Re-invigorating the insecticide discovery pipeline for vector control: GPCRs as targets for the identification of next gen insecticides

G protein-coupled receptors (GPCRs) comprise a large family of membrane-bound molecules that mediate critical physiological roles in both vertebrates and invertebrates. GPCRs are widely exploited targets of the pharmaceutical industry; approximately 50% of human drugs interact with these receptors. GPCRs are also candidate targets for next-generation insecticides and provide opportunities to discover new mode-of-action chemistries for insect control. We present an overview of the Purdue Insecticide Discovery Pipeline which employs a target-based “genome-to-lead” approach to identify novel insecticidal molecules. The pipeline is focused on invertebrate GPCRs, with an emphasis on mosquito and tick dopamine receptors (DARs). We summarize published studies describing the characteristics of D1-like (Gαs coupled) DARs from the yellow fever mosquito, Aedes aegypti (AaDOP1, AaDOP2) and Lyme disease tick, Ixodes scapularis (IsDOP1, IsDOP2), and review our ongoing cell-based chemical library screening efforts to discover small molecule ligands and modulators of AaDOP2 and IsDOP2. We discuss “hit-to-lead” optimization of AaDOP2 antagonists and present in vivo assay data demonstrating that lead antagonists cause rapid and high mortality of Ae. aegypti larvae. To expand capabilities of the pipeline, we developed an in vitro screen to identify small molecule agonists of AaDOP2. Twenty-five agonists were discovered in the screen that exhibited significant potency at AaDOP2, although a subset of the hits that were tested (SKF82958, SKF81297) showed no evidence of in vivo toxicity to Ae. aegypti larvae. Finally, we analyze the conceptual protein sequence of D1-like DARs from the malaria mosquito, Anopheles gambiae and the northern-house mosquito, Culex quinquefasciatus, and discuss the potential application of GPCR target-based insecticide discovery for other mosquito vectors of importance to human health.