about 5-fold lower than BoNT/A1 or/B1. In this report, species specificity was examined by cell-based assays using primary neurons from mice and examining VAMP1 and 2 cleavage. The data indicated similar potency of BoNT/FA in primary mouse spinal cord neurons as previously observed in primary rat and human induced pluripotent stem cell (hiPSC) derived neuronal cell models, and equal enzymatic cleavage of mouse VAMP1 and 2 isoforms. Since the duration of action of BoNTs is due to continuous enzymatic activity of the LC in the neuronal cytosol, BoNT/FA was expected to have a short duration of action due to its F-type LC. In this report the duration of action of BoNT/FA was compared to that of BoNT/F1,/F5, and/B1 in both hiPSC derived neurons and in the in vivo mouse model. The data indicate a duration of action of BoNT/FA similar to BoNT/B1, while BoNT/F5 had a short duration of action similar to BoNT/F1.

  • Jacobson AR, Adler M, Silvaggi NR, Allen KN, Smith GM, Fredenburg RA, Stein RL, Park JB, Feng X, Shoemaker CB, Deshpande SS, Goodnough MC, Malizio CJ, Johnson EA, Pellett S, Tepp WH, Tzipori S (2017) Small molecule metalloprotease inhibitor with in vitro, ex vivo and in vivo efficacy against botulinum neurotoxin serotype A. Toxicon : official journal of the International Society on Toxinology 137:36-47 PMC5694348 · Pubmed · DOI

    Botulinum neurotoxins (BoNTs) are the most toxic substances known to mankind and are the causative agents of the neuroparalytic disease botulism. Their ease of production and extreme toxicity have caused these neurotoxins to be classified as Tier 1 bioterrorist threat agents and have led to a sustained effort to develop countermeasures to treat intoxication in case of a bioterrorist attack. While timely administration of an approved antitoxin is effective in reducing the severity of botulism, reversing intoxication requires different strategies. In the present study, we evaluated ABS 252 and other mercaptoacetamide small molecule active-site inhibitors of BoNT/A light chain using an integrated multi-assay approach. ABS 252 showed inhibitory activity in enzymatic, cell-based and muscle activity assays, and importantly, produced a marked delay in time-to-death in mice. The results suggest that a multi-assay approach is an effective strategy for discovery of potential BoNT therapeutic candidates.

  • Bremer PT, Pellett S, Carolan JP, Tepp WH, Eubanks LM, Allen KN, Johnson EA, Janda KD (2017) Metal Ions Effectively Ablate the Action of Botulinum Neurotoxin A. Journal of the American Chemical Society 139((21)):7264-7272 PMC5612488 · Pubmed · DOI

    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 (K ≈ 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.

  • Pellett S, Tepp WH, Johnson EA, Sesardic D (2017) Assessment of ELISA as endpoint in neuronal cell-based assay for BoNT detection using hiPSC derived neurons. Journal of pharmacological and toxicological methods 88((Pt 1)):1-6 PMC5623611 · Pubmed · DOI

    Botulinum neurotoxins (BoNTs), the causative agents of botulism, are widely used as powerful bio-pharmaceuticals to treat neuro-muscular disorders. Due to the high potency and potential lethality of BoNTs, careful monitoring of the biologic activity of BoNT-based pharmaceuticals is required to ensure safe usage. For decades, the only approved method for potency determination of pharmaceutical BoNTs was the mouse bioassay (MBA), but in recent years improvements in cell-assay technologies have enabled MBA replacement by cell-based assays for specific product evaluations. This project details a method for quantitative and sensitive detection of biologic activity of BoNT/A1 in human induced pluripotent stem cell (hiPSC) derived neurons using an ELISA as a method to determine SNAP-25 cleavage by BoNT/A1 following toxin exposure.

  • Seki H, Xue S, Pellett S, Šilhár P, Johnson EA, Janda KD (2016) Cellular Protection of SNAP-25 against Botulinum Neurotoxin/A: Inhibition of Thioredoxin Reductase through a Suicide Substrate Mechanism. Journal of the American Chemical Society 138((17)):5568-75 PMC4881748 · Pubmed · DOI

    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.

  • Pellett S, Yaksh TL, Ramachandran R (2015) Current status and future directions of botulinum neurotoxins for targeting pain processing. Toxins 7((11)):4519-63 PMC4663519 · Pubmed · DOI

    Current evidence suggests that botulinum neurotoxins (BoNTs) A1 and B1, given locally into peripheral tissues such as skin, muscles, and joints, alter nociceptive processing otherwise initiated by inflammation or nerve injury in animal models and humans. Recent data indicate that such locally delivered BoNTs exert not only local action on sensory afferent terminals but undergo transport to central afferent cell bodies (dorsal root ganglia) and spinal dorsal horn terminals, where they cleave SNAREs and block transmitter release. Increasing evidence supports the possibility of a trans-synaptic movement to alter postsynaptic function in neuronal and possibly non-neuronal (glial) cells. The vast majority of these studies have been conducted on BoNT/A1 and BoNT/B1, the only two pharmaceutically developed variants. However, now over 40 different subtypes of botulinum neurotoxins (BoNTs) have been identified. By combining our existing and rapidly growing understanding of BoNT/A1 and /B1 in altering nociceptive processing with explorations of the specific characteristics of the various toxins from this family, we may be able to discover or design novel, effective, and long-lasting pain therapeutics. This review will focus on our current understanding of the molecular mechanisms whereby BoNTs alter pain processing, and future directions in the development of these agents as pain therapeutics.

  • Chen C, Przedpelski A, Tepp WH, Pellett S, Johnson EA, Barbieri JT (2015) Heat-Labile Enterotoxin IIa, a Platform To Deliver Heterologous Proteins into Neurons. mBio 6((4)):e00734 PMC4542185 · Pubmed · DOI

    Cholera toxin (CT) and the related heat-labile enterotoxins (LT) of Escherichia coli have been implicated as adjuvants in human therapies, but reactivity upon intranasal delivery dampened efforts to develop other clinical applications. However, each CT family member variant has unique biological properties that may warrant development as therapeutic platforms. In the current study, a nontoxic variant of the heat-labile enterotoxin IIa (LTIIa) was engineered to deliver heterologous, functional proteins into the cytosol of neurons. As proof of principle, the LTIIa variant delivered two cargos into neurons. LTIIa delivered β-lactamase efficiently into cells containing complex gangliosides, such as GD1b, as host receptors. LTIIa delivery of β-lactamase was sensitive to brefeldin A, an inhibitor that collapses the Golgi compartment into the endoplasmic reticulum, but not sensitive to treatment with botulinum neurotoxin D (BoNT/D), an inhibitor of synaptic vesicle cycling. LTIIa delivered a single-chain, anti-BoNT/A camelid antibody that inhibited SNAP25 cleavage during post-BoNT/A exposure of neurons. Delivery of functional, heterologous protein cargos into neurons demonstrates the potential of LTII variants as platforms to deliver therapies to inactivate toxins and microbial infections and to reverse the pathology of human neurodegenerative diseases.

  • Pellett S, Tepp WH, Scherf JM, Johnson EA (2015) Botulinum Neurotoxins Can Enter Cultured Neurons Independent of Synaptic Vesicle Recycling. PloS one 10((7)):e0133737 PMC4514655 · Pubmed · DOI

    Botulinum neurotoxins (BoNTs) are the causative agent of the severe and long-lasting disease botulism. At least seven different serotypes of BoNTs (denoted A-G) have been described. All BoNTs enter human or animal neuronal cells via receptor mediated endocytosis and cleave cytosolic SNARE proteins, resulting in a block of synaptic vesicle exocytosis, leading to the flaccid paralysis characteristic of botulism. Previous data have indicated that once a neuronal cell has been intoxicated by a BoNT, further entry of the same or other BoNTs is prevented due to disruption of synaptic vesicle recycling. However, it has also been shown that cultured neurons exposed to BoNT/A are still capable of taking up BoNT/E. In this report we show that in general BoNTs can enter cultured human or mouse neuronal cells that have previously been intoxicated with another BoNT serotype. Quantitative analysis of cell entry by assessing SNARE cleavage revealed none or only a minor difference in the efficiency of uptake of BoNTs into previously intoxicated neurons. Examination of the endocytic entry pathway by specific endocytosis inhibitors indicated that BoNTs are taken up by clathrin coated pits in both non pre-exposed and pre-exposed neurons. LDH release assays indicated that hiPSC derived neurons exposed consecutively to two different BoNT serotypes remained viable and healthy except in the case of BoNT/E or combinations of BoNT/E with BoNT/B, /D, or /F. Overall, our data indicate that previous intoxication of neuronal cells with BoNT does not inhibit further uptake of BoNTs.

  • Pellett S, Tepp WH, Whitemarsh RC, Bradshaw M, Johnson EA (2015) In vivo onset and duration of action varies for botulinum neurotoxin A subtypes 1-5. Toxicon : official journal of the International Society on Toxinology 107((Pt A)):37-42 PMC4658214 · Pubmed · DOI

    To date, over 40 subtypes of botulinum neurotoxins (BoNTs) have been identified. BoNTs are classified into 7 serotypes distinguished primarily by their antigenic properties, but also characterized by their unique SNARE targets and cleavage sites, host specificity, and duration of action. Sequencing efforts in the last decade have identified several subtypes within the serotypes. Subtypes are currently defined as distinct based solely on amino acid sequence comparison, with a similarity cut-off of 2.5% difference. Ten subtypes have been identified for BoNT/A, which is the serotype associated with the most severe human botulism and also the most commonly used serotype for clinical purposes. Analyses of several of these subtypes have revealed distinct characteristics, ranging from differences in cell entry and enzyme kinetics to differences in potency in mice and cell-model specific potency. A long-term activity study in cultured primary neurons has indicated that BoNT/A1, 2, 4, and 5 have a similar duration of action, whereas BoNT/A3 has a significantly shorter duration of action. This report describes an in vivo mouse study, showing that after local injection BoNT/A2 resulted in faster onset of local paralysis than BoNT/A1, 3, 4, and 5, whereas BoNT/A3 resulted in significantly faster recovery of motor-neuron deficiency.

  • Maslanka SE, Lúquez C, Dykes JK, Tepp WH, Pier CL, Pellett S, Raphael BH, Kalb SR, Barr JR, Rao A, Johnson EA (2015) A Novel Botulinum Neurotoxin, Previously Reported as Serotype H, Has a Hybrid-Like Structure With Regions of Similarity to the Structures of Serotypes A and F and Is Neutralized With Serotype A Antitoxin. The Journal of infectious diseases 213((3)):379-85 PMC4704661 · Pubmed · DOI

    Botulism is a potentially fatal paralytic disease caused by the action of botulinum neurotoxin (BoNT) on nerve cells. There are 7 known serotypes (A-G) of BoNT and up to 40 genetic variants. Clostridium botulinum strain IBCA10-7060 was recently reported to produce BoNT serotype B (BoNT/B) and a novel BoNT, designated as BoNT/H. The BoNT gene (bont) sequence of BoNT/H was compared to known bont sequences. Genetic analysis suggested that BoNT/H has a hybrid-like structure containing regions of similarity to the structures of BoNT/A1 and BoNT/F5. This novel BoNT was serologically characterized by the mouse neutralization assay and a neuronal cell-based assay. The toxic effects of this hybrid-like BoNT were completely eliminated by existing serotype A antitoxins, including those contained in multivalent therapeutic antitoxin products that are the mainstay of human botulism treatment.

  • Pellett S, Tepp WH, Scherf JM, Pier CL, Johnson EA (2015) Activity of botulinum neurotoxin type D (strain 1873) in human neurons. Toxicon : official journal of the International Society on Toxinology 101:63-9 PMC4458207 · Pubmed · DOI

    Botulinum Neurotoxin type D (BoNT/D) causes periodic outbreaks of botulism in cattle and horses, but is rarely associated with human botulism. Previous studies have shown that humans responded poorly to peripheral injection of up to 10U of BoNT/D. Isolated human pyramidalis muscle preparations were resistant to BoNT/D, whereas isolated human intercostal muscle preparations responded to BoNT/D similarly as to other BoNT serotypes. In vitro data indicate that BoNT/D does not cleave human VAMP1 efficiently, and differential expression of the VAMP 1 and 2 isoforms may be responsible for the above observations. Here we examined sensitivity of cultured human neurons derived from human induced pluripotent stem cells to BoNT/D. Our data indicate that BoNT/D can enter and cleave VAMP 2 in human neurons, but at significantly lower efficiency than other BoNT serotypes. In addition, BoNT/D had a short duration of action in the cultured neurons, similar to that of BoNT/E. In vivo analyses indicated a slower time to death in mice, as well as a later onset and shorter duration of action than BoNT/A1. Finally, examination of BoNT/D activity in various rodent and human cell models resulted in dramatic differences in sensitivity, indicating a unique cell entry mechanism of BoNT/D.

  • Seki H, Xue S, Hixon MS, Pellett S, Remes M, Johnson EA, Janda KD (2015) Toward the discovery of dual inhibitors for botulinum neurotoxin A: concomitant targeting of endocytosis and light chain protease activity. Chemical communications (Cambridge, England) 51((28)):6226-9 · Pubmed · DOI

    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.

  • Scherf JM, Hu XS, Tepp WH, Ichtchenko K, Johnson EA, Pellett S (2014) Analysis of gene expression in induced pluripotent stem cell-derived human neurons exposed to botulinum neurotoxin A subtype 1 and a type A atoxic derivative. PloS one 9((10)):e111238 PMC4206481 · Pubmed · DOI

    Botulinum neurotoxin type A1 (BoNT/A1) is a potent protein toxin responsible for the potentially fatal human illness botulism. Notwithstanding, the long-lasting flaccid muscle paralysis caused by BoNT/A has led to its utility as a powerful and versatile bio-pharmaceutical. The flaccid paralysis is due to specific cleavage of neuronal SNAREs by BoNTs. However, actions of BoNTs on intoxicated neurons besides the cleavage of SNAREs have not been studied in detail. In this study we investigated by microarray analysis the effects of BoNT/A and a catalytically inactive derivative (BoNT/A ad) on the transcriptome of human induced pluripotent stem cell (hiPSC)-derived neurons at 2 days and 2 weeks after exposure. While there were only minor changes in expression levels at 2 days post exposure, at 2 weeks post exposure 492 genes were differentially expressed more than 2-fold in BoNT/A1-exposed cells when compared to non-exposed populations, and 682 genes were differentially expressed in BoNT/A ad-exposed cells. The vast majority of genes were similarly regulated in BoNT/A1 and BoNT/A ad-exposed neurons, and the few genes differentially regulated between BoNT/A1 and BoNT/A ad-exposed neurons were differentially expressed less than 3.5 fold. These data indicate a similar response of neurons to BoNT/A1 and BoNT/A ad exposure. The most highly regulated genes in cells exposed to either BoNT/A1 or BoNT/A ad are involved in neurite outgrowth and calcium channel sensitization.

  • Bradshaw M, Tepp WH, Whitemarsh RC, Pellett S, Johnson EA (2014) Holotoxin Activity of Botulinum Neurotoxin Subtype A4 Originating from a Nontoxigenic Clostridium botulinum Expression System. Applied and environmental microbiology 80((23)):7415-22 PMC4249187 · Pubmed · DOI

    Clostridium botulinum subtype A4 neurotoxin (BoNT/A4) is naturally expressed in the dual-toxin-producing C. botulinum strain 657Ba at 100× lower titers than BoNT/B. In this study, we describe purification of recombinant BoNT/A4 (rBoNT/A4) expressed in a nonsporulating and nontoxigenic C. botulinum expression host strain. The rBoNT/A4 copurified with nontoxic toxin complex components provided in trans by the expression host and was proteolytically cleaved to the active dichain form. Activity of the recombinant BoNT/A4 in mice and in human neuronal cells was about 1,000-fold lower than that of BoNT/A1, and the recombinant BoNT/A4 was effectively neutralized by botulism heptavalent antitoxin. A previous report using recombinant truncated BoNT/A4 light chain (LC) expressed in Escherichia coli has indicated reduced stability and activity of BoNT/A4 LC compared to BoNT/A1 LC, which was surmounted by introduction of a single-amino-acid substitution, I264R. In order to determine whether this mutation would also affect the holotoxin activity of BoNT/A4, a recombinant full-length BoNT/A4 carrying this mutation as well as a second mutation predicted to increase solubility (L260F) was produced in the clostridial expression system. Comparative analyses of the in vitro, cellular, and in vivo activities of rBoNT/A4 and rBoNT/A4-L260F I264R showed 1,000-fold-lower activity than BoNT/A1 in both the mutated and nonmutated BoNT/A4. This indicates that these mutations do not alter the activity of BoNT/A4 holotoxin. In summary, a recombinant BoNT from a dual-toxin-producing strain was expressed and purified in an endogenous clostridial expression system, allowing analysis of this toxin.

  • Whitemarsh RC, Tepp WH, Johnson EA, Pellett S (2014) Persistence of botulinum neurotoxin a subtypes 1-5 in primary rat spinal cord cells. PloS one 9((2)):e90252 PMC3937374 · Pubmed · DOI

    Botulinum neurotoxins (BoNTs) are the most poisonous substances known and cause the severe disease botulism. BoNTs have also been remarkably effective as therapeutics in treating many neuronal and neuromuscular disorders. One of the hallmarks of BoNTs, particularly serotype A, is its long persistence of 2-6 months in patients at concentrations as low as fM or pM. The mechanisms for this persistence are currently unclear. In this study we determined the persistence of the BoNT/A subtypes 1 through 5 in primary rat spinal neurons. Remarkably, the duration of intracellular enzymatic activity of BoNT/A1, /A2, /A4 and /A5 was shown to be at least 10 months. Conversely, the effects of BoNT/A3 were observed for up to ∼5 months. An intermittent dosing with BoNT/E showed intracellular activity of the shorter acting BoNT/E for 2-3 weeks, followed by reoccurrence and persistence of BoNT/A-induced SNAP-25 cleavage products.

  • Seki H, Pellett S, Silhár P, Stowe GN, Blanco B, Lardy MA, Johnson EA, Janda KD (2013) Synthesis/biological evaluation of hydroxamic acids and their prodrugs as inhibitors for Botulinum neurotoxin A light chain. Bioorganic & medicinal chemistry 22((3)):1208-17 PMC3919520 · Pubmed · DOI

    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.

  • Wang D, Krilich J, Pellett S, Baudys J, Tepp WH, Barr JR, Johnson EA, Kalb SR (2013) Comparison of the catalytic properties of the botulinum neurotoxin subtypes A1 and A5. Biochimica et biophysica acta 1834((12)):2722-8 PMC4582773 · Pubmed · DOI

    Clostridium botulinum neurotoxins (BoNTs) cause the life-threatening disease botulism through the inhibition of neurotransmitter release by cleaving essential SNARE proteins. There are seven serologically distinctive types of BoNTs and many subtypes within a serotype have been identified. BoNT/A5 is a recently discovered subtype of type A botulinum neurotoxin which possesses a very high degree of sequence similarity and identity to the well-studied A1 subtype. In the present study, we examined the endopeptidase activity of these two BoNT/A subtypes and our results revealed significant differences in substrate binding and cleavage efficiency between subtype A5 and A1. Distinctive hydrolysis efficiency was observed between the two toxins during cleavage of the native substrate SNAP-25 versus a shortened peptide mimic. N-terminal truncation studies demonstrated that a key region of the SNAP-25, including the amino acid residues at 151 through 154 located in the remote binding region of the substrate, contributed to the differential catalytic properties between A1 and A5. Elevated binding affinity of the peptide substrate resulted from including these important residues and enhanced BoNT/A5's hydrolysis efficiency. In addition, mutations of these amino acid residues affect the proteolytic performance of the two toxins in different ways. This study provides a better understanding of the biological activity of these toxins, their performance characteristics in the Endopep-MS assay to detect BoNT in clinical samples and foods, and is useful for the development of peptide substrates.

  • Whitemarsh RC, Tepp WH, Bradshaw M, Lin G, Pier CL, Scherf JM, Johnson EA, Pellett S (2013) Characterization of botulinum neurotoxin A subtypes 1 through 5 by investigation of activities in mice, in neuronal cell cultures, and in vitro. Infection and immunity 81((10)):3894-902 PMC3811745 · Pubmed · DOI

    Botulinum neurotoxins (BoNTs) are synthesized by Clostridium botulinum and exist as seven immunologically distinct serotypes designated A through G. For most serotypes, several subtypes have now been described based on nominal differences in the amino acid sequences. BoNT/A1 is the most well-characterized subtype of the BoNT/A serotype, and many of its properties, including its potency, its prevalence as a food poison, and its utility as a pharmaceutical, have been thoroughly studied. In contrast, much remains unknown of the other BoNT/A subtypes. In this study, BoNT/A subtype 1 (BoNT/A1) to BoNT/A5 were characterized utilizing a mouse bioassay, an in vitro cleavage assay, and several neuronal cell-based assays. The data indicate that BoNT/A1 to -5 have distinct in vitro and in vivo toxicological properties and that, unlike those for BoNT/A1, the neuronal and mouse results for BoNT/A2 to -5 do not correlate with their enzymatic activity. These results indicate that BoNT/A1 to -5 have distinct characteristics, which are of importance for a greater understanding of botulism and for pharmaceutical applications.

  • Šilhár P, Silvaggi NR, Pellett S, Čapková K, Johnson EA, Allen KN, Janda KD (2013) Evaluation of adamantane hydroxamates as botulinum neurotoxin inhibitors: synthesis, crystallography, modeling, kinetic and cellular based studies. Bioorganic & medicinal chemistry 21((5)):1344-8 PMC3574188 · Pubmed · DOI

    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.

  • Pellett S (2012) Progress in cell based assays for botulinum neurotoxin detection. Current topics in microbiology and immunology 364:257-85 PMC3644986 · Pubmed · DOI

    Botulinum neurotoxins (BoNTs) are the most potent human toxins known and the causative agent of botulism, and are widely used as valuable pharmaceuticals. The BoNTs are modular proteins consisting of a heavy chain and a light chain linked by a disulfide bond. Intoxication of neuronal cells by BoNTs is a multi-step process including specific cell binding, endocytosis, conformational change in the endosome, translocation of the enzymatic light chain into the cells cytosol, and SNARE target cleavage. The quantitative and reliable potency determination of fully functional BoNTs produced as active pharmaceutical ingredient (API) requires an assay that considers all steps in the intoxication pathway. The in vivo mouse bioassay has for years been the 'gold standard' assay used for this purpose, but it requires the use of large numbers of mice and thus causes associated costs and ethical concerns. Cell-based assays are currently the only in vitro alternative that detect fully functional BoNTs in a single assay and have been utilized for years for research purposes. Within the last 5 years, several cell-based BoNT detection assays have been developed that are able to quantitatively determine BoNT potency with similar or greater sensitivity than the mouse bioassay. These assays now offer an alternative method for BoNT potency determination. Such quantitative and reliable BoNT potency determination is a crucial step in basic research, in the development of pharmaceutical BoNTs, and in the quantitative detection of neutralizing antibodies.

  • Whitemarsh RC, Pier CL, Tepp WH, Pellett S, Johnson EA (2012) Model for studying Clostridium botulinum neurotoxin using differentiated motor neuron-like NG108-15 cells. Biochemical and biophysical research communications 427((2)):426-30 PMC3486637 · Pubmed · DOI

    Cancerous cell lines have traditionally shown low sensitivity to laboratory or pharmaceutical preparations of botulinum neurotoxin. The work presented here demonstrates that the mouse neuroblastoma/rat glioma hybrid cell line NG108-15 is capable of more sensitively detecting BoNT/A1 than any cell line previously described. This cell line has previously been described to have motor neuron like characteristics, therefore making it a good model to study BoNTs. Differentiation of NG108-15 cells in serum-free medium containing retinoic acid and purmorphamine dramatically increased sensitivity of the neurons to BoNT/A (EC(50) = ~16 LD(50) U). Additional pre-treatment with triasialoganglioside GT1B prior to toxin exposure reduced the EC(50) further to ~11 LD(50) U. Co-culture of the neurons with C2C12 myotubes also significantly increased BoNT/A sensitivity of NG108-15 cells (EC(50) = 26 U) in the absence of differentiation factors.

  • Pellett S (2012) Learning from the past: historical aspects of bacterial toxins as pharmaceuticals. Current opinion in microbiology 15((3)):292-9 · Pubmed · DOI

    Botulinum neurotoxins are the most poisonous substances known to humankind, but also are the bacterial toxins most frequently used as pharmaceuticals to benefit humans. The discovery of botulinum toxins and development into a useful drug is unique and fascinating, dating back to the early 19th century, when Justinus Kerner first recognized that botulism was caused by a biological toxin and suggested its use for medicinal purposes. This was translated into reality in 1980, when Alan Scott for the first time used the toxins to successfully treat strabismus. Now a subset of botulinum toxins are widely used for cosmetic applications, treatment of various movement disorders, pain and many other syndromes, and further developments using other botulinum toxins or recombinant molecules engineered from subdomains are promising.

  • Whitemarsh RC, Strathman MJ, Chase LG, Stankewicz C, Tepp WH, Johnson EA, Pellett S (2012) Novel application of human neurons derived from induced pluripotent stem cells for highly sensitive botulinum neurotoxin detection. Toxicological sciences : an official journal of the Society of Toxicology 126((2)):426-35 PMC3307606 · Pubmed · DOI

    Human induced pluripotent stem cells (hiPSC) hold great promise for providing various differentiated cell models for in vitro toxigenicity testing. For Clostridium botulinum neurotoxin (BoNT) detection and mechanistic studies, several cell models currently exist, but none examine toxin function with species-specific relevance while exhibiting high sensitivity. The most sensitive cell models to date are mouse or rat primary cells and neurons derived from mouse embryonic stem cells, both of which require significant technical expertise for culture preparation. This study describes for the first time the use of hiPSC-derived neurons for BoNT detection. The neurons used in this study were differentiated and cryopreserved by Cellular Dynamics International (Madison, WI) and consist of an almost pure pan-neuronal population of predominantly gamma aminoisobutyric acidergic and glutamatergic neurons. Western blot and quantitative PCR data show that these neurons express all the necessary receptors and substrates for BoNT intoxication. BoNT/A intoxication studies demonstrate that the hiPSC-derived neurons reproducibly and quantitatively detect biologically active BoNT/A with high sensitivity (EC(50) ∼0.3 U). Additionally, the quantitative detection of BoNT serotypes B, C, E, and BoNT/A complex was demonstrated, and BoNT/A specificity was confirmed through antibody protection studies. A direct comparison of BoNT detection using primary rat spinal cord cells and hiPSC-derived neurons showed equal or increased sensitivity, a steeper dose-response curve and a more complete SNARE protein target cleavage for hiPSC-derived neurons. In summary, these data suggest that neurons derived from hiPSCs provide an ideal and highly sensitive platform for BoNT potency determination, neutralizing antibody detection and for mechanistic studies.

  • White DM, Pellett S, Jensen MA, Tepp WH, Johnson EA, Arnason BG (2011) Rapid immune responses to a botulinum neurotoxin Hc subunit vaccine through in vivo targeting to antigen-presenting cells. Infection and immunity 79((8)):3388-96 PMC3147575 · Pubmed · DOI

    The clostridial botulinum neurotoxins (BoNTs) are the most potent protein toxins known. The carboxyl-terminal fragment of the toxin heavy chain (Hc) has been intensively investigated as a BoNT vaccine immunogen. We sought to determine whether targeting Hc to antigen-presenting cells (APCs) could accelerate the immune responses to vaccination with BoNT serotype A (BoNT/A) Hc. To test this hypothesis, we targeted Hc to the Fc receptors for IgG (FcγRs) expressed by dendritic cells (DCs) and other APCs. Hc was expressed as a fusion protein with a recombinant ligand for human FcγRs (R4) to produce HcR4 or a similar ligand for murine FcγRs to produce HcmR4. HcR4, HcmR4, and Hc were produced as secreted proteins using baculovirus-mediated expression in SF9 insect cells. In vitro receptor binding assays showed that HcR4 effectively targets Hc to all classes of FcγRs. APCs loaded with HcR4 or HcmR4 are substantially more effective at stimulating Hc-reactive T cells than APCs loaded with nontargeted Hc. Mice immunized with a single dose of HcmR4 or HcR4 had earlier and markedly higher Hc-reactive antibody titers than mice immunized with nontargeted Hc. These results extend to BoNT neutralizing antibody titers, which are substantially higher in mice immunized with HcmR4 than in mice immunized with Hc. Our results demonstrate that targeting Hc to FcγRs augments the pace and magnitude of immune responses to Hc.

  • Pellett S, Tepp WH, Stanker LH, Band PA, Johnson EA, Ichtchenko K (2011) Neuronal targeting, internalization, and biological activity of a recombinant atoxic derivative of botulinum neurotoxin A. Biochemical and biophysical research communications 405((4)):673-7 PMC3046291 · Pubmed · DOI

    Non-toxic derivatives of botulinum neurotoxin A (BoNT/A) have potential use as neuron-targeting delivery vehicles, and as reagents to study intracellular trafficking. We have designed and expressed an atoxic derivative of BoNT/A (BoNT/A ad) as a full-length 150 kDa molecule consisting of a 50 kDa light chain (LC) and a 100 kDa heavy chain (HC) joined by a disulfide bond and rendered atoxic through the introduction of metalloprotease-inactivating point mutations in the light chain. Studies in neuronal cultures demonstrated that BoNT/A ad cannot cleave synaptosomal-associated protein 25 (SNAP25), the substrate of wt BoNT/A, and that it effectively competes with wt BoNT/A for binding to endogenous neuronal receptors. In vitro and in vivo studies indicate accumulation of BoNT/A ad at the neuromuscular junction of the mouse diaphragm. Immunoprecipitation studies indicate that the LC of BoNT/A ad forms a complex with SNAP25 present in the neuronal cytosolic fraction, demonstrating that the atoxic LC retains the SNAP25 binding capability of the wt toxin. Toxicity of BoNT/A ad was found to be reduced approximately 100,000-fold relative to wt BoNT/A.

  • Pellett S, Du ZW, Pier CL, Tepp WH, Zhang SC, Johnson EA (2010) Sensitive and quantitative detection of botulinum neurotoxin in neurons derived from mouse embryonic stem cells. Biochemical and biophysical research communications 404((1)):388-92 PMC3033726 · Pubmed · DOI

    Botulinum neurotoxins (BoNTs), the most poisonous protein toxins known, represent a serious bioterrorism threat but are also used as a unique and important bio-pharmaceutical to treat an increasing myriad of neurological disorders. The only currently accepted detection method by the United States Food and Drug Administration for biological activity of BoNTs and for potency determination of pharmaceutical preparations is the mouse bioassay (MBA). Recent advances have indicated that cell-based assays using primary neuronal cells can provide an equally sensitive and robust detection platform as the MBA to reliably and quantitatively detect biologically active BoNTs. This study reports for the first time a BoNT detection assay using mouse embryonic stem cells to produce a neuronal cell culture. The data presented indicate that this assay can reliably detect BoNT/A with a similar sensitivity as the MBA.

  • Pier CL, Chen C, Tepp WH, Lin G, Janda KD, Barbieri JT, Pellett S, Johnson EA (2010) Botulinum neurotoxin subtype A2 enters neuronal cells faster than subtype A1. FEBS letters 585((1)):199-206 PMC3041152 · Pubmed · DOI

    Botulinum neurotoxins (BoNTs), the causative agent of human botulism, are the most potent naturally occurring toxins known. BoNT/A1, the most studied BoNT, is also used as an important biopharmaceutical. In this study, the biological activity of BoNT/A1 is compared to that of BoNT/A2 using neuronal cell models. The data obtained indicate faster and increased intoxication of neuronal cells by BoNT/A2 than BoNT/A1, and that the mechanism underlying this increased toxicity is faster and more efficient cell entry that is independent of ganglioside binding. These results have important implications for the development of new BoNT based therapeutics and BoNT countermeasures.

  • Pellett S, Tepp WH, Toth SI, Johnson EA (2010) Comparison of the primary rat spinal cord cell (RSC) assay and the mouse bioassay for botulinum neurotoxin type A potency determination. Journal of pharmacological and toxicological methods 61((3)):304-10 · Pubmed · DOI

    Botulinum neurotoxin (BoNT) type A is increasingly used in humans for pharmaceutical and cosmetic purposes. Currently, the standard assay used to determine potency of clinical samples, and the only assay approved by the FDA, is the in vivo mouse bioassay (MBA). However, due to several drawbacks of this assay (relatively large error, high cost, no standardization, requirement of high technical expertise, and use of large numbers of mice), there is an increasing need to replace this assay. A cell-based assay using primary rat spinal cord cells (RSC assay) has been previously reported to sensitively detect purified botulinum neurotoxin type A, and requires all biological properties of the toxin for detection.

  • Nakai Y, Pellett S, Tepp WH, Johnson EA, Janda KD (2010) Toosendanin: synthesis of the AB-ring and investigations of its anti-botulinum properties (Part II). Bioorganic & medicinal chemistry 18((3)):1280-7 PMC2819598 · Pubmed · DOI

    Botulinum neurotoxins (BoNTs) are the etiological agents responsible for botulism, a disease characterized by peripheral neuromuscular blockade and a characteristic flaccid paralysis of humans. The natural product toosendanin, a limonoid, is a traditional Chinese medicine that has reported anti-botulinum properties in animal models. Toosendanin effectively inhibits the biological activity of BoNT/A in neuronal cells at concentrations of 200 nM, and partial inhibition can be observed with concentrations as low as 8 nM. Mechanistically, toosendanin's inhibition is due to prevention of transduction of the BoNT LC through the HC channel. Intriguing questions as to the molecular architecture of toosendanin as related to its anti-botulinum properties have focused our attention on a synthesis of toosendanin's unusual AB-ring, containing a unique bridged hemi-acetal. Within the current work, a synthetic strategy allowing access to the AB-fragment of toosendanin was achieved from a trans-decalin system. In addition, this fragment was examined for its modulation of BoNT/A intoxication in a rat spinal cord cellular assay.

  • Capková K, Hixon MS, Pellett S, Barbieri JT, Johnson EA, Janda KD (2009) Benzylidene cyclopentenediones: First irreversible inhibitors against botulinum neurotoxin A's zinc endopeptidase. Bioorganic & medicinal chemistry letters 20((1)):206-8 PMC2818383 · Pubmed · DOI

    A series of benzylidene cyclopentenedione-based inhibitors, acting through covalent modification of the active site of botulinum neurotoxin A light chain metalloprotease, are reported.

  • Fischer A, Nakai Y, Eubanks LM, Clancy CM, Tepp WH, Pellett S, Dickerson TJ, Johnson EA, Janda KD, Montal M (2009) Bimodal modulation of the botulinum neurotoxin protein-conducting channel. Proceedings of the National Academy of Sciences of the United States of America 106((5)):1330-5 PMC2635780 · Pubmed · DOI

    Clostridium botulinum neurotoxin (BoNT) is the causative agent of botulism, a neuroparalytic disease. We describe here a semisynthetic strategy to identify inhibitors based on toosendanin, a traditional Chinese medicine reported to protect from BoNT intoxication. Using a single molecule assay of BoNT serotypes A and E light chain (LC) translocation through the heavy chain (HC) channel in neurons, we discovered that toosendanin and its tetrahydrofuran analog selectively arrest the LC translocation step of intoxication with subnanomolar potency, and increase the unoccluded HC channel propensity to open with micromolar efficacy. The inhibitory profile on LC translocation is accurately recapitulated in 2 different BoNT intoxication assays, namely the mouse protection and the primary rat spinal cord cell assays. Toosendanin has an unprecedented dual mode of action on the protein-conducting channel acting as a cargo-dependent inhibitor of translocation and as cargo-free channel activator. These results imply that the bimodal modulation by toosendanin depends on the dynamic interactions between channel and cargo, highlighting their tight interplay during the progression of LC transit across endosomes.

  • Zhou H, Zhou B, Pellett S, Johnson EA, Janda KD (2008) Selection and characterization of a human monoclonal neutralizing antibody for Clostridium Botulinum neurotoxin serotype B. Bioorganic & medicinal chemistry letters 19((3)):662-4 PMC2645068 · Pubmed · DOI

    Botulinum neurotoxins (BoNTs) are causative agents for botulism and are identified as a category A bioterror agents by the Centers for Disease Control and Prevention (CDC). Current antitoxins against BoNTs intoxication have some limitations including side effects or limited supply. As an alternative, neutralizing monoclonal antibodies will play an increasing role as BoNTs therapeutics. To date, no human anti-BoNT/B neutralizing monoclonal antibodies have yet to be reported. Herein, we describe an improved selection approach and characterization of a human monoclonal antibody, F2, which is capable of binding BoNT/B with high specificity and displays neutralizing activity in an in vitro cell-based assay. Through surface plasmon resonance studies, we have determined its association and dissociation rate constants. In sum, our data demonstrate that monoclonal antibody F2 is a promising BoNT/B therapeutic lead for further development.

  • Zhou B, Pellett S, Tepp WH, Zhou H, Johnson EA, Janda KD (2008) Delineating the susceptibility of botulinum neurotoxins to denaturation through thermal effects. FEBS letters 582((10)):1526-31 · Pubmed · DOI

    Botulinum neurotoxins (BoNT) are the etiological agents responsible for botulism and are acknowledged terrorist threat agents. Passive immunotherapy may provide one countermeasure. Importantly, in the virtually unlimited repertoire of antibody specificities, enzyme linked immunosorbent assays (ELISA) has become an indispensable method for antibody selection. We report that of the BoNTs, BoNT/E is highly susceptible to polystyrene induced denaturation. To further dissect this result and the potential susceptibility of other BoNTs to denaturation we selected a thermal platform, which could be readily quantified using surface plasmon resonance (SPR), a primary rat spinal cord cell-based assay and an animal lethality model.

  • Pellett S, Tepp WH, Clancy CM, Borodic GE, Johnson EA (2007) A neuronal cell-based botulinum neurotoxin assay for highly sensitive and specific detection of neutralizing serum antibodies. FEBS letters 581((25)):4803-8 PMC2748649 · Pubmed · DOI

    Clostridium botulinum neurotoxin (BoNT) serotypes A and B are widely used as pharmaceuticals to treat various neurological disorders and in cosmetic applications. The major adverse effect of these treatments has been resistance to treatment after multiple injections. Currently, patients receiving BoNT therapies and patients enrolled in clinical trials for new applications and/or new formulations of BoNTs are not routinely monitored for the formation of neutralizing antibodies, since no assay other than the mouse protection procedure is commercially available that reliably tests for the presence of such antibodies. This report presents a highly sensitive and specific neuronal cell-based assay that provides sensitive and specific detection of neutralizing antibodies to BoNT/A.

  • Marshall KM, Bradshaw M, Pellett S, Johnson EA (2007) Plasmid encoded neurotoxin genes in Clostridium botulinum serotype A subtypes. Biochemical and biophysical research communications 361((1)):49-54 PMC2346372 · Pubmed · DOI

    Clostridium botulinum, an important pathogen of humans and animals, produces botulinum neurotoxin (BoNT), the most poisonous toxin known. We have determined by pulsed-field gel electrophoresis (PFGE) and Southern hybridizations that the genes encoding BoNTs in strains Loch Maree (subtype A3) and 657Ba (type B and subtype A4) are located on large (approximately 280 kb) plasmids. This is the first demonstration of plasmid-borne neurotoxin genes in Clostridium botulinum serotypes A and B. The finding of BoNT type A and B genes on extrachromosomal elements has important implications for the evolution of neurotoxigenicity in clostridia including the origin, expression, and lateral transfer of botulinum neurotoxin genes.

  • Pellett S, Tracy JW (2006) Mak16p is required for the maturation of 25S and 5.8S rRNAs in the yeast Saccharomyces cerevisiae. Yeast (Chichester, England) 23((7)):495-506 · Pubmed · DOI

    The nucleolar Mak16p protein of Saccharomyces cerevisiae has been implicated in 60S ribosome biogenesis. To learn more about the role of Mak16p in this process, ribosomal RNA processing was examined in a mak16-1 temperature-sensitive yeast strain. Steady-state levels of the 25S and 5.8S mature rRNA species dropped dramatically over a 4 h period in the mak16-1 yeast after a shift to the non-permissive temperature, while 18S and 5S rRNA levels decreased only moderately. Ribosomal RNA processing (rRNA) analyses showed that the most prominent defect at the non-permissive temperature was a dramatic decrease in 27SB precursor RNA levels, with no significant increase in the levels of any precursor. These data indicate an essential role for Mak16p in the stability of the 27SB precursor rRNA. Association of Mak16p with the 66S preribosomal complex does not appear to be sufficient for its function, because the mutant Mak16-1p protein was detected in sucrose density gradient fractions corresponding to the 66S pre-RNP complex.