Voltage-dependent activation of Rac1 by Nav 1.5 channels promotes cell migration

Influences of physical stimulations on the migration and differentiation of Schwann cells involved in peripheral nerve repair

Peripheral nerve injury repair has always been a research concern of scientists. At the tissue level, axonal regeneration has become a research spotlight in peripheral nerve repair. Through transplantation of autologous nerve grafts or other emerging biomaterials functional recovery after facial nerve injury is not ideal in clinical scenarios. Great strides have been made to improve facial nerve repair at the micro-cellular level. Physical stimulation techniques can trigger Schwann cells (SCs) to migrate and differentiate into cells required for peripheral nerve repair. Classified by the sources of physical stimulations, SCs repair peripheral nerves through galvanotaxis, magnetotaxis and durotaxis. This article summarized the activation, directional migration and differentiation of SCs induced by physical stimulations, thus providing new ideas for the research of peripheral nerve repair.

Effects of NaV1.5 and Rac1 on the Epithelial-Mesenchymal Transition in Breast Cancer

Breast cancer is a disease that seriously endangers the health of women. However, it is difficult to treat due to the emergence of metastasis and drug resistance. Exploring the metastasis mechanism of breast cancer is helpful to aim for the appropriate target. The epithelial-mesenchymal transition (EMT) is an important mechanism of breast cancer metastasis. Sodium channel 1.5(NaV1.5) and the GTPase Rac1 are factors related to the degree of malignancy of breast tumors. The expression of NaV1.5 and the activation of Rac1 are both involved in EMT. In addition, NaV1.5 can change the plasma membrane potential (Vm) by promoting the inflow of Na+ to depolarize the cell membrane, induce the activation of Rac1 and produce a cascade of reactions that lead to EMT in breast cancer cells; this sequence of events further induces the movement, migration and invasion of tumor cells and affects the prognosis of breast cancer patients. In this paper, the roles of NaV1.5 and Rac1 in EMT-mediated breast cancer progression were reviewed.

Neuronal mimicry in tumors: lessons from neuroscience to tackle cancer

Cellular plasticity and the ability to avoid terminal differentiation are hallmarks of cancer. Here, we review the evidence that tumor cells themselves can take on properties of neurons of the central nervous system, which can regulate tumor growth and metastasis. We discuss recent evidence that axon guidance molecules and regulators of electrical activity and synaptic transmission, such as ion channels and neurotransmitters, can drive the oncogenic and invasive properties of tumor cells from a range of cancers. We also review how FDA-approved treatments for neurological disorders are being tested in pre-clinical models and clinical trials for repurposing as anti-cancer agents, offering the potential for new therapies for cancer patients that can be accessed more quickly.

Modulating voltage-gated sodium channels to enhance differentiation and sensitize glioblastoma cells to chemotherapy

BACKGROUND

Glioblastoma (GBM) stands as the most prevalent and aggressive form of adult gliomas. Despite the implementation of intensive therapeutic approaches involving surgery, radiation, and chemotherapy, Glioblastoma Stem Cells contribute to tumor recurrence and poor prognosis. The induction of Glioblastoma Stem Cells differentiation by manipulating the transcriptional machinery has emerged as a promising strategy for GBM treatment. Here, we explored an innovative approach by investigating the role of the depolarized resting membrane potential (RMP) observed in patient-derived GBM sphereforming cell (GSCs), which allows them to maintain a stemness profile when they reside in the G0 phase of the cell cycle.

METHODS

We conducted molecular biology and electrophysiological experiments, both in vitro and in vivo, to examine the functional expression of the voltage-gated sodium channel (Nav) in GSCs, particularly focusing on its cell cycle-dependent functional expression. Nav activity was pharmacologically manipulated, and its effects on GSCs behavior were assessed by live imaging cell cycle analysis, self-renewal assays, and chemosensitivity assays. Mechanistic insights into the role of Nav in regulating GBM stemness were investigated through pathway analysis in vitro and through tumor proliferation assay in vivo.

RESULTS

We demonstrated that Nav is functionally expressed by GSCs mainly during the G0 phase of the cell cycle, suggesting its pivotal role in modulating the RMP. The pharmacological blockade of Nav made GBM cells more susceptible to temozolomide (TMZ), a standard drug for this type of tumor, by inducing cell cycle re-entry from G0 phase to G1/S transition. Additionally, inhibition of Nav substantially influenced the self-renewal and multipotency features of GSCs, concomitantly enhancing their degree of differentiation. Finally, our data suggested that Nav positively regulates GBM stemness by depolarizing the RMP and suppressing the ERK signaling pathway. Of note, in vivo proliferation assessment confirmed the increased susceptibility to TMZ following pharmacological blockade of Nav.

CONCLUSIONS

This insight positions Nav as a promising prognostic biomarker and therapeutic target for GBM patients, particularly in conjunction with temozolomide treatment.

A novel Nav1.5-dependent feedback mechanism driving glycolytic acidification in breast cancer metastasis

Solid tumours have abnormally high intracellular [Na+]. The activity of various Na+ channels may underlie this Na+ accumulation. Voltage-gated Na+ channels (VGSCs) have been shown to be functionally active in cancer cell lines, where they promote invasion. However, the mechanisms involved, and clinical relevance, are incompletely understood. Here, we show that protein expression of the Nav1.5 VGSC subtype strongly correlates with increased metastasis and shortened cancer-specific survival in breast cancer patients. In addition, VGSCs are functionally active in patient-derived breast tumour cells, cell lines, and cancer-associated fibroblasts. Knockdown of Nav1.5 in a mouse model of breast cancer suppresses expression of invasion-regulating genes. Nav1.5 activity increases ATP demand and glycolysis in breast cancer cells, likely by upregulating activity of the Na+/K+ ATPase, thus promoting H+ production and extracellular acidification. The pH of murine xenograft tumours is lower at the periphery than in the core, in regions of higher proliferation and lower apoptosis. In turn, acidic extracellular pH elevates persistent Na+ influx through Nav1.5 into breast cancer cells. Together, these findings show positive feedback between extracellular acidification and the movement of Na+ into cancer cells which can facilitate invasion. These results highlight the clinical significance of Nav1.5 activity as a potentiator of breast cancer metastasis and provide further evidence supporting the use of VGSC inhibitors in cancer treatment.

Therapeutic targeting of voltage-gated sodium channel NaV1.7 for cancer metastasis

This review focuses on the expression and function of voltage-gated sodium channel subtype NaV1.7 in various cancers and explores its impact on the metastasis driving cell functions such as proliferation, migration, and invasiveness. An overview of its structural characteristics, drug binding sites, inhibitors and their likely mechanisms of action are presented. Despite the lack of clarity on the precise mechanism by which NaV1.7 contributes to cancer progression and metastasis; many studies have suggested a connection between NaV1.7 and proteins involved in multiple signaling pathways such as PKA and EGF/EGFR-ERK1/2. Moreover, the functional activity of NaV1.7 appears to elevate the expression levels of MACC1 and NHE-1, which are controlled by p38 MAPK activity, HGF/c-MET signaling and c-Jun activity. This cascade potentially enhances the secretion of extracellular matrix proteases, such as MMPs which play critical roles in cell migration and invasion activities. Furthermore, the NaV1.7 activity may indirectly upregulate Rho GTPases Rac activity, which is critical for cytoskeleton reorganization, cell adhesion, and actin polymerization. The relationship between NaV1.7 and cancer progression has prompted researchers to investigate the therapeutic potential of targeting NaV1.7 using inhibitors. The positive outcome of such studies resulted in the discovery of several inhibitors with the ability to reduce cancer cell migration, invasion, and tumor growth underscoring the significance of NaV1.7 as a promising pharmacological target for attenuating cancer cell proliferation and metastasis. The research findings summarized in this review suggest that the regulation of NaV1.7 expression and function by small molecules and/or by genetic engineering is a viable approach to discover novel therapeutics for the prevention and treatment of metastasis of cancers with elevated NaV1.7 expression.

The role of lidocaine in cancer progression and patient survival

Since its development in 1943, lidocaine has been one of the most commonly used local anesthesia agents for surgical procedures. Lidocaine alters neuronal signal transmission by prolonging the inactivation of fast voltage-gated sodium channels in the cell membrane of neurons, which are responsible for action potential propagation. Recently, it has attracted attention due to emerging evidence suggesting its potential antitumor properties, particularly in the in vitro setting. Further, local administration of lidocaine around the tumor immediately prior to surgical removal has been shown to improve overall survival in breast cancer patients. However, the exact mechanisms driving these antitumor effects remain largely unclear. In this article, we will review the existing literature on the mechanism of lidocaine as a local anesthetic, its effects on the cancer cells and the tumor microenvironment, involved pathways, and cancer progression. Additionally, we will explore recent reports highlighting its impact on clinical outcomes in cancer patients. Taken together, there remains significant ambiguity surrounding lidocaine's functions and roles in cancer biology, particularly in perioperative setting.

An Ultrasensitive Genetically Encoded Voltage Indicator Uncovers the Electrical Activity of Non-Excitable Cells

Most animal cell types are classified as non-excitable because they do not generate action potentials observed in excitable cells, such as neurons and muscle cells. Thus, resolving voltage signals in non-excitable cells demands sensors with exceptionally high voltage sensitivity. In this study, the ultrabright, ultrasensitive, and calibratable genetically encoded voltage sensor rEstus is developed using structure-guided engineering. rEstus is most sensitive in the resting voltage range of non-excitable cells and offers a 3.6-fold improvement in brightness change for fast voltage spikes over its precursor ASAP3. Using rEstus, it is uncovered that the membrane voltage in several non-excitable cell lines (A375, HEK293T, MCF7) undergoes spontaneous endogenous alterations on a second to millisecond timescale. Correlation analysis of these optically recorded voltage alterations provides a direct, real-time readout of electrical cell-cell coupling, showing that visually connected A375 and HEK293T cells are also largely electrically connected, while MCF7 cells are only weakly coupled. The presented work provides enhanced tools and methods for non-invasive voltage imaging in living cells and demonstrates that spontaneous endogenous membrane voltage alterations are not limited to excitable cells but also occur in a variety of non-excitable cell types.

Ranolazine: a potential anti-metastatic drug targeting voltage-gated sodium channels

BACKGROUND

Multi-faceted evidence from a range of cancers suggests strongly that de novo expression of voltage-gated sodium channels (VGSCs) plays a significant role in driving cancer cell invasiveness. Under hypoxic conditions, common to growing tumours, VGSCs develop a persistent current (INaP) which can be blocked selectively by ranolazine.

METHODS

Several different carcinomas were examined. We used data from a range of experimental approaches relating to cellular invasiveness and metastasis. These were supplemented by survival data mined from cancer patients.

RESULTS

In vitro, ranolazine inhibited invasiveness of cancer cells especially under hypoxia. In vivo, ranolazine suppressed the metastatic abilities of breast and prostate cancers and melanoma. These data were supported by a major retrospective epidemiological study on breast, colon and prostate cancer patients. This showed that risk of dying from cancer was reduced by ca.60% among those taking ranolazine, even if this started 4 years after the diagnosis. Ranolazine was also shown to reduce the adverse effects of chemotherapy on heart and brain. Furthermore, its anti-cancer effectiveness could be boosted by co-administration with other drugs.

CONCLUSIONS

Ranolazine, alone or in combination with appropriate therapies, could be reformulated as a safe anti-metastatic drug offering many potential advantages over current systemic treatment modalities.

Voltage-gated sodium channels, sodium transport and progression of solid tumours

Sodium (Na+) concentration in solid tumours of different origin is highly dysregulated, and this corresponds to the aberrant expression of Na+ transporters. In particular, the α subunits of voltage gated Na+ channels (VGSCs) raise intracellular Na+ concentration ([Na+]i) in malignant cells, which influences the progression of solid tumours, predominantly driving cancer cells towards a more aggressive and metastatic phenotype. Conversely, re-expression of VGSC β subunits in cancer cells can either enhance tumour progression or promote anti-tumourigenic properties. Metastasis is the leading cause of cancer-related mortality, highlighting an important area of research which urgently requires improved therapeutic interventions. Here, we review the extent to which VGSC subunits are dysregulated in solid tumours, and consider the implications of such dysregulation on solid tumour progression. We discuss current understanding of VGSC-dependent mechanisms underlying increased invasive and metastatic potential of solid tumours, and how the complex relationship between the tumour microenvironment (TME) and VGSC expression may further drive tumour progression, in part due to the interplay of infiltrating immune cells, cancer-associated fibroblasts (CAFs) and insufficient supply of oxygen (hypoxia). Finally, we explore past and present clinical trials that investigate utilising existing VGSC modulators as potential pharmacological options to support adjuvant chemotherapies to prevent cancer recurrence. Such research demonstrates an exciting opportunity to repurpose therapeutics in order to improve the disease-free survival of patients with aggressive solid tumours.

SKCa- and Kv1-type potassium channels and cancer: Promising therapeutic targets?

Ion channels are transmembrane structures that allow the passage of ions across cell membranes such as the plasma membrane or the membranes of various organelles like the nucleus, endoplasmic reticulum, Golgi apparatus or mitochondria. Aberrant expression of various ion channels has been demonstrated in several tumor cells, leading to the promotion of key functions in tumor development, such as cell proliferation, resistance to apoptosis, angiogenesis, invasion and metastasis. The link between ion channels and these key biological functions that promote tumor development has led to the classification of cancers as oncochannelopathies. Among all ion channels, the most varied and numerous, forming the largest family, are the potassium channels, with over 70 genes encoding them in humans. In this context, this review will provide a non-exhaustive overview of the role of plasma membrane potassium channels in cancer, describing 1) the nomenclature and structure of potassium channels, 2) the role of these channels in the control of biological functions that promotes tumor development such as proliferation, migration and cell death, and 3) the role of two particular classes of potassium channels, the SKCa- and Kv1- type potassium channels in cancer progression.

The elusive Nav1.7: From pain to cancer

Voltage-gated sodium channels (Nav) are protein complexes that play fundamental roles in the transmission of signals in the nervous system, at the neuromuscular junction and in the heart. They are mainly present in excitable cells where they are responsible for triggering action potentials. Dysfunctions in Nav ion conduction give rise to a wide range of conditions, including neurological disorders, hypertension, arrhythmia, pain and cancer. Nav family 1 is composed of nine members, named numerically from 1 to 9. A Nax family also exists and is involved in body-fluid homeostasis. Of particular interest is Nav1.7 which is highly expressed in the sensory neurons of the dorsal root ganglions, where it is involved in the propagation of pain sensation. Gain-of-function mutations in Nav1.7 cause pathologies associated with increased pain sensitivity, while loss-of-function mutations cause reduced sensitivity to pain. The last decade has seen considerable effort in developing highly specific Nav1.7 blockers as pain medications, nonetheless, sufficient efficacy has yet to be achieved. Evidence is now conclusively showing that Navs are also present in many types of cancer cells, where they are involved in cell migration and invasiveness. Nav1.7 is anomalously expressed in endometrial, ovarian and lung cancers. Nav1.7 is also involved in Chemotherapy Induced Peripheral Neuropathy (CIPN). We propose that the knowledge and tools developed to study the role of Nav1.7 in pain can be exploited to develop novel cancer therapies. In this chapter, we illustrate the various aspects of Nav1.7 function in pain, cancer and CIPN, and outline therapeutic approaches.

Voltage-gated sodium channels: from roles and mechanisms in the metastatic cell behavior to clinical potential as therapeutic targets

During the second half of the last century, the prevalent knowledge recognized the voltage-gated sodium channels (VGSCs) as the proteins responsible for the generation and propagation of action potentials in excitable cells. However, over the last 25 years, new non-canonical roles of VGSCs in cancer hallmarks have been uncovered. Their dysregulated expression and activity have been associated with aggressive features and cancer progression towards metastatic stages, suggesting the potential use of VGSCs as cancer markers and prognostic factors. Recent work has elicited essential information about the signalling pathways modulated by these channels: coupling membrane activity to transcriptional regulation pathways, intracellular and extracellular pH regulation, invadopodia maturation, and proteolytic activity. In a promising scenario, the inhibition of VGSCs with FDA-approved drugs as well as with new synthetic compounds, reduces cancer cell invasion in vitro and cancer progression in vivo. The purpose of this review is to present an update regarding recent advances and ongoing efforts to have a better understanding of molecular and cellular mechanisms on the involvement of both pore-forming α and auxiliary β subunits of VGSCs in the metastatic processes, with the aim at proposing VGSCs as new oncological markers and targets for anticancer treatments.

Effect of Peritumoral Infiltration of Local Anesthetic Before Surgery on Survival in Early Breast Cancer

PURPOSE

Preventing metastases by using perioperative interventions has not been adequately explored. Local anesthesia blocks voltage-gated sodium channels and thereby prevents activation of prometastatic pathways. We conducted an open-label, multicenter randomized trial to test the impact of presurgical, peritumoral infiltration of local anesthesia on disease-free survival (DFS).

METHODS

Women with early breast cancer planned for upfront surgery without prior neoadjuvant treatment were randomly assigned to receive peritumoral injection of 0.5% lidocaine, 7-10 minutes before surgery (local anesthetics [LA] arm) or surgery without lidocaine (no LA arm). Random assignment was stratified by menopausal status, tumor size, and center. Participants received standard postoperative adjuvant treatment. Primary and secondary end points were DFS and overall survival (OS), respectively.

RESULTS

Excluding eligibility violations, 1,583 of 1,600 randomly assigned patients were included in this analysis (LA, 796; no LA, 804). At a median follow-up of 68 months, there were 255 DFS events (LA, 109; no LA, 146) and 189 deaths (LA, 79; no LA, 110). In LA and no LA arms, 5-year DFS rates were 86.6% and 82.6% (hazard ratio [HR], 0.74; 95% CI, 0.58 to 0.95; P = .017) and 5-year OS rates were 90.1% and 86.4%, respectively (HR, 0.71; 95% CI, 0.53 to 0.94; P = .019). The impact of LA was similar in subgroups defined by menopausal status, tumor size, nodal metastases, and hormone receptor and human epidermal growth factor receptor 2 status. Using competing risk analyses, in LA and no LA arms, 5-year cumulative incidence rates of locoregional recurrence were 3.4% and 4.5% (HR, 0.68; 95% CI, 0.41 to 1.11), and distant recurrence rates were 8.5% and 11.6%, respectively (HR, 0.73; 95% CI, 0.53 to 0.99). There were no adverse events because of lidocaine injection.

CONCLUSION

Peritumoral injection of lidocaine before breast cancer surgery significantly increases DFS and OS. Altering events at the time of surgery can prevent metastases in early breast cancer (CTRI/2014/11/005228).[Media: see text].

Sodium channels and the ionic microenvironment of breast tumours

Cancers of epithelial origin such as breast, prostate, cervical, gastric, colon and lung cancer account for a large proportion of deaths worldwide. Better treatment of metastasis, the main cause of cancer deaths, is therefore urgently required. Several of these tumours have been shown to have an abnormally high concentration of Na+ ([Na+ ]) and emerging evidence points to this accumulation being due to elevated intracellular [Na+ ]. This poses intriguing questions about the cellular mechanisms underlying Na+ dysregulation in cancer, and its pathophysiological significance. Elevated intracellular [Na+ ] may be due to alterations in activity of the Na+ /K+ -ATPase, and/or increased influx via Na+ channels and Na+ -linked transporters. Maintenance of the electrochemical Na+ gradient across the plasma membrane is vital to power many cellular processes that are highly active in cancer cells, including glucose and glutamine import. Na+ channels are also upregulated in cancer cells, which in turn promotes tumour growth and metastasis. For example, ENaC and ASICs are overexpressed in cancers, increasing invasion and proliferation. In addition, voltage-gated Na+ channels are also upregulated in a range of tumour types, where they promote metastatic cell behaviours via various mechanisms, including membrane potential depolarisation and altered pH regulation. Together, recent findings relating to elevated Na+ in the tumour microenvironment and how this may be regulated by several classes of Na+ channels provide a link between altered Na+ handling and poor clinical outcome. There are new opportunities to leverage this altered Na+ microenvironment for therapeutic benefit, as exemplified by several ongoing clinical trials.

Sodium regulates PLC and IP3 R-mediated calcium signaling in invasive breast cancer cells

Intracellular Ca2+ signaling and Na+ homeostasis are inextricably linked via ion channels and co-transporters, with alterations in the concentration of one ion having profound effects on the other. Evidence indicates that intracellular Na+ concentration ([Na+ ]i ) is elevated in breast tumors, and that aberrant Ca2+ signaling regulates numerous key cancer hallmark processes. The present study therefore aimed to determine the effects of Na+ depletion on intracellular Ca2+ handling in metastatic breast cancer cell lines. The relationship between Na+ and Ca2+ was probed using fura-2 and SBFI fluorescence imaging and replacement of extracellular Na+ with equimolar N-methyl-D-glucamine (0Na+ /NMDG) or choline chloride (0Na+ /ChoCl). In triple-negative MDA-MB-231 and MDA-MB-468 cells and Her2+ SKBR3 cells, but not ER+ MCF-7 cells, 0Na+ /NMDG and 0Na+ /ChoCl resulted in a slow, sustained depletion in [Na+ ]i that was accompanied by a rapid and sustained increase in intracellular Ca2+ concentration ([Ca2+ ]i ). Application of La3+ in nominal Ca2+ -free conditions had no effect on this response, ruling out reverse-mode NCX activity and Ca2+ entry channels. Moreover, the Na+ -linked [Ca2+ ]i increase was independent of membrane potential hyperpolarization (NS-1619), but was inhibited by pharmacological blockade of IP3 receptors (2-APB), phospholipase C (PLC, U73122) or following depletion of endoplasmic reticulum Ca2+ stores (cyclopiazonic acid). Thus, Na+ is linked to PLC/IP3 -mediated activation of endoplasmic reticulum Ca2+ release in metastatic breast cancer cells and this may have an important role in breast tumors where [Na+ ]i is perturbed.

Sodium channel-inhibiting drugs and cancer-specific survival: a population-based study of electronic primary care data

OBJECTIVES

Antiepileptic and antiarrhythmic drugs inhibit voltage-gated sodium (Na+) channels (VGSCs), and preclinical studies show that these medications reduce tumour growth, invasion and metastasis. We investigated the association between VGSC inhibitor use and survival in patients with breast, bowel and prostate cancer.

DESIGN

Retrospective cohort study.

SETTING

Individual electronic primary healthcare records extracted from the Clinical Practice Research Datalink.

PARTICIPANTS

Records for 132 996 patients with a diagnosis of breast, bowel or prostate cancer.

OUTCOME MEASURES

Adjusted Cox proportional hazards regression was used to analyse cancer-specific survival associated with exposure to VGSC inhibitors. Exposure to non-VGSC-inhibiting antiepileptic medication and other non-VGSC blockers were also considered. Drug exposure was treated as a time-varying covariate to account for immortal time bias.

RESULTS

During 1 002 225 person-years of follow-up, there were 42 037 cancer-specific deaths. 53 724 (40.4%) patients with cancer had at least one prescription for a VGSC inhibitor of interest. Increased risk of cancer-specific mortality was associated with exposure to this group of drugs (HR 1.59, 95% CI 1.56 to 1.63, p<0.001). This applied to VGSC-inhibiting tricyclic antidepressants (HR 1.61, 95% CI 1.50 to 1.65, p<0.001), local anaesthetics (HR 1.49, 95% CI 1.43 to 1.55, p<0.001) and anticonvulsants (HR 1.40, 95% CI 1.34 to 1.48, p<0.001) and persisted in sensitivity analyses. In contrast, exposure to VGSC-inhibiting class 1c and 1d antiarrhythmics was associated with significantly improved cancer-specific survival (HR 0.75, 95% CI 0.64 to 0.88, p<0.001 and HR 0.54, 95% CI 0.33 to 0.88, p=0.01, respectively).

CONCLUSIONS

Association between VGSC inhibitor use and mortality in patients with cancer varies according to indication. Exposure to VGSC-inhibiting antiarrhythmics, but not anticonvulsants, supports findings from preclinical data, with improved survival. However, additional confounding factors may underlie these associations, highlighting the need for further study.

One-Pot Synthesis of Bi2 S3 /TiO2 /rGO Heterostructure with Red Light-Driven Photovoltaic Effect for Remote Electrotherapy-Assisted Wound Repair

The past decades have witnessed the rational design of novel functional nanomaterials and the potential to revolutionize many applications. With the increasing focus on electronic biological processes, novel photovoltaic nanomaterials are highly expectable for empowering new therapeutic strategies such as establishing a link between endogenous electric field (EEF) and electrotherapy. Compared to traditional invasive stimulation, the light-initiating strategy has the advantages of non-invasion, non-power supply, and precise controllability. Whereas, common photoactivated materials require short-wavelength light excitation accompanied by poor tissue penetration and biohazard. Herein, by the construction of p-n heterostructured Bi₂ S₃ /TiO₂ /rGO (BTG) nanoparticles, broadener light absorption and higher light conversion than regular UV excitation are realized. Simultaneously, the photoelectric performance of BTG heterostructure, as well as the synergistic effect of Bi₂ S₃ morphology, are revealed. Besides, the rationally designed biomimetic hydrogel matrix consisting of collagen and hyaluronic acid provides appropriate bioactivity, interface adhesion, mechanical matching, and electron transfer. Therefore, the photovoltaic BTG-loaded matrix provides a platform of light-driven electrical stimulation, coupling the EEF to modulate the electrophysiological and regeneration microenvironment. The implementation of photoelectric stimulation holds broad prospects for non-drug therapy and electrical-related biological process modulation including osseointegration, nerve regeneration, electronic skin, and wound healing.

Voltage imaging reveals the dynamic electrical signatures of human breast cancer cells

Cancer cells feature a resting membrane potential (Vm) that is depolarized compared to normal cells, and express active ionic conductances, which factor directly in their pathophysiological behavior. Despite similarities to 'excitable' tissues, relatively little is known about cancer cell Vm dynamics. Here high-throughput, cellular-resolution Vm imaging reveals that Vm fluctuates dynamically in several breast cancer cell lines compared to non-cancerous MCF-10A cells. We characterize Vm fluctuations of hundreds of human triple-negative breast cancer MDA-MB-231 cells. By quantifying their Dynamic Electrical Signatures (DESs) through an unsupervised machine-learning protocol, we identify four classes ranging from "noisy" to "blinking/waving". The Vm of MDA-MB-231 cells exhibits spontaneous, transient hyperpolarizations inhibited by the voltage-gated sodium channel blocker tetrodotoxin, and by calcium-activated potassium channel inhibitors apamin and iberiotoxin. The Vm of MCF-10A cells is comparatively static, but fluctuations increase following treatment with transforming growth factor-β1, a canonical inducer of the epithelial-to-mesenchymal transition. These data suggest that the ability to generate Vm fluctuations may be a property of hybrid epithelial-mesenchymal cells or those originated from luminal progenitors.

Sodium accumulation in breast cancer predicts malignancy and treatment response

BACKGROUND

Breast cancer remains a leading cause of death in women and novel imaging biomarkers are urgently required. Here, we demonstrate the diagnostic and treatment-monitoring potential of non-invasive sodium (23Na) MRI in preclinical models of breast cancer.

METHODS

Female Rag2-/- Il2rg-/- and Balb/c mice bearing orthotopic breast tumours (MDA-MB-231, EMT6 and 4T1) underwent MRI as part of a randomised, controlled, interventional study. Tumour biology was probed using ex vivo fluorescence microscopy and electrophysiology.

RESULTS

23Na MRI revealed elevated sodium concentration ([Na+]) in tumours vs non-tumour regions. Complementary proton-based diffusion-weighted imaging (DWI) linked elevated tumour [Na+] to increased cellularity. Combining 23Na MRI and DWI measurements enabled superior classification accuracy of tumour vs non-tumour regions compared with either parameter alone. Ex vivo assessment of isolated tumour slices confirmed elevated intracellular [Na+] ([Na+]i); extracellular [Na+] ([Na+]e) remained unchanged. Treatment with specific inward Na+ conductance inhibitors (cariporide, eslicarbazepine acetate) did not affect tumour [Na+]. Nonetheless, effective treatment with docetaxel reduced tumour [Na+], whereas DWI measures were unchanged.

CONCLUSIONS

Orthotopic breast cancer models exhibit elevated tumour [Na+] that is driven by aberrantly elevated [Na+]i. Moreover, 23Na MRI enhances the diagnostic capability of DWI and represents a novel, non-invasive biomarker of treatment response with superior sensitivity compared to DWI alone.

Subcellular dynamics and functional activity of the cleaved intracellular domain of the Na+ channel β1 subunit

The voltage-gated Na⁺ channel β1 subunit, encoded by SCN1B, regulates cell surface expression and gating of α subunits and participates in cell adhesion. β1 is cleaved by α/β and γ-secretases, releasing an extracellular domain and intracellular domain (ICD), respectively. Abnormal SCN1B expression/function is linked to pathologies including epilepsy, cardiac arrhythmia, and cancer. In this study, we sought to determine the effect of secretase cleavage on β1 function in breast cancer cells. Using a series of GFP-tagged β1 constructs, we show that β1-GFP is mainly retained intracellularly, particularly in the endoplasmic reticulum and endolysosomal pathway, and accumulates in the nucleus. Reduction in endosomal β1-GFP levels occurred following γ-secretase inhibition, implicating endosomes and/or the preceding plasma membrane as important sites for secretase processing. Using live-cell imaging, we also report β1ICD-GFP accumulation in the nucleus. Furthermore, β1-GFP and β1ICD-GFP both increased Na⁺ current, whereas β1STOP-GFP, which lacks the ICD, did not, thus highlighting that the β1-ICD is necessary and sufficient to increase Na⁺ current measured at the plasma membrane. Importantly, although the endogenous Na⁺ current expressed in MDA-MB-231 cells is tetrodotoxin (TTX)-resistant (carried by Na_v1.5), the Na⁺ current increased by β1-GFP or β1ICD-GFP was TTX-sensitive. Finally, we found β1-GFP increased mRNA levels of the TTX-sensitive α subunits SCN1A/Na_v1.1 and SCN9A/Na_v1.7. Taken together, this work suggests that the β1-ICD is a critical regulator of α subunit function in cancer cells. Our data further highlight that γ-secretase may play a key role in regulating β1 function in breast cancer.

A computational model of organism development and carcinogenesis resulting from cells' bioelectric properties and communication

A sound theory of biological organization is clearly missing for a better interpretation of observational results and faster progress in understanding life complexity. The availability of such a theory represents a fundamental progress in explaining both normal and pathological organism development. The present work introduces a computational implementation of some principles of a theory of organism development, namely that the default state of cells is proliferation and motility, and includes the principle of variation and organization by closure of constraints. In the present model, the bioelectric context of cells and tissue is the field responsible for organization, as it regulates cell proliferation and the level of communication driving the system's evolution. Starting from a depolarized (proliferative) cell, the organism grows to a certain size, limited by the increasingly polarized state after successive proliferation events. The system reaches homeostasis, with a depolarized core (proliferative cells) surrounded by a rim of polarized cells (non-proliferative in this condition). This state is resilient to cell death (random or due to injure) and to limited depolarization (potentially carcinogenic) events. Carcinogenesis is introduced through a localized event (a spot of depolarized cells) or by random depolarization of cells in the tissue, which returns cells to their initial proliferative state. The normalization of the bioelectric condition can reverse this out-of-equilibrium state to a new homeostatic one. This simplified model of embryogenesis, tissue organization and carcinogenesis, based on non-excitable cells' bioelectric properties, can be made more realistic with the introduction of other components, like biochemical fields and mechanical interactions, which are fundamental for a more faithful representation of reality. However, even a simple model can give insight for new approaches in complex systems and suggest new experimental tests, focused in its predictions and interpreted under a new paradigm.

Anti-invasive effects of minoxidil on human breast cancer cells: combination with ranolazine

A plethora of ion channels have been shown to be involved systemically in the pathophysiology of cancer and ion channel blockers can produce anti-metastatic effects. However, although ion channels are known to frequently function in concerted action, little is known about possible combined effects of ion channel modulators on metastatic cell behaviour. Here, we investigated functional consequences of pharmacologically modulating ATP-gated potassium (K_ATP) channel and voltage-gated sodium channel (VGSC) activities individually and in combination. Two triple-negative human breast cancer cell lines were used: MDA-MB-231 and MDA-MB-468, the latter mainly for comparison. Most experiments were carried out on hypoxic cells. Electrophysiological effects were studied by whole-cell patch clamp recording. Minoxidil (a K_ATP channel opener) and ranolazine (a blocker of the VGSC persistent current) had no effect on cell viability and proliferation, alone or in combination. In contrast, invasion was significantly reduced in a dose-dependent manner by clinical concentrations of minoxidil and ranolazine. Combining the two drugs produced significant additive effects at concentrations as low as 0.625 μM ranolazine and 2.5 μM minoxidil. Electrophysiologically, acute application of minoxidil shifted VGSC steady-state inactivation to more hyperpolarised potentials and slowed recovery from inactivation, consistent with inhibition of VGSC activation. We concluded (i) that clinically relevant doses of minoxidil and ranolazine individually could inhibit cellular invasiveness dose dependently and (ii) that their combination was additionally effective. Accordingly, ranolazine, minoxidil and their combination may be repurposed as novel anti-metastatic agents.

Ion Transporting Proteins and Cancer: Progress and Perspectives

Ion transporting proteins (ITPs) comprise a wide range of ion channels, exchangers, pumps and ionotropic receptors many of which are expressed in tumours and contribute dynamically to the different components and stages of the complex cancer process, from initiation to metastasis. In this promising major field of biomedical research, several candidate ITPs have emerged as clinically viable. Here, we consider a series of general issues concerning the oncological potential of ITPs focusing on voltage-gated sodium channels as a 'case study'. First, we outline some key properties of 'cancer' as a whole. These include epigenetics, stemness, metastasis, heterogeneity, neuronal characteristics and bioelectricity. Cancer specificity of ITP expression is evaluated in relation to tissue restriction, splice variance, functional specificity and macro-molecular complexing. As regards clinical potential, diagnostics is covered with emphasis on enabling early detection. For therapeutics, we deal with molecular approaches, drug repurposing and combinations. Importantly, we emphasise the need for carefully designed clinical trials. We highlight also the area of 'social responsibility' and the need to involve the public (cancer patients and healthy individuals) in the work of cancer research professionals as well as clinicians. In advising patients how best to manage cancer, and live with it, we offer the following four principles: Awareness and prevention, early detection, specialist, integrated care, and psychological support. Finally, we highlight four key prerequisites for commercialisation of ITP-based technologies against cancer. We conclude that ITPs offer significant potential as regards both understanding the intricacies of the complex process of cancer and for developing much needed novel therapies.

Harnessing the Membrane Potential to Combat Cancer Progression

Rapid fluctuations in the plasma membrane potential (Vm) provide the basis underlying the action potential waveform in electrically excitable cells; however, a growing body of literature shows that the Vm is also functionally instructive in nonexcitable cells, including cancer cells. Various ion channels play a key role in setting and fine tuning the Vm in cancer and stromal cells within the tumor microenvironment (TME), raising the possibility that the Vm could be targeted therapeutically using ion channel-modulating compounds. Emerging evidence points to the Vm as a viable therapeutic target, given its functional significance in regulating cell cycle progression, migration, invasion, immune infiltration, and pH regulation. Several compounds are now undergoing clinical trials and there is increasing interest in therapeutic manipulation of the Vm via application of pulsed electric fields. The purpose of this article is to update the reader on the significant recent and ongoing progress to elucidate the functional significance of Vm regulation in tumors, to highlight key remaining questions and the prospect of future therapeutic targeting. In particular, we focus on key developments in understanding the functional consequences of Vm alteration on tumor development via the activation of small GTPase (K-Ras and Rac1) signaling, as well as the impact of Vm changes within the heterogeneous TME on immune cell function and cancer progression.

Ion Channel Drugs Suppress Cancer Phenotype in NG108-15 and U87 Cells: Toward Novel Electroceuticals for Glioblastoma

Glioblastoma is a lethal brain cancer that commonly recurs after tumor resection and chemotherapy treatment. Depolarized resting membrane potentials and an acidic intertumoral extracellular pH have been associated with a proliferative state and drug resistance, suggesting that forced hyperpolarization and disruption of proton pumps in the plasma membrane could be a successful strategy for targeting glioblastoma overgrowth. We screened 47 compounds and compound combinations, most of which were ion-modulating, at different concentrations in the NG108-15 rodent neuroblastoma/glioma cell line. A subset of these were tested in the U87 human glioblastoma cell line. A FUCCI cell cycle reporter was stably integrated into both cell lines to monitor proliferation and cell cycle response. Immunocytochemistry, electrophysiology, and a panel of physiological dyes reporting voltage, calcium, and pH were used to characterize responses. The most effective treatments on proliferation in U87 cells were combinations of NS1643 and pantoprazole; retigabine and pantoprazole; and pantoprazole or NS1643 with temozolomide. Marker analysis and physiological dye signatures suggest that exposure to bioelectric drugs significantly reduces proliferation, makes the cells senescent, and promotes differentiation. These results, along with the observed low toxicity in human neurons, show the high efficacy of electroceuticals utilizing combinations of repurposed FDA approved drugs.

Inhibition of the Na+/K+-ATPase by cardiac glycosides suppresses expression of the IDO1 immune checkpoint in cancer cells by reducing STAT1 activation

Despite extensive basic and clinical research on immune checkpoint regulatory pathways, little is known about the effects of the ionic tumor microenvironment on immune checkpoint expression and function. Here we describe a mechanistic link between Na+/K+-ATPase (NKA) inhibition and activity of the immune checkpoint protein indoleamine-pyrrole 2',3'-dioxygenase 1 (IDO1). We found that IDO1 was necessary and sufficient for production of kynurenine, a downstream tryptophan metabolite, in cancer cells. We developed a spectrophotometric assay to screen a library of 31 model ion transport-targeting compounds for potential effects on IDO1 function in A549 lung and MDA-MB-231 breast cancer cells. This revealed that the cardiac glycosides ouabain and digoxin inhibited kynurenine production at concentrations that did not affect cell survival. NKA inhibition by ouabain and digoxin resulted in increased intracellular Na+ levels and downregulation of IDO1 mRNA and protein levels, which was consistent with the reduction in kynurenine levels. Knockdown of ATP1A1, the ɑ1 subunit of the NKA and target of cardiac glycosides, increased Na+ levels to a lesser extent than cardiac glycoside treatment and did not affect IDO1 expression. However, ATP1A1 knockdown significantly enhanced the effect of cardiac glycosides on IDO1 expression and kynurenine production. Mechanistically, we show that cardiac glycoside treatment resulted in curtailing the length of phosphorylation-mediated stabilization of STAT1, a transcriptional regulator of IDO1 expression, an effect enhanced by ATP1A1 knockdown. Our findings reveal cross talk between ionic modulation via cardiac glycosides and immune checkpoint protein expression in cancer cells with broad mechanistic and clinical implications.

Discovering the Triad between Nav1.5, Breast Cancer, and the Immune System: A Fundamental Review and Future Perspectives

Nav1.5 is one of the nine voltage-gated sodium channel-alpha subunit (VGSC-α) family members. The Nav1.5 channel typically carries an inward sodium ion current that depolarises the membrane potential during the upstroke of the cardiac action potential. The neonatal isoform of Nav1.5, nNav1.5, is produced via VGSC-α alternative splicing. nNav1.5 is known to potentiate breast cancer metastasis. Despite their well-known biological functions, the immunological perspectives of these channels are poorly explored. The current review has attempted to summarise the triad between Nav1.5 (nNav1.5), breast cancer, and the immune system. To date, there is no such review available that encompasses these three components as most reviews focus on the molecular and pharmacological prospects of Nav1.5. This review is divided into three major subsections: (1) the review highlights the roles of Nav1.5 and nNav1.5 in potentiating the progression of breast cancer, (2) focuses on the general connection between breast cancer and the immune system, and finally (3) the review emphasises the involvements of Nav1.5 and nNav1.5 in the functionality of the immune system and the immunogenicity. Compared to the other subsections, section three is pretty unexploited; it would be interesting to study this subsection as it completes the triad.

Potassium channel-driven bioelectric signalling regulates metastasis in triple-negative breast cancer

BACKGROUND

There is a critical need to better understand the mechanisms that drive local cell invasion and metastasis to develop new therapeutics targeting metastatic disease. Bioelectricity is an important mediator of cellular processes and changes in the resting membrane potential (RMP) are associated with increased cancer cell invasion. However, whether the RMP can be used to target invading cancer cells is unknown.

METHODS

We employed both genetic and pharmacological manipulation of potassium channel activity and characterized the effects on breast cancer cell migration and invasion in vitro, and metastasis in an animal model of breast cancer.

FINDINGS

Our data demonstrate that altering the RMP of triple-negative breast cancer (TNBC) cells by manipulating potassium channel expression increases in vitro invasion, in vivo tumour growth and metastasis, and is accompanied by changes in gene expression associated with cell adhesion.

INTERPRETATION

We describe a novel mechanism for RMP-mediated cell migration involving cadherin-11 and the MAPK pathway. Importantly, we identify a new strategy to target metastatic TNBC in vivo by repurposing an FDA-approved potassium channel blocker. Our results demonstrate that bioelectricity regulates cancer cell invasion and metastasis which could lead to a new class of therapeutics for patients with metastatic disease.

FUNDING

This work was supported by the National Institutes of Health (R00-CA207866 to M.J.O.), Tufts University (Start-up funds from the School of Engineering to M.J.O., Tufts Collaborates Award to M.J.O. and M.L.), Allen Discovery centre program (Paul G. Allen Frontiers Group (12,171) to M.L.), and Breast Cancer Alliance Young Investigator Grant to M.J.O, Laidlaw Scholar funding to D.S. M.L. also gratefully acknowledges support of the Barton Family Foundation.

Pharmacological and nutritional targeting of voltage-gated sodium channels in the treatment of cancers

Voltage-gated sodium (NaV) channels, initially characterized in excitable cells, have been shown to be aberrantly expressed in non-excitable cancer tissues and cells from epithelial origins such as in breast, lung, prostate, colon, and cervix, whereas they are not expressed in cognate non-cancer tissues. Their activity was demonstrated to promote aggressive and invasive potencies of cancer cells, both in vitro and in vivo, whereas their deregulated expression in cancer tissues has been associated with metastatic progression and cancer-related death. This review proposes NaV channels as pharmacological targets for anticancer treatments providing opportunities for repurposing existing NaV-inhibitors or developing new pharmacological and nutritional interventions.

Targeting the Stromal Pro-Tumoral Hyaluronan-CD44 Pathway in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest malignancies. Present-day treatments have not shown real improvements in reducing the high mortality rate and the short survival of the disease. The average survival is less than 5% after 5 years. New innovative treatments are necessary to curtail the situation. The very dense pancreatic cancer stroma is a barrier that impedes the access of chemotherapeutic drugs and at the same time establishes a pro-proliferative symbiosis with the tumor, thus targeting the stroma has been suggested by many authors. No ideal drug or drug combination for this targeting has been found as yet. With this goal in mind, here we have explored a different complementary treatment based on abundant previous publications on repurposed drugs. The cell surface protein CD44 is the main receptor for hyaluronan binding. Many malignant tumors show over-expression/over-activity of both. This is particularly significant in pancreatic cancer. The independent inhibition of hyaluronan-producing cells, hyaluronan synthesis, and/or CD44 expression, has been found to decrease the tumor cell's proliferation, motility, invasion, and metastatic abilities. Targeting the hyaluronan-CD44 pathway seems to have been bypassed by conventional mainstream oncological practice. There are existing drugs that decrease the activity/expression of hyaluronan and CD44: 4-methylumbelliferone and bromelain respectively. Some drugs inhibit hyaluronan-producing cells such as pirfenidone. The association of these three drugs has never been tested either in the laboratory or in the clinical setting. We present a hypothesis, sustained by hard experimental evidence, suggesting that the simultaneous use of these nontoxic drugs can achieve synergistic or added effects in reducing invasion and metastatic potential, in PDAC. A non-toxic, low-cost scheme for inhibiting this pathway may offer an additional weapon for treating pancreatic cancer.

TRP Channels Regulation of Rho GTPases in Brain Context and Diseases

Neurological and neuropsychiatric disorders are mediated by several pathophysiological mechanisms, including developmental and degenerative abnormalities caused primarily by disturbances in cell migration, structural plasticity of the synapse, and blood-vessel barrier function. In this context, critical pathways involved in the pathogenesis of these diseases are related to structural, scaffolding, and enzymatic activity-bearing proteins, which participate in Ca²⁺- and Ras Homologs (Rho) GTPases-mediated signaling. Rho GTPases are GDP/GTP binding proteins that regulate the cytoskeletal structure, cellular protrusion, and migration. These proteins cycle between GTP-bound (active) and GDP-bound (inactive) states due to their intrinsic GTPase activity and their dynamic regulation by GEFs, GAPs, and GDIs. One of the most important upstream inputs that modulate Rho GTPases activity is Ca²⁺ signaling, positioning ion channels as pivotal molecular entities for Rho GTPases regulation. Multiple non-selective cationic channels belonging to the Transient Receptor Potential (TRP) family participate in cytoskeletal-dependent processes through Ca²⁺-mediated modulation of Rho GTPases. Moreover, these ion channels have a role in several neuropathological events such as neuronal cell death, brain tumor progression and strokes. Although Rho GTPases-dependent pathways have been extensively studied, how they converge with TRP channels in the development or progression of neuropathologies is poorly understood. Herein, we review recent evidence and insights that link TRP channels activity to downstream Rho GTPase signaling or modulation. Moreover, using the TRIP database, we establish associations between possible mediators of Rho GTPase signaling with TRP ion channels. As such, we propose mechanisms that might explain the TRP-dependent modulation of Rho GTPases as possible pathways participating in the emergence or maintenance of neuropathological conditions.

Inhibitory Effect of Eslicarbazepine Acetate and S-Licarbazepine on Nav1.5 Channels

Eslicarbazepine acetate (ESL) is a dibenzazepine anticonvulsant approved as adjunctive treatment for partial-onset epileptic seizures. Following first pass hydrolysis of ESL, S-licarbazepine (S-Lic) represents around 95% of circulating active metabolites. S-Lic is the main enantiomer responsible for anticonvulsant activity and this is proposed to be through the blockade of voltage-gated Na⁺ channels (VGSCs). ESL and S-Lic both have a voltage-dependent inhibitory effect on the Na⁺ current in N1E-115 neuroblastoma cells expressing neuronal VGSC subtypes including Na_v1.1, Na_v1.2, Na_v1.3, Na_v1.6, and Na_v1.7. ESL has not been associated with cardiotoxicity in healthy volunteers, although a prolongation of the electrocardiographic PR interval has been observed, suggesting that ESL may also inhibit cardiac Na_v1.5 isoform. However, this has not previously been studied. Here, we investigated the electrophysiological effects of ESL and S-Lic on Na_v1.5 using whole-cell patch clamp recording. We interrogated two model systems: (1) MDA-MB-231 metastatic breast carcinoma cells, which endogenously express the "neonatal" Na_v1.5 splice variant, and (2) HEK-293 cells stably over-expressing the "adult" Na_v1.5 splice variant. We show that both ESL and S-Lic inhibit transient and persistent Na⁺ current, hyperpolarise the voltage-dependence of fast inactivation, and slow the recovery from channel inactivation. These findings highlight, for the first time, the potent inhibitory effects of ESL and S-Lic on the Na_v1.5 isoform, suggesting a possible explanation for the prolonged PR interval observed in patients on ESL treatment. Given that numerous cancer cells have also been shown to express Na_v1.5, and that VGSCs potentiate invasion and metastasis, this study also paves the way for future investigations into ESL and S-Lic as potential invasion inhibitors.

pH-Channeling in Cancer: How pH-Dependence of Cation Channels Shapes Cancer Pathophysiology

Tissue acidosis plays a pivotal role in tumor progression: in particular, interstitial acidosis promotes tumor cell invasion, and is a major contributor to the dysregulation of tumor immunity and tumor stromal cells. The cell membrane and integral membrane proteins commonly act as important sensors and transducers of altered pH. Cell adhesion molecules and cation channels are prominent membrane proteins, the majority of which is regulated by protons. The pathophysiological consequences of proton-sensitive ion channel function in cancer, however, are scarcely considered in the literature. Thus, the main focus of this review is to highlight possible events in tumor progression and tumor immunity where the pH sensitivity of cation channels could be of great importance.

Targeting Ion Channels for Cancer Treatment: Current Progress and Future Challenges

Ion channels are key regulators of cancer cell pathophysiology. They contribute to a variety of processes such as maintenance of cellular osmolarity and membrane potential, motility (via interactions with the cytoskeleton), invasion, signal transduction, transcriptional activity and cell cycle progression, leading to tumour progression and metastasis. Ion channels thus represent promising targets for cancer therapy. Ion channels are attractive targets because many of them are expressed at the plasma membrane and a broad range of existing inhibitors are already in clinical use for other indications. However, many of the ion channels identified in cancer cells are also active in healthy normal cells, so there is a risk that certain blockers may have off-target effects on normal physiological function. This review describes recent research advances into ion channel inhibitors as anticancer therapeutics. A growing body of evidence suggests that a range of existing and novel Na⁺, K⁺, Ca²⁺ and Cl^- channel inhibitors may be effective for suppressing cancer cell proliferation, migration and invasion, as well as enhancing apoptosis, leading to suppression of tumour growth and metastasis, either alone or in combination with standard-of-care therapies. The majority of evidence to date is based on preclinical in vitro and in vivo studies, although there are several examples of ion channel-targeting strategies now reaching early phase clinical trials. Given the strong links between ion channel function and regulation of tumour growth, metastasis and chemotherapy resistance, it is likely that further work in this area will facilitate the development of new therapeutic approaches which will reach the clinic in the future.

Evaluation of active Rac1 levels in cancer cells: A case of misleading conclusions from immunofluorescence analysis

A large number of aggressive cancer cell lines display elevated levels of activated Rac1, a small GTPase widely implicated in cytoskeleton reorganization, cell motility, and metastatic dissemination. A commonly accepted methodological approach for detecting Rac1 activation in cancer cells involves the use of a conformation-sensitive antibody that detects the active (GTP-bound) Rac1 without interacting with the GDP-bound inactive form. This antibody has been extensively used in fixed cell immunofluorescence and immunohistochemistry. Taking advantage of prostate and pancreatic cancer cell models known to have high basal Rac1-GTP levels, here we have established that this antibody does not recognize Rac1 but rather detects the intermediate filament protein vimentin. Indeed, Rac1-null PC3 prostate cancer cells or cancer models with low levels of Rac1 activation still show a high signal with the anti-Rac1-GTP antibody, which is lost upon silencing of vimentin expression. Moreover, this antibody was unable to detect activated Rac1 in membrane ruffles induced by epidermal growth factor stimulation. These results have profound implications for the study of this key GTPase in cancer, particularly because a large number of cancer cell lines with characteristic mesenchymal features show simultaneous up-regulation of vimentin and high basal Rac1-GTP levels when measured biochemically. This misleading correlation can lead to assumptions about the validity of this antibody and inaccurate conclusions that may affect the development of appropriate therapeutic approaches for targeting the Rac1 pathway.

The Functional Role of Voltage-Gated Sodium Channel Nav1.5 in Metastatic Breast Cancer

Voltage-gated sodium channels (VGSCs), which are abnormally expressed in various types of cancers such as breast cancer, prostate cancer, lung cancer, and cervical cancer, are involved in the metastatic process of invasion and migration. Nav1.5 is a pore-forming α subunit of VGSC encoded by SCN5A. Various studies have demonstrated that Nav1.5, often as its neonatal splice form, is highly expressed in metastatic breast cancer cells. Abnormal activation and expression of Nav1.5 trigger a variety of cellular mechanisms, including changing H+ efflux, promoting epithelial-to-mesenchymal transition (EMT) and the expression of cysteine cathepsin, to potentiate the metastasis and invasiveness of breast cancer cells in vitro and in vivo. Here, we systematically review the latest available data on the pro-metastatic effect of Nav1.5 and its underlying mechanisms in breast cancer. We summarize the factors affecting Nav1.5 expression in breast cancer cells, and discuss the potential of Nav1.5 blockers serving as candidates for breast cancer treatment.

Human Breast Cancer Cells Demonstrate Electrical Excitability

Breast cancer is one of the most prevalent types of cancers worldwide and yet, its pathophysiology is poorly understood. Single-cell electrophysiological studies have provided evidence that membrane depolarization is implicated in the proliferation and metastasis of breast cancer. However, metastatic breast cancer cells are highly dynamic microscopic systems with complexities beyond a single-cell level. There is an urgent need for electrophysiological studies and technologies capable of decoding the intercellular signaling pathways and networks that control proliferation and metastasis, particularly at a population level. Hence, we present for the first time non-invasive in vitro electrical recordings of strongly metastatic MDA-MB-231 and weakly/non-metastatic MCF-7 breast cancer cell lines. To accomplish this, we fabricated an ultra-low noise sensor that exploits large-area electrodes, of 2 mm², which maximizes the double-layer capacitance and concomitant detection sensitivity. We show that the current recorded after adherence of the cells is dominated by the opening of voltage-gated sodium channels (VGSCs), confirmed by application of the highly specific inhibitor, tetrodotoxin (TTX). The electrical activity of MDA-MB-231 cells surpasses that of the MCF-7 cells, suggesting a link between the cells’ bioelectricity and invasiveness. We also recorded an activity pattern with characteristics similar to that of Random Telegraph Signal (RTS) noise. RTS patterns were less frequent than the asynchronous VGSC signals. The RTS noise power spectral density showed a Lorentzian shape, which revealed the presence of a low-frequency signal across MDA-MB-231 cell populations with propagation speeds of the same order as those reported for intercellular Ca²⁺ waves. Our recording platform paves the way for real-time investigations of the bioelectricity of cancer cells, their ionic/pharmacological properties and relationship to metastatic potential.

Voltage-dependent activation of Rac1 by Nav 1.5 channels promotes cell migration

Ion channels can regulate the plasma membrane potential (Vm ) and cell migration as a result of altered ion flux. However, the mechanism by which Vm regulates motility remains unclear. Here, we show that the Nav 1.5 sodium channel carries persistent inward Na+ current which depolarizes the resting Vm at the timescale of minutes. This Nav 1.5-dependent Vm depolarization increases Rac1 colocalization with phosphatidylserine, to which it is anchored at the leading edge of migrating cells, promoting Rac1 activation. A genetically encoded FRET biosensor of Rac1 activation shows that depolarization-induced Rac1 activation results in acquisition of a motile phenotype. By identifying Nav 1.5-mediated Vm depolarization as a regulator of Rac1 activation, we link ionic and electrical signaling at the plasma membrane to small GTPase-dependent cytoskeletal reorganization and cellular migration. We uncover a novel and unexpected mechanism for Rac1 activation, which fine tunes cell migration in response to ionic and/or electric field changes in the local microenvironment.

Hyponatremia and Cancer Progression: Possible Association with Sodium-Transporting Proteins

Hyponatremia, the phenomenon of serum sodium level falling below 135 mmol/L, is seen frequently in cancer patients and has been correlated with poor prognosis. Hyponatremia has classically been attributed to the "syndrome of inappropriate antidiuretic hormone secretion," leading to prolonged fluid retention. However, this is unlikely to be the only mechanism. In this study, we advance the hypothesis that upregulation of various sodium-transporting proteins during the cancer process makes a significant contribution to the pathophysiology of cancer-associated hyponatremia. Such sodium-transporting proteins include voltage-gated sodium channels, especially its hypoxia-promoted persistent current, epithelial sodium channels, and transient receptor potential channels. Thus, hyponatremia follows cancer, whereby drop in blood serum level occurs as a result of uptake of sodium from extracellular fluid by cancer cells. Indeed, the sodium content of cancer cells/tissues is higher than normal. In turn, the rise in the intracellular sodium concentration brings about a range of cellular effects, including extracellular acidification that promotes invasiveness and thus leads to poor prognosis. This perspective offers novel therapies for cancer and the associated hyponatremia.