A channel involved in pain perception Voltage-gated sodium (Nav) channels propagate electrical signals in muscle cells and neurons. In humans, Nav1.7 plays a key role in pain perception. It is challenging to target a particular Nav isoform; however, arylsulfonamide antagonists selective for Nav1.7 have been reported recently. Ahuja et al. characterized the binding of these small molecules to human Nav channels. To further investigate the mechanism, they engineered a bacterial Nav channel to contain features of the Nav1.7 voltage-sensing domain that is targeted by the antagonist and determined the crystal structure of the chimera bound to an inhibitor. The structure gives insight into the mechanism of voltage sensing and will enable the design of more-selective Nav channel antagonists. Science , this issue p. 10.1126/science.aac5464
An enantioselective synthesis of the antifungal natural product (+)-ambruticin S has been accomplished starting with the readily available methyl alpha-d-glucopyranoside, (R)-Roche ester, and (S)-glycidol as chirons, which encompassed seven of the 10 stereogenic centers of the target molecule. The remaining three centers were set by a highly diastereoselective, asymmetric cyclopropanation employing a chiral, nonracemic phosphonamide reagent. Our strategy for the construction of the dihydropyran subunit involved a highly syn-selective Lewis acid catalyzed 6-endo-trig cyclization. Other key steps in the synthesis featured an epoxide opening with a dithiane anion, two efficient phosphonamide-anion based olefinations, and a late-stage C-glycosylation.
ABSTRACT:We report on a novel series of aryl sulfonamides that act as nanomolar potent, isoform-selective inhibitors of the human sodium channel hNa V 1.7. The optimization of these inhibitors is described. We aimed to improve potency against hNa V 1.7 while minimizing off-target safety concerns and generated compound 3. This agent displayed significant analgesic effects in rodent models of acute and inflammatory pain and demonstrated that binding to the voltage sensor domain 4 site of Na V 1.7 leads to an analgesic effect in vivo. Our findings corroborate the importance of hNa V 1.7 as a drug target for the treatment of pain. KEYWORDS: Sodium channel, Na V 1.7, Na V 1.5, pain, aryl sulfonamide, formalin model, cold allodynia T he sodium channel Na V 1.7 belongs to a family of transmembrane voltage gated sodium channels, which consists of nine isoforms in mammals (Na V 1.1 to Na V 1.9).1−4 Na V 1.7 plays a crucial role in pain sensation, and there is strong genetic evidence linking Na V 1.7 and its encoding SCN9A gene to painful disorders in humans. Gain-of-function mutations in the SCN9A gene result in painful conditions such as inherited erythromelalgia, paroxysmal extreme pain disorder, and idiopathic small fiber neuropathies. In contrast, loss-of-function mutations in the SCN9A gene were found to be the genetic cause of a rare disorder called congenital insensitivity to pain, characterized by a complete loss of the ability to sense painful stimuli. It is noteworthy that no significant side effects have been reported in people lacking Na V 1.7, such as cognitive, motor, or non-nociceptive sensory impairments other than anosmia, giving further support to the concept of Na V 1.7 antagonists as analgesics.1−4 The predominant expression of the Na V 1.7 isoform in the PNS may offer a pathway to limit CNS-related adverse effects by developing compounds that do not cross the blood−brain barrier. Combined, these observations and findings have made Na V 1.7 a promising target for drug development for the treatment of pain. Indeed, there has been tremendous interest in the development of small molecule Na V 1.7 inhibitors as analgesics, particularly isoform-selective inhibitors, and coverage of the progress has been the subject of several excellent reviews. 1−7 In recent years, a series of aryl sulfonamides as Na V inhibitors have been reported that appear to be highly selective for Na V 1.7 over the cardiac ion channel Na V 1.5. [4][5][6]8 Since block of the Na V 1.5 channel may lead to arrhythmia and thus limit the therapeutic potential of nonselective Na V 1.7 inhibitors, isoform-selective inhibitors have attracted considerable interest due to their potential to avoid these adverse events.3,5 An example is aryl sulfonamide PF-04856264 ( Figure 1), which selectively blocks Na V 1.7 over Na V 1.5 and Na V 1.3.
Herein, we report the discovery and optimization of a series of orally bioavailable acyl sulfonamide NaV1.7 inhibitors that are selective for NaV1.7 over NaV1.5 and highly efficacious in in vivo models of pain and hNaV1.7 target engagement. An analysis of the physicochemical properties of literature NaV1.7 inhibitors suggested that acyl sulfonamides with high fsp3 could overcome some of the pharmacokinetic (PK) and efficacy challenges seen with existing series. Parallel library syntheses lead to the identification of analogue 7, which exhibited moderate potency against NaV1.7 and an acceptable PK profile in rodents, but relatively poor stability in human liver microsomes. Further, design strategy then focused on the optimization of potency against hNaV1.7 and improvement of human metabolic stability, utilizing induced fit docking in our previously disclosed X-ray cocrystal of the NaV1.7 voltage sensing domain. These investigations culminated in the discovery of tool compound 33, one of the most potent and efficacious NaV1.7 inhibitors reported to date.
Nonselective antagonists of voltage-gated sodium (Na V ) channels have been long used for the treatment of epilepsies. The efficacy of these drugs is thought to be due to the block of sodium channels on excitatory neurons, primarily Na V 1.6 and Na V 1.2. However, these currently marketed drugs require high drug exposure and suffer from narrow therapeutic indices. Selective inhibition of Na V 1.6, while sparing Na V 1.1, is anticipated to provide a more effective and better tolerated treatment for epilepsies. In addition, block of Na V 1.2 may complement the anticonvulsant activity of Na V 1.6 inhibition. We discovered a novel series of aryl sulfonamides as CNS-penetrant, isoform-selective Na V 1.6 inhibitors, which also displayed potent block of Na V 1.2. Optimization focused on increasing selectivity over Na V 1.1, improving metabolic stability, reducing active efflux, and addressing a pregnane Xreceptor liability. We obtained compounds 30−32, which produced potent anticonvulsant activity in mouse seizure models, including a direct current maximal electroshock seizure assay.
NBI-921352 (formerly XEN901) is a novel sodium channel inhibitor designed to specifically target NaV1.6 channels. Such a molecule provides a precision-medicine approach to target SCN8A-related epilepsy syndromes (SCN8A-RES), where gain-of-function (GoF) mutations lead to excess NaV1.6 sodium current, or other indications where NaV1.6 mediated hyper-excitability contributes to disease (Gardella & Moller, 2019; Johannesen et al., 2019; Veeramah et al., 2012). NBI-921352 is a potent inhibitor of NaV1.6 (IC50 0.051 µM), with exquisite selectivity over other sodium channel isoforms (selectivity ratios of 756X for NaV1.1, 134X for NaV1.2, 276X for NaV1.7, and >583X for NaV1.3, NaV1.4, and NaV1.5). NBI-921352 is a state-dependent inhibitor, preferentially inhibiting inactivated channels. The state dependence leads to potent stabilization of inactivation, inhibiting NaV1.6 currents, including resurgent and persistent NaV1.6 currents, while sparing the closed/rested channels. The isoform-selective profile of NBI-921352 led to a robust inhibition of action-potential firing in glutamatergic excitatory pyramidal neurons, while sparing fast-spiking inhibitory interneurons, where NaV1.1 predominates. Oral administration of NBI-921352 prevented electrically induced seizures in a Scn8a GoF mouse, as well as in wild-type mouse and rat seizure models. NBI-921352 was effective in preventing seizures at lower brain and plasma concentrations than commonly prescribed sodium channel inhibitor anti-seizure medicines (ASMs) carbamazepine, phenytoin, and lacosamide. NBI-921352 was well tolerated at higher multiples of the effective plasma and brain concentrations than those ASMs. NBI-921352 is entering phase II proof-of-concept trials for the treatment of SCN8A-developmental epileptic encephalopathy (SCN8A-DEE) and adult focal-onset seizures.
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