Development of a μO-Conotoxin Analogue with Improved Lipid Membrane Interactions and Potency for the Analgesic Sodium Channel NaV1.8

Abstract

The O-conotoxins MrVIA, MrVIB, and MfVIA inhibit the voltage-gated sodium channel Na V 1.8, a well described target for the treatment of pain; however, little is known about the residues or structural elements that define this activity. In this study, we determined the three-dimensional structure of MfVIA, examined its membrane binding properties, performed alaninescanning mutagenesis, and identified residues important for its activity at human Na V 1.8. A second round of mutations resulted in (E5K,E8K)MfVIA, a double mutant with greater positive surface charge and greater affinity for lipid membranes compared with MfVIA. This analogue had increased potency at Na V 1.8 and was analgesic in the mouse formalin assay.Voltage-gated sodium channels (Na V s) 5 are responsible for the initiation and propagation of action potentials (1). Nine subtypes have been described to date (Na V 1.1-1.9), each with a distinct expression profile and subsequent functional role (1). For example, Na V 1.4 is predominantly expressed in skeletal muscle where it is important in the generation and propagation of action potentials that initiate muscle contraction (2), whereas Na V 1.5 is predominately expressed in cardiac tissue where it is crucial in setting the electrical conduction properties of the heart (3). Several subtypes (Na V 1.1 and Na V 1.6 -1.9) are expressed in peripheral sensory neurons, and it is due to this expression profile that some of these subtypes have gained attention as potential therapeutic targets for pain (4). Na V 1.8 is of particular interest as an analgesic target because it is expressed almost exclusively in peripheral sensory neurons and is present in the majority of nociceptive neurons (5, 6) where it is a major contributor to the sodium current underlying action potentials (7-9). Accordingly, Na V 1.8-null mice have reduced responses to nociceptive mechanical and thermal stimuli as well as deficits in the development of inflammatory pain, visceral pain, and to a lesser extent neuropathic pain (10 -14). Therefore, pharmacological inhibition of Na V 1.8 is considered a promising therapeutic strategy for the treatment of pain.The recently discovered O-conotoxin MfVIA (15) and the related MrVIA and MrVIB (16) (see Fig. 1A) are some of a few venom-derived peptides that inhibit Na V 1.8 and the only peptides known to selectively inhibit Na V 1.8 over the other neuronal Na V subtypes expressed in peripheral sensory neurons (15,17,18). However, despite this unique selectivity, little is known about structure-activity relationships of the O-conotoxins. This gap in knowledge arises from difficulties in the synthesis of sufficient quantities to permit detailed studies (19), which is in part due to the hydrophobic nature of these peptides. Characterization of the structural elements contributing to the high affinity inhibition of Na V 1.8 by the O-conotoxins is of particular interest given that the O-conotoxins also potently inhibit the skeletal muscle isoform Na V 1.4, and reduced activity at Na V 1.4 while maintain...

Pharmacological characterisation of the highly NaV1.7 selective spider venom peptide Pn3a

“…For hNa V 1.1–1.8 and rNa V 1.7, whole-cell patch-clamp experiments were performed on a QPatch-16 automated electrophysiology platform (Sophion Bioscience, Ballerup, Denmark) as described61. The extracellular solution contained in mM: NaCl 145, KCl 4, CaCl 2 2, MgCl 2 1, HEPES 10 and glucose 10; pH 7.4; osmolarity 305 mOsm.…”

Addition of K22 Converts Spider Venom Peptide Pme2a from an Activator to an Inhibitor of NaV1.7

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The pharmacology of voltage-gated sodium channel activators

“…response in cells heterologously expressing Na V 1.8 (Deuis et al, 2016a;Vickery et al, 2004). As Na V channel activators used in fluorescence-based assays likely stabilise different channel conformations, it is unclear if these assays exhibit bias towards detection of Na V channel modulators with a specific mechanism of action and/or binding site.…”