Development of insecticides targeting inward rectifying potassium channels in the malaria vector, Anopheles gambiae

The emergence of insecticide-resistant mosquitoes has highlighted the need to develop new classes of insecticides for vector-borne disease control. We recently reported that a small-molecule inhibitor of Aedes aegypti (Ae) inward rectifying potassium channel 1 (AeKir1) leads to impaired Malpighian (renal) tubule function, incapacitation, and death (Raphemot et al., PLOS ONE, 2013). The inhibitor exhibits insecticidal activity against Anopheles gambiae, Aedes albopictus, and Culex pipiens, suggesting that Kir channels represent viable insecticide targets in a broad range of mosquito species. We therefore set out to develop potent and selective small-molecule antagonists of the Kir1 channel expressed in the malaria vector Anopheles gambiae (AnKir1). A fluorescence-based, quantitative, thallium (Tl⁺)-flux assay was developed to enable the interrogation of large small-molecule libraries for AnKir1 modulators. A pilot screen of a few hundred confirmed AeKir1 inhibitors revealed several compounds that inhibit AnKir1 in the low micromolar range, but were up to four-fold less potent when compared to AeKir1. This suggests that, despite the strong conservation of amino acid sequence between AeKir1 and AnKir1, it may be possible to develop species-specific insecticides targeting Kir channels. We are currently performing a primary screen of approximately 30,000 compounds from the Vanderbilt Institute of Chemical Biology library for AnKir1 modulators. The potency and selectivity of confirmed modulators will be assessed using a panel of high-throughput Tl⁺-flux assays for AeKir1 and several human Kir channels. Insecticidal activity will be evaluated by topical and injection application. Funded by a grant from the Foundation for the NIH, VCTR program.