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Avril A, Guillier S, Rasetti-Escargueil C. Development of Effective Medical Countermeasures Against the Main Biowarfare Agents: The Importance of Antibodies. Microorganisms 2024; 12:2622. [PMID: 39770824 PMCID: PMC11677989 DOI: 10.3390/microorganisms12122622] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2024] [Revised: 12/05/2024] [Accepted: 12/10/2024] [Indexed: 01/11/2025] Open
Abstract
The COVID-19 and mpox crisis has reminded the world of the potentially catastrophic consequences of biological agents. Aside from the natural risk, biological agents can also be weaponized or used for bioterrorism. Dissemination in a population or among livestock could be used to destabilize a nation by creating a climate of terror, by negatively impacting the economy and undermining institutions. The Centers for Disease Control and Prevention (CDC) classify biological agents into three categories (A or Tier 1, B and C) according to the risk they pose to the public and national security. Category A or Tier 1 consists of the six pathogens with the highest risk to the population (Bacillus anthracis, Yersinia pestis, Francisella tularensis, botulinum neurotoxins, smallpox and viral hemorrhagic fevers). Several medical countermeasures, such as vaccines, antibodies and chemical drugs, have been developed to prevent or cure the diseases induced by these pathogens. This review presents an overview of the primary medical countermeasures, and in particular, of the antibodies available against the six pathogens on the CDC's Tier 1 agents list, as well as against ricin.
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Affiliation(s)
- Arnaud Avril
- Unité Interaction Hôte-Pathogène, Département Microbiologie et Maladies Infectieuses, Institut de Recherche Biomédicale des Armées, 91220 Brétigny-sur-Orge, France
| | - Sophie Guillier
- Unité Bactériologie, Département Microbiologie et Maladies Infectieuses, Institut de Recherche Biomédicale des Armées, 91220 Brétigny-sur-Orge, France;
- UMR_MD1, Inserm U1261, 91220 Brétigny sur Orge, France
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2
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Leucine 232 and hydrophobic residues at the ribosomal P stalk binding site are critical for biological activity of ricin. Biosci Rep 2020; 39:BSR20192022. [PMID: 31548364 PMCID: PMC6822507 DOI: 10.1042/bsr20192022] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2019] [Revised: 08/15/2019] [Accepted: 08/21/2019] [Indexed: 01/16/2023] Open
Abstract
Ricin interacts with the ribosomal P stalk to cleave a conserved adenine from the α-sarcin/ricin loop (SRL) of the rRNA. Ricin toxin A chain (RTA) uses Arg235 as the most critical arginine for binding to the P stalk through electrostatic interactions to facilitate depurination. Structural analysis showed that a P2 peptide binds to a hydrophobic pocket on RTA and the last two residues form hydrogen bonds with Arg235. The importance of hydrophobic residues relative to Arg235 in the interaction with the P stalk in vivo and on the toxicity of RTA is not known. Here, we mutated residues in the hydrophobic pocket to analyze their contribution to toxicity and depurination activity in yeast and in mammalian cells. We found that Leu232, Tyr183 and Phe240 contribute cumulatively to toxicity, with Leu232 being the most significant. A quadruple mutant, Y183A/L232A/R235A/F240A, which combined mutations in critical hydrophobic residues with R235A completely abolished the activity of RTA, indicating that Arg235 and hydrophobic residues are required for full biological activity. Y183A and F240A mutants had reduced activity on RNA, but higher activity on ribosomes compared with R235A in vitro, suggesting that they could partially regain activity upon interaction with ribosomes. These results expand the region of interaction between RTA and the P stalk critical for cellular activity to include the hydrophobic pocket and provide the first evidence that interaction of P stalk with the hydrophobic pocket promotes a conformational rearrangement of RTA to correctly position the active site residues for catalytic attack on the SRL.
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3
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Acosta W, Cramer CL. Targeting Macromolecules to CNS and Other Hard-to-Treat Organs Using Lectin-Mediated Delivery. Int J Mol Sci 2020; 21:ijms21030971. [PMID: 32024082 PMCID: PMC7037663 DOI: 10.3390/ijms21030971] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2020] [Revised: 01/28/2020] [Accepted: 01/29/2020] [Indexed: 02/07/2023] Open
Abstract
The greatest challenges for therapeutic efficacy of many macromolecular drugs that act on intracellular are delivery to key organs and tissues and delivery into cells and subcellular compartments. Transport of drugs into critical cells associated with disease, including those in organs protected by restrictive biological barriers such as central nervous system (CNS), bone, and eye remains a significant hurdle to drug efficacy and impacts commercial risk and incentives for drug development for many diseases. These limitations expose a significant need for the development of novel strategies for macromolecule delivery. RTB lectin is the non-toxic carbohydrate-binding subunit B of ricin toxin with high affinity for galactose/galactosamine-containing glycolipids and glycoproteins common on human cell surfaces. RTB mediates endocytic uptake into mammalian cells by multiple routes exploiting both adsorptive-mediated and receptor-mediated mechanisms. In vivo biodistribution studies in lysosomal storage disease models provide evidence for the theory that the RTB-lectin transports corrective doses of enzymes across the blood–brain barrier to treat CNS pathologies. These results encompass significant implications for protein-based therapeutic approaches to address lysosomal and other diseases having strong CNS involvement.
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Rudolph MJ, Vance DJ, Kelow S, Angalakurthi SK, Nguyen S, Davis SA, Rong Y, Middaugh CR, Weis DD, Dunbrack R, Karanicolas J, Mantis NJ. Contribution of an unusual CDR2 element of a single domain antibody in ricin toxin binding affinity and neutralizing activity. Protein Eng Des Sel 2018; 31:277-287. [PMID: 30265352 PMCID: PMC6277176 DOI: 10.1093/protein/gzy022] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Accepted: 08/03/2018] [Indexed: 11/13/2022] Open
Abstract
Ricin toxin's enzymatic subunit (RTA) has been subjected to intensive B cell epitope mapping studies using a combination of competition ELISAs, hydrogen exchange-mass spectrometry and X-ray crystallography. Those studies identified four spatially distinct clusters (I-IV) of toxin-neutralizing epitopes on the surface of RTA. Here we describe A9, a new single domain camelid antibody (VHH) that was proposed to recognize a novel epitope on RTA that straddles clusters I and III. The X-ray crystal structure of A9 bound to RTA (2.6 Å resolution) revealed extensive antibody contact with RTA's β-strand h (732 Å2 buried surface area; BSA), along with limited engagement with α-helix D (90 Å2) and α-helix C (138 Å2). Collectively, these contacts explain the overlap between epitope clusters I and III, as identified by competition ELISA. However, considerable binding affinity, and, consequently, toxin-neutralizing activity of A9 is mediated by an unusual CDR2 containing five consecutive Gly residues that interact with α-helix B (82 Å2), a known neutralizing hotspot on RTA. Removal of a single Gly residue from the penta-glycine stretch in CDR2 reduced A9's binding affinity by 10-fold and eliminated toxin-neutralizing activity. Computational modeling indicates that removal of a Gly from CDR2 does not perturb contact with RTA per se, but results in the loss of an intramolecular hydrogen bond network involved in stabilizing CDR2 in the unbound state. These results reveal a novel configuration of a CDR2 element involved in neutralizing ricin toxin.
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Affiliation(s)
| | - David J Vance
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY, USA
| | - Simon Kelow
- Department of Biochemistry and Molecular Biophysics Graduate Group, University of Pennsylvania, Philadelphia, PA, USA
| | - Siva Krishna Angalakurthi
- Department of Pharmaceutical Chemistry and Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, KS, USA
| | - Sophie Nguyen
- New York Structural Biology Center, New York, NY, USA
| | - Simon A Davis
- New York Structural Biology Center, New York, NY, USA
| | - Yinghui Rong
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY, USA
| | - C Russell Middaugh
- Department of Pharmaceutical Chemistry and Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, KS, USA
| | - David D Weis
- Department of Chemistry and Ralph Adams Institute for Bioanalytical Chemistry, University of Kansas, Lawrence, KS, USA
| | - Roland Dunbrack
- Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, PA, USA
| | - John Karanicolas
- Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, PA, USA
| | - Nicholas J Mantis
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY, USA
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Zhou Y, Li XP, Kahn JN, Tumer NE. Functional Assays for Measuring the Catalytic Activity of Ribosome Inactivating Proteins. Toxins (Basel) 2018; 10:toxins10060240. [PMID: 29899209 PMCID: PMC6024586 DOI: 10.3390/toxins10060240] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2018] [Revised: 06/01/2018] [Accepted: 06/07/2018] [Indexed: 12/11/2022] Open
Abstract
Ribosome-inactivating proteins (RIPs) are potent toxins that inactivate ribosomes by catalytically removing a specific adenine from the α-sarcin/ricin loop (SRL) of the large rRNA. Direct assays for measuring depurination activity and indirect assays for measuring the resulting translation inhibition have been employed to determine the enzyme activity of RIPs. Rapid and sensitive methods to measure the depurination activity of RIPs are critical for assessing their reaction mechanism, enzymatic properties, interaction with ribosomal proteins, ribotoxic stress signaling, in the search for inhibitors and in the detection and diagnosis of enteric infections. Here, we review the major assays developed for measuring the catalytic activity of RIPs, discuss their advantages and disadvantages and explain how they are used in understanding the catalytic mechanism, ribosome specificity, and dynamic enzymatic features of RIPs.
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Affiliation(s)
- Yijun Zhou
- Department of Plant Biology, School of Environmental and Biological Sciences, Rutgers University, New Brunswick, NJ 08901-8520, USA.
| | - Xiao-Ping Li
- Department of Plant Biology, School of Environmental and Biological Sciences, Rutgers University, New Brunswick, NJ 08901-8520, USA.
| | - Jennifer N Kahn
- Department of Plant Biology, School of Environmental and Biological Sciences, Rutgers University, New Brunswick, NJ 08901-8520, USA.
| | - Nilgun E Tumer
- Department of Plant Biology, School of Environmental and Biological Sciences, Rutgers University, New Brunswick, NJ 08901-8520, USA.
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High-Definition Mapping of Four Spatially Distinct Neutralizing Epitope Clusters on RiVax, a Candidate Ricin Toxin Subunit Vaccine. CLINICAL AND VACCINE IMMUNOLOGY : CVI 2017; 24:CVI.00237-17. [PMID: 29046307 DOI: 10.1128/cvi.00237-17] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2017] [Accepted: 10/12/2017] [Indexed: 12/20/2022]
Abstract
RiVax is a promising recombinant ricin toxin A subunit (RTA) vaccine antigen that has been shown to be safe and immunogenic in humans and effective at protecting rhesus macaques against lethal-dose aerosolized toxin exposure. We previously used a panel of RTA-specific monoclonal antibodies (MAbs) to demonstrate, by competition enzyme-linked immunosorbent assay (ELISA), that RiVax elicits similar serum antibody profiles in humans and macaques. However, the MAb binding sites on RiVax have yet to be defined. In this study, we employed hydrogen exchange-mass spectrometry (HX-MS) to localize the epitopes on RiVax recognized by nine toxin-neutralizing MAbs and one nonneutralizing MAb. Based on strong protection from hydrogen exchange, the nine MAbs grouped into four spatially distinct epitope clusters (namely, clusters I to IV). Cluster I MAbs protected RiVax's α-helix B (residues 94 to 107), a protruding immunodominant secondary structure element known to be a target of potent toxin-neutralizing antibodies. Cluster II consisted of two subclusters located on the "back side" (relative to the active site pocket) of RiVax. One subcluster involved α-helix A (residues 14 to 24) and α-helices F-G (residues 184 to 207); the other encompassed β-strand d (residues 62 to 69) and parts of α-helices D-E (154 to 164) and the intervening loop. Cluster III involved α-helices C and G on the front side of RiVax, while cluster IV formed a sash from the front to back of RiVax, spanning strands b, c, and d (residues 35 to 59). Having a high-resolution B cell epitope map of RiVax will enable the development and optimization of competitive serum profiling assays to examine vaccine-induced antibody responses across species.
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Gal Y, Mazor O, Falach R, Sapoznikov A, Kronman C, Sabo T. Treatments for Pulmonary Ricin Intoxication: Current Aspects and Future Prospects. Toxins (Basel) 2017; 9:E311. [PMID: 28972558 PMCID: PMC5666358 DOI: 10.3390/toxins9100311] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2017] [Revised: 09/26/2017] [Accepted: 09/29/2017] [Indexed: 12/13/2022] Open
Abstract
Ricin, a plant-derived toxin originating from the seeds of Ricinus communis (castor beans), is one of the most lethal toxins known, particularly if inhaled. Ricin is considered a potential biological threat agent due to its high availability and ease of production. The clinical manifestation of pulmonary ricin intoxication in animal models is closely related to acute respiratory distress syndrome (ARDS), which involves pulmonary proinflammatory cytokine upregulation, massive neutrophil infiltration and severe edema. Currently, the only post-exposure measure that is effective against pulmonary ricinosis at clinically relevant time-points following intoxication in pre-clinical studies is passive immunization with anti-ricin neutralizing antibodies. The efficacy of this antitoxin treatment depends on antibody affinity and the time of treatment initiation within a limited therapeutic time window. Small-molecule compounds that interfere directly with the toxin or inhibit its intracellular trafficking may also be beneficial against ricinosis. Another approach relies on the co-administration of antitoxin antibodies with immunomodulatory drugs, thereby neutralizing the toxin while attenuating lung injury. Immunomodulators and other pharmacological-based treatment options should be tailored according to the particular pathogenesis pathways of pulmonary ricinosis. This review focuses on the current treatment options for pulmonary ricin intoxication using anti-ricin antibodies, disease-modifying countermeasures, anti-ricin small molecules and their various combinations.
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Affiliation(s)
- Yoav Gal
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Ohad Mazor
- Department of Infectious Diseases, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Reut Falach
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Anita Sapoznikov
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Chanoch Kronman
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Tamar Sabo
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
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8
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Zhou Y, Li XP, Chen BY, Tumer NE. Ricin uses arginine 235 as an anchor residue to bind to P-proteins of the ribosomal stalk. Sci Rep 2017; 7:42912. [PMID: 28230053 PMCID: PMC5322317 DOI: 10.1038/srep42912] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2016] [Accepted: 01/17/2017] [Indexed: 01/24/2023] Open
Abstract
Ricin toxin A chain (RTA) binds to stalk P-proteins to reach the α-sarcin/ricin loop (SRL) where it cleaves a conserved adenine. Arginine residues at the RTA/RTB interface are involved in this interaction. To investigate the individual contribution of each arginine, we generated single, double and triple arginine mutations in RTA. The R235A mutation reduced toxicity and depurination activity more than any other single arginine mutation in yeast. Further reduction in toxicity, depurination activity and ribosome binding was observed when R235A was combined with a mutation in a nearby arginine. RTA interacts with the ribosome via a two-step process, which involves slow and fast interactions. Single arginine mutations eliminated the fast interactions with the ribosome, indicating that they increase the binding rate of RTA. Arginine residues form a positively charged patch to bind to negatively charged residues at the C-termini of P-proteins. When electrostatic interactions conferred by the arginines are lost, hydrophobic interactions are also abolished, suggesting that the hydrophobic interactions alone are insufficient to allow binding. We propose that Arg235 serves as an anchor residue and cooperates with nearby arginines and the hydrophobic interactions to provide the binding specificity and strength in ribosome targeting of RTA.
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Affiliation(s)
- Yijun Zhou
- Department of Plant Biology and Pathology, School of Environmental and Biological Sciences, Rutgers University, New Brunswick, New Jersey 08901-8520, USA
| | - Xiao-Ping Li
- Department of Plant Biology and Pathology, School of Environmental and Biological Sciences, Rutgers University, New Brunswick, New Jersey 08901-8520, USA
| | - Brian Y Chen
- Department of Computer Science and Engineering, Lehigh University, Bethlehem, Pennsylvania 18015-3084, USA
| | - Nilgun E Tumer
- Department of Plant Biology and Pathology, School of Environmental and Biological Sciences, Rutgers University, New Brunswick, New Jersey 08901-8520, USA
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Vance DJ, Mantis NJ. Progress and challenges associated with the development of ricin toxin subunit vaccines. Expert Rev Vaccines 2016; 15:1213-22. [PMID: 26998662 PMCID: PMC5193006 DOI: 10.1586/14760584.2016.1168701] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The past several years have seen major advances in the development of a safe and efficacious ricin toxin vaccine, including the completion of two Phase I clinical trials with two different recombinant A subunit (RTA)-based vaccines: RiVax™ and RVEc™ adsorbed to aluminum salt adjuvant, as well as a non-human primate study demonstrating that parenteral immunization with RiVax elicits a serum antibody response that was sufficient to protect against a lethal dose aerosolized ricin exposure. One of the major obstacles moving forward is assessing vaccine efficacy in humans, when neither ricin-specific serum IgG endpoint titers nor toxin-neutralizing antibody levels are accepted as definitive predictors of protective immunity. In this review we summarize ongoing efforts to leverage recent advances in our understanding of RTA-antibody interactions at the structural level to develop novel assays to predict vaccine efficacy in humans.
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Affiliation(s)
- David J. Vance
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, USA
| | - Nicholas J. Mantis
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, USA
- Department of Biomedical Sciences, University at Albany, Albany, New York, USA
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Rudolph MJ, Vance DJ, Cassidy MS, Rong Y, Shoemaker CB, Mantis NJ. Structural analysis of nested neutralizing and non-neutralizing B cell epitopes on ricin toxin's enzymatic subunit. Proteins 2016; 84:1162-72. [PMID: 27159829 DOI: 10.1002/prot.25062] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2016] [Revised: 03/31/2016] [Accepted: 04/28/2016] [Indexed: 11/10/2022]
Abstract
In this report, we describe the X-ray crystal structures of two single domain camelid antibodies (VH H), F5 and F8, each in complex with ricin toxin's enzymatic subunit (RTA). F5 has potent toxin-neutralizing activity, while F8 has weak neutralizing activity. F5 buried a total of 1760 Å(2) in complex with RTA and made contact with three prominent secondary structural elements: α-helix B (Residues 98-106), β-strand h (Residues 113-117), and the C-terminus of α-helix D (Residues 154-156). F8 buried 1103 Å(2) in complex with RTA that was centered primarily on β-strand h. As such, the structural epitope of F8 is essentially nested within that of F5. All three of the F5 complementarity determining regions CDRs were involved in RTA contact, whereas F8 interactions were almost entirely mediated by CDR3, which essentially formed a seventh β-strand within RTA's centrally located β-sheet. A comparison of the two structures reported here to several previously reported (RTA-VH H) structures identifies putative contact sites on RTA, particularly α-helix B, associated with potent toxin-neutralizing activity. This information has implications for rational design of RTA-based subunit vaccines for biodefense. Proteins 2016; 84:1162-1172. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
| | - David J Vance
- Division of Infectious Diseases, New York State Department of Health, Wadsworth Center, Albany, New York, 12208
| | | | - Yinghui Rong
- Division of Infectious Diseases, New York State Department of Health, Wadsworth Center, Albany, New York, 12208
| | - Charles B Shoemaker
- Tufts Cummings School of Veterinary Medicine, North Grafton, Massachusetts, 01536
| | - Nicholas J Mantis
- Division of Infectious Diseases, New York State Department of Health, Wadsworth Center, Albany, New York, 12208.,Department of Biomedical Sciences, University at Albany, Albany, New York, 12201
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11
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Wahome N, Sully E, Singer C, Thomas JC, Hu L, Joshi SB, Volkin DB, Fang J, Karanicolas J, Jacobs DJ, Mantis NJ, Middaugh CR. Novel Ricin Subunit Antigens With Enhanced Capacity to Elicit Toxin-Neutralizing Antibody Responses in Mice. J Pharm Sci 2016; 105:1603-1613. [PMID: 26987947 PMCID: PMC4846473 DOI: 10.1016/j.xphs.2016.02.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2015] [Revised: 01/26/2016] [Accepted: 02/09/2016] [Indexed: 02/07/2023]
Abstract
RiVax is a candidate ricin toxin subunit vaccine antigen that has proven to be safe in human phase I clinical trials. In this study, we introduced double and triple cavity-filling point mutations into the RiVax antigen with the expectation that stability-enhancing modifications would have a beneficial effect on overall immunogenicity of the recombinant proteins. We demonstrate that 2 RiVax triple mutant derivatives, RB (V81L/C171L/V204I) and RC (V81I/C171L/V204I), when adsorbed to aluminum salts adjuvant and tested in a mouse prime-boost-boost regimen were 5- to 10-fold more effective than RiVax at eliciting toxin-neutralizing serum IgG antibody titers. Increased toxin neutralizing antibody values and seroconversion rates were evident at different antigen dosages and within 7 days after the first booster. Quantitative stability/flexibility relationships analysis revealed that the RB and RC mutations affect rigidification of regions spanning residues 98-103, which constitutes a known immunodominant neutralizing B-cell epitope. A more detailed understanding of the immunogenic nature of RB and RC may provide insight into the fundamental relationship between local protein stability and antibody reactivity.
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Affiliation(s)
- Newton Wahome
- Department of Pharmaceutical Chemistry, Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, Kansas 66047
| | - Erin Sully
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York 12208
| | - Christopher Singer
- Department of Physics and Optical Science, University of North Carolina at Charlotte, Charlotte, North Carolina 28223
| | - Justin C Thomas
- Department of Pharmaceutical Chemistry, Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, Kansas 66047
| | - Lei Hu
- Department of Pharmaceutical Chemistry, Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, Kansas 66047
| | - Sangeeta B Joshi
- Department of Pharmaceutical Chemistry, Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, Kansas 66047
| | - David B Volkin
- Department of Pharmaceutical Chemistry, Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, Kansas 66047
| | - Jianwen Fang
- Applied Bioinformatics Laboratory, Department of Medicinal Chemistry, University of Kansas, Lawrence, Kansas 66047
| | - John Karanicolas
- Department of Molecular Biosciences, Center for Computational Biology, University of Kansas, Lawrence, Kansas 66045
| | - Donald J Jacobs
- Department of Physics and Optical Science, University of North Carolina at Charlotte, Charlotte, North Carolina 28223.
| | - Nicholas J Mantis
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York 12208; Department of Biomedical Sciences, School of Public Health, University at Albany, Albany, New York 12201.
| | - C Russell Middaugh
- Department of Pharmaceutical Chemistry, Macromolecule and Vaccine Stabilization Center, University of Kansas, Lawrence, Kansas 66047.
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Zhang T, Yang H, Kang L, Gao S, Xin W, Yao W, Zhuang X, Ji B, Wang J. Strong protection against ricin challenge induced by a novel modified ricin A-chain protein in mouse model. Hum Vaccin Immunother 2016; 11:1779-87. [PMID: 26038805 PMCID: PMC4514271 DOI: 10.1080/21645515.2015.1038446] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Ricin toxin (RT) is an extremely potent toxin derived from the castor bean plant. As a possible bioterrorist weapon, it was categorized as a level B agent in international society. With the growing awareness and concerns of the “white powder incident” in recent years, it is indispensable to develop an effective countermeasure against RT intoxication. In this study we used site-directed mutagenesis and polymerase chain reaction (PCR) techniques to modify the gene of ricin A-chain (RTA). As a result, we have generated a mutated and truncated ricin A-chain (mtRTA) vaccine antigen by E.coli strain. The cytotoxicity assay was used to evaluate the safety of the as-prepared mtRTA antigen, and the results showed that there was no residual toxicity observed when compared to the recombinant RTA (rRTA) or native RT. Furthermore, BALB/c mice were subcutaneously (s.c.) vaccinated with mtRTA 3 times at an interval of 2 weeks, and then the survivals were evaluated after intraperitoneal (i.p.) or intratracheal challenge of RT. The vaccinated mice developed a strong protective immune response that was wholly protective against 40 × LD50 of RT i.p. injection or 20 × LD50 of RT intratracheal spraying. The mtRTA antigen has great potential to be a vaccine candidate for future application in humans.
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Key Words
- ELISA, enzyme-linked immunosorbent assay
- FBS, fetal bovine serum
- HRP, horseradish peroxidase
- IPTG, isopropyl-1-thio-β-galactopyranoside
- LD50, median lethal dose
- RT, ricin toxin
- RTA, ricin toxin A chain
- RTB, ricin toxin B chain
- SD, standard deviation
- i.p, intraperitoneally
- i.p., intraperitoneal
- immunity
- intratracheal
- mRTA, mutated RTA
- mtRTA, mutated and truncated RTA
- mutant
- rRTA, recombinant RTA
- ricin
- s.c., subcutaneously subcutaneous
- toxicity
- toxin
- truncation
- vaccine
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Affiliation(s)
- Tao Zhang
- a State Key Laboratory of Pathogen and Biosecurity; Beijing Institute of Microbiology and Epidemiology ; Beijing , China
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Noy-Porat T, Rosenfeld R, Ariel N, Epstein E, Alcalay R, Zvi A, Kronman C, Ordentlich A, Mazor O. Isolation of Anti-Ricin Protective Antibodies Exhibiting High Affinity from Immunized Non-Human Primates. Toxins (Basel) 2016; 8:toxins8030064. [PMID: 26950154 PMCID: PMC4810209 DOI: 10.3390/toxins8030064] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2016] [Revised: 02/25/2016] [Accepted: 02/26/2016] [Indexed: 11/16/2022] Open
Abstract
Ricin, derived from the castor bean plant Ricinus communis, is one of the most potent and lethal toxins known, against which there is no available antidote. To date, the use of neutralizing antibodies is the most promising post-exposure treatment for ricin intoxication. The aim of this study was to isolate high affinity anti-ricin antibodies that possess potent toxin-neutralization capabilities. Two non-human primates were immunized with either a ricin-holotoxin- or subunit-based vaccine, to ensure the elicitation of diverse high affinity antibodies. By using a comprehensive set of primers, immune scFv phage-displayed libraries were constructed and panned. A panel of 10 antibodies (five directed against the A subunit of ricin and five against the B subunit) was isolated and reformatted into a full-length chimeric IgG. All of these antibodies were found to neutralize ricin in vitro, and several conferred full protection to ricin-intoxicated mice when given six hours after exposure. Six antibodies were found to possess exceptionally high affinity toward the toxin, with KD values below pM (koff < 1 × 10−7 s−1) that were well correlated with their ability to neutralize ricin. These antibodies, alone or in combination, could be used for the development of a highly-effective therapeutic preparation for post-exposure treatment of ricin intoxication.
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Affiliation(s)
- Tal Noy-Porat
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Ronit Rosenfeld
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Naomi Ariel
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Eyal Epstein
- Department of Biotechnology, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Ron Alcalay
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Anat Zvi
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Chanoch Kronman
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Arie Ordentlich
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
| | - Ohad Mazor
- Department of Biochemistry and Molecular Genetics, Israel Institute for Biological Research, Ness-Ziona 76100, Israel.
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14
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Brey RN, Mantis NJ, Pincus SH, Vitetta ES, Smith LA, Roy CJ. Recent advances in the development of vaccines against ricin. Hum Vaccin Immunother 2016; 12:1196-201. [PMID: 26810367 DOI: 10.1080/21645515.2015.1124202] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
Abstract
Several promising subunit vaccines against ricin toxin (RT) have been developed during the last decade and are now being tested for safety and immunogenicity in humans and for efficacy in nonhuman primates. The incentive to develop a preventive vaccine as a countermeasure against RT use as a bioweapon is based on the high toxicity of RT after aerosol exposure, its environmental stability, abundance, and ease of purification. RT is the second most lethal biological toxin and is considered a "universal toxin" because it can kill all eukaryotic cells through binding to ubiquitous cell surface galactosyl residues. RT has two subunits conjoined by a single disulfide linkage: RTB, which binds galactosyl residues and RTA which enzymatically inactivates ribosomes intracellularly by cleavage ribosomal RNA. Attenuation of toxicity by elimination of the active site or introduction of other structural mutations of RTA has generated two similar clinical subunit vaccine candidates which induce antibodies in both humans and nonhuman primates. In rhesus macaques, inhaled RT causes rapid lung necrosis and fibrosis followed by death. After parenteral vaccination with RTA vaccine, macaques can be protected against aerosol RT exposure, suggesting that circulating antibodies can protect lung mucosa. Vaccination induces RT-neutralizing antibodies, the most likely correlate of protection. Macaques responded to conformational determinants in an RTA vaccine formulation, indicating preservation of RTA structure during initial manufacture. Comparative mapping studies have also demonstrated that macaques and humans recognize the same epitopes, significant in the study of macaques as a model during development of vaccines which cannot be tested for efficacy in humans.
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Affiliation(s)
| | - Nicholas J Mantis
- b Division of Infectious Disease , Wadsworth Center, New York State Department of Health, Albany, NY, USA Department of Biomedical Sciences, University of Albany School of Public Health , Albany , NY , USA
| | - Seth H Pincus
- c Departments of Pediatrics and Microbiology , Louisiana State University School of Medicine, Children's Hospital , New Orleans , LA , USA
| | - Ellen S Vitetta
- d Departments of Immunology and Microbiology , The University of Texas Southwestern Medical Center , Dallas , TX , USA
| | - Leonard A Smith
- e Medical Countermeasures Technology, US Army Medical Research Institute of Infectious Diseases , Fort Detrick , MD , USA
| | - Chad J Roy
- f Division of Microbiology, Tulane National Primate Research Center , Covington , LA , USA.,g Department of Microbiology and Immunology , Tulane School of Medicine , New Orleans , LA , USA
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15
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Dong J, Zhang Y, Chen Y, Niu X, Zhang Y, Li R, Yang C, Wang Q, Li X, Deng X. Baicalin inhibits the lethality of ricin in mice by inducing protein oligomerization. J Biol Chem 2015; 290:12899-907. [PMID: 25847243 DOI: 10.1074/jbc.m114.632828] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Indexed: 12/11/2022] Open
Abstract
Toxic ribosome-inactivating proteins abolish cell viability by inhibiting protein synthesis. Ricin, a member of these lethal proteins, is a potential bioterrorism agent. Despite the grave challenge posed by these toxins to public health, post-exposure treatment for intoxication caused by these agents currently is unavailable. In this study, we report the identification of baicalin extracted from Chinese herbal medicine as a compound capable of inhibiting the activity of ricin. More importantly, post-exposure treatment with baicalin significantly increased the survival of mice poisoned by ricin. We determined the mechanism of action of baicalin by solving the crystal structure of its complex with the A chain of ricin (RTA) at 2.2 Å resolution, which revealed that baicalin interacts with two RTA molecules at a novel binding site by hydrogen bond networks and electrostatic force interactions, suggesting its role as molecular glue of the RTA. Further biochemical and biophysical analyses validated the amino acids directly involved in binding the inhibitor, which is consistent with the hypothesis that baicalin exerts its inhibitory effects by inducing RTA to form oligomers in solution, a mechanism that is distinctly different from previously reported inhibitors. This work offers promising leads for the development of therapeutics against ricin and probably other ribosome-inactivating proteins.
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Affiliation(s)
- Jing Dong
- From the Key Laboratory of Zoonosis, Ministry of Education, Institute of Zoonosis, College of Veterinary Medicine, Jilin University, Changchun 130062, the Yangtze River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Wuhan 430223
| | - Yong Zhang
- From the Key Laboratory of Zoonosis, Ministry of Education, Institute of Zoonosis, College of Veterinary Medicine, Jilin University, Changchun 130062
| | - Yutao Chen
- the National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101
| | - Xiaodi Niu
- the Department of Food Quality and Safety, Jilin University, Changchun 130062, and
| | - Yu Zhang
- From the Key Laboratory of Zoonosis, Ministry of Education, Institute of Zoonosis, College of Veterinary Medicine, Jilin University, Changchun 130062
| | - Rui Li
- From the Key Laboratory of Zoonosis, Ministry of Education, Institute of Zoonosis, College of Veterinary Medicine, Jilin University, Changchun 130062
| | - Cheng Yang
- the College of Pharmacy, NanKai University, Tianjin 300071, China
| | - Quan Wang
- the National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101
| | - Xuemei Li
- the National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101,
| | - Xuming Deng
- From the Key Laboratory of Zoonosis, Ministry of Education, Institute of Zoonosis, College of Veterinary Medicine, Jilin University, Changchun 130062,
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16
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Vance DJ, Rong Y, Brey RN, Mantis NJ. Combination of two candidate subunit vaccine antigens elicits protective immunity to ricin and anthrax toxin in mice. Vaccine 2015; 33:417-21. [PMID: 25475957 PMCID: PMC4274239 DOI: 10.1016/j.vaccine.2014.11.036] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2014] [Revised: 09/30/2014] [Accepted: 11/17/2014] [Indexed: 10/24/2022]
Abstract
In an effort to develop combination vaccines for biodefense, we evaluated a ricin subunit antigen, RiVax, given in conjunction with an anthrax protective antigen, DNI. The combination led to high endpoint titer antibody response, neutralizing antibodies, and protective immunity against ricin and anthrax lethal toxin. This is a natural combination vaccine, since both antigens are recombinant subunit proteins that would be given to the same target population.
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Affiliation(s)
- David J Vance
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY, USA
| | - Yinghui Rong
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY, USA
| | | | - Nicholas J Mantis
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY, USA; Department of Biomedical Sciences, University at Albany, Albany, NY, USA.
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17
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Characterization and epitope mapping of the polyclonal antibody repertoire elicited by ricin holotoxin-based vaccination. CLINICAL AND VACCINE IMMUNOLOGY : CVI 2014; 21:1534-40. [PMID: 25209559 DOI: 10.1128/cvi.00510-14] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Ricin, one of the most potent and lethal toxins known, is classified by the Centers for Disease Control and Prevention (CDC) as a select agent. Currently, there is no available antidote against ricin exposure, and the most promising therapy is based on neutralizing antibodies elicited by active vaccination or that are given passively. The aim of this study was to characterize the repertoire of anti-ricin antibodies generated in rabbits immunized with ricin toxoid. These anti-ricin antibodies exhibit an exceptionally high avidity (thiocyanate-based avidity index, 9 M) toward ricin and an apparent affinity of 1 nM. Utilizing a novel tissue culture-based assay that enables the determination of ricin activity within a short time period, we found that the anti-ricin antibodies also possess a very high neutralizing titer. In line with these findings, these antibodies conferred mice with full protection against pulmonary ricinosis when administered as a passive vaccination. Epitope mapping analysis using phage display random peptide libraries revealed that the polyclonal serum contains four immunodominant epitopes, three of which are located on the A subunit and one on the B subunit of ricin. Only two of the four epitopes were found to have a significant role in ricin neutralization. To the best of our knowledge, this is the first work that characterizes these immunological aspects of the polyclonal response to ricin holotoxin-based vaccination. These findings provide useful information and a possible strategy for the development and design of an improved ricin holotoxin-based vaccine.
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18
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Rudolph MJ, Vance DJ, Cheung J, Franklin MC, Burshteyn F, Cassidy MS, Gary EN, Herrera C, Shoemaker CB, Mantis NJ. Crystal structures of ricin toxin's enzymatic subunit (RTA) in complex with neutralizing and non-neutralizing single-chain antibodies. J Mol Biol 2014; 426:3057-68. [PMID: 24907552 PMCID: PMC4128236 DOI: 10.1016/j.jmb.2014.05.026] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2014] [Revised: 05/17/2014] [Accepted: 05/25/2014] [Indexed: 10/25/2022]
Abstract
Ricin is a select agent toxin and a member of the RNA N-glycosidase family of medically important plant and bacterial ribosome-inactivating proteins. In this study, we determined X-ray crystal structures of the enzymatic subunit of ricin (RTA) in complex with the antigen binding domains (VHH) of five unique single-chain monoclonal antibodies that differ in their respective toxin-neutralizing activities. None of the VHHs made direct contact with residues involved in RTA's RNA N-glycosidase activity or induced notable allosteric changes in the toxin's subunit. Rather, the five VHHs had overlapping structural epitopes on the surface of the toxin and differed in the degree to which they made contact with prominent structural elements in two folding domains of the RTA. In general, RTA interactions were influenced most by the VHH CDR3 (CDR, complementarity-determining region) elements, with the most potent neutralizing antibody having the shortest and most conformationally constrained CDR3. These structures provide unique insights into the mechanisms underlying toxin neutralization and provide critically important information required for the rational design of ricin toxin subunit vaccines.
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Affiliation(s)
| | - David J Vance
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY 12208, USA
| | - Jonah Cheung
- New York Structural Biology Center, New York, NY 10027, USA
| | | | | | | | - Ebony N Gary
- New York Structural Biology Center, New York, NY 10027, USA
| | - Cristina Herrera
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY 12208, USA; Department of Biomedical Sciences, University at Albany, Albany, NY 12201, USA
| | | | - Nicholas J Mantis
- Division of Infectious Diseases, Wadsworth Center, New York State Department of Health, Albany, NY 12208, USA; Department of Biomedical Sciences, University at Albany, Albany, NY 12201, USA.
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19
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Herrera C, Vance DJ, Eisele LE, Shoemaker CB, Mantis NJ. Differential neutralizing activities of a single domain camelid antibody (VHH) specific for ricin toxin's binding subunit (RTB). PLoS One 2014; 9:e99788. [PMID: 24918772 PMCID: PMC4053406 DOI: 10.1371/journal.pone.0099788] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2014] [Accepted: 05/17/2014] [Indexed: 11/18/2022] Open
Abstract
Ricin, a member of the A-B family of ribosome-inactivating proteins, is classified as a Select Toxin by the Centers for Disease Control and Prevention because of its potential use as a biothreat agent. In an effort to engineer therapeutics for ricin, we recently produced a collection of alpaca-derived, heavy-chain only antibody VH domains (VHH or “nanobody”) specific for ricin’s enzymatic (RTA) and binding (RTB) subunits. We reported that one particular RTB-specific VHH, RTB-B7, when covalently linked via a peptide spacer to different RTA-specific VHHs, resulted in heterodimers like VHH D10/B7 that were capable of passively protecting mice against a lethal dose challenge with ricin. However, RTB-B7 itself, when mixed with ricin at a 1∶10 toxin:antibody ratio did not afford any protection in vivo, even though it had demonstrable toxin-neutralizing activity in vitro. To better define the specific attributes of antibodies associated with ricin neutralization in vitro and in vivo, we undertook a more thorough characterization of RTB-B7. We report that RTB-B7, even at 100-fold molar excess (toxin:antibody) was unable to alter the toxicity of ricin in a mouse model. On the other hand, in two well-established cytotoxicity assays, RTB-B7 neutralized ricin with a 50% inhibitory concentration (IC50) that was equivalent to that of 24B11, a well-characterized and potent RTB-specific murine monoclonal antibody. In fact, RTB-B7 and 24B11 were virtually identical when compared across a series of in vitro assays, including adherence to and neutralization of ricin after the toxin was pre-bound to cell surface receptors. RTB-B7 differed from both 24B11 and VHH D10/B7 in that it was relatively less effective at blocking ricin attachment to receptors on host cells and was not able to form high molecular weight toxin:antibody complexes in solution. Whether either of these activities is important in ricin toxin neutralizing activity in vivo remains to be determined.
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Affiliation(s)
- Cristina Herrera
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, United States of America
- Department of Biomedical Sciences, University at Albany School of Public Health, Albany, New York, United States of America
| | - David J. Vance
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, United States of America
| | - Leslie E. Eisele
- Scientific Cores, Wadsworth Center, New York State Department of Health, Albany, New York, United States of America
| | - Charles B. Shoemaker
- Department of Infectious Disease and Global Health, Tufts Cummings School of Veterinary Medicine, North Grafton, Massachusetts, United States of America
| | - Nicholas J. Mantis
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, United States of America
- Department of Biomedical Sciences, University at Albany School of Public Health, Albany, New York, United States of America
- * E-mail:
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20
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Abstract
Ricin is a member of the ubiquitous family of plant and bacterial AB toxins that gain entry into the cytosol of host cells through receptor-mediated endocytosis and retrograde traffic through the trans-Golgi network (TGN) and endoplasmic reticulum (ER). While a few ricin toxin-specific neutralizing monoclonal antibodies (MAbs) have been identified, the mechanisms by which these antibodies prevent toxin-induced cell death are largely unknown. Using immunofluorescence confocal microscopy and a TGN-specific sulfation assay, we demonstrate that 24B11, a MAb against ricin’s binding subunit (RTB), associates with ricin in solution or when prebound to cell surfaces and then markedly enhances toxin uptake into host cells. Following endocytosis, however, toxin-antibody complexes failed to reach the TGN; instead, they were shunted to Rab7-positive late endosomes and LAMP-1-positive lysosomes. Monovalent 24B11 Fab fragments also interfered with toxin retrograde transport, indicating that neither cross-linking of membrane glycoproteins/glycolipids nor the recently identified intracellular Fc receptor is required to derail ricin en route to the TGN. Identification of the mechanism(s) by which antibodies like 24B11 neutralize ricin will advance our fundamental understanding of protein trafficking in mammalian cells and may lead to the discovery of new classes of toxin inhibitors and therapeutics for biodefense and emerging infectious diseases. Ricin is the prototypic member of the AB family of medically important plant and bacterial toxins that includes cholera and Shiga toxins. Ricin is also a category B biothreat agent. Despite ongoing efforts to develop vaccines and antibody-based therapeutics against ricin, very little is known about the mechanisms by which antibodies neutralize this toxin. In general, it is thought that antibodies simply prevent toxins from attaching to cell surface receptors or promote their clearance through Fc receptor (FcR)-mediated uptake. In this report, however, we describe a neutralizing monoclonal antibody (MAb) against ricin’s binding subunit (RTB) that not only associates with ricin after the toxin has bound to the cell’s surface but actually enhances toxin uptake into host cells. Following endocytosis, the antibody-toxin complexes are then routed for degradation. The results of this study are important because they reveal a previously unappreciated role for B-subunit-specific antibodies in intracellular neutralization of ricin toxin.
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21
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O'Hara JM, Kasten-Jolly JC, Reynolds CE, Mantis NJ. Localization of non-linear neutralizing B cell epitopes on ricin toxin's enzymatic subunit (RTA). Immunol Lett 2014; 158:7-13. [PMID: 24269767 PMCID: PMC4070743 DOI: 10.1016/j.imlet.2013.11.009] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2013] [Accepted: 11/07/2013] [Indexed: 12/16/2022]
Abstract
Efforts to develop a vaccine for ricin toxin are focused on identifying highly immunogenic, safe, and thermostable recombinant derivatives of ricin's enzymatic A subunit (RTA). As a means to guide vaccine design, we have embarked on an effort to generate a comprehensive neutralizing and non-neutralizing B cell epitope map of RTA. In a series of previous studies, we identified three spatially distinct linear (continuous), neutralizing epitopes on RTA, as defined by monoclonal antibodies (mAbs) PB10 (and R70), SyH7, and GD12. In this report we now describe a new collection of 19 toxin-neutralizing mAbs that bind non-linear epitopes on RTA. The most potent toxin-neutralizing mAbs in this new collection, namely WECB2, TB12, PA1, PH12 and IB2 each had nanamolar (or sub-nanomolar) affinities for ricin and were each capable of passively protecting mice against a 5-10xLD50 toxin challenge. Competitive binding assays by surface plasmon resonance revealed that WECB2 binds an epitope that overlaps with PB10 and R70; TB12, PA1, PH12 recognize epitope(s) close to or overlapping with SyH7's epitope; and GD12 and IB2 recognize epitopes that are spatially distinct from all other toxin-neutralizing mAbs. We estimate that we have now accounted for ∼75% of the predicted epitopes on the surface of RTA and that toxin-neutralizing mAbs are directed against a very limited number of these epitopes. Having this information provides a framework for further refinement of RTA mutagenesis and vaccine design.
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Affiliation(s)
- Joanne M O'Hara
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States; Department of Biomedical Sciences, University at Albany School of Public Health, Albany, NY 12201, United States
| | - Jane C Kasten-Jolly
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States
| | - Claire E Reynolds
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States
| | - Nicholas J Mantis
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States; Department of Biomedical Sciences, University at Albany School of Public Health, Albany, NY 12201, United States.
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22
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Vance DJ, Tremblay JM, Mantis NJ, Shoemaker CB. Stepwise engineering of heterodimeric single domain camelid VHH antibodies that passively protect mice from ricin toxin. J Biol Chem 2013; 288:36538-47. [PMID: 24202178 DOI: 10.1074/jbc.m113.519207] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
In an effort to engineer countermeasures for the category B toxin ricin, we produced and characterized a collection of epitopic tagged, heavy chain-only antibody VH domains (VHHs) specific for the ricin enzymatic (RTA) and binding (RTB) subunits. Among the 20 unique ricin-specific VHHs we identified, six had toxin-neutralizing activity: five specific for RTA and one specific for RTB. Three neutralizing RTA-specific VHHs were each linked via a short peptide spacer to the sole neutralizing anti-RTB VHH to create VHH "heterodimers." As compared with equimolar concentrations of their respective monovalent monomers, all three VHH heterodimers had higher affinities for ricin and, in the case of heterodimer D10/B7, a 6-fold increase in in vitro toxin-neutralizing activity. When passively administered to mice at a 4:1 heterodimer:toxin ratio, D10/B7 conferred 100% survival in response to a 10 × LD50 ricin challenge, whereas a 2:1 heterodimer:toxin ratio conferred 20% survival. However, complete survival was achievable when the low dose of D10/B7 was combined with an IgG1 anti-epitopic tag monoclonal antibody, possibly because decorating the toxin with up to four IgGs promoted serum clearance. The two additional ricin-specific heterodimers, when tested in vivo, provided equal or greater passive protection than D10/B7, thereby warranting further investigation of all three heterodimers as possible therapeutics.
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Affiliation(s)
- David J Vance
- From the Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York 12208 and
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23
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Hassett KJ, Cousins MC, Rabia LA, Chadwick CM, O’Hara JM, Nandi P, Brey RN, Mantis NJ, Carpenter JF, Randolph TW. Stabilization of a recombinant ricin toxin A subunit vaccine through lyophilization. Eur J Pharm Biopharm 2013; 85:279-86. [PMID: 23583494 PMCID: PMC3797224 DOI: 10.1016/j.ejpb.2013.03.029] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2013] [Revised: 03/12/2013] [Accepted: 03/23/2013] [Indexed: 10/26/2022]
Abstract
Lyophilization was used to prepare dry, glassy solid vaccine formulations of recombinant ricin toxin A-chain containing suspensions of colloidal aluminum hydroxide adjuvant. Four lyophilized formulations were prepared by using combinations of rapid or slow cooling during lyophilization and one of two buffers, histidine or ammonium acetate. Trehalose was used as the stabilizing excipient. Aggregation of the colloidal aluminum hydroxide suspension was reduced in formulations processed with a rapid cooling rate. Aluminum hydroxide particle size distributions, glass transition temperatures, water contents, and immunogenicities of lyophilized vaccines were independent of incubation time at 40 °C for up to 15 weeks. Mice immunized with reconstituted ricin toxin subunit A (RTA) vaccines produced RTA-specific antibodies and toxin-neutralizing antibodies (TNAs) regardless of the length of high temperature vaccine storage or the degree of aluminum adjuvant aggregation that occurred during lyophilization. In murine studies, lyophilized formulations of vaccines conferred protection against exposure to lethal doses of ricin, even after the lyophilized formulations had been stored at 40 °C for 4 weeks. A corresponding liquid formulation of vaccine stored at 40 °C elicited RTA-specific antibody titers but failed to confer immunity during a ricin challenge.
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Affiliation(s)
- Kimberly J. Hassett
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80303, United States
| | - Megan C. Cousins
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80303, United States
| | - Lilia A. Rabia
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80303, United States
| | - Chrystal M. Chadwick
- Wadsworth Center, New York Department of Health, Albany, New York 12208, United States
| | - Joanne M. O’Hara
- Wadsworth Center, New York Department of Health, Albany, New York 12208, United States
- Department of Biomedical Sciences, University at Albany School of Public Health, Albany, NY 12201, United States
| | - Pradyot Nandi
- Department of Pharmaceutical Sciences, University of Colorado Denver, Aurora, Colorado 80045, United States
| | - Robert N. Brey
- Soligenix, Inc., Princeton, New Jersey 08540, United States
| | - Nicholas J. Mantis
- Wadsworth Center, New York Department of Health, Albany, New York 12208, United States
- Department of Biomedical Sciences, University at Albany School of Public Health, Albany, NY 12201, United States
| | - John F. Carpenter
- Department of Pharmaceutical Sciences, University of Colorado Denver, Aurora, Colorado 80045, United States
| | - Theodore W. Randolph
- Department of Chemical and Biological Engineering, University of Colorado, Boulder, Colorado 80303, United States
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24
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Li XP, Kahn PC, Kahn JN, Grela P, Tumer NE. Arginine residues on the opposite side of the active site stimulate the catalysis of ribosome depurination by ricin A chain by interacting with the P-protein stalk. J Biol Chem 2013; 288:30270-30284. [PMID: 24003229 DOI: 10.1074/jbc.m113.510966] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Ricin inhibits protein synthesis by depurinating the α-sarcin/ricin loop (SRL). Ricin holotoxin does not inhibit translation unless the disulfide bond between the A (RTA) and B (RTB) subunits is reduced. Ricin holotoxin did not bind ribosomes or depurinate them but could depurinate free RNA. When RTA is separated from RTB, arginine residues located at the interface are exposed to the solvent. Because this positively charged region, but not the active site, is blocked by RTB, we mutated arginine residues at or near the interface of RTB to determine if they are critical for ribosome binding. These variants were structurally similar to wild type RTA but could not bind ribosomes. Their K(m) values and catalytic rates (k(cat)) for an SRL mimic RNA were similar to those of wild type, indicating that their activity was not altered. However, they showed an up to 5-fold increase in K(m) and up to 38-fold decrease in kcat toward ribosomes. These results suggest that the stalk binding stimulates the catalysis of ribosome depurination by RTA. The mutated arginines have side chains behind the active site cleft, indicating that the ribosome binding surface of RTA is on the opposite side of the surface that interacts with the SRL. We propose that stalk binding stimulates the catalysis of ribosome depurination by orienting the active site of RTA toward the SRL and thereby allows docking of the target adenine into the active site. This model may apply to the translation factors that interact with the stalk.
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Affiliation(s)
- Xiao-Ping Li
- From the Departments of Plant Biology and Pathology and
| | - Peter C Kahn
- Biochemistry and Microbiology, School of Environmental and Biological Sciences, Rutgers University, New Brunswick, New Jersey 08901-8520
| | | | | | - Nilgun E Tumer
- From the Departments of Plant Biology and Pathology and.
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25
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Gerber HP, Koehn FE, Abraham RT. The antibody-drug conjugate: an enabling modality for natural product-based cancer therapeutics. Nat Prod Rep 2013; 30:625-39. [PMID: 23525375 DOI: 10.1039/c3np20113a] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The Antibody Drug Conjugate (ADC) is a therapeutic modality consisting of a monoclonal antibody attached to a cytotoxic, small-molecule payload. The antibody portion of the ADC serves as a transport vehicle that recognizes and binds to a protein antigen expressed in tumor tissues. The localized delivery and release of the payload within or near malignant cells allows for targeted delivery of a potent cytotoxic agent to diseased tissue, while reducing damage to antigen-negative, normal tissues. Recent years have witnessed an explosive increase in ADC-based therapies, due mainly to clinical reports of activity in both hematologic and epithelial cancers. Accompanying this upsurge in ADC development is a renewed interest in natural product cytotoxins, which are typically highly potent cell-killing agents, but suffer from poor drug-like properties and narrow safety margins when systemically administered as conventional chemotherapeutics. In this review, we discuss recent advances related to the construction of ADCs, the optimization of ADC safety and efficacy, and the increasingly pivotal roles of natural product payloads in the current and future landscape of ADC therapy.
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Affiliation(s)
- Hans-Peter Gerber
- Pfizer Worldwide Research and Development, Oncology Research Unit, 401 Middletown Road, Pearl River, NY, USA.
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26
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O'Hara JM, Mantis NJ. Neutralizing monoclonal antibodies against ricin's enzymatic subunit interfere with protein disulfide isomerase-mediated reduction of ricin holotoxin in vitro. J Immunol Methods 2013; 395:71-8. [PMID: 23774033 DOI: 10.1016/j.jim.2013.06.004] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2012] [Revised: 05/26/2013] [Accepted: 06/06/2013] [Indexed: 11/15/2022]
Abstract
The penultimate event in the intoxication of mammalian cells by ricin toxin is the reduction, in the endoplasmic reticulum (ER), of the intermolecular disulfide bond that links ricin's enzymatic (RTA) and binding (RTB) subunits. In this report we adapted an in vitro protein disulfide isomerase (PDI)-mediated reduction assay to test the hypothesis that the RTA-specific neutralizing monoclonal antibody (mAb) IB2 interferes with the liberation of RTA from RTB. IB2 recognizes an epitope located near the interface between RTA and RTB and, like a number of other RTA-specific neutralizing mAbs, is proposed to neutralize ricin intracellularly. In this study, we found that IB2 virtually eliminated the reduction of ricin holotoxin into RTA and RTB in vitro. Surprisingly, three other neutralizing mAbs (GD12, R70 and SyH7) that bind epitopes at considerable distance from ricin's disulfide bond were as effective (or nearly as effective) as IB2 in interfering with PDI-mediated liberation of RTA from RTB. By contrast, two non-neutralizing RTA-specific mAbs, FGA12 and SB1, did not affect PDI-mediated reduction of ricin. These data reveal a possible mechanism by which RTA-specific antibodies may neutralize ricin intracellularly, provided they are capable of trafficking in association with ricin from the cell surface to the ER.
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Affiliation(s)
- Joanne M O'Hara
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, United States
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27
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Yermakova A, Mantis NJ. Neutralizing activity and protective immunity to ricin toxin conferred by B subunit (RTB)-specific Fab fragments. Toxicon 2013; 72:29-34. [PMID: 23603317 DOI: 10.1016/j.toxicon.2013.04.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2013] [Revised: 03/22/2013] [Accepted: 04/03/2013] [Indexed: 01/13/2023]
Abstract
SylH3 and 24B11 are murine monoclonal antibodies directed against different epitopes on ricin toxin's binding (RTB) subunit that have been shown to passively protect mice against ricin challenge. Here we report that Fab fragments of SylH3 and 24B11 neutralize ricin in a cell based assay, and in a mouse challenge model as effectively as their respective full length parental IgGs. These data demonstrate that immunity to ricin can occur independent of Fc-mediated clearance.
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Affiliation(s)
- Anastasiya Yermakova
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, NY 12208, USA
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28
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Thomas JC, O'Hara JM, Hu L, Gao FP, Joshi SB, Volkin DB, Brey RN, Fang J, Karanicolas J, Mantis NJ, Middaugh CR. Effect of single-point mutations on the stability and immunogenicity of a recombinant ricin A chain subunit vaccine antigen. Hum Vaccin Immunother 2013; 9:744-52. [PMID: 23563512 DOI: 10.4161/hv.22998] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
There is great interest in the design and development of highly thermostable and immunogenic protein subunit vaccines for biodefense. In this study, we used two orthogonal and complementary computational protein design approaches to generate a series of single-point mutants of RiVax, an attenuated recombinant ricin A chain (RTA) protein subunit vaccine antigen. As assessed by differential scanning calorimetry, the conformational stabilities of the designed mutants ranged from 4°C less stable to 4.5°C more stable than RiVax, depending on solution pH. Two more thermostable (V18P, C171L) and two less thermostable (T13V, S89T) mutants that displayed native-like secondary and tertiary structures (as determined by circular dichroism and fluorescence spectral analysis, respectively) were tested for their capacity to elicit RTA-specific antibodies and toxin-neutralizing activity. Following a prime-boost regimen, we found qualitative differences with respect to specific antibody titers and toxin neutralizing antibody levels induced by the different mutants. Upon a second boost with the more thermostable mutant C171L, a statistically significant increase in RTA-specific antibody titers was observed when compared with RiVax-immunized mice. Notably, the results indicate that single residue changes can be made to the RiVax antigen that increase its thermal stability without adversely impacting the efficacy of the vaccine.
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Affiliation(s)
- Justin C Thomas
- Macromolecule and Vaccine Stabilization Center; Department of Pharmaceutical Chemistry; University of Kansas; Lawrence, KS USA
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29
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Conformation-dependent high-affinity potent ricin-neutralizing monoclonal antibodies. BIOMED RESEARCH INTERNATIONAL 2012; 2013:471346. [PMID: 23484120 PMCID: PMC3591125 DOI: 10.1155/2013/471346] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/25/2012] [Revised: 10/26/2012] [Accepted: 11/10/2012] [Indexed: 12/23/2022]
Abstract
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.
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30
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Yermakova A, Vance DJ, Mantis NJ. Sub-domains of ricin's B subunit as targets of toxin neutralizing and non-neutralizing monoclonal antibodies. PLoS One 2012; 7:e44317. [PMID: 22984492 PMCID: PMC3439471 DOI: 10.1371/journal.pone.0044317] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2012] [Accepted: 08/01/2012] [Indexed: 12/30/2022] Open
Abstract
The B subunit (RTB) of ricin toxin is a galactose (Gal)−/N-acetylgalactosamine (GalNac)-specific lectin that mediates attachment, entry, and intracellular trafficking of ricin in host cells. Structurally, RTB consists of two globular domains with identical folding topologies. Domains 1 and 2 are each comprised of three homologous sub-domains (α, β, γ) that likely arose by gene duplication from a primordial carbohydrate recognition domain (CRD), although only sub-domains 1α and 2γ retain functional lectin activity. As part of our ongoing effort to generate a comprehensive B cell epitope map of ricin, we report the characterization of three new RTB-specific monoclonal antibodies (mAbs). All three mAbs, JB4, B/J F9 and C/M A2, were initially identified based on their abilities to neutralize ricin in a Vero cell cytotoxicty assay and to partially (or completely) block ricin attachment to cell surfaces. However, only JB4 proved capable of neutralizing ricin in a macrophage apoptosis assay and in imparting passive immunity to mice in a model of systemic intoxication. Using a combination of techniques, including competitive ELISAs, pepscan analysis, differential reactivity by Western blot, as well as affinity enrichment of phage displayed peptides, we tentatively localized the epitopes recognized by the non-neutralizing mAbs B/J F9 and C/M A2 to sub-domains 2α and 2β, respectively. Furthermore, we propose that the epitope recognized by JB4 is within sub-domain 2γ, adjacent to RTB’s high affinity Gal/GalNAc CRD. These data suggest that recognition of RTB’s sub-domains 1α and 2γ are critical determinants of antibody neutralizing activity and protective immunity to ricin.
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Affiliation(s)
- Anastasiya Yermakova
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, United States of America
- Department of Biomedical Sciences, University at Albany School of Public Health, Albany, New York, United States of America
| | - David J. Vance
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, United States of America
| | - Nicholas J. Mantis
- Division of Infectious Disease, Wadsworth Center, New York State Department of Health, Albany, New York, United States of America
- Department of Biomedical Sciences, University at Albany School of Public Health, Albany, New York, United States of America
- * E-mail:
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Resolution of two overlapping neutralizing B cell epitopes within a solvent exposed, immunodominant α-helix in ricin toxin's enzymatic subunit. Toxicon 2012; 60:874-7. [PMID: 22750533 DOI: 10.1016/j.toxicon.2012.06.014] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2012] [Revised: 06/18/2012] [Accepted: 06/20/2012] [Indexed: 11/22/2022]
Abstract
Residues Y₉₁-T₁₁₆ of ricin toxin's enzymatic subunit (RTA) constitute an immunodominant loop-helix-loop motif that is the target of two potent toxin neutralizing monoclonal antibodies (mAbs), PB10 and R70. To define the exact epitope(s) recognized by these mAbs, we affinity enriched from a phage-displayed peptide library 12 mers that bound one or both of these mAbs. We report that PB10 recognizes a distinct but overlapping epitope with R70, in which residues Q₉₈, E₁₀₂, T₁₀₅, and H₁₀₆ are central to mAb recognition.
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