Voltage-gated sodium channel expression and potentiation of human breast cancer metastasis

Voltage-Gated Na+ Channels: Not Just for Conduction

Voltage-gated sodium channels (VGSCs), composed of a pore-forming α subunit and up to two associated β subunits, are critical for the initiation of the action potential (AP) in excitable tissues. Building on the monumental discovery and description of sodium current in 1952, intrepid researchers described the voltage-dependent gating mechanism, selectivity of the channel, and general structure of the VGSC channel. Recently, crystal structures of bacterial VGSC α subunits have confirmed many of these studies and provided new insights into VGSC function. VGSC β subunits, first cloned in 1992, modulate sodium current but also have nonconducting roles as cell-adhesion molecules and function in neurite outgrowth and neuronal pathfinding. Mutations in VGSC α and β genes are associated with diseases caused by dysfunction of excitable tissues such as epilepsy. Because of the multigenic and drug-resistant nature of some of these diseases, induced pluripotent stem cells and other novel approaches are being used to screen for new drugs and further understand how mutations in VGSC genes contribute to pathophysiology.

Na(+) Micro-Current Value Detection as a New Modality for Identification of Benign and Malignant Disease in Surgery

Increase of intracellular positive ions (mainly Na(+)) indicates greater possibility of cell malignancy. The present study investigated the correlation between the Na(+) micro-current value (MCV) and tissue characteristics (normal, benign or malignant). 346 tissue samples have been detected within 30 min after surgical isolation by Na(+) detector. MCV in 102 malignant tumor was significantly higher than that in benign/borderline tumor or normal tissue (33.3 ± 8.9 μA vs. 24.4 ± 8.6 μA and 14.0 ± 4.0 μA, p < 0.001, respectively). MCV in malignant tumor parenchyma was significantly higher than that in the paired paracanceroustissue, normal tissue and surgical margin tissue (33.3 ± 8.9 μA vs. 18.9 ± 4.1, 14.2 ± 4.0 or 15.2 ± 3.3, p < 0.001, respectively). However, the coincidence rate between Na(+) detector and pathological examination was different in tissues from different organs or systems, which was high in pancreas, bile duct system, gastrointestinal system, esophagus, breasts, lungs, nose &throat and thyroids, but poor in urinary tissue. The overall coincidence rate was 83.1% (108/130) between Na(+) detector and pathological examination. The sensitivity and specificity of correct diagnosis by Na(+) detector was 83.3% (70/84) and 82.6% (38/46), respectively. This new modality may have diagnostic potential in complementing frozen examination in differentiating malignant tumor from benign or normal tissue, justifying tumor metastatic scope and confirming surgical margin.

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.

Inverse Association between Sodium Channel-Blocking Antiepileptic Drug Use and Cancer: Data Mining of Spontaneous Reporting and Claims Databases

PURPOSE

Voltage-gated sodium channels (VGSCs) are drug targets for the treatment of epilepsy. Recently, a decreased risk of cancer associated with sodium channel-blocking antiepileptic drugs (AEDs) has become a research focus of interest. The purpose of this study was to test the hypothesis that the use of sodium channel-blocking AEDs are inversely associated with cancer, using different methodologies, algorithms, and databases.

METHODS

A total of 65,146,507 drug-reaction pairs from the first quarter of 2004 through the end of 2013 were downloaded from the US Food and Drug Administration Adverse Event Reporting System. The reporting odds ratio (ROR) and information component (IC) were used to detect an inverse association between AEDs and cancer. Upper limits of the 95% confidence interval (CI) of < 1 and < 0 for the ROR and IC, respectively, signified inverse associations. Furthermore, using a claims database, which contains 3 million insured persons, an event sequence symmetry analysis (ESSA) was performed to identify an inverse association between AEDs and cancer over the period of January 2005 to May 2014. The upper limit of the 95% CI of adjusted sequence ratio (ASR) < 1 signified an inverse association.

RESULTS

In the FAERS database analyses, significant inverse associations were found between sodium channel-blocking AEDs and individual cancers. In the claims database analyses, sodium channel-blocking AED use was inversely associated with diagnoses of colorectal cancer, lung cancer, gastric cancer, and hematological malignancies, with ASRs of 0.72 (95% CI: 0.60 - 0.86), 0.65 (0.51 - 0.81), 0.80 (0.65 - 0.98), and 0.50 (0.37 - 0.66), respectively. Positive associations between sodium channel-blocking AEDs and cancer were not found in the study.

CONCLUSION

Multi-methodological approaches using different methodologies, algorithms, and databases suggest that sodium channel-blocking AED use is inversely associated with colorectal cancer, lung cancer, gastric cancer, and hematological malignancies.

Caffeic acid phenethyl ester: Inhibition of metastatic cell behaviours via voltage-gated sodium channel in human breast cancer in vitro

Caffeic acid phenethyl ester, derived from natural propolis, has been reported to have anti-cancer properties. Voltage-gated sodium channels are upregulated in many cancers where they promote metastatic cell behaviours, including invasiveness. We found that micromolar concentrations of caffeic acid phenethyl ester blocked voltage-gated sodium channel activity in several invasive cell lines from different cancers, including breast (MDA-MB-231 and MDA-MB-468), colon (SW620) and non-small cell lung cancer (H460). In the MDA-MB-231 cell line, which was adopted as a 'model', long-term (48 h) treatment with 18 μM caffeic acid phenethyl ester reduced the peak current density by 91% and shifted steady-state inactivation to more hyperpolarized potentials and slowed recovery from inactivation. The effects of long-term treatment were also dose-dependent, 1 μM caffeic acid phenethyl ester reducing current density by only 65%. The effects of caffeic acid phenethyl ester on metastatic cell behaviours were tested on the MDA-MB-231 cell line at a working concentration (1 μM) that did not affect proliferative activity. Lateral motility and Matrigel invasion were reduced by up to 14% and 51%, respectively. Co-treatment of caffeic acid phenethyl ester with tetrodotoxin suggested that the voltage-gated sodium channel inhibition played a significant intermediary role in these effects. We conclude, first, that caffeic acid phenethyl ester does possess anti-metastatic properties. Second, the voltage-gated sodium channels, commonly expressed in strongly metastatic cancers, are a novel target for caffeic acid phenethyl ester. Third, more generally, ion channel inhibition can be a significant mode of action of nutraceutical compounds.

Regional anaesthesia and analgesia: relationship to cancer recurrence and survival

Cancer treatment is associated with significant morbidity and mortality. Surgery is a mainstay of treatment for many tumours, and anaesthetists care for cancer patients on a daily basis. Surgery itself induces a stress response and inhibits the immune system, and cancer surgery is associated with the release of tumour cells systemically. Preclinical and clinical studies suggest that the anaesthetics and adjuvants given in the perioperative period can affect cancer recurrence and survival, perhaps tipping the balance in some instances to determine whether cancer progresses or regresses. Retrospective studies have hinted that regional anaesthesia can play a protective role in cancer surgery, but many of these studies are small and subject to bias. We eagerly await the results of several large, randomized controlled trials examining the impact of regional anaesthesia and analgesia on cancer recurrence and survival.

Sodium channel-inhibiting drugs and survival of breast, colon and prostate cancer: a population-based study

Metastasis is the leading cause of cancer-related deaths. Voltage-gated sodium channels (VGSCs) regulate invasion and metastasis. Several VGSC-inhibiting drugs reduce metastasis in murine cancer models. We aimed to test the hypothesis that patients taking VGSC-inhibiting drugs who developed cancer live longer than those not taking these drugs. A cohort study was performed on primary care data from the QResearch database, including patients with breast, bowel or prostate cancer. Cox proportional hazards regression was used to compare the survival from cancer diagnosis of patients taking VGSC-inhibiting drugs with those not exposed to these drugs. Median time to death was 9.7 years in the exposed group and 18.4 years in the unexposed group, and exposure to these medications significantly increased mortality. Thus, exposure to VGSC-inhibiting drugs associates with reduced survival in breast, bowel and prostate cancer patients. This finding is not consistent with the preclinical data. Despite the strengths of this study including the large sample size, the study is limited by missing information on potentially important confounders such as cancer stage, co-morbidities and cause of death. Further research, which is able to account for these confounding issues, is needed to investigate the relationship between VGSC-inhibiting drugs and cancer survival.

Therapeutic Value of Voltage-Gated Sodium Channel Inhibitors in Breast, Colorectal, and Prostate Cancer: A Systematic Review

Although survival rates of breast, colon, and prostate cancers are improving, deaths from these tumors frequently occur due to metastasis. Voltage-gated Na(+) channels (VGSCs) are membrane proteins, which regulate membrane current and cellular migration during nervous system organogenesis. VGSCs are also expressed in fibroblasts, immune cells, glia, and metastatic cancer cells. VGSCs regulate migration and invasion of breast, bowel, and prostate cancer cells, suggesting that they may be novel anti-metastatic targets. We conducted a systematic review of clinical and preclinical studies testing the effects of VGSC-inhibiting drugs in cancer. Two-hundred and four publications were identified, of which two human, two mouse, and 20 in vitro publications were included. In the clinical studies, the effect of these drugs on survival and metastatic relapse is not clear. The 22 preclinical studies collectively suggest that several VGSC-inhibiting drugs inhibit cancer proliferation, migration, and invasion. None of the human and only six of the preclinical studies directly investigated the effect of the drugs on VGSC activity. Studies were difficult to compare due to lack of standardized methodology and outcome measures. We conclude that the benefits of VGSC inhibitors require further investigation. Standardization of future studies and outcome measures should enable meaningful study comparisons.

Blockade of voltage-gated sodium channels inhibits invasion of endocrine-resistant breast cancer cells

Voltage-gated Na⁺ channels (VGSCs) are membrane proteins which are normally expressed in excitable cells but have also been detected in cancer cells, where they are thought to be involved in malignancy progression. In this study we examined the ion current and expression profile of VGSC (Na_v1.5) in estrogen receptor (ER)-positive (MCF-7) and silenced (pII) breast cancer cells and its possible influence on their proliferation, motility and invasion. VGSC currents were analysed by whole cell patch clamp recording. Na_v1.5 expression and localization, in response to EGF stimulation, was examined by western blotting and immunofluorescence respectively. Cell invasion (under-agarose and Matrigel assays), motility (wound healing assay) and proliferation (MTT assay) were assessed in pII cells in response to VGSC blockers, phenytoin (PHT) and tetrodotoxin (TTX), or by siRNA knockdown of Na_v1.5. The effect of PHT and TTX on modulating EGF-induced phosphorylation of Akt and ERK1/2 was determined by western blotting. Total matrix metalloproteinase (MMP) was determined using a fluorometric-based activity assay. The level of various human proteases was detected by using proteome profiler array kit. VGSC currents were detected in pII cells, but were absent in MCF-7. Na_v1.5 showed cytoplasmic and perinuclear expression in both MCF-7 and pII cells, with enhanced expression upon EGF stimulation. Treatment of pII cells with PHT, TTX or siRNA significantly reduced invasion towards serum components and EGF, in part through reduction of P-ERK1/2 and proteases such as cathepsin E, kallikrein-10 and MMP-7, as well as total MMP activity. At high concentrations, PHT inhibited motility while TTX reduced cell proliferation. Pharmacological or genetic blockade of Na_v1.5 may serve as a potential anti-metastatic therapy for breast cancer.

cAMP/PKA Pathways and S56 Phosphorylation Are Involved in AA/PGE2-Induced Increases in rNaV1.4 Current

Arachidonic acid (AA) and its metabolites are important second messengers for ion channel modulation. The effects of extracellular application of AA and its non-metabolized analogue on muscle rNa_V1.4 Na⁺ current has been studied, but little is known about the effects of intracellular application of AA on this channel isoform. Here, we report that intracellular application of AA significantly augmented the rNa_V1.4 current peak without modulating the steady-state activation and inactivation properties of the rNa_V1.4 channel. These results differed from the effects of extracellular application of AA on rNa_V1.4 current. The effects of intracellular AA were mimicked by prostaglandin E₂ but not eicosatetraynoic acid (ETYA), the non-metabolized analogue of AA, and were eliminated by treatment with cyclooxygenase inhibitors, flufenamic acid, or indomethacin. AA/PGE₂-induced activation of rNa_V1.4 channels was mimicked by a cAMP analogue (db-cAMP) and eliminated by a PKA inhibitor, PKAi. Furthermore, inhibition of EP2 and EP4 (PGE₂ receptors) with AH6809 and AH23848 reduced the intracellular AA/PGE₂-induced increase of rNa_V1.4 current. Two mutated channels, rNa_V1.4S56A and rNa_V1.4T21A, were designed to investigate the role of predicted phosphorylation sites in the AA/PGE₂–mediated regulation of rNa_V1.4 currents. In rNa_V1.4S56A, the effects of intracellular db-cAMP, AA, and PGE₂ were significantly reduced. The results of the present study suggest that intracellular AA augments rNa_V1.4 current by PGE₂/EP receptor-mediated activation of the cAMP/PKA pathway, and that the S56 residue on the channel protein is important for this process.

In vitro effects of phenytoin and DAPT on MDA-MB-231 breast cancer cells

Voltage-gated sodium channel (VGSC) activity enhances cell behaviors related to metastasis, such as motility, invasion, and oncogene expression. Neonatal alternative splice form of Nav1.5 isoform is expressed in metastatic breast cancers. Furthermore, aberrant Notch signaling pathway can induce oncogenesis and may promote the progression of breast cancers. In this study, we aimed to analyze the effect of the nNav1.5 inhibitor phenytoin and Notch signal inhibitor N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine-t-butyl ester (DAPT) on triple negative breast cancer cell line (MDA-MB-231) via inhibition of nNav1.5 VGSC activity and Notch signaling, respectively. In order to determine the individual and combined effects of these inhibitors, the 4-[3-(4-iyodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate (WST-1) test, wound healing assay, and zymography were performed to detect the proliferation, lateral motility, and matrix metalloproteinase-9 (MMP9) activity, respectively. The expressions of nNav1.5, Notch4, MMP9, and tissue inhibitor of metalloproteinases-1 (TIMP1) were also detected by quantitative real-time reverse transcriptase-polymerase chain reaction. DAPT caused an antiproliferative effect when the doses were higher than 10 µM, whereas phenytoin showed no inhibitory action either alone or in combination with DAPT on the MDA-MB-231 cells. Furthermore, it was found that the lateral motility was inhibited by both inhibitors; however, this inhibitory effect was partially rescued when they were used in combination. Meanwhile, the results showed that the MMP9 activity and the ratio of MMP9 mRNA to TIMP1 mRNA were only decreased by DAPT. Thus, we conclude that the combined effect of DAPT and phenytoin is not as beneficial as using DAPT alone on MDA-MB-231 breast cancer cells.

Inhibition of Calcium-Activated Chloride Channel ANO1/TMEM16A Suppresses Tumor Growth and Invasion in Human Lung Cancer

Lung cancer or pulmonary carcinoma is primarily derived from epithelial cells that are thin and line on the alveolar surfaces of the lung for gas exchange. ANO1/TMEM16A, initially identified from airway epithelial cells, is a member of Ca2+-activated Cl- channels (CaCCs) that function to regulate epithelial secretion and cell volume for maintenance of ion and tissue homeostasis. ANO1/TMEM16A has recently been shown to be highly expressed in several epithelium originated carcinomas. However, the role of ANO1 in lung cancer remains unknown. In this study, we show that inhibition of calcium-activated chloride channel ANO1/TMEM16A suppresses tumor growth and invasion in human lung cancer. ANO1 is upregulated in different human lung cancer cell lines. Knocking-down ANO1 by small hairpin RNAs inhibited proliferation, migration and invasion of GLC82 and NCI-H520 cancel cells evaluated by CCK-8, would-healing, transwell and 3D soft agar assays. ANO1 protein is overexpressed in 77.3% cases of human lung adenocarcinoma tissues detected by immunohistochemistry. Furthermore, the tumor growth in nude mice implanted with GLC82 cells was significantly suppressed by ANO1 silencing. Taken together, our findings provide evidence that ANO1 overexpression contributes to tumor growth and invasion of lung cancer; and suppressing ANO1 overexpression may have therapeutic potential in lung cancer therapy.

Alteration of ASIC1 expression in clear cell renal cell carcinoma

Background

Acidic extracellular pH is a major feature of tumor tissue. Acid-sensing ion channels (ASICs) represent an H⁺-gated subgroup of the degenerin/epithelial Na⁺ channel family and are activated by acidic microenvironment. Little is known about the expression and clinical significance of ASICs in solid tumors. The purpose of this study was to examine the expression of ASIC1 in human clear cell renal cell carcinoma (CCRCC) and to determine if the expression of ASIC1 is associated with clinicopathological features.

Methods

The expression of ASIC1 in CCRCC tissues at the mRNA and protein levels was determined by real-time quantitative polymerase chain reaction and Western blot analysis, respectively. A tissue microarray was used to assess the expression of ASIC1 protein in tumor tissue and matched adjacent normal tissues from 75 patients with CCRCC.

Results

ASIC1 expression was detected in normal renal and CCRCC samples. The expressions of ASIC1 protein and mRNA were significantly decreased in the CCRCC tissues compared with matched normal renal tissues (P<0.05). The staining density measurement showed that the expression of ASIC1 was significantly decreased in stage I (P=0.037), stage II (P=0.026), and stage III (P=0.026), grades I–II CCRCC (P=0.004), and CCRCC from male patients (P=0.00002). However, no significant difference was observed for ASIC1 expression between CCRCC and normal tissue in patients with stage IV CCRCC (P=0.236), patients with grades III–IV CCRCC (P=0.314), and female patients (P=0.095). Spearman correlations demonstrated that ASIC1 expression did not correlate to tumor stage (correlation coefficient [CC =0.168], P=0.149) and the age of patients (CC −0.147, P=0.688) but showed a positive correlation to higher tumor grades (CC =0.270, P=0.018).

Conclusion

ASIC1 is downregulated in CCRCC. ASIC1 expression may be potentially used as a novel biomarker and even a CCRCC therapeutic target. Further efforts will be made to clarify the mechanism of ASIC1 in occurrence, progression, and metastasis of CCRCC.

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

Voltage-gated sodium channels (Na_V) are molecular characteristics of excitable cells. Their activation, triggered by membrane depolarization, generates transient sodium currents that initiate action potentials in neurons and muscle cells. Sodium currents were discovered by Hodgkin and Huxley using the voltage clamp technique and reported in their landmark series of papers in 1952. It was only in the 1980's that sodium channel proteins from excitable membranes were molecularly characterized by Catterall and his collaborators. Non-excitable cells can also express Na_V channels in physiological conditions as well as in pathological conditions. These Na_V channels can sustain biological roles that are not related to the generation of action potentials. Interestingly, it is likely that the abnormal expression of Na_V in pathological tissues can reflect the re-expression of a fetal phenotype. This is especially true in epithelial cancer cells for which these channels have been identified and sodium currents recorded, while it was not the case for cells from the cognate normal tissues. In cancers, the functional activity of Na_V appeared to be involved in regulating the proliferative, migrative, and invasive properties of cells. This review is aimed at addressing the non-excitable roles of Na_V channels with a specific emphasis in the regulation of cancer cell biology.

Molecular bioelectricity: how endogenous voltage potentials control cell behavior and instruct pattern regulation in vivo

In addition to biochemical gradients and transcriptional networks, cell behavior is regulated by endogenous bioelectrical cues originating in the activity of ion channels and pumps, operating in a wide variety of cell types. Instructive signals mediated by changes in resting potential control proliferation, differentiation, cell shape, and apoptosis of stem, progenitor, and somatic cells. Of importance, however, cells are regulated not only by their own V_mem but also by the V_mem of their neighbors, forming networks via electrical synapses known as gap junctions. Spatiotemporal changes in V_mem distribution among nonneural somatic tissues regulate pattern formation and serve as signals that trigger limb regeneration, induce eye formation, set polarity of whole-body anatomical axes, and orchestrate craniofacial patterning. New tools for tracking and functionally altering V_mem gradients in vivo have identified novel roles for bioelectrical signaling and revealed the molecular pathways by which V_mem changes are transduced into cascades of downstream gene expression. Because channels and gap junctions are gated posttranslationally, bioelectrical networks have their own characteristic dynamics that do not reduce to molecular profiling of channel expression (although they couple functionally to transcriptional networks). The recent data provide an exciting opportunity to crack the bioelectric code, and learn to program cellular activity at the level of organs, not only cell types. The understanding of how patterning information is encoded in bioelectrical networks, which may require concepts from computational neuroscience, will have transformative implications for embryogenesis, regeneration, cancer, and synthetic bioengineering.

Blood pressure and risk of cancer progression - A possible connection with salt and voltage-gated sodium channel

Although it is well known that high blood pressure promotes cancer, the underlying cause(s) is not well understood. Here, we advance the hypothesis that the extracellular sodium level could be a contributing factor. The hypothesis is based upon emerging evidence showing (i) that voltage-gated sodium channels are expressed de novo in cancer cells and tissues, and (ii) that the influx of sodium from the extracellular medium into cancer cells, mediated by the channel activity, promotes their metastatic potential. Clinical and lifestyle implications of the hypothesis are discussed.

Voltage-gated sodium channel as a target for metastatic risk reduction with re-purposed drugs

Objective: To determine the exact role of sodium channel proteins in migration, invasion and metastasis and understand the possible anti-invasion and anti-metastatic activity of repurposed drugs with voltage gated sodium channel blocking properties.

Material and methods: A review of the published medical literature was performed searching for pharmaceuticals used in daily practice, with inhibitory activity on voltage gated sodium channels. For every drug found, the literature was reviewed in order to define if it may act against cancer cells as an anti-invasion and anti-metastatic agent and if it was tested with this purpose in the experimental and clinical settings.

Results: The following pharmaceuticals that fulfill the above mentioned effects, were found: phenytoin, carbamazepine, valproate, lamotrigine, ranolazine, resveratrol, ropivacaine, lidocaine, mexiletine, flunarizine, and riluzole. Each of them are independently described and analyzed.

Conclusions: The above mentioned pharmaceuticals have shown anti-metastatic and anti-invasion activity and many of them deserve to be tested in well-planned clinical trials as adjunct therapies for solid tumors and as anti-metastatic agents. Antiepileptic drugs like phenytoin, carbamazepine and valproate and the vasodilator flunarizine emerged as particularly useful for anti-metastatic purposes.

Voltage-gated Na+ Channel Activity Increases Colon Cancer Transcriptional Activity and Invasion Via Persistent MAPK Signaling

Functional expression of voltage-gated Na⁺ channels (VGSCs) has been demonstrated in multiple cancer cell types where channel activity induces invasive activity. The signaling mechanisms by which VGSCs promote oncogenesis remain poorly understood. We explored the signal transduction process critical to VGSC-mediated invasion on the basis of reports linking channel activity to gene expression changes in excitable cells. Coincidentally, many genes transcriptionally regulated by the SCN5A isoform in colon cancer have an over-representation of cis-acting sites for transcription factors phosphorylated by ERK1/2 MAPK. We hypothesized that VGSC activity promotes MAPK activation to induce transcriptional changes in invasion-related genes. Using pharmacological inhibitors/activators and siRNA-mediated gene knockdowns, we correlated channel activity with Rap1-dependent persistent MAPK activation in the SW620 human colon cancer cell line. We further demonstrated that VGSC activity induces downstream changes in invasion-related gene expression via a PKA/ERK/c-JUN/ELK-1/ETS-1 transcriptional pathway. This is the first study illustrating a molecular mechanism linking functional activity of VGSCs to transcriptional activation of invasion-related genes.

Voltage-gated ion channels in cancer cell proliferation

Changes of the electrical charges across the surface cell membrane are absolutely necessary to maintain cellular homeostasis in physiological as well as in pathological conditions. The opening of ion channels alter the charge distribution across the surface membrane as they allow the diffusion of ions such as K+, Ca++, Cl.

How do voltage-gated sodium channels enhance migration and invasiveness in cancer cells?

Voltage-gated sodium channels are abnormally expressed in tumors, often as neonatal isoforms, while they are not expressed, or only at a low level, in the matching normal tissue. The level of their expression and their activity is related to the aggressiveness of the disease and to the formation of metastases. A vast knowledge on the regulation of their expression and functioning has been accumulated in normal excitable cells. This helped understand their regulation in cancer cells. However, how voltage-gated sodium channels impose a pro-metastatic behavior to cancer cells is much less documented. This aspect will be addressed in the review. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Role of ion channels in regulating Ca²⁺ homeostasis during the interplay between immune and cancer cells

Ion channels are abundantly expressed in both excitable and non-excitable cells, thereby regulating the Ca²⁺ influx and downstream signaling pathways of physiological processes. The immune system is specialized in the process of cancer cell recognition and elimination, and is regulated by different ion channels. In comparison with the immune cells, ion channels behave differently in cancer cells by making the tumor cells more hyperpolarized and influence cancer cell proliferation and metastasis. Therefore, ion channels comprise an important therapeutic target in anti-cancer treatment. In this review, we discuss the implication of ion channels in regulation of Ca²⁺ homeostasis during the crosstalk between immune and cancer cell as well as their role in cancer progression.

Identification and functional characterization of voltage-gated sodium channels in lymphocytes

A variety of ion channels has been discovered in lymphocytes. RT-PCR and real-time PCR analysis revealed that ALL (acute lymphocytic leukemia) cell lines and human peripheral blood mononuclear cells mainly expressed TTX (tetrodotoxin)-sensitive voltage-gated sodium channels (VGSCs). Expression of VGSC protein was confirmed by western blots and Immunofluorescence. Whole-cell patch-clamp recordings showed that a sub-population (20%) of MOLT-4 cells expressed functional VGSCs, which were TTX-sensitive. Importantly, 2 μM TTX decreased the invasion of Jurkat and MOLT-4 cells ∼90%. These results indicate that the activity of VGSCs could represent a novel mechanism potentiating the invasive capacity of these cells.

The sodium channel-blocking antiepileptic drug phenytoin inhibits breast tumour growth and metastasis

Background

Voltage-gated Na⁺ channels (VGSCs) are heteromeric protein complexes containing pore-forming α subunits and smaller, non-pore-forming β subunits. VGSCs are classically expressed in electrically excitable cells, e.g. neurons. VGSCs are also expressed in tumour cells, including breast cancer (BCa) cells, where they enhance cellular migration and invasion. However, despite extensive work defining in detail the molecular mechanisms underlying the expression of VGSCs and their pro-invasive role in cancer cells, there has been a notable lack of clinically relevant in vivo data exploring their value as potential therapeutic targets.

Findings

We have previously reported that the VGSC-blocking antiepileptic drug phenytoin inhibits the migration and invasion of metastatic MDA-MB-231 cells in vitro. The purpose of the present study was to establish whether VGSCs might be viable therapeutic targets by testing the effect of phenytoin on tumour growth and metastasis in vivo. We found that expression of Na_v1.5, previously detected in MDA-MB-231 cells in vitro, was retained on cells in orthotopic xenografts. Treatment with phenytoin, at a dose equivalent to that used to treat epilepsy (60 mg/kg; daily), significantly reduced tumour growth, without affecting animal weight. Phenytoin also reduced cancer cell proliferation in vivo and invasion into surrounding mammary tissue. Finally, phenytoin significantly reduced metastasis to the liver, lungs and spleen.

Conclusions

This is the first study showing that phenytoin reduces breast tumour growth and metastasis in vivo. We propose that pharmacologically targeting VGSCs, by repurposing antiepileptic or antiarrhythmic drugs, should be further studied as a potentially novel anti-cancer therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-014-0277-x) contains supplementary material, which is available to authorized users.

Transmembrane voltage potential of somatic cells controls oncogene-mediated tumorigenesis at long-range

The microenvironment is increasingly recognized as a crucial aspect of cancer. In contrast and complement to the field's focus on biochemical factors and extracellular matrix, we characterize a novel aspect of host:tumor interaction - endogenous bioelectric signals among non-excitable somatic cells. Extending prior work focused on the bioelectric state of cancer cells themselves, we show for the first time that the resting potentials of distant cells are critical for oncogene-dependent tumorigenesis. In the Xenopus laevis tadpole model, we used human oncogenes such as mutant KRAS to drive formation of tumor-like structures that exhibited overproliferation, increased nuclear size, hypoxia, acidity, and leukocyte attraction. Remarkably, misexpression of hyperpolarizing ion channels at distant sites within the tadpole significantly reduced the incidence of these tumors. The suppression of tumorigenesis could also be achieved by hyperpolarization using native CLIC1 chloride channels, suggesting a treatment modality not requiring gene therapy. Using a dominant negative approach, we implicate HDAC1 as the mechanism by which resting potential changes affect downstream cell behaviors. Based on published data on the voltage-mediated changes of butyrate flux through the SLC5A8 transporter, we present a model linking resting potentials of host cells to the ability of oncogenes to initiate tumorigenesis. Antibiotic data suggest that the relevant butyrate is generated by a native bacterial species, identifying a novel link between the microbiome and cancer that is mediated by alterations in bioelectric signaling.

Long-range gap junctional signaling controls oncogene-mediated tumorigenesis in Xenopus laevis embryos

In addition to the immediate microenvironment, long-range signaling may be an important component of cancer. Molecular-genetic analyses have implicated gap junctions-key mediators of cell-cell communication-in carcinogenesis. We recently showed that the resting voltage potential of distant cell groups is a key determinant of metastatic transformation and tumor induction. Here, we show in the Xenopus laevis model that gap junctional communication (GJC) is a modulator of the long-range bioelectric signaling that regulates tumor formation. Genetic disruption of GJC taking place within tumors, within remote host tissues, or between the host and tumors significantly lowers the incidence of tumors induced by KRAS mutations. The most pronounced suppression of tumor incidence was observed upon GJC disruption taking place farther away from oncogene-expressing cells, revealing a role for GJC in distant cells in the control of tumor growth. In contrast, enhanced GJC communication through the overexpression of wild-type connexin Cx26 increased tumor incidence. Our data confirm a role for GJC in tumorigenesis, and reveal that this effect is non-local. Based on these results and on published data on movement of ions through GJs, we present a quantitative model linking the GJC coupling and bioelectrical state of cells to the ability of oncogenes to initiate tumorigenesis. When integrated with data on endogenous bioelectric signaling during left-right patterning, the model predicts differential tumor incidence outcomes depending on the spatial configurations of gap junction paths relative to tumor location and major anatomical body axes. Testing these predictions, we found that the strongest influence of GJ modulation on tumor suppression by hyperpolarization occurred along the embryonic left-right axis. Together, these data reveal new, long-range aspects of cancer control by the host's physiological parameters.

Endogenous bioelectrical networks store non-genetic patterning information during development and regeneration

Pattern formation, as occurs during embryogenesis or regeneration, is the crucial link between genotype and the functions upon which selection operates. Even cancer and aging can be seen as challenges to the continuous physiological processes that orchestrate individual cell activities toward the anatomical needs of an organism. Thus, the origin and maintenance of complex biological shape is a fundamental question for cell, developmental, and evolutionary biology, as well as for biomedicine. It has long been recognized that slow bioelectrical gradients can control cell behaviors and morphogenesis. Here, I review recent molecular data that implicate endogenous spatio-temporal patterns of resting potentials among non-excitable cells as instructive cues in embryogenesis, regeneration, and cancer. Functional data have implicated gradients of resting potential in processes such as limb regeneration, eye induction, craniofacial patterning, and head-tail polarity, as well as in metastatic transformation and tumorigenesis. The genome is tightly linked to bioelectric signaling, via ion channel proteins that shape the gradients, downstream genes whose transcription is regulated by voltage, and transduction machinery that converts changes in bioelectric state to second-messenger cascades. However, the data clearly indicate that bioelectric signaling is an autonomous layer of control not reducible to a biochemical or genetic account of cell state. The real-time dynamics of bioelectric communication among cells are not fully captured by transcriptomic or proteomic analyses, and the necessary-and-sufficient triggers for specific changes in growth and form can be physiological states, while the underlying gene loci are free to diverge. The next steps in this exciting new field include the development of novel conceptual tools for understanding the anatomical semantics encoded in non-neural bioelectrical networks, and of improved biophysical tools for reading and writing electrical state information into somatic tissues. Cracking the bioelectric code will have transformative implications for developmental biology, regenerative medicine, and synthetic bioengineering.

Augmenting anti-cancer natural products with a small molecule adjuvant

Aquatic microbes produce diverse secondary metabolites with interesting biological activities. Cytotoxic metabolites have the potential to become lead compounds or drugs for cancer treatment. Many cytotoxic compounds, however, show undesirable toxicity at higher concentrations. Such undesirable activity may be reduced or eliminated by using lower doses of the cytotoxic compound in combination with another compound that modulates its activity. Here, we have examined the cytotoxicity of four microbial metabolites [ethyl N-(2-phenethyl) carbamate (NP-1), Euglenophycin, Anabaenopeptin, and Glycolipid 652] using three in vitro cell lines [human breast cancer cells (MCF-7), mouse neuroblastoma cells (N2a), and rat pituitary epithelial cells (GH4C1)]. The compounds showed variable cytotoxicity, with Euglenophycin displaying specificity for N2a cells. We have also examined the modulatory power of NP-1 on the cytotoxicity of the other three compounds and found that at a permissible concentration (125 µg/mL), NP-1 sensitized N2a and MCF-7 cells to Euglenophycin and Glycolipid 652 induced cytotoxicity.

Ion channel expression as promising cancer biomarker

Cancer is a disease with marked heterogeneity in both response to therapy and survival. Clinical and histopathological characteristics have long determined prognosis and therapy. The introduction of molecular diagnostics has heralded an explosion in new prognostic factors. Overall, histopathology, immunohistochemistry and molecular biology techniques have described important new prognostic subgroups in the different cancer categories. Ion channels and transporters (ICT) are a new class of membrane proteins which are aberrantly expressed in several types of human cancers. Besides regulating different aspect of cancer cell behavior, ICT can now represent novel cancer biomarkers. A summary of the data obtained so far and relative to breast, prostate, lung, colorectal, esophagus, pancreatic and gastric cancers are reported. Special emphasis is given to those studies aimed at relating specific ICT or a peculiar ICT profile with current diagnostic methods. Overall, we are close to exploit ICTs for diagnostic, prognostic or predictive purposes in cancer. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Ranolazine inhibits NaV1.5-mediated breast cancer cell invasiveness and lung colonization

BACKGROUND

Na(V)1.5 voltage-gated sodium channels are abnormally expressed in breast tumours and their expression level is associated with metastatic occurrence and patients' death. In breast cancer cells, Na(V)1.5 activity promotes the proteolytic degradation of the extracellular matrix and enhances cell invasiveness.

FINDINGS

In this study, we showed that the extinction of Na(V)1.5 expression in human breast cancer cells almost completely abrogated lung colonisation in immunodepressed mice (NMRI nude). Furthermore, we demonstrated that ranolazine (50 μM) inhibited Na(V)1.5 currents in breast cancer cells and reduced Na(V)1.5-related cancer cell invasiveness in vitro. In vivo, the injection of ranolazine (50 mg/kg/day) significantly reduced lung colonisation by Na(V)1.5-expressing human breast cancer cells.

CONCLUSIONS

Taken together, our results demonstrate the importance of Na(V)1.5 in the metastatic colonisation of organs by breast cancer cells and indicate that small molecules interfering with Na(V) activity, such as ranolazine, may represent powerful pharmacological tools to inhibit metastatic development and improve cancer treatments.

Ion channels and transporters in metastasis

An elaborate interplay between ion channels and transporters, components of the cytoskeleton, adhesion molecules, and signaling cascades provides the basis for each major step of the metastatic cascade. Ion channels and transporters contribute to cell motility by letting through or transporting ions essential for local Ca2+, pH and--in cooperation with water permeable aquaporins--volume homeostasis. Moreover, in addition to the actual ion transport they, or their auxiliary subunits, can display non-conducting activities. They can exert kinase activity in order to phosphorylate cytoskeletal constituents or their associates. They can become part of signaling processes by permeating Ca2+, by generating local pH-nanodomains or by being final downstream effectors. A number of channels and transporters are found at focal adhesions, interacting directly or indirectly with proteins of the extracellular matrix, with integrins or with components of the cytoskeleton. We also include the role of aquaporins in cell motility. They drive the outgrowth of lamellipodia/invadopodia or control the number of β1 integrins in the plasma membrane. The multitude of interacting ion channels and transporters (called transportome) including the associated signaling events holds great potential as therapeutic target(s) for anticancer agents that are aimed at preventing metastasis. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Exposure to sodium channel-inhibiting drugs and cancer survival: protocol for a cohort study using the QResearch primary care database

INTRODUCTION

Metastasis from solid tumours is associated with significant morbidity and mortality, and is the leading cause of cancer-related deaths. Voltage-gated sodium channels (VGSCs) are drug targets for the treatment of epilepsy. VGSCs are also present in cancer cells, where they regulate metastatic cell behaviours, including cellular movement and invasion. Treating cancer cells with the VGSC-inhibiting anticonvulsant phenytoin reduces cellular invasion and migration. Together, these suggest that VGSCs may be useful targets for inhibiting metastasis. The purpose of this study is to test the hypothesis that use of VGSC-inhibiting drugs will reduce metastasis, and therefore increase survival time in patients with cancer.

METHODS AND ANALYSIS

A cohort study based on primary care data from the QResearch database will include patients with one of the three common tumours: breast, bowel and prostate. The primary outcome will be overall survival from the date of cancer diagnosis. Cox proportional hazards regression will be used to compare the survival of patients with cancer taking VGSC-inhibiting drugs (including anticonvulsants and class I antiarrhythmic agents) with patients with cancer not exposed to these drugs, adjusting for age and sex. Exposure to VGSC-inhibiting drugs will be defined as having at least one prescription for these drugs prior to cancer diagnosis. High and low exposure groups will be identified based on the length of use. A number of sensitivity and secondary analyses will be conducted.

ETHICS AND DISSEMINATION

The protocol has been independently peer-reviewed and approved by the QResearch Scientific Board. The project has also been approved by the University of York Ethical Review Process. The results will be presented at international conferences and published in an open access peer-reviewed journal, in accordance with the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) criteria.

HERG1 functions as an oncogene in pancreatic cancer and is downregulated by miR-96

Pancreatic cancer is an aggressive malignancy with an extremely poor prognosis. The human ether-a-go-go-related potassium channel (HERG1) is a human rapid delayed rectifier, which is involved in many crucial cellular events. In this article, we find that HERG1 expression is dramatically increased both in pancreatic cancer tissues and cell lines, and that increased HERG1 expression is significantly related to the development of pancreatic cancer. HERG1 silencing in pancreatic cancer-derived cell lines PANC-1 and CFPAC-1 strongly inhibits their malignant capacity in vitro as well as tumorigenicity and metastasis in nude mice. In addition, HERG1 is identified as a direct target of miR-96, which is downregulated in pancreatic cancer tissues and cell lines. Ectopic expression of miR-96 represses the HERG1 expression in pancreatic cancer and significantly inhibits malignant behavior of pancreatic cancer cells in vitro and in vivo. Collectively, our findings suggest that miR-96 acts as a tumor suppressor in pancreatic cancer and may therefore serve as a useful therapeutic target for the development of new anticancer therapy.

Alteration of bioelectrically-controlled processes in the embryo: a teratogenic mechanism for anticonvulsants

Maternal use of anticonvulsants during the first trimester of pregnancy has been associated with an elevated risk of major congenital malformations in the offspring. Whether the increased risk is caused by the specific pharmacological mechanisms of certain anticonvulsants, the underlying epilepsy, or common genetic or environmental risk factors shared by epilepsy and malformations has been controversial. We hypothesize that anticonvulsant therapies during pregnancy that attain more successful inhibition of neurotransmission might lead to both better seizure control in the mother and stronger alteration of bioelectrically-controlled processes in the embryo that result in structural malformations. We propose that development of pharmaceuticals that do not alter cell resting transmembrane voltage levels could result in safer drugs.

Voltage-gated sodium channels were differentially expressed in human normal prostate, benign prostatic hyperplasia and prostate cancer cells

Voltage-gated sodium channels (VGSCs) are expressed not only in excitable cells but also in numerous metastatic cells, particularly in certain types of cancer cells. In some types of cancer, including prostate cancer, the expression of VGSCs is associated with cancer migration, invasion and metastasis in vivo. However, the detailed expression profiles of VGSC α subunits in normal human prostate, in prostatic hyperplasia and prostatic cancer remain controversial. In the present study, quantitative polymerase chain reaction was used to systematically detect all subtypes of VGSC α subunits in normal human prostate, benign prostatic hyperplasia (BPH) and prostate cancer cells. The expression profile of VGSC α subunits was observed to differ between these cell types. Nav1.5 was the major isoform expressed in normal human prostate tissue, while Nav1.5 and Nav1.2 were the predominant isoforms in BPH tissue. However, in PC-3 and LNCaP cells, two typical prostate cancer cell lines, Nav1.6 and Nav1.7 were abundantly expressed. By comparing the relative expression levels of Nav1.5, Nav1.6 and Nav1.7 in these cells, the mRNA levels of Nav1.6 and Nav1.7 were identified to be 6- to 27-fold higher in PC-3 and LNCaP cells than in either normal or BPH samples (P<0.05); however, Nav1.5 mRNA levels were relatively lower compared with those of Nav1.6 or Nav1.7 in all cells analyzed. To confirm whether Nav1.6 and Nav1.7 expression in cancer cells was functional, a patch-clamp technique was used to record whole-cell currents. A tetrodotoxin-sensitive sodium current was successfully recorded in PC-3 cells, but not in LNCaP cells. It was concluded that although all types of VGSC α subunits exhibited low expression levels in normal prostate and BPH cells, both Nav1.6 and Nav1.7 were significantly upregulated in the prostate cancer cell lines, suggesting these subtypes may be potential diagnostic markers and therapeutic targets for certain types of prostate cancer in humans.

The sodium channel β1 subunit mediates outgrowth of neurite-like processes on breast cancer cells and promotes tumour growth and metastasis

Voltage-gated Na⁺ channels (VGSCs) are heteromeric proteins composed of pore-forming α subunits and smaller β subunits. The β subunits are multifunctional channel modulators and are members of the immunoglobulin superfamily of cell adhesion molecules (CAMs). β1, encoded by SCN1B, is best characterized in the central nervous system (CNS), where it plays a critical role in regulating electrical excitability, neurite outgrowth and migration during development. β1 is also expressed in breast cancer (BCa) cell lines, where it regulates adhesion and migration in vitro. In the present study, we found that SCN1B mRNA/β1 protein were up-regulated in BCa specimens, compared with normal breast tissue. β1 upregulation substantially increased tumour growth and metastasis in a xenograft model of BCa. β1 over-expression also increased vascularization and reduced apoptosis in the primary tumours, and β1 over-expressing tumour cells had an elongate morphology. In vitro, β1 potentiated outgrowth of processes from BCa cells co-cultured with fibroblasts, via trans-homophilic adhesion. β1-mediated process outgrowth in BCa cells required the presence and activity of fyn kinase, and Na⁺ current, thus replicating the mechanism by which β1 regulates neurite outgrowth in CNS neurons. We conclude that when present in breast tumours, β1 enhances pathological growth and cellular dissemination. This study is the first demonstration of a functional role for β1 in tumour growth and metastasis in vivo. We propose that β1 warrants further study as a potential biomarker and targeting β1-mediated adhesion interactions may have value as a novel anti-cancer therapy.

Expression of neonatal Nav1.5 in human brain astrocytoma and its effect on proliferation, invasion and apoptosis of astrocytoma cells

In the present study, we designed and conducted a series of assays to determine the expression of voltage-gated sodium channel (VGSC) neonatal isoform Nav1.5 (nNav1.5) in human brain astrocytoma and its effect on the proliferation, migration, invasion and apoptosis of astrocytoma U251 cells. The results showed that nNav1.5 mRNA and protein were expressed in both human brain astrocytoma and normal brain tissues, but their expression levels in astrocytoma were significantly higher (P<0.05). In astrocytomas, nNav1.5 mRNA and protein levels were also different (P<0.05) and were correlated with pathological grades. The immunofluorescence confocal microscopy observations demonstrated that nNav1.5 protein was expressed in the nucleus, cytoplasm and membrane of the astrocytoma cells. After transfection, the small interfering RNA (siRNA) targeted to nNav1.5 significantly reduced the expression levels of SCN5A/nNav1.5 mRNA and protein by 57.2% (P<0.05) and 66.6% (P<0.05), respectively. The MTT, wound healing, Matrigel invasion and flow cytometric assays confirmed that following siRNA downregulation of the expression of the SCN5A/nNav1.5 gene, the in vitro proliferation and in vitro invasiveness of the U251 cells were significantly reduced (P<0.05 for both comparisons), and the apoptosis rate was significantly increased (P<0.05). These results revealed that nNav1.5 expression in human brain astrocytoma was upregulated, and its expression was positively correlated with the degree of malignancy. Additionally, reduced nNav1.5 expression significantly suppressed the proliferation and invasiveness of astrocytoma cells, indicating a new target in the molecular diagnosis and therapy of astrocytoma.

Computational modelling of multi-cell migration in a multi-signalling substrate

Cell migration is a vital process in many biological phenomena ranging from wound healing to tissue regeneration. Over the past few years, it has been proven that in addition to cell-cell and cell-substrate mechanical interactions (mechanotaxis), cells can be driven by thermal, chemical and/or electrical stimuli. A numerical model was recently presented by the authors to analyse single cell migration in a multi-signalling substrate. That work is here extended to include multi-cell migration due to cell-cell interaction in a multi-signalling substrate under different conditions. This model is based on balancing the forces that act on the cell population in the presence of different guiding cues. Several numerical experiments are presented to illustrate the effect of different stimuli on the trajectory and final location of the cell population within a 3D heterogeneous multi-signalling substrate. Our findings indicate that although multi-cell migration is relatively similar to single cell migration in some aspects, the associated behaviour is very different. For instance, cell-cell interaction may delay single cell migration towards effective cues while increasing the magnitude of the average net cell traction force as well as the local velocity. Besides, the random movement of a cell within a cell population is slightly greater than that of single cell migration. Moreover, higher electrical field strength causes the cell slug to flatten near the cathode. On the other hand, as with single cell migration, the existence of electrotaxis dominates mechanotaxis, moving the cells to the cathode or anode pole located at the free surface. The numerical results here obtained are qualitatively consistent with related experimental works.

Scorpion venoms as a potential source of novel cancer therapeutic compounds

Scorpions and their venoms have been used in traditional medicine for thousands of years in China, India and Africa. The scorpion venom is a highly complex mixture of salts, nucleotides, biogenic amines, enzymes, mucoproteins, as well as peptides and proteins (e.g. neurotoxins). One of the recently observed biological properties of animal venoms and toxins is that they possess anticancer potential. An increasing number of studies have shown that scorpion venoms and toxins can decrease cancer growth, induce apoptosis and inhibit cancer progression and metastasis in vitro and in vivo. Several active molecules with anticancer activities, ranging from inhibition of proliferation and cell cycle arrest to induction of apoptosis and decreasing cell migration and invasion, have been isolated from scorpion venoms. These observations have shed light on the application of scorpion venoms and toxins as potential novel cancer therapeutics. This mini-review focuses on the anticancer potential of scorpion venoms and toxins and the possible mechanisms for their antitumor activities.

Purification, characterization, and bioactivity of a new analgesic-antitumor peptide from Chinese scorpion Buthus martensii Karsch

Scorpion venoms are complex mixtures of dozens or even hundreds of distinct proteins, many of which have diverse bioactivities. In this study, after bioassay-driven chromatographic purification, a new dual-function peptide with analgesic and antitumor activities was isolated and designated BmK AGAP-SYPU2. The first 12 amino acid residues were sequenced with Edman degradation. The cDNA was cloned by using rapid amplification of cDNA ends from the cDNA pool from scorpion glands. The amino acid sequence of BmK AGAP-SYPU2 was then deduced, and is consistent with the molecular mass measured with MALDI-TOF-MS. A preliminary pharmacological analysis revealed the following: in the dose-effect curve plotted with the mouse-twisting test, BmK AGAP-SYPU2 showed analgesic activity with an ED50 value of 1.42 mg/kg; in the time-effect curves plotted with a hot-plate procedure, BmK AGAP-SYPU2 had similar effects to those of the painkiller morphine, except for its longer duration. BmK AGAP-SYPU2 also showed antitumor activity against Ehrlich ascites tumor and S-180 fibrosarcoma models in vivo. Sequence alignment and homology modeling showed that BmK AGAP-SYPU2 is highly conserved relative to other scorpion α-toxins. However, a few different amino acids endow it with unique molecular properties, which may be responsible for its specific bioactivities. BmK AGAP-SYPU2, a new scorpion neurotoxin with dual functions, is a potential candidate drug amenable to exploitation and modification.

Regulation of voltage-gated sodium channel expression in cancer: hormones, growth factors and auto-regulation

Although ion channels are increasingly being discovered in cancer cells in vitro and in vivo, and shown to contribute to different aspects and stages of the cancer process, much less is known about the mechanisms controlling their expression. Here, we focus on voltage-gated Na⁺ channels (VGSCs) which are upregulated in many types of carcinomas where their activity potentiates cell behaviours integral to the metastatic cascade. Regulation of VGSCs occurs at a hierarchy of levels from transcription to post-translation. Importantly, mainstream cancer mechanisms, especially hormones and growth factors, play a significant role in the regulation. On the whole, in major hormone-sensitive cancers, such as breast and prostate cancer, there is a negative association between genomic steroid hormone sensitivity and functional VGSC expression. Activity-dependent regulation by positive feedback has been demonstrated in strongly metastatic cells whereby the VGSC is self-sustaining, with its activity promoting further functional channel expression. Such auto-regulation is unlike normal cells in which activity-dependent regulation occurs mostly via negative feedback. Throughout, we highlight the possible clinical implications of functional VGSC expression and regulation in cancer.

Ion channels and transporters in tumour cell migration and invasion

Cell migration is a central component of the metastatic cascade requiring a concerted action of ion channels and transporters (migration-associated transportome), cytoskeletal elements and signalling cascades. Ion transport proteins and aquaporins contribute to tumour cell migration and invasion among other things by inducing local volume changes and/or by modulating Ca(2+) and H(+) signalling. Targeting cell migration therapeutically bears great clinical potential, because it is a prerequisite for metastasis. Ion transport proteins appear to be attractive candidate target proteins for this purpose because they are easily accessible as membrane proteins and often overexpressed or activated in cancer. Importantly, a number of clinically widely used drugs are available whose anticipated efficacy as anti-tumour drugs, however, has now only begun to be evaluated.