Eag1 Voltage-Dependent Potassium Channels: Structure, Electrophysiological Characteristics, and Function in Cancer

Liensinine, a Novel and Food-Derived Compound, Exerts Potent Antihepatoma Efficacy via Inhibiting the Kv10.1 Channel

Plant metabolites from natural product extracts offer unique advantages against carcinogenesis in the development of drugs. The target-based virtual screening from food-derived compounds represents a promising approach for tumor therapy. In this study, we performed virtual screening to target the presumed inhibitor-binding pocket and identified a highly potent Kv10.1 inhibitor, liensinine (Lien), which can inhibit the channel in a dose-dependent way with an IC50 of 0.24 ± 0.07 μM. Combining molecular dynamics simulations with mutagenesis experiments, our data show that Lien interacts with Kv10.1 by binding with Y539, T543, D551, E553, and H601 in the C-linker domain of Kv10.1. In addition, the interaction of sequence alignment and 3D structural modeling revealed differences between the C-linker domain of the Kv10.1 channel and the Kv11.1 channel. Furthermore, antitumor experiments revealed that Lien suppresses the proliferation and migration of HCC both in vitro and in vivo. In summary, the food-derived compound, Lien, may serve as a lead compound for antihepatoma therapeutic drugs targeting Kv10.1.

Corydaline binds to a druggable pocket of hEAG1 channel and inhibits hepatic carcinoma cell viability

Ether-à-go-go (EAG) potassium channels play a crucial role in the regulation of neuronal excitability and cancer progression, rendering them potential drug targets for cancer therapy. However, the scarcity of information regarding the selection sites on hEAG1 has posed a challenge in the discovery of new hEAG1 inhibitors. In this study, we introduced a novel natural product, corydaline, which selectively inhibits the hEAG1 channel without sensitivity to other KCNH channels. The IC50 of corydaline for the hEAG1 channel was 11.3 ± 0.6 μM, whereas the IC50 for hEAG2 and hERG1 were 73.6 ± 9.9 μM and 111.4 ± 8.5 μM, respectively. Molecular dynamics simulations together with site-directed mutagenesis, have unveiled that the site corydaline forms interactions with Lys217, Phe273, Pro276, Trp295 and Arg366, situated within the intracellular transmembrane segments S1-S4 of the voltage-sensor domain, be considered a novel drug pocket for hEAG1. Additionally, the intergaration of sequence alignment and 3D structural modeling revealed differences between the voltage sensor domain of hEAG1 channel and other EAG channels, suggesting the feasibility of a VSD modulation approach that could potentially lead to the selective inhibition of hEAG1 channels. Furthermore, antitumor experiments demonstrated that corydaline can inhibit the proliferation and migration of hepatic carcinoma cells by targeting hEAG1. The identification of this novel druggable pocket offers the possibility for drug screening against diseases linked to abnormal hEAG1 channels.

Circ_0016347 Promotes Osteosarcoma Progression by Regulating miR-1225-3p/KCNH1 Axis

Background: Osteosarcoma (OS) is a common malignant bone cancer and usually occurs in adolescents and children. Circular RNAs (circRNAs) play essential roles in tumor development and progression. This study aimed to explore the function and molecular basis of circ_0016347 in OS progression. Materials and Methods: The levels of circ_0016347, miR-1225-3p, and ether à go-go 1 (KCNH1) were measured by quantitative real-time polymerase chain reaction or Western blot assay. Cell proliferation was assessed by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay and colony formation assay. Cell migration and invasion were evaluated by transwell assay. Glucose consumption and lactate production were detected by glucose detection and lactic acid detection kits. The levels of Ki-67, matrix metalloproteinase-9 (MMP-9), and hexokinase-2 (HK2) were examined by Western blot assay. The interaction among circ_0016347, miR-1225-3p, and KCNH1 was validated by dual-luciferase reporter assay. Xenograft assay was conducted to analyze tumor growth in vivo. Results: Circ_0016347 and KCNH1 were upregulated, while miR-1225-3p was downregulated in OS tissues or cells. Circ_0016347 and KCNH1 promoted proliferation, migration, invasion, and glycolysis of OS cells. Circ_0016347 regulated OS progression by modulating KCNH1. Circ_0016347 was a sponge of miR-1225-3p, and miR-1225-3p targeted KCNH1. Circ_0016347 regulated KCNH1 expression via sponging miR-1225-3p. Moreover, silencing of circ_0016347 inhibited tumor growth in vivo. Conclusion: Circ_0016347 contributed to OS progression through the miR-1225-3p/KCNH1 axis, which might provide a promising biomarker for OS therapy.

Potassium Channel KCNH1 Activating Variants Cause Altered Functional and Morphological Ciliogenesis

The primary cilium is a non-motile sensory organelle that extends from the surface of most vertebrate cells and transduces signals regulating proliferation, differentiation, and migration. Primary cilia dysfunctions have been observed in cancer and in a group of heterogeneous disorders called ciliopathies, characterized by renal and liver cysts, skeleton and limb abnormalities, retinal degeneration, intellectual disability, ataxia, and heart disease and, recently, in autism spectrum disorder, schizophrenia, and epilepsy. The potassium voltage-gated channel subfamily H member 1 (KCNH1) gene encodes a member of the EAG (ether-à-go-go) family, which controls potassium flux regulating resting membrane potential in both excitable and non-excitable cells and is involved in intracellular signaling, cell proliferation, and tumorigenesis. KCNH1 missense variants have been associated with syndromic neurodevelopmental disorders, including Zimmermann-Laband syndrome 1 (ZLS1, MIM #135500), Temple-Baraitser syndrome (TMBTS, MIM #611816), and, recently, with milder phenotypes as epilepsy. In this work, we provide evidence that KCNH1 localizes at the base of the cilium in pre-ciliary vesicles and ciliary pocket of human dermal fibroblasts and retinal pigment epithelial (hTERT RPE1) cells and that the pathogenic missense variants (L352V and R330Q; NP_002229.1) perturb cilia morphology, assembly/disassembly, and Sonic Hedgehog signaling, disclosing a multifaceted role of the protein. The study of KCNH1 localization, its functions related to primary cilia, and the alterations introduced by mutations in ciliogenesis, cell cycle coordination, cilium morphology, and cilia signaling pathways could help elucidate the molecular mechanisms underlying neurological phenotypes and neurodevelopmental disorders not considered as classical ciliopathies but for which a significant role of primary cilia is emerging.

Potassium Channels as a Target for Cancer Therapy: Current Perspectives

Potassium (K⁺) channels are highly regulated membrane proteins that control the potassium ion flux and respond to different cellular stimuli. These ion channels are grouped into three major families, Kv (voltage-gated K⁺ channel), Kir (inwardly rectifying K⁺ channel) and K2P (two-pore K⁺ channels), according to the structure, to mediate the K⁺ currents. In cancer, alterations in K⁺ channel function can promote the acquisition of the so-called hallmarks of cancer – cell proliferation, resistance to apoptosis, metabolic changes, angiogenesis, and migratory capabilities – emerging as targets for the development of new therapeutic drugs. In this review, we focus our attention on the different K⁺ channels associated with the most relevant and prevalent cancer types. We summarize our knowledge about the potassium channels structure and function, their cancer dysregulated expression and discuss the K⁺ channels modulator and the strategies for designing new drugs.

Thallium-sensitive fluorescent assay reveals loperamide as a new inhibitor of the potassium channel Kv10.1

BACKGROUND

Ion channels have been proposed as therapeutic targets for different types of malignancies. One of the most studied ion channels in cancer is the voltage-gated potassium channel ether-à-go-go 1 or Kv10.1. Various studies have shown that Kv10.1 expression induces the proliferation of several cancer cell lines and in vivo tumor models, while blocking or silencing inhibits proliferation. Kv10.1 is a promising target for drug discovery modulators that could be used in cancer treatment. This work aimed to screen for new Kv10.1 channel modulators using a thallium influx-based assay.

METHODS

Pharmacological effects of small molecules on Kv10.1 channel activity were studied using a thallium-based fluorescent assay and patch-clamp electrophysiological recordings, both performed in HEK293 stably expressing the human Kv10.1 potassium channel.

RESULTS

In thallium-sensitive fluorescent assays, we found that the small molecules loperamide and amitriptyline exert a potent inhibition on the activity of the oncogenic potassium channel Kv10.1. These results were confirmed by electrophysiological recordings, which showed that loperamide and amitriptyline decreased the amplitude of Kv10.1 currents in a dose-dependent manner. Both drugs could be promising tools for further studies.

CONCLUSIONS

Thallium-sensitive fluorescent assay represents a reliable methodological tool for the primary screening of different molecules with potential activity on Kv10.1 channels or other K⁺ channels.

Methadone-mediated sensitization of glioblastoma cells is drug and cell line dependent

PURPOSE

D,L-methadone (MET), an analgesic drug used for pain treatment and opiate addiction, has achieved attention from oncologists and social media as possible chemoensitizing agent in cancer therapy, notably brain cancer (glioblastoma multiforme, GBM). MET has been reported to enhance doxorubicin-induced cytotoxicity in GBM cells via activation of the µ-opioid receptor (MOR). Here, we extended this work and quantified the toxic effect of MET in comparison to other opioids alone and in combination with doxorubicin and the clinically more relevant alkylating drug temozolomide (TMZ), using a set of GBM cell lines and primary GBM cells.

METHODS

MOR expression in GBM cells was investigated by immunofluorescence and immunoblotting. Resistance to drugs alone and in combination with anticancer drugs was assessed by MTT assays. Concentration effect curves were fitted by nonlinear regression analysis and IC50 values were calculated. Apoptosis and necrosis rates were determined by annexin V/propidium iodide (PI)-flow cytometry.

RESULTS

MET alone was cytotoxic in all GBM cell lines and primary GBM cells at high micromolar concentrations (IC50 ~ 60-130 µM), observed both in the metabolic MTT assay and by quantifying apoptosis and necrosis, while morphine and oxycodone were not cytotoxic in this concentration range. Naloxone was not able to block MET-induced cytotoxicity, indicating that cell death-inducing effects of MET are not MOR-dependent. We recorded doxorubicin and TMZ concentration- response curves in combination with fixed MET concentrations. MET enhanced doxorubicin-induced cytotoxicity in only one cell line, and in primary cells it was observed only in a particular MET concentration range. In all assays, MET was not effective in sensitizing cells to TMZ. In two cell lines, MET even decreased the cell's sensitivity to TMZ.

CONCLUSION

MET was found to be cytotoxic in GBM cells in vitro only at high, clinically not relevant concentrations, where it was effective in inducing apoptosis and necrosis. Sensitizing effects were only observed in combination with doxorubicin, but not with TMZ, and are dependent on cell line and the applied drug concentration. Therefore, our findings do not support the use of MET in the treatment of GBM in combination with TMZ, as no sensitizing effect of MET was observed.

EAG1 enhances hepatocellular carcinoma proliferation by modulating SKP2 and metastasis through pseudopod formation

Ether-à-go-go-1 (EAG1), one of the potassium channels, is involved in various physiological processes and plays an important role in the tumorigenesis of many kinds of cancer. EAG1 is highly expressed in hepatocarcinoma cells and is closely related to clinical prognosis, but the molecular mechanism remains elusive. In this study, we verified that EAG1 promotes the proliferation of hepatocellular carcinoma (HCC) both in vitro and in vivo. It promotes cell cycle progression by inhibiting the ubiquitination of SKP2. In addition, EAG1 promotes the migration and invasion of HCC by promoting cell pseudopod formation. Furthermore, in a high-pressure plasmid-injected mouse liver orthotopic carcinoma model, astemizole, an EAG family blocker, can significantly inhibit the formation of liver cancer. Meanwhile, liver-specific EAG1 knockout mice show resistance to hepatocarcinogenesis. This research demonstrated that EAG1 plays an important role in the progression of HCC, and could be a potential therapeutic target for HCC.

Voltage-Gated K+/Na+ Channels and Scorpion Venom Toxins in Cancer

Ion channels have recently been recognized as novel therapeutic targets in cancer research since they are overexpressed in different histological tissues, and their activity is linked to proliferation, tumor progression, angiogenesis, metastasis, and apoptosis. Voltage gated-potassium channels (VGKC) are involved in cell proliferation, cancer progression, cell cycle transition, and apoptosis. Moreover, voltage-dependent sodium channels (VGSC) contribute to decreases in extracellular pH, which, in turn, promotes cancer cell migration and invasion. Furthermore, VGSC and VGKC modulate voltage-sensitive Ca²⁺ channel activity by controlling the membrane potential and regulating Ca²⁺ influx, which functions as a second messenger in processes related to proliferation, invasion, migration, and metastasis. The subgroup of these types of channels that have shown a high oncogenic potential have become known as “oncochannels”, and the evidence has highlighted them as key potential therapeutic targets. Scorpion venoms contain a high proportion of peptide toxins that act by modulating voltage-gated Na⁺/K⁺ channel activity. Increasing scientific data have pointed out that scorpion venoms and their toxins can affect the activity of oncochannels, thus showing their potential for anticancer therapy. In this review, we provide an update of the most relevant voltage-gated Na⁺\K⁺ ion channels as cellular targets and discuss the possibility of using scorpion venom and toxins for anticancer therapy.

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.

A novel anti-cancer mechanism of Nutlin-3 through downregulation of Eag1 channel and PI3K/AKT pathway

Nutlin-3 shows a potent antitumor efficacy through downregulation of the cancerogenic ether à go-go 1 (Eag1) channel. However, the molecular mechanisms responsible for the regulation of Eag1 by Nutlin-3 in cancer cells remain unclear. In this study, we propose a novel anticancer mechanism of Nutlin-3, in which Nutlin-3 acts through the p53-Eag1-PI3K/AKT pathway. We first confirmed that Eag1 was downregulated through the activation of p53 by Nutlin-3. We then revealed that the inhibition of Eag1 electrophysiological function resulted in the decrease of viability, migration and invasion of HeLa cells. It is worth noting that the antitumor effect of Nutlin-3 was abolished in the Eag1 knockdown HeLa cell lines by siRNA. And Nutlin-3 can decrease the cell viability of H8 cells which were stably transfected with Eag1, but has no obvious inhibitory effect on blank H8 cells. Finally, we demonstrated that the decrease in Eag1 channel activity induced by Nutlin-3 treatment exerts anticancer activity by inhibiting the PI3K/AKT pathway. Our study therefore fills the gap between p53 pathway and its cellular function mediated by Eag1, shedding light on the new anti-cancer mechanism of Nutlin-3.

Computational Approaches for Elucidating Protein-Protein Interactions in Cation Channel Signaling

BACKGROUND

The lipid bilayer of the plasma membrane is impermeable to ions, yet changes in the flux of ions across the cell membrane are critical regulatory events in cells. Because of their regulatory roles in a range of physiological processes, such as electrical signaling in muscles and neurons, to name a few, these proteins are one of the most important drug targets.

OBJECTIVE

This review mainly focused on the computational approaches for elucidating proteinprotein interactions in cation channel signaling.

DISCUSSION

Due to continuously advanced facilities and technologies in computer sciences, the physical contacts of macromolecules of channel structures have been virtually visualized. Indeed, techniques like protein-protein docking, homology modeling, and molecular dynamics simulation are valuable tools for predicting the protein complex and refining channels with unreleased structures. Undoubtedly, these approaches will greatly expand the cation channel signaling research, thereby speeding up structure-based drug design and discovery.

CONCLUSION

We introduced a series of valuable computational tools for elucidating protein-protein interactions in cation channel signaling, including molecular graphics, protein-protein docking, homology modeling, and molecular dynamics simulation.

Signatures of gene expression, DNA methylation and microRNAs of hepatocellular carcinoma with vascular invasion

Aim: Micro and macro vascular invasion (VI) are known as independent predictors of tumor recurrence and poor survival after surgical treatment of hepatocellular carcinoma (HCC). Here, we aimed to re-analyze The Cancer Genome Atlas of liver hepatocellular carcinoma datasets to identify the VI-expression signatures. Materials & methods: We filtered The Cancer Genome Atlas liver hepatocellular carcinoma (LIHC) datasets into three groups: no VI (NVI = 198); micro VI (MIVI = 89) and macro VI (MAVI = 16). We performed differential gene expression, methylation and microRNA analyses. Results & conclusion: We identified 12 differentially expressed genes and 55 differentially methylated genes in MAVI compared with no VI. The GPD1L gene appeared in all of the comparative analyses. Higher GPD1L expression was associated with VI and poor outcomes in the HCC patients.