BACKGROUND AND PURPOSEThe development of subtype-selective ligands to inhibit voltage-sensitive sodium channels (VSSCs) has been attempted with the aim of developing therapeutic compounds. Tetrodotoxin (TTX) is a toxin from pufferfish that strongly inhibits VSSCs. Many TTX analogues have been identified from marine and terrestrial sources, although their specificity for particular VSSC subtypes has not been investigated. Herein, we describe the binding of 11 TTX analogues to human VSSC subtypes Na v 1.1-Na v 1.7. EXPERIMENTAL APPROACHEach VSSC subtype was transiently expressed in HEK293T cells. The inhibitory effects of TTX analogues on each subtype were assessed using whole-cell patch-clamp recordings.

An ovel series of C12-keto-type saxitoxin (STX) derivatives bearinga nu nusualn onhydrated form of the ketone at C12 has been synthesized,a nd their Na V -inhibitory activity has been evaluated in ac ell-based assay as well as whole-cell patch-clamp recording. Among these compounds, 11-benzylidene STX (3a)s howedp otent inhibitory activity againstn euroblastoma Neuro2Ai nboth cell-baseda nd electrophysiological analyses,w ithE C 50 and IC 50 valueso f8 .5 and 30.7 nm,r espectively.I nterestingly,t he compound showed potent inhibitory activity against tetrodotoxin-resistant subtype of Na V 1.5, with an IC 50 value of 94.1 nm.D erivatives 3a-d and 3f showedl ow recovery rates from Na V 1.2 subtype (ca4 5-79 %) comparedt on atural dcSTX (2), strongly suggesting an irreversible mode of interaction. We propose an interaction model for the C12-ketod erivatives with Na V in which the enonem oiety in the STX derivatives 3 worksa sM ichaela cceptorf or the carboxylateo fA sp 1717 .