Pharmacological Validation of an Inward-Rectifier Potassium (Kir) Channel as an Insecticide Target in the Yellow Fever Mosquito Aedes aegypti

Abstract

Mosquitoes are important disease vectors that transmit a wide variety of pathogens to humans, including those that cause malaria and dengue fever. Insecticides have traditionally been deployed to control populations of disease-causing mosquitoes, but the emergence of insecticide resistance has severely limited the number of active compounds that are used against mosquitoes. Thus, to improve the control of resistant mosquitoes there is a need to identify new insecticide targets and active compounds for insecticide development. Recently we demonstrated that inward rectifier potassium (Kir) channels and small molecule inhibitors of Kir channels offer promising new molecular targets and active compounds, respectively, for insecticide development. Here we provide pharmacological validation of a specific mosquito Kir channel (AeKir1) in the yellow fever mosquito Aedes aegypti. We show that VU590, a small-molecule inhibitor of mammalian Kir1.1 and Kir7.1 channels, potently inhibits AeKir1 but not another mosquito Kir channel (AeKir2B) in vitro. Moreover, we show that a previously identified inhibitor of AeKir1 (VU573) elicits an unexpected agonistic effect on AeKir2B in vitro. Injection of VU590 into the hemolymph of adult female mosquitoes significantly inhibits their capacity to excrete urine and kills them within 24 h, suggesting a mechanism of action on the excretory system. Importantly, a structurally-related VU590 analog (VU608), which weakly blocks AeKir1 in vitro, has no significant effects on their excretory capacity and does not kill mosquitoes. These observations suggest that the toxic effects of VU590 are associated with its inhibition of AeKir1.

Two inwardly rectifying potassium channels,Irk1andIrk2, play redundant roles inDrosophilarenal tubule function

“…In contrast, compounds that inhibit AeKir1 and AeKir2B have inhibitory effects on whole-mosquito urine excretion (31,32,38) and on transepithelial fluid secretion and K ϩ flux in the Ramsay assay (28,36). This is broadly consistent with our results that both Irk1 and Irk2 play roles in the fly tubule although there are interesting differences; in Aedes, AeKir1 is located in the stellate cell, whereas AeKir2B is in the principal cell, and inhibition of both AeKir1 and AeKir2 has additive effects on K ϩ flux.…”

“…In addition, transcripts for inwardly rectifying K ϩ channels are expressed in the Malpighian tubules of Aedes aegypti, the vector for yellow fever, dengue, and chikungunya (29); Anopheles gambiae, the malaria vector (30); and the bed bug Cimex lectularius (21). Drugs targeting renal tubule inwardly rectifying K ϩ channels are currently being developed as mosquitocidal insecticides in Aedes aegypti (31,32,38). These channels may represent targets for the control of other insect pests as well, although killing of benign or beneficial insects will need to be avoided.…”

“…For example, in mosquitoes, pharmacological inhibition of inwardly rectifying K ϩ channels decreases renal tubule fluid secretion and alters both transepithelial ion fluxes in the tubule as well as whole-body ion clearances and urine excretion (28,31,32,36,38,41). This results in decreased viability and flight capacity (31,32,38). As such, inwardly rectifying K ϩ channels are potential targets for insecticidal agents.…”

Localization and role of inward rectifier K+ channels in Malpighian tubules of the yellow fever mosquito Aedes aegypti

“…VU0477688), and VU608 were synthesized by the Vanderbilt Institute of Chemical Biology as described previously Rouhier et al, 2014b). VU590 was purchased from Sigma Aldrich (St. Louis, MO).…”

“…VU590 is an inhibitor of AeKir1 that does not affect the activity of AeKir2B , whereas VU625 is an inhibitor of both AeKir1 and AeKir2B, with a preference for AeKir1 . Both of these compounds decrease the capacity of adult female mosquitoes to excrete urine as assessed with an in vivo diuresis assay Rouhier et al, 2014b), but their effects on isolated Malpighian tubules are unstudied.…”