Ricin toxin, an extremely potent and heat-stable toxin produced from the bean of the ubiquitous Ricinus communis (castor bean plant), has been categorized by the US Centers for Disease Control and Prevention (CDC) as a category B biothreat agent that is moderately easy to disseminate. Ricin has the potential to be used as an agent of biological warfare and bioterrorism. Therefore, there is a critical need for continued development of ricin countermeasures. A safe and effective prophylactic vaccine against ricin that was FDA approved for “at risk” individuals would be an important first step in assuring the availability of medical countermeasures against ricin. 1. Introduction In the aftermath of September 11, 2001, it has become increasingly clear that there is a need to enhance readiness against attack from both state sponsors and nonstate sponsors of bioterrorism. Ricin toxin, an extremely potent and heat-stable toxin produced from the bean of the Ricinus communis (castor bean plant) [1], has been categorized by the US Centers for Disease Control and Prevention (CDC) as a category B biothreat agent for biological warfare and bioterrorism [2]. In fact, according to Cookson and Nottingham, ricin was code named compound W and considered for weaponization during the US offensive Biological Warfare Program [3]. The US intelligence community believes that ricin was a component of the biowarfare program of the former Soviet Union, Iraq, and possibly other countries as well [4, 5]. Ricin toxin is relatively easy to produce and potentially lethal when delivered orally, intramuscularly, or through inhalation [4]. While the primary large-scale threat to US military personnel would be through powdered material that could be inhaled, ricin has been used successfully to assassinate individuals, to carry out suicide, and in 2003-2004, to terrorize US postal and Senate workers [4]. This paper reviews the rationale for development of ricin countermeasures and the progress toward achieving effective ricin countermeasures. 2. Background Ricin is a 65 kilodalton (kDa) polypeptide toxin comprised of two dissimilar polypeptide chains (an A-chain and a B-chain) held together by a disulfide bond [1, 4, 5]. The A-chain, ~32？kDa, targets the ribosome and is therefore a potent inhibitor of protein synthesis [4, 5]. Consequently, the A-chain has been classified as a ribosome-inactivating protein (RIP) [4, 5]. The B-chain, ~34？kDa, is a galactose or an N-acetylgalactosamine-binding lectin that attaches to cell-surface receptors [4, 5]. After binding and subsequent endocytosis,
References
[1]
G. A. Balint, “Ricin: the toxic protein of castor oil seeds,” Toxicology, vol. 2, no. 1, pp. 77–102, 1974.
[2]
Centers for Disease Control and Prevention, “Biological and chemical terrorism: strategic plan for preparedness and response,” Morbidity and Mortality Weekly Report, vol. 49, no. RR-4, pp. 1–14, 2000.
[3]
J. Cookson and J. Nottingham, A Survey of Chemical and Biological Warfare, vol. 6, Monthly Review Press, New York, NY, USA, 1969.
[4]
M. A. Poli, C. Roy, K. D. Huebner, D. R. Franz, and N. K. Jaax, “Ricin,” in Medical Aspects of Biological Warfare, Z. F. Dembek, Ed., pp. 323–335, Borden Institute, Washington, DC, USA, 2007.
[5]
J. Audi, M. Belson, M. Patel, J. Schier, and J. Osterloh, “Ricin poisoning a comprehensive review,” Journal of the American Medical Association, vol. 294, no. 18, pp. 2342–2351, 2005.
[6]
K. S. Eiklid, S. Olsnes, and A. Pihl, “Entry of lethal doses of abrin, ricin and modeccin into the cytosol of HeLa cells,” Experimental Cell Research, vol. 126, no. 2, pp. 321–326, 1980.
[7]
A. M. Soler-Rodriguez, J. W. Uhr, J. Richardson, and E. S. Vitetta, “The toxicity of chemically deglycosylated ricin A-chain in mice,” International Journal of Immunopharmacology, vol. 14, no. 2, pp. 281–291, 1992.
[8]
V. Radosavljevic and G. Belojevic, “A new model of bioterrorism risk assessment,” Biosecurity and Bioterrorism, vol. 7, no. 4, pp. 443–451, 2009.
[9]
L. J. Schep, W. A. Temple, G. A. Butt, and M. D. Beasley, “Ricin as a weapon of mass terror—separating fact from fiction,” Environment International, vol. 35, no. 8, pp. 1267–1271, 2009.
[10]
W. T. Porter, An Introduction to Physiology, The University Press, Cambridge, Mass, USA, 1906.
[11]
A. C. Cope, Ricin in Summary Technical Report of Division 9 on Chemical Warfare and Related Problems, chapter 12, Office of Scientific Research and Development, Washington, DC, USA, 1946, Parts I–II. National Defense Research Committee.
[12]
M. A. Poli, V. R. Rivera, M. L. M. Pitt, and P. Vogel, “Aerosolized specific antibody protects mice from lung injury associated with aerosolized ricin exposure,” Toxicon, vol. 33, p. 289, 1996.
[13]
M. A. Poli, V. R. Rivera, M. L. M. Pitt, and P. Vogel, “Aerosolized specific antibody protects mice from lung injury associated with aerosolized ricin exposure,” Toxicon, vol. 34, no. 9, pp. 1037–1044, 1996.
[14]
P. V. Lemley, P. Amanatides, D. Creasia, J. Ruvo, A. O’Neill, and D. C. Stafford, “Chicken antitoxin neutralizes ricin in vitro and in vivo,” Toxicon, vol. 31, p. 527, 1993.
[15]
P. V. Lemley and D. C. Wright, “Active immunization after passive monoclonal antibody and ricin toxin challenge,” Toxicon, vol. 30, p. 531, 1992.
[16]
P. V. Lemley, P. Amanatides, and D. C. Wright, “Identification and characterization of a monoclonal antibody that neutralizes ricin toxicity in vitro and in vivo,” Hybridoma, vol. 13, no. 5, pp. 417–421, 1994.
[17]
P. V. Lemley and D. C. Wright, “Mice are actively immunized after passive monoclonal antibody prophylaxis and ricin toxin challenge,” Immunology, vol. 76, no. 3, pp. 511–513, 1992.
[18]
A. Assaad, J. Hewetson, O. Parker, et al., “A ricin toxoid attenuates acute pulmonary toxicity and improves survival in rats exposed to a lethal dose of ricin aerosol,” Toxicon, vol. 33, p. 277, 1995.
[19]
J. F. Hewetson, V. R. Rivera, P. V. Lemley, M. L. Pitt, D. A. Creasia, and W. L. Thompson, “A formalinized toxoid for protection of mice from inhaled ricin,” Vaccine Research, vol. 4, no. 4, pp. 179–187, 1995.
[20]
R. B. Reisler, “Development and pre-clinical evaluation of a recombitant ricin vaccine (RVEc),” in Proceedings of the 9th ASM Biodefense and Emerging Diseases Research Meeting, Poster 210 (H), Washington, DC, USA, February 2011.
[21]
J. F. Hewetson, et al., “Immune response and protection of rats and mice from ricin aerosol exposure after vaccination with deglycosylated ricin A chain,” Fundamental and Applied Toxicology, vol. 30, supplement, article 59, 1996.
[22]
P. V. Lemley, D. A. Creasia, M. Plesha, D. Walters, and D. O’Neill, “Ricin sub-unit vaccination in mice and protection from challenge,” Toxicon, vol. 32, pp. 545–546, 1994.
[23]
J. E. Smallshaw, A. Firan, J. R. Fulmer, S. L. Ruback, V. Ghetie, and E. S. Vitetta, “A novel recombinant vaccine which protects mice against ricin intoxication,” Vaccine, vol. 20, no. 27-28, pp. 3422–3427, 2002.
[24]
J. E. Smallshaw, J. A. Richardson, S. Pincus, J. Schindler, and E. S. Vitetta, “Preclinical toxicity and efficacy testing of RiVax, a recombinant protein vaccine against ricin,” Vaccine, vol. 23, no. 39, pp. 4775–4784, 2005.
[25]
E. S. Vitetta, J. E. Smallshaw, E. Coleman et al., “A pilot clinical trial of a recombinant ricin vaccine in normal humans,” Proceedings of the National Academy of Sciences of the United States of America, vol. 103, no. 7, pp. 2268–2273, 2006.
[26]
J. E. Smallshaw and E. S. Vitetta, “A lyophilized formulation of RiVax, a recombinant ricin subunit vaccine, retains immunogenicity,” Vaccine, vol. 28, no. 12, pp. 2428–2435, 2010.
[27]
P. S. Marconescu, J. E. Smallshaw, L. M. Pop, S. L. Ruback, and E. S. Vitetta, “Intradermal administration of RiVax protects mice from mucosal and systemic ricin intoxication,” Vaccine, vol. 28, no. 32, pp. 5315–5322, 2010.
[28]
Phase 1B Study of RiVax. ClinicalTrials.gov, 2011http://www.clinicaltrials.gov/ct2/show/NCT00812071?term=rivax&rank=1.
M. A. Olson, J. H. Carra, V. Roxas-Duncan, R. W. Wannemacher, L. A. Smith, and C. B. Millard, “Finding a new vaccine in the ricin protein fold,” Protein Engineering, Design and Selection, vol. 17, no. 4, pp. 391–397, 2004.
[31]
J. H. Carra, R. W. Wannemacher, R. F. Tammariello et al., “Improved formulation of a recombinant ricin A-chain vaccine increases its stability and effective antigenicity,” Vaccine, vol. 25, no. 21, pp. 4149–4158, 2007.
[32]
M. M. Meagher, J. G. Seravalli, S. T. Swanson, et al., “Process development and cGMP manufacturing of a recombinant ricin vaccine: an effective and stable recombinant ricin a-chain vaccine-RVEc,” Biotechnology Progress, vol. 27, no. 4, p. 1036, 2011.
[33]
D. E. McLain, T. L. Horn, C. J. Detrisac, C. Y. Lindsey, and L. A. Smith, “Progress in biological threat agent vaccine development: a repeat-dose toxicity study of a recombinant ricin toxin A-chain (rRTA) 1-33/44-198 vaccine (RVEc) in male and female New Zealand white rabbits,” International Journal of Toxicology, vol. 30, no. 2, pp. 143–152, 2011.
[34]
A. Porter, G. Phillips, L. Smith, et al., “Evaluation of a ricin vaccine candidate (RVEc) for human toxicity using an in vitro vascular leak assay,” Toxicon, vol. 58, no. 1, pp. 68–75, 2011.
[35]
RVEc Phase I Human Clinical Trial, 2011, http://www.usamriid.army.mil/newsroom.cfm.
[36]
Safety and Immunogenicity Study of Recombinant Ricin Toxin A-Chain Vaccine (RVEc), 2011, http://www.clinicaltrials.gov/ct2/show/NCT01317667?term=rvec&rank=1.
[37]
L. M. Neal, J. O'Hara, R. N. Brey, and N. J. Mantis, “A monoclonal immunoglobulin G antibody directed against an immunodominant linear epitope on the ricin A chain confers systemic and mucosal immunity to ricin,” Infection and Immunity, vol. 78, no. 1, pp. 552–561, 2010.
[38]
L. M. Neal, E. A. McCarthy, C. R. Morris, and N. J. Mantis, “Vaccine-induced intestinal immunity to ricin toxin in the absence of secretory IgA,” Vaccine, vol. 29, no. 4, pp. 681–689, 2011.
[39]
J. Prigent, L. Panigai, P. Lamourette et al., “Neutralising antibodies against Ricin Toxin,” Plos ONE, vol. 6, no. 5, Article ID e20166, 2011.
[40]
B. Stechmann, S. K. Bai, E. Gobbo et al., “Inhibition of retrograde transport protects mice from lethal ricin challenge,” Cell, vol. 141, no. 2, pp. 231–242, 2010.
[41]
P. G. Wahome, J. D. Robertus, and N. J. Mantis, “Small-molecule inhibitors of ricin and shiga toxins,” Current Topics in Microbiology and Immunology, vol. 357, pp. 179–207, 2012.
[42]
V. St. Georgiev, “National institute of allergy and infectious diseases,” in Impact on Global Health, vol. 2, pp. 274–277, Humana Press, New York, NY, USA, 2009.
