Identification of potent nanobodies to neutralize the most poisonous polypeptide from scorpion venom

Pharmacokinetic evaluation of a single chain antibody fragment against scorpion toxins in sheep

A key aspect during the development of antivenoms is the evaluation of the efficiency and security of the therapeutic molecules. In this work, we report the pharmacokinetic analysis of a neutralizing single chain antibody fragment named LR (scFv LR) where three sheep were used as a large animal model. The animals were injected through i.v. route with 2 mg of scFv LR. Blood samples were drawn every minute within the first 15 min, the sampling continues at 20, 25, 30, 45, 60, 90, 120 min, subsequently at 1-h intervals, 3, 4, 5, 6 h, two more samples at 9 and 12 h and, two more samples at 24 and 48 h and finally at one-day intervals during 4 days. scFv LR levels were measured from blood serum and urine samples by an ELISA. The pharmacokinetics of the experimental data was analyzed using the three-exponential kinetics. The value of the fast initial component (τ1=0.409±0.258min) indicated that the scFv is distributed rapidly into the tissues. The mean residence time, MRT, was 45 ± 0.51 min and the clearance (CL), 114.3 ± 14.3 mL/min. From urine samples it was possible to detect significant amounts of scFv LR, which is evidence of renal elimination.

Characterization of novel CD19-specific VHHs isolated from a camelid immune library by phage display

BACKGROUND

Monoclonal antibody (mAb)-based immunotherapies have achieved promising outcomes in the treatment of immunological and oncological indications. CD19 is considered one of the most qualified antigens in the treatment of B-cell neoplasms. VHHs (nanobodies) are known for their physicochemical advantages over conventional mAbs rendering them suitable therapeutics and diagnostic tools. Herein, we aimed to isolate CD19-specific VHHs from a novel immune library using phage display.

METHODS

An immune VHH gene library was constructed. Using phage display and after five biopanning rounds, two monoclonal CD19-specific VHHs were isolated. The selected VHHs were expressed, purified, and characterized in terms of their affinity, specificity, sensitivity, and ability to target CD19-positive cell lines. Moreover, in silico analyses were employed for further characterization.

RESULTS

A VHH library was developed, and because the outputs of the 4th biopanning round exhibited the most favorable characteristics, a panel of random VHHs was selected from them. Ultimately, two of the most favorable VHHs were selected and DNA sequenced (designated as GR37 and GR41). Precise experiments indicated that GR37 and GR41 exhibited considerable specificity, sensitivity, and affinity (1.15 × 107 M-1 and 2.08 × 107 M-1, respectively) to CD19. Flow cytometric analyses revealed that GR37 and GR41 could bind CD19 on the surface of cell lines expressing the antigen. Moreover, in silico experiments predicted that both VHHs target epitopes that are distinct from that targeted by the CD19-specific single-chain variable fragment (scFv) FMC63.

CONCLUSION

The selected VHHs can be used as potential targeting tools for the development of CD19-based immunotherapeutics.

Production of recombinant scorpion antivenoms in E. coli: current state and perspectives

Scorpion envenomation is a serious health problem in tropical and subtropical zones. The access to scorpion antivenom is sometimes limited in availability and specificity. The classical production process is cumbersome, from the hyper-immunization of the horses to the IgG digestion and purification of the F(ab)'₂ antibody fragments. The production of recombinant antibody fragments in Escherichia coli is a popular trend due to the ability of this microbial host to produce correctly folded proteins. Small recombinant antibody fragments, such as single-chain variable fragments (scFv) and nanobodies (V_HH), have been constructed to recognize and neutralize the neurotoxins responsible for the envenomation symptoms in humans. They are the focus of interest of the most recent studies and are proposed as potentially new generation of pharmaceuticals for their use in immunotherapy against scorpion stings of the Buthidae family. This literature review comprises the current status on the scorpion antivenom market and the analyses of cross-reactivity of commercial scorpion anti-serum against non-specific scorpion venoms. Recent studies on the production of new recombinant scFv and nanobodies will be presented, with a focus on the Androctonus and Centruroides scorpion species. Protein engineering-based technology could be the key to obtaining the next generation of therapeutics capable of neutralizing and cross-reacting against several types of scorpion venoms. KEY POINTS: • Commercial antivenoms consist of predominantly purified equine F(ab)'₂fragments. • Nanobody-based antivenom can neutralize Androctonus venoms and have a low immunogenicity. • Affinity maturation and directed evolution are used to obtain potent scFv families against Centruroides scorpions.

Characterization of rabbit polyclonal antibody against camel recombinant nanobodies

Nanobodies (Nbs) are recombinant single-domain fragments derived from camelids’ heavy-chain antibodies (HCAbs). Nanobodies are increasingly used in numerous biotechnological and medical applications because of their high stability, solubility, and yield. However, one major obstacle prohibiting Nb expansion is the affordability of specific detector antibodies for their final revelation. In this work, the production of a specific anti-Nb antibody as a general detector for camel antibodies, conventional cIgG, and HCAb, and their derived Nbs was sought. Thus, a T7 promoter plasmid was constructed and used to highly express six different Nbs that were used in a successful rabbit immunization. Affinity-purified rabbit anti-Nb rIgG was able to detect immobilized or antigen-bound Nbs via enzyme-linked immunosorbent assay, and its performance was comparable to that of a commercial anti-6× His antibody. Its capacities in dosing impure Nbs, detecting Nbs displayed on M13 phages, and revealing denatured Nbs in immune blotting were all proven. As expected, and because of shared epitopes, rabbit anti-Nb cross-reacted with cIgG, HCAbs, and 6× His-tagged proteins, and the percentage of each fraction within anti-Nb rIgG was determined. Anti-Nb is a promising tool for the checkpoints throughout the recombinant Nb technology.

Neutralizing Dromedary-Derived Nanobodies Against BotI-Like Toxin From the Most Hazardous Scorpion Venom in the Middle East and North Africa Region

Scorpion envenoming is a severe health problem in many regions causing significant clinical toxic effects and fatalities. In the Middle East/North Africa (MENA) region, Buthidae scorpion stings are responsible for devastating toxic outcomes in human. The only available specific immunotherapeutic treatment is based on IgG fragments of animal origin. To overcome the limitations of classical immunotherapy, we have demonstrated the in vivo efficacy of NbF12-10 bispecific nanobody at preclinical level. Nanobodies were developed against BotI analogues belonging to a distinct structural and antigenic group of scorpion toxins, occurring in the MENA region. From Buthus occitanus tunetanus venom, BotI-like toxin was purified. The 41 N-terminal amino acid residues were sequenced, and the LD₅₀ was estimated at 40 ng/mouse. The BotI-like toxin was used for dromedary immunization. An immune VHH library was constructed, and after screening, two nanobodies were selected with nanomolar and sub-nanomolar affinity and recognizing an overlapping epitope. NbBotI-01 was able to neutralize 50% of the lethal effect of 13 LD₅₀ BotI-like toxins in mice when injected by i.c.v route, whereas NbBotI-17 neutralized 50% of the lethal effect of 7 LD₅₀. Interestingly, NbBotI-01 completely reduced the lethal effect of the 2 LD₅₀ of BotG50 when injected at 1:4 molar ratio excess. More interestingly, an equimolar mixture of NbBotI-01 with NbF12-10 neutralized completely the lethal effect of 7 and 5 LD₅₀ of BotG50 or AahG50, at 1:4 and 1:2 molar ratio, respectively. Hence, NbBotI-01 and NbF12-10 display synergic effects, leading to a novel therapeutic candidate for treating Buthus occitanus scorpion stings in the MENA region.

The Pharmacological and Structural Basis of the AahII–NaV1.5 Interaction and Modulation by the Anti-AahII Nb10 Nanobody

Scorpion α-toxins are neurotoxins that target the fast inactivation mechanism of voltage-gated sodium (Na_V) channels leading to several neuro- and cardiotoxic effects in mammals. The toxin AahII is the most active α-toxin from the North African scorpion Androctonus australis Hector that slows the fast inactivation of Na_V channels. To fight scorpion envenomation, an anti-AahII nanobody named NbAahII10 (Nb10) was developed. The efficiency of this nanobody has been evaluated in vivo on mice, but its mechanism of action at the cellular level remains unknown. Here we have shown that AahII toxin slows the fast inactivation of the adult cardiac Na_V1.5 channels, expressed in HEK293 cells, in a dose-dependent manner, while current amplitude was not affected. The inactivation of Na_V1.5 is slower by a factor of 4, 7, and 35 in the presence of [AahII] at 75, 150, and 300 nM, respectively. The washout partially reversed the toxin effect on inactivation from 8.3 ± 0.9 ms to 5.2 ± 1.2 ms at 75 nM. We have also demonstrated that the highly neutralizing Nb10 can fully reverse the effect of AahII toxin on the channel inactivation kinetics even at the 1:1 M ratio. However, the 1:0.5 M ratio is not able to neutralize completely the AahII effect. Therefore, the application of Nb10 promotes a partial abolishment of AahII action. Bioinformatic analysis and prediction of Na_V1.5-driven docking with AahII show that Ala39 and Arg62 of AahII play a crucial role to establish a stable interaction through H-bound interactions with Gln1615 and Lys1616 (S3–S4 extracellular loop) and Asp1553 (S1–S2 loop) from the voltage-sensing domain IV (VSD4) of Na_V1.5, respectively. From this, we notice that AahII shares the same contact surface with Nb10. This strongly suggests that Nb10 dynamically replaces AahII toxin from its binding site on the Na_V1.5 channel. At the physiopathological level, Nb10 completely neutralized the enhancement of breast cancer cell invasion induced by AahII. In summary, for the first time, we made an electrophysiological and structural characterization of the neutralization potent of Nb10 against the α-scorpion toxin AahII in a cellular model overexpressing Na_V1.5 channels.

Novel Human Tenascin-C Function-Blocking Camel Single Domain Nanobodies

The extracellular matrix (ECM) molecule Tenascin-C (TNC) is well-known to promote tumor progression by multiple mechanisms. However, reliable TNC detection in tissues of tumor banks remains limited. Therefore, we generated dromedary single-domain nanobodies Nb3 and Nb4 highly specific for human TNC (hTNC) and characterized the interaction with TNC by several approaches including ELISA, western blot, isothermal fluorescence titration and negative electron microscopic imaging. Our results revealed binding of both nanobodies to distinct sequences within fibronectin type III repeats of hTNC. By immunofluroescence and immunohistochemical imaging we observed that both nanobodies detected TNC expression in PFA and paraffin embedded human tissue from ulcerative colitis, solid tumors and liver metastasis. As TNC impairs cell adhesion to fibronectin we determined whether the nanobodies abolished this TNC function. Indeed, Nb3 and Nb4 restored adhesion of tumor and mesangial cells on a fibronectin/TNC substratum. We recently showed that TNC orchestrates the immune-suppressive tumor microenvironment involving chemoretention, causing tethering of CD11c+ myeloid/dendritic cells in the stroma. Here, we document that immobilization of DC2.4 dendritic cells by a CCL21 adsorbed TNC substratum was blocked by both nanobodies. Altogether, our novel TNC specific nanobodies could offer valuable tools for detection of TNC in the clinical practice and may be useful to inhibit the immune-suppressive and other functions of TNC in cancer and other diseases.

Effect of temperature on the production of a recombinant antivenom in fed-batch mode

In the pharmaceutical industry, nanobodies show promising properties for its application in serotherapy targeting the highly diffusible scorpion toxins. The production of recombinant nanobodies in Escherichia coli has been widely studied in shake flask cultures in rich medium. However, there are no upstream bioprocess studies of nanobody production in defined minimal medium and the effect of the induction temperature on the production kinetics. In this work, the effect of the temperature during the expression of the chimeric bispecific nanobody CH10-12 form, showing high scorpion antivenom potential, was studied in bioreactor cultures of E. coli. High biomass concentrations (25 g cdw/L) were achieved in fed-batch mode, and the expression of the CH10-12 nanobody was induced at temperatures 28, 29, 30, 33, and 37°C with a constant glucose feed. For the bispecific form NbF12-10, the induction was performed at 29°C. Biomass and carbon dioxide yields were reported for each culture phase, and the maintenance coefficient was obtained for each strain. Nanobody production in the CH10-12 strain was higher at low temperatures (lower than 30°C) and declined with the increase of the temperature. At 29°C, the CH10-12, NbF12-10, and WK6 strains were compared. Strains CH10-12 and NbF12-10 had a productivity of 0.052 and 0.021 mg/L/h of nanobody, respectively, after 13 h of induction. The specific productivity of the nanobodies was modeled as a function of the induction temperature and the specific growth rates. Experimental results confirm that low temperatures increase the productivity of the nanobody.Key points• Nanobodies with scorpion antivenom activity produced using two recombinant strains.• Nanobodies production was achieved in fed-batch cultures at different induction temperatures.• Low induction temperatures result in high volumetric productivities of the nanobody CH10-12.

Inhibitory Potential of Polyclonal Camel Antibodies against New Delhi Metallo-β-lactamase-1 (NDM-1)

New Delhi Metallo-β-lactamase-1 (NDM-1) is the most prevalent type of metallo-β-lactamase, able to hydrolyze almost all antibiotics of the β-lactam group, leading to multidrug-resistant bacteria. To date, there are no clinically relevant inhibitors to fight NDM-1. The use of dromedary polyclonal antibody inhibitors against NDM-1 represents a promising new class of molecules with inhibitory activity. In the current study, immunoreactivities of dromedary Immunoglobulin G (IgG) isotypes containing heavy-chain and conventional antibodies were tested after successful immunization of dromedary using increasing amounts of the recombinant NDM-1 enzyme. Inhibition kinetic assays, performed using a spectrophotometric method with nitrocefin as a reporter substrate, demonstrated that IgG1, IgG2, and IgG3 were able to inhibit not only the hydrolytic activity of NDM-1 but also Verona integron-encoded metallo-β-lactamase (VIM-1) (subclass B1) and L1 metallo-β-lactamase (L1) (subclass B3) with inhibitory concentration (IC₅₀₎ values ranging from 100 to 0.04 μM. Investigations on the ability of IgG subclasses to reduce the growth of recombinant Escherichia coli BL21(DE3)/codon plus cells containing the recombinant plasmid expressing NDM-1, L1, or VIM-1 showed that the addition of IgGs (4 and 8 mg/L) to the cell culture was unable to restore the susceptibility of carbapenems. Interestingly, IgGs were able to interact with NDM-1, L1, and VIM-1 when tested on the periplasm extract of each cultured strain. The inhibitory concentration was in the micromolar range for all β-lactams tested. A visualization of the 3D structural basis using the three enzyme Protein Data Bank (PDB) files supports preliminarily the recorded inhibition of the three MBLs.

Recombinant antibodies against Iranian cobra venom as a new emerging therapy by phage display technology

Background:

The production of antivenom from immunized animals is an established treatment for snakebites; however, antibody phage display technology may have the capacity to delivery results more quickly and with a better match to local need. Naja oxiana, the Iranian cobra, is a medically important species, responsible for a significant number of deaths annually. This study was designed as proof of principle to determine whether recombinant antibodies with the capacity to neutralize cobra venom could be isolated by phage display.

Methods:

Toxic fractions from cobra venom were prepared by chromatography and used as targets in phage display to isolate recombinant antibodies from a human scFv library. Candidate antibodies were expressed in E. coli HB2151 and purified by IMAC chromatography. The selected clones were analyzed in in vivo and in vitro experiments.

Results:

Venom toxicity was contained in two fractions. Around a hundred phage clones were isolated against each fraction, those showing the best promise were G12F3 and G1F4. While all chosen clones showed low but detectable neutralizing effect against Naja oxiana venom, clone G12F3 could inhibit PLA₂ activity.

Conclusion:

Therefore, phage display is believed to have a good potential as an approach to the development of snake antivenom.

Serotherapy against Voltage-Gated Sodium Channel-Targeting αToxins from Androctonus Scorpion Venom

Because of their venom lethality towards mammals, scorpions of the Androctonus genus are considered a critical threat to human health in North Africa. Several decades of exploration have led to a comprehensive inventory of their venom components at chemical, pharmacological, and immunological levels. Typically, these venoms contain selective and high affinity ligands for the voltage-gated sodium (Na_v) and potassium (K_v) channels that dictate cellular excitability. In the well-studied Androctonus australis and Androctonus mauretanicus venoms, almost all the lethality in mammals is due to the so-called α-toxins. These peptides commonly delay the fast inactivation process of Na_v channels, which leads to increased sodium entry and a subsequent cell membrane depolarization. Markedly, their neutralization by specific antisera has been shown to completely inhibit the venom’s lethal activity, because they are not only the most abundant venom peptide but also the most fatal. However, the structural and antigenic polymorphisms in the α-toxin family pose challenges to the design of efficient serotherapies. In this review, we discuss past and present accomplishments to improve serotherapy against Androctonus scorpion stings.

mRNA as novel technology for passive immunotherapy

While active immunization elicits a lasting immune response by the body, passive immunotherapy transiently equips the body with exogenously generated immunological effectors in the form of either target-specific antibodies or lymphocytes functionalized with target-specific receptors. In either case, administration or expression of recombinant proteins plays a fundamental role. mRNA prepared by in vitro transcription (IVT) is increasingly appreciated as a drug substance for delivery of recombinant proteins. With its biological role as transient carrier of genetic information translated into protein in the cytoplasm, therapeutic application of mRNA combines several advantages. For example, compared to transfected DNA, mRNA harbors inherent safety features. It is not associated with the risk of inducing genomic changes and potential adverse effects are only temporary due to its transient nature. Compared to the administration of recombinant proteins produced in bioreactors, mRNA allows supplying proteins that are difficult to manufacture and offers extended pharmacokinetics for short-lived proteins. Based on great progress in understanding and manipulating mRNA properties, efficacy data in various models have now demonstrated that IVT mRNA constitutes a potent and flexible platform technology. Starting with an introduction into passive immunotherapy, this review summarizes the current status of IVT mRNA technology and its application to such immunological interventions.

Nanobodies as novel therapeutic agents in envenomation

BACKGROUND

An effective therapy against envenoming should be a priority in view of the high number scorpion stings and snakebites. Serum therapy is still widely applied to treat the envenomation victims; however this approach suffers from several shortcomings. The employment of monoclonal antibodies might be an outcome as these molecules are at the core of a variety of applications from protein structure determination to cancer treatment. The progress of activities in the twilight zone between genetic and antibody engineering have led to the development of a unique class of antibody fragments. These molecules possess several benefits and lack many possible disadvantages over classical antibodies. Within recombinant antibody formats, nanobodies or single domain antigen binding fragments derived from heavy chain only antibodies in camelids occupy a privileged position.

SCOPE OF REVIEW

In this paper we will briefly review the common methods of envenomation treatment and focus on details of various in vivo research activities that investigate the performance of recombinant, monoclonal nanobodies in venom neutralization.

MAJOR CONCLUSIONS

Nanobodies bind to their cognate target with high specificity and affinity, they can be produced in large quantities from microbial expression systems and are very robust even when challenged with harsh environmental conditions. Upon administering, they rapidly distribute throughout the body and seem to be well tolerated in humans posing low immunogenicity.

GENERAL SIGNIFICANCE

Scorpion and snake envenomation is a major issue in developing countries and nanobodies as a venom-neutralizing agent can be considered as a valuable and promising candidate in envenomation therapy.

Thermal stabilization of anti-α-cobratoxin single domain antibodies

There is an unmet need for snake antivenoms that can be stored ready to use near the point of care. To address that need we have taken two anti-α-cobratoxin single domain antibodies and increased their thermal stability to improve their ambient temperature shelf-life. The anti-α-cobratoxin single domain antibodies C2 and C20 were first isolated, and demonstrated to be toxin neutralizing by Richard et al., 2013 (Richard, G., Meyers, A.J., McLean, M.D., Arbabi-Ghahroudi, M., MacKenzie, R., Hall, J.C., 2013. In vivo neutralization of alpha-cobratoxin with high-affinity llama single-domain antibodies (VHHs) and a VHH-Fc antibody. PLoS One 8, e69495). To thermal stabilize C2 and C20, we first made changes to their frame work 1 region that we had previously identified to be stabilizing, as well as reverted to the hallmark amino acids highly conserved in VHH domains; these changes improved their melting temperature (Tm) by 2 and 6 °C respectively. The further addition of a non-canonical disulfide bond raised the Tm an additional 13 and 9 °C respectively; giving final Tm values of 86 and 75 °C. Testing these mutants at 1 mg/mL at a range of elevated temperatures for an hour; we found that at 65 °C the wild type C2 and C20 had lost 35 and 95% of their binding activity respectively, while the mutants with the added disulfide bond retained nearly 100% of their initial binding activity. While significant work remains to formulate and field a shelf-stable antivenom, our results indicate such a product should be attainable in the near future.

Exploiting Nanobodies in the Detection and Quantification of Human Growth Hormone via Phage-Sandwich Enzyme-Linked Immunosorbent Assay

BACKGROUND

Monitoring blood levels of human growth hormone (hGH) in most children with short stature deficiencies is crucial for taking a decision of treatment with extended course of daily and expensive doses of recombinant hGH (rhGH or Somatropin^®). Besides, misusing of rhGH by sportsmen is banned by the World Anti-Doping Agency and thus sensitive GH-detecting methods are highly welcome in this field. Nanobodies are the tiniest antigen-binding entity derived from camel heavy chain antibodies. They were successfully generated against numerous antigens including hormones.

METHODS

A fully nanobody-based sandwich ELISA method was developed in this work for direct measurement of GH in biological samples.

RESULTS

Two major characteristics of nanobody were exploited for this goal: the robust and stable structure of the nanobody (NbGH04) used to capture hGH from tested samples, and the great ability of tailoring, enabling the display of the anti-GH detector nanobody (NbGH07) on the tip of M13-phage. Such huge, stable, and easy-to-prepare phage-Nb was used in ELISA to provide an amplified signal. Previously, NbGH04 was retrieved on immobilized hGH by phage display from a wide "immune" cDNA library prepared from a hGH-immunized camel. Here, and in order to assure epitope heterogeneity, NbGH07 was isolated from the same library using NbGH04-captured hGH as bait. Interaction of both nanobodies with hGH was characterized and compared with different anti-GH nanobodies and antibodies. The sensitivity (~0.5 ng/ml) and stability of the nanobody-base sandwich ELISA were assessed using rhGH before testing in the quantification of hGH in blood sera and cell culture supernatants.

CONCLUSION

In regard to all advantages of nanobodies; stability, solubility, production affordability in Escherichia coli, and gene tailoring, nanobody-based phage sandwich ELISA developed here would provide a valuable method for hGH detection and quantification.

Biotechnological Trends in Spider and Scorpion Antivenom Development

Spiders and scorpions are notorious for their fearful dispositions and their ability to inject venom into prey and predators, causing symptoms such as necrosis, paralysis, and excruciating pain. Information on venom composition and the toxins present in these species is growing due to an interest in using bioactive toxins from spiders and scorpions for drug discovery purposes and for solving crystal structures of membrane-embedded receptors. Additionally, the identification and isolation of a myriad of spider and scorpion toxins has allowed research within next generation antivenoms to progress at an increasingly faster pace. In this review, the current knowledge of spider and scorpion venoms is presented, followed by a discussion of all published biotechnological efforts within development of spider and scorpion antitoxins based on small molecules, antibodies and fragments thereof, and next generation immunization strategies. The increasing number of discovery and development efforts within this field may point towards an upcoming transition from serum-based antivenoms towards therapeutic solutions based on modern biotechnology.

Optimal Neutralization of Centruroides noxius Venom Is Understood through a Structural Complex between Two Antibody Fragments and the Cn2 Toxin

The current trend of using recombinant antibody fragments in research to develop novel antidotes against scorpion stings has achieved excellent results. The polyclonal character of commercial antivenoms, obtained through the immunization of animals and which contain several neutralizing antibodies that recognize different epitopes on the toxins, guarantees the neutralization of the venoms. To avoid the use of animals, we aimed to develop an equivalent recombinant antivenom composed of a few neutralizing single chain antibody fragments (scFvs) that bind to two different epitopes on the scorpion toxins. In this study, we obtained scFv RU1 derived from scFv C1. RU1 showed a good capacity to neutralize the Cn2 toxin and whole venom of the scorpion Centruroides noxius. Previously, we had produced scFv LR, obtained from a different parental fragment (scFv 3F). LR also showed a similar neutralizing capacity. The simultaneous administration of both scFvs resulted in improved protection, which was translated as a rapid recovery of previously poisoned animals. The crystallographic structure of the ternary complex scFv LR-Cn2-scFv RU1 allowed us to identify the areas of interaction of both scFvs with the toxin, which correspond to non-overlapping sites. The epitope recognized by scFv RU1 seems to be related to a greater efficiency in the neutralization of the whole venom. In addition, the structural analysis of the complex helped us to explain the cross-reactivity of these scFvs and how they neutralize the venom.

Development of protective agent against Hottentotta saulcyi venom using camelid single-domain antibody

Hottentotta saulcyi, medically important scorpion species, causes some of harmful toxic exposure in Iran. Administrated, conventional antivenom-based immunotherapy is still limited and hardly meet ideal characteristic of effective treatment for scorpion envenomation. In this study we aimed to develop a neutralizing agent directed against scorpion venom based on VHH, variable domain of the Camelidae heavy chain antibody or Nanobody. This promising biomolecule is well-established as an advantageous tool for therapeutic purposes due to its small size, stability, monomeric performance and less immunogenicity. In this study, a large Nb library was constructed and phage displayed after successful camel immunization using H. saulcyi scorpion crude venom. After a series of biopanning rounds on Sephadex G50 purified venom fraction and screening by monoclonal phage ELISA, the best reactive Nb was retrieved and designated Nb12. The selected Nb was then expressed as soluble protein in Escherichia coli, purified and confirmed by SDS-PAGE analysis and western blotting. The lead candidate Nb12 bound scorpion venom with Kaff value of 5×10(7)M(-1). Nb12 was shown to be capable of neutralizing 2 LD50 of whole venom of scorpion toxin when injected in the ratio of the Nb/toxin of 1.4:1 into C57BL/6 mice. In challenge experiment, Nb succeeded to rescue all i.p. lethal dose injected mice even when administrated i.v., 20min after envenoming. These results with ease of production and superior neutralizing activity make Nb a suitable anti-toxin candidate for treatment of scorpion envenoming.

Evolution of alternative methodologies of scorpion antivenoms production

Scorpionism represents a serious public health problem resulting in the death of children and debilitated individuals. Scorpion sting treatment employs various strategies including the use of specific medicines such as antiserum, especially for patients with severe symptoms. In 1909 Charles Todd described the production of an antiserum against the venom of the scorpion Buthus quinquestriatus. Based on Todd's work, researchers worldwide began producing antiserum using the same approach i.e., immunization of horses with crude venom as antigen. Despite achieving satisfactory results using this approach, researchers in this field have developed alternative approaches for the production of scorpion antivenom serum. In this review, we describe the work published by experts in toxinology to the development of scorpion venom antiserum. Methods and results describing the use of specific antigens, detoxified venom or toxins, purified toxins and or venom fractions, native toxoids, recombinant toxins, synthetic peptides, monoclonal and recombinant antibodies, and alternative animal models are presented.

A heterodimer of a VHH (variable domains of camelid heavy chain-only) antibody that inhibits anthrax toxin cell binding linked to a VHH antibody that blocks oligomer formation is highly protective in an anthrax spore challenge model

Anthrax disease is caused by a toxin consisting of protective antigen (PA), lethal factor, and edema factor. Antibodies against PA have been shown to be protective against the disease. Variable domains of camelid heavy chain-only antibodies (VHHs) with affinity for PA were obtained from immunized alpacas and screened for anthrax neutralizing activity in macrophage toxicity assays. Two classes of neutralizing VHHs were identified recognizing distinct, non-overlapping epitopes. One class recognizes domain 4 of PA at a well characterized neutralizing site through which PA binds to its cellular receptor. A second neutralizing VHH (JKH-C7) recognizes a novel epitope. This antibody inhibits conversion of the PA oligomer from "pre-pore" to its SDS and heat-resistant "pore" conformation while not preventing cleavage of full-length 83-kDa PA (PA83) by cell surface proteases to its oligomer-competent 63-kDa form (PA63). The antibody prevents endocytosis of the cell surface-generated PA63 subunit but not preformed PA63 oligomers formed in solution. JKH-C7 and the receptor-blocking VHH class (JIK-B8) were expressed as a heterodimeric VHH-based neutralizing agent (VNA2-PA). This VNA displayed improved neutralizing potency in cell assays and protected mice from anthrax toxin challenge with much better efficacy than the separate component VHHs. The VNA protected virtually all mice when separately administered at a 1:1 ratio to toxin and protected mice against Bacillus anthracis spore infection. Thus, our studies show the potential of VNAs as anthrax therapeutics. Due to their simple and stable nature, VNAs should be amenable to genetic delivery or administration via respiratory routes.

Antibody light chain variable domains and their biophysically improved versions for human immunotherapy

We set out to gain deeper insight into the potential of antibody light chain variable domains (V_Ls) as immunotherapeutics. To this end, we generated a naïve human V_L phage display library and, by using a method previously shown to select for non-aggregating antibody heavy chain variable domains (V_Hs), we isolated a diversity of V_L domains by panning the library against B cell super-antigen protein L. Eight domains representing different germline origins were shown to be non-aggregating at concentrations as high as 450 µM, indicating V_L repertoires are a rich source of non-aggregating domains. In addition, the V_Ls demonstrated high expression yields in E. coli, protein L binding and high reversibility of thermal unfolding. A side-by-side comparison with a set of non-aggregating human V_Hs revealed that the V_Ls had similar overall profiles with respect to melting temperature (T_m), reversibility of thermal unfolding and resistance to gastrointestinal proteases. Successful engineering of a non-canonical disulfide linkage in the core of V_Ls did not compromise the non-aggregation state or protein L binding properties. Furthermore, the introduced disulfide bond significantly increased their T_ms, by 5.5–17.5 °C, and pepsin resistance, although it somewhat reduced expression yields and subtly changed the structure of V_Ls. Human V_Ls and engineered versions may make suitable therapeutics due to their desirable biophysical features. The disulfide linkage-engineered V_Ls may be the preferred therapeutic format because of their higher stability, especially for oral therapy applications that necessitate high resistance to the stomach’s acidic pH and pepsin.

Engineering venom's toxin-neutralizing antibody fragments and its therapeutic potential

Serum therapy remains the only specific treatment against envenoming, but anti-venoms are still prepared by fragmentation of polyclonal antibodies isolated from hyper-immunized horse serum. Most of these anti-venoms are considered to be efficient, but their production is tedious, and their use may be associated with adverse effects. Recombinant antibodies and smaller functional units are now emerging as credible alternatives and constitute a source of still unexploited biomolecules capable of neutralizing venoms. This review will be a walk through the technologies that have recently been applied leading to novel antibody formats with better properties in terms of homogeneity, specific activity and possible safety.

Generation and characterization of nanobodies against rhGH expressed as sfGFP fusion protein

Growth hormone (GH) deficiencies are diagnosed in most children with short stature and treated with a long course of administrating expensive and daily doses of recombinant human GH (rhGH or Somatropin®). This work describes for the first time the production of several GH specific nanobodies with great potential in the field of GH production and detection. Nanobodies are the smallest intact antigen binders derived from heavy chain-only antibodies (HCAbs) of camelids. They are very stable, highly soluble and are produced as recombinant proteins in Escherichiacoli at an affordable cost for various biotechnological applications. To increase its solubility and immunogenicity, GH was produced as fusion with superfolder green fluorescent protein (sfGFP) and was used in this form to successfully immunize an adult camel. The active involvement of HCAbs in the specific camel immune response encouraged the preparation of large nanobody "immune" library. Phage display biopanning of this library against GH resulted in the isolation of five interesting and different nanobodies, referred to as NbGH01, 02, 03, 04 and 06. All nanobodies were able to recognize GH in its fusion and free formats and the detection sensitivity ranged from 0.5 to 10 ng/ml in sandwich ELISA. Pure rhGH was successfully purified by affinity chromatography, using immobilized NbGH06, from the cleavage reaction of fusion proteins with the tobaccos etch virus (TEV) protease. These specific molecular binders, especially NbGH06, provide valuable tools for rhGH diagnostic as well as for production purposes.

Wheat germ in vitro translation to produce one of the most toxic sodium channel specific toxins

Envenoming following scorpion sting is a common emergency in many parts of the world. During scorpion envenoming, highly toxic small polypeptides of the venom diffuse rapidly within the victim causing serious medical problems. The exploration of toxin structure-function relationship would benefit from the generation of soluble recombinant scorpion toxins in Escherichia coli. We developed an in vitro wheat germ translation system for the expression of the highly toxic Aah (Androctonus australis hector)II protein that requires the proper formation of four disulphide bonds. Soluble, recombinant N-terminal GST (glutathione S-transferase)-tagged AahII toxin is obtained in this in vitro translation system. After proteolytic removal of the GST-tag, purified rAahII (recombinant AahII) toxin, which contains two extra amino acids at its N terminal relative to the native AahII, is highly toxic after i.c.v. (intracerebroventricular) injection in Swiss mice. An LD₅₀ (median lethal dose)-value of 10 ng (or 1.33 pmol), close to that of the native toxin (LD₅₀ of 3 ng) indicates that the wheat germ in vitro translation system produces properly folded and biological active rAahII. In addition, NbAahII10 (Androctonus australis hector nanobody 10), a camel single domain antibody fragment, raised against the native AahII toxin, recognizes its cognate conformational epitope on the recombinant toxin and neutralizes the toxicity of purified rAahII upon injection in mice.

A wheat germ embryo derived cell-free translation system expresses a biologically active, highly toxic scorpion venom protein that is fully neutralized by a camel single domain antibody fragment raised against the native scorpion toxin.

Novel therapy based on camelid nanobodies

Nanobodies (Nbs) are small antibody fragments derived from camelid heavy chain antibodies through recombinant gene technology. Their exceptional physicochemical properties, possibility of humanization and unique antigen recognition properties make them excellent candidates for targeted delivery of biologically active components. Several different therapeutic approaches based on the novel camelid Nbs have been developed to treat a wide range of diseases ranging from immune, bone, blood and neurological disorders; infectious diseases and cancer. This review provides a comprehensive overview of the current state of the use of camelid-derived Nbs as novel therapeutic agents against multiple diseases.

In vivo neutralization of α-cobratoxin with high-affinity llama single-domain antibodies (VHHs) and a VHH-Fc antibody

Small recombinant antibody fragments (e.g. scFvs and VHHs), which are highly tissue permeable, are being investigated for antivenom production as conventional antivenoms consisting of IgG or F(ab')2 antibody fragments do not effectively neutralize venom toxins located in deep tissues. However, antivenoms composed entirely of small antibody fragments may have poor therapeutic efficacy due to their short serum half-lives. To increase serum persistence and maintain tissue penetration, we prepared low and high molecular mass antivenom antibodies. Four llama VHHs were isolated from an immune VHH-displayed phage library and were shown to have high affinity, in the low nM range, for α-cobratoxin (α-Cbtx), the most lethal component of Naja kaouthia venom. Subsequently, our highest affinity VHH (C2) was fused to a human Fc fragment to create a VHH2-Fc antibody that would offer prolonged serum persistence. After in planta (Nicotiana benthamiana) expression and purification, we show that our VHH2-Fc antibody retained high affinity binding to α-Cbtx. Mouse α-Cbtx challenge studies showed that our highest affinity VHHs (C2 and C20) and the VHH2-Fc antibody effectively neutralized lethality induced by α-Cbtx at an antibody:toxin molar ratio as low as ca. 0.75×:1. Further research towards the development of an antivenom therapeutic involving these anti-α-Cbtx VHHs and VHH2-Fc antibody molecules should involve testing them as a combination, to determine whether they maintain tissue penetration capability and low immunogenicity, and whether they exhibit improved serum persistence and therapeutic efficacy.

Diabody mixture providing full protection against experimental scorpion envenoming with crude Androctonus australis venom

Androctonus australis is primarily involved in envenomations in North Africa, notably in Tunisia and Algeria, and constitutes a significant public health problem in this region. The toxicity of the venom is mainly due to various neurotoxins that belong to two distinct structural and immunological groups, group I (the AahI and AahIII toxins) and group II (AahII). Here, we report the use of a diabody mixture in which the molar ratio matches the characteristics of toxins and polymorphism of the venom. The mixture consists of the Db9C2 diabody (anti-group I) and the Db4C1op diabody (anti-AahII), the latter being modified to facilitate in vitro production and purification. The effectiveness of the antivenom was tested in vivo under conditions simulating scorpion envenomation. The intraperitoneal injection of 30 μg of the diabody mixture protected almost all the mice exposed to 3 LD(50) s.c. of venom. We also show that the presence of both diabodies is necessary for the animals to survive. Our results are the first demonstration of the strong protective power of small quantities of antivenom used in the context of severe envenomation with crude venom.

Structural insights into antibody sequestering and neutralizing of Na+ channel α-type modulator from old world scorpion venom

The Old World scorpion Androctonus australis hector (Aah) produces one of the most lethal venoms for humans. Peptidic α-toxins AahI to AahIV are responsible for its potency, with AahII accounting for half of it. All four toxins are high affinity blockers of the fast inactivation phase of mammalian voltage-activated Na(+) channels. However, the high antigenic polymorphism of α-toxins prevents production of a polyvalent neutralizing antiserum, whereas the determinants dictating their trapping by neutralizing antibodies remain elusive. From an anti-AahII mAb, we generated an antigen binding fragment (Fab) with high affinity and selectivity for AahII and solved a 2.3 Å-resolution crystal structure of the complex. Sequestering of the C-terminal region of the bound toxin within a groove formed by the Fab combining loops is associated with a toxin orientation and main and side chain conformations that dictate the AahII antigenic specificity and efficient neutralization. From an anti-AahI mAb, we also preformed and crystallized a high affinity AahI-Fab complex. The 1.6 Å-resolution structure solved revealed a Fab molecule devoid of a bound AahI and with combining loops involved in packing interactions, denoting expulsion of the bound antigen upon crystal formation. Comparative analysis of the groove-like combining site of the toxin-bound anti-AahII Fab and planar combining surface of the unbound anti-AahI Fab along with complementary data from a flexible docking approach suggests occurrence of distinctive trapping orientations for the two toxins relative to their respective Fab. This study provides complementary templates for designing new molecules aimed at capturing Aah α-toxins and suitable for immunotherapy.

Research strategies to improve snakebite treatment: challenges and progress

Antivenom is an effective treatment of snakebite but, because of the complex interplay of fiscal, epidemiological, therapeutic efficacy and safety issues, the mortality of snakebite remains unacceptably high. Efficiently combating this high level of preventable death amongst the world's most disadvantaged communities requires the globally-coordinated action of multiple intervention programmes. This is the overall objective of the Global Snakebite Initiative. This paper describes the challenges facing the research community to develop snakebite treatments that are more efficacious, safe and affordable than current therapy.

Biotechnological applications of recombinant single-domain antibody fragments

BACKGROUND

Single-domain antibody fragments possess structural features, such as a small dimension, an elevated stability, and the singularity of recognizing epitopes non-accessible for conventional antibodies that make them interesting for several research and biotechnological applications.

RESULTS

The discovery of the single-domain antibody's potentials has stimulated their use in an increasing variety of fields. The rapid accumulation of articles describing new applications and further developments of established approaches has made it, therefore, necessary to update the previous reviews with a new and more complete summary of the topic.

CONCLUSIONS

Beside the necessary task of updating, this work analyses in detail some applicative aspects of the single-domain antibodies that have been overseen in the past, such as their efficacy in affinity chromatography, as co-crystallization chaperones, protein aggregation controllers, enzyme activity tuners, and the specificities of the unconventional single-domain fragments.

Exploiting cross-reactivity to neutralize two different scorpion venoms with one single chain antibody fragment

We report the optimization of a family of human single chain antibody fragments (scFv) for neutralizing two scorpion venoms. The parental scFv 3F recognizes the main toxins of Centruroides noxius Hoffmann (Cn2) and Centruroides suffusus suffusus (Css2), albeit with low affinity. This scFv was subjected to independent processes of directed evolution to improve its recognition toward Cn2 (Riaño-Umbarila, L., Juárez-González, V. R., Olamendi-Portugal, T., Ortíz-León, M., Possani, L. D., and Becerril, B. (2005) FEBS J. 272, 2591-2601) and Css2 (this work). Each evolved variant showed strong cross-reactivity against several toxins, and was capable of neutralizing Cn2 and Css2. Furthermore, each variant neutralized the whole venoms of the above species. As far as we know, this is the first report of antibodies with such characteristics. Maturation processes revealed key residue changes to attain expression, stability, and affinity improvements as compared with the parental scFv. Combination of these changes resulted in the scFv LR, which is capable of rescuing mice from severe envenomation by 3 LD(50) of freshly prepared whole venom of C. noxius (7.5 μg/20 g of mouse) and C. suffusus (26.25 μg/20 g of mouse), with surviving rates between 90 and 100%. Our research is leading to the formulation of an antivenom consisting of a discrete number of human scFvs endowed with strong cross-reactivity and low immunogenicity.

A recombinant dromedary antibody fragment (VHH or nanobody) directed against human Duffy antigen receptor for chemokines

Fy blood group antigens are carried by the Duffy antigen receptor for chemokines (DARC), a red cells receptor for Plasmodium vivax broadly implicated in human health and diseases. Recombinant VHHs, or nanobodies, the smallest intact antigen binding fragment derivative from the heavy chain-only antibodies present in camelids, were prepared from a dromedary immunized against DARC N-terminal extracellular domain and selected for DARC binding. A described VHH, CA52, does recognize native DARC on cells. It inhibits P. vivax invasion of erythrocytes and displaces interleukin-8 bound to DARC. The targeted epitope overlaps the well-defined DARC Fy6 epitope. K (D) of CA52-DARC equilibrium is sub-nanomolar, hence ideal to develop diagnostic or therapeutic compounds. Immunocapture by immobilized CA52 yielded highly purified DARC from engineered K562 cells. This first report on a VHH with specificity for a red blood cell protein exemplifies VHHs' potentialities to target, to purify, and to modulate the function of cellular markers.

Isolation and optimization of camelid single-domain antibodies: Dirk Saerens’ work on nanobodies

It is well established that all camelids have unique antibodies circulating in their blood. Unlike antibodies from all other species, these special antibodies are devoid of light chains, and are composed of a heavy chain homodimer. These so-called heavy-chain antibodies (HCAbs) are expressed after a V-D-J rearrangement and require dedicated constant gamma genes. An immune response is raised in these HCAbs following a classical immunization protocol. These HCAbs are easily purified from serum, and their antigen-binding fragment interacts with parts of the target that are less antigenic to conventional antibodies. The antigen binding site of the dromedary HCAb comprises one single domain, referred to as VHH or nanobody (Nb), therefore, a strategy was designed to clone the Nb repertoire of an immunized dromedary and to select the Nb with specificity for our target antigens. The monoclonal Nb is produced well in bacteria, is very stable and highly soluble, and it binds the antigen with high affinity and specificity. Currently, the recombinant Nb has been developed successfully for research purposes, as a probe in biosensors, to diagnose infections, or to treat diseases such as cancer or trypanosomiasis.

Multiple interests in structural models of DARC transmembrane protein

Duffy Antigen Receptor for Chemokines (DARC) is an unusual transmembrane chemokine receptor which (i) binds the two main chemokine families and (ii) does not transduct any signal as it lacks the DRY consensus sequence. It is considered as silent chemokine receptor, a tank useful for chemiotactism. DARC had been particularly studied as a major actor of malaria infection by Plasmodium vivax. It is also implicated in multiple chemokine inflammation, inflammatory diseases, in cancer and might play a role in HIV infection and AIDS. In this review, we focus on the interest to build structural model of DARC to understand more precisely its abilities to bind its physiological ligand CXCL8 and its malaria ligand. We also present innovative development on VHHs able to bind DARC protein. We underline difficulties and limitations of such bioinformatics approaches and highlight the crucial importance of biological data to conduct these kinds of researches.

Toxin-specific antibodies for the treatment of Clostridium difficile: current status and future perspectives

Therapeutic agents targeting bacterial virulence factors are gaining interest as non-antibiotic alternatives for the treatment of infectious diseases. Clostridium difficile is a Gram-positive pathogen that produces two primary virulence factors, enterotoxins A and B (TcdA and TcdB), which are responsible for Clostridium difficile-associated disease (CDAD) and are targets for CDAD therapy. Antibodies specific for TcdA and TcdB have been shown to effectively treat CDAD and prevent disease relapse in animal models and in humans. This review summarizes the various toxin-specific antibody formats and strategies under development, and discusses future directions for CDAD immunotherapy, including the use of engineered antibody fragments with robust biophysical properties for systemic and oral delivery.