Developing botanical-derived chemical tools for controlling mosquito vectors

Project Summary: The yellow fever mosquito Aedes aegypti is the principal vector of several medically-important arboviruses that have recently emerged or re-emerged globally, such as chikungunya, dengue, and Zika. The mitigation of mosquito-borne diseases often relies on preventing mosquitoes from biting humans via the use of chemical control tools, such as insecticides and/or repellents. However, the emergence of insecticide resistance in mosquitoes has reduced the efficacy of the most widely used control agents (e.g., pyrethroids), resulting in a need to develop insecticides with novel modes of action. Moreover, only a few mosquito repellents are currently registered by the Environmental Protection Agency and recommended by the Centers for Disease Control. Limited knowledge on the modes of action of these repellents has hampered development and optimization of biorational mosquito repellents. Thus, chemical control tools with novel modes of action are needed to improve the management of mosquito vectors. With the support of an R21 grant, we discovered a drimane sesquiterpene (cinnamodial, CDIAL) from the bark of an endemic medicinal plant of Madagascar (Cinnamosma fragrans; family Canellaceae) that kills larval and adult female Ae. aegypti. The mode of toxic action of CDIAL in mosquitoes involves paralysis of visceral muscle associated with activation of Ca2+ channels, a unique mode of action compared to pyrethroids. Moreover, we found that CDIAL is a potent agonist of mosquito transient receptor potential ankyrin 1 (TRPA1) channels, an established mode of action for some mosquito repellents and antifeedants. The goal of the proposed R01 research is to develop novel CDIAL-based chemical tools for controlling mosquitoes with Ae. aegypti as our primary study species. In Aim 1, we will use natural products, medicinal chemistry, in vivo bioassays, and machine learning to develop quantitative structure-activity relationship (QSAR) models of the insecticidal and visceral muscle paralysis activities of CDIAL. These models will inform the iterative design of CDIAL derivatives that are at least 100-fold more potent than CDIAL as insecticides. In Aim 2, we will use in silico modeling and heterologous expression approaches to determine how CDIAL respectively binds to mosquito and human TRPA1 channels. This knowledge will inform the design and iterative QSAR-based optimization of CDIAL-based agonists that are at least 100-times more specific for mosquito over human TRPA1 channels and repel adult female mosquitoes. In addition, the in silico structural models of mosquito TRPA1 will be used to virtually screen a natural product library of over 400,000 compounds to discover novel mosquito-selective TRPA1 agonists that repel mosquitoes. Lead compounds from both Aims will be considered ‘candidates’ if they meet mammalian cytotoxicity benchmarks and are efficacious against multiple mosquito vectors (Anopheles gambiae, Culex quinquefasciatus). Collectively, results from both aims will facilitate development of next-generation chemical tools to control mosquito vectors.