Voltage-gated sodium channels and cancer: is excitability their primary role?

Hydrogen Ion Dynamics of Cancer and a New Molecular, Biochemical and Metabolic Approach to the Etiopathogenesis and Treatment of Brain Malignancies

The treatment of cancer has been slowly but steadily progressing during the last fifty years. Some tumors with a high mortality in the past are curable nowadays. However, there is one striking exception: glioblastoma multiforme. No real breakthrough has been hitherto achieved with this tumor with ominous prognosis and very short survival. Glioblastomas, being highly glycolytic malignancies are strongly pH-dependent and driven by the sodium hydrogen exchanger 1 (NHE1) and other proton (H⁺) transporters. Therefore, this is one of those pathologies where the lessons recently learnt from the new pH-centered anticancer paradigm may soon bring a promising change to treatment. This contribution will discuss how the pH-centric molecular, biochemical and metabolic perspective may introduce some urgently needed and integral novel treatments. Such a prospective therapeutic approach for malignant brain tumors is developed here, either to be used alone or in combination with more standard therapies.

Epidermal Growth Factor Potentiates Migration of MDA-MB 231 Breast Cancer Cells by Increasing NaV1.5 Channel Expression

INTRODUCTION

Breast cancer is one of the leading causes of death worldwide and is the result of dysregulation of various signaling pathways in mammary epithelial cells. The mortality rate in patients suffering from breast cancer is high because the tumor cells have a prominent invasive capacity towards the surrounding tissues. Previous studies carried out in tumor cell models show that voltage-gated ion channels may be important molecular actors that contribute to the migratory and invasive capacity of the tumor cells.

METHODS

In this study, by using an experimental strategy that combines cell and molecular biology assays with electrophysiological recording, we sought to determine whether the voltage-dependent sodium channel NaV1.5 regulates the migratory capacity of the human breast cancer cell line MDA-MB 231, when cells are maintained in the presence of epidermal growth factor (EGF), as an inductor of the epithelial-mesenchymal transition.

RESULTS

Our data show that EGF stimulates the migratory capacity of MDA-MB 231 cells, by regulating the functional expression of NaV1.5 channels. Consistent with this, the stimulatory actions of the growth factor were prevented by the use of tetrodotoxin, an Na+ channel selective blocker, as well as by resveratrol, an antioxidant that can also affect Na+ channel activity.

DISCUSSION

The understanding of molecular mechanisms, such as the EGF pathway in the progression of breast cancer is fundamental for the design of more effective therapeutic strategies for the disease.

No transcriptional evidence for active Nav channels in two classes of cancer cell

Voltage-gated sodium channel (Na_v) expression in non-excitable cells has raised questions regarding their non-canonical roles. Interestingly, a growing body of evidence also points towards the prevalence of aberrant Na_v expression in malignant tumors, potentially opening a new therapeutic window. In this study, the transcriptional consequences of channel inhibition were investigated in non-small cell lung carcinoma H460 and neuroblastoma SH-SYSY cell lines, that both express Na_v1.7. Channel activity was blocked by the application of both selective, ProTx-II, and non-selective, tetrodotoxin, inhibitors. Global gene expression profiling did not point to any statistically significant inhibition-associated perturbation of the transcriptome. A small subset of genes that showed relatively consistent changes across multiple treatments were further assayed in the context of a multiplex bead expression array which failed to recapitulate the changes seen in the global array. We conclude that there is no robust transcriptional signature associated with the inhibition of two sodium channel expressing cancer cell lines and consequently sodium channel inhibition will not lend itself to therapeutic approaches such as transcription-based drug repurposing.

Ion Channels in Cancer: Are Cancer Hallmarks Oncochannelopathies?

Genomic instability is a primary cause and fundamental feature of human cancer. However, all cancer cell genotypes generally translate into several common pathophysiological features, often referred to as cancer hallmarks. Although nowadays the catalog of cancer hallmarks is quite broad, the most common and obvious of them are 1) uncontrolled proliferation, 2) resistance to programmed cell death (apoptosis), 3) tissue invasion and metastasis, and 4) sustained angiogenesis. Among the genes affected by cancer, those encoding ion channels are present. Membrane proteins responsible for signaling within cell and among cells, for coupling of extracellular events with intracellular responses, and for maintaining intracellular ionic homeostasis ion channels contribute to various extents to pathophysiological features of each cancer hallmark. Moreover, tight association of these hallmarks with ion channel dysfunction gives a good reason to classify them as special type of channelopathies, namely oncochannelopathies. Although the relation of cancer hallmarks to ion channel dysfunction differs from classical definition of channelopathies, as disease states causally linked with inherited mutations of ion channel genes that alter channel's biophysical properties, in a broader context of the disease state, to which pathogenesis ion channels essentially contribute, such classification seems absolutely appropriate. In this review the authors provide arguments to substantiate such point of view.

The invasiveness of human cervical cancer associated to the function of NaV1.6 channels is mediated by MMP-2 activity

Voltage-gated sodium (Na_V) channels have been related with cell migration and invasiveness in human cancers. We previously reported the contribution of Na_V1.6 channels activity with the invasion capacity of cervical cancer (CeCa) positive to Human Papilloma Virus type 16 (HPV16), which accounts for 50% of all CeCa cases. Here, we show that Na_V1.6 gene (SCN8A) overexpression is a general characteristic of CeCa, regardless of the HPV type. In contrast, no differences were observed in Na_V1.6 channel expression between samples of non-cancerous and cervical intraepithelial neoplasia. Additionally, we found that CeCa cell lines, C33A, SiHa, CaSki and HeLa, express mainly the splice variant of SCN8A that lacks exon 18, shown to encode for an intracellularly localized Na_V1.6 channel, whereas the full-length adult form was present in CeCa biopsies. Correlatively, patch-clamp experiments showed no evidence of whole-cell sodium currents (I_Na) in CeCa cell lines. Heterologous expression of full-length Na_V1.6 isoform in C33A cells produced I_Na, which were sufficient to significantly increase invasion capacity and matrix metalloproteinase type 2 (MMP-2) activity. These data suggest that upregulation of Na_V1.6 channel expression occurs when cervical epithelium have been transformed into cancer cells, and that Na_V1.6-mediated invasiveness of CeCa cells involves MMP-2 activity. Thus, our findings support the notion about using Na_V channels as therapeutic targets against cancer metastasis.

Blocking the Nav1.5 channel using eicosapentaenoic acid reduces migration and proliferation of ovarian cancer cells

Activity of the voltage-gated Nav1.5 sodium channel has been reported to be involved in cell proliferation, cancer invasion and gene expression. In addition, eicosapentaenoic acid (EPA) has recently been suggested to inhibit ovarian cancer cell growth and suppress tumor metastasis. The present study aimed to explore the association between EPA, the Nav1.5 sodium channel and ovarian cancer cells. Using patch-clamp technique and RNA interference approaches, sodium currents were recorded in epithelial ovarian cancer cells, and it was confirmed that the Nav1.5 channel carried the sodium currents. Furthermore, EPA effectively inhibited sodium currents in a dose-dependent manner, shifted the steady-state inactivation curve of sodium currents to the hyperpolarizing direction and reduced sodium window currents. In addition, EPA induced a shift in the inactivation curve in a dose-dependent manner. Inhibition of the sodium channel, either by EPA or by Nav1.5 knockdown, attenuated ovarian cancer cell migration and proliferation. To the best of our knowledge, the present study is the first to conduct sodium current recording in ovarian cancer cells, and revealed that EPA may inhibit Nav1.5-mediated ovarian cancer cell migration and growth. These findings not only present a potential prognostic biomarker for ovarian cancer, but also provide a strategy towards the development of novel pharmacological treatments for patients with ovarian cancer.

Profiling plasma extracellular vesicle by pluronic block-copolymer based enrichment method unveils features associated with breast cancer aggression, metastasis and invasion

Extracellular vesicle (EV)-based liquid biopsies have been proposed to be a readily obtainable biological substrate recently for both profiling and diagnostics purposes. Development of a fast and reliable preparation protocol to enrich such small particles could accelerate the discovery of informative, disease-related biomarkers. Though multiple EV enrichment protocols are available, in terms of efficiency, reproducibility and simplicity, precipitation-based methods are most amenable to studies with large numbers of subjects. However, the selectivity of the precipitation becomes critical. Here, we present a simple plasma EV enrichment protocol based on pluronic block copolymer. The enriched plasma EV was able to be verified by multiple platforms. Our results showed that the particles enriched from plasma by the copolymer were EV size vesicles with membrane structure; proteomic profiling showed that EV-related proteins were significantly enriched, while high-abundant plasma proteins were significantly reduced in comparison to other precipitation-based enrichment methods. Next-generation sequencing confirmed the existence of various RNA species that have been observed in EVs from previous studies. Small RNA sequencing showed enriched species compared to the corresponding plasma. Moreover, plasma EVs enriched from 20 advanced breast cancer patients and 20 age-matched non-cancer controls were profiled by semi-quantitative mass spectrometry. Protein features were further screened by EV proteomic profiles generated from four breast cancer cell lines, and then selected in cross-validation models. A total of 60 protein features that highly contributed in model prediction were identified. Interestingly, a large portion of these features were associated with breast cancer aggression, metastasis as well as invasion, consistent with the advanced clinical stage of the patients. In summary, we have developed a plasma EV enrichment method with improved precipitation selectivity and it might be suitable for larger-scale discovery studies.

Discovery and evaluation of nNav1.5 sodium channel blockers with potent cell invasion inhibitory activity in breast cancer cells

Voltage-gated sodium channels (VGSC) are a well-established drug target for anti-epileptic, anti-arrhythmic and pain medications due to their presence and the important roles that they play in excitable cells. Recently, their presence has been recognized in non-excitable cells such as cancer cells and their overexpression has been shown to be associated with metastatic behavior in a variety of human cancers. The neonatal isoform of the VGSC subtype, Na_v1.5 (nNa_v1.5) is overexpressed in the highly aggressive human breast cancer cell line, MDA-MB-231. The activity of nNa_v1.5 is known to promote the breast cancer cell invasion in vitro and metastasis in vivo, and its expression in primary mammary tumors has been associated with metastasis and patient death. Metastasis development is responsible for the high mortality of breast cancer and currently there is no treatment available to specifically prevent or inhibit breast cancer metastasis. In the present study, a 3D-QSAR model is used to assist the development of low micromolar small molecule VGSC blockers. Using this model, we have designed, synthesized and evaluated five small molecule compounds as blockers of nNa_v1.5-dependent inward currents in whole-cell patch-clamp experiments in MDA-MB-231 cells. The most active compound identified from these studies blocked sodium currents by 34.9 ± 6.6% at 1 μM. This compound also inhibited the invasion of MDA-MB-231 cells by 30.3 ± 4.5% at 1 μM concentration without affecting the cell viability. The potent small molecule compounds presented here have the potential to be developed as drugs for breast cancer metastasis treatment.

Ciguatoxins activate the Calcineurin signalling pathway in Yeasts: Potential for development of an alternative detection tool?

Ciguatoxins (CTXs) are lipid-soluble polyether compounds produced by dinoflagellates from the genus Gambierdiscus spp. typically found in tropical and subtropical zones. This endemic area is however rapidly expanding due to environmental perturbations, and both toxic Gambierdiscus spp. and ciguatoxic fishes have been recently identified in the North Atlantic Ocean (Madeira and Canary islands) and Mediterranean Sea. Ciguatoxins bind to Voltage Gated Sodium Channels on the membranes of sensory neurons, causing Ciguatera Fish Poisoning (CFP) in humans, a disease characterized by a complex array of gastrointestinal, neurological, neuropsychological, and cardiovascular symptoms. Although CFP is the most frequently reported non bacterial food-borne poisoning worldwide, there is still no simple and quick way of detecting CTXs in contaminated samples. In the prospect to engineer rapid and easy-to-use CTXs live cells-based tests, we have studied the effects of CTXs on the yeast Saccharomyces cerevisiae, a unicellular model which displays a remarkable conservation of cellular signalling pathways with higher eukaryotes. Taking advantage of this high level of conservation, yeast strains have been genetically modified to encode specific transcriptional reporters responding to CTXs exposure. These yeast strains were further exposed to different concentrations of either purified CTX or micro-algal extracts containing CTXs. Our data establish that CTXs are not cytotoxic to yeast cells even at concentrations as high as 1μM, and cause an increase in the level of free intracellular calcium in yeast cells. Concomitantly, a dose-dependent activation of the calcineurin signalling pathway is observed, as assessed by measuring the activity of specific transcriptional reporters in the engineered yeast strains. These findings offer promising prospects regarding the potential development of a yeast cells-based test that could supplement or, in some instances, replace current methods for the routine detection of CTXs in seafood products.

Triple negative breast cancer: Emerging therapeutic modalities and novel combination therapies

Triple negative breast cancer (TNBC) is a complex and aggressive subtype of breast cancer which lacks oestrogen receptors, progesterone receptors and HER2 amplification, thereby making it difficult to target therapeutically. In addition, TNBC has the highest rates of metastatic disease and the poorest overall survival of all breast cancer subtypes. Resultantly, development of targeted therapies for TNBC is urgently needed. Recent efforts aimed at molecular characterisation of TNBCs have revealed various emerging therapeutic targets including PARP1, receptor and non-receptor tyrosine kinases, immune-checkpoints, androgen receptor and epigenetic proteins. Key successes include that of the PARP inhibitor, olaparib, which prolonged progression-free survival in a trial of BRCA-mutated breast cancer and for which clinical approval (in this setting) appears imminent. Nevertheless, the heterogeneity of TNBC has limited the clinical benefits of many trialled therapies in 'unselected' patients. Further, drug resistance develops following use of many targeted monotherapies due to upregulation of compensatory signalling pathways. In this review, we evaluate the current status of investigational targeted treatments and present evidence for the role of novel biomarkers and combination therapies in increasing response rates and circumventing drug-induced resistance. Additionally, we discuss promising novel targets in metastatic TNBC identified through preclinical and/or epidemiological studies.

Is there a role for voltage-gated Na+ channels in the aggressiveness of breast cancer?

Breast cancer is the most common cancer among women and its metastatic potential is responsible for numerous deaths. Thus, the need to find new targets for improving treatment, and even finding the cure, becomes increasingly greater. Ion channels are known to participate in several physiological functions, such as muscle contraction, cell volume regulation, immune response and cell proliferation. In breast cancer, different types of ion channels have been associated with tumorigenesis. Recently, voltage-gated Na⁺ channels (VGSC) have been implicated in the processes that lead to increased tumor aggressiveness. To explain this relationship, different theories, associated with pH changes, gene expression and intracellular Ca²⁺, have been proposed in an attempt to better understand the role of these ion channels in breast cancer. However, these theories are having difficulty being accepted because most of the findings are contrary to the present scientific knowledge. Several studies have shown that VGSC are related to different types of cancer, making them a promising pharmacological target against this debilitating disease. Molecular biology and cell electrophysiology have been used to look for new forms of treatment aiming to reduce aggressiveness and the disease progress.

Viral dependence on cellular ion channels - an emerging anti-viral target?

The broad range of cellular functions governed by ion channels represents an attractive target for viral manipulation. Indeed, modulation of host cell ion channel activity by viral proteins is being increasingly identified as an important virus-host interaction. Recent examples have demonstrated that virion entry, virus egress and the maintenance of a cellular environment conducive to virus persistence are, in part, dependent on virus manipulation of ion channel activity. Most excitingly, evidence has emerged that targeting ion channels pharmacologically can impede virus life cycles. Here, we discuss current examples of virus-ion channel interactions and the potential of targeting ion channel function as a new, pharmacologically safe and broad-ranging anti-viral therapeutic strategy.

Ion channels or aquaporins as novel molecular targets in gastric cancer

Gastric cancer (GC) is a common disease with few effective treatment choices and poor prognosis, and has the second-highest mortality rates among all cancers worldwide. Dysregulation and/or malfunction of ion channels or aquaporins (AQPs) are common in various human cancers. Furthermore, ion channels are involved in numerous important aspects of the tumor aggressive phonotype, such as proliferation, cell cycle, apoptosis, motility, migration, and invasion. Indeed, by localizing in the plasma membrane, ion channels or AQPs can sense and respond to extracellular environment changes; thus, they play a crucial role in cell signaling and cancer progression. These findings have expanded a new area of pharmaceutical exploration for various types of cancer, including GC. The involvement of multiple ion channels, such as voltage-gated potassium and sodium channels, intracellular chloride channels, ‘transient receptor potential’ channels, and AQPs, which have been shown to facilitate the pathogenesis of other tumors, also plays a role in GC. In this review, an overview of ion channel and aquaporin expression and function in carcinogenesis of GC is presented. Studies of ion channels or AQPs will advance our understanding of the molecular genesis of GC and may identify novel and effective targets for the clinical application of GC.

Cellular acidification as a new approach to cancer treatment and to the understanding and therapeutics of neurodegenerative diseases

During the last few years, the understanding of the dysregulated hydrogen ion dynamics and reversed proton gradient of cancer cells has resulted in a new and integral pH-centric paradigm in oncology, a translational model embracing from cancer etiopathogenesis to treatment. The abnormalities of intracellular alkalinization along with extracellular acidification of all types of solid tumors and leukemic cells have never been described in any other disease and now appear to be a specific hallmark of malignancy. As a consequence of this intracellular acid-base homeostatic failure, the attempt to induce cellular acidification using proton transport inhibitors and other intracellular acidifiers of different origins is becoming a new therapeutic concept and selective target of cancer treatment, both as a metabolic mediator of apoptosis and in the overcoming of multiple drug resistance (MDR). Importantly, there is increasing data showing that different ion channels contribute to mediate significant aspects of cancer pH regulation and etiopathogenesis. Finally, we discuss the extension of this new pH-centric oncological paradigm into the opposite metabolic and homeostatic acid-base situation found in human neurodegenerative diseases (HNDDs), which opens novel concepts in the prevention and treatment of HNDDs through the utilization of a cohort of neural and non-neural derived hormones and human growth factors.

Functional Studies of Sodium Channels: From Target to Compound Identification

Over the last six decades, voltage-gated sodium (Na_v ) channels have attracted a great deal of scientific and pharmaceutical interest, driving fundamental advances in both biology and technology. The structure and physiological function of these channels have been extensively studied; clinical and genetic data have uncovered their implication in diseases such as epilepsy, arrhythmias, and pain, bringing them into focus as current and future drug targets. While different techniques have been established to record the activity of Na_v channels, proper determination of their properties still presents serious challenges, depending upon the experimental conditions and the desired subtype of channel to be characterized. The aim of this unit is to review the characteristics of Na_v channels, their properties, the cells in which they can be studied, and the currently available techniques. Topics covered include the determination of Na_v -channel biophysical properties as well as the use of toxins to discriminate between subtypes using electrophysiological or optical methods. Perspectives on the development of high-throughput screening assays with their advantages and limitations are also discussed to allow a better understanding of the challenges encountered in voltage-gated sodium channel preclinical drug discovery. © 2016 by John Wiley & Sons, Inc.

SCN4B acts as a metastasis-suppressor gene preventing hyperactivation of cell migration in breast cancer

The development of metastases largely relies on the capacity of cancer cells to invade extracellular matrices (ECM) using two invasion modes termed ‘mesenchymal' and ‘amoeboid', with possible transitions between these modes. Here we show that the SCN4B gene, encoding for the β4 protein, initially characterized as an auxiliary subunit of voltage-gated sodium channels (Na_V) in excitable tissues, is expressed in normal epithelial cells and that reduced β4 protein levels in breast cancer biopsies correlate with high-grade primary and metastatic tumours. In cancer cells, reducing β4 expression increases RhoA activity, potentiates cell migration and invasiveness, primary tumour growth and metastatic spreading, by promoting the acquisition of an amoeboid–mesenchymal hybrid phenotype. This hyperactivated migration is independent of Na_V and is prevented by overexpression of the intracellular C-terminus of β4. Conversely, SCN4B overexpression reduces cancer cell invasiveness and tumour progression, indicating that SCN4B/β4 represents a metastasis-suppressor gene.

The capacity of cancer cells to migrate is intimately linked to their ability to induce metastasis. Here the authors show that the sodium channel β4 subunit regulates breast cancer cell migration via inhibition of RhoA activation, independently from its function as an auxiliary protein of the sodium channel.

Diphenhydramine induces melanoma cell apoptosis by suppressing STAT3/MCL-1 survival signaling and retards B16-F10 melanoma growth in vivo

Melanoma is the most aggressive skin malignancy with a high rate of mortality and is frequently refractory to many therapeutics, thus demanding the discovery of novel effective anti-melanoma agents. Diphenhydramine (DPH) is an H1 histamine receptor antagonist and a relatively safe drug. Previous studies have revealed the in vitro cytotoxicity of DPH against melanoma cells, but the mechanisms involved concerning its cytotoxicity and the in vivo anti-melanoma effect remain unknown. We herein present the first evidence supporting that DPH is selectively proapoptotic for a panel of melanoma cell lines irrespective of BRAFV600E status while sparing normal melanocytes. Of note, DPH effectively suppressed tumor growth and prolonged the length of survival of mice bearing B16-F10 melanoma. Mechanistic investigation further revealed that DPH downregulated antiapoptotic MCL-1, whereas MCL-1 overexpression impeded the proapoptotic action of DPH. Moreover, DPH attenuated STAT3 activation, as evidenced by the reduced levels of tyrosine 705-phosphorylated STAT3. Notably, ectopic expression of constitutively active STAT3 mutant reduced DPH-induced apoptosis but also protected MCL-1 from downregulation by DPH, illustrating that DPH impairs STAT3 activation to block STAT3-mediated induction of MCL-1 in eliciting apoptosis. Collectively, we for the first time validate the in vivo anti‑melanoma effect of DPH and also establish DPH as a drug targeting STAT3/MCL-1 survival signaling pathway to induce apoptosis. Our discovery therefore suggests the potential to repurpose DPH as an anti-melanoma therapeutic agent.

The interplay between genetic and bioelectrical signaling permits a spatial regionalisation of membrane potentials in model multicellular ensembles

The single cell-centred approach emphasises ion channels as specific proteins that determine individual properties, disregarding their contribution to multicellular outcomes. We simulate the interplay between genetic and bioelectrical signals in non-excitable cells from the local single-cell level to the long range multicellular ensemble. The single-cell genetic regulation is based on mean-field kinetic equations involving the mRNA and protein concentrations. The transcription rate factor is assumed to depend on the absolute value of the cell potential, which is dictated by the voltage-gated cell ion channels and the intercellular gap junctions. The interplay between genetic and electrical signals may allow translating single-cell states into multicellular states which provide spatio-temporal information. The model results have clear implications for biological processes: (i) bioelectric signals can override slightly different genetic pre-patterns; (ii) ensembles of cells initially at the same potential can undergo an electrical regionalisation because of persistent genetic differences between adjacent spatial regions; and (iii) shifts in the normal cell electrical balance could trigger significant changes in the genetic regulation.

Comparison of fluorescence probes for intracellular sodium imaging in prostate cancer cell lines

Sodium (Na⁺) ions are known to regulate many signaling pathways involved in both physiological and pathological conditions. In particular, alterations in intracellular concentrations of Na⁺ and corresponding changes in membrane potential are known to be major actors of cancer progression to metastatic phenotype. Though the functionality of Na⁺ channels and the corresponding Na⁺ currents can be investigated using the patch-clamp technique, the latter is rather invasive and a technically difficult method to study intracellular Na⁺ transients compared to Na⁺ fluorescence imaging. Despite the fact that Na⁺ signaling is considered an important controller of cancer progression, only few data using Na⁺ imaging approaches are available so far, suggesting the persisting challenge within the scientific community. In this study, we describe in detail the approach for application of Na⁺ imaging technique to measure intracellular Na⁺ variations in human prostate cancer cells. Accordingly, we used three Na⁺-specific fluorescent dyes-Na⁺-binding benzofuran isophthalate (SBFI), CoroNa™ Green (Corona) and Asante NaTRIUM Green-2 (ANG-2). These dyes have been assessed for optimal loading conditions, dissociation constant and working range after different calibration methods, and intracellular Na⁺ sensitivity, in order to determine which probe can be considered as the most reliable to visualize Na⁺ fluctuations in vitro.

Voltage-gated sodium channel Nav 1.7 promotes gastric cancer progression through MACC1-mediated upregulation of NHE1

Voltage-gated sodium channels (VGSCs), which are aberrantly expressed in several human cancers, affect cancer cell behavior; however, their role in gastric cancer (GC) and the link between these channels and tumorigenic signaling remain unclear. The aims of this study were to determine the clinicopathological significance and role of the VGSC Nav 1.7 in GC progression and to investigate the associated mechanisms. Here, we report that the SCN9A gene encoding Nav 1.7 was the most abundantly expressed VGSC subtype in GC tissue samples and two GC cell lines (BGC-823 and MKN-28 cells). SCN9A expression levels were also frequently found to be elevated in GC samples compared to nonmalignant tissues by real-time PCR. In the 319 GC specimens evaluated by immunohistochemistry, Nav 1.7 expression was correlated with prognosis, and transporter Na(+) /H(+) exchanger-1 (NHE1) and oncoprotein metastasis-associated in colon cancer-1 (MACC1) expression. Nav 1.7 suppression resulted in reduced voltage-gated sodium currents, decreased NHE1 expression, increased extracellular pH and decreased intracellular pH, and ultimately, reduced invasion and proliferation rates of GC cells and growth of GC xenografts in nude mice. Nav 1.7 inhibition led to reduced MACC1 expression, while MACC1 inhibition resulted in reduced NHE1 expression in vitro and in vivo. Mechanistically, the suppression of Nav 1.7 decreased NF-κB p65 nuclear translocation via p38 activation, thus reducing MACC1 expression. Downregulation of MACC1 decreased c-Jun phosphorylation and subsequently reduced NHE1 expression, whereas the addition of hepatocyte growth factor (HGF), a c-Met physiological ligand, reversed the effect. These results indicate that Nav 1.7 promotes GC progression through MACC1-mediated upregulation of NHE1. Therefore, Nav 1.7 is a potential prognostic marker and/or therapeutic target for GC.

Sodium channels in astroglia and microglia

Voltage-gated sodium channels are required for electrogenesis in excitable cells. Their activation, triggered by membrane depolarization, generates transient sodium currents that initiate action potentials in neurons, cardiac, and skeletal muscle cells. Cells that have not traditionally been considered to be excitable (nonexcitable cells), including glial cells, also express sodium channels in physiological conditions as well as in pathological conditions. These channels contribute to multiple functional roles that are seemingly unrelated to the generation of action potentials. Here, we discuss the dynamics of sodium channel expression in astrocytes and microglia, and review evidence for noncanonical roles in effector functions of these cells including phagocytosis, migration, proliferation, ionic homeostasis, and secretion of chemokines/cytokines. We also examine possible mechanisms by which sodium channels contribute to the activity of glial cells, with an eye toward therapeutic implications for central nervous system disease. GLIA 2016;64:1628-1645.

Sodium Channels in Pain and Cancer: New Therapeutic Opportunities

Voltage-gated sodium channels (VGSCs) underpin electrical activity in the nervous system through action potential propagation. First predicted by the modeling studies of Hodgkin and Huxley, they were subsequently identified at the molecular level by groups led by Catterall and Numa. VGSC dysfunction has long been linked to neuronal and cardiac disorders with some nonselective sodium channel blockers in current use in the clinic. The lack of selectivity means that side effect issues are a major impediment to the use of broad spectrum sodium channel blockers. Nine different sodium channels are known to exist, and selective blockers are now being developed. The potential utility of these drugs to target diseases ranging from migraine, multiple sclerosis, muscle, and immune system disorders, to cancer and pain is being explored. Four channels are potential targets for pain disorders. This conclusion comes from mouse knockout studies and human mutations that prove the involvement of Nav1.3, Nav1.7, Nav1.8, and Nav1.9 in the development and maintenance of acute and chronic pain. In this chapter, we present a short overview of the possible role of Nav1.3, Nav1.7, Nav1.8, and Nav1.9 in human pain and the emerging and unexpected role of sodium channels in cancer pathogenesis.