Advanced Situation with Recombinant Toxins: Diversity, Production and Application Purposes

Today, the production and use of various samples of recombinant protein/polypeptide toxins is known and is actively developing. This review presents state-of-the-art in research and development of such toxins and their mechanisms of action and useful properties that have allowed them to be implemented into practice to treat various medical conditions (including oncology and chronic inflammation applications) and diseases, as well as to identify novel compounds and to detoxify them by diverse approaches (including enzyme antidotes). Special attention is given to the problems and possibilities of the toxicity control of the obtained recombinant proteins. The recombinant prions are discussed in the frame of their possible detoxification by enzymes. The review discusses the feasibility of obtaining recombinant variants of toxins in the form of protein molecules modified with fluorescent proteins, affine sequences and genetic mutations, allowing us to investigate the mechanisms of toxins' bindings to their natural receptors.

Brown Spider Venom Phospholipase-D Activity upon Different Lipid Substrates

Brown spider envenomation results in dermonecrosis, characterized by an intense inflammatory reaction. The principal toxins of brown spider venoms are phospholipase-D isoforms, which interact with different cellular membrane components, degrade phospholipids, and generate bioactive mediators leading to harmful effects. The Loxosceles intermedia phospholipase D, LiRecDT1, possesses a loop that modulates the accessibility to the active site and plays a crucial role in substrate. In vitro and in silico analyses were performed to determine aspects of this enzyme's substrate preference. Sphingomyelin d18:1/6:0 was the preferred substrate of LiRecDT1 compared to other Sphingomyelins. Lysophosphatidylcholine 16:0/0:0 was preferred among other lysophosphatidylcholines, but much less than Sphingomyelin d18:1/6:0. In contrast, phosphatidylcholine d18:1/16:0 was not cleaved. Thus, the number of carbon atoms in the substrate plays a vital role in determining the optimal activity of this phospholipase-D. The presence of an amide group at C2 plays a key role in recognition and activity. In silico analyses indicated that a subsite containing the aromatic residues Y228 and W230 appears essential for choline recognition by cation-π interactions. These findings may help to explain why different cells, with different phospholipid fatty acid compositions exhibit distinct susceptibilities to brown spider venoms.

IL13 Fused Pseudomonas Exotoxin Targets Various Cancers In Vitro

BACKGROUND/AIM

Pseudomonas exotoxin (PE) is one of the most widely used toxins in the construction of therapeutic fusion proteins in pre-clinical studies followed by phase trials. In principle, PE acts by blocking protein synthesis through catalyzing the inactivation of elongation factor-2 (EF-2). The interleukin-13 fused PE (IL13-PE) cytotoxin was previously designed to target GBM cells. In this study, the cytotoxic effects of IL13-PE were evaluated in 5 different types of cancers and the therapeutic effects were further analyzed in a lung cancer cell line, NCI-H460. Conceptually, in another lung cancer cell line (A549), IL13Rα2 was overexpressed by lentiviruses (A549-IL13Rα2) and evaluated for cytotoxic efficacy of IL13-PE.

MATERIALS AND METHODS

The expression profile of IL13Rα2 in different cancer cell lines was determined by RT-PCR. Secretable toxin fusion was expressed in the toxin resistant HEK-293T cell line (293T-TxR) by using a plasmid coding for IL13-PE and IRES-GFP (LV-IL13-PE-IRES/GFP). Next, the cells were shown to produce and secrete functional IL13-PE by dot blot analysis, followed by cell viability assays and cell death analysis.

RESULTS

Upon treatment with IL13-PE, a significant decrease in cell viability was selectively demonstrated in cancer cells with cognate receptor expression. IL13-PE treatment increased the apoptotic/necrotic cell populations in the NCI-H460 cell line.

CONCLUSION

Our results demonstrate that IL13-PE can be a therapeutic target for tumors bearing mostly IL13Rα2 positive cell populations. Our findings also suggest a cell-based delivery option for the recombinant toxins in the treatment of different cancers which can provide a solution for the clinical use of toxin therapy.

Bioengineering of Bordetella pertussis Adenylate Cyclase Toxin for Vaccine Development and Other Biotechnological Purposes

The adenylate cyclase toxin, CyaA, is one of the key virulent factors produced by Bordetella pertussis, the causative agent of whooping cough. This toxin primarily targets innate immunity to facilitate bacterial colonization of the respiratory tract. CyaA exhibits several remarkable characteristics that have been exploited for various applications in vaccinology and other biotechnological purposes. CyaA has been engineered as a potent vaccine vehicle to deliver antigens into antigen-presenting cells, while the adenylate cyclase catalytic domain has been used to design a robust genetic assay for monitoring protein-protein interactions in bacteria. These two biotechnological applications are briefly summarized in this chapter.

Engineering Botulinum Neurotoxins for Enhanced Therapeutic Applications and Vaccine Development

Botulinum neurotoxins (BoNTs) show increasing therapeutic applications ranging from treatment of locally paralyzed muscles to cosmetic benefits. At first, in the 1970s, BoNT was used for the treatment of strabismus, however, nowadays, BoNT has multiple medical applications including the treatment of muscle hyperactivity such as strabismus, dystonia, movement disorders, hemifacial spasm, essential tremor, tics, cervical dystonia, cerebral palsy, as well as secretory disorders (hyperhidrosis, sialorrhea) and pain syndromes such as chronic migraine. This review summarizes current knowledge related to engineering of botulinum toxins, with particular emphasis on their potential therapeutic applications for pain management and for retargeting to non-neuronal tissues. Advances in molecular biology have resulted in generating modified BoNTs with the potential to act in a variety of disorders, however, in addition to the modifications of well characterized toxinotypes, the diversity of the wild type BoNT toxinotypes or subtypes, provides the basis for innovative BoNT-based therapeutics and research tools. This expanding BoNT superfamily forms the foundation for new toxins candidates in a wider range of therapeutic options.

Innovative Immunization Strategies for Antivenom Development

Snakes, scorpions, and spiders are venomous animals that pose a threat to human health, and severe envenomings from the bites or stings of these animals must be treated with antivenom. Current antivenoms are based on plasma-derived immunoglobulins or immunoglobulin fragments from hyper-immunized animals. Although these medicines have been life-saving for more than 120 years, opportunities to improve envenoming therapy exist. In the later decades, new biotechnological tools have been applied with the aim of improving the efficacy, safety, and affordability of antivenoms. Within the avenues explored, novel immunization strategies using synthetic peptide epitopes, recombinant toxins (or toxoids), or DNA strings as immunogens have demonstrated potential for generating antivenoms with high therapeutic antibody titers and broad neutralizing capacity. Furthermore, these approaches circumvent the need for venom in the production process of antivenoms, thereby limiting some of the complications associated with animal captivity and venom collection. Finally, an important benefit of innovative immunization approaches is that they are often compatible with existing antivenom manufacturing setups. In this review, we compile all reported studies examining venom-independent innovative immunization strategies for antivenom development. In addition, a brief description of toxin families of medical relevance found in snake, scorpion, and spider venoms is presented, as well as how biochemical, bioinformatic, and omics tools could aid the development of next-generation antivenoms.

Proton probing of the charybdotoxin binding site of Shaker K+ channels

We have investigated the interaction of charybdotoxin (CTX) with Shaker K channels. We substituted a histidine residue for the wild-type phenylalanine (at position 425) in an inactivation-removed channel. The nature of the imidazole ring of the histidine provides the ability to change the charge on this amino acid side chain with solution hydrogen ion concentration. Wild-type, recombinant CTX blocked wild-type Shaker channels in a bimolecular fashion with a half-blocking concentration (Kd) of 650 nM (at a membrane potential of 0 mV). The F425H mutant channels were much more sensitive to CTX block with an apparent Kd (at pH 7.0) of 75 nM. Block of F425H but not wild-type channels was strongly pH sensitive. A pH change from 7 to 5.5 rendered the F425H channels >200-fold less sensitive to CTX. The pH dependence of CTX block was steeper than expected for inhibition produced by H+ ions binding to identical, independent sites. The data were consistent with H+ ions interacting with subunits of the channel homotetrameric structure. The in situ pK for the imidazole group on the histidine at channel position 425 was determined to be near 6.4 and the dissociation constant for binding of toxin to the unprotonated channel was near 50 nM. We estimate that the binding of a H+ ion to each subunit adds 0.8 kcal/mol or more of interaction energy with CTX. We used mutant toxins to test electrostatic and steric interactions between specific CTX residues and channel position 425. Our results are consistent with a model in which protons on F425H channel subunits interact with three positive charges on CTX at an effective distance 6-7 A from this channel position.