Cell-Free Synthesis and Electrophysiological Analysis of Multipass Voltage-Gated Ion Channels Tethered in Microsomal Membranes.

Cell-free protein synthesis (CFPS) has emerged as a powerful tool for the rapid synthesis and analysis of various structurally and functionally distinct proteins. These include 'difficult-to-express' membrane proteins such as large multipass ion channel receptors. Owing to their membrane localization, eukaryotic CFPS supplemented with endoplasmic reticulum (ER)-derived microsomal vesicles has proven to be an efficient system for the synthesis of functional membrane proteins. Here we demonstrate the applicability of the eukaryotic cell-free systems based on lysates from the mammalian Chinese Hamster Ovary (CHO) and insect Spodoptera frugiperda (Sf21) cells. We demonstrate the efficiency of the systems in the de novo cell-free synthesis of the human cardiac ion channels: ether-a-go-go potassium channel (hERG) KV11.1 and the voltage-gated sodium channel hNaV1.5.

The Phytochemical α-Mangostin Inhibits Cervical Cancer Cell Proliferation and Tumor Growth by Downregulating E6/E7-HPV Oncogenes and KCNH1 Gene Expression.

Cervical cancer is the fourth most common cancer among women worldwide. The main factor associated with the onset and progression of this neoplasia is the human papillomavirus (HPV) infection. The HPV-oncogenes E6 and E7 are critical drivers of cellular transformation, promoting the expression of oncogenes such as KCNH1. The phytochemical α-mangostin (AM) is a potent antineoplastic and antiviral compound. However, its effects on HPV oncogenes and KCNH1 gene expression remain unknown. This study evaluated the effects of AM on cell proliferation, cell cycle distribution and gene expression, including its effects on tumor growth in xenografted mice. AM inhibited cell proliferation in a concentration-dependent manner, being the most sensitive cell lines those with the highest number of HPV16 copies. In addition, AM promoted G1-cell cycle arrest in CaSki cells, while led to cell death in SiHa and HeLa cells. Of interest was the finding of an AM-dependent decreased gene expression of E6, E7 and KCNH1 both in vitro and in vivo, as well as the modulation of cytokine expression, Ki-67, and tumor growth inhibition. On these bases, we suggest that AM represents a good option as an adjuvant for the treatment and prevention of cervical cancer.

Nitidine chloride inhibits fibroblast like synoviocytes-mediated rheumatoid synovial inflammation and joint destruction by targeting KCNH1.

OBJECTIVE: Nitidine chloride (NC), a natural small molecular compound from traditional Chinese herbal medicine zanthoxylum nitidum, has been shown to exhibit anti-tumor effect. However, its role in autoimmune diseases such as rheumatoid arthritis (RA) is unknown. Here, we investigate the effect of NC in controlling fibroblast-like synoviocytes (FLS)-mediated synovial inflammation and joint destruction in RA and further explore its underlying mechanism(s). METHODS: FLSs were separated from synovial tissues obtained from patients with RA. Protein expression was analyzed by Western blot or immunohistochemistry. Gene expression was measured using quantitative RT-PCR. ELISA was used to measure the levels of cytokines and MMPs. Cell proliferation was detected using EdU incorporation. Migration and invasion were evaluated by Boyden chamber assay. RNA sequencing analysis was used to identify the target of NC. Collagen-induced arthritis (CIA) model was used to evaluate the in vivo effect of NC. RESULTS: NC treatment reduced the proliferation, migration, invasion, and lamellipodia formation but not apoptosis of RA FLSs. We also demonstrated the inhibitory effect of NC on TNF-α-induced expression and secretion of IL-6, IL-8, CCL-2, MMP-1 and MMP-13. Furthermore, we identified KCNH1, a gene that encodes ether-à-go-go-1 channel, as a novel targeting gene of NC in RA FLSs. KCNH1 expression was increased in FLSs and synovial tissues from patients with RA compared to healthy controls. KCNH1 knockdown or NC treatment decreased the TNF-α-induced phosphorylation of AKT. Interestingly, NC treatment ameliorated the severity of arthritis and reduced synovial KCNH1 expression in mice with CIA. CONCLUSIONS: Our data demonstrate that NC treatment inhibits aggressive and inflammatory actions of RA FLSs by targeting KCNH1 and sequential inhibition of AKT phosphorylation. Our findings suggest that NC might control FLS-mediated rheumatoid synovial inflammation and joint destruction, and be a novel therapeutic agent for RA.

Regional heritability mapping identifies several novel loci (STAT4, ULK4, and KCNH5) for primary biliary cholangitis in the Japanese population.

While the advent of GWAS more than a decade ago has ushered in remarkable advances in our understanding of complex traits, the limitations of single-SNP analysis have also led to the development of several other approaches. Simulation studies have shown that the regional heritability mapping (RHM) method, which makes use of multiple adjacent SNPs jointly to estimate the genetic effect of a given region of the genome, generally has higher detection power than single-SNP GWAS. However, thus far its use has been mostly limited to agricultural settings, and its potential for the discovery of new genes in human diseases is yet to be fully exploited. In this study, by applying the RHM method to primary biliary cholangitis (PBC) in the Japanese population, we identified three novel loci (STAT4, ULK4, and KCNH5) at the genome-wide significance level, two of which (ULK4 and KCNH5) have not been found associated with PBC in any population previously. Notably, these genes could not be detected by using conventional single-SNP GWAS, highlighting the potential of the RHM method for the detection of new susceptibility loci in human diseases. These findings thereby provide strong empirical evidence that RHM is an effective and practical complementary approach to GWAS in this context. Also, liver tissue mRNA microarray analysis revealed higher gene expression levels in ULK4 in PBC patients (P < 0.01). Lastly, we estimated the common SNP heritability of PBC in the Japanese population (0.210 ± 0.026).

Eag1 Gene and Protein Expression in Human Retinoblastoma Tumors and its Regulation by pRb in HeLa Cells.

Retinoblastoma is the most common pediatric intraocular malignant tumor. Unfortunately, low cure rates and low life expectancy are observed in low-income countries. Thus, alternative therapies are needed for patients who do not respond to current treatments or those with advanced cases of the disease. Ether à-go-go-1 (Eag1) is a voltage-gated potassium channel involved in cancer. Eag1 expression is upregulated by the human papilloma virus (HPV) oncogene E7, suggesting that retinoblastoma protein (pRb) may regulate Eag1. Astemizole is an antihistamine that is suggested to be repurposed for cancer treatment; it targets proteins implicated in cancer, including histamine receptors, ATP binding cassette transporters, and Eag channels. Here, we investigated Eag1 regulation using pRb and Eag1 expression in human retinoblastoma. The effect of astemizole on the cell proliferation of primary human retinoblastoma cultures was also studied. HeLa cervical cancer cells (HPV-positive and expressing Eag1) were transfected with RB1. Eag1 mRNA expression was studied using qPCR, and protein expression was assessed using western blotting and immunochemistry. Cell proliferation was evaluated with an MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. RB1 transfection down-regulated Eag1 mRNA and protein expression. The human retinoblastoma samples displayed heterogeneous Eag1 mRNA and protein expression. Astemizole decreased cell proliferation in primary retinoblastoma cultures. Our results suggest that Eag1 mRNA and protein expression was regulated by pRb in vitro, and that human retinoblastoma tissues had heterogeneous Eag1 mRNA and protein expression. Furthermore, our results propose that the multitarget drug astemizole may have clinical relevance in patients with retinoblastoma, for instance, in those who do not respond to current treatments.

Increased Expression of Kv10.2 in the Hippocampus Attenuates Valproic Acid-Induced Autism-Like Behaviors in Rats.

The role of potassium channels provides suggestive evidence for the etiology of autism. The voltage-gated potassium channel Kv10.2 (KCNH5) is widely expressed in the brain. However, the inherent relationship between Kv10.2 and autism is still unclear. Herein, a rat valproic acid (VPA)-induced autism spectrum disorder model was established. The expression level of Kv10.2 was obviously decreased in the hippocampus of VPA rats. Kv10.2 was mainly localized in neurons. Subsequently, a recombinant lentivirus expressing Kv10.2 was used to upregulate the expression of Kv10.2 in the hippocampus of VPA-exposed rats. The results were promising as injection of the Kv10.2 lentivirus in the hippocampus relieved anxiety and stereotypical behavior, and improved the social and exploratory abilities of rats that were prenatally exposed to VPA. In addition, spectral analysis of electroencephalogram data revealed that animals exposed to VPA exhibited increased high-frequency activity compared with the control rats, and this activity recovered to a certain extent after upregulation of Kv10.2 expression by lentivirus injection. These results suggest that changes in Kv10.2 may play an important role in the etiology of autism, thus providing a promising direction for further research on autism.

Tetrandrine, a novel inhibitor of ether-à-go-go-1 (Eag1), targeted to cervical cancer development.

Mortality-to-incidence ratios in patients with cancer are extremely high, positioning cancer as a major cause of death worldwide. Ether-à-go-go-1 (Eag1) is an ion channel that plays important roles in tumour proliferation, malignant transformation, invasion, metastasis, recurrence, and prognosis. Therefore, identifying potent and specific Eag1 channel inhibitors is crucial. In this study, we identified the first natural inhibitor of Eag1, the traditional Chinese medicine agent tetrandrine, and explored the underlying mechanism. Tetrandrine directly interacted with Eag1 and inhibited the currents in a concentration-dependent manner (IC50 of 69.97 ± 5.2 µM), and the amino acids Ile 550 , Thr 552 , and Gln 557 in the Eag1 C-linker domain were critical for tetrandrine's inhibitory effect. Moreover, tetrandrine reduced the proliferation of HeLa cells and Chinese hamster ovary (CHO) cells stably expressing Eag1 in a concentration-dependent manner. Finally, tetrandrine (30 mg/kg/day) inhibited tumor growth in mice, demonstrating a 64.21% inhibitory rate of HeLa cell-transplanted tumors. These results suggest that tetrandrine is a potent and selective Eag1 channel inhibitor, and could act as a leading compound in the development of therapies for Eag1 ion channel dysfunction-induced diseases.

Identification of small-molecule ion channel modulators in C. elegans channelopathy models.

Ion channels are important therapeutic targets, but the discovery of ion channel drugs remains challenging due to a lack of assays that allow high-throughput screening in the physiological context. Here we report C. elegans phenotype-based methods for screening ion channel drugs. Expression of modified human ether-a-go-go-related gene (hERG) potassium channels in C. elegans results in egg-laying and locomotive defects, which offer indicators for screening small-molecule channel modulators. Screening in worms expressing hERGA561V, which carries a trafficking-defective mutation A561V known to associate with long-QT syndrome, identifies two functional correctors Prostratin and ingenol-3,20-dibenzoate. These compounds activate PKCε signaling and consequently phosphorylate S606 at the pore region of the channel to promote hERGA561V trafficking to the plasma membrane. Importantly, the compounds correct electrophysiological abnormalities in hiPSC-derived cardiomyocytes bearing a heterozygous CRISPR/Cas9-edited hERGA561V. Thus, we have developed an in vivo high-throughput method for screening compounds that have therapeutic potential in treating channelopathies.

The effects of deoxyelephantopin on the cardiac delayed rectifier potassium channel current (IKr) and human ether-a-go-go-related gene (hERG) expression.

Elephantopus scaber Linn and its major bioactive component, deoxyelephantopin are known for their medicinal properties and are often reported to have various cytotoxic and antitumor activities. This plant is widely used as folk medicine for a plethora of indications although its safety profile remains unknown. Human ether-a-go-go-related gene (hERG) encodes the cardiac IKr current which is a determinant of the duration of ventricular action potentials and QT interval. The hERG potassium channel is an important antitarget in cardiotoxicity evaluation. This study investigated the effects of deoxyelephantopin on the current, mRNA and protein expression of hERG channel in hERG-transfected HEK293 cells. The hERG tail currents following depolarization pulses were insignificantly affected by deoxyelephantopin in the transfected cell line. Current reduction was less than 40% as compared with baseline at the highest concentration of 50 µM. The results were consistent with the molecular docking simulation and hERG surface protein expression. Interestingly, it does not affect the hERG expression at both transcriptional and translational level at most concentrations, although higher concentration at 10 µM caused protein accumulation. In conclusion, deoxyelephantopin is unlikely a clinically significant hERG channel and Ikr blocker.

Discovery of novel somatostatin receptor subtype 5 (SSTR5) antagonists: Pharmacological studies and design to improve pharmacokinetic profiles and human Ether-a-go-go-related gene (hERG) inhibition.

Somatostatin (SST) is a peptide hormone comprising 14 or 28 amino acids that inhibits endocrine and exocrine secretion via five distinct G-protein-coupled receptors (SSTR1-5). SSTR5 has an important role in inhibiting the secretion of pancreatic and gastrointestinal hormones (e.g., insulin, GLP-1, PYY) through the binding of SSTs; hence, SSTR5 antagonists are expected to be novel anti-diabetic drugs. In the course of our lead generation program of SSTR5 antagonists, we have discovered a novel spiroazetidine derivative 3a. However, pharmacological evaluation of 3a revealed that it had to be administered at a high dose (100mg/kg) to show a persistent glucose-lowering effect in an oral glucose tolerance test (OGTT). We therefore initiated an optimization study based on 3a aimed at improving the antagonistic activity and mean residence time (MRT), resulting in the identification of 2-cyclopropyl-5-methoxybiphenyl derivative 3k. However, 3k did not show a sufficient persistent glucose-lowering effect in an OGTT; moreover, hERG inhibition was observed. Hence, further optimization study of the biphenyl moiety of compound 3k, focused on improving the pharmacokinetic (PK) profile and hERG inhibition, was conducted. Consequently, the introduction of a chlorine atom at the 6-position on the biphenyl moiety addressed a putative metabolic soft spot and increased the dihedral angle of the biphenyl moiety, leading to the discovery of 3p with an improved PK profile and hERG inhibition. Furthermore, 3p successfully exhibited a persistent glucose-lowering effect in an OGTT at a dose of 3mg/kg.

Natural products modulating the hERG channel: heartaches and hope.

Covering: 1996-December 2016The human Ether-à-go-go Related Gene (hERG) channel is a voltage-gated potassium channel playing an essential role in the normal electrical activity in the heart. It is involved in the repolarization and termination of action potentials in excitable cardiac cells. Mutations in the hERG gene and hERG channel blockage by small molecules are associated with increased risk of fatal arrhythmias. Several drugs have been withdrawn from the market due to hERG channel-related cardiotoxicity. Moreover, as a result of its notorious ligand promiscuity, this ion channel has emerged as an important antitarget in early drug discovery and development. Surprisingly, the hERG channel blocking profile of natural compounds present in frequently consumed botanicals (i.e. dietary supplements, spices, and herbal medicinal products) is not routinely assessed. This comprehensive review will address these issues and provide a critical compilation of hERG channel data for isolated natural products and extracts over the past two decades (1996-2016). In addition, the review will provide (i) a solid basis for the molecular understanding of the physiological functions of the hERG channel, (ii) the translational potential of in vitro/in vivo results to cardiotoxicity in humans, (iii) approaches for the identification of hERG channel blockers from natural sources, (iv) future perspectives for cardiac safety guidelines and their applications within phytopharmaceuticals and dietary supplements, and (v) novel applications of hERG channel modulation (e.g. as a drug target).

Administration of Non-Torsadogenic human Ether-à-go-go-Related Gene Inhibitors Is Associated with Better Survival for High hERG-Expressing Glioblastoma Patients.

PURPOSE: Glioblastoma is the most malignant primary brain tumor, with a median survival of less than 2 years. More effective therapeutic approaches are needed to improve clinical outcomes. EXPERIMENTAL DESIGN: Glioblastoma patient-derived cells (GPDC) were isolated from patient glioblastomas and implanted in mice to form xenografts. IHC was performed for human Ether-à-go-go-Related Gene (hERG) expression and tumor proliferation. Sphere-forming assays with the hERG blocker E-4031 were performed on a high and low hERG-expressing lines. A glioblastoma tissue microarray (TMA; 115 patients) was used to correlate hERG expression with patient survival. Clinical data were analyzed to determine whether patient survival was affected by incidental administration of hERG inhibitory drugs and the correlative effect of patient glioblastoma hERG expression levels. RESULTS: hERG expression was upregulated in glioblastoma xenografts with higher proliferative indices. High hERG-expressing GPDCs showed a reduction in sphere formation when treated with hERG inhibitors compared with low hERG-expressing GPDCs. Glioblastoma TMA analysis showed worse survival for glioblastoma patients with high hERG expression versus low expression-43.5 weeks versus 60.9 weeks, respectively (P = 0.022). Furthermore, patients who received at least one hERG blocker had a better survival rate compared with patients who did not (P = 0.0015). Subgroup analysis showed that glioblastoma patients with high hERG expression who received hERG blockers had improved survival (P = 0.0458). There was no difference in survival for low hERG-expressing glioblastoma patients who received hERG blockers (P = 0.4136). CONCLUSIONS: Our findings suggest that hERG is a potential glioblastoma survival marker, and that already approved drugs with non-torsadogenic hERG inhibitory activity may potentially be repurposed as adjuvant glioblastoma therapy in high hERG-expressing glioblastoma patients. Clin Cancer Res; 23(1); 73-80. ©2016 AACRSee related commentary by Arcangeli and Becchetti, p. 3.

Discovery of 5-Chloro-1-(5-chloro-2-(methylsulfonyl)benzyl)-2-imino-1,2-dihydropyridine-3-carboxamide (TAK-259) as a Novel, Selective, and Orally Active α1D Adrenoceptor Antagonist with Antiurinary Frequency Effects: Reducing Human Ether-a-go-go-Related Gene (hERG) Liabilities.

A novel structural class of iminopyridine derivative 1 was identified as a potent and selective human α1D adrenoceptor (α1D adrenergic receptor; α1D-AR) antagonist against α1A- and α1B-AR through screening of an in-house compound library. From initial structure-activity relationship studies, we found lead compound 9m with hERG K(+) channel liability. To develop analogues with reduced hERG K(+) channel inhibition, a combination of site-directed mutagenesis and docking studies was employed. Further optimization led to the discovery of (R)-9s and 9u, which showed antagonistic activity by a bladder strip test in rats with bladder outlet obstruction, as well as ameliorated cystitis-induced urinary frequency in rats. Ultimately, 9u was selected as a clinical candidate. This is the first study to show the utility of iminopyridine derivatives as selective α1D-AR antagonists and evaluate their effects in vivo.

Functional Characterization of Rare Variants Implicated in Susceptibility to Lone Atrial Fibrillation.

BACKGROUND: Few rare variants in atrial fibrillation (AF)-associated genes have been functionally characterized to identify a causal relationship between these variants and development of AF. We here sought to determine the clinical effect of rare variants in AF-associated genes in patients with lone AF and characterized these variants electrophysiologically and bioinformatically. METHODS AND RESULTS: We screened all coding regions in 12 AF-associated genes in 90 patients with lone AF, with an onset of 47±11 years (66 men; mean age, 56±13 years) by high-resolution melting curve analysis and DNA sequencing. The potassium and sodium currents were analyzed using whole-cell patch clamping. In addition to using 4 individual in silico prediction tools, we extended those predictions to an integrated tool (Combined Annotation Dependent Depletion). We identified 7 rare variants in KCNA5, KCNQ1, KCNH2, SCN5A, and SCN1B genes in 8 patients: 2 of 8 probands had a family history of AF. Electrophysiological studies revealed that 2 variants showed a loss-of-function, and 4 variants showed a gain-of-function. Five of 6 variants with electrophysiological abnormalities were predicted as pathogenic by Combined Annotation Dependent Depletion scores. CONCLUSIONS: In our cohort of patients with lone AF, 7 rare variants in cardiac ion channels were identified in 8 probands. A combination of electrophysiological studies and in silico predictions showed that these variants could contribute to the development of lone AF, although further in vivo study is necessary to confirm these results. More than half of AF-associated rare variants showed gain-of-function behavior, which may be targeted using genotype-specific pharmacological therapy.

Inhibition of Schistosoma mansoni ether-a-go-go related gene-encoded potassium channels leads to hypermotility and impaired egg production.

The purpose of this work was to investigate the effect of ether-a-go-go related gene (ERG) potassium channel inhibition on Schistosoma mansoni. Use of dofetilide to block the schistosome ERGs resulted in a striking 'corkscrew' effect. The worms were unable to control their motility; they were hypermotile. The treated worms produced abnormal eggs, some of which consisted of little more than a spine. One of the S. mansoni ERGs (SmERGs), Smp_161140, was chosen for further study by RNAi. The transcript was knocked down to 50% compared to the controls. These RNAi-treated worms demonstrated seizure-like movements. In S. mansoni, as in other organisms, ERG channels seem to play a role in regulating muscle excitability. This work shows that egg production can be greatly reduced by effectively targeting muscle coordination in these important parasites.

Development and validation of a method for the analysis of hydroxyzine hydrochloride in extracellular solution used in in vitro preclinical safety studies.

In the process of drug development, preclinical safety studies are to be performed that require the analysis of the compound at very low concentrations with high demands on the performance of the analytical methods. In the current study, a UPLC-MS/MS method was developed and validated to quantify hydroxyzine hydrochloride in an extracellular solution used in a hERG assay in concentrations ranging from 0.01 to 10µM (4.5ng/ml-4.5µg/ml). Chromatographic separation was achieved isocratically on an Acquity BEH C18 analytical column. The assay was validated at concentrations of 0.11-1.1ng/ml in end solution for hydroxyzine hydrochloride. Linearity was demonstrated over the range of concentrations of 0.06-0.17ng/ml and over the range of concentrations of 0.6-1.7ng/ml in end solution with the coefficient of correlation r>0.99. Accuracy of the achieved concentration, intra-run, and inter-run precision of the method were well within the acceptance criteria (being mean recovery of 80-120% and relative standard deviation ≤10.0%). The limit of quantification in extracellular solution was 0.09ng/ml. Hydroxyzine hydrochloride in extracellular solution proved to be stable when stored in the fridge at 4-8°C for at least 37 days, at room temperature for at least 16 days and at +35°C for at least 16 days. The analytical method was successfully applied in hERG assay.

Knockdown of Eag1 Expression by RNA Interference Increases Chemosensitivity to Cisplatin in Ovarian Cancer Cells.

Ether á go-go 1 (Eag1) is frequently highly expressed in various malignant cancers and its excessive expression is correlated with poor prognosis in various cancers. However, the relationship of Eag1 expression with the clinical outcome of patients having ovarian cancer treated with cisplatin-based adjuvant chemotherapy is still unknown. In this study, we measured the expression of Eag1 in ovarian cancer and investigated the association between cisplatin chemosensitivity of ovarian cancer cells and Eag1 expression level. We demonstrate that decreased expression of Eag1 correlates with favorable prognosis in patients treated with cisplatin-based adjuvant chemotherapy and predicts higher cisplatin sensitivity in ovarian cancer cells. In vitro, knockdown of Eag1 by small interfering RNA facilitated the sensitivity of ovarian cancer cells (SKOV3 and TYK) to cisplatin-induced apoptosis via nuclear factor κ-light chain-enhancer of activated B cells (NF-κB) pathway. Furthermore, knockdown of Eag1 expression was associated with decreased expression of the P-glycoprotein without affecting multidrug resistance-associated protein 1 expression. Taken together, Eag1 may serve as a potential indicator to predict Eag1 chemosensitivity, and silencing Eag1 may represent a potential therapeutic strategy for ovarian cancer.

High yield purification of full-length functional hERG K+ channels produced in Saccharomyces cerevisiae.

The hERG potassium channel is essential for repolarization of the cardiac action potential. Due to this vital function, absence of unintended and potentially life-threatening interactions with hERG is required for approval of new drugs. The structure of hERG is therefore one of the most sought-after. To provide purified hERG for structural studies and new hERG biomimetic platforms for detection of undesirable interactions, we have developed a hERG expression platform generating unprecedented amounts of purified and functional hERG channels. Full-length hERG, with or without a C-terminally fused green fluorescent protein (GFP) His 8-tag was produced from a codon-optimized hERG cDNA in Saccharomyces cerevisiae. Both constructs complemented the high potassium requirement of a knock-out Saccharomyces cerevisiae strain, indicating correct tetramer assembly in vivo. Functionality was further demonstrated by Astemizole binding to membrane embedded hERG-GFP-His 8 with a stoichiometry corresponding to tetramer assembly. The 156 kDa hERG-GFP protein accumulated to a membrane density of 1.6%. Fluorescence size exclusion chromatography of hERG-GFP-His 8 solubilized in Fos-Choline-12 supplemented with cholesteryl-hemisuccinate and Astemizole resulted in a monodisperse elution profile demonstrating a high quality of the hERG channels. hERG-GFP-His 8 purified by Ni-affinity chromatography maintained the ability to bind Astemizole with the correct stoichiometry indicating that the native, tetrameric structure was preserved. To our knowledge this is the first reported high-yield production and purification of full length, tetrameric and functional hERG. This significant breakthrough will be paramount in obtaining hERG crystal structures, and in establishment of new high-throughput hERG drug safety screening assays.

The Eag domain regulates the voltage-dependent inactivation of rat Eag1 K+ channels.

Eag (Kv10) and Erg (Kv11) belong to two distinct subfamilies of the ether-à-go-go K+ channel family (KCNH). While Erg channels are characterized by an inward-rectifying current-voltage relationship that results from a C-type inactivation, mammalian Eag channels display little or no voltage-dependent inactivation. Although the amino (N)-terminal region such as the eag domain is not required for the C-type inactivation of Erg channels, an N-terminal deletion in mouse Eag1 has been shown to produce a voltage-dependent inactivation. To further discern the role of the eag domain in the inactivation of Eag1 channels, we generated N-terminal chimeras between rat Eag (rEag1) and human Erg (hERG1) channels that involved swapping the eag domain alone or the complete cytoplasmic N-terminal region. Functional analyses indicated that introduction of the homologous hERG1 eag domain led to both a fast phase and a slow phase of channel inactivation in the rEag1 chimeras. By contrast, the inactivation features were retained in the reverse hERG1 chimeras. Furthermore, an eag domain-lacking rEag1 deletion mutant also showed the fast phase of inactivation that was notably attenuated upon co-expression with the rEag1 eag domain fragment, but not with the hERG1 eag domain fragment. Additionally, we have identified a point mutation in the S4-S5 linker region of rEag1 that resulted in a similar inactivation phenotype. Biophysical analyses of these mutant constructs suggested that the inactivation gating of rEag1 was distinctly different from that of hERG1. Overall, our findings are consistent with the notion that the eag domain plays a critical role in regulating the inactivation gating of rEag1. We propose that the eag domain may destabilize or mask an inherent voltage-dependent inactivation of rEag1 K+ channels.

Experimentally validated HERG pharmacophore models as cardiotoxicity prediction tools.

The goal of this study was to design, experimentally validate, and apply a virtual screening workflow to identify novel hERG channel blockers. The hERG channel is an important antitarget in drug development since cardiotoxic risks remain as a major cause of attrition. A ligand-based pharmacophore model collection was developed and theoretically validated. The seven most complementary and suitable models were used for virtual screening of in-house and commercially available compound libraries. From the hit lists, 50 compounds were selected for experimental validation through bioactivity assessment using patch clamp techniques. Twenty compounds inhibited hERG channels expressed in HEK 293 cells with IC50 values ranging from 0.13 to 2.77 µM, attesting to the suitability of the models as cardiotoxicity prediction tools in a preclinical stage.