Voltage-gated sodium (Nav) channel inhibitors are used clinically as analgesics and local anesthetics. However, the absence of Nav channel isoform selectivity of current treatment options can result in adverse cardiac and central nervous system side effects, limiting their therapeutic utility. Human hereditary gain- or loss-of-pain disorders have demonstrated an essential role of Nav1.7 sodium channels in the sensation of pain, thus making this channel an attractive target for new pain therapies. We previously identified a novel, state-dependent human Nav1.7 selective inhibitor (PF-05089771, IC50 = 11 nM) that interacts with the voltage-sensor domain (VSD) of domain IV. We further characterized the state-dependent interaction of PF-05089771 by systematically varying the voltage, frequency, and duration of conditioning prepulses to provide access to closed, open, and fast- or slow-inactivated states. The current study demonstrates that PF-05089771 exhibits a slow onset of block that is depolarization and concentration dependent, with a similarly slow recovery from block. Furthermore, the onset of block by PF-05089771 develops with similar rates using protocols that bias channels into predominantly fast- or slow-inactivated states, suggesting that channel inhibition is less dependent on the availability of a particular inactivated state than the relative time that the channel is depolarized. Taken together, the inhibitory profile of PF-05089771 suggests that a conformational change in the domain IV VSD after depolarization is necessary and sufficient to reveal a high-affinity binding site with which PF-05089771 interacts, stabilizing the channel in a nonconducting conformation from which recovery is slow.
Copyright © 2016 by The American Society for Pharmacology and Experimental Therapeutics.