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Introduction There is a high unmet need for safe and effective non-opioid medicines to treat moderate to severe pain without risk of addiction. Voltage-gated sodium channel 1.8 (Na V 1.8) is a genetically and pharmacologically validated pain target that is selectively expressed in peripheral pain-sensing neurons and not in the central nervous system (CNS). Suzetrigine (VX-548) is a potent and selective inhibitor of Na V 1.8, which has demonstrated clinical efficacy and safety in multiple acute pain studies. Our study was designed to characterize the mechanism of action of suzetrigine and assess both nonclinical and clinical data to test the hypothesis that selective Na V 1.8 inhibition translates into clinical efficacy and safety, including lack of addictive potential. Methods Preclinical pharmacology and mechanism of action studies were performed in vitro using electrophysiology and radiolabeled binding methods in cells recombinantly expressing human Na V channels, human proteins, and primary human dorsal root ganglion (DRG) sensory neurons. Safety and addictive potential assessments included in vitro secondary pharmacology studies, nonclinical repeat-dose toxicity and dependence studies in rats and/or monkeys, and a systematic analysis of adverse event data generated from 2447 participants from phase 3 acute pain studies of suzetrigine. Results Suzetrigine is selective against all other Na V subtypes (≥ 31,000-fold) and 180 other molecular targets. Suzetrigine inhibits Na V 1.8 by binding to the protein’s second voltage sensing domain (VSD2) to stabilize the closed state of the channel. This novel allosteric mechanism results in tonic inhibition of Na V 1.8 and reduces pain signals in primary human DRG sensory neurons. Nonclinical and clinical safety assessments with suzetrigine demonstrate no adverse CNS, cardiovascular or behavioral effects and no evidence of addictive potential or dependence. Conclusions The comprehensive pharmacology assessment presented here indicates that suzetrigine represents the first in a new class of non-opioid analgesics that are selective Na V 1.8 pain signal inhibitors acting in the peripheral nervous system to safely treat pain without addictive potential.

Many patients experience inadequate pain control due to limited options that are both efficacious and safe for treating moderate-to-severe acute pain; therefore, opioids are still frequently prescribed for their effectiveness despite known tolerability issues and safety concerns. Suzetrigine, an oral, non-opioid, offers a promising alternative by selectively inhibiting the voltage-gated sodium channel 1.8 (NaV1.8), a novel therapeutic target for pain management. Given the high selectivity of suzetrigine for NaV1.8 (does not bind to other sodium channels/receptors with CNS activity), suzetrigine does not have CNS side effects or addictive potential associated with opioids. In the largest randomized, controlled phase 3 trials in established acute pain models, suzetrigine monotherapy demonstrated statistically significant and clinically meaningful reduction in moderate-to-severe acute pain compared to placebo.BackgroundMany patients experience inadequate pain control due to limited options that are both efficacious and safe for treating moderate-to-severe acute pain; therefore, opioids are still frequently prescribed for their effectiveness despite known tolerability issues and safety concerns. Suzetrigine, an oral, non-opioid, offers a promising alternative by selectively inhibiting the voltage-gated sodium channel 1.8 (NaV1.8), a novel therapeutic target for pain management. Given the high selectivity of suzetrigine for NaV1.8 (does not bind to other sodium channels/receptors with CNS activity), suzetrigine does not have CNS side effects or addictive potential associated with opioids. In the largest randomized, controlled phase 3 trials in established acute pain models, suzetrigine monotherapy demonstrated statistically significant and clinically meaningful reduction in moderate-to-severe acute pain compared to placebo.To evaluate the safety and effectiveness of suzetrigine for the treatment of moderate-to-severe-acute surgical and non-surgical pain conditions, we conducted a phase 3, single-arm study in adults with moderate or severe acute pain on the verbal categorical rating scale and ≥4 on the numeric pain rating scale following surgical procedures or after presenting to a medical facility with moderate or severe acute pain of new origin. Participants received suzetrigine (100mg then 50mg every 12hrs) for 14 days or pain resolution, whichever came first. The primary endpoint was safety. The secondary endpoint was participant perception of suzetrigine's effectiveness in treating acute pain at the end of treatment using a patient global assessment.MethodsTo evaluate the safety and effectiveness of suzetrigine for the treatment of moderate-to-severe-acute surgical and non-surgical pain conditions, we conducted a phase 3, single-arm study in adults with moderate or severe acute pain on the verbal categorical rating scale and ≥4 on the numeric pain rating scale following surgical procedures or after presenting to a medical facility with moderate or severe acute pain of new origin. Participants received suzetrigine (100mg then 50mg every 12hrs) for 14 days or pain resolution, whichever came first. The primary endpoint was safety. The secondary endpoint was participant perception of suzetrigine's effectiveness in treating acute pain at the end of treatment using a patient global assessment.Suzetrigine was generally safe and well-tolerated in participants (N=256) with a range of surgical and non-surgical acute pain conditions; the maximum severity for most participants who had adverse events was mild (71 participants; 27.7%) or moderate (21 participants; 8.2%). Most participants (213 participants; 83.2%) rated suzetrigine's effectiveness for treating pain on a patient global assessment as good, very good, or excellent.ResultsSuzetrigine was generally safe and well-tolerated in participants (N=256) with a range of surgical and non-surgical acute pain conditions; the maximum severity for most participants who had adverse events was mild (71 participants; 27.7%) or moderate (21 participants; 8.2%). Most participants (213 participants; 83.2%) rated suzetrigine's effectiveness for treating pain on a patient global assessment as good, very good, or excellent.Suzetrigine provides a safe and effective non-opioid, non-addictive treatment with broad applicability for moderate-to-severe acute pain.ConclusionSuzetrigine provides a safe and effective non-opioid, non-addictive treatment with broad applicability for moderate-to-severe acute pain.NCT05661734.Clinicaltrialsgov RegistrationNCT05661734.

Cystic fibrosis (CF) is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene that impair the function of CFTR, an epithelial chloride channel required for proper function of the lung, pancreas, and other organs. Most patients with CF carry the F508del CFTR mutation, which causes defective CFTR protein folding and processing in the endoplasmic reticulum, resulting in minimal amounts of CFTR at the cell surface. One strategy to treat these patients is to correct the processing of F508del-CFTR with small molecules. Here we describe the in vitro pharmacology of VX-809, a CFTR corrector that was advanced into clinical development for the treatment of CF. In cultured human bronchial epithelial cells isolated from patients with CF homozygous for F508del, VX-809 improved F508del-CFTR processing in the endoplasmic reticulum and enhanced chloride secretion to approximately 14% of non-CF human bronchial epithelial cells (EC50, 81 ± 19 nM), a level associated with mild CF in patients with less disruptive CFTR mutations. F508del-CFTR corrected by VX-809 exhibited biochemical and functional characteristics similar to normal CFTR, including biochemical susceptibility to proteolysis, residence time in the plasma membrane, and single-channel open probability. VX-809 was more efficacious and selective for CFTR than previously reported CFTR correctors. VX-809 represents a class of CFTR corrector that specifically addresses the underlying processing defect in F508del-CFTR.

Cystic fibrosis (CF) is a fatal genetic disease caused by mutations in the gene encoding the CF transmembrane conductance regulator (CFTR), a protein kinase A (PKA)-activated epithelial anion channel involved in salt and fluid transport in multiple organs, including the lung. Most CF mutations either reduce the number of CFTR channels at the cell surface (e.g., synthesis or processing mutations) or impair channel function (e.g., gating or conductance mutations) or both. There are currently no approved therapies that target CFTR. Here we describe the in vitro pharmacology of VX-770, an orally bioavailable CFTR potentiator in clinical development for the treatment of CF. In recombinant cells VX-770 increased CFTR channel open probability (Po) in both the F508del processing mutation and the G551D gating mutation. VX-770 also increased Cl⁻ secretion in cultured human CF bronchial epithelia (HBE) carrying the G551D gating mutation on one allele and the F508del processing mutation on the other allele by [almost equal to]10-fold, to [almost equal to]50% of that observed in HBE isolated from individuals without CF. Furthermore, VX-770 reduced excessive Na⁺ and fluid absorption to prevent dehydration of the apical surface and increased cilia beating in these epithelial cultures. These results support the hypothesis that pharmacological agents that restore or increase CFTR function can rescue epithelial cell function in human CF airway.

Voltage-gated ion channels regulate many physiological functions and are targets for a number of drugs. Patch-clamp electrophysiology is the standard method for measuring channel activity because it fulfils the requirements for voltage control, repetitive stimulation and high temporal resolution, but it is laborious and costly. Here we report an electro-optical technology and automated instrument, called the electrical stimulation voltage ion probe reader (E-VIPR), that measures the activity of voltage-gated ion channels using extracellular electrical field stimulation and voltage-sensitive fluorescent probes. We demonstrate that E-VIPR can sensitively detect drug potency and mechanism of block on the neuronal human type III voltage-gated sodium channel expressed in human embryonic kidney cells. Results are compared with voltage-clamp and show that E-VIPR provides sensitive and information-rich compound blocking activity. Furthermore, we screened ∼400 drugs and observed sodium channel–blocking activity for ∼25% of them, including the antidepressants sertraline (Zoloft) and paroxetine (Paxil).

In previous work, participants with a G970R mutation in cystic fibrosis transmembrane conductance regulator (CFTR) (c.2908G>C) had numerically lower sweat chloride responses during ivacaftor treatment than participants with other CFTR gating mutations. The objective of this substudy was to characterize the molecular defect of the G970R mutation in vitro and assess the benefit of ivacaftor in participants with this mutation. This substudy assessed sweat chloride, spirometry findings, and nasal potential difference on and off ivacaftor treatment in three participants with a G970R/F508del genotype. Intestinal organoids derived from rectal biopsy specimens were used to assess ivacaftor response ex vivo and conduct messenger RNA splice and protein analyses. No consistent or meaningful trends were observed between on‐treatment and off‐treatment clinical assessments. Organoids did not respond to ivacaftor in forskolin‐induced swelling assays; no mature CFTR protein was detected in Western blots. Organoid RNA analysis demonstrated that 3 novel splice variants were created by G970R‐CFTR: exon 17 truncation, exons 13–15 and 17 skipping, and intron 17 retention. Functional and molecular analyses indicated that the c.2908G>C mutation caused a cryptic splicing defect. Organoids lacked an ex vivo response with ivacaftor and supported identification of the mechanism underlying the CFTR defect caused by c.2908G>C. Analysis of CFTR mutations indicated that cryptic splicing was a rare cause of mutation misclassification in engineered cell lines. This substudy used organoids as an alternative in vitro model for mutations, such as cryptic splice mutations that cannot be fully assessed using cDNA expressed in recombinant cell systems.

Cyclic AMP controls several signalling cascades within cells, and changes in the amounts of this second messenger have an essential role in many cellular events. Here we describe a new methodology for monitoring the fluctuations of cAMP in living cells. By tagging the cAMP effector protein kinase A with two suitable green fluorescent protein mutants, we have generated a probe in which the fluorescence resonance energy transfer between the two fluorescent moieties is dependent on the levels of cAMP. This new methodology opens the way to the elucidation of the biochemistry of cAMP in vivo .

AbstractBackgroundThe NaV1.8 voltage-gated sodium channel, expressed in peripheral nociceptive neurons, plays a role in transmitting nociceptive signals. The effect of VX-548, an oral, highly selective inhibitor of NaV1.8, on control of acute pain is being studied.MethodsAfter establishing the selectivity of VX-548 for NaV1.8 inhibition in vitro, we conducted two phase 2 trials involving participants with acute pain after abdominoplasty or bunionectomy. In the abdominoplasty trial, participants were randomly assigned in a 1:1:1:1 ratio to receive one of the following over a 48-hour period: a 100-mg oral loading dose of VX-548, followed by a 50-mg maintenance dose every 12 hours (the high-dose group); a 60-mg loading dose of VX-548, followed by a 30-mg maintenance dose every 12 hours (the middle-dose group); hydrocodone bitartrate–acetaminophen (5 mg of hydrocodone bitartrate and 325 mg of acetaminophen every 6 hours); or oral placebo every 6 hours. In the bunionectomy trial, participants were randomly assigned in a 2:2:1:2:2 ratio to receive one of the following over a 48-hour treatment period: oral high-dose VX-548; middle-dose VX-548; low-dose VX-548 (a 20-mg loading dose, followed by a 10-mg maintenance dose every 12 hours); oral hydrocodone bitartrate–acetaminophen (5 mg of hydrocodone bitartrate and 325 mg of acetaminophen every 6 hours); or oral placebo every 6 hours. The primary end point was the time-weighted sum of the pain-intensity difference (SPID) over the 48-hour period (SPID48), a measure derived from the score on the Numeric Pain Rating Scale (range, 0 to 10; higher scores indicate greater pain) at 19 time points after the first dose of VX-548 or placebo. The main analysis compared each dose of VX-548 with placebo.ResultsA total of 303 participants were enrolled in the abdominoplasty trial and 274 in the bunionectomy trial. The least-squares mean difference between the high-dose VX-548 and placebo groups in the time-weighted SPID48 was 37.8 (95% confidence interval [CI], 9.2 to 66.4) after abdominoplasty and 36.8 (95% CI, 4.6 to 69.0) after bunionectomy. In both trials, participants who received lower doses of VX-548 had results similar to those with placebo. Headache and constipation were common adverse events with VX-548.ConclusionsAs compared with placebo, VX-548 at the highest dose, but not at lower doses, reduced acute pain over a period of 48 hours after abdominoplasty or bunionectomy. VX-548 was associated with adverse events that were mild to moderate in severity. (Funded by Vertex Pharmaceuticals; VX21-548-101 and VX21-548-102 ClinicalTrials.gov numbers, NCT04977336 and NCT05034952.)

In T lymphocytes, intracellular Ca2+concentration ([Ca2+]i) rises within seconds of T-cell antigen-receptorstimulation and initiates the synthesis and secretion of interleukin 2, a cytokine essential for T-cell proliferation and the immune response. Using video-imaging techniques, we tracked [Ca2+]isignals in individual T cells and measured subsequent expression of a β-galactosidase reporter gene (lacZ) controlled by the NF-AT element of the interleukin 2 enhancer. [Ca2+]ispikes elicited by monoclonal antibody binding to the CD3ε subunit of the T-cell receptor were positively correlated with gene expression, but varied widely between individual cells and were therefore difficult to relate quantitatively to lacZ expression. The [Ca2+]idependence of NF-AT-regulated gene expression was determined by elevating [Ca2+]iwith either thapsigargin or ionomycin and then \"clamping\" [Ca2+]ito various, stable levels by altering either extracellular [Ca2+] or extracellular [K+]. Raising [Ca2+]ifrom resting levels of 70 nM to between 200 nM and 1.6 μ M increased the fraction of cells expressing lacZ, with Kd≈ 1 μM. Activation of protein kinase C enhanced the [Ca2+]isensitivity of gene expression (Kd= 210 nM), whereas stimulation of protein kinase A inhibited [Ca2+]i-dependent gene expression. The experiments described here provide single-cell measurements linking a second messenger to gene expression in individual cells.

The Na 1.8 voltage-gated sodium channel, expressed in peripheral nociceptive neurons, plays a role in transmitting nociceptive signals. The effect of VX-548, an oral, highly selective inhibitor of Na 1.8, on control of acute pain is being studied. After establishing the selectivity of VX-548 for Na 1.8 inhibition in vitro, we conducted two phase 2 trials involving participants with acute pain after abdominoplasty or bunionectomy. In the abdominoplasty trial, participants were randomly assigned in a 1:1:1:1 ratio to receive one of the following over a 48-hour period: a 100-mg oral loading dose of VX-548, followed by a 50-mg maintenance dose every 12 hours (the high-dose group); a 60-mg loading dose of VX-548, followed by a 30-mg maintenance dose every 12 hours (the middle-dose group); hydrocodone bitartrate-acetaminophen (5 mg of hydrocodone bitartrate and 325 mg of acetaminophen every 6 hours); or oral placebo every 6 hours. In the bunionectomy trial, participants were randomly assigned in a 2:2:1:2:2 ratio to receive one of the following over a 48-hour treatment period: oral high-dose VX-548; middle-dose VX-548; low-dose VX-548 (a 20-mg loading dose, followed by a 10-mg maintenance dose every 12 hours); oral hydrocodone bitartrate-acetaminophen (5 mg of hydrocodone bitartrate and 325 mg of acetaminophen every 6 hours); or oral placebo every 6 hours. The primary end point was the time-weighted sum of the pain-intensity difference (SPID) over the 48-hour period (SPID48), a measure derived from the score on the Numeric Pain Rating Scale (range, 0 to 10; higher scores indicate greater pain) at 19 time points after the first dose of VX-548 or placebo. The main analysis compared each dose of VX-548 with placebo. A total of 303 participants were enrolled in the abdominoplasty trial and 274 in the bunionectomy trial. The least-squares mean difference between the high-dose VX-548 and placebo groups in the time-weighted SPID48 was 37.8 (95% confidence interval [CI], 9.2 to 66.4) after abdominoplasty and 36.8 (95% CI, 4.6 to 69.0) after bunionectomy. In both trials, participants who received lower doses of VX-548 had results similar to those with placebo. Headache and constipation were common adverse events with VX-548. As compared with placebo, VX-548 at the highest dose, but not at lower doses, reduced acute pain over a period of 48 hours after abdominoplasty or bunionectomy. VX-548 was associated with adverse events that were mild to moderate in severity. (Funded by Vertex Pharmaceuticals; VX21-548-101 and VX21-548-102 ClinicalTrials.gov numbers, NCT04977336 and NCT05034952.).