title: Discovery of sarolaner: A novel, orally administered, broad-spectrum, isoxazoline ectoparasiticide for dogs.
abstract: The novel isoxazoline ectoparasiticide, sarolaner, was identified during a lead optimization program for an orally-active compound with efficacy against fleas and ticks on dogs. The aim of the discovery program was to identify a novel isoxazoline specifically for use in companion animals, beginning with de novo synthesis in the Zoetis research laboratories. The sarolaner molecule has unique structural features important for its potency and pharmacokinetic (PK) properties, including spiroazetidine and sulfone moieties. The flea and tick activity resides in the chirally pure S-enantiomer, which was purified to alleviate potential off-target effects from the inactive enantiomer. The mechanism of action was established in electrophysiology assays using CHO-K1 cell lines stably expressing cat flea (Ctenocephalides felis) RDL (resistance-to-dieldrin) genes for assessment of GABA-gated chloride channel (GABACls) pharmacology. As expected, sarolaner inhibited GABA-elicited currents at both susceptible (CfRDL-A285) and resistant (CfRDL-S285) flea GABACls with similar potency. Initial whole organism screening was conducted in vitro using a blood feeding assay against C. felis. Compounds which demonstrated robust activity in the flea feed assay were subsequently tested in an in vitro ingestion assay against the soft tick, Ornithodoros turicata. Efficacious compounds which were confirmed safe in rodents at doses up to 30mg/kg were progressed to safety, PK and efficacy studies in dogs. In vitro sarolaner demonstrated an LC80 of 0.3μg/mL against C. felis and an LC100 of 0.003μg/mL against O. turicata. In a head-to-head comparative in vitro assay with both afoxolaner and fluralaner, sarolaner demonstrated superior flea and tick potency. In exploratory safety studies in dogs, sarolaner demonstrated safety in dogs≥8 weeks of age upon repeated monthly dosing at up to 20mg/kg. Sarolaner was rapidly and well absorbed following oral dosing. Time to maximum plasma concentration occurred within the first day post-dose. Bioavailability for sarolaner was calculated at >85% and the compound was highly protein bound (>99.9%). The half-life for sarolaner was calculated at 11-12 days. Sarolaner plasma concentrations indicated dose proportionality over the range 1.25-5mg/kg, and these same doses provided robust efficacy (>99%) for ≥35days against both fleas (C. felis) and multiple species of ticks (Rhipicephalus sanguineus, Ixodes ricinus and Dermacentor reticulatus) after oral administration to dogs. As a result of these exploratory investigations, sarolaner was progressed for development as an oral monthly dose for treatment and control of fleas and ticks on dogs.
authors.affiliation: Zoetis, Veterinary Medicine Research and Development, 333 Portage St., Kalamazoo, MI 49007, USA. Electronic address: tom.mctier@zoetis.com.
authors.forename: Tom L
authors.initials: TL
authors.lastname: McTier
authors.affiliation: Zoetis, Veterinary Medicine Research and Development, 333 Portage St., Kalamazoo, MI 49007, USA.
authors.forename: Nathan
authors.initials: N
authors.lastname: Chubb
authors.affiliation: Zoetis, Veterinary Medicine Research and Development, 333 Portage St., Kalamazoo, MI 49007, USA.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Curtis
authors.affiliation: Zoetis, Veterinary Medicine Research and Development, 333 Portage St., Kalamazoo, MI 49007, USA.
authors.forename: Laura
authors.initials: L
authors.lastname: Hedges
authors.affiliation: Zoetis, Veterinary Medicine Research and Development, 333 Portage St., Kalamazoo, MI 49007, USA.
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Inskeep
authors.affiliation: Zoetis, Veterinary Medicine Research and Development, 333 Portage St., Kalamazoo, MI 49007, USA.
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Knauer
authors.affiliation: Zoetis, Veterinary Medicine Research and Development, 333 Portage St., Kalamazoo, MI 49007, USA.
authors.forename: Sanjay
authors.initials: S
authors.lastname: Menon
authors.affiliation: Zoetis, Veterinary Medicine Research and Development, 333 Portage St., Kalamazoo, MI 49007, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Mills
authors.affiliation: Zoetis, Veterinary Medicine Research and Development, 333 Portage St., Kalamazoo, MI 49007, USA.
authors.forename: Aleah
authors.initials: A
authors.lastname: Pullins
authors.affiliation: Zoetis, Veterinary Medicine Research and Development, 333 Portage St., Kalamazoo, MI 49007, USA.
authors.forename: Erich
authors.initials: E
authors.lastname: Zinser
authors.affiliation: Zoetis, Veterinary Medicine Research and Development, 333 Portage St., Kalamazoo, MI 49007, USA.
authors.forename: Debra J
authors.initials: DJ
authors.lastname: Woods
authors.affiliation: Zoetis, Veterinary Medicine Research and Development, 333 Portage St., Kalamazoo, MI 49007, USA.
authors.forename: Patrick
authors.initials: P
authors.lastname: Meeus
mesh_terms: D000284:Administration, Oral; D000818:Animals; D004283:Dog Diseases / Q000517:prevention & control*; D004285:Dogs; D004478:Ectoparasitic Infestations / Q000517:prevention & control / Q000662:veterinary*; D006207:Half-Life; D007306:Insecticides / Q000493:pharmacokinetics / Q000494:pharmacology / Q000592:standards; D007555:Isoxazoles / Q000493:pharmacokinetics / Q000494:pharmacology / Q000592:standards; D005423:Siphonaptera / Q000187:drug effects; D013987:Ticks / Q000187:drug effects
chemical_list: D007306:Insecticides; D007555:Isoxazoles
keywords: Dog; Flea; GABA antagonist; Isoxazoline; Oral; Sarolaner; Tick