Discovery of a selective NaV1.7 inhibitor from centipede venom with analgesic efficacy exceeding morphine in rodent pain models

Loss-of-function mutations in the human voltage-gated sodium channel Na_V1.7 result in a congenital indifference to pain. Selective inhibitors of Na_V1.7 are therefore likely to be powerful analgesics for treating a broad range of pain conditions. Herein we describe the identification of µ-SLPTX-Ssm6a, a unique 46-residue peptide from centipede venom that potently inhibits Na_V1.7 with an IC₅₀ of ∼25 nM. µ-SLPTX-Ssm6a has more than 150-fold selectivity for Na_V1.7 over all other human Na_V subtypes, with the exception of Na_V1.2, for which the selectivity is 32-fold. µ-SLPTX-Ssm6a contains three disulfide bonds with a unique connectivity pattern, and it has no significant sequence homology with any previously characterized peptide or protein. µ-SLPTX-Ssm6a proved to be a more potent analgesic than morphine in a rodent model of chemical-induced pain, and it was equipotent with morphine in rodent models of thermal and acid-induced pain. This study establishes µ-SPTX-Ssm6a as a promising lead molecule for the development of novel analgesics targeting Na_V1.7, which might be suitable for treating a wide range of human pain pathologies.Normal pain is a key adaptive response that serves to limit our exposure to potentially damaging or life-threatening events. In contrast, aberrant long-lasting pain transforms this adaptive response into a debilitating and often poorly managed disease. Chronic pain affects ∼20% of the population, with the incidence rising significantly in elderly cohorts (1). The economic burden of chronic pain in the United States was recently estimated to be ∼$600 billion per annum, which exceeds the combined annual cost of cancer, heart disease, and diabetes (2). There are few drugs available for treatment of chronic pain, and many of these have limited efficacy and dose-limiting side-effects.Voltage-gated sodium (Na_V) channels are integral transmembrane proteins that provide a current pathway for the rapid depolarization of excitable cells (1, 3), and they play a key role in conveying nociceptor responses to synapses in the dorsal horn (4). Humans contain nine different Na_V channel subtypes, denoted Na_V1.1 to Na_V1.9 (5, 6). In recent years, Na_V1.7 has emerged as a promising analgesic target based on several remarkable human genetic studies. Gain-of-function mutations in the SNC9A gene encoding the pore-forming α-subunit of Na_V1.7 cause severe episodic pain in inherited neuropathies, such as erythromelalgia and paroxysmal extreme pain disorder (7), whereas loss-of-function mutations in SCN9A result in a congenital indifference to pain (CIP) (8). The latter phenotype can be recapitulated in rodents via complete knockout of Na_V1.7 in all sensory and sympathetic neurons (9). Moreover, certain polymorphisms in SCN9A correlate with sensitivity to nociceptive inputs (10). Remarkably, apart from their inability to sense pain, loss of smell (anosmia) is the only other sensory impairment in individuals with CIP (11, 12). Thus, the combined genetic data suggest that subtype-selective blockers of Na_V1.7 are likely to be useful analgesics for treating a broad range of pain conditions.Centipedes are one of the oldest extant arthropods, with the fossil record dating back 430 million y (13). Centipedes were one of the first terrestrial taxa to use venom as a predation strategy, and they have adapted to capture a wide variety of prey, including insects, fish, molluscs, amphibians, reptiles, and even mammals (13, 14). The centipede venom apparatus, which is unique and bears little resemblance to that of other arthropods, evolved by modification of the first pair of walking legs into a set of pincer-like claws (forcipules) (13). Venom is secreted via a pore located near the tip of each forcipule. There are ∼3,300 extant species of centipedes, yet the venom of only a handful has been studied in any detail. We recently demonstrated that the venom of the Chinese red-headed centipede Scolopendra subspinipes mutilans is replete with unique, disulfide-rich peptides that potently modulate the activity of mammalian voltage-gated ion channels (14), and therefore we decided to explore this venom as a potential source of Na_V1.7 inhibitors. We describe the purification from this venom of a highly selective inhibitor of Na_V1.7 that is a more effective analgesic than morphine in rodent pain models.