Isoform selective voltage-gated sodium channel modulators and the therapy of pain

Voltage-gated sodium channels are large transmembrane protein complexes responsible for the propagation and transmission of electrical impulses through nerve, muscle and endocrine cells and cell systems. Dysregulated expression and/or functional changes of ion channel isoforms are found in many associated pathological conditions. In such cases, modulation of voltage gated sodium channels (Na(V) channels) is a recognised approach in medicinal chemistry. Multiple small-molecule active compounds are used for a plethora of Na(V) channel-linked indications, for example epilepsy and CNS disorders, arrhythmia, stroke and pain states such as congenital analgesia/hyperalgesia and neuropathic pain. As existent Na(V) channel modulators suffer mainly from selectivity issues and thus exert significant side effects, novel and selective Na(V) channel modulators would be beneficial. Consequently, the increased research on voltage-gated sodium channels has led to a large number of novel compounds that exploit classic binding site selectivity with state-dependence or functional selectivity. Such compounds offer selective targeting and new possibilities for studying the physiology of Na(V) channels and pathophysiology of the associated ailment conditions. This review consolidates the recent literature on Na(V) 1.3, 1.7 and 1.8 channel isoform selective and/or state-dependent modulators. In particular, their structure-activity relationship is illustrated, especially in the context of selectivity on a particular isoform, and their applicability in the therapy of neuropathic pain is described.