Identification of powerful repellents that target mosquito olfaction, gustation and the Na-channel - ABSTRACT Mosquitoes use their chemosensory systems to smell and taste the human host skin, and in the process of subsequent blood feeding, transmit diseases like malaria and Dengue to hundreds of millions of people each year. The olfactory and gustatory systems are thus excellent targets to design repellents that reduce mosquito bites and disease incidence. Topical repellents like DEET are effective against mosquitoes, but are rarely used by at-risk populations in tropical countries for reasons of high-cost relative to incomes, inconvenience of concentrated and repeated application on the skin, and poor cosmetic properties. Globally, the most widely-used intervention is spatial protection from pyrethroid insecticides emitted at low doses from heated dispensers or burning coils. However, the rapid spread of pyrethroid resistance in mosquitoes is cause for great concern about the continued effectiveness of these measures. There is an urgent need to develop safer and more effective repellents and pyrethroid analogs, but traditional chemical ecology approaches, pharmaceutical screens, or receptor targeting have not yielded candidates, and have prohibitive costs for testing for human use approval. In a recent breakthrough, we developed an AI-based cheminformatic method to predict new repellents and new pyrethroid-like molecules from in silico screening of >10 M compounds. In preliminary studies, we tested a subset of the top repellent hits in a behavior assay and validated a high success rate in finding pleasant-smelling repellents from natural sources, including food and flavor compounds. We also tested several pyrethroid-like hits, which identified two new pyrethroid analogs that appear to be up to 100x more effective than allethrin, an industry standard. We now propose to identify the best-in-class insect control compounds that exceed current actives in four important categories: a pleasant topical repellent with longer protection (>12-24 hours), a spatial repellent for indoor or small outdoor spaces, a pyrethroid analog that is active on resistant mosquitoes for bednets or uniforms, and a spatial repellent-pyrethroid formulation that is effective against knockdown-resistant mosquitoes. Our approach is to validate a larger subset of computationally-predicted repellents, representing diverse chemical structures and properties, in various topical and spatial behavior assays. We will apply additional secondary screening criteria to group and select hits for further analysis: responses in taste neurons for topical repellents, prolonged activation of CO2 neurons for spatial repellents, and receptor pathway function as determined from analysis of available Aedes aegypti co-receptor mutants for blends. We will also determine the efficacy of the two newly discovered pyrethroids using topical and spatial assays. Finally, we will test combinations of identified repellents and pyrethroid analogs. Completion of this work will identify safe, affordable, and pleasant-smelling blends that are better than existing actives in reducing contact between humans and mosquitoes. The proposed studies will also provide insight into modes of repellency action and lay the groundwork for future identification of selective receptors for developing targeted control approaches.
