Indoxacarb, metaflumizone, and other sodium channel inhibitor insecticides: Mechanism and site of action on mammalian voltage-gated sodium channels

• Sodium channel inhibitor (SCI) insecticides silence endogenous neural activity.
• SCI insecticides interact selectively with slow-inactivated sodium channels.
• The SCI insecticide receptor includes elements of the local anesthetic receptor.
• Metaflumizone exhibits unique actions that are not shared with other SCI insecticides.

Sodium channel inhibitor (SCI) insecticides were discovered almost four decades ago but have only recently yielded important commercial products (e.g., indoxacarb and metaflumizone). SCI insecticides inhibit sodium channel function by binding selectively to slow-inactivated (non-conducting) sodium channel states. Characterization of the action of SCI insecticides on mammalian sodium channels using both biochemical and electrophysiological approaches demonstrates that they bind at or near a drug receptor site, the “local anesthetic (LA) receptor.” This mechanism and site of action on sodium channels differentiates SCI insecticides from other insecticidal agents that act on sodium channels. However, SCI insecticides share a common mode of action with drugs currently under investigation as anticonvulsants and treatments for neuropathic pain. In this paper we summarize the development of the SCI insecticide class and the evidence that this structurally diverse group of compounds have a common mode of action on sodium channels. We then review research that has used site-directed mutagenesis and heterologous expression of cloned mammalian sodium channels in Xenopus laevis oocytes to further elucidate the site and mechanism of action of SCI insecticides. The results of these studies provide new insight into the mechanism of action of SCI insecticides on voltage-gated sodium channels, the location of the SCI insecticide receptor, and its relationship to the LA receptor that binds therapeutic SCI agents.

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