title: The novel isoxazoline ectoparasiticide fluralaner: selective inhibition of arthropod γ-aminobutyric acid- and L-glutamate-gated chloride channels and insecticidal/acaricidal activity.
abstract: Isoxazolines are a novel class of parasiticides that are potent inhibitors of γ-aminobutyric acid (GABA)-gated chloride channels (GABACls) and L-glutamate-gated chloride channels (GluCls). In this study, the effects of the isoxazoline drug fluralaner on insect and acarid GABACl (RDL) and GluCl and its parasiticidal potency were investigated. We report the identification and cDNA cloning of Rhipicephalus (R.) microplus RDL and GluCl genes, and their functional expression in Xenopus laevis oocytes. The generation of six clonal HEK293 cell lines expressing Rhipicephalus microplus RDL and GluCl, Ctenocephalides felis RDL-A285 and RDL-S285, as well as Drosophila melanogaster RDLCl-A302 and RDL-S302, combined with the development of a membrane potential fluorescence dye assay allowed the comparison of ion channel inhibition by fluralaner with that of established insecticides addressing RDL and GluCl as targets. In these assays fluralaner was several orders of magnitude more potent than picrotoxinin and dieldrin, and performed 5-236 fold better than fipronil on the arthropod RDLs, while a rat GABACl remained unaffected. Comparative studies showed that R. microplus RDL is 52-fold more sensitive than R. microplus GluCl to fluralaner inhibition, confirming that the GABA-gated chloride channel is the primary target of this new parasiticide. In agreement with the superior RDL on-target activity, fluralaner outperformed dieldrin and fipronil in insecticidal screens on cat fleas (Ctenocephalides felis), yellow fever mosquito larvae (Aedes aegypti) and sheep blowfly larvae (Lucilia cuprina), as well as in acaricidal screens on cattle tick (R. microplus) adult females, brown dog tick (Rhipicephalus sanguineus) adult females and Ornithodoros moubata nymphs. These findings highlight the potential of fluralaner as a novel ectoparasiticide.
authors.affiliation: MSD Animal Health Innovation GmbH, Zur Propstei, 55270 Schwabenheim, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Gassel
authors.affiliation: MSD Animal Health Innovation GmbH, Zur Propstei, 55270 Schwabenheim, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Wolf
authors.affiliation: MSD Animal Health Innovation GmbH, Zur Propstei, 55270 Schwabenheim, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Noack
authors.affiliation: MSD Animal Health Innovation GmbH, Zur Propstei, 55270 Schwabenheim, Germany.
authors.forename: Heike
authors.initials: H
authors.lastname: Williams
authors.affiliation: MSD Animal Health Innovation GmbH, Zur Propstei, 55270 Schwabenheim, Germany. Electronic address: thomas.ilg@msd.de.
authors.forename: Thomas
authors.initials: T
authors.lastname: Ilg
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D018118:Chloride Channels / Q000037:antagonists & inhibitors*; D003001:Cloning, Molecular; D058251:Ctenocephalides / Q000235:genetics; D018076:DNA, Complementary / Q000737:chemistry; D004026:Dieldrin / Q000737:chemistry; D004331:Drosophila melanogaster / Q000235:genetics; D018756:GABA Antagonists / Q000737:chemistry*; D057809:HEK293 Cells; D006801:Humans; D019476:Insect Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D007306:Insecticides / Q000737:chemistry*; D007555:Isoxazoles / Q000737:chemistry*; D008969:Molecular Sequence Data; D010802:Phylogeny; D010852:Picrotoxin / Q000031:analogs & derivatives / Q000737:chemistry; D011720:Pyrazoles / Q000737:chemistry; D048494:Rhipicephalus / Q000235:genetics*; D016415:Sequence Alignment; D054830:Sesterterpenes; D014982:Xenopus laevis; D005680:gamma-Aminobutyric Acid
chemical_list: D018118:Chloride Channels; D018076:DNA, Complementary; D004026:Dieldrin; D018756:GABA Antagonists; D019476:Insect Proteins; D007306:Insecticides; D007555:Isoxazoles; D010852:Picrotoxin; D011720:Pyrazoles; D054830:Sesterterpenes; D005680:gamma-Aminobutyric Acid; C000591860:A1443 compound; C022961:picrotoxinin; C082360:fipronil
keywords: Cat flea; Cattle tick; Ectoparasiticidal target; Fipronil; Fluralaner; GABA-gated chloride channel; Glutamate-gated chloride channel; Isoxazoline