Download PDF Winter Issue of The Bridge on Frontiers of Engineering December 25, 2021 Volume 51 Issue 4 The NAE’s Frontiers of Engineering symposium series forged ahead despite the challenges of the pandemic, with virtual and hybrid events in 2021. This issue features selected papers from early-career engineers reporting on new developments in a variety of areas. Peptides as a New Class of Biopesticide Tuesday, January 4, 2022 Author: Kyle D. Schneider Biologic peptides are safe, effective alternatives to current synthetic agrochemical pesticides. A stable and affordable food supply is critical to the foundation and growth of any nation’s economic prosperity. In the United States, agricultural productivity has steadily increased since the Industrial Revolution, and the last 60 years have seen a threefold rise in total crop yield, all while using 25 percent less land (Wang et al. 2018). Innovations like chemical fertilizers, pesticides, plant breeding and trait development, and enhanced cultivation methods are the major drivers of this productivity improvement that affords Americans some of the lowest food prices per capita anywhere in the world. Recent analysis, however, suggests that productivity gains have slowed, threatening the nation’s food security (Steensland and Thompson 2021). In particular, the crop protection industry is suffering from an innovation crisis. Background Pesticides become less effective over time as target pests become resistant (Hawkins et al. 2018). At the same time, the development rate of new pesticides has decreased dramatically and others have been pulled from the market because of safety concerns (Windley et al. 2012). Thus crop protection options for farmers are dwindling (figure 1), resulting in overuse of the limited available options and further reducing pesticide efficacy as pest resistance increases. FIGURE 1 Innovation crisis in agricultural insecticides. Left: In 1991 US farmers had hundreds of crop protection options to control pests. More than half of those options have since been removed from the market because of toxicity concerns. Right: At the same time, the rate of novel active insecticide product launches has been declining, resulting in far fewer options for farmers to control insect pests. Even with the existing options for pest management, 5–20 percent of all US crops are lost to insect damage, and in parts of the world without effective pest control crop losses can exceed 50 percent (Savary et al. 2019). If the current reduced rate of crop protection development continues, staggering crop losses may be anticipated. Innovations are urgently needed to address the coming shortfall in safe, effective pesticides and to maintain at least current levels of food security. This paper details some of the challenges facing the insecticide industry and proposes biologic peptides as safe, effective alternatives to synthetic agrochemical products The Innovation Challenge for Crop Protection The causes of the declining supply of effective crop protection solutions are multiple but include the higher rate of pest resistance, restrictions on current pesticides, and the increased time and cost to develop new synthetic products. Pest Resistance Insects evolve resistance to pesticides over time (much as bacterial pathogens can become resistant to antibiotics), putting a lifespan on the effectiveness of every insecticide. As an example, fall armyworm, an annual corn pest that can destroy entire harvests, has evolved resistance to 29 insecticides (Gutiérrez-Moreno et al. 2019). For this and other pests, the rate of resistance development is proportional to its exposure to any one insecticide. The development of pest resistance can be mitigated with integrated pest management options such as rotation of different insecticides across seasons. In many cases, however, the lack of new insecticides has left farmers with few options. The US Environmental Protection Agency (EPA) has had to allow special use exemptions for more toxic pesticides to be applied in some instances. Regulatory Restrictions Regulatory agencies charged with protecting consumers and the environment have been enforcing more stringent environmental and toxicity safety regulations over the last several decades. Such efforts can be credited for an industrywide shift away from pesticides that are toxic to people and other vertebrates. For example, the midcentury use of organophosphates has largely been banned or limited because of their human toxicity, especially in children. And the banning of DDT has been widely credited for the recovery of several endangered avian species (Grier 1982). Banned pesticides have been replaced with new classes that have much better target specificity and thus much less toxicity for vertebrates. However, the toxicity burden has now shifted to beneficial insects such as pollinators like bees, with the result that these new chemicals also face restrictions or bans (Schulz et al. 2021). Regulatory agencies face a dilemma as in some instances there may be no effective alternative to current synthetic agrochemical products. Increased Cost and Time to Develop Synthetic Pesticides In 1958 it cost around $2–3 million (~$20–30 million in 2021 dollars) to bring an insecticide to market (Barnard 1958). Today, costs are estimated to range from $150 to $300 million to develop a similar product. In addition, the time it takes to develop and register an insecticide continues to increase. Whereas in the early 1990s a new product could be developed and marketed within 8 years, it now takes over a decade to commercialize a synthetic insecticide (Olson 2015; Sparks 2013). The higher costs and long development times have led to reduced productivity and fewer products in the market. Advantages of Peptide Biologics for Crop Protection The slowing rate of innovation threatens food supplies as pests develop resistance to existing pesticides. The dual challenge is that new products are needed to avoid a crisis and environmental safety and sustainability cannot be compromised. I propose the use of peptide biologics to design environmentally sustainable pesticides that work as effectively as standard synthetic agrochemicals while resetting the resistance clock through the expedient introduction of more (and safer) products. Biopesticides represent a small fraction of the $58 billion crop protection market but are growing at a rate above 15 percent per year and are expected to equal the synthetic market in the next 2 decades (Damalas and Koutroubas 2017). The potential promise of biologics as biopesticides has been known for several decades, but manufacturing and delivery challenges have prevented their widescale commercialization until recently. Large protein biologics (e.g., antibodies or enzymes) have driven a biotechnology revolution in the pharmaceutical industry thanks to their high efficacy, predictable safety profile, and ease to develop. In crop protection, however, they have had less success as biopesticides because they typically have limited stability in the field, they require cold supply chains, and they have difficulty penetrating the insect cuticle to reach essential targets. To ensure a sustainable future and move away from synthetic agrochemicals, these challenges must be addressed. Smaller versions of proteins called peptides can overcome these stability and delivery challenges and target the exact same receptors as synthetic agrochemicals. In nature, insect-specific peptide neurotoxins are used by many species of spiders, scorpions, and centipedes to immobilize and kill their prey, offering a model for the derivation of safe, effective pesticides (King 2019). Further advantages include peptides’ smaller size, which facilitates their penetration across outer barriers (as discussed below) and could allow for more efficient manufacturing, lowering input costs for farmers. Another manufacturing and delivery benefit is the fact that peptides can be made highly stable through crosslinking, ensuring long-lasting field performance and stability through the supply chain. Because stable peptides do not need a cold supply chain, they eliminate a problematic and costly barrier for the adoption of biologics in crop protection. Importantly, peptide pesticides have little environmental toxicity, thanks to their amino acid building blocks and lack of toxic metabolites. They have high specificity for target pests and receptors, and so no risk of unexpected toxicity for vertebrates or beneficial insects like honeybees. Challenges and Opportunities for a Peptide Biologic Future Three factors play a role in the widespread commercialization of peptide biopesticides: bioavailability, manufacturing cost, and regulation. Bioavailability Bioavailability has been the most significant barrier to the commercialization of biologics that target insect receptors (Windley et al. 2012). This challenge can be conceptualized by thinking of the outer structures of an insect pest (exoskeleton or gut lining) as a filter that discriminates by size. Larger molecules, such as proteins or nucleic acids, are mostly prevented from entering, while small molecules like chemical synthetics can pass relatively unimpeded. Peptides are between synthetic agrochemicals and protein biologics in size, and thus have an intermediate ability to cross these barriers. The intrinsic bioavailability of peptides can be sufficient to directly target internal receptors such as those in the nervous system. The recently approved peptide GS-w/k-Hxtx-Hv1a, for example, targets the same receptor as two major classes of synthetic agrochemicals and can kill insects on contact in a commercial formulation. Manufacturing Cost The cost to manufacture biologics can be too high for the application rate needed to ensure contact, such as outdoor applications where less of the spray reaches its destination. In these instances, bioavailability enhancers may be necessary to reduce peptide use rates. This has been successfully demonstrated for a caterpillar application of the GS-w/k-Hxtx-Hv1a peptide combined with microbial Bacillus thuringiensis, dramatically reducing necessary peptide application rates by permeabilizing the insect gut and increasing peptide access to the target. By pairing a microbial with a peptide biologic, the environmental safety profile is maintained while also providing synthetic agrochemical insect control. Biologic manufacturing costs have fallen 100-fold since the 1990s and are expected to continue to fall as manufacturing capacity increases, raw inputs become commoditized, and cell-based manufacturing strains become engineered for greater efficiency. Declining costs will support the expansion of peptide use in a wide range of pesticide markets and applications (Farid et al. 2020). Regulation Existing regulatory frameworks do not apply well to new and emerging biotechnologies (e.g., gene editing, nucleic acids, peptides/proteins). New frameworks are needed, and the US EPA and European Environment Agency have begun to update them for novel biotechnology solutions, including peptides, in crop protection. But the changes may create challenges if the proper tools or expertise to evaluate a new technology are not available. The best path forward is transparency, to give the most certainty possible to developers as they navigate the evolving regulatory process and ensure safety for growers and consumers. Conclusion Innovation is required to keep up with insect resistance. Synthetic agrochemicals are too expensive and slow to develop and are unsustainable for the environment. Biopesticides address these shortcomings: they are faster and cheaper to develop, and sustainable for the environment. Specifically, peptides offer the safety profile of microbial biopesticides combined with the efficacy of synthetic agrochemicals. Combined, these properties make peptides a sustainable alternative to synthetic agrochemicals. The biotechnology revolution in agriculture is fast approaching. For crop protection, a move away from synthetic agrochemicals toward more sustainable pesticides is highly desirable but may increase risks to food security if pesticide effectiveness cannot be maintained. Peptide-based biologics offer an alternative to synthetics as they possess the dual traits of sustainability and efficacy, making them ideal candidates to form the backbone of a green future in crop protection. References Damalas C, Koutroubas S. 2017. Current status and recent developments in biopesticide use. Agriculture 8(1). Barnard CO. 1958. Pesticide development costs. Agricultural and Food Chemistry 6(7):12–13. Farid SS, Baron M, Stamatis C, Nie W, Coffman J. 2020. Benchmarking biopharmaceutical process development and manufacturing cost contributions to R&D. mAbs 12(1). Fisher MC, Henk DA, Briggs CJ, Brownstein JS, Madoff LC, McCraw SL, Gurr SJ. 2012. Emerging fungal threats to animal, plant and ecosystem health. Nature 484:186–94. Grier JW. 1982. Ban of DDT and subsequent recovery of reproduction in bald eagles. Science 218(4578):1232–35. Gutiérrez-Moreno R, Mota-Sanchez D, Blanco CA, Whalon ME, Terán-Santofimio H, Rodriguez-Maciel JC, DiFonzo C. 2019. Field-evolved resistance of the fall armyworm (Lepidoptera: Noctuidae) to synthetic insecticides in Puerto Rico and Mexico. Journal of Economic Entomology 112(2):792–802. Hawkins NJ, Bass C, Dixon A, Neve P. 2018. The evolutionary origins of pesticide resistance. Biological Reviews 94(1):135–55. King GF. 2019. Tying pest insects in knots: The deployment of spider-venom-derived knottins as bioinsecticides. Pest Management Science 75(9):2437–45. Savary S, Willocquet L, Pethybridge SJ, Esker P, McRoberts N, Nelson A. 2019. The global burden of pathogens and pests on major food crops. Nature Ecology and Evolution 3(1):430–39. Schulz R, Bub S, Petschick LL, Stehle S, Wolfram J. 2021. Applied pesticide toxicity shifts toward plants and invertebrates, even in GM crops. Science 372(6537):81–84. Sparks TC. 2013. Insecticide discovery: An evaluation and analysis. Pesticide Biochemistry and Physiology 107:8–17. Steensland A, Thompson T, eds. 2021. Strengthening the Climate for Sustainable Agricultural Growth: Global Agricultural Productivity (GAP) Report. Blacksburg: Virginia Tech College of Agriculture and Life Sciences. Wang SL, Nehring R, Mosheim R. 2018. Agricultural productivity growth in the United States: 1948-2015. Amber Waves, Mar 5. Washington: US Department of Agriculture Economic Research Service. Windley MJ, Herzig V, Dziemborowicz SA, Hardy MC, King GF, Nicholson GM. 2012. Spider-venom peptides as bioinsecticides. Toxins 4(3):191–227.  USDA table: Percent of consumer expenditures spent on food, alcoholic beverages, and tobacco that were consumed at home, by selected countries, 2015–20; available at https://www.ers.usda.gov/media/e2pbwgyg/2015-2020-food- spending_update-july-2021.xlsx.  See the EPA Emergency Exemption Database at https://ordspub.epa.gov/ords/pesticides/f?p=124:2::::: : (updated October 19, 2021). About the Author:Kyle Schneider is a senior scientist of peptide development at Vestaron Corporation.