Toxicity and mode of action of experimental aryl amide insecticides

Authors: BLOOMQUIST, JEFFREY - University Of Florida; COQUEREL, QUENTIN - University Of Florida; DEMARES, FABIEN - University Of Florida; Norris, Edmund; RICHOUX, GARY - University Of Florida; YANG, LIU - University Of Florida; Linthicum, Kenneth - Ken; SWALE, DANIEL - Louisana State University

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/26/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: A series of aryl amides were synthesized and screened for toxicity against the Orlando (susceptible) and Puerto Rico (pyrethroid-resistant) strains of Aedes aegypti mosquitoes. Twenty-two compounds produced > 92% mortality in 24 hr vapor phase exposures and thus warranted further investigation to determine LC50 values. Of significant interest is a compound (138) that approached the LC50 of transfluthrin and exhibited greater toxicity than metofluthrin when screened against Orlando A. aegypti. Select compounds were screened against the Puerto Rico (PR) strain and we found that these N-arylamides displayed little cross resistance, and some were actually more potent against PR mosquitoes. Additionally, the most active compounds were found to have mouse oral toxicity LD50 values well above the minimum level as set by the Innovative Vector Control Consortium (50 mg/kg). Mode of action studies evaluated the effects of these compounds as GABA antagonists, since they were designed as a truncated form of an isoxazoline-type insecticide. Using compounds 031 and 138 as representative members of this group, we found that 031 blocked the firing of Drosophila melanogaster larval CNS at 1 µM and reversed the inhibitory effect of GABA at 10 µM, but surprisingly was without effect on GABA-induced currents in Anopheles gambiae rdl homomultimeric receptors expressed in Xenopus oocytes. Studies in other model systems found that 138 gave near complete block of An. gambiae Kv2 channel currents at 10 µM. In contrast, 031 was a weak inhibitor (20% at 10 µM) in this assay, but could depolarize cockroach giant axons or mosquito larval muscle with a threshold concentration of 1 µM and did so in a Cl- ion dependent manner. At this point, the possibility that these compounds were acting as anion exchange inhibitors led us to test their potency on A. aegypti potassium-chloride cotransporter (KCC) using an established cell-based thallium-flux assay. Both molecules were shown to be mid nanomolar inhibitors of Ae. aegypti KCC with GMR031 and GMR138 being 4.8- and 2.8-fold more potent than the established KCC inhibitor, VU00463271. The implications of these findings for insecticide discovery efforts will be discussed.