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Abstract
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The paradigm of antivirulence
therapy dictates that bacterial pathogens
are specifically disarmed but not killed by neutralizing their virulence
factors. Clearance of the invading pathogen by the immune system is
promoted. As compared to antibiotics, the pathogen-selective antivirulence
drugs hold promise to minimize collateral damage to the beneficial
microbiome. Also, selective pressure for resistance is expected to
be lower because bacterial viability is not directly affected. Antivirulence
drugs are being developed for stand-alone prophylactic and therapeutic
treatments but also for combinatorial use with antibiotics. This Review
focuses on drug modalities that target bacterial exotoxins after the
secretion or release-upon-lysis. Exotoxins have a significant and
sometimes the primary role as the disease-causing virulence factor,
and thereby they are attractive targets for drug development. We describe
the key pre-clinical and clinical trial data that have led to the
approval of currently used exotoxin-targeted drugs, namely the monoclonal
antibodies bezlotoxumab (toxin B/TcdB, Clostridioides difficile), raxibacumab (anthrax toxin, Bacillus anthracis), and obiltoxaximab (anthrax toxin, Bacillus anthracis), but also to challenges with some of the promising leads. We also
highlight the recent developments in pre-clinical research sector
to develop exotoxin-targeted drug modalities, i.e., monoclonal antibodies,
antibody fragments, antibody mimetics, receptor analogs, neutralizing
scaffolds, dominant-negative mutants, and small molecules. We describe
how these exotoxin-targeted drug modalities work with high-resolution
structural knowledge and highlight their advantages and disadvantages
as antibiotic alternatives.
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Affiliation(s)
- Moona Sakari
- Institute of Biomedicine, Research Unit for Infection and Immunity, University of Turku, Kiinamyllynkatu 10, FI-20520 Turku, Finland
| | - Arttu Laisi
- Institute of Biomedicine, Research Unit for Infection and Immunity, University of Turku, Kiinamyllynkatu 10, FI-20520 Turku, Finland
| | - Arto T. Pulliainen
- Institute of Biomedicine, Research Unit for Infection and Immunity, University of Turku, Kiinamyllynkatu 10, FI-20520 Turku, Finland
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Couse Z, Cui X, Li Y, Moayeri M, Leppla S, Eichacker PQ. A Review of the Efficacy of FDA-Approved B. anthracis Anti-Toxin Agents When Combined with Antibiotic or Hemodynamic Support in Infection- or Toxin-Challenged Preclinical Models. Toxins (Basel) 2021; 13:53. [PMID: 33450877 PMCID: PMC7828353 DOI: 10.3390/toxins13010053] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Revised: 01/05/2021] [Accepted: 01/09/2021] [Indexed: 12/29/2022] Open
Abstract
Anti-toxin agents for severe B. anthracis infection will only be effective if they add to the benefit of the two mainstays of septic shock management, antibiotic therapy and titrated hemodynamic support. Both of these standard therapies could negate benefits related to anti-toxin treatment. At present, three anthrax anti-toxin antibody preparations have received US Food and Drug Administration (FDA) approval: Raxibacumab, Anthrax Immune Globulin Intravenous (AIGIV) and ETI-204. Each agent is directed at the protective antigen component of lethal and edema toxin. All three agents were compared to placebo in antibiotic-treated animal models of live B. anthracis infection, and Raxibacumab and AIGIV were compared to placebo when combined with standard hemodynamic support in a 96 h canine model of anthrax toxin-associated shock. However, only AIG has actually been administered to a group of infected patients, and this experience was not controlled and offers little insight into the efficacy of the agents. To provide a broader view of the potential effectiveness of these agents, this review examines the controlled preclinical experience either in antibiotic-treated B. anthracis models or in titrated hemodynamic-supported toxin-challenged canines. The strength and weaknesses of these preclinical experiences are discussed.
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Affiliation(s)
- Zoe Couse
- Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda, MD 20892, USA; (Z.C.); (X.C.); (Y.L.)
| | - Xizhong Cui
- Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda, MD 20892, USA; (Z.C.); (X.C.); (Y.L.)
| | - Yan Li
- Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda, MD 20892, USA; (Z.C.); (X.C.); (Y.L.)
| | - Mahtab Moayeri
- National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA; (M.M.); (S.L.)
| | - Stephen Leppla
- National Institutes of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892, USA; (M.M.); (S.L.)
| | - Peter Q. Eichacker
- Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda, MD 20892, USA; (Z.C.); (X.C.); (Y.L.)
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Tournier JN, Rougeaux C, Biot FV, Goossens PL. Questionable Efficacy of Therapeutic Antibodies in the Treatment of Anthrax. mSphere 2019; 4:e00282-19. [PMID: 31217301 PMCID: PMC6584371 DOI: 10.1128/msphere.00282-19] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Inhalational anthrax caused by Bacillus anthracis, a spore-forming Gram-positive bacterium, is a highly lethal infection. Antibodies targeting the protective antigen (PA) binding component of the toxins have recently been authorized as an adjunct to antibiotics, although no conclusive evidence demonstrates that anthrax antitoxin therapy has any significant benefit. We discuss here the rational basis of anti-PA development regarding the pathogenesis of the disease. We argue that inductive reasoning may induce therapeutic bias. We identified anthrax animal model analysis as another bias. Further studies are needed to assess the benefit of anti-PA antibodies in the treatment of inhalational anthrax, while a clearer consensus should be established around what evidence should be proven in an anthrax model.
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Affiliation(s)
- Jean-Nicolas Tournier
- Institut de Recherche Biomédicale des Armées, Bacteriology, Anti-infectious Biotherapies, and Immunity Unit, Brétigny-sur-Orge, France
- Institut Pasteur, Viral Genomics and Vaccination Unit, CNRS UMR-3569, Paris, France
- National Reference Center for Anthrax (CNR-LE Charbon), Brétigny-sur-Orge, France
- Ecole du Val-de-Grâce, Paris, France
| | - Clémence Rougeaux
- Institut de Recherche Biomédicale des Armées, Bacteriology, Anti-infectious Biotherapies, and Immunity Unit, Brétigny-sur-Orge, France
| | - Fabrice V Biot
- Institut de Recherche Biomédicale des Armées, Bacteriology, Anti-infectious Biotherapies, and Immunity Unit, Brétigny-sur-Orge, France
- National Reference Center for Anthrax (CNR-LE Charbon), Brétigny-sur-Orge, France
| | - Pierre L Goossens
- Institut de Recherche Biomédicale des Armées, Bacteriology, Anti-infectious Biotherapies, and Immunity Unit, Brétigny-sur-Orge, France
- Institut Pasteur, Yersinia Unit, Paris, France
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Caldwell M, Hathcock T, Brock KV. Passive protection against anthrax in mice with plasma derived from horses hyper-immunized against Bacillus anthracis Sterne strain. PeerJ 2017; 5:e3907. [PMID: 29259839 PMCID: PMC5733894 DOI: 10.7717/peerj.3907] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Accepted: 09/19/2017] [Indexed: 11/20/2022] Open
Abstract
In this study, equine source polyclonal anti-Bacillus anthracis immunoglobulins were generated and utilized to demonstrate passive protection of mice in a lethal challenge assay. Four horses were hyper-immunized with B. anthracis Sterne strain for approximately one year. The geometric mean anti-PA titer in the horses at maximal response following immunization was 1:77,936 (Log2 mean titer 16.25, SEM ± 0.25 95% CI [15.5 -17.0]). The geometric mean neutralizing titer at maximal response was 1:128 (Log2 mean titer 7, SEM ± 0.0, 95% CI 7). Treatment with hyper-immune plasma or purified immunoglobulins was successful in passively protecting A/J mice from a lethal B. anthracis Sterne strain challenge. The treatment of mice with hyper-immune plasma at time 0 h and 24 h post-infection had no effect on survival, but did significantly increase mean time to death (p < 0.0001). Mice treated with purified immunoglobulins at time 0 h and 24 h post-infection in showed significant increase in survival rate (p < 0.001). Bacterial loads in lung, liver and spleen tissue were also assessed and were not significantly different in mice treated with hyper-immune plasma from placebo treated control mice. Mice treated with purified antibodies demonstrated mean colony forming units/gram tissue fourfold less than mice receiving placebo treatment (p < 0.0001). Immunotherapeutics harvested from horses immunized against B. anthracis Sterne strain represent a rapidly induced, inexpensive and effective expansion to the arsenal of treatments against anthrax.
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Affiliation(s)
- Marc Caldwell
- Department of Pathobiology, Auburn University, Auburn, AL, United States of America
| | - Terri Hathcock
- Department of Pathobiology, Auburn University, Auburn, AL, United States of America
| | - Kenny V. Brock
- Edward Via College of Osteopathic Medicine, Auburn University, Auburn, AL, United States of America
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Anthrax immune globulin improves hemodynamics and survival during B. anthracis toxin-induced shock in canines receiving titrated fluid and vasopressor support. Intensive Care Med Exp 2017; 5:48. [PMID: 29058092 PMCID: PMC5651533 DOI: 10.1186/s40635-017-0159-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2017] [Accepted: 09/22/2017] [Indexed: 11/10/2022] Open
Abstract
Background Although anthrax immune globulin (AIG) improved survival in antibiotic-treated Bacillus anthracis-challenged animal models, whether it adds to the benefit of conventional hemodynamic support for B. anthracis toxin-associated shock is unknown. Methods We therefore tested AIG in sedated, mechanically ventilated canines challenged with 24-h B. anthracis lethal and edema toxin infusions and supported for 96 h with a previously demonstrated protective regimen of titrated normal saline and norepinephrine. Results Compared to controls, proportional survival (%) was increased with AIG treatment started 4 h before (33 vs. 100%, n = 6 each) or 2 h (17 vs. 86%, n = 6 and 7 respectively) or 5 h (0 vs. 67%, n = 3 each) after the start of toxin (p ≤ 0.05) and overall [3 survivors of 15 controls (20%) vs. 14 of 16 AIG animals (88%); p = 0.006]. Averaged across treatment times, AIG increased blood pressure at 48 h and decreased norepinephrine requirements at 72 h (p ≤ 0.02), increased left ventricular ejection fraction at 48 and 72 h (p ≤ 0.02), and increased urine output and decreased net fluid balance at 72 and 96 h (p ≤ 0.04). AIG also reduced acidosis and renal and hepatic injury markers between 24 and 96 h. Conclusions These findings further support AIG’s potential benefit for patients with B. anthracis infection and developing toxin-associated shock. Electronic supplementary material The online version of this article (10.1186/s40635-017-0159-9) contains supplementary material, which is available to authorized users.
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Suffredini DA, Li Y, Xu W, Moayeri M, Leppla S, Fitz Y, Cui X, Eichacker PQ. Shock and lethality with anthrax edema toxin in rats are associated with reduced arterial responsiveness to phenylephrine and are reversed with adefovir. Am J Physiol Heart Circ Physiol 2017; 313:H946-H958. [PMID: 28887331 DOI: 10.1152/ajpheart.00285.2017] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Revised: 08/22/2017] [Accepted: 08/24/2017] [Indexed: 12/18/2022]
Abstract
Although edema toxin (ETx) and lethal toxin (LTx) contribute to Bacillus anthracis shock and lethality, the mechanisms underlying their cardiovascular effects are unclear. We have previously shown that ETx but not LTx inhibited phenylephrine-stimulated contraction of aortic rings prepared from healthy rats and that adefovir, a selective inhibitor of ETx cAMP production, blocked this effect. Here, we examined arterial function in rats that received 24-h ETx or LTx infusions. Compared with control rats, ETx reduced mean arterial pressure (MAP) and survival over 48 h (P ≤ 0.0003) and increased plasma cAMP at 4, 24, and 48 h (P < 0.0001) and nitric oxide (NO) at 24 and 48 h (P ≤ 0.01). Compared with control animals, at 24- and 48-h phenylephrine stimulation of aortic rings from ETx animals produced decreased maximal contractile force (MCF; P = 0.05 and 0.006) and in vivo phenylephrine infusion in ETx animals produced decreased proportional increases in MAP (P < 0.0001 and P = 0.05). In ETx-treated animals, compared with placebo-treated animals, adefovir treatment prevented all lethality (P = 0.01), increased MAP (P ≤ 0.0001), decreased plasma and aortic tissue cAMP at 24 and 48 h, respectively (P ≤ 0.03), and plasma NO at both times (P ≤ 0.004), and increased phenylephrine-stimulated increases in MCF in aortic rings and MAP in vivo at 48 h (P = 0.02). LTx decreased MAP and survival also, but it did not alter the response to phenylephrine of MCF in aortic rings prepared from LTx animals or of MAP in vivo. In conclusion, in rats, hypotension and lethality are associated with reduced arterial contractile function with ETx but not LTx and adefovir improves ETx-induced hypotension and lethality.NEW & NOTEWORTHY The most important aspects of the present study are the findings that 1) in vivo challenge with anthrax edema but not lethal toxin depresses arterial contractile function measured both ex vivo and in vivo and 2) adefovir inhibits the effects of edema toxin on arterial hypotension and improves survival with lethal dose of edema toxin challenge.
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Affiliation(s)
- Dante A Suffredini
- Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda, Maryland; and
| | - Yan Li
- Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda, Maryland; and
| | - Wanying Xu
- Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda, Maryland; and
| | - Mahtab Moayeri
- National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland
| | - Stephen Leppla
- National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland
| | - Yvonne Fitz
- Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda, Maryland; and
| | - Xizhong Cui
- Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda, Maryland; and
| | - Peter Q Eichacker
- Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda, Maryland; and
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Xu W, Ohanjandian L, Sun J, Cui X, Suffredini D, Li Y, Welsh J, Eichacker PQ. A systematic review and meta-analysis of preclinical trials testing anti-toxin therapies for B. anthracis infection: A need for more robust study designs and results. PLoS One 2017; 12:e0182879. [PMID: 28797061 PMCID: PMC5552191 DOI: 10.1371/journal.pone.0182879] [Citation(s) in RCA: 15] [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: 04/01/2017] [Accepted: 07/26/2017] [Indexed: 12/29/2022] Open
Abstract
BACKGROUND B. anthracis anti-toxin agents are approved and included in the Strategic National Stockpile based primarily on animal infection trials. However, in the only anthrax outbreak an approved anti-toxin agent was administered in, survival did not differ comparing recipients and non-recipients, although recipients appeared sicker. OBJECTIVE Employ a systematic review and meta-analysis to investigate preclinical studies supporting anthrax anti-toxin agents. DATA SOURCE PubMed, EMBASE, and Scopus. STUDY ELIGIBILITY Compared survival with an anti-toxin agent versus control in B. anthracis challenged, antibiotic treated animals. STUDY METHODS Examine model and study design and the effect of anti-toxin agents on relative risk of death(95%CI) (RR). RESULTS From 9 studies, 29 experiments were analyzed which included 4 species (748 animals) and 5 agents; LFI, AIG, AVP-21D9, Raxibacumab, and ETI-204. Only five experiments were blinded and no experiment included the cardiopulmonary support sick B. anthracis patients receive. Only one agent in a single un-blinded experiment reduced RR significantly [0.45(0.22,0.940]. However, in six studies testing an agent in more than one experiment in the same species, agents had consistent survival effects across experiments [I2 = 0, p≥0.55 in five and I2 = 42%, p = 0.16 in one]. Within each species, agents had effects on the side of benefit; in one study testing AVP-21D9 in mice [0.11(0.01,1.82)] or guinea pigs [0.70(0.48,1.03)]; across eight rabbit studies testing LFI, Raxibacumab, AIG or ETI-204 [0.62(0.45,0.87); I2 = 17.4%, p = 0.29]; and across three monkey studies testing Raxibacumab, AIG or ETI-204 [0.66(0.34,1.27); I2 = 25.3%, p = 0.26]. Across all agents and species, agents decreased RR [0.64(0.52,0.79); I2 = 5.3%, p = 0.39]. LIMITATIONS Incidence of selective reporting not identifiable. CONCLUSIONS Although overall significant, individually anti-toxin agents had weak beneficial effects. Lack of study blinding and relevant clinical therapies further weakened studies. Although difficult, preclinical studies with more robust designs and results are warranted to justify the resources necessary to maintain anti-toxin agents in national stockpiles.
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Affiliation(s)
- Wanying Xu
- Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Lernik Ohanjandian
- Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Junfeng Sun
- Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Xizhong Cui
- Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Dante Suffredini
- Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Yan Li
- Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Judith Welsh
- National Institutes of Health Library, National Institutes of Health, Bethesda, Maryland, United States of America
| | - Peter Q. Eichacker
- Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda, Maryland, United States of America
- * E-mail:
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Bacillus anthracis Edema Toxin Increases Fractional Free Water and Sodium Reabsorption in an Isolated Perfused Rat Kidney Model. Infect Immun 2017; 85:IAI.00264-17. [PMID: 28438974 DOI: 10.1128/iai.00264-17] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2017] [Accepted: 04/13/2017] [Indexed: 11/20/2022] Open
Abstract
Bacillus anthracis edema toxin (ET) consists of protective antigen (PA), necessary for host cell toxin uptake, and edema factor (EF), the toxic moiety which increases host cell cyclic AMP (cAMP). Since vasopressin stimulates renal water and sodium reabsorption via increased tubular cell cAMP levels, we hypothesized the ET would also do so. To test this hypothesis, we employed an isolated perfused rat kidney model. Kidneys were isolated and perfused with modified Krebs-Henseleit buffer. Perfusate and urine samples were obtained at baseline and every 10 min over 150 min following the addition of challenges with or without treatments to the perfusate. In kidneys perfused under constant flow or constant pressure, compared to PA challenge (n = 14 or 15 kidneys, respectively), ET (13 or 15 kidneys, respectively) progressively increased urine cAMP levels, water and sodium reabsorption, and urine osmolality and decreased urine output (P ≤ 0.04, except for sodium reabsorption under constant pressure [P = 0.17]). In ET-challenged kidneys, compared to placebo treatment, adefovir, an EF inhibitor, decreased urine cAMP levels, water and sodium reabsorption, and urine osmolality and increased urine output, while raxibacumab, a PA-directed monoclonal antibody (MAb), decreased urine cAMP levels, free water reabsorption, and urine osmolality and increased urine output (P ≤ 0.03 except for urine output with raxibacumab [P = 0.17]). Upon immunohistochemistry, aquaporin 2 was concentrated along the apical membrane of tubular cells with ET but not PA, and urine aquaporin 2 levels were higher with ET (5.52 ± 1.06 ng/ml versus 1.51 ± 0.44 ng/ml [means ± standard errors of the means {SEM}; P = 0.0001). Edema toxin has renal effects that could contribute to extravascular fluid collection characterizing anthrax infection clinically.
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