Discovery and biological evaluation of 5-aryl-2-furfuramides, potent and selective blockers of the Nav1.8 sodium channel with efficacy in models of neuropathic and inflammatory pain

Na(v)1.8 (also known as PN3) is a tetrodotoxin-resistant (TTx-r) voltage-gated sodium channel (VGSC) that is highly expressed on small diameter sensory neurons and has been implicated in the pathophysiology of inflammatory and neuropathic pain. Recent studies using an Na(v)1.8 antisense oligonucleotide in an animal model of chronic pain indicated that selective blockade of Na(v)1.8 was analgesic and could provide effective analgesia with a reduction in the adverse events associated with nonselective VGSC blocking therapeutic agents. Herein, we describe the preparation and characterization of a series of 5-substituted 2-furfuramides, which are potent, voltage-dependent blockers (IC50 < 10 nM) of the human Na(v)1.8 channel. Selected derivatives, such as 7 and 27, also blocked TTx-r sodium currents in rat dorsal root ganglia (DRG) neurons with comparable potency and displayed > 100-fold selectivity versus human sodium (Na(v)1.2, Na(v)1.5, Na(v)1.7) and human ether-a-go-go (hERG) channels. Following systemic administration, compounds 7 and dose-dependently reduced neuropathic and inflammatory pain in experimental rodent models.