RESUMEN
Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are used for genetic models of cardiac diseases. We report an arrhythmia syndrome consisting of Early Repolarization Syndrome (ERS) and Short QT Syndrome (SQTS). The index patient (MMRL1215) developed arrhythmia-mediated syncope after electrocution and was found to carry six mutations. Functional alterations resulting from these mutations were examined in patient-derived hiPSC-CMs. Electrophysiological recordings were made in hiPSC-CMs from MMRL1215 and healthy controls. ECG analysis of the index patient showed slurring of the QRS complex and QTc = 326 ms. Action potential (AP) recordings from MMRL1215 myocytes showed slower spontaneous activity and AP duration was shorter. Field potential recordings from MMRL1215 hiPSC-CMs lack a "pseudo" QRS complex suggesting reduced inward current(s). Voltage clamp analysis of ICa showed no difference in the magnitude of current. Measurements of INa reveal a 60% reduction in INa density in MMRL1215 hiPSC-CMs. Steady inactivation and recovery of INa was unaffected. mRNA analysis revealed ANK2 and SCN5A are significantly reduced in hiPSC-CM derived from MMRL1215, consistent with electrophysiological recordings. The polygenic cause of ERS/SQTS phenotype is likely due to a loss of INa due to a mutation in PKP2 coupled with and a gain of function in IK,ATP due to a mutation in ABCC9.
Asunto(s)
Arritmias Cardíacas/genética , Miocitos Cardíacos/metabolismo , Potenciales de Acción/genética , Adenosina Trifosfato/metabolismo , Ancirinas/genética , Ancirinas/metabolismo , Arritmias Cardíacas/fisiopatología , Fenómenos Electrofisiológicos , Variación Genética/genética , Humanos , Células Madre Pluripotentes Inducidas/metabolismo , Células Madre Pluripotentes Inducidas/fisiología , Miocitos Cardíacos/fisiología , Canal de Sodio Activado por Voltaje NAV1.5/genética , Canal de Sodio Activado por Voltaje NAV1.5/metabolismo , Técnicas de Placa-Clamp/métodos , Placofilinas/genética , Potasio/metabolismo , Sodio/metabolismo , Receptores de Sulfonilureas/genéticaRESUMEN
Conventionally, manual patch-clamp electrophysiological approaches are the gold standard for studying ion channel function in neurons. However, these approaches are labor-intensive, yielding low-throughput results, and are therefore not amenable for compound profiling efforts during the early stages of drug discovery. The SyncroPatch 384PE has been successfully implemented for pharmacological experiments in heterologous overexpression systems that may not reproduce the function of voltage-gated ion channels in a native, heterogeneous environment. Here, we describe a protocol allowing the characterization of endogenous voltage-gated potassium (Kv) and sodium (Nav) channel function in developing primary rat cortical cultures, allowing investigations at a significantly improved throughput compared with manual approaches. Key neuronal marker expression and microelectrode array recordings of electrophysiological activity over time correlated well with neuronal maturation. Gene expression data revealed high molecular diversity in Kv and Nav subunit composition throughout development. Voltage-clamp experiments elicited three major current components composed of inward and outward conductances. Further pharmacological experiments confirmed the endogenous expression of functional Kv and Nav channels in primary cortical neurons. The major advantages of this approach compared with conventional manual patch-clamp systems include unprecedented improvements in experimental ease and throughput for ion channel research in primary neurons. These efforts demonstrated feasibility for primary neuronal ion channel investigation with the SyncroPatch, providing the foundation for future studies characterizing biophysical changes in endogenous ion channels in primary systems associated with disease or development.
Asunto(s)
Descubrimiento de Drogas , Ensayos Analíticos de Alto Rendimiento , Canales Iónicos/genética , Técnicas de Placa-Clamp , Animales , Corteza Cerebelosa/citología , Corteza Cerebelosa/fisiología , Electrofisiología , Regulación de la Expresión Génica , Humanos , Cultivo Primario de Células , RatasRESUMEN
BACKGROUND: Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are used for many applications including safety pharmacology. However, a deficiency or complete absence of several K+ currents suggests repolarization reserve is low in hiPSC-CMs. We determined whether a dual Ito and IKr activator can improve repolarization reserve in hiPSC-CMs resulting in a more electrophysiologically mature phenotype. METHODS AND RESULTS: Human iPSC were maintained on growth factor and differentiated into the cardiac phenotype by addition of selective Wnt molecules. Current and voltage clamp recordings in single cells were made using patch electrodes. Extracellular field potentials were made using a microelectrode array on hiPSC monolayers. Action potential recordings from hiPSC-CMs following application of an IKr inhibitor resulted in depolarization of the membrane potential and prolongation of the APD. A flattening of the T-wave was noted on the pseudo-ECG. In contrast, application of the IKr and Ito agonist, NS3623, resulted in hyperpolarization of the membrane, slowing of the spontaneous rate and shortening of the APD. Voltage clamp recording showed a significant increase in IKr; no enhancement of Ito in hiPSC-CMs was noted. AP clamp experiments revealed that IKr plays a role in both phase 3 repolarization and phase 4 depolarization. mRNA analysis revealed that KCNH2 is abundantly expressed in hiPSC-CM, consistent with electrophysiological recordings. CONCLUSIONS: Although NS3623 is a dual Ito and IKr activator in ventricular myocytes, application of this compound to hiPSC-CMs enhanced only IKr and no effect on Ito was noted. Our results suggest IKr enhancement can improve repolarization reserve in this cell type. The disconnect between a dramatic increase in Ito in adult myocytes versus the lack of effect in hiPSC-CMs suggest that the translation of pharmacological effects in hiPSC-CM to adult myocytes should be viewed with caution.
Asunto(s)
Células Madre Pluripotentes Inducidas/citología , Miocitos Cardíacos/efectos de los fármacos , Potenciales de Acción/efectos de los fármacos , Diferenciación Celular , Células Cultivadas , Humanos , Miocitos Cardíacos/fisiología , Compuestos de Fenilurea/farmacología , Piperidinas/farmacología , Canales de Potasio/fisiología , Piridinas/farmacología , Tetrazoles/farmacologíaRESUMEN
We report the investigation of sulfonamide-derived Cav2.2 inhibitors to address drug-metabolism liabilities with this lead class of analgesics. Modification of the benzamide substituent provided improvements in both potency and selectivity. However, we discovered that formation of the persistent 3-(trifluoromethyl)benzenesulfonamide metabolite was an endemic problem in the sulfonamide series and that the replacement of the center aminopiperidine scaffold failed to prevent this metabolic pathway. This issue was eventually addressed by application of a bioisostere strategy. The new gem-dimethyl sulfone series retained Cav2.2 potency without the liability of the circulating sulfonamide metabolite.
RESUMEN
The voltage-gated calcium channel Ca(v)2.2 (N-type calcium channel) is a critical regulator of synaptic transmission and has emerged as an attractive target for the treatment of chronic pain. We report here the discovery of sulfonamide-derived, state-dependent inhibitors of Ca(v)2.2. In particular, 19 is an inhibitor of Ca(v)2.2 that is selective over cardiac ion channels, with a good preclinical PK and biodistribution profile. This compound exhibits dose-dependent efficacy in preclinical models of inflammatory hyperalgesia and neuropathic allodynia and is devoid of ancillary cardiovascular or CNS pharmacology at the doses tested. Importantly, 19 exhibited no efficacy in Ca(v)2.2 gene-deleted mice. The discovery of metabolite 26 confounds further development of members of this aminopiperidine sulfonamide series. This discovery also suggests specific structural liabilities of this class of compounds that must be addressed.
Asunto(s)
Bloqueadores de los Canales de Calcio/farmacología , Canales de Calcio Tipo N/química , Canales de Calcio Tipo N/fisiología , Dolor Crónico/tratamiento farmacológico , Hiperalgesia/tratamiento farmacológico , Inflamación/tratamiento farmacológico , Neuralgia/tratamiento farmacológico , Piperidinas/farmacología , Sulfonamidas/farmacología , Animales , Bloqueadores de los Canales de Calcio/síntesis química , Bloqueadores de los Canales de Calcio/farmacocinética , Canales de Calcio Tipo N/metabolismo , Células Cultivadas , Perros , Humanos , Ratones , Ratones Noqueados , Microsomas Hepáticos/efectos de los fármacos , Técnicas de Placa-Clamp , Piperidinas/síntesis química , Piperidinas/farmacocinética , Ratas , Ratas Sprague-Dawley , Sulfonamidas/síntesis química , Sulfonamidas/farmacocinética , Distribución TisularRESUMEN
Biological, genetic, and clinical evidence provide validation for N-type calcium channels (Ca(V)2.2) as therapeutic targets for chronic pain. A state-dependent Ca(V)2.2 inhibitor may provide an improved therapeutic window over ziconotide, the peptidyl Ca(V)2.2 inhibitor used clinically. Supporting this notion, we recently reported that in preclinical models, the state-dependent Ca(V)2 inhibitor (3R)-5-(3-chloro-4-fluorophenyl)-3-methyl-3-(pyrimidin-5-ylmethyl)-1-(1H-1,2,4-triazol-3-yl)-1,3-dihydro-2H-indol-2-one (TROX-1) has an improved therapeutic window compared with ziconotide. Here we characterize TROX-1 inhibition of Cav2.2 channels in more detail. When channels are biased toward open/inactivated states by depolarizing the membrane potential under voltage-clamp electrophysiology, TROX-1 inhibits Ca(V)2.2 channels with an IC(50) of 0.11 µM. The voltage dependence of Ca(V)2.2 inhibition was examined using automated electrophysiology. TROX-1 IC(50) values were 4.2, 0.90, and 0.36 µM at -110, -90, and -70 mV, respectively. TROX-1 displayed use-dependent inhibition of Ca(V)2.2 with a 10-fold IC(50) separation between first (27 µM) and last (2.7 µM) pulses in a train. In a fluorescence-based calcium influx assay, TROX-1 inhibited Ca(V)2.2 channels with an IC(50) of 9.5 µM under hyperpolarized conditions and 0.69 µM under depolarized conditions. Finally, TROX-1 potency was examined across the Ca(V)2 subfamily. Depolarized IC(50) values were 0.29, 0.19, and 0.28 µM by manual electrophysiology using matched conditions and 1.8, 0.69, and 1.1 µM by calcium influx for Ca(V)2.1, Ca(V)2.2, and Ca(V)2.3, respectively. Together, these in vitro data support the idea that a state-dependent, non-subtype-selective Ca(V)2 channel inhibitor can achieve an improved therapeutic window over the relatively state-independent Ca(V)2.2-selective inhibitor ziconotide in preclinical models of chronic pain.
Asunto(s)
Bloqueadores de los Canales de Calcio/química , Canales de Calcio Tipo N/efectos de los fármacos , Indoles/química , Triazoles/química , Bloqueadores de los Canales de Calcio/farmacología , Línea Celular , Humanos , Indoles/farmacología , Concentración 50 Inhibidora , Potenciales de la Membrana/efectos de los fármacos , Técnicas de Placa-Clamp , Triazoles/farmacologíaRESUMEN
N-type calcium channels (Ca(v)2.2) have been shown to play a critical role in pain. A series of low molecular weight 2-aryl indoles were identified as potent Ca(v)2.2 blockers with good in vitro and in vivo potency.
Asunto(s)
Bloqueadores de los Canales de Calcio/uso terapéutico , Canales de Calcio Tipo N/metabolismo , Indoles/uso terapéutico , Dolor/tratamiento farmacológico , Animales , Bloqueadores de los Canales de Calcio/farmacocinética , Bloqueadores de los Canales de Calcio/farmacología , Perros , Haplorrinos , Humanos , Indoles/farmacocinética , Indoles/farmacología , RatasRESUMEN
The voltage-gated potassium channel, human Ether-à-go-go related gene (hERG), represents the molecular component of IKr, one of the potassium currents involved in cardiac action potential repolarization. Inhibition of IKr increases the duration of the ventricular action potential, reflected as a prolongation of the QT interval in the electrocardiogram, and increases the risk for potentially fatal ventricular arrhythmias. Because hERG is an appropriate surrogate for IKr, hERG assays that can identify potential safety liabilities of compounds during lead identification and optimization have been implemented. Although the gold standard for hERG evaluation is electrophysiology, this technique, even with the medium capacity, automated instruments that are currently available, does not meet the throughput demands for supporting typical medicinal chemistry efforts in the pharmaceutical environment. Assays that could provide reliable molecular pharmacology data, while operating in high capacity mode, are therefore desirable. In the present study, we describe a high-capacity, 384- and 1,536-well plate, functional thallium flux assay for the hERG channel that fulfills these criteria. This assay was optimized and validated using different structural classes of hERG inhibitors. An excellent correlation was found between the potency of these agents in the thallium flux assay and in electrophysiological recordings of channel activity using the QPatch automated patch platform. Extension of this study to include 991 medicinal chemistry compounds from different internal drug development programs indicated that the thallium flux assay was a good predictor of in vitro hERG activity. These data suggest that the hERG thallium flux assay can play an important role in supporting drug development efforts.
Asunto(s)
Canales de Potasio Éter-A-Go-Go/antagonistas & inhibidores , Ensayos Analíticos de Alto Rendimiento , Bloqueadores de los Canales de Potasio/farmacología , Potenciales de Acción/efectos de los fármacos , Animales , Células CHO , Cricetinae , Cricetulus , Canales de Potasio Éter-A-Go-Go/genética , Canales de Potasio Éter-A-Go-Go/fisiología , Células HEK293 , Humanos , Técnicas de Placa-Clamp , Talio/metabolismoRESUMEN
Voltage-gated calcium channel (Ca(v))2.2 (N-type calcium channels) are key components in nociceptive transmission pathways. Ziconotide, a state-independent peptide inhibitor of Ca(v)2.2 channels, is efficacious in treating refractory pain but exhibits a narrow therapeutic window and must be administered intrathecally. We have discovered an N-triazole oxindole, (3R)-5-(3-chloro-4-fluorophenyl)-3-methyl-3-(pyrimidin-5-ylmethyl)-1-(1H-1,2,4-triazol-3-yl)-1,3-dihydro-2H-indol-2-one (TROX-1), as a small-molecule, state-dependent blocker of Ca(v)2 channels, and we investigated the therapeutic advantages of this compound for analgesia. TROX-1 preferentially inhibited potassium-triggered calcium influx through recombinant Ca(v)2.2 channels under depolarized conditions (IC(50) = 0.27 microM) compared with hyperpolarized conditions (IC(50) > 20 microM). In rat dorsal root ganglion (DRG) neurons, TROX-1 inhibited omega-conotoxin GVIA-sensitive calcium currents (Ca(v)2.2 channel currents), with greater potency under depolarized conditions (IC(50) = 0.4 microM) than under hyperpolarized conditions (IC(50) = 2.6 microM), indicating state-dependent Ca(v)2.2 channel block of native as well as recombinant channels. TROX-1 fully blocked calcium influx mediated by a mixture of Ca(v)2 channels in calcium imaging experiments in rat DRG neurons, indicating additional block of all Ca(v)2 family channels. TROX-1 reversed inflammatory-induced hyperalgesia with maximal effects equivalent to nonsteroidal anti-inflammatory drugs, and it reversed nerve injury-induced allodynia to the same extent as pregabalin and duloxetine. In contrast, no significant reversal of hyperalgesia was observed in Ca(v)2.2 gene-deleted mice. Mild impairment of motor function in the Rotarod test and cardiovascular functions were observed at 20- to 40-fold higher plasma concentrations than required for analgesic activities. TROX-1 demonstrates that an orally available state-dependent Ca(v)2 channel blocker may achieve a therapeutic window suitable for the treatment of chronic pain.
Asunto(s)
Analgésicos/farmacología , Bloqueadores de los Canales de Calcio/farmacología , Canales de Calcio Tipo N/fisiología , Indoles/farmacología , Triazoles/farmacología , Analgésicos/efectos adversos , Analgésicos/farmacocinética , Animales , Barorreflejo/efectos de los fármacos , Disponibilidad Biológica , Bloqueadores de los Canales de Calcio/efectos adversos , Bloqueadores de los Canales de Calcio/farmacocinética , Canales de Calcio Tipo N/genética , Canales de Calcio Tipo R/fisiología , Proteínas de Transporte de Catión/fisiología , Línea Celular , Perros , Ganglios Espinales/efectos de los fármacos , Ganglios Espinales/fisiología , Hiperalgesia/tratamiento farmacológico , Hipotensión Ortostática/inducido químicamente , Indoles/efectos adversos , Indoles/farmacocinética , Masculino , Ratones , Ratones Noqueados , Neuronas/efectos de los fármacos , Neuronas/fisiología , Dolor/tratamiento farmacológico , Dolor/etiología , Técnicas de Placa-Clamp , Ratas , Ratas Sprague-Dawley , Triazoles/efectos adversos , Triazoles/farmacocinéticaRESUMEN
Cav2.2 channels play a critical role in pain signaling by controlling synaptic transmission between dorsal root ganglion neurons and dorsal horn neurons. The Cav2.2-selective peptide blocker ziconotide (Prialt, Elan Pharmaceuticals, Dublin, Ireland) has proven efficacious in pain relief, but has a poor therapeutic index and requires intrathecal administration. This has provided impetus for finding an orally active, state-dependent Cav2.2 inhibitor with an improved safety profile. Members of the Cav2 subfamily of calcium channels are the main contributors to central and peripheral synaptic transmission, but the pharmacological effects of blocking each subtype is not yet defined. Here we describe a high-throughput fluorescent assay using a fluorometric imaging plate reader (FLIPR [Molecular Devices, Sunnyvale, CA]) designed to quickly evaluate the state dependence and selectivity of inhibitors across the Cav2 subfamily. Stable cell lines expressing functional Cav2 channels (Ca(V)alpha, beta(3), and alpha(2)delta subunits) were co-transfected with an inward rectifier (Kir2.3) so that membrane potential, and therefore channel state, could be controlled by external potassium concentration. Following cell incubation in drug with varying concentrations of potassium, a high potassium trigger was added to elicit calcium influx through available, unblocked channels. State-dependent inhibitors that preferentially bind to channels in the open or inactivated state can be identified by their increased potency at higher potassium concentrations, where cells are depolarized and channels are biased towards these states. Although the Cav2 channel subtypes differ in their voltage dependence of inactivation, by adjusting pre-trigger potassium concentrations, the degree of steady-state inactivation can be more closely matched across Cav2 subtypes to assess molecular selectivity.
Asunto(s)
Bloqueadores de los Canales de Calcio/farmacología , Caveolina 2/efectos de los fármacos , Caveolina 2/fisiología , Evaluación Preclínica de Medicamentos/métodos , Western Blotting , Calcio/metabolismo , Línea Celular , Electrofisiología , Humanos , Inmunohistoquímica , Potenciales de la Membrana/efectos de los fármacos , Técnicas de Placa-Clamp , Potasio/farmacología , Canales de Potasio de Rectificación Interna/efectos de los fármacos , Canales de Potasio de Rectificación Interna/fisiología , Reacción en Cadena de la Polimerasa de Transcriptasa InversaRESUMEN
Neurons exhibit long-term excitability changes necessary for maintaining proper cell and network activity in response to various inputs and perturbations. For instance, the adult crustacean pyloric network can spontaneously recover rhythmic activity after complete shutdown resulting from permanent removal of neuromodulatory inputs. Dissociated lobster stomatogastric ganglion (STG) neurons have been shown to spontaneously develop oscillatory activity via excitability changes. Rhythmic electrical stimulation can eliminate these oscillatory patterns in some cells. The ionic mechanisms underlying these changes are only partially understood. We used dissociated crab STG neurons to study the ionic mechanisms underlying spontaneous recovery of rhythmic activity and stimulation-induced activity changes. Similar to lobster neurons, rhythmic activity spontaneously develops in crab STG neurons. Rhythmic hyperpolarizing stimulation can eliminate, but more commonly accelerate, the emergence of stable oscillatory activity depending on Ca(2+) influx at hyperpolarized voltages. Our main finding is that upregulation of a Ca(2+) current and downregulation of a high-threshold K(+) current underlies the spontaneous homeostatic development of oscillatory activity. However, because of a nonlinear dependence on stimulus frequency, hyperpolarization-induced oscillations appear to be inconsistent with a homeostatic regulation of activity. We find no difference in the activity patterns or the underlying ionic currents involved between neurons of the fast pyloric and the slow gastric mill networks during the first 10 days in isolation. Dynamic-clamp experiments confirm that these conductance modifications can explain the observed activity changes. We conclude that spontaneous and stimulation-induced excitability changes in STG neurons can both result in intrinsic oscillatory activity via regulation of the same two conductances.