Binding of imidacloprid, thiamethoxam and N-desmethylthiamethoxam to nicotinic receptors of Myzus persicae: pharmacological profiling using neonicotinoids, natural agonists and antagonists

BACKGROUNDThe increasing structural diversity of the neonicotinoid class of insecticides presently used in crop protection calls for a more detailed analysis of their mode of action at their cellular targets, the nicotinic acetylcholine receptors. RESULTSComparative radioligand binding studies using membranes of Myzus persicae (Sulzer) and representatives of the chloropyridyl subclass (imidacloprid), the chlorothiazolyl subclass (thiamethoxam), the tetrahydrofuranyl subclass (dinotefuran), as well as the novel sulfoximine type (sulfoxaflor), which is not a neonicotinoid, reveal significant differences in the number of binding sites, the displacing potencies and the mode of binding interference. Furthermore, the mode of interaction of [H-3]thiamethoxam and the nicotinic antagonists methyllycaconitine and dihydro--erythroidine is unique, with Hill values of >1, clearly different to the values of around unity for [H-3]imidacloprid and [H-3]N-desmethylthiamethoxam. The interaction of [H-3]N-desmethylthiamethoxam with the agonist (-)nicotine is also characterised by a Hill value of >1. CONCLUSIONSThere is no single conserved site or mode of binding of neonicotinoids and related nicotinic ligands to their target receptor, but a variety of binding pockets depending on the combination of receptor subunits, the receptor subtype, its functional state, as well as the structural flexibility of both the binding pockets and the ligands. (c) 2016 Society of Chemical Industry