Abstract
Lacosamide, developed as an anti-epileptic drug, has been used for the treatment of pain. Unlike typical anticonvulsants and local anesthetics which enhance fast-inactivation and bind within the pore of sodium channels, lacosamide enhances slow-inactivation of these channels, suggesting different binding mechanisms and mode of action. It has been reported that lacosamide’s effect on NaV1.5 is sensitive to a mutation in the local anesthetic binding site, and that it binds with slow kinetics to the fast-inactivated state of NaV1.7. We recently showed that the NaV1.7-W1538R mutation in the voltage-sensing domain 4 completely abolishes NaV1.7 inhibition by clinically-achievable concentration of lacosamide. Our molecular docking analysis suggests a role for W1538 and pore residues as high affinity binding sites for lacosamide. Aryl sulfonamide sodium channel blockers are also sensitive to substitutions of the W1538 residue but not of pore residues. To elucidate the mechanism by which lacosamide exerts its effects, we used voltage-clamp recordings and show that lacosamide requires an intact local anesthetic binding site to inhibit NaV1.7 channels. Additionally, the W1538R mutation does not abrogate local anesthetic lidocaine-induced blockade. We also show that the naturally occurring arginine in NaV1.3 (NaV1.3-R1560), which corresponds to NaV1.7-W1538R, is not sufficient to explain the resistance of NaV1.3 to clinically-relevant concentrations of lacosamide. However, the NaV1.7-W1538R mutation conferred sensitivity to the NaV1.3-selective aryl-sulfonamide blocker ICA-121431. Together, the W1538 residue and an intact local anesthetic site are required for lacosamide’s block of NaV1.7 at a clinically-achievable concentration. Moreover, the contribution of W1538 to lacosamide inhibitory effects appears to be isoform-specific.
Highlights
Chronic pain affects 20–25% of the global population (McCarberg and Billington, 2006; Reid et al, 2011; Kennedy et al, 2014) and is commonly associated with impaired quality of life, opioid addiction, and psychiatric comorbidities (Menefee et al, 2000; Breivik et al, 2006; Ballantyne and LaForge, 2007; Hojsted and Sjogren, 2007; Tunks et al, 2008; Reid et al, 2011)
We show that the reciprocal mutation (R1560W) in NaV1.3 was insufficient to render NaV1.3 channels sensitive to lacosamide at clinicallyachievable concentrations, suggesting that the effect of the tryptophan residue in VSD4 on lacosamide block is isoformdependent
While the most energetically favorable site for lacosamide binding is near to W1538, lacosamide readily binds in many positions around the local anesthetics (LAs) binding site
Summary
Chronic pain affects 20–25% of the global population (McCarberg and Billington, 2006; Reid et al, 2011; Kennedy et al, 2014) and is commonly associated with impaired quality of life, opioid addiction, and psychiatric comorbidities (Menefee et al, 2000; Breivik et al, 2006; Ballantyne and LaForge, 2007; Hojsted and Sjogren, 2007; Tunks et al, 2008; Reid et al, 2011). Unlike typical antiepileptic drugs (AEDs) such as carbamazepine, phenytoin, and lamotrigine, as well as local anesthetics (LAs), such as lidocaine and benzocaine, lacosamide enhances the voltage-dependence of slow inactivation but not steady-state fast inactivation, and increases use-dependent inhibition of sodium channels (Errington et al, 2008; Sheets et al, 2008; Wang et al, 2011; Niespodziany et al, 2013; Rogawski et al, 2015) This suggested that lacosamide exerts its effect on VGSCs by a different mechanism than AEDs and LAs and Jo and Bean reported slow binding of lacosamide to the fast-inactivated state (Jo and Bean, 2017). Previous studies have posited that lacosamide’s binding site is within the permeation pathway, overlapping with the binding site for batrachotoxins and LAs in the S6 helix (Stevens et al, 2011; Wang and Wang, 2014; Jo and Bean, 2017); radio-ligands essays have failed to assign a specific residue to lacosamide binding against hundreds of known receptors and binding sites (Errington et al, 2006)
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