Sodium accumulation in breast cancer predicts malignancy and treatment response

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.

Metabolic heterogeneity in tumor microenvironment - A novel landmark for immunotherapy

The surrounding non-cancer cells and tumor cells that make up the tumor microenvironment (TME) have various metabolic rhythms. TME metabolic heterogeneity is influenced by the intricate network of metabolic control within and between cells. DNA, protein, transport, and microbial levels are important regulators of TME metabolic homeostasis. The effectiveness of immunotherapy is also closely correlated with alterations in TME metabolism. The response of a tumor patient to immunotherapy is influenced by a variety of variables, including intracellular metabolic reprogramming, metabolic interaction between cells, ecological changes within and between tumors, and general dietary preferences. Although immunotherapy and targeted therapy have made great strides, their use in the accurate identification and treatment of tumors still has several limitations. The function of TME metabolic heterogeneity in tumor immunotherapy is summarized in this article. It focuses on how metabolic heterogeneity develops and is regulated as a tumor progresses, the precise molecular mechanisms and potential clinical significance of imbalances in intracellular metabolic homeostasis and intercellular metabolic coupling and interaction, as well as the benefits and drawbacks of targeted metabolism used in conjunction with immunotherapy. This offers insightful knowledge and important implications for individualized tumor patient diagnosis and treatment plans in the future.

Bioelectric pharmacology of cancer: A systematic review of ion channel drugs affecting the cancer phenotype

Cancer is a pernicious and pressing medical problem; moreover, it is a failure of multicellular morphogenesis that sheds much light on evolutionary developmental biology. Numerous classes of pharmacological agents have been considered as cancer therapeutics and evaluated as potential carcinogenic agents; however, these are spread throughout the primary literature. Here, we briefly review recent work on ion channel drugs as promising anti-cancer treatments and present a systematic review of the known cancer-relevant effects of 109 drugs targeting ion channels. The roles of ion channels in cancer are consistent with the importance of bioelectrical parameters in cell regulation and with the functions of bioelectric signaling in morphogenetic signals that act as cancer suppressors. We find that compounds that are well-known for having targets in the nervous system, such as voltage-gated ion channels, ligand-gated ion channels, proton pumps, and gap junctions are especially relevant to cancer. Our review suggests further opportunities for the repurposing of numerous promising candidates in the field of cancer electroceuticals.

23Na MRI: inter-reader reproducibility of normal fibroglandular sodium concentration measurements at 3 T

BACKGROUND

To study the reproducibility of 23Na magnetic resonance imaging (MRI) measurements from breast tissue in healthy volunteers.

METHODS

Using a dual-tuned bilateral 23Na/1H breast coil at 3-T MRI, high-resolution 23Na MRI three-dimensional cones sequences were used to quantify total sodium concentration (TSC) and fluid-attenuated sodium concentration (FASC). B1-corrected TSC and FASC maps were created. Two readers manually measured mean, minimum and maximum TSC and mean FASC values using two sampling methods: large regions of interest (LROIs) and small regions of interest (SROIs) encompassing fibroglandular tissue (FGT) and the highest signal area at the level of the nipple, respectively. The reproducibility of the measurements and correlations between density, age and FGT apparent diffusion coefficient (ADC) values were evaluatedss.

RESULTS

Nine healthy volunteers were included. The inter-reader reproducibility of TSC and FASC using SROIs and LROIs was excellent (intraclass coefficient range 0.945-0.979, p < 0.001), except for the minimum TSC LROI measurements (p = 0.369). The mean/minimum LROI TSC and mean LROI FASC values were lower than the respective SROI values (p < 0.001); the maximum LROI TSC values were higher than the SROI TSC values (p = 0.009). TSC correlated inversely with age but not with FGT ADCs. The mean and maximum FGT TSC and FASC values were higher in dense breasts in comparison to non-dense breasts (p < 0.020).

CONCLUSIONS

The chosen sampling method and the selected descriptive value affect the measured TSC and FASC values, although the inter-reader reproducibility of the measurements is in general excellent.

RELEVANCE STATEMENT

23Na MRI at 3 T allows the quantification of TSC and FASC sodium concentrations. The sodium measurements should be obtained consistently in a uniform manner.

KEY POINTS

• 23Na MRI allows the quantification of total and fluid-attenuated sodium concentrations (TSC/FASC). • Sampling method (large/small region of interest) affects the TSC and FASC values. • Dense breasts have higher TSC and FASC values than non-dense breasts. • The inter-reader reproducibility of TSC and FASC measurements was, in general, excellent. • The results suggest the importance of stratifying the sodium measurements protocol.

Chronic High-Salt Diet Activates Tumor-Initiating Stem Cells Leading to Breast Cancer Proliferation

Several chronic inflammatory diseases have been linked to high-salt (HS) diets. Chronic inflammation is an established causative hallmark of cancer. However, a direct role of HS diets in tumorigenesis is yet to be defined. Previous orthotopic murine breast tumor studies have shown that short-term HS diets caused inhibition of tumor growth through the activation of cytotoxic adaptive immune responses. However, there have been experimental challenges in developing a viable chronic HS-diet-based murine tumor model. To address this, we have developed a novel chronic HS diet tumor model through the sequential passaging of tumor cells in mice under HS dietary conditions. Two orthotopic murine triple-negative breast cancer models, 4T1 tumor cells injected into BALB/c mice and Py230 tumor cells injected into C57Bl/6 mice, were utilized in our study. For the HS diet cohort, prior to orthotopic injection with tumor cells, the mice were kept on a 4% NaCl diet for 2 weeks. For the regular salt (RS) diet cohort, the mice were kept on a 1% NaCl diet. Following syngeneic cancer cell injection, tumors were allowed to grow for 28 days, following which they were collected to isolate immune cell-depleted cancer cells (passage 1, P1). The tumor cells from P1 were reinjected into the next set of non-tumor-bearing mice. This procedure was repeated for three cycles (P2-P4). In P1, compared to the RS diet cohort, we observed reduced tumor kinetics in both murine tumor models on the HS diet. In contrast, by P4, there was significantly higher tumor progression in the HS diet cohort over the RS diet cohort. Flow cytometry analysis demonstrated an 8-fold increase in tumor-initiating stem cells (TISCs) from P1 to P4 of the HS diet cohort, while there were no significant change in TISC frequency with sequential passaging in the RS diet cohort. Molecular studies showed enhanced expression of TGFβR2 and CD80 on TISCs isolated from the P4 HS diet cohort. In vitro studies demonstrated that TGFβ stimulation of these TISCs increased the cellular expression of CD80 molecules. Further, the chronic HS diet selectively induced the glycolytic metabolic phenotype over the mitochondrial oxidative phosphorylation phenotype in TISCs, which is needed for the production of metabolites during tumor cell differentiation and proliferation. The infiltrating CD8 and CD4 T-lymphocytes in P4 tumors demonstrated increased expression of the immune checkpoint inhibitor (ICI) CTLA4, a known binding partner of CD80, to cause immune exhaustion and pro-tumorigenic effects. Interestingly, anti-TGFβ monoclonal antibodies (mAbs) played a synergistic role in further enhancing the anti-tumor effect of anti-CTLA4 mAb. In summary, our findings demonstrated that chronic HS diet increased the frequency of TISCs in tumors leading to blunting of cytotoxic adaptive immune responses causing tumor proliferation. Furthermore, a combination of anti-TGFβ with current ICI-based immunotherapies could exert more favorable anti-cancer clinical outcomes.

Disrupting Na+ ion homeostasis and Na+/K+ ATPase activity in breast cancer cells directly modulates glycolysis in vitro and in vivo

BACKGROUND

Glycolytic flux is regulated by the energy demands of the cell. Upregulated glycolysis in cancer cells may therefore result from increased demand for adenosine triphosphate (ATP), however it is unknown what this extra ATP turnover is used for. We hypothesise that an important contribution to the increased glycolytic flux in cancer cells results from the ATP demand of Na+/K+-ATPase (NKA) due to altered sodium ion homeostasis in cancer cells.

METHODS

Live whole-cell measurements of intracellular sodium [Na+]i were performed in three human breast cancer cells (MDA-MB-231, HCC1954, MCF-7), in murine breast cancer cells (4T1), and control human epithelial cells MCF-10A using triple quantum filtered 23Na nuclear magnetic resonance (NMR) spectroscopy. Glycolytic flux was measured by 2H NMR to monitor conversion of [6,6-2H2]D-glucose to [2H]-labelled L-lactate at baseline and in response to NKA inhibition with ouabain. Intracellular [Na+]i was titrated using isotonic buffers with varying [Na+] and [K+] and introducing an artificial Na+ plasma membrane leak using the ionophore gramicidin-A. Experiments were carried out in parallel with cell viability assays, 1H NMR metabolomics of intracellular and extracellular metabolites, extracellular flux analyses and in vivo measurements in a MDA-MB-231 human-xenograft mouse model using 2-deoxy-2-[18F]fluoroglucose (18F-FDG) positron emission tomography (PET).

RESULTS

Intracellular [Na+]i was elevated in human and murine breast cancer cells compared to control MCF-10A cells. Acute inhibition of NKA by ouabain resulted in elevated [Na+]i and inhibition of glycolytic flux in all three human cancer cells which are ouabain sensitive, but not in the murine cells which are ouabain resistant. Permeabilization of cell membranes with gramicidin-A led to a titratable increase of [Na+]i in MDA-MB-231 and 4T1 cells and a Na+-dependent increase in glycolytic flux. This was attenuated with ouabain in the human cells but not in the murine cells. 18FDG PET imaging in an MDA-MB-231 human-xenograft mouse model recorded lower 18FDG tumour uptake when treated with ouabain while murine tissue uptake was unaffected.

CONCLUSIONS

Glycolytic flux correlates with Na+-driven NKA activity in breast cancer cells, providing evidence for the 'centrality of the [Na+]i-NKA nexus' in the mechanistic basis of the Warburg effect.

Blocking channels to metastasis: targeting sodium transport in breast cancer

The development of therapies that can suppress invasion and prevent metastasis, 'anti-metastatic drugs', is an important area of unmet therapeutic need. The new results of a recent open-label, multicentre randomised trial published in J Clin Oncol showed a significant disease-free survival (DFS) benefit for breast cancer patients receiving presurgical, peritumoral injection of lidocaine, an amide local anaesthetic, which blocks voltage-gated sodium channels (VGSCs). VGSCs are expressed on electrically excitable cells, including neurons and cardiomyocytes, where they sustain rapid membrane depolarisation during action potential firing. As a result of this key biophysical function, VGSCs are important drug targets for excitability-related disorders, including epilepsy, neuropathic pain, affective disorders and cardiac arrhythmia. A growing body of preclinical evidence highlights VGSCs as key protagonists in regulating altered sodium influx in breast cancer cells, thus driving invasion and metastasis. Furthermore, prescription of certain VGSC-inhibiting medications has been associated with reduced cancer incidence and improved survival in several observational studies. Thus, VGSC-inhibiting drugs already in clinical use may be ideal candidates for repurposing as possible anti-metastatic therapies. While these results are promising, further work is required to establish whether other VGSC inhibitors may afford superior metastasis suppression. Finally, increasing preclinical evidence suggests that several other ion channels are also key drivers of cancer hallmarks; thus, there are undoubtedly further opportunities to harness ion transport inhibition that should also be explored.

Recent technical developments and clinical research applications of sodium (23Na) MRI

Sodium is an essential ion that plays a central role in many physiological processes including the transmembrane electrochemical gradient and the maintenance of the body's homeostasis. Due to the crucial role of sodium in the human body, the sodium nucleus is a promising candidate for non-invasively assessing (patho-)physiological changes. Almost 10 years ago, Madelin et al. provided a comprehensive review of methods and applications of sodium (23Na) MRI (Madelin et al., 2014) [1]. More recent review articles have focused mainly on specific applications of 23Na MRI. For example, several articles covered 23Na MRI applications for diseases such as osteoarthritis (Zbyn et al., 2016, Zaric et al., 2020) [2,3], multiple sclerosis (Petracca et al., 2016, Huhn et al., 2019) [4,5] and brain tumors (Schepkin, 2016) [6], or for imaging certain organs such as the kidneys (Zollner et al., 2016) [7], the brain (Shah et al., 2016, Thulborn et al., 2018) [8,9], and the heart (Bottomley, 2016) [10]. Other articles have reviewed technical developments such as radiofrequency (RF) coils for 23Na MRI (Wiggins et al., 2016, Bangerter et al., 2016) [11,12], pulse sequences (Konstandin et al., 2014) [13], image reconstruction methods (Chen et al., 2021) [14], and interleaved/simultaneous imaging techniques (Lopez Kolkovsky et al., 2022) [15]. In addition, 23Na MRI topics have been covered in review articles with broader topics such as multinuclear MRI or ultra-high-field MRI (Niesporek et al., 2019, Hu et al., 2019, Ladd et al., 2018) [16-18]. During the past decade, various research groups have continued working on technical improvements to sodium MRI and have investigated its potential to serve as a diagnostic and prognostic tool. Clinical research applications of 23Na MRI have covered a broad spectrum of diseases, mainly focusing on the brain, cartilage, and skeletal muscle (see Fig. 1). In this article, we aim to provide a comprehensive summary of methodological and hardware developments, as well as a review of various clinical research applications of sodium (23Na) MRI in the last decade (i.e., published from the beginning of 2013 to the end of 2022).

Photoacoustic Chemical Imaging Sodium Nano-Sensor Utilizing a Solvatochromic Dye Transducer for In Vivo Application

Sodium has many vital and diverse roles in the human body, including maintaining the cellular pH, generating action potential, and regulating osmotic pressure. In cancer, sodium dysregulation has been correlated with tumor growth, metastasis, and immune cell inhibition. However, most in vivo sodium measurements are performed via Na23 NMR, which is handicapped by slow acquisition times, a low spatial resolution (in mm), and low signal-to-noise ratios. We present here a plasticizer-free, ionophore-based sodium-sensing nanoparticle that utilizes a solvatochromic dye transducer to circumvent the pH cross-sensitivity of most previously reported sodium nano-sensors. We demonstrate that this nano-sensor is non-toxic, boasts a 200 μM detection limit, and is over 1000 times more selective for sodium than potassium. Further, the in vitro photoacoustic calibration curve presented demonstrates the potential of this nano-sensor for performing the in vivo chemical imaging of sodium over the entire physiologically relevant concentration range.

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.

SCN5A channelopathy: arrhythmia, cardiomyopathy, epilepsy and beyond

Influx of sodium ions through voltage-gated sodium channels in cardiomyocytes is essential for proper electrical conduction within the heart. Both acquired conditions associated with sodium channel dysfunction (myocardial ischaemia, heart failure) as well as inherited disorders secondary to mutations in the gene SCN5A encoding for the cardiac sodium channel Nav1.5 are associated with life-threatening arrhythmias. Research in the last decade has uncovered the complex nature of Nav1.5 distribution, function, in particular within distinct subcellular subdomains of cardiomyocytes. Nav1.5-based channels furthermore display previously unrecognized non-electrogenic actions and may impact on cardiac structural integrity, leading to cardiomyopathy. Moreover, SCN5A and Nav1.5 are expressed in cell types other than cardiomyocytes as well as various extracardiac tissues, where their functional role in, e.g. epilepsy, gastrointestinal motility, cancer and the innate immune response is increasingly investigated and recognized. This review provides an overview of these novel insights and how they deepen our mechanistic knowledge on SCN5A channelopathies and Nav1.5 (dys)function. This article is part of the theme issue 'The heartbeat: its molecular basis and physiological mechanisms'.

Boosting intracellular sodium selectively kills hepatocarcinoma cells and induces hepatocellular carcinoma tumor shrinkage in mice

Pharmacological treatments for advanced hepatocellular carcinoma (HCC) have a partial efficacy. Augmented Na⁺ content and water retention are observed in human cancers and offer unexplored targets for anticancer therapies. Na⁺ levels are evaluated upon treatments with the antibiotic cation ionophore Monensin by fluorimetry, ICP-MS, ²³Na-MRI, NMR relaxometry, confocal or time-lapse analysis related to energy production, water fluxes and cell death, employing both murine and human HCC cell lines, primary murine hepatocytes, or HCC allografts in NSG mice. Na⁺ levels of HCC cells and tissue are 8-10 times higher than that of healthy hepatocytes and livers. Monensin further increases Na⁺ levels in HCC cells and in HCC allografts but not in primary hepatocytes and in normal hepatic and extrahepatic tissue. The Na⁺ increase is associated with energy depletion, mitochondrial Na⁺ load and inhibition of O₂ consumption. The Na⁺ increase causes an enhancement of the intracellular water lifetime and death of HCC cells, and a regression and necrosis of allograft tumors, without affecting the proliferating activity of either HCCs or healthy tissues. These observations indicate that HCC cells are, unlike healthy cells, energetically incapable of compensating and surviving a pharmacologically induced Na⁺ load, highlighting Na⁺ homeostasis as druggable target for HCC therapy.

Voltage-Gated Sodium Channel NaV1.7 Inhibitors with Potent Anticancer Activities in Medullary Thyroid Cancer Cells

Our results from quantitative RT-PCR, Western blotting, immunohistochemistry, and the tissue microarray of medullary thyroid cancer (MTC) cell lines and patient specimens confirm that VGSC subtype NaV1.7 is uniquely expressed in aggressive MTC and not expressed in normal thyroid cells and tissues. We establish the druggability of NaV1.7 in MTC by identifying a novel inhibitor (SV188) and investigate its mode of binding and ability to inhibit INa current in NaV1.7. The whole-cell patch-clamp studies of the SV188 in the NaV1.7 channels expressed in HEK-293 cells show that SV188 inhibited the INa current in NaV1.7 with an IC50 value of 3.6 µM by a voltage- and use-dependent blockade mechanism, and the maximum inhibitory effect is observed when the channel is open. SV188 inhibited the viability of MTC cell lines, MZ-CRC-1 and TT, with IC50 values of 8.47 μM and 9.32 μM, respectively, and significantly inhibited the invasion of MZ-CRC-1 cells by 35% and 52% at 3 μM and 6 μM, respectively. In contrast, SV188 had no effect on the invasion of TT cells derived from primary tumor, which have lower basal expression of NaV1.7. In addition, SV188 at 3 μM significantly inhibited the migration of MZ-CRC-1 and TT cells by 27% and 57%, respectively.

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.

A bioinformatics analysis: ZFHX4 is associated with metastasis and poor survival in ovarian cancer

Background

Metastasis was the major cause of the high mortality in ovarian cancer. Although some mechanisms of metastasis in ovarian cancer were proposed, few have been targeted in the clinical practice. In the study, we aimed to identify novel genes contributing to metastasis and poor clinical outcome in ovarian cancer from bioinformatics databases.

Methods

Studies collecting matched primary tumors and metastases from ovarian cancer patients were searched in the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) were screened by software R language. Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis for the DEGs were implemented by Metascape. Venn diagram was plotted to present overlapping DEGs. The associations between the overlapping DEGs and prognosis were tested by Cox proportional hazard regression model using a cohort of ovarian cancer patients from the TCGA database. Genes affecting patients’ outcomes significantly were served as hub genes. The mechanisms of the hub genes in promoting ovarian cancer metastasis were then predicted by R software.

Results

Two gene expression profiles (GSE30587 and GSE73168) met the inclusion criteria and were finally analyzed. A total of 259 genes were significantly differentially expressed in GSE30587, whereas 712 genes were in GSE73168. In GSE30587, DEGs were mainly involved in extracellular matrix (ECM) organization; For GSE73168, most of DEGs showed ion trans-membrane transport activity. There were 9 overlapping genes between the two datasets (RUNX2, FABP4, CLDN20, SVEP1, FAM169A, PGM5, ZFHX4, DCN and TAS2R50). ZFHX4 was proved to be an independent adverse prognostic factor for ovarian cancer patients (HR = 1.44, 95%CI: 1.13–1.83, p = 0.003). Mechanistically, ZFHX4 was positively significantly correlated with epithelial-mesenchymal transition (EMT) markers (r = 0.54, p = 2.59 × 10⁻²⁹) and ECM-related genes (r = 0.52, p = 2.86 × 10⁻²⁷).

Conclusions

ZFHX4 might promote metastasis in ovarian cancer by regulating EMT and reprogramming ECM. For clinical applications, ZFHX4 was expected to be a prognostic biomarker for ovarian cancer metastasis.