Insecticides have been a central tool in agriculture and medicine throughout all of history, increasing the yield and quality of much of the food that we eat, and protecting us from vector-borne diseases. However, selectivity is a considerable concern, as insecticides have been known to affect marine life, humans and other mammals. Additionally, the use of insecticides decimates pollinator networks, which have been increasingly appreciated as an integral part of agricultural crop health.
These phenomena clearly underscore the need for insecticides that selectively target only pest insects. The ecdysone receptor (ECR) is an interesting prospect as a target for new and selective insecticides. ECR is a heterodimeric transcription factor present in arthropods, which has been targeted by insecticides in the past; for example, tebufenozide displays selectivity for Lepidoptera over other arthropod orders. These findings suggest ECR as a target for the design of other selective insecticides.
This project focuses on the green peach aphid (GPA). GPA is a generalist pest insect that feeds on and transmits viruses to a broad range of crops, including cruciferous vegetables and oilseeds. However, GPA has become resistant to the most common insecticide classes (such as pyrethroids and neonicotinoids), and new control mechanisms are needed to reduce the strain the GPA causes on the agricultural system.
This project describes the initial phase of such an insecticide program: the production and characterisation of the ligand-binding domain (LBD) of GPA ECR, and the initial fragment-based drug discovery (FBDD) primary screen.
The two subunits comprising the LBD of GPA ECR were co-expressed and purified from E. coli. SEC-MALLS confirmed that purified protein was heterodimeric, and a fluorescence polarization assay demonstrated that ECR bound with nanomolar affinity to a fluorescent ecdysone analogue, therefore being functional. Following optimization of buffer conditions, FBDD was conducted using ligand-detected NMR spectroscopy. Hits were compared to fragment screens carried out against two other arthropod ECRs, which revealed that selectivity could be observed at this early stage of the design process. This result is extremely encouraging for the prospect of using FBDD as a route to developing selective insecticides targeting GPA and other arthropod pests