Toxin Neutralization Using Alternative Binding Proteins

Abstract

Animal toxins present a major threat to human health worldwide, predominantly through snakebite envenomings, which are responsible for over 100,000 deaths each year. To date, the only available treatment against snakebite envenoming is plasma-derived antivenom. However, despite being key to limiting morbidity and mortality among snakebite victims, current antivenoms suffer from several drawbacks, such as immunogenicity and high cost of production. Consequently, avenues for improving envenoming therapy, such as the discovery of toxin-sequestering monoclonal antibodies against medically important target toxins through phage display selection, are being explored. However, alternative binding protein scaffolds that exhibit certain advantages compared to the well-known immunoglobulin G scaffold, including high stability under harsh conditions and low cost of production, may pose as possible low-cost alternatives to antibody-based therapeutics. There is now a plethora of alternative binding protein scaffolds, ranging from antibody derivatives (e.g., nanobodies), through rationally designed derivatives of other human proteins (e.g., DARPins), to derivatives of non-human proteins (e.g., affibodies), all exhibiting different biochemical and pharmacokinetic profiles. Undeniably, the high level of engineerability and potentially low cost of production, associated with many alternative protein scaffolds, present an exciting possibility for the future of snakebite therapeutics and merit thorough investigation. In this review, a comprehensive overview of the different types of binding protein scaffolds is provided together with a discussion on their relevance as potential modalities for use as next-generation antivenoms.

Cost of Manufacturing for Recombinant Snakebite Antivenoms

“…IgG antibodies have many advantages, such as a long serum half-life, extensive clinical validation, and established manufacturing strategies. Yet, other smaller formats, including Fabs, scFvs, DARPins, nanobodies, and Avimers, have their own set of advantages ( Jenkins et al, 2019 ; Knudsen et al, 2019 ). Indeed, these formats have more binding sites per mass unit due to their smaller molar mass, which could have a favorable influence on cost dynamics, as the amount of antitoxin required for neutralizing a given venom may be less (in terms of gram).…”

“…This demonstrates that even in rare cases where IgGs might not be financially viable, alternative antitoxin scaffolds could be used instead to achieve economic viability. There are, however, other variables to consider when calculating the costs of a recombinant antivenom using alternative antitoxin scaffolds, such as their short half-life (likely requiring administration of larger amounts of the antivenom) and different volumes of distribution ( Jenkins et al, 2019 ). Many alternative antitoxin scaffolds can be produced via microbial expression, rather than mammalian cell cultivation, which may have the potential to be even more cost-competitive at large production volumes.…”

“…Many alternative antitoxin scaffolds can be produced via microbial expression, rather than mammalian cell cultivation, which may have the potential to be even more cost-competitive at large production volumes. However, given the lack of manufacturing cost data for microbial expression, we decided not to overspeculate in this regard and use the same COGM API for all antitoxin formats ( Jenkins et al, 2019 ). The actual costs for alternative antitoxin scaffolds may, thus, be even more attractive than presented here.…”

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

“…Phage display technology and the production of recombinant antibodies in bacteria, yeast, insect, and mammalian expression systems have the potential to overcome these contraindications [ 13 ] and studies of recombinant antibodies against venoms from snakes [ 31 , 32 ] and scorpions [ 33 , 34 ] show the feasibility of this approach. While phage display is usually applied to antibody discovery, other non-antibody scaffolds also can be considered for the design of anti-venoms [ 35 ].…”

An interactive database for the investigation of high-density peptide microarray guided interaction patterns and antivenom cross-reactivity

“…When administered promptly, antivenoms derived from the plasma of hyper-immunized animals are effective in neutralizing the main clinical manifestations of snakebite envenoming, particularly the systemic effects [2][3][4]. Despite this, antivenoms have many limitations relating to their specificity, safety and affordability, and thus there is a strong rationale to develop new snakebite therapeutics with higher efficacy and broader species coverage, as well as at a lowered cost [5,6]. Toxicovenomics is a proteomicsbased approach that can be used to analyze snake venoms to provide an overview of which toxins are medically relevant in envenomings, and this approach shows promise for selecting the most effective venom mixtures for immunization [7][8][9].…”