This study tested a series of potassium channel blockers, including 1-((2-chlorophenyl)diphenylmethyl)-1H-pyrazole (TRAM-34), 11-dansylaminoundecanoic acid (DAUDA), and 5-hydroxydecanoic acid (5-HDC), because their effects have not been explored on insect voltage-gated Kv2 channels. We evaluated the action of these compounds in patch clamp recordings of engineered HEK cells expressing Anopheles gambiae Kv2.1 channels. They were also tested for insecticidal effects through topical application to adult mosquitoes (Anopheles gambiae and Aedes aegypti), for paralysis in a headless larvae assay with 4th instar Anopheles gambiae, as well as in central nervous system (CNS) recordings from 3rd instar larvae of Drosophila melanogaster. Patch clamp studies revealed that fatty acid compounds without functional groups in the alkyl chain (e.g., decanoate, DAUDA) yielded a more potent blocking action on Kv2.1 currents than substituted fatty acids (e.g., 5-HDC). Also, in comparison to 2-methoxy-N-((1-phenylcyclopentyl)methyl)benzamide (2S-65465), a known Kv2 channel blocker (IC50 = 100 nM), decanoate and DAUDA were 6-fold and 12-fold less active, respectively, as blockers of potassium current. TRAM-34 was the least potent inhibitor tested in patch clamp studies (IC50 = 30 μM). When tested on D. melanogaster CNS, the compounds typically gave an initial increase in firing rate, followed by a decrease, both effects at micromolar concentrations. Paralysis obtained from headless larvae assays had the same potency ranking as that obtained through patch-clamp recordings, indicating a possible connection between channel block and whole organism toxicity. Moreover, when DAUDA and decanoate were tested on adult mosquitoes, they were not as lethal as 2S-65465. As expected from its low activity on Kv2 channels, in vitro, TRAM-34 showed little toxicity in any whole insect screen. In order to possibly improve the insecticidal activity of the fatty acids, we are currently working on derivatized analogs (e.g., methyl esters) that could better penetrate the cuticular barrier.

Toxicity and physiological actions of fatty acids and related potassium channel blockers to mosquitoes

256th National Meeting (2018)

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