RARE DISEASE
Ricin poisoning
Ricin poisoning
Ricin poisoning
Drug discovery
5
drugs
With orphan designations
Overview
Ricin poisoning is a life-threatening toxidrome caused by exposure to ricin, a plant-derived toxin inhibiting cellular protein synthesis. Clinical manifestations depend on exposure route: inhalation (respiratory failure), ingestion (hemorrhagic gastroenteritis), or injection (organ failure). No antidote exists; treatment focuses on decontamination (activated charcoal, irrigation) and supportive care (mechanical ventilation, fluid resuscitation). Diagnosis relies on clinical history and ricinine detection in urine [1][4][12].
Therapies
Immediate decontamination (skin/eye irrigation, gastric lavage if ≤1 hr post-ingestion) [1][11]
Symptomatic management: IV fluids, vasopressors, mechanical ventilation, and anti-seizure medications [3][7][16]
Experimental approaches: Anti-ricin antibodies (preclinical), immunomodulators (e.g., dexamethasone) [3][8]
Categories: rare disorders due to toxic effects, rare hematological diseases
Research Papers
811 drug discovery papers about Ricin poisoning, with 3 first-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
811 drug discovery papers about Ricin poisoning, with 3 first-in-class emerging drug candidates forecasted to outperform the average preclinical success rate. Recent publications:
categories:
Small molecules
small molecules
2026-06-25 | Biophysical and Biochemical Assays for Screening Small Molecule Inhibitors Targeting Toxin-Ribosome Interactions.
Ribosome-inactivating proteins are a class of toxins that target eukaryotic ribosomes, inhibit protein synthesis, and ultimately induce cell death. Several of these toxins pose significant clinical and public health threats. Among these, ricin, derived from the castor bean plant (Ricinus communis), is a highly potent biotoxin with recognized bioterrorism potential. Other ribosome-inactivating proteins, including Shiga toxin produced by pathogenic Shigella and Escherichia coli, as well as mucoricin from Mucorales fungi, contribute to disease severity and can lead to life-threatening complications. Despite these risks, no approved therapeutics are currently available. The development of effective inhibitors depends on robust and well-defined strategies to identify and validate small molecules that disrupt toxin-ribosome interactions. Efforts to target the catalytic active site have met with limited success, largely due to its broad, shallow, and highly polar architecture, which is not conducive to high-affinity binding by drug-like molecules. In contrast, the ribosome-binding interface represents a more tractable target, as it is essential for toxin recruitment and offers more structurally defined and druggable features. Inhibitors targeting this interface can also exert allosteric effects by disrupting long-range conformational coupling between the ribosome-binding region and the active site, thereby attenuating catalytic activity without directly engaging the catalytic pocket. In this review, we compile and evaluate biophysical and biochemical assays for the discovery and characterization of small-molecule inhibitors that target toxin-ribosome interactions. We examine in vitro binding approaches, including surface plasmon resonance-based fragment screening and fluorescence anisotropy assays for ranking inhibitory activity. We further review biochemical and molecular assays that assess ribosome protection from toxin-mediated depurination, along with complementary cell-based assays that evaluate functional rescue in cellular systems. Collectively, this review consolidates current screening methodologies and highlights opportunities to refine assay strategies, thereby supporting the advancement of targeted therapeutics.
2026-03-02 | PROTAC-Mediated Ternary Complex Stability with Ricin Toxin A: A Computational Perspective.
Ricin is a potent toxin present in the seeds of the castor plant (Ricinus communis), which is widely distributed in tropical regions. To date, there are no approved antidotes or vaccines against ricin poisoning. Reported inhibitors have not yet achieved sufficient affinity, and vaccine candidates have shown limited efficacy, highlighting the need to explore alternative strategies for RTA neutralization. In this work, we performed a computational study to investigate the potential of using PROTACs (proteolysis-targeting chimeras) to induce the ubiquitination and subsequent proteasomal degradation of ricin. Specifically, we assessed the stability of RTA, the catalytic subunit of ricin, in complex with the E3 ligases VHL and CRBN, both widely employed in the PROTAC design. Several PROTAC candidates with distinct linkers were evaluated to identify linkers with greater potential to mediate the stable ternary complex formation between RTA and the ligases. Molecular docking and molecular dynamics simulations revealed three promising PROTACs, one targeting CRBN and two targeting VHL, as potential candidates for further in vitro validation. Overall, this study introduces PROTAC-mediated degradation as a novel and unexplored therapeutic strategy against ricin intoxication, laying the groundwork for future experimental investigations.
2025-08-28 | Ricin Toxicity to Intestinal Cells Leads to Multiple Cell Death Pathways Mediated by Oxidative Stress.
Ricin, a type 2 ribosome-inactivating protein, is a lethal toxin found in castor bean seeds. Although the systemic toxicity of ricin has been extensively studied, its localized effect on the gastrointestinal tract remains a critical concern, particularly in the case of oral ingestion. This study investigates the cytotoxic effects of ricin on human intestinal epithelial cell lines and its impact on epithelial barrier integrity. Ricin cytotoxicity was assessed on the intestinal-derived HT29 and Caco-2 cell lines using dose- and time-response assays, while the epithelial integrity was evaluated via Trans-Epithelial Electrical Resistance (TEER) measurements in Caco-2 monolayers. Cell death was determined through flow cytometry analysis, and the protective effects of cell death inhibitors and antioxidant scavengers were investigated on ricin-intoxicated cells. Ricin showed high cytotoxicity on HT29 and Caco-2 cells, with EC50 values in the nM range after 24-72 h of intoxication. Moreover, ricin strongly reduced TEER values in Caco-2 cells at 0.1-1 nM after 24 h of treatment. At a 1 nM concentration, ricin cytotoxicity can be significantly prevented by pre-incubating cells with the cell death inhibitors Z-VAD or necrostatin-1 and the antioxidant scavenger catalase, butylated hydroxyanisole or sodium pyruvate, demonstrating the involvement of apoptosis/necroptosis and oxidative stress in ricin cell death pathways and mechanisms.
2025-05-27 | TM9SF2 Maintains Golgi Integrity and Regulates Ricin-Induced Cytotoxicity.
TM9SF2 belongs to a family of highly conserved nonaspanin proteins, and has been frequently identified as one of the important host factors for a plethora of lethal pathogens and toxins in previous genome-wide screening studies. We reported herein a novel molecular mechanism of TM9SF2 in mediating the cytotoxicity of ricin, a type II ribosome-inactivating protein. We first showed that TM9SF2 displays a non-redundant requirement for ricin-induced cytotoxicity within the nonaspanin family. Then we found that genetic interference of TM9SF2 substantially affects/remodels intracellular cholesterol trafficking, which results in abnormal cholesterol accumulation in Golgi compartments and causes severe Golgi fragmentation. The disruption of Golgi integrity and network impedes the retrograde transport of ricin and thus attenuates ricin-induced cytotoxicity. We further verified this mechanism by pharmacological manipulation of cholesterol metabolism (e.g., by using A939572 and avasimibe, etc.), which well restores the integrity of the Golgi apparatus and reverses the ricin-resistant phenotype induced by TM9SF2 knockdown. Our finding provides new mechanistic insights into the pathology and toxicology of ricin and could potentially be applied to other ribosome-inactivating toxins.
2025-05-03 | Fibroblast EGFR signaling mediates ricin toxin-induced acute lung injury via EGR1/CXCL1 axis.
Ricin toxin (RT), a highly potent plant-derived toxin, represents a critical threat due to its capacity to induce fatal acute lung injury (ALI) upon inhalation. While the epidermal growth factor receptor (EGFR), a receptor tyrosine kinase predominantly expressed on epithelial cells and fibroblasts, regulates cellular processes such as growth, proliferation, differentiation and inflammation, its involvement in RT-induced ALI remains unexplored. This study investigates this relationship using a mouse model of ALI induced by aerosolized RT at a dose of 2.0 × LD50 (approximately 0.01 mg kg -1). The results demonstrate that damage to alveolar epithelial type II (AT2) cells leads to the release of heparin-binding epidermal growth factor-like growth factor (HB-EGF), which activates EGFR on fibroblasts, exacerbating lung injury pathology and reducing survival. Mechanistically, EGFR activation in fibroblasts induces the early growth response protein 1 (EGR1), which subsequently enhances chemokine C-X-C motif ligand 1 (CXCL1) secretion 24 h post-exposure, promoting neutrophil infiltration in the lung. RNA sequencing analysis corroborates these findings. Notably, pharmacological inhibition of EGFR phosphorylation using Erlotinib (ERL) significantly mitigates the inflammatory response in RT-induced ALI. These results not only illuminate the immune response in lung tissue but also highlight EGFR signaling in fibroblasts as a pivotal mediator of RT-induced ALI. This study identifies a novel therapeutic strategy targeting EGFR signaling in fibroblasts for the treatment of inflammatory lung diseases.
proteins
2024-06-14 | A fluorescence anisotropy-based competition assay to identify inhibitors against ricin and Shiga toxin ribosome interactions.
Ricin is one of the most toxic substances known and a type B biothreat agent. Shiga toxins (Stxs) produced by E. coli (STEC) and Shigella dysenteriae are foodborne pathogens. There is no effective therapy against ricin or STEC and there is an urgent need for inhibitors. Ricin toxin A subunit (RTA) and A1 subunit of Stx2a (Stx2A1) bind to the C-terminal domain (CTD) of the ribosomal P-stalk proteins to depurinate the sarcin/ricin loop. Modulation of toxin-ribosome interactions has not been explored as a strategy for inhibition. Therefore, development of assays that detect inhibitors targeting toxin-ribosome interactions remains a critical need. Here we describe a fluorescence anisotropy (FA)-based competitive binding assay using a BODIPY-TMR labeled 11-mer peptide (P11) derived from the P-stalk CTD to measure the binding affinity of peptides ranging from 3 to 11 amino acids for the P-stalk pocket of RTA and Stx2A1. Comparison of the affinity with the surface plasmon resonance (SPR) assay indicated that although the rank order was the same by both methods, the FA assay could differentiate better between peptides that show nonspecific interactions by SPR. The FA assay detects only interactions that compete with the labeled P11 and can validate inhibitor specificity and mechanism of action.
2022-05-02 | Gdf15 deletion exacerbates acute lung injuries induced by intratracheal inoculation of aerosolized ricin in mice.
Ricin toxin (RT) is a potent toxin derived from castor beans and has a high risk of mortality following inhalation-induced acute lung injury (ALI). Growth differentiation factor 15 (GDF15) is a member of the transforming growth factor β superfamily and acts as a protective effect in diverse inflammatory diseases. Yet, the role of GDF15 in ALI has not been evaluated. In this study, we investigated the intrinsic role of Gdf15 in ALI induced by intratracheal inoculation of a 1.5 × LD50 (lethal dose for 50%) of aerosolized RT in Gdf15 knockout (KO) mice compared to wild-type (WT) mice. In this model, Gdf15 deletion significantly increased pathology in lung tissues for RT-induced ALI in mice, led to significantly decreased body weights and survival rates and increased expression of inflammatory-related cytokine and chemokine levels at 24 and 72 h post-exposure. Infiltration of myeloid cells in lung tissue were quantified using flow cytometry. Although a similar infiltration pattern of inflammatory cells was observed in Gdf15 KO and WT groups, Gdf15 KO mice had elevated levels of neutrophils and decreased levels of Ly6Clo monocytes (cells with distinct destructive and protective roles, respectively) in the early stage of ALI. Gene expression profiles revealed similar effects as observed through RNA-seq. Bioinformatics analysis confirmed that pro-inflammatory signaling pathways were activated and the expression of inflammatory genes was significantly up-regulated after RT exposure compared to the corresponding baseline control in Gdf15 KO and WT mice. Compared to WT mice, inflammatory genes were more pronounced in Gdf15 KO groups after RT exposure. To our knowledge, this study presents the first research to systematically evaluate the role of Gdf15 in RT-induced ALI. These results collectively uncovered an immune response signature in lung tissues and reveal a critical role of Gdf15 in this ALI mice model. Our findings expose novel opportunities to investigate the contribution of GDF15 for the treatment of lung inflammatory diseases.
2021-12-21 | Lyophyllin, a Mushroom Protein from the Peptidase M35 Superfamily Is an RNA N-Glycosidase.
Ribosome-inactivating proteins (RIPs) hydrolyze the N-glycosidic bond and depurinate a specific adenine residue (A-4324 in rat 28S ribosomal RNA, rRNA) in the conserved α-sarcin/ricin loop (α-SRL) of rRNA. In this study, we have purified and characterized lyophyllin, an unconventional RIP from Lyophyllum shimeji, an edible mushroom. The protein resembles peptidase M35 domain of peptidyl-Lys metalloendopeptidases. Nevertheless, protein either from the mushroom or in recombinant form possessed N-glycosidase and protein synthesis inhibitory activities. A homology model of lyophyllin was constructed. It was found that the zinc binding pocket of this protein resembles the catalytic cleft of a classical RIP, with key amino acids that interact with the adenine substrate in the appropriate positions. Mutational studies showed that E122 may play a role in stabilizing the positively charged oxocarbenium ion and H121 for protonating N-3 of adenine. The tyrosine residues Y137 and Y104 may be used for stacking the target adenine ring. This work first shows a protein in the peptidase M35 superfamily based on conserved domain search possessing N-glycosidase activity.
2021-11-16 | Intramuscular Exposure to a Lethal Dose of Ricin Toxin Leads to Endothelial Glycocalyx Shedding and Microvascular Flow Abnormality in Mice and Swine
Ricin toxin isolated from the castor bean (Ricinus communis) is one of the most potent and lethal molecules known. While the pathophysiology and clinical consequences of ricin poisoning by the parenteral route, i.e., intramuscular penetration, have been described recently in various animal models, the preceding mechanism underlying the clinical manifestations of systemic ricin poisoning has not been completely defined. Here, we show that following intramuscular administration, ricin bound preferentially to the vasculature in both mice and swine, leading to coagulopathy and widespread hemorrhages. Increased levels of circulating VEGF and decreased expression of vascular VE-cadherin caused blood vessel impairment, thereby promoting hyperpermeability in various organs. Elevated levels of soluble heparan sulfate, hyaluronic acid and syndecan-1 were measured in blood samples following ricin intoxication, indicating that the vascular glycocalyx of both mice and swine underwent extensive damage. Finally, by using side-stream dark field intravital microscopy imaging, we determined that ricin poisoning leads to microvasculature malfunctioning, as manifested by aberrant blood flow and a significant decrease in the number of diffused microvessels. These findings, which suggest that glycocalyx shedding and microcirculation dysfunction play a major role in the pathology of systemic ricin poisoning, may serve for the formulation of specifically tailored therapies for treating parenteral ricin intoxication.
2021-09-27 | Phosphorylation of the conserved C-terminal domain of ribosomal P-proteins impairs the mode of interaction with plant toxins.
The ribosome is subjected to post-translational modifications, including phosphorylation, that affect its biological activity. Among ribosomal elements, the P-proteins undergo phosphorylation within the C terminus, the element which interacts with trGTPases or ribosome-inactivating proteins (RIPs); however, the role of phosphorylation has never been elucidated. Here, we probed the function of phosphorylation on the interaction of P-proteins with RIPs using the ribosomal P1-P2 dimer. We determined the kinetic parameters of the interaction with the toxins using biolayer interferometry and microscale thermophoresis. The results present the first mechanistic insight into the function of P-protein phosphorylation, showing that introduction of a negative charge into the C terminus of P1-P2 proteins promotes α-helix formation and decreases the affinity of the P-proteins for the RIPs.
antibodies
2026-01-21 | Intoxication of cattle by Ricinus communis in northwestern Argentina.
Here we describe 2 outbreaks of intoxication by Ricinus communis in cattle in Argentina. In outbreak 1, in 2010, 180 heifers were introduced to a paddock heavily invaded by R. communis. Thirty-two animals developed watery diarrhea, and 6 of them were drooling, and had constant chewing motions, blindness, incoordination, depression, and prostration. Four affected animals died 12-14 h after the onset of clinical signs; another died 4 d later. The surviving 27 animals were removed from the paddock and recovered. At autopsy, several organs were congested and hemorrhagic, and abundant pericarps, leaves, and seeds of R. communis were found in the rumen content. The main microscopic lesion was acute, diffuse, superficial necrotizing gastroenteritis, and intestinal congestion and hemorrhage. In outbreak 2, in 2013, severe neurologic signs were observed in 12 of 300 cows after being introduced into a corn paddock without grain production that had been severely invaded by R. communis. Affected animals were excited and had tremors, drooling, incoordination, and prostration. The herd was immediately transferred to another paddock, and all affected cows recovered without treatment. In outbreak 1, the clinical signs and lesions were characteristic of simultaneous poisoning by R. communis fruits, which contain ricin and cause mainly digestive signs and lesions, and by leaves and pericarps, which contain ricinine and cause nervous signs. In outbreak 2, clinical signs and the recovery of the animals suggest that the intoxication was caused by ricinine, which is present in the leaves of R. communis.
2023-02-28 | Medical Countermeasures against Ricin Intoxication.
Ricin toxin is a disulfide-linked glycoprotein (AB toxin) comprising one enzymatic A chain (RTA) and one cell-binding B chain (RTB) contained in the castor bean, a Ricinus species. Ricin inhibits peptide chain elongation via disruption of the binding between elongation factors and ribosomes, resulting in apoptosis, inflammation, oxidative stress, and DNA damage, in addition to the classically known rRNA damage. Ricin has been used in traditional medicine throughout the world since prehistoric times. Because ricin toxin is highly toxic and can be readily extracted from beans, it could be used as a bioweapon (CDC B-list). Due to its extreme lethality and potential use as a biological weapon, ricin toxin remains a global public health concern requiring specific countermeasures. Currently, no specific treatment for ricin intoxication is available. This review focuses on the drugs under development. In particular, some examples are reviewed to demonstrate the proof of concept of antibody-based therapy. Chemical inhibitors, small proteins, and vaccines can serve as alternatives to antibodies or may be used in combination with antibodies.
2022-06-14 | Ricin toxin and its neutralizing antibodies: A review.
Ricin toxin (RT) belongs to the ribosome-inactivating protein (RIP) family of toxins and is considered to be a moderate threat by the US Center of Disease Control and Prevention (CDC). RT poses a great potential threat to the public, but there has been a lack of effective treatment options so far. Over the past few decades, researches on the prevention and treatment of RT poisoning have been investigated, among which neutralizing antibodies targeting RT specifically have always been a research hotspot. In this review, we have summarized the mechanism of action of RT, the research results and the design strategies of RT neutralizing antibodies, and discussed the key issues in the development of RT neutralizing antibody researches.
2022-04-26 | Single-domain antibodies neutralize ricin toxin intracellularly by blocking access to ribosomal P-stalk proteins.
During ricin intoxication in mammalian cells, ricin's enzymatic (RTA) and binding (RTB) subunits disassociate in the endoplasmic reticulum. RTA is then translocated into the cytoplasm where, by virtue of its ability to depurinate a conserved residue within the sarcin-ricin loop (SRL) of 28S rRNA, it functions as a ribosome-inactivating protein. It has been proposed that recruitment of RTA to the SRL is facilitated by ribosomal P-stalk proteins, whose C-terminal domains interact with a cavity on RTA normally masked by RTB; however, evidence that this interaction is critical for RTA activity within cells is lacking. Here, we characterized a collection of single-domain antibodies (VHHs) whose epitopes overlap with the P-stalk binding pocket on RTA. The crystal structures of three such VHHs (V9E1, V9F9, and V9B2) in complex with RTA revealed not only occlusion of the ribosomal P-stalk binding pocket but also structural mimicry of C-terminal domain peptides by complementarity-determining region 3. In vitro assays confirmed that these VHHs block RTA-P-stalk peptide interactions and protect ribosomes from depurination. Moreover, when expressed as "intrabodies," these VHHs rendered cells resistant to ricin intoxication. One VHH (V9F6), whose epitope was structurally determined to be immediately adjacent to the P-stalk binding pocket, was unable to neutralize ricin within cells or protect ribosomes from RTA in vitro. These findings are consistent with the recruitment of RTA to the SRL by ribosomal P-stalk proteins as a requisite event in ricin-induced ribosome inactivation.
2021-09-20 | Structural Analysis of Toxin-Neutralizing, Single-Domain Antibodies that Bridge Ricin's A-B Subunit Interface.
Ricin toxin kills mammalian cells with notorious efficiency. The toxin's B subunit (RTB) is a Gal/GalNAc-specific lectin that attaches to cell surfaces and promotes retrograde transport of ricin's A subunit (RTA) to the trans Golgi network (TGN) and endoplasmic reticulum (ER). RTA is liberated from RTB in the ER and translocated into the cell cytoplasm, where it functions as a ribosome-inactivating protein. While antibodies against ricin's individual subunits have been reported, we now describe seven alpaca-derived, single-domain antibodies (VHHs) that span the RTA-RTB interface, including four Tier 1 VHHs with IC50 values <1 nM. Crystal structures of each VHH bound to native ricin holotoxin revealed three different binding modes, based on contact with RTA's F-G loop (mode 1), RTB's subdomain 2γ (mode 2) or both (mode 3). VHHs in modes 2 and 3 were highly effective at blocking ricin attachment to HeLa cells and immobilized asialofetuin, due to framework residues (FR3) that occupied the 2γ Gal/GalNAc-binding pocket and mimic ligand. The four Tier 1 VHHs also interfered with intracellular functions of RTB, as they neutralized ricin in a post-attachment cytotoxicity assay (e.g., the toxin was bound to cell surfaces before antibody addition) and reduced the efficiency of toxin transport to the TGN. We conclude that the RTA-RTB interface is a target of potent toxin-neutralizing antibodies that interfere with both extracellular and intracellular events in ricin's cytotoxic pathway.
oligonucleotides
2026-03-29 | Advancing subunit vaccine efficacy against ricin toxin with a novel DNA hydrogel adjuvant tandem assembly by CpG motifs.
The development of effective countermeasures against ricin toxin, a potent biological threat, remains a pressing public health challenge. Subunit vaccines based on the ricin toxin A subunit offer a favorable safety profile but often suffer from limited immunogenicity, necessitating advanced adjuvants to elicit protective immunity. Here, we report a novel injectable CpG-motif-based hydrogel that serves as both adjuvant and delivery vehicle for a mutated and truncated RTA antigen. This CpG-gel adjuvant, synthesized via rolling circle amplification, incorporated with guanine-rich sequences that could self-assemble into stable G-quadruplex networks to form a structurally robust scaffold with flower-like microarchitecture. Notably, the CpG-gel significantly outperformed conventional CpG 1826 by enhancing antigen persistence and promoting sustained immune activation, leading to more potent and durable humoral and cellular responses. In murine studies, the CpG-gel elicited robust high titers of antigen-specific IgG antibodies, achieved complete protection against lethal-dose RT challenge. These results demonstrated that the CpG-gel adjuvant could significantly enhances the immunogenicity of subunit vaccines, highlighting its potential for broad implications for next-generation vaccine development.
2026-03-27 | An innovative ricin-degrading antidote based on aptamer-autophagy-tethering compound strategy.
Ricin is classified as a Category B biothreat agent due to its high toxicity and wide availability, posing a substantial threat to public security. Currently, no effective antidotes have been approved, and the development of medical countermeasures-including small-molecule inhibitors, antibodies, and vaccines-face substantial challenges. In this study, we designed innovative ricin-degrading antidotes based on the aptamer-autophagosome-tethering compound (aptamer-ATTEC) strategy. A series of aptamer-ATTEC chimeras were constructed by conjugating a high-affinity ricin aptamer with an LC3-recruiting moiety via click chemistry. The optimal compound, designated DP3-D-B0, exhibited potent anti-ricin efficacy at molecular, cellular, and animal levels. Experimental results confirmed that DP3-D-B0 mediated the formation of an intracellular ternary complex (LC3-ATTEC-ricin) that hijacks the autophagy machinery for lysosome-mediated degradation. Moreover, DP3-D-B0 was found can partially blocks ricin uptake extracellularly when administered simultaneously. This work broadens the application scope of ATTEC technology and provides a novel strategy for the targeted degradation of exogenous toxins, thus advancing the development of therapeutics against biothreat agents.
2026-01-14 | Design and evaluation of DNA aptamers with "stem-loop-chain" structures for spectrum neutralization of ricin and abrin.
Ricin and abrin are classified as Type II ribosome-inactivating proteins (RIPs) toxins, posing significant potential threats to public safety and in bioterrorism incidents. They exert catalytic N-glycosidase activity by specifically recognizing highly conserved structural domains within the α-sarcin/ricin loop (SRL) of ribosomal rRNA, consequently inhibiting protein synthesis and ultimately inducing cell death. Currently, no licensed drugs are available for Type II RIPs, making the development of antidotes with broad-spectrum activity highly imperative. In this study, we engineered a series of DNA aptamers featuring "stem-loop-chain" structures, designed to mimic the natural substrate, enabling spectrum inhibition of ricin and abrin toxins. Results indicated that most aptamers effectively inhibited the activities of ricin and abrin in both molecular and cellular screening models. The optimal aptamer, C-1, was demonstrated to be efficiently internalized into cells and had high-affinity binding to both toxins. In the cell poisoning protection assays, C-1 exhibited activity with IC50 values of 80.2 ± 26.8 nM against ricin and 282.8 ± 19.5 nM against abrin. In the ICR mouse model, the survival rate of C-1 group was significantly higher than that of the control group. This work provides novel aptamer-based lead compounds with potential broad-spectrum inhibitory activity and establishes a technical framework for developing therapeutics against other biological toxins.
2025-04-21 | Nanostructured aptasensors for ricin detection and tumor therapy: exploring aptamer-protein interactions and conformational stability in biological complexities.
Aptamers are distinctive single-stranded oligonucleotides derived through in vitro evolution, and exhibit exceptional ability in binding to target proteins. Structural modifications of aptamers can profoundly regulate their interactions with proteins, thereby influencing associated cellular behavior. Recent research focused on modulating aptamer-protein interaction in complex biological environments to regulate various biological processes. However, in such crowded conditions, aptamer conformation and stability are susceptible to nuclease degradation, which can impair stable binding to target. Ricin is recognized as a significant biological toxin protein, distinguished by its widespread availability, remarkable dissemination, and resilience including wide pH tolerance, remarkable thermostability, and solubility. RTA is an enzymatic subunit of ricin, that can inactivate approximately 2000 ribosomes per minute, rapidly halting protein synthesis, making it a powerful candidate for tumor therapy. By leveraging the potent cytotoxicity of ricin, coupled with the targeting precision of aptamers and the versatility of nanomaterials, a powerful approach emerges for both targeted tumor therapy and highly sensitive detection of ricin. Although there have been some insightful reports on aptamers applied in ricin detection, a systematic discussion remains limited. In this context, we provide an in-depth overview of techniques used to analyze aptamer-ricin interactions and explore the potential of ricin-aptamer interactions in clinical diagnosis.
2024-11-27 | Development of a Graphene Oxide-Based Aptamer Nanoarray for Improved Neutralization and Protection Effects Against Ricin.
Background/Objectives: Ricin's high toxicity and potential as a bioweapon underscore the need for effective antidotes. Monoclonal antibodies, though effective, are limited by complex production. This study aimed to develop a graphene oxide-based aptamer nanoarray (ARMAN) for improved neutralization and protection against ricin. Methods: High-affinity aptamers targeting ricin's RTA and RTB subunits were selected using SELEX technology and conjugated to graphene oxide (GO) via click chemistry. ARMAN's characteristics, including morphology, stability, and biosecurity, were assessed. Its performance was evaluated in terms of affinity for ricin, neutralization capacity, and therapeutic effects in cellular assays and a mouse model of ricin poisoning. Results: ARMAN exhibited a uniform morphology with an average particle size of 217 nm and demonstrated significantly enhanced affinity for ricin compared to free aptamers. ARMAN showed rapid and effective neutralization ability, significantly increasing cell viability in BEAS-2B, GES-1, and HL7702 cell lines exposed to ricin. In vivo, ARMAN treatment led to a notable prolongation of survival in ricin-poisoned mice, highlighting its potential for both pre- and post-exposure treatment. These findings indicate that ARMAN not only neutralizes ricin effectively but also provides a therapeutic window for treatment. Conclusions: ARMAN's superior binding affinity, serum stability, biocompatibility, and broad therapeutic efficacy make it a promising new antidote against ricin poisoning. This study's findings represent significant progress in the development of rapid-response antidotes, with ARMAN offering a potential solution for both military and civilian emergency response scenarios.
other
2025-02-13 | The use of adeno-associated vírus-based gene therapy to achieve long-term expression of recombinant neutralizing antibody against ricin.
Ricin is a highly toxic plant protein for which there are no specific antidotes. Current prophylactic and emergency treatments for ricin intoxication are limited by the need for prior vaccination and the short half-life of antibody drugs in the circulation. To address these limitations, we developed a novel immunotherapeutic strategy using adeno-associated virus (AAV) gene transfer to achieve prolonged systemic serum levels of immunoglobulins to ricin. In this study, a single administration of rAAV was used to deliver protein immunotherapeutics, and its efficacy in protecting mice against lethal doses of ricin was investigated. The results revealed that the single administration of rAAV three days prior to ricin exposure effectively protected mice from lethal doses of ricin. Remarkably, this protection was sustained for up to 90 days after AAV injection, demonstrating long-term efficacy. Overall, our findings suggest that the rAAV-mediated approach holds promise for both early and long-term prevention of ricin intoxication. The favorable safety profile of this system and its potential for the development of novel ricin antibody therapeutics make it a noteworthy candidate for further exploration and development in the field.
2019-07-03 | Bio-detoxification of ricin in castor bean (Ricinus communis L.) seeds.
Ricin is a highly toxic ribosome-inactivating lectin occurring in the seeds of castor bean (Ricinus communis L.). Castor bean grows throughout tropical and sub-tropical regions and is a very important crop due to its high seed content of ricinoleic acid, an unusual fatty acid, which has several industrial applications. However, due to the presence of the toxin, castor bean can cause death after the exposure of animals to low doses of ricin through skin contact, injection, inhalation or oral routes. Aiming to generate a detoxified genotype, we explored the RNAi concept in order to silence the ricin coding genes in the endosperm of castor bean seeds. Results indicated that ricin genes were effectively silenced in genetically modified (GM) plants, and ricin proteins were not detected by ELISA. Hemagglutination activity was not observed with proteins isolated from GM seeds. In addition, we demonstrated that seed proteins from GM plants were not toxic to rat intestine epithelial cells or to Swiss Webster mice. After oil extraction, bio-detoxified castor bean cake, which is very rich in valuable proteins, can be used for animal feeding. Gene silencing would make castor bean cultivation safer for farmers, industrial workers and society.
2018-01-01 | Biotechnological Means for Genetic Improvement in Castor Bean as a Crop of the Future
Profitable cultivation of castor bean is beset with problems of vulnerability of cultivars and hybrids to a multitude of insect pests and diseases. The presence of the toxic proteins ricin and hyperallergenic Ricinus communis agglutinin (RCA) in the endosperm restricts the use of deoiled seed cake as cattle feed. Due to this crop’s low genetic diversity, genetic engineering can be an efficient approach to introduce resistance to biotic and abiotic stresses as well as seed quality traits. Recently, castor oil gained attention as a sustainable second-generation feedstock for biojet fuel that would reduce carbon dioxide emissions. Because of a growing interest in castor oil as a biofuel and the presence of the powerful toxin ricin in its seed, metabolic pathways and regulatory genes involved in both oil and ricin production have been analyzed and characterized. Genetic engineering of castor bean offers new possibilities to increase oil yield and oxidative stability, confers stress tolerance, and improves other agronomics traits, such as reduced plant height to facilitate mechanical harvesting. However, difficulties in tissue culture-based regeneration and poor reproducibility of results are major bottlenecks for genetic transformation of castor bean. Despite advances in tissue culture research over the past four decades, direct or callus-mediated adventitious shoot regeneration systems that are genotype-independent remain a much sought-after goal in castor bean. Genetic transformation attempts to develop insect-resistant and ricin-free transgenic castor bean lines have been based on shoot proliferation from meristematic tissues. This chapter describes new transformation methods under development and the progress achieved so far in genetic engineering of castor bean for agronomically desirable attributes.
1996-12-27 | Cell-specific delivery of bacteriophage-encapsidated ricin A chain.
We have used covalent coupling of deglycosylated ricin A chain (RAC) to the assembly initiation/translational repression RNA stem-loop (TR) of the bacteriophage MS2 to direct encapsulation of the toxin in bacteriophage capsids. Multiple copies of the TR-RAC conjugate can be incorporated into single capsid shells. The resultant particles can then be directed to specific cells by receptor-mediated endocytosis (RME) of complexes formed with anti-MS2 coat protein antibodies or by further covalent modification of the capsids by addition of human transferrin molecules. The results suggest that bacteriophage encapsulation and targeting is an efficient way to deliver toxins in a cell-specific fashion. The system may have widespread application in the field of targeted drug delivery, including antisense reagents.
1995-08-07 | (Patho)physiologic pathways to drug targeting: artificial viral envelopes.
The goal of this study was to exploit molecular recognition of cell surface receptors by viral surface glycoproteins as a means for the selective intracellular delivery of macromolecules. To accomplish this, artificial viral envelopes (AVE) resembling the human immunodeficiency virus-1 (HIV-1) were designed as a model system. Recombinant HIV-1 surface glycoprotein gp160 (HIV-1 rgp160) was inserted in the artificial envelope by a two-step detergent dialysis process. The artificial HIV-1 envelope recognized the CD4 cell surface receptor. FITC-dextran and ricin A were employed as model macromolecules as they cannot passively diffuse across cell membranes. Selective transfer of FITC-dextran encapsulated in HIV-1 rgp160 AVE into a CD4-positive cell line (REX-1B) versus a CD4-negative cell line (KG-1) was demonstrated. Ricin A at concentrations as low as 2 ng/ml arrested cell growth of CD4-positive MOLT-4 cells, whereas 8 ng/ml ricin A in solution had no effect on cell growth. The arrest of cell growth was reverted in the presence of excess anti-gp120 monoclonal antibody. Naked envelopes (without HIV-1 rgp160 inserted) were also found to interact with cells and transfer material, although less efficiently and in a non-specific manner. Viral mimicry using AVE may be a means for targeted intracellular delivery of peptides, proteins, enzymes, toxins, oligodeoxynucleotides, gene constructs, and other non-diffusive, labile or toxic macromolecules.
small molecules
2026-06-25 | Biophysical and Biochemical Assays for Screening Small Molecule Inhibitors Targeting Toxin-Ribosome Interactions.
Ribosome-inactivating proteins are a class of toxins that target eukaryotic ribosomes, inhibit protein synthesis, and ultimately induce cell death. Several of these toxins pose significant clinical and public health threats. Among these, ricin, derived from the castor bean plant (Ricinus communis), is a highly potent biotoxin with recognized bioterrorism potential. Other ribosome-inactivating proteins, including Shiga toxin produced by pathogenic Shigella and Escherichia coli, as well as mucoricin from Mucorales fungi, contribute to disease severity and can lead to life-threatening complications. Despite these risks, no approved therapeutics are currently available. The development of effective inhibitors depends on robust and well-defined strategies to identify and validate small molecules that disrupt toxin-ribosome interactions. Efforts to target the catalytic active site have met with limited success, largely due to its broad, shallow, and highly polar architecture, which is not conducive to high-affinity binding by drug-like molecules. In contrast, the ribosome-binding interface represents a more tractable target, as it is essential for toxin recruitment and offers more structurally defined and druggable features. Inhibitors targeting this interface can also exert allosteric effects by disrupting long-range conformational coupling between the ribosome-binding region and the active site, thereby attenuating catalytic activity without directly engaging the catalytic pocket. In this review, we compile and evaluate biophysical and biochemical assays for the discovery and characterization of small-molecule inhibitors that target toxin-ribosome interactions. We examine in vitro binding approaches, including surface plasmon resonance-based fragment screening and fluorescence anisotropy assays for ranking inhibitory activity. We further review biochemical and molecular assays that assess ribosome protection from toxin-mediated depurination, along with complementary cell-based assays that evaluate functional rescue in cellular systems. Collectively, this review consolidates current screening methodologies and highlights opportunities to refine assay strategies, thereby supporting the advancement of targeted therapeutics.
2026-03-02 | PROTAC-Mediated Ternary Complex Stability with Ricin Toxin A: A Computational Perspective.
Ricin is a potent toxin present in the seeds of the castor plant (Ricinus communis), which is widely distributed in tropical regions. To date, there are no approved antidotes or vaccines against ricin poisoning. Reported inhibitors have not yet achieved sufficient affinity, and vaccine candidates have shown limited efficacy, highlighting the need to explore alternative strategies for RTA neutralization. In this work, we performed a computational study to investigate the potential of using PROTACs (proteolysis-targeting chimeras) to induce the ubiquitination and subsequent proteasomal degradation of ricin. Specifically, we assessed the stability of RTA, the catalytic subunit of ricin, in complex with the E3 ligases VHL and CRBN, both widely employed in the PROTAC design. Several PROTAC candidates with distinct linkers were evaluated to identify linkers with greater potential to mediate the stable ternary complex formation between RTA and the ligases. Molecular docking and molecular dynamics simulations revealed three promising PROTACs, one targeting CRBN and two targeting VHL, as potential candidates for further in vitro validation. Overall, this study introduces PROTAC-mediated degradation as a novel and unexplored therapeutic strategy against ricin intoxication, laying the groundwork for future experimental investigations.
2025-08-28 | Ricin Toxicity to Intestinal Cells Leads to Multiple Cell Death Pathways Mediated by Oxidative Stress.
Ricin, a type 2 ribosome-inactivating protein, is a lethal toxin found in castor bean seeds. Although the systemic toxicity of ricin has been extensively studied, its localized effect on the gastrointestinal tract remains a critical concern, particularly in the case of oral ingestion. This study investigates the cytotoxic effects of ricin on human intestinal epithelial cell lines and its impact on epithelial barrier integrity. Ricin cytotoxicity was assessed on the intestinal-derived HT29 and Caco-2 cell lines using dose- and time-response assays, while the epithelial integrity was evaluated via Trans-Epithelial Electrical Resistance (TEER) measurements in Caco-2 monolayers. Cell death was determined through flow cytometry analysis, and the protective effects of cell death inhibitors and antioxidant scavengers were investigated on ricin-intoxicated cells. Ricin showed high cytotoxicity on HT29 and Caco-2 cells, with EC50 values in the nM range after 24-72 h of intoxication. Moreover, ricin strongly reduced TEER values in Caco-2 cells at 0.1-1 nM after 24 h of treatment. At a 1 nM concentration, ricin cytotoxicity can be significantly prevented by pre-incubating cells with the cell death inhibitors Z-VAD or necrostatin-1 and the antioxidant scavenger catalase, butylated hydroxyanisole or sodium pyruvate, demonstrating the involvement of apoptosis/necroptosis and oxidative stress in ricin cell death pathways and mechanisms.
2025-05-27 | TM9SF2 Maintains Golgi Integrity and Regulates Ricin-Induced Cytotoxicity.
TM9SF2 belongs to a family of highly conserved nonaspanin proteins, and has been frequently identified as one of the important host factors for a plethora of lethal pathogens and toxins in previous genome-wide screening studies. We reported herein a novel molecular mechanism of TM9SF2 in mediating the cytotoxicity of ricin, a type II ribosome-inactivating protein. We first showed that TM9SF2 displays a non-redundant requirement for ricin-induced cytotoxicity within the nonaspanin family. Then we found that genetic interference of TM9SF2 substantially affects/remodels intracellular cholesterol trafficking, which results in abnormal cholesterol accumulation in Golgi compartments and causes severe Golgi fragmentation. The disruption of Golgi integrity and network impedes the retrograde transport of ricin and thus attenuates ricin-induced cytotoxicity. We further verified this mechanism by pharmacological manipulation of cholesterol metabolism (e.g., by using A939572 and avasimibe, etc.), which well restores the integrity of the Golgi apparatus and reverses the ricin-resistant phenotype induced by TM9SF2 knockdown. Our finding provides new mechanistic insights into the pathology and toxicology of ricin and could potentially be applied to other ribosome-inactivating toxins.
2025-05-03 | Fibroblast EGFR signaling mediates ricin toxin-induced acute lung injury via EGR1/CXCL1 axis.
Ricin toxin (RT), a highly potent plant-derived toxin, represents a critical threat due to its capacity to induce fatal acute lung injury (ALI) upon inhalation. While the epidermal growth factor receptor (EGFR), a receptor tyrosine kinase predominantly expressed on epithelial cells and fibroblasts, regulates cellular processes such as growth, proliferation, differentiation and inflammation, its involvement in RT-induced ALI remains unexplored. This study investigates this relationship using a mouse model of ALI induced by aerosolized RT at a dose of 2.0 × LD50 (approximately 0.01 mg kg -1). The results demonstrate that damage to alveolar epithelial type II (AT2) cells leads to the release of heparin-binding epidermal growth factor-like growth factor (HB-EGF), which activates EGFR on fibroblasts, exacerbating lung injury pathology and reducing survival. Mechanistically, EGFR activation in fibroblasts induces the early growth response protein 1 (EGR1), which subsequently enhances chemokine C-X-C motif ligand 1 (CXCL1) secretion 24 h post-exposure, promoting neutrophil infiltration in the lung. RNA sequencing analysis corroborates these findings. Notably, pharmacological inhibition of EGFR phosphorylation using Erlotinib (ERL) significantly mitigates the inflammatory response in RT-induced ALI. These results not only illuminate the immune response in lung tissue but also highlight EGFR signaling in fibroblasts as a pivotal mediator of RT-induced ALI. This study identifies a novel therapeutic strategy targeting EGFR signaling in fibroblasts for the treatment of inflammatory lung diseases.
proteins
2024-06-14 | A fluorescence anisotropy-based competition assay to identify inhibitors against ricin and Shiga toxin ribosome interactions.
Ricin is one of the most toxic substances known and a type B biothreat agent. Shiga toxins (Stxs) produced by E. coli (STEC) and Shigella dysenteriae are foodborne pathogens. There is no effective therapy against ricin or STEC and there is an urgent need for inhibitors. Ricin toxin A subunit (RTA) and A1 subunit of Stx2a (Stx2A1) bind to the C-terminal domain (CTD) of the ribosomal P-stalk proteins to depurinate the sarcin/ricin loop. Modulation of toxin-ribosome interactions has not been explored as a strategy for inhibition. Therefore, development of assays that detect inhibitors targeting toxin-ribosome interactions remains a critical need. Here we describe a fluorescence anisotropy (FA)-based competitive binding assay using a BODIPY-TMR labeled 11-mer peptide (P11) derived from the P-stalk CTD to measure the binding affinity of peptides ranging from 3 to 11 amino acids for the P-stalk pocket of RTA and Stx2A1. Comparison of the affinity with the surface plasmon resonance (SPR) assay indicated that although the rank order was the same by both methods, the FA assay could differentiate better between peptides that show nonspecific interactions by SPR. The FA assay detects only interactions that compete with the labeled P11 and can validate inhibitor specificity and mechanism of action.
2022-05-02 | Gdf15 deletion exacerbates acute lung injuries induced by intratracheal inoculation of aerosolized ricin in mice.
Ricin toxin (RT) is a potent toxin derived from castor beans and has a high risk of mortality following inhalation-induced acute lung injury (ALI). Growth differentiation factor 15 (GDF15) is a member of the transforming growth factor β superfamily and acts as a protective effect in diverse inflammatory diseases. Yet, the role of GDF15 in ALI has not been evaluated. In this study, we investigated the intrinsic role of Gdf15 in ALI induced by intratracheal inoculation of a 1.5 × LD50 (lethal dose for 50%) of aerosolized RT in Gdf15 knockout (KO) mice compared to wild-type (WT) mice. In this model, Gdf15 deletion significantly increased pathology in lung tissues for RT-induced ALI in mice, led to significantly decreased body weights and survival rates and increased expression of inflammatory-related cytokine and chemokine levels at 24 and 72 h post-exposure. Infiltration of myeloid cells in lung tissue were quantified using flow cytometry. Although a similar infiltration pattern of inflammatory cells was observed in Gdf15 KO and WT groups, Gdf15 KO mice had elevated levels of neutrophils and decreased levels of Ly6Clo monocytes (cells with distinct destructive and protective roles, respectively) in the early stage of ALI. Gene expression profiles revealed similar effects as observed through RNA-seq. Bioinformatics analysis confirmed that pro-inflammatory signaling pathways were activated and the expression of inflammatory genes was significantly up-regulated after RT exposure compared to the corresponding baseline control in Gdf15 KO and WT mice. Compared to WT mice, inflammatory genes were more pronounced in Gdf15 KO groups after RT exposure. To our knowledge, this study presents the first research to systematically evaluate the role of Gdf15 in RT-induced ALI. These results collectively uncovered an immune response signature in lung tissues and reveal a critical role of Gdf15 in this ALI mice model. Our findings expose novel opportunities to investigate the contribution of GDF15 for the treatment of lung inflammatory diseases.
2021-12-21 | Lyophyllin, a Mushroom Protein from the Peptidase M35 Superfamily Is an RNA N-Glycosidase.
Ribosome-inactivating proteins (RIPs) hydrolyze the N-glycosidic bond and depurinate a specific adenine residue (A-4324 in rat 28S ribosomal RNA, rRNA) in the conserved α-sarcin/ricin loop (α-SRL) of rRNA. In this study, we have purified and characterized lyophyllin, an unconventional RIP from Lyophyllum shimeji, an edible mushroom. The protein resembles peptidase M35 domain of peptidyl-Lys metalloendopeptidases. Nevertheless, protein either from the mushroom or in recombinant form possessed N-glycosidase and protein synthesis inhibitory activities. A homology model of lyophyllin was constructed. It was found that the zinc binding pocket of this protein resembles the catalytic cleft of a classical RIP, with key amino acids that interact with the adenine substrate in the appropriate positions. Mutational studies showed that E122 may play a role in stabilizing the positively charged oxocarbenium ion and H121 for protonating N-3 of adenine. The tyrosine residues Y137 and Y104 may be used for stacking the target adenine ring. This work first shows a protein in the peptidase M35 superfamily based on conserved domain search possessing N-glycosidase activity.
2021-11-16 | Intramuscular Exposure to a Lethal Dose of Ricin Toxin Leads to Endothelial Glycocalyx Shedding and Microvascular Flow Abnormality in Mice and Swine
Ricin toxin isolated from the castor bean (Ricinus communis) is one of the most potent and lethal molecules known. While the pathophysiology and clinical consequences of ricin poisoning by the parenteral route, i.e., intramuscular penetration, have been described recently in various animal models, the preceding mechanism underlying the clinical manifestations of systemic ricin poisoning has not been completely defined. Here, we show that following intramuscular administration, ricin bound preferentially to the vasculature in both mice and swine, leading to coagulopathy and widespread hemorrhages. Increased levels of circulating VEGF and decreased expression of vascular VE-cadherin caused blood vessel impairment, thereby promoting hyperpermeability in various organs. Elevated levels of soluble heparan sulfate, hyaluronic acid and syndecan-1 were measured in blood samples following ricin intoxication, indicating that the vascular glycocalyx of both mice and swine underwent extensive damage. Finally, by using side-stream dark field intravital microscopy imaging, we determined that ricin poisoning leads to microvasculature malfunctioning, as manifested by aberrant blood flow and a significant decrease in the number of diffused microvessels. These findings, which suggest that glycocalyx shedding and microcirculation dysfunction play a major role in the pathology of systemic ricin poisoning, may serve for the formulation of specifically tailored therapies for treating parenteral ricin intoxication.
2021-09-27 | Phosphorylation of the conserved C-terminal domain of ribosomal P-proteins impairs the mode of interaction with plant toxins.
The ribosome is subjected to post-translational modifications, including phosphorylation, that affect its biological activity. Among ribosomal elements, the P-proteins undergo phosphorylation within the C terminus, the element which interacts with trGTPases or ribosome-inactivating proteins (RIPs); however, the role of phosphorylation has never been elucidated. Here, we probed the function of phosphorylation on the interaction of P-proteins with RIPs using the ribosomal P1-P2 dimer. We determined the kinetic parameters of the interaction with the toxins using biolayer interferometry and microscale thermophoresis. The results present the first mechanistic insight into the function of P-protein phosphorylation, showing that introduction of a negative charge into the C terminus of P1-P2 proteins promotes α-helix formation and decreases the affinity of the P-proteins for the RIPs.
antibodies
2026-01-21 | Intoxication of cattle by Ricinus communis in northwestern Argentina.
Here we describe 2 outbreaks of intoxication by Ricinus communis in cattle in Argentina. In outbreak 1, in 2010, 180 heifers were introduced to a paddock heavily invaded by R. communis. Thirty-two animals developed watery diarrhea, and 6 of them were drooling, and had constant chewing motions, blindness, incoordination, depression, and prostration. Four affected animals died 12-14 h after the onset of clinical signs; another died 4 d later. The surviving 27 animals were removed from the paddock and recovered. At autopsy, several organs were congested and hemorrhagic, and abundant pericarps, leaves, and seeds of R. communis were found in the rumen content. The main microscopic lesion was acute, diffuse, superficial necrotizing gastroenteritis, and intestinal congestion and hemorrhage. In outbreak 2, in 2013, severe neurologic signs were observed in 12 of 300 cows after being introduced into a corn paddock without grain production that had been severely invaded by R. communis. Affected animals were excited and had tremors, drooling, incoordination, and prostration. The herd was immediately transferred to another paddock, and all affected cows recovered without treatment. In outbreak 1, the clinical signs and lesions were characteristic of simultaneous poisoning by R. communis fruits, which contain ricin and cause mainly digestive signs and lesions, and by leaves and pericarps, which contain ricinine and cause nervous signs. In outbreak 2, clinical signs and the recovery of the animals suggest that the intoxication was caused by ricinine, which is present in the leaves of R. communis.
2023-02-28 | Medical Countermeasures against Ricin Intoxication.
Ricin toxin is a disulfide-linked glycoprotein (AB toxin) comprising one enzymatic A chain (RTA) and one cell-binding B chain (RTB) contained in the castor bean, a Ricinus species. Ricin inhibits peptide chain elongation via disruption of the binding between elongation factors and ribosomes, resulting in apoptosis, inflammation, oxidative stress, and DNA damage, in addition to the classically known rRNA damage. Ricin has been used in traditional medicine throughout the world since prehistoric times. Because ricin toxin is highly toxic and can be readily extracted from beans, it could be used as a bioweapon (CDC B-list). Due to its extreme lethality and potential use as a biological weapon, ricin toxin remains a global public health concern requiring specific countermeasures. Currently, no specific treatment for ricin intoxication is available. This review focuses on the drugs under development. In particular, some examples are reviewed to demonstrate the proof of concept of antibody-based therapy. Chemical inhibitors, small proteins, and vaccines can serve as alternatives to antibodies or may be used in combination with antibodies.
2022-06-14 | Ricin toxin and its neutralizing antibodies: A review.
Ricin toxin (RT) belongs to the ribosome-inactivating protein (RIP) family of toxins and is considered to be a moderate threat by the US Center of Disease Control and Prevention (CDC). RT poses a great potential threat to the public, but there has been a lack of effective treatment options so far. Over the past few decades, researches on the prevention and treatment of RT poisoning have been investigated, among which neutralizing antibodies targeting RT specifically have always been a research hotspot. In this review, we have summarized the mechanism of action of RT, the research results and the design strategies of RT neutralizing antibodies, and discussed the key issues in the development of RT neutralizing antibody researches.
2022-04-26 | Single-domain antibodies neutralize ricin toxin intracellularly by blocking access to ribosomal P-stalk proteins.
During ricin intoxication in mammalian cells, ricin's enzymatic (RTA) and binding (RTB) subunits disassociate in the endoplasmic reticulum. RTA is then translocated into the cytoplasm where, by virtue of its ability to depurinate a conserved residue within the sarcin-ricin loop (SRL) of 28S rRNA, it functions as a ribosome-inactivating protein. It has been proposed that recruitment of RTA to the SRL is facilitated by ribosomal P-stalk proteins, whose C-terminal domains interact with a cavity on RTA normally masked by RTB; however, evidence that this interaction is critical for RTA activity within cells is lacking. Here, we characterized a collection of single-domain antibodies (VHHs) whose epitopes overlap with the P-stalk binding pocket on RTA. The crystal structures of three such VHHs (V9E1, V9F9, and V9B2) in complex with RTA revealed not only occlusion of the ribosomal P-stalk binding pocket but also structural mimicry of C-terminal domain peptides by complementarity-determining region 3. In vitro assays confirmed that these VHHs block RTA-P-stalk peptide interactions and protect ribosomes from depurination. Moreover, when expressed as "intrabodies," these VHHs rendered cells resistant to ricin intoxication. One VHH (V9F6), whose epitope was structurally determined to be immediately adjacent to the P-stalk binding pocket, was unable to neutralize ricin within cells or protect ribosomes from RTA in vitro. These findings are consistent with the recruitment of RTA to the SRL by ribosomal P-stalk proteins as a requisite event in ricin-induced ribosome inactivation.
2021-09-20 | Structural Analysis of Toxin-Neutralizing, Single-Domain Antibodies that Bridge Ricin's A-B Subunit Interface.
Ricin toxin kills mammalian cells with notorious efficiency. The toxin's B subunit (RTB) is a Gal/GalNAc-specific lectin that attaches to cell surfaces and promotes retrograde transport of ricin's A subunit (RTA) to the trans Golgi network (TGN) and endoplasmic reticulum (ER). RTA is liberated from RTB in the ER and translocated into the cell cytoplasm, where it functions as a ribosome-inactivating protein. While antibodies against ricin's individual subunits have been reported, we now describe seven alpaca-derived, single-domain antibodies (VHHs) that span the RTA-RTB interface, including four Tier 1 VHHs with IC50 values <1 nM. Crystal structures of each VHH bound to native ricin holotoxin revealed three different binding modes, based on contact with RTA's F-G loop (mode 1), RTB's subdomain 2γ (mode 2) or both (mode 3). VHHs in modes 2 and 3 were highly effective at blocking ricin attachment to HeLa cells and immobilized asialofetuin, due to framework residues (FR3) that occupied the 2γ Gal/GalNAc-binding pocket and mimic ligand. The four Tier 1 VHHs also interfered with intracellular functions of RTB, as they neutralized ricin in a post-attachment cytotoxicity assay (e.g., the toxin was bound to cell surfaces before antibody addition) and reduced the efficiency of toxin transport to the TGN. We conclude that the RTA-RTB interface is a target of potent toxin-neutralizing antibodies that interfere with both extracellular and intracellular events in ricin's cytotoxic pathway.
oligonucleotides
2026-03-29 | Advancing subunit vaccine efficacy against ricin toxin with a novel DNA hydrogel adjuvant tandem assembly by CpG motifs.
The development of effective countermeasures against ricin toxin, a potent biological threat, remains a pressing public health challenge. Subunit vaccines based on the ricin toxin A subunit offer a favorable safety profile but often suffer from limited immunogenicity, necessitating advanced adjuvants to elicit protective immunity. Here, we report a novel injectable CpG-motif-based hydrogel that serves as both adjuvant and delivery vehicle for a mutated and truncated RTA antigen. This CpG-gel adjuvant, synthesized via rolling circle amplification, incorporated with guanine-rich sequences that could self-assemble into stable G-quadruplex networks to form a structurally robust scaffold with flower-like microarchitecture. Notably, the CpG-gel significantly outperformed conventional CpG 1826 by enhancing antigen persistence and promoting sustained immune activation, leading to more potent and durable humoral and cellular responses. In murine studies, the CpG-gel elicited robust high titers of antigen-specific IgG antibodies, achieved complete protection against lethal-dose RT challenge. These results demonstrated that the CpG-gel adjuvant could significantly enhances the immunogenicity of subunit vaccines, highlighting its potential for broad implications for next-generation vaccine development.
2026-03-27 | An innovative ricin-degrading antidote based on aptamer-autophagy-tethering compound strategy.
Ricin is classified as a Category B biothreat agent due to its high toxicity and wide availability, posing a substantial threat to public security. Currently, no effective antidotes have been approved, and the development of medical countermeasures-including small-molecule inhibitors, antibodies, and vaccines-face substantial challenges. In this study, we designed innovative ricin-degrading antidotes based on the aptamer-autophagosome-tethering compound (aptamer-ATTEC) strategy. A series of aptamer-ATTEC chimeras were constructed by conjugating a high-affinity ricin aptamer with an LC3-recruiting moiety via click chemistry. The optimal compound, designated DP3-D-B0, exhibited potent anti-ricin efficacy at molecular, cellular, and animal levels. Experimental results confirmed that DP3-D-B0 mediated the formation of an intracellular ternary complex (LC3-ATTEC-ricin) that hijacks the autophagy machinery for lysosome-mediated degradation. Moreover, DP3-D-B0 was found can partially blocks ricin uptake extracellularly when administered simultaneously. This work broadens the application scope of ATTEC technology and provides a novel strategy for the targeted degradation of exogenous toxins, thus advancing the development of therapeutics against biothreat agents.
2026-01-14 | Design and evaluation of DNA aptamers with "stem-loop-chain" structures for spectrum neutralization of ricin and abrin.
Ricin and abrin are classified as Type II ribosome-inactivating proteins (RIPs) toxins, posing significant potential threats to public safety and in bioterrorism incidents. They exert catalytic N-glycosidase activity by specifically recognizing highly conserved structural domains within the α-sarcin/ricin loop (SRL) of ribosomal rRNA, consequently inhibiting protein synthesis and ultimately inducing cell death. Currently, no licensed drugs are available for Type II RIPs, making the development of antidotes with broad-spectrum activity highly imperative. In this study, we engineered a series of DNA aptamers featuring "stem-loop-chain" structures, designed to mimic the natural substrate, enabling spectrum inhibition of ricin and abrin toxins. Results indicated that most aptamers effectively inhibited the activities of ricin and abrin in both molecular and cellular screening models. The optimal aptamer, C-1, was demonstrated to be efficiently internalized into cells and had high-affinity binding to both toxins. In the cell poisoning protection assays, C-1 exhibited activity with IC50 values of 80.2 ± 26.8 nM against ricin and 282.8 ± 19.5 nM against abrin. In the ICR mouse model, the survival rate of C-1 group was significantly higher than that of the control group. This work provides novel aptamer-based lead compounds with potential broad-spectrum inhibitory activity and establishes a technical framework for developing therapeutics against other biological toxins.
2025-04-21 | Nanostructured aptasensors for ricin detection and tumor therapy: exploring aptamer-protein interactions and conformational stability in biological complexities.
Aptamers are distinctive single-stranded oligonucleotides derived through in vitro evolution, and exhibit exceptional ability in binding to target proteins. Structural modifications of aptamers can profoundly regulate their interactions with proteins, thereby influencing associated cellular behavior. Recent research focused on modulating aptamer-protein interaction in complex biological environments to regulate various biological processes. However, in such crowded conditions, aptamer conformation and stability are susceptible to nuclease degradation, which can impair stable binding to target. Ricin is recognized as a significant biological toxin protein, distinguished by its widespread availability, remarkable dissemination, and resilience including wide pH tolerance, remarkable thermostability, and solubility. RTA is an enzymatic subunit of ricin, that can inactivate approximately 2000 ribosomes per minute, rapidly halting protein synthesis, making it a powerful candidate for tumor therapy. By leveraging the potent cytotoxicity of ricin, coupled with the targeting precision of aptamers and the versatility of nanomaterials, a powerful approach emerges for both targeted tumor therapy and highly sensitive detection of ricin. Although there have been some insightful reports on aptamers applied in ricin detection, a systematic discussion remains limited. In this context, we provide an in-depth overview of techniques used to analyze aptamer-ricin interactions and explore the potential of ricin-aptamer interactions in clinical diagnosis.
2024-11-27 | Development of a Graphene Oxide-Based Aptamer Nanoarray for Improved Neutralization and Protection Effects Against Ricin.
Background/Objectives: Ricin's high toxicity and potential as a bioweapon underscore the need for effective antidotes. Monoclonal antibodies, though effective, are limited by complex production. This study aimed to develop a graphene oxide-based aptamer nanoarray (ARMAN) for improved neutralization and protection against ricin. Methods: High-affinity aptamers targeting ricin's RTA and RTB subunits were selected using SELEX technology and conjugated to graphene oxide (GO) via click chemistry. ARMAN's characteristics, including morphology, stability, and biosecurity, were assessed. Its performance was evaluated in terms of affinity for ricin, neutralization capacity, and therapeutic effects in cellular assays and a mouse model of ricin poisoning. Results: ARMAN exhibited a uniform morphology with an average particle size of 217 nm and demonstrated significantly enhanced affinity for ricin compared to free aptamers. ARMAN showed rapid and effective neutralization ability, significantly increasing cell viability in BEAS-2B, GES-1, and HL7702 cell lines exposed to ricin. In vivo, ARMAN treatment led to a notable prolongation of survival in ricin-poisoned mice, highlighting its potential for both pre- and post-exposure treatment. These findings indicate that ARMAN not only neutralizes ricin effectively but also provides a therapeutic window for treatment. Conclusions: ARMAN's superior binding affinity, serum stability, biocompatibility, and broad therapeutic efficacy make it a promising new antidote against ricin poisoning. This study's findings represent significant progress in the development of rapid-response antidotes, with ARMAN offering a potential solution for both military and civilian emergency response scenarios.
other
2025-02-13 | The use of adeno-associated vírus-based gene therapy to achieve long-term expression of recombinant neutralizing antibody against ricin.
Ricin is a highly toxic plant protein for which there are no specific antidotes. Current prophylactic and emergency treatments for ricin intoxication are limited by the need for prior vaccination and the short half-life of antibody drugs in the circulation. To address these limitations, we developed a novel immunotherapeutic strategy using adeno-associated virus (AAV) gene transfer to achieve prolonged systemic serum levels of immunoglobulins to ricin. In this study, a single administration of rAAV was used to deliver protein immunotherapeutics, and its efficacy in protecting mice against lethal doses of ricin was investigated. The results revealed that the single administration of rAAV three days prior to ricin exposure effectively protected mice from lethal doses of ricin. Remarkably, this protection was sustained for up to 90 days after AAV injection, demonstrating long-term efficacy. Overall, our findings suggest that the rAAV-mediated approach holds promise for both early and long-term prevention of ricin intoxication. The favorable safety profile of this system and its potential for the development of novel ricin antibody therapeutics make it a noteworthy candidate for further exploration and development in the field.
2019-07-03 | Bio-detoxification of ricin in castor bean (Ricinus communis L.) seeds.
Ricin is a highly toxic ribosome-inactivating lectin occurring in the seeds of castor bean (Ricinus communis L.). Castor bean grows throughout tropical and sub-tropical regions and is a very important crop due to its high seed content of ricinoleic acid, an unusual fatty acid, which has several industrial applications. However, due to the presence of the toxin, castor bean can cause death after the exposure of animals to low doses of ricin through skin contact, injection, inhalation or oral routes. Aiming to generate a detoxified genotype, we explored the RNAi concept in order to silence the ricin coding genes in the endosperm of castor bean seeds. Results indicated that ricin genes were effectively silenced in genetically modified (GM) plants, and ricin proteins were not detected by ELISA. Hemagglutination activity was not observed with proteins isolated from GM seeds. In addition, we demonstrated that seed proteins from GM plants were not toxic to rat intestine epithelial cells or to Swiss Webster mice. After oil extraction, bio-detoxified castor bean cake, which is very rich in valuable proteins, can be used for animal feeding. Gene silencing would make castor bean cultivation safer for farmers, industrial workers and society.
2018-01-01 | Biotechnological Means for Genetic Improvement in Castor Bean as a Crop of the Future
Profitable cultivation of castor bean is beset with problems of vulnerability of cultivars and hybrids to a multitude of insect pests and diseases. The presence of the toxic proteins ricin and hyperallergenic Ricinus communis agglutinin (RCA) in the endosperm restricts the use of deoiled seed cake as cattle feed. Due to this crop’s low genetic diversity, genetic engineering can be an efficient approach to introduce resistance to biotic and abiotic stresses as well as seed quality traits. Recently, castor oil gained attention as a sustainable second-generation feedstock for biojet fuel that would reduce carbon dioxide emissions. Because of a growing interest in castor oil as a biofuel and the presence of the powerful toxin ricin in its seed, metabolic pathways and regulatory genes involved in both oil and ricin production have been analyzed and characterized. Genetic engineering of castor bean offers new possibilities to increase oil yield and oxidative stability, confers stress tolerance, and improves other agronomics traits, such as reduced plant height to facilitate mechanical harvesting. However, difficulties in tissue culture-based regeneration and poor reproducibility of results are major bottlenecks for genetic transformation of castor bean. Despite advances in tissue culture research over the past four decades, direct or callus-mediated adventitious shoot regeneration systems that are genotype-independent remain a much sought-after goal in castor bean. Genetic transformation attempts to develop insect-resistant and ricin-free transgenic castor bean lines have been based on shoot proliferation from meristematic tissues. This chapter describes new transformation methods under development and the progress achieved so far in genetic engineering of castor bean for agronomically desirable attributes.
1996-12-27 | Cell-specific delivery of bacteriophage-encapsidated ricin A chain.
We have used covalent coupling of deglycosylated ricin A chain (RAC) to the assembly initiation/translational repression RNA stem-loop (TR) of the bacteriophage MS2 to direct encapsulation of the toxin in bacteriophage capsids. Multiple copies of the TR-RAC conjugate can be incorporated into single capsid shells. The resultant particles can then be directed to specific cells by receptor-mediated endocytosis (RME) of complexes formed with anti-MS2 coat protein antibodies or by further covalent modification of the capsids by addition of human transferrin molecules. The results suggest that bacteriophage encapsulation and targeting is an efficient way to deliver toxins in a cell-specific fashion. The system may have widespread application in the field of targeted drug delivery, including antisense reagents.
1995-08-07 | (Patho)physiologic pathways to drug targeting: artificial viral envelopes.
The goal of this study was to exploit molecular recognition of cell surface receptors by viral surface glycoproteins as a means for the selective intracellular delivery of macromolecules. To accomplish this, artificial viral envelopes (AVE) resembling the human immunodeficiency virus-1 (HIV-1) were designed as a model system. Recombinant HIV-1 surface glycoprotein gp160 (HIV-1 rgp160) was inserted in the artificial envelope by a two-step detergent dialysis process. The artificial HIV-1 envelope recognized the CD4 cell surface receptor. FITC-dextran and ricin A were employed as model macromolecules as they cannot passively diffuse across cell membranes. Selective transfer of FITC-dextran encapsulated in HIV-1 rgp160 AVE into a CD4-positive cell line (REX-1B) versus a CD4-negative cell line (KG-1) was demonstrated. Ricin A at concentrations as low as 2 ng/ml arrested cell growth of CD4-positive MOLT-4 cells, whereas 8 ng/ml ricin A in solution had no effect on cell growth. The arrest of cell growth was reverted in the presence of excess anti-gp120 monoclonal antibody. Naked envelopes (without HIV-1 rgp160 inserted) were also found to interact with cells and transfer material, although less efficiently and in a non-specific manner. Viral mimicry using AVE may be a means for targeted intracellular delivery of peptides, proteins, enzymes, toxins, oligodeoxynucleotides, gene constructs, and other non-diffusive, labile or toxic macromolecules.
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Drug Discovery Landscape
5 orphan drug designations for Ricin poisoning.
5 orphan drug designations for Ricin poisoning.
Drug | Therapy type | Regulator | Orphan designation | Approval | Sponsor |
|---|---|---|---|---|---|
Equine polyclonal immunoglobulin F(ab')2 fragments against ricin | antibodies | EMA | 2025-05-22 | — | Fabentech |
Ovine polyclonal fragment antigen-binding against ricin | proteins | EMA | 2023-12-13 | — | Serb |
Ricin Immune Fab | antibodies | FDA | 2023-11-16 | — | BTG International Inc |
Recombinant modified ricin toxin A-chain subunit | proteins | EMA | 2018-03-21 | — | Soligenix NE B.V. |
ricin vaccine | vaccines | FDA | 2011-01-07 | — | Soligenix, Inc. |
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