Mode of action of fluopyram in plant-parasitic nematodes.

Plant-parasitic nematodes (PPN) are responsible for severe yield losses in crop production. Management is challenging as effective and safe means are rare. Recently, it has been discovered that the succinate dehydrogenase (SDH) inhibitor fluopyram is highly effective against PPN while accompanying an excellent safety profile. Here we show that fluopyram is a potent inhibitor of SDH in nematodes but not in mammals, insects and earthworm, explaining the selectivity on molecular level. As a consequence of SDH inhibition, fluopyram impairs ATP generation and causes paralysis in PPN and Caenorhabditis elegans. Interestingly, efficacy differences of fluopyram amongst PPN species can be observed. Permanent exposure to micromolar to nanomolar amounts of fluopyram prevents Meloidogyne spp. and Heterodera schachtii infection and their development at the root. Preincubation of Meloidogyne incognita J2 with fluopyram followed by a recovery period effectively reduces gall formation. However, the same procedure does not inhibit H. schachtii infection and development. Sequence comparison of sites relevant for ligand binding identified amino acid differences in SDHC which likely mediate selectivity, coincidently revealing a unique amino acid difference within SDHC conserved among Heterodera spp. Docking and C. elegans mutant studies suggest that this minute difference mediates altered sensitivity of H. schachtii towards fluopyram.

Assessing the anti-resistance potential of public health vaporizer formulations and insecticide mixtures with pyrethroids using transgenic Drosophila lines.

BACKGROUND: Insecticide resistance-and especially pyrethroid resistance-is a major challenge for vector control in public health. The use of insecticide mixtures utilizing alternative modes of action, as well as new formulations facilitating their uptake, is likely to break resistance and slow the development of resistance. METHODS: We used genetically defined highly resistant lines of Drosophila melanogaster with distinct target-site mutations and detoxification enzymes to test the efficacy and anti-resistance potential of novel mixture formulations (i.e. Fludora® Fusion consisting of deltamethrin and clothianidin), as well as emulsifiable concentrate transfluthrin, compared to alternative, currently used pyrethroid insecticide formulations for vector control. RESULTS: The commercial mixture Fludora® Fusion, consisting of both a pyrethroid (deltamethrin) and a neonicotinoid (clothianidin), performed better than either of the single active ingredients against resistant transgenic flies. Transfluthrin, a highly volatile active ingredient with a different molecular structure and primary exposure route (respiration), was also efficient and less affected by the combination of metabolic and target-site resistance. Both formulations substantially reduced insecticide resistance across different pyrethroid-resistant Drosophila transgenic strains. CONCLUSIONS: The use of mixtures containing two unrelated modes of action as well as a formulation based on transfluthrin showed increased efficacy and resistance-breaking potential against genetically defined highly resistant Drosophila flies. The experimental model remains to be validated with mosquito populations in the field. The possible introduction of new transfluthrin-based products and mixtures for indoor residual spraying, in line with other combination and mixture vector control products recently evaluated for use in public health, will provide solutions for better insecticide resistance management.

AzoCholine Enables Optical Control of Alpha 7 Nicotinic Acetylcholine Receptors in Neural Networks.

Nicotinic acetylcholine receptors (nAChRs) are essential for cellular communication in higher organisms. Even though a vast pharmacological toolset to study cholinergic systems has been developed, control of endogenous neuronal nAChRs with high spatiotemporal precision has been lacking. To address this issue, we have generated photoswitchable nAChR agonists and re-evaluated the known photochromic ligand, BisQ. Using electrophysiology, we found that one of our new compounds, AzoCholine, is an excellent photoswitchable agonist for neuronal α7 nAChRs, whereas BisQ was confirmed to be an agonist for the muscle-type nAChR. AzoCholine could be used to modulate cholinergic activity in a brain slice and in dorsal root ganglion neurons. In addition, we demonstrate light-dependent perturbation of behavior in the nematode, Caenorhabditis elegans.

Orthogonal Optical Control of a G Protein-Coupled Receptor with a SNAP-Tethered Photochromic Ligand.

The covalent attachment of synthetic photoswitches is a general approach to impart light sensitivity onto native receptors. It mimics the logic of natural photoreceptors and significantly expands the reach of optogenetics. Here we describe a novel photoswitch design-the photoswitchable orthogonal remotely tethered ligand (PORTL)-that combines the genetically encoded SNAP-tag with photochromic ligands connected to a benzylguanine via a long flexible linker. We use the method to convert the G protein-coupled receptor mGluR2, a metabotropic glutamate receptor, into a photoreceptor (SNAG-mGluR2) that provides efficient optical control over the neuronal functions of mGluR2: presynaptic inhibition and control of excitability. The PORTL approach enables multiplexed optical control of different native receptors using distinct bioconjugation methods. It should be broadly applicable since SNAP-tags have proven to be reliable, many SNAP-tagged receptors are already available, and photochromic ligands on a long leash are readily designed and synthesized.

Development of a new photochromic ion channel blocker via azologization of fomocaine.

Photochromic blockers of voltage gated ion channels are powerful tools for the control of neuronal systems with high spatial and temporal precision. We now introduce fotocaine, a new type of photochromic channel blocker based on the long-lasting anesthetic fomocaine. Fotocaine is readily taken up by neurons in brain slices and enables the optical control of action potential firing by switching between 350 and 450 nm light. It also provides an instructive example for "azologization", that is, the systematic conversion of an established drug into a photoswitchable one.