In 2006, humans with a congenital insensitivity to pain (CIP) were found to lack functional Na V 1.7 channels. In the subsequent 15 years there was a rush to develop selective inhibitors of Na V 1.7 channels with the goal of producing broadly effective analgesics without the problems of addiction and tolerance associated with opioids.Pharmacologically, this mission has been highly successful, leading to a number of highly potent and selective inhibitors of Na V 1.7 channels. However, there are very few examples where these inhibitors have yielded effective analgesia in preclinical pain models or human clinical trials. In this review, we summarise the role of the Na V 1.7 channel in nociception, its history as a therapeutic target and the quest to develop potent inhibitors of this channel. Finally, we discuss possible reasons why the pain-free state seen in humans with CIP has been so difficult to replicate pharmacologically.
Venoms are excellent model systems for studying evolutionary processes associated with predator–prey interactions. Here, we present the discovery of a peptide toxin, MIITX2-Mg1a, which is a major component of the venom of the Australian giant red bull ant Myrmecia gulosa and has evolved to mimic, both structurally and functionally, vertebrate epidermal growth factor (EGF) peptide hormones. We show that Mg1a is a potent agonist of the mammalian EGF receptor ErbB1, and that intraplantar injection in mice causes long-lasting hypersensitivity of the injected paw. These data reveal a previously undescribed venom mode of action, highlight a role for ErbB receptors in mammalian pain signaling, and provide an example of molecular mimicry driven by defensive selection pressure.
The voltage‐gated sodium channel NaV1.7 is involved in various pain phenotypes and is physiologically regulated by the NaV‐β3‐subunit. Venom toxins ProTx‐II and OD1 modulate NaV1.7 channel function and may be useful as therapeutic agents and/or research tools. Here, we use patch‐clamp recordings to investigate how the β3‐subunit can influence and modulate the toxin‐mediated effects on NaV1.7 function, and we propose a putative binding mode of OD1 on NaV1.7 to rationalise its activating effects. The inhibitor ProTx‐II slowed the rate of NaV1.7 activation, whilst the activator OD1 reduced the rate of fast inactivation and accelerated recovery from inactivation. The β3‐subunit partially abrogated these effects. OD1 induced a hyperpolarising shift in the V1/2 of steady‐state activation, which was not observed in the presence of β3. Consequently, OD1‐treated NaV1.7 exhibited an enhanced window current compared with OD1‐treated NaV1.7‐β3 complex. We identify candidate OD1 residues that are likely to prevent the upward movement of the DIV S4 helix and thus impede fast inactivation. The binding sites for each of the toxins and the predicted location of the β3‐subunit on the NaV1.7 channel are distinct. Therefore, we infer that the β3‐subunit influences the interaction of toxins with NaV1.7 via indirect allosteric mechanisms. The enhanced window current shown by OD1‐treated NaV1.7 compared with OD1‐treated NaV1.7‐β3 is discussed in the context of differing cellular expressions of NaV1.7 and the β3‐subunit in dorsal root ganglion (DRG) neurons. We propose that β3, as the native binding partner for NaV1.7 in DRG neurons, should be included during screening of molecules against NaV1.7 in relevant analgesic discovery campaigns.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.