Blockage of chloride channels and anion transporters with pesticidal natural products and their synthetic analogs

Abstract

Ligand-gated chloride channels mediate a variety of functions in excitable membranes of nerve and muscle in insects, and have a long history as targets for neurotoxic insecticides. Recent findings from our laboratory confirm that the natural product silphinenes and their semi-synthetic analogs share a mode of action with the established ligand-gated chloride channel antagonist, picrotoxinin. The silphinenes are non-selective, being roughly equipotent on insect and mammalian receptors, but also possess lethal and neurotoxic effects on a dieldrinresistant strain of Drosophila melanogaster. These findings suggest that silphinenes act on insect GABA receptors in a way that is different from picrotoxinin, and it is possible that resistant insect populations in the field could be controlled with insecticidal compounds derived from the silphinenes. Voltage-gated chloride channels and anion transporters provide additional classes of validated targets for insecticidal/ nematicidal action. Anion transporter blockers are toxic to insects via an action on the gut, and RNAi studies implicate voltage-gated chloride channels in nematode muscle as another possible target. There was no cross resistance to DIDS in a dieldrin-resistant strain of Drosophila melanogaster, and no evidence for neurotoxicity. The potent paralytic actions of anion transporter blockers against nematodes, and stomach poisoning activity against lepidopteran larvae suggests they are worthy of further investigation as commercial insecticidal/nematicidal agents.

The discovery of a novel antagonist – Manduca sexta allatotropin analogue – as an insect midgut active ion transport inhibitor

“…Manse-AT is a peptide that possesses multiple effects on diverse targets in vitro, including the stimulation of JH biosynthesis by adult female CA in lepidopteran insects and the inhibition of AIT across the larval midgut epithelium of M. sexta. Kataoka et al 9 demonstrated that the biologically active core of Manse-AT was the octapeptide Manse-AT (6)(7)(8)(9)(10)(11)(12)(13), because its effect on JH biosynthesis stimulation was similar to that of Manse-AT. On the midgut, Manse-AT (6-13) has less potency (defined as the IC 50 ) than the native peptide Manse-AT.…”

“…Manse-AT (7-13), Manse-AT (8-13) and Manse-AT (9-13) at 1000 nM exhibited a maximum inhibition of AIT of 14.80 ± 1.27%, 9.39 ± 1.32% and 3.05 ± 0.88%, respectively, compared with 17.09 ± 1.73% for Manse-AT (6-13), the lead peptide. Manse-AT (10-13) and Manse-AT (11)(12)(13) were both no different from zero according to the t-test (data not shown). Thus, the tetrapeptide and tripeptide were completely inactive in this assay.…”

“…16 Five minutes after adding saline to the luminal side, 10 μL of the peptide solution (dissolved in 50 mM of imidazole buffer and 1 mM of methionine, pH 7.2) was then added to the haemolymph side of the tissue for the assays. 10 For the antagonist assays, the peptide solutions were configured with both Manse-AT (10)(11)(12)(13) or Manse-AT (11)(12)(13) and Manse-AT in the same solution described above.…”

“…Their insecticidal activity against lepidopterous larvae indicated that they were potential insecticides. 13 In the past half-century, only Bt has been widely used for pest control as a commercial insecticide to inhibit insect AIT. More lead compounds are necessary for designing new inhibitors of insect ion transport.…”

Insecticide sensitivity of native chloride and sodium channels in a mosquito cell line

“…The present study used established pharmacological probes, cell growth, and patch clamp techniques, to detect expression of targets in Sua1B cells, a cell line first isolated from neonate Anopheles gambiae larvae [6]. Screens focused mostly on compounds affecting VSCCs, since these are known to exist in Sua1B cells [7], and blockers of these channels are insecticidal [8]. Special attention was made to correlate ion channel effects with changes in cell growth.…”