Epigenetic dysregulation of KCa 3.1 channels induces poor prognosis in lung cancer

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.

Intracellular acidity impedes KCa3.1 activation by Riluzole and SKA-31

Background

The unique microenvironment in tumors inhibits the normal functioning of tumor-infiltrating lymphocytes, leading to immune evasion and cancer progression. Over-activation of KCa3.1 using positive modulators has been proposed to rescue the anti-tumor response. One of the key characteristics of the tumor microenvironment is extracellular acidity. Herein, we analyzed how intra- and extracellular pH affects K+ currents through KCa3.1 and if the potency of two of its positive modulators, Riluzole and SKA-31, is pH sensitive.

Methods

Whole-cell patch-clamp was used to measure KCa3.1 currents either in activated human peripheral lymphocytes or in CHO cells transiently transfected with either the H192A mutant or wild-type hKCa3.1 in combination with T79D-Calmodulin, or with KCa2.2.

Results

We found that changes in the intra- and extracellular pH minimally influenced the KCa3.1-mediated K+ current. Extracellular pH, in the range of 6.0-8.0, does not interfere with the capacity of Riluzole and SKA-31 to robustly activate the K+ currents through KCa3.1. Contrariwise, an acidic intracellular solution causes a slow, but irreversible loss of potency of both the activators. Using different protocols of perfusion and depolarization we demonstrated that the loss of potency is strictly time and pH-dependent and that this peculiar effect can be observed with a structurally similar channel KCa2.2. While two different point mutations of both KCa3.1 (H192A) and its associated protein Calmodulin (T79D) do not limit the effect of acidity, increasing the cytosolic Ca2+ concentration to saturating levels eliminated the loss-of-potency phenotype.

Conclusion

Based on our data we conclude that KCa3.1 currents are not sensitive the either the intracellular or the extracellular pH in the physiological and pathophysiological range. However, intracellular acidosis in T cells residing in the tumor microenvironment could hinder the potentiating effect of KCa3.1 positive modulators administered to boost their activity. Further research is warranted both to clarify the molecular interactions between the modulators and KCa3.1 at different intracellular pH conditions and to define whether this loss of potency can be observed in cancer models as well.

Overexpression of KCNN4 channels in principal neurons produces an anti-seizure effect without reducing their coding ability

Gene therapy offers a potential alternative to the surgical treatment of epilepsy, which affects millions of people and is pharmacoresistant in ~30% of cases. Aimed at reducing the excitability of principal neurons, the engineered expression of K+ channels has been proposed as a treatment due to the outstanding ability of K+ channels to hyperpolarize neurons. However, the effects of K+ channel overexpression on cell physiology remain to be investigated. Here we report an adeno-associated virus (AAV) vector designed to reduce epileptiform activity specifically in excitatory pyramidal neurons by expressing the human Ca2+-gated K+ channel KCNN4 (KCa3.1). Electrophysiological and pharmacological experiments in acute brain slices showed that KCNN4-transduced cells exhibited a Ca2+-dependent slow afterhyperpolarization that significantly decreased the ability of KCNN4-positive neurons to generate high-frequency spike trains without affecting their lower-frequency coding ability and action potential shapes. Antiepileptic activity tests showed potent suppression of pharmacologically induced seizures in vitro at both single cell and local field potential levels with decreased spiking during ictal discharges. Taken together, our findings strongly suggest that the AAV-based expression of the KCNN4 channel in excitatory neurons is a promising therapeutic intervention as gene therapy for epilepsy.

Targeting KCa3.1 channels to overcome erlotinib resistance in non-small cell lung cancer cells

Almost all non-small cell lung cancer (NSCLC) patients initially responding to EGFR tyrosine kinase inhibitors (TKIs) develop acquired resistance. Since KCa3.1 channels, expressed in mitochondria and plasma membrane, regulate similar behavioral traits of NSCLC cells as EGFR, we hypothesized that their blockade contributes to overcoming EGFR-TKI resistance. Meta-analysis of microarray data revealed that KCa3.1 channel expression in erlotinib-resistant NSCLC cells correlates with that of genes of integrin and apoptosis pathways. Using erlotinib-sensitive and -resistant NSCLC cells we monitored the role of mitochondrial KCa3.1 channels in integrin signaling by studying cell-matrix adhesion with single-cell force spectroscopy. Apoptosis was quantified with fluorescence-based assays. The function of mitochondrial KCa3.1 channels in these processes was assessed by measuring the mitochondrial membrane potential and by quantifying ROS production. Functional assays were supplemented by biochemical analyses. We show that KCa3.1 channel inhibition with senicapoc in erlotinib-resistant NSCLC cells increases cell adhesion by increasing β1-integrin expression, that in turn depends on mitochondrial ROS release. Increased adhesion impairs migration of NSCLC cells in a 3D matrix. At the same time, the senicapoc-dependent ROS production induces cytochrome C release and triggers apoptosis of erlotinib-resistant NSCLC cells. Thus, KCa3.1 channel blockade overcomes EGFR-TKI resistance by inhibiting NSCLC motility and inducing apoptosis.

IK Channel-Independent Effects of Clotrimazole and Senicapoc on Cancer Cells Viability and Migration

Many studies highlighted the importance of the IK channel for the proliferation and the migration of different types of cancer cells, showing how IK blockers could slow down cancer growth. Based on these data, we wanted to characterize the effects of IK blockers on melanoma metastatic cells and to understand if such effects were exclusively IK-dependent. For this purpose, we employed two different blockers, namely clotrimazole and senicapoc, and two cell lines: metastatic melanoma WM266-4 and pancreatic cancer Panc-1, which is reported to have little or no IK expression. Clotrimazole and senicapoc induced a decrease in viability and the migration of both WM266-4 and Panc-1 cells irrespective of IK expression levels. Patch-clamp experiments on WM266-4 cells revealed Ca2+-dependent, IK-like, clotrimazole- and senicapoc-sensitive currents, which could not be detected in Panc-1 cells. Neither clotrimazole nor senicapoc altered the intracellular Ca2+ concentration. These results suggest that the effects of IK blockers on cancer cells are not strictly dependent on a robust presence of the channel in the plasma membrane, but they might be due to off-target effects on other cellular targets or to the blockade of IK channels localized in intracellular organelles.

Ion channels in lung cancer: biological and clinical relevance

Despite improvements in treatment, lung cancer is still a major health problem worldwide. Among lung cancer subtypes, the most frequent is represented by adenocarcinoma (belonging to the Non-Small Cell Lung Cancer class) although the most challenging and harder to treat is represented by Small Cell Lung Cancer, that occurs at lower frequency but has the worst prognosis. For these reasons, the standard of care for these patients is represented by a combination of surgery, radiation therapy and chemotherapy. In this view, searching for novel biomarkers that might help both in diagnosis and therapy is mandatory. In the last 30 years it was demonstrated that different families of ion channels are overexpressed in both lung cancer cell lines and primary tumours. The altered ion channel profile may be advantageous for diagnostic and therapeutic purposes since most of them are localised on the plasma membrane thus their detection is quite easy, as well as their block with specific drugs and antibodies. This review focuses on ion channels (Potassium, Sodium, Calcium, Chloride, Anion and Nicotinic Acetylcholine receptors) in lung cancer (both Non-Small Cell Lung Cancer and Small Cell Lung Cancer) and recapitulate the up-to-date knowledge about their role and clinical relevance for a potential use in the clinical setting, for lung cancer diagnosis and therapy.

Predicting tumor repopulation through the gene panel derived from radiation resistant colorectal cancer cells

BACKGROUND

Tumor cells with the capability of radiation resistance can escape the fate of cell death after radiotherapy, serving as the main cause of treatment failure. Repopulation of tumors after radiotherapy is dominated by this group of residual cells, which greatly reduce the sensitivity of recurrent tumors to the therapy, resulting in poor clinical outcomes. Therefore, revealing the mechanism of radiation resistant cells participating in tumor repopulation is of vital importance for cancer patients to obtain a better prognosis.

METHODS

Co-expressed genes were searched by using genetic data of radiation resistant cells (from GEO database) and TCGA colorectal cancer. Univariate and multivariate Cox regression analysis were performed to define the most significant co-expressed genes for establishing prognostic indicator. Logistic analysis, WGCNA analysis, and other types of tumors were included to verify the predictive ability of the indicator. RT-qPCR was carried out to test expression level of key genes in colorectal cancer cell lines. Colongenic assay was utilized to test the radio-sensitivity and repopulation ability of key gene knockdown cells.

RESULTS

Prognostic indicator based on TCGA colorectal cancer patients containing four key radiation resistance genes (LGR5, KCNN4, TNS4, CENPH) was established. The indicator was shown to be significantly correlated with the prognosis of colorectal cancer patients undergoing radiotherapy, and also had an acceptable predictive effect in the other five types of cancer. RT-qPCR showed that expression level of key genes was basically consistent with the radiation resistance level of colorectal cancer cells. The clonogenic ability of all key gene knockdown cells decreased after radiation treatment compared with the control groups.

CONCLUSIONS

Our data suggest that LGR5, KCNN4, TNS4 and CENPH are correlated with radiation sensitivity of colorectal cancer cells, and the indicator composed by them can reflect the prognosis of colorectal cancer patients undergoing radiation therapy. Our data provide an evidence of radiation resistant tumor cells involved in tumor repopulation, and give patients undergoing radiotherapy an approving prognostic indicator with regard to tumor progression.

Role of Calcium-Activated Potassium Channels in Proliferation, Migration and Invasion of Human Chronic Myeloid Leukemia K562 Cells

Calcium-activated potassium channels (KCa) are important participants in calcium signaling pathways due to their ability to be activated by an increase in intracellular free calcium concentration. KCa channels are involved in the regulation of cellular processes in both normal and pathophysiological conditions, including oncotransformation. Previously, using patch-clamp, we registered the KCa currents in the plasma membrane of human chronic myeloid leukemia K562 cells, whose activity was controlled by local Ca²⁺ entry via mechanosensitive calcium-permeable channels. Here, we performed the molecular and functional identification of KCa channels and have uncovered their role in the proliferation, migration and invasion of K562 cells. Using a combined approach, we identified the functional activity of SK2, SK3 and IK channels in the plasma membrane of the cells. Selective SK and IK channel inhibitors, apamin and TRAM-34, respectively, reduced the proliferative, migratory and invasive capabilities of human myeloid leukemia cells. At the same time, the viability of K562 cells was not affected by KCa channel inhibitors. Ca²⁺ imaging showed that both SK and IK channel inhibitors affect Ca²⁺ entry and this could underlie the observed suppression of pathophysiological reactions of K562 cells. Our data imply that SK/IK channel inhibitors could be used to slow down the proliferation and spreading of chronic myeloid leukemia K562 cells that express functionally active KCa channels in the plasma membrane.

Ion Channels as Potential Tools for the Diagnosis, Prognosis, and Treatment of HPV-Associated Cancers

The human papilloma virus (HPV) group comprises approximately 200 genetic types that have a special affinity for epithelial tissues and can vary from producing benign symptoms to developing into complicated pathologies, such as cancer. The HPV replicative cycle affects various cellular and molecular processes, including DNA insertions and methylation and relevant pathways related to pRb and p53, as well as ion channel expression or function. Ion channels are responsible for the flow of ions across cell membranes and play very important roles in human physiology, including the regulation of ion homeostasis, electrical excitability, and cell signaling. However, when ion channel function or expression is altered, the channels can trigger a wide range of channelopathies, including cancer. In consequence, the up- or down-regulation of ion channels in cancer makes them attractive molecular markers for the diagnosis, prognosis, and treatment of the disease. Interestingly, the activity or expression of several ion channels is dysregulated in HPV-associated cancers. Here, we review the status of ion channels and their regulation in HPV-associated cancers and discuss the potential molecular mechanisms involved. Understanding the dynamics of ion channels in these cancers should help to improve early diagnosis, prognosis, and treatment in the benefit of HPV-associated cancer patients.

Potassium Channels, Glucose Metabolism and Glycosylation in Cancer Cells

Potassium channels emerge as one of the crucial groups of proteins that shape the biology of cancer cells. Their involvement in processes like cell growth, migration, or electric signaling, seems obvious. However, the relationship between the function of K+ channels, glucose metabolism, and cancer glycome appears much more intriguing. Among the typical hallmarks of cancer, one can mention the switch to aerobic glycolysis as the most favorable mechanism for glucose metabolism and glycome alterations. This review outlines the interconnections between the expression and activity of potassium channels, carbohydrate metabolism, and altered glycosylation in cancer cells, which have not been broadly discussed in the literature hitherto. Moreover, we propose the potential mediators for the described relations (e.g., enzymes, microRNAs) and the novel promising directions (e.g., glycans-orinented drugs) for further research.

Imaging of KCa 3.1 Channels in Tumor Cells with PET and Small-Molecule Fluorescent Probes

The Ca²⁺ activated K⁺ channel K_Ca 3.1 is overexpressed in several human tumor cell lines, e. g. clear cell renal carcinoma, prostate cancer, non-small cell lung cancer. Highly aggressive cancer cells use this ion channel for key processes of the metastatic cascade such as migration, extravasation and invasion. Therefore, small molecules, which are able to image this K_Ca 3.1 channel in vitro and in vivo represent valuable diagnostic and prognostic tool compounds. The [¹⁸ F]fluoroethyltriazolyl substituted senicapoc was used as positron emission tomography (PET) tracer and showed promising properties for imaging of K_Ca 3.1 channels in lung adenocarcinoma cells in mice. The novel senicapoc BODIPY conjugates with two F-atoms (9 a) and with a F-atom and a methoxy moiety (9 b) at the B-atom led to the characteristic punctate staining pattern resulting from labeling of single K_Ca 3.1 channels in A549-3R cells. This punctate pattern was completely removed by preincubation with an excess of senicapoc confirming the high specificity of K_Ca 3.1 labeling. Due to the methoxy moiety at the B-atom and the additional oxyethylene unit in the spacer, 9 b exhibits higher polarity, which improves solubility and handling without reduction of fluorescence quantum yield. Docking studies using a cryo-electron microscopy (EM) structure of the K_Ca 3.1 channel confirmed the interaction of 9 a and 9 b with a binding pocket in the channel pore.

Potassium channels: Novel targets for tumor diagnosis and chemoresistance

In recent years, the role of potassium channels in tumors has been intensively studied. Potassium channel proteins are widely involved in various physiological and pathological processes of cells. The expression and dysfunction of potassium channels are closely related to tumor progression. Potassium channel blockers or activators present antitumor effects by directly inhibiting tumor growth or enhancing the potency of classical antitumor agents in combination therapy. This article reviews the mechanisms by which potassium channels contribute to tumor development in various tumors in recent years, introduces the potential of potassium channels as diagnostic targets and therapeutic means for tumors, and provides further ideas for the proper individualized treatment of tumors.

CRAC and SK Channels: Their Molecular Mechanisms Associated with Cancer Cell Development

Cancer represents a major health burden worldwide. Several molecular targets have been discovered alongside treatments with positive clinical outcomes. However, the reoccurrence of cancer due to therapy resistance remains the primary cause of mortality. Endeavors in pinpointing new markers as molecular targets in cancer therapy are highly desired. The significance of the co-regulation of Ca²⁺-permeating and Ca²⁺-regulated ion channels in cancer cell development, proliferation, and migration make them promising molecular targets in cancer therapy. In particular, the co-regulation of the Orai1 and SK3 channels has been well-studied in breast and colon cancer cells, where it finally leads to an invasion-metastasis cascade. Nevertheless, many questions remain unanswered, such as which key molecular components determine and regulate their interplay. To provide a solid foundation for a better understanding of this ion channel co-regulation in cancer, we first shed light on the physiological role of Ca²⁺ and how this ion is linked to carcinogenesis. Then, we highlight the structure/function relationship of Orai1 and SK3, both individually and in concert, their role in the development of different types of cancer, and aspects that are not yet known in this context.

Regulatory role of KCa3.1 in immune cell function and its emerging association with rheumatoid arthritis

Rheumatoid arthritis (RA) is a common autoimmune disease characterized by chronic inflammation. Immune dysfunction is an essential mechanism in the pathogenesis of RA and directly linked to synovial inflammation and cartilage/bone destruction. Intermediate conductance Ca²⁺-activated K⁺ channel (KCa3.1) is considered a significant regulator of proliferation, differentiation, and migration of immune cells by mediating Ca²⁺ signal transduction. Earlier studies have demonstrated abnormal activation of KCa3.1 in the peripheral blood and articular synovium of RA patients. Moreover, knockout of KCa3.1 reduced the severity of synovial inflammation and cartilage damage to a significant extent in a mouse collagen antibody-induced arthritis (CAIA) model. Accumulating evidence implicates KCa3.1 as a potential therapeutic target for RA. Here, we provide an overview of the KCa3.1 channel and its pharmacological properties, discuss the significance of KCa3.1 in immune cells and feasibility as a drug target for modulating the immune balance, and highlight its emerging role in pathological progression of RA.

Relevance of Abnormal KCNN1 Expression and Osmotic Hypersensitivity in Ewing Sarcoma

Simple Summary

The main oncogene in Ewing sarcoma directly drives a high expression of a previously unknown variant KCNN1 (encoding the K_Ca2.1 channel) that we also verified in samples from >200 patients. Yet, we found that the channel is not functional and does not modulate Ewing sarcoma cell behavior. We could explain this lack of functional impact by the surprising absence of any K_Ca2.1-carried K⁺ current in Ewing sarcoma cells. However, we show in a proof-of-principle study that the essential lack of a K⁺ conductance can be exploited by applying hypoosmotic stress and effectively and selectively killing the Ewing sarcoma cells.

Abstract

Ewing sarcoma (EwS) is a rare and highly malignant bone tumor occurring mainly in childhood and adolescence. Physiologically, the bone is a central hub for Ca²⁺ homeostasis, which is severely disturbed by osteolytic processes in EwS. Therefore, we aimed to investigate how ion transport proteins involved in Ca²⁺ homeostasis affect EwS pathophysiology. We characterized the expression of 22 candidate genes of Ca²⁺-permeable or Ca²⁺-regulated ion channels in three EwS cell lines and found the Ca²⁺-activated K⁺ channel K_Ca2.1 (KCNN1) to be exceptionally highly expressed. We revealed that KCNN1 expression is directly regulated by the disease-driving oncoprotein EWSR1-FL1. Due to its consistent overexpression in EwS, KCNN1 mRNA could be a prognostic marker in EwS. In a large cohort of EwS patients, however, KCNN1 mRNA quantity does not correlate with clinical parameters. Several functional studies including patch clamp electrophysiology revealed no evidence for K_Ca2.1 function in EwS cells. Thus, elevated KCNN1 expression is not translated to K_Ca2.1 channel activity in EwS cells. However, we found that the low K⁺ conductance of EwS cells renders them susceptible to hypoosmotic solutions. The absence of a relevant K⁺ conductance in EwS thereby provides an opportunity for hypoosmotic therapy that can be exploited during tumor surgery.

Potassium Ion Channels in Malignant Central Nervous System Cancers

Malignant central nervous system (CNS) cancers are among the most difficult to treat, with low rates of survival and a high likelihood of recurrence. This is primarily due to their location within the CNS, hindering adequate drug delivery and tumour access via surgery. Furthermore, CNS cancer cells are highly plastic, an adaptive property that enables them to bypass targeted treatment strategies and develop drug resistance. Potassium ion channels have long been implicated in the progression of many cancers due to their integral role in several hallmarks of the disease. Here, we will explore this relationship further, with a focus on malignant CNS cancers, including high-grade glioma (HGG). HGG is the most lethal form of primary brain tumour in adults, with the majority of patient mortality attributed to drug-resistant secondary tumours. Hence, targeting proteins that are integral to cellular plasticity could reduce tumour recurrence, improving survival. This review summarises the role of potassium ion channels in malignant CNS cancers, specifically how they contribute to proliferation, invasion, metastasis, angiogenesis, and plasticity. We will also explore how specific modulation of these proteins may provide a novel way to overcome drug resistance and improve patient outcomes.

Imaging of the calcium activated potassium channel 3.1 (KCa 3.1) in vivo using a senicapoc-derived positron emission tomography tracer

The calcium-activated potassium channel 3.1 (K_Ca 3.1) is overexpressed in many tumor entities and has predictive power concerning disease progression and outcome. Imaging of the K_Ca 3.1 channel in vivo using a radiotracer for positron emission tomography (PET) could therefore establish a potentially powerful diagnostic tool. Senicapoc shows high affinity and excellent selectivity toward the K_Ca 3.1 channel. We have successfully pursued the synthesis of the ¹⁸ F-labeled derivative [¹⁸ F]3 of senicapoc using the prosthetic group approach with 1-azido-2-[¹⁸ F]fluoroethane ([¹⁸ F]6) in a "click" reaction. The biological activity of the new PET tracer was evaluated in vitro and in vivo. Inhibition of the K_Ca 3.1 channel by 3 was demonstrated by patch clamp experiments and the binding pose was analyzed by docking studies. In mouse and human serum, [¹⁸ F]3 was stable for at least one half-life of [¹⁸ F]fluorine. Biodistribution experiments in wild-type mice were promising, showing rapid and predominantly renal excretion. An in vivo study using A549-based tumor-bearing mice was performed. The tumor signal could be delineated and image analysis showed a tumor-to-muscle ratio of 1.47 ± 0.24. The approach using 1-azido-2-[¹⁸ F]fluoroethane seems to be a good general strategy to achieve triarylacetamide-based fluorinated PET tracers for imaging of the K_Ca 3.1 channel in vivo.

Functional expression of mitochondrial KCa3.1 channels in non-small cell lung cancer cells

Lung cancer is one of the leading causes of cancer-related deaths worldwide. The Ca²⁺-activated K⁺ channel K_Ca3.1 contributes to the progression of non-small cell lung cancer (NSCLC). Recently, K_Ca3.1 channels were found in the inner membrane of mitochondria in different cancer cells. Mitochondria are the main sources for the generation of reactive oxygen species (ROS) that affect the progression of cancer cells. Here, we combined Western blotting, immunofluorescence, and fluorescent live-cell imaging to investigate the expression and function of K_Ca3.1 channels in the mitochondria of NSCLC cells. Western blotting revealed K_Ca3.1 expression in mitochondrial lysates from different NSCLC cells. Using immunofluorescence, we demonstrate a co-localization of K_Ca3.1 channels with mitochondria of NSCLC cells. Measurements of the mitochondrial membrane potential with TMRM reveal a hyperpolarization following the inhibition of K_Ca3.1 channels with the cell-permeable blocker senicapoc. This is not the case when cells are treated with the cell-impermeable peptidic toxin maurotoxin. The hyperpolarization of the mitochondrial membrane potential is accompanied by an increased generation of ROS in NSCLC cells. Collectively, our results provide firm evidence for the functional expression of K_Ca3.1 channels in the inner membrane of mitochondria of NSCLC cells.

Potassium in Solid Cancers

Electrolyte disorders are a frequent finding in cancer patients. In the majority of cases the etiologies of such disorders are common to all cancer types (i.e. diuretic-induced hyponatremia or hypokalemia). Sometimes, electrolyte disorders are caused by paraneoplastic syndromes or are due to cancer therapy. Potassium is one of the most important electrolytes of the human body since it is involved in the regulation of muscle contraction, maintenance of the integrity of the skeleton, blood pressure and nerve transmission as well as in the normal function of cells. Potassium homeostasis is strictly regulated since the gap between the recommended daily dietary intake (120 mEq/day) and the levels stored in the extracellular fluid (around 70 mEq) is huge. Alterations of potassium homeostasis are frequent in cancer patients as well alterations in potassium channels, the transmembrane proteins that mediate potassium fluxes within the cells. The present chapter is focused on the clinical significance of potassium homeostasis and potassium channels in patients with solid tumors.

KCNN4 Promotes the Stemness Potentials of Liver Cancer Stem Cells by Enhancing Glucose Metabolism

The presence of liver cancer stem cells (LCSCs) is one of the reasons for the treatment failure of hepatocellular carcinoma (HCC). For LCSCs, one of their prominent features is metabolism plasticity, which depends on transporters and ion channels to exchange metabolites and ions. The K⁺ channel protein KCNN4 (Potassium Calcium-Activated Channel Subfamily N Member 4) has been reported to promote cell metabolism and malignant progression of HCCs, but its influence on LCSC stemness has remained unclear. Here, we demonstrated that KCNN4 was highly expressed in L-CSCs by RT-PCR and Western blot. Then, we illustrated that KCNN4 promoted the stemness of HC-C cells by CD133⁺CD44⁺ LCSC subpopulation ratio analysis, in vitro stemness transcription factor detection, and sphere formation assay, as well as in vivo orthotopic liver tumor formation and limiting dilution tumorigenesis assays. We also showed that KCNN4 enhanced the glucose metabolism in LCSCs by metabolic enzyme detections and seahorse analysis, and the KCNN4-promoted increase in LCSC ratios was abolished by glycolysis inhibitor 2-DG or OXPHOS inhibitor oligomycin. Collectively, our results suggested that KCNN4 promoted LCSC stemness via enhancing glucose metabolism, and that KCNN4 would be a potential molecular target for eliminating LCSCs in HCC.

KCNN4-mediated Ca2+/MET/AKT axis is promising for targeted therapy of pancreatic ductal adenocarcinoma

As a member of the potassium calcium-activated channel subfamily, increasing evidence suggests that KCNN4 was associated with malignancies. However, the roles and regulatory mechanisms of KCNN4 in PDAC have been little explored. In this work, we demonstrated that the level of KCNN4 in PDAC was abnormally elevated, and the overexpression of KCNN4 was induced by transcription factor AP-1. KCNN4 was closely correlated with unfavorable clinicopathologic characteristics and poor survival. Functionally, we found that overexpression of KCNN4 promoted PDAC cell proliferation, migration and invasion. Conversely, the knockdown of KCNN4 attenuated the growth and motility of PDAC cells. In addition to these, knockdown of KCNN4 promoted PDAC cell apoptosis and led to cell cycle arrest in the S phase. In mechanistic investigations, RNA-sequence revealed that the MET-mediated AKT axis was essential for KCNN4, encouraging PDAC cell proliferation and migration. Collectively, these findings reveal a function of KCNN4 in PDAC and suggest it's an attractive therapeutic target and tumor marker. Our studies underscore a better understanding of the biological mechanism of KCNN4 in PDAC and suggest novel strategies for cancer therapy.

Impact of the Nuclear Envelope on Malignant Transformation, Motility, and Survival of Lung Cancer Cells

Nuclear pore complexes (NPCs) selectively mediate all nucleocytoplasmic transport and engage in fundamental cell-physiological processes. It is hypothesized that NPCs are critical for malignant transformation and survival of lung cancer cells, and test the hypothesis in lowly and highly metastatic non-small human lung cancer cells (NSCLCs). It is shown that malignant transformation is paralleled by an increased NPCs density, and a balanced pathological weakening of the physiological stringency of the NPC barrier. Pharmacological interference using barrier-breaking compounds collapses the stringency. Concomitantly, it induces drastic overall structural changes of NSCLCs, terminating their migration. Moreover, the degree of malignancy is found to be paralleled by substantially decreased lamin A/C levels. The latter provides crucial structural and mechanical stability to the nucleus, and interacts with NPCs, cytoskeleton, and nucleoskeleton for cell maintenance, survival, and motility. The recent study reveals the physiological importance of the NPC barrier stringency for mechanical and structural resilience of normal cell nuclei. Hence, reduced lamin A/C levels in conjunction with controlled pathological weakening of the NPC barrier stringency may facilitate deformability of NSCLCs during the metastasis steps. Modulation of the NPC barrier presents a potential strategy for suppressing the malignant phenotype or enhancing the effectiveness of currently existing chemotherapeutics.

Targeting ion channels for the treatment of lung cancer

Lung cancer is caused by several environmental and genetic variables and is globally associated with elevated morbidity and mortality. Among these variables, membrane-bound ion channels have a key role in regulating multiple signaling pathways in tumor cells and dysregulation of ion channel expression and function is closely related to proliferation, migration, and metastasis of lung cancer. This work reviews and summarizes current knowledge about the role of ion channels in lung cancer, focusing on the changes in the expression and function of various ion channels in lung cancer and how these changes affect lung cancer cell biology both in vitro and in vivo as evidenced by both genetic and pharmacological studies. It can help understand the molecular mechanisms of various ion channels influencing the initiation and progression of lung cancer and shed new insights into their roles in the development and treatment of this deadly disease.

Clinical-pathological and molecular characterization of long-term survivors with advanced non-small cell lung cancer

Objective: Long-term survivors (LS) of non-small cell lung cancer (NSCLC) without driver alterations, displaying an overall survival (OS) of more than 3 years, comprise around 10% of cases in several series treated with chemotherapy. There are classical prognosis factors for these cases [stage, Eastern Cooperative Oncology Group (ECOG), etc.], but more data are required in the literature. In this multi-center study, we focused on LS of advanced NSCLC with OS above 36 months to perform a clinical-pathological and molecular characterization.

Methods: In the first step, we conducted a clinical-pathological characterization of the patients. Afterwards, we carried out a genetic analysis by comparing LS to a sample of short-term survivors (SS) (with an OS less than 9 months). We initially used whole-genome RNA-seq to identify differentiating profiles of LS and SS, and later confirmed these with reverse transcription-polymerase chain reaction (RT-PCR) for the rest of the samples.

Results: A total of 94 patients were included, who were mainly men, former smokers, having adenocarcinoma (AC)-type NSCLC with an ECOG of 0–1. We obtained an initial differential transcriptome expression, displaying 5 over- and 33 under-expressed genes involved in different pathways: namely, the secretin receptor, surfactant protein, trefoil factor 1 (TFF1), serpin, Ca-channels, and Toll-like receptor (TLRs) families. Finally, RT-PCR analysis of 40 (20 LS/20 SS) samples confirmed that four genes (surfactant proteins and SFTP) were significantly down-regulated in SS compared to LS by using an analysis of covariance (ANCOVA) model: SFTPA1 (P = 0.023), SFTPA2 (P = 0.027), SFTPB (P = 0.02), and SFTPC (P = 0.047).

Conclusions: We present a sequential genetic analysis of a sample of NSCLC LS with no driver alterations, obtaining a differential RNA-seq/RT-PCR profile showing an abnormal expression of SF genes.

KCa channel blockers increase effectiveness of the EGF receptor TK inhibitor erlotinib in non-small cell lung cancer cells (A549)

Non-small cell lung cancer (NSCLC) has a poor prognosis with a 5 year survival rate of only ~ 10%. Important driver mutations underlying NSCLC affect the epidermal growth factor receptor (EGFR) causing the constitutive activation of its tyrosine kinase domain. There are efficient EGFR tyrosine kinase inhibitors (TKIs), but patients develop inevitably a resistance against these drugs. On the other hand, K_Ca3.1 channels contribute to NSCLC progression so that elevated K_Ca3.1 expression is a strong predictor of poor NSCLC patient prognosis. The present study tests whether blocking K_Ca3.1 channels increases the sensitivity of NSCLC cells towards the EGFR TKI erlotinib and overcomes drug resistance. mRNA expression of K_Ca3.1 channels in erlotinib-sensitive and -resistant NSCLC cells was analysed in datasets from Gene expression omnibus (GEO) and ArrayExpress. We assessed proliferation and migration of NSCLC cells. These (live cell-imaging) experiments were complemented by patch clamp experiments and Western blot analyses. We identified three out of four datasets comparing erlotinib-sensitive and -resistant NSCLC cells which revealed an altered expression of K_Ca3.1 mRNA in erlotinib-resistant NSCLC cells. Therefore, we evaluated the combined effect of erlotinib and the K_Ca3.1 channel inhibition with sencapoc. Erlotinib elicits a dose-dependent inhibition of migration and proliferation of NSCLC cells. The simultaneous application of the K_Ca3.1 channel blocker senicapoc increases the sensitivity towards a low dose of erlotinib (300 nmol/L) which by itself has no effect on migration and proliferation. Partial erlotinib resistance can be overcome by K_Ca3.1 channel blockade. The sensitivity towards erlotinib as well as the potentiating effect of K_Ca3.1 blockade is further increased by mimicking hypoxia. Our results suggest that K_Ca3.1 channel blockade may constitute a therapeutic concept for treating NSCLC and overcome EGFR TKI resistance. We propose that this is due to complementary mechanisms of action of both blockers.

Synthesis and biological evaluation of PET tracers designed for imaging of calcium activated potassium channel 3.1 (KCa3.1) channels in vivo

Expression of the Ca²⁺ activated potassium channel 3.1 (K_Ca3.1) channel (also known as the Gàrdos channel) is dysregulated in many tumor entities and has predictive power with respect to patient survival. Therefore, a positron emission tomography (PET) tracer targeting this ion channel could serve as a potential diagnostic tool by imaging the K_Ca3.1 channel in vivo. It was envisaged to synthesize [¹⁸F]senicapoc ([¹⁸F]1) since senicapoc (1) shows high affinity and excellent selectivity towards the K_Ca3.1 channels. Because problems occurred during ¹⁸F-fluorination, the [¹⁸F]fluoroethoxy senicapoc derivative [¹⁸F]28 was synthesized to generate an alternative PET tracer targeting the K_Ca3.1 channel. Inhibition of the K_Ca3.1 channel by 28 was confirmed by patch clamp experiments. In vitro stability in mouse and human serum was shown for 28. Furthermore, biodistribution experiments in wild type mice were performed. Since [¹⁸F]fluoride was detected in vivo after application of [¹⁸F]28, an in vitro metabolism study was conducted. A potential degradation route of fluoroethoxy derivatives in vivo was found which in general should be taken into account when designing new PET tracers for different targets with a [¹⁸F]fluoroethoxy moiety as well as when using the popular prosthetic group [¹⁸F]fluoroethyl tosylate for the alkylation of phenols.

Expression of the Ca²⁺ activated potassium channel 3.1 (K_Ca3.1) channel (also known as the Gàrdos channel) is dysregulated in many tumor entities and has predictive power with respect to patient survival.

Potassium and Chloride Ion Channels in Cancer: A Novel Paradigm for Cancer Therapeutics

Cancer is a collection of diseases caused by specific changes at the genomic level that support cell proliferation indefinitely. Traditionally, ion channels are known to control a variety of cellular processes including electrical signal generation and transmission, secretion, and contraction by controlling ionic gradients. However, recent studies had brought to light important facts on ion channels in cancer biology.In this review we discuss the mechanism linking potassium or chloride ion channel activity to biochemical pathways controlling proliferation in cancer cells and the potential advantages of targeting ion channels as an anticancer therapeutic option.

Midazolam's Effects on Delayed-Rectifier K+ Current and Intermediate-Conductance Ca2+-Activated K+ Channel in Jurkat T-lymphocytes

Midazolam (MDZ) could affect lymphocyte immune functions. However, the influence of MDZ on cell’s K⁺ currents has never been investigated. Thus, in the present study, the effects of MDZ on Jurkat T lymphocytes were studied using the patch-clamp technique. Results showed that MDZ suppressed the amplitude of delayed-rectifier K⁺ current (I_K(DR)) in concentration-, time-, and state-dependent manners. The IC₅₀ for MDZ-mediated reduction of I_K(DR) density was 5.87 μM. Increasing MDZ concentration raised the rate of current-density inactivation and its inhibitory action on I_K(DR) density was estimated with a dissociation constant of 5.14 μM. In addition, the inactivation curve of I_K(DR) associated with MDZ was shifted to a hyperpolarized potential with no change on the slope factor. MDZ-induced inhibition of I_K(DR) was not reversed by flumazenil. In addition, the activity of intermediate-conductance Ca²⁺-activated K⁺ (IK_Ca) channels was suppressed by MDZ. Furthermore, inhibition by MDZ on both I_K(DR) and IK_Ca-channel activity appeared to be independent from GABAA receptors and affected immune-regulating cytokine expression in LPS/PMA-treated human T lymphocytes. In conclusion, MDZ suppressed current density of I_K(DR) in concentration-, time-, and state-dependent manners in Jurkat T-lymphocytes and affected immune-regulating cytokine expression in LPS/PMA-treated human T lymphocytes.

Comparison of the Effect of Oral Versus Intravenous Bisphosphonate Administration on Osteoclastogenesis in Advanced-Stage Medication-Related Osteonecrosis of the Jaw Patients

It is yet unknown whether the intravenous administration route alone can fully account for the exacerbation of medication-related osteonecrosis of the jaw (MRONJ). The purpose of this retrospective study was to identify the potential role of the bisphosphonate (BP) administration route as an independent prognostic factor for non-cancerous, stage III MRONJ patients. Bone samples were retrospectively obtained from two groups of osteoporosis patients who underwent surgery for the treatment of stage III MRONJ. Among the subjects, 10 had a history of only oral BP consumption and 10 of intravenous (IV) BP administration. The samples were assessed for osteoclast morphology and immunohistochemical expression of the receptor activator of NF-κB ligand (RANKL), osteoprotegerin (OPG), and potassium calcium-activated channel subfamily N member 4 (Kcnn4). Although the osteoclasts derived from both groups exhibited no significant differences in the mean quantity, diameter, and nuclearity, significantly attenuated tartrate-resistant acid phosphatase activity was noted among the IV BP-induced MRONJ bones compared to those of the oral BP group. Significant suppression of the RANKL/OPG ratio and Kcnn4 expression among the retrieved bones of IV BP group patients was also noted. Our results indicate the potential of the BP administration route as an independent prognostic factor for advanced-stage MRONJ, regardless of the dosage or indication for which the BP was prescribed.

KCNN4 promotes the progression of lung adenocarcinoma by activating the AKT and ERK signaling pathways

BACKGROUND

Potassium channels, encoded by more than seventy genes, are cell excitability transmembrane proteins and become evident to play essential roles in tumor biology.

OBJECTIVE

The deregulation of potassium channel genes has been related to cancer development and patient prognosis. The objective of this study is to understand the role of potassium channels in lung cancer.

METHODS

We examined all potassium channel genes and identified that KCNN4 is the most significantly overexpressed one in lung adenocarcinoma. The role and mechanism of KCNN4 in lung adenocarcinoma were further investigated by in vitro cell and molecular assay and in vivo mouse xenograft models.

RESULTS

We revealed that the silencing of KCNN4 significantly inhibits cell proliferation, migration, invasion, and tumorigenicity of lung adenocarcinoma. Further studies showed that knockdown of KCNN4 promotes cell apoptosis, induces cell cycle arrested in the S phase, and is associated with the epithelial to mesenchymal transition (EMT) process. Most importantly, we demonstrated that KCNN4 regulates the progression of lung adenocarcinoma through P13K/AKT and MEK/ERK signaling pathways. The use of inhibitors that targeted AKT and ERK also significantly inhibit the proliferation and metastasis of lung adenocarcinoma cells.

CONCLUSIONS

This study investigated the function and mechanism of KCNN4 in lung adenocarcinoma. On this basis, this means that KCNN4 can be used as a tumor marker for lung adenocarcinoma and is expected to become an important target for a potential drug.

A549 in-silico 1.0: A first computational model to simulate cell cycle dependent ion current modulation in the human lung adenocarcinoma

Lung cancer is still a leading cause of death worldwide. In recent years, knowledge has been obtained of the mechanisms modulating ion channel kinetics and thus of cell bioelectric properties, which is promising for oncological biomarkers and targets. The complex interplay of channel expression and its consequences on malignant processes, however, is still insufficiently understood. We here introduce the first approach of an in-silico whole-cell ion current model of a cancer cell, in particular of the A549 human lung adenocarcinoma, including the main functionally expressed ion channels in the plasma membrane as so far known. This hidden Markov-based model represents the electrophysiology behind proliferation of the A549 cell, describing its rhythmic oscillation of the membrane potential able to trigger the transition between cell cycle phases, and it predicts membrane potential changes over the cell cycle provoked by targeted ion channel modulation. This first A549 in-silico cell model opens up a deeper insight and understanding of possible ion channel interactions in tumor development and progression, and is a valuable tool for simulating altered ion channel function in lung cancer electrophysiology.

KCNN4 is a potential prognostic marker and critical factor affecting the immune status of the tumor microenvironment in kidney renal clear cell carcinoma

Background

The tumor microenvironment (TME) has emerged as a crucial factor in cancer development and progression. Recent findings have indicated that tumor-infiltrating immune cells (TICs) in the TME may predict cancer prognosis and response to treatment. Herein, we sought to identify critical modulators of the kidney renal clear cell carcinoma (KIRC) TME.

Methods

KIRC datasets from The Cancer Genome Atlas (TCGA) were analyzed using the ESTIMATE algorithm to determine the ImmuneScore and StromalScore. By profiling the differentially expressed genes (DEGs) in the ImmuneScore and StromalScore, we finally identified the immune- and stromal-related DEGs of the cases, through which we then performed intersection analysis to determine the immune-related genes (IRGs). Cox regression analysis and least absolute shrinkage and selection operator (LASSO) regression analysis were used to identify critical IRGs and construct a prognostic model. The CIBERSORT algorithm was used to calculate the relative content of 22 immune cell types. Finally, the datasets from the Gene Expression Omnibus (GEO) database were analyzed to validate results from the above analyses. Experimental validation was used on KIRC tissues by quantitative polymerase chain reaction (qPCR) and western blot.

Results

We found that the ImmuneScore was negatively correlated with patients’ prognosis. Intersection analysis of the ImmuneScore and StromalScore identified 118 IRGs that were enriched in immune-related functions. Following IRGs screening by Cox and LASSO regression analyses, six genes were identified and used to construct a KIRC prognostic model. Intersection analysis of these six genes and protein-protein interaction (PPI) were performed and obtained the most critical gene: Potassium Calcium-Activated Channel Subfamily N Member 4 (KCNN4). Further analysis showed that KCNN4 expression was higher in tumor samples relative to normal controls, and was negatively correlated with prognosis. CIBERSORT analysis revealed significant correlation between KCNN4 expression and multiple types of TICs, demonstrating that KCNN4 may affect KIRC prognosis by influencing the TME immune status. Ultimately, the GEO datasets and validation experiments confirmed that KCNN4 was highly expressed in tumor tissues compared to the corresponding normal tissues.

Conclusions

Our study demonstrated that KCNN4 might be a potential prognostic marker in KIRC, offering a novel therapeutic avenue.

First Tandem Repeat of a Potassium Channel KCNN4 Minisatellite Folds into a V-Loop G-Quadruplex Structure

The KCNN4 gene encoding a potassium channel protein whose expression has been correlated with tumor progression was found to comprise a guanine-rich minisatellite region with the ability to form a putative G-quadruplex (G4). Given the suggested regulatory role of G4s in gene expression, G-quadruplex formation for the polymorphic first repeat of the minisatellite was studied by nuclear magnetic resonance spectroscopy. A stable G-quadruplex of a truncated mutant sequence was shown to represent one of several coexisting species of the wild-type sequence. The high-resolution structure features a noncanonical G4 with a broken G-column and a V-shaped loop. The presence of a 3'-flanking thymidine interacting with the lateral loop preceding the V loop seems to be critical for the formation of this G4 topology. On the contrary, an additional 5'-flanking residue disfavored but still allowed folding into the V-loop structure. The latter may therefore serve as a putative therapeutic target in strategies for G4-based modulation of KCNN4 expression.

Mitochondrial K+ channels and their implications for disease mechanisms

The field of mitochondrial ion channels underwent a rapid development during the last decade, thanks to the molecular identification of some of the nuclear-encoded organelle channels and to advances in strategies allowing specific pharmacological targeting of these proteins. Thereby, genetic tools and specific drugs aided definition of the relevance of several mitochondrial channels both in physiological as well as pathological conditions. Unfortunately, in the case of mitochondrial K⁺ channels, efforts of genetic manipulation provided only limited results, due to their dual localization to mitochondria and to plasma membrane in most cases. Although the impact of mitochondrial K⁺ channels on human diseases is still far from being genuinely understood, pre-clinical data strongly argue for their substantial role in the context of several pathologies, including cardiovascular and neurodegenerative diseases as well as cancer. Importantly, these channels are druggable targets, and their in-depth investigation could thus pave the way to the development of innovative small molecules with huge therapeutic potential. In the present review we summarize the available experimental evidence that mechanistically link mitochondrial potassium channels to the above pathologies and underline the possibility of exploiting them for therapy.

SK4 oncochannels regulate calcium entry and promote cell migration in KRAS-mutated colorectal cancer

BACKGROUND

Colorectal cancer (CRC) metastases are the main cause of CRC mortality. Intracellular Ca2+ regulates cell migration and invasion, key factors for metastases. Ca2+ also activates Ca2+-dependent potassium channels which in turn affect Ca2+ driving force. We have previously reported that the expression of the Ca2+ activated potassium channel KCNN4 (SK4) is higher in CRC primary tumors compared to normal tissues. Here, we aimed to investigate the role of SK4 in the physiology of CRC.

RESULTS

SK4 protein expression is enhanced in CRC tissues compared to normal colon tissues, with a higher level of KCNN4 in CRC patients with KRAS mutations. At the cellular level, we found that SK4 regulates the membrane potential of HCT116 cells. We also found that its inhibition reduced store operated Ca2+ entry (SOCE) and constitutive Ca2+ entry (CCE), while reducing cell migration. We also found that the activity of SK4 is linked to resistance pathways such as KRAS mutation and the expression of NRF2 and HIF-1α. In addition, the pharmacological inhibition of SK4 reduced intracellular reactive oxygen species (ROS) production, NRF2 expression and HIF1α stabilization.

CONCLUSION

Our results suggest that SK4 contributes to colorectal cancer cell migration and invasion by modulating both Ca2+ entry and ROS regulation. Therefore, SK4 could be a potential target to reduce metastasis in KRAS-mutated CRC.

Screening and identification of potential biomarkers and therapeutic drugs in melanoma via integrated bioinformatics analysis

Melanoma is a highly aggressive malignant skin tumor with a high rate of metastasis and mortality. In this study, a comprehensive bioinformatics analysis was used to clarify the hub genes and potential drugs. Download the GSE3189, GSE22301, and GSE35388 microarray datasets from the Gene Expression Omnibus (GEO), which contains a total of 33 normal samples and 67 melanoma samples. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) approach analyze DEGs based on the DAVID. Use STRING to construct protein-protein interaction network, and use MCODE and cytoHubba plug-ins in Cytoscape to perform module analysis and identified hub genes. Use Gene Expression Profile Interactive Analysis (GEPIA) to assess the prognosis of genes in tumors. Finally, use the Drug-Gene Interaction Database (DGIdb) to screen targeted drugs related to hub genes. A total of 140 overlapping DEGs were identified from the three microarray datasets, including 59 up-regulated DEGs and 81 down-regulated DEGs. GO enrichment analysis showed that these DEGs are mainly involved in the biological process such as positive regulation of gene expression, positive regulation of cell proliferation, positive regulation of MAP kinase activity, cell migration, and negative regulation of the apoptotic process. The cellular components are concentrated in the membrane, dendritic spine, the perinuclear region of cytoplasm, extracellular exosome, and membrane raft. Molecular functions include protein homodimerization activity, calmodulin-binding, transcription factor binding, protein binding, and cytoskeletal protein binding. KEGG pathway analysis shows that these DEGs are mainly related to protein digestion and absorption, PPAR signaling pathway, signaling pathways regulating stem cells' pluripotency, and Retinol metabolism. The 23 most closely related DEGs were identified from the PPI network and combined with the GEPIA prognostic analysis, CDH3, ESRP1, FGF2, GBP2, KCNN4, KIT, SEMA4D, and ZEB1 were selected as hub genes, which are considered to be associated with poor prognosis of melanoma closely related. Besides, ten related drugs that may have therapeutic effects on melanoma were also screened. These newly discovered genes and drugs provide new ideas for further research on melanoma.

Ion Channels Orchestrate Pancreatic Ductal Adenocarcinoma Progression and Therapy

Pancreatic ductal adenocarcinoma is a devastating disease with a dismal prognosis. Therapeutic interventions are largely ineffective. A better understanding of the pathophysiology is required. Ion channels contribute substantially to the "hallmarks of cancer." Their expression is dysregulated in cancer, and they are "misused" to drive cancer progression, but the underlying mechanisms are unclear. Ion channels are located in the cell membrane at the interface between the intracellular and extracellular space. They sense and modify the tumor microenvironment which in itself is a driver of PDAC aggressiveness. Ion channels detect, for example, locally altered proton and electrolyte concentrations or mechanical stimuli and transduce signals triggered by these microenvironmental cues through association with intracellular signaling cascades. While these concepts have been firmly established for other cancers, evidence has emerged only recently that ion channels are drivers of PDAC aggressiveness. Particularly, they appear to contribute to two of the characteristic PDAC features: the massive fibrosis of the tumor stroma (desmoplasia) and the efficient immune evasion. Our critical review of the literature clearly shows that there is still a remarkable lack of knowledge with respect to the contribution of ion channels to these two typical PDAC properties. Yet, we can draw parallels from ion channel research in other fibrotic and inflammatory diseases. Evidence is accumulating that pancreatic stellate cells express the same "profibrotic" ion channels. Similarly, it is at least in part known which major ion channels are expressed in those innate and adaptive immune cells that populate the PDAC microenvironment. We explore potential therapeutic avenues derived thereof. Since drugs targeting PDAC-relevant ion channels are already in clinical use, we propose to repurpose those in PDAC. The quest for ion channel targets is both motivated and complicated by the fact that some of the relevant channels, for example, KCa3.1, are functionally expressed in the cancer, stroma, and immune cells. Only in vivo studies will reveal which arm of the balance we should put our weights on when developing channel-targeting PDAC therapies. The time is up to explore the efficacy of ion channel targeting in (transgenic) murine PDAC models before launching clinical trials with repurposed drugs.

Co-staining of KCa 3.1 Channels in NSCLC Cells with a Small-Molecule Fluorescent Probe and Antibody-Based Indirect Immunofluorescence

The Ca2+ activated potassium channel 3.1 (KCa 3.1) is involved in critical steps of the metastatic cascade, such as proliferation, migration, invasion and extravasation. Therefore, a fast and efficient protocol for imaging of KCa 3.1 channels was envisaged. The novel fluorescently labeled small molecule imaging probes 1 and 2 were synthesized by connecting a dimethylpyrrole-based BODIPY dye with a derivative of the KCa 3.1 channel inhibitor senicapoc via linkers of different length. Patch-clamp experiments revealed the inhibition of KCa 3.1 channels by the probes confirming interaction with the channel. Both probes 1 and 2 were able to stain KCa 3.1 channels in non-small-cell lung cancer (NSCLC) cells following a simple, fast and efficient protocol. Pre-incubation with unlabeled senicapoc removed the punctate staining pattern showing the specificity of the new probes 1 and 2. Staining of the channel with the fluorescently labeled senicapoc derivatives 1 or 2 or with antibody-based indirect immunofluorescence yielded identical or very similar densities of stained KCa 3.1 channels. However, co-staining using both methods did not lead to the expected overlapping punctate staining pattern. This observation was explained by docking studies showing that the antibody used for indirect immunofluorescence and the probes 1 and 2 label different channel populations. Whereas the antibody binds at the closed channel conformation, the probes 1 and 2 bind within the open channel.

Ion Channels in Cancer: Orchestrators of Electrical Signaling and Cellular Crosstalk

Ion channels are pore-forming transmembrane proteins that govern ion flux to regulate a myriad of biological processes in development, physiology, and disease. Across various types of cancer, ion channel expression and activity are often dysregulated. We review the contribution of ion channels to multiple stages of tumorigenesis based on data from in vivo model systems. As intertumoral and intratumoral heterogeneities are major obstacles in developing effective therapies, we provide perspectives on how ion channels in tumor cells and their microenvironment represent targetable vulnerabilities in the areas of tumor-stromal cell interactions, cancer neuroscience, and cancer mechanobiology.

How Dysregulated Ion Channels and Transporters Take a Hand in Esophageal, Liver, and Colorectal Cancer

Over the last two decades, the understanding of how dysregulated ion channels and transporters are involved in carcinogenesis and tumor growth and progression, including invasiveness and metastasis, has been increasing exponentially. The present review specifies virtually all ion channels and transporters whose faulty expression or regulation contributes to esophageal, hepatocellular, and colorectal cancer. The variety reaches from Ca²⁺, K⁺, Na⁺, and Cl^- channels over divalent metal transporters, Na⁺ or Cl^- coupled Ca²⁺, HCO₃^- and H⁺ exchangers to monocarboxylate carriers and organic anion and cation transporters. In several cases, the underlying mechanisms by which these ion channels/transporters are interwoven with malignancies have been fully or at least partially unveiled. Ca²⁺, Akt/NF-κB, and Ca²⁺- or pH-dependent Wnt/β-catenin signaling emerge as cross points through which ion channels/transporters interfere with gene expression, modulate cell proliferation, trigger epithelial-to-mesenchymal transition, and promote cell motility and metastasis. Also miRs, lncRNAs, and DNA methylation represent potential links between the misexpression of genes encoding for ion channels/transporters, their malfunctioning, and cancer. The knowledge of all these molecular interactions has provided the basis for therapeutic strategies and approaches, some of which will be broached in this review.

Development of a Cell-Based Assay for Identifying KCa3.1 Inhibitors Using Intestinal Epithelial Cell Lines

Inhibition of the K_Ca3.1 potassium channel has therapeutic potential in a variety of human diseases, including inflammation-associated disorders and cancers. However, K_Ca3.1 inhibitors with high therapeutic promise are currently not available. This study aimed to establish a screening assay for identifying inhibitors of K_Ca3.1 in native cells and from library compounds derived from natural products in Thailand. The screening platform was successfully developed based on a thallium flux assay in intestinal epithelial (T84) cells with a Z' factor of 0.52. The screening of 1352 compounds and functional validation using electrophysiological analyses identified 8 compounds as novel K_Ca3.1 inhibitors with IC₅₀ values ranging from 0.14 to 6.57 µM. These results indicate that the assay developed is of excellent quality for high-throughput screening and capable of identifying K_Ca3.1 inhibitors. This assay may be useful in identifying novel K_Ca3.1 inhibitors that may have therapeutic potential for inflammation-associated disorders and cancers.

Synthesis of Small-Molecule Fluorescent Probes for the In Vitro Imaging of Calcium-Activated Potassium Channel KCa 3.1

Small-molecule probes for the in vitro imaging of KCa 3.1 channel-expressing cells were developed. Senicapoc, showing high affinity and selectivity for the KCa 3.1 channels, was chosen as the targeting component. BODIPY dyes 15-20 were synthesized and connected by a CuI -catalyzed azide-alkyne [3+2]cycloaddition with propargyl ether senicapoc derivative 8, yielding fluorescently labeled ligands 21-26. The dimethylpyrrole-based imaging probes 25 and 26 allow staining of KCa 3.1 channels in NSCLC cells. The specificity was shown by removing the punctate staining pattern by pre-incubation with senicapoc. The density of KCa 3.1 channels detected with 25 and by immunostaining was identical. The punctate structure of the labeled channels could also be observed in living cells. Molecular modeling showed binding of the senicapoc-targeting component towards the binding site within the ion channel and orientation of the linker with the dye along the inner surface of the ion channel.

Ion Channels in Lung Cancer

Ion channels are a major class of membrane proteins that play central roles in signaling within and among cells, as well as in the coupling of extracellular events with cellular responses. Dysregulated ion channel activity plays a causative role in many diseases including cancer. Here, we will review their role in lung cancer. Lung cancer is one of the most frequently diagnosed cancers, and it causes the highest number of deaths of all cancer types. The overall 5-year survival rate of lung cancer patients is only 19% and decreases to 5% when patients are diagnosed with stage IV. Thus, new therapeutical strategies are urgently needed. The important contribution of ion channels to the progression of various types of cancer has been firmly established so that ion channel-based therapeutic concepts are currently developed. Thus far, the knowledge on ion channel function in lung cancer is still relatively limited. However, the published studies clearly show the impact of ion channel inhibitors on a number of cellular mechanisms underlying lung cancer cell aggressiveness such as proliferation, migration, invasion, cell cycle progression, or adhesion. Additionally, in vivo experiments reveal that ion channel inhibitors diminish tumor growth in mice. Furthermore, some studies give evidence that ion channel inhibitors can have an influence on the resistance or sensitivity of lung cancer cells to common chemotherapeutics such as paclitaxel or cisplatin.

Expression of potassium channel genes predicts clinical outcome in lung cancer

Lung cancer is the most common cause of cancer deaths worldwide and several molecular signatures have been developed to predict survival in lung cancer. Increasing evidence suggests that proliferation and migration to promote tumor growth are associated with dysregulated ion channel expression. In this study, by analyzing high-throughput gene expression data, we identify the differentially expressed K⁺ channel genes in lung cancer. In total, we prioritize ten dysregulated K⁺ channel genes (5 up-regulated and 5 down-regulated genes, which were designated as K-10) in lung tumor tissue compared with normal tissue. A risk scoring system combined with the K-10 signature accurately predicts clinical outcome in lung cancer, which is independent of standard clinical and pathological prognostic factors including patient age, lymph node involvement, tumor size, and tumor grade. We further indicate that the K-10 potentially predicts clinical outcome in breast and colon cancers. Molecular signature discovered through K⁺ gene expression profiling may serve as a novel biomarker to assess the risk in lung cancer.

KCNN4 promotes invasion and metastasis through the MAPK/ERK pathway in hepatocellular carcinoma

Hepatocellular Carcinoma (HCC) is one of the most common malignancies in the world, and is well-known for its bad prognosis. Potassium calcium-activated channel subfamily N member 4 (KCNN4) is a type of intermediate conductance calcium-activated potassium channel, and increasing evidence suggests that KCNN4 contributes to the regulation of invasion and metastasis in a number of cancers. However, its clinical significance and biological function remain unclear in the HCC disease process. In this study, the expression levels of KCNN4 in 86 HCC samples were compared with corresponding paracancerous tissues. sh-RNA was used to reduce the expression of KCNN4 in Hep3B HCC cells in vitro; this was confirmed by Real time-PCR and western blotting. Wound healing, transwell assays and high content analysis were performed to investigate the tumor-promoting characteristics of KCNN4 in Hep3B HCC cells. As results, KCNN4 expression was significantly associated with preoperative serum alpha-fetoprotein level (p=0.038) and TNM stage (p=0.039). Additionally, patients with high KCNN4 amplification in HCC tissue exhibited shorter disease-free survival, whereas there was no statistical significance between KCNN4 amplification and overall survival. Wound healing and transwell assays showed that knockdown of KCNN4 expression could reduce migration and invasion abilities of HCC cells. High content analysis result showed that down-regulated KCNN4 could inhibit the ability of HCC cell proliferation. The mitogen-activated protein kinase (MAPK) pathway is active in cell proliferation, differentiation, migration, senescence, and apoptosis. Matrix metallopeptidase 9 and extracellular signal regulated kinase 1/2 (ERK1/2) were important biomarkers of MAPK/ERK pathway, knockdown of KCNN4 reduced the expression of MMP9 and ERK1/2. These findings showed that KCNN4 promotes HCC invasion and metastasis through the MAPK/ERK pathway.

Mechanosensitive ion channels push cancer progression

In many cases, the mechanical properties of a tumor are different from those of the host tissue. Mechanical cues regulate cancer development by affecting both tumor cells and their microenvironment, by altering cell migration, proliferation, extracellular matrix remodeling and metastatic spread. Cancer cells sense mechanical stimuli such as tissue stiffness, shear stress, tissue pressure of the extracellular space (outside-in mechanosensation). These mechanical cues are transduced into a cellular response (e. g. cell migration and proliferation; inside-in mechanotransduction) or to a response affecting the microenvironment (e. g. inducing a fibrosis or building up growth-induced pressure; inside-out mechanotransduction). These processes heavily rely on mechanosensitive membrane proteins, prominently ion channels. Mechanosensitive ion channels are involved in the Ca²⁺-signaling of the tumor and stroma cells, both directly, by mediating Ca²⁺ influx (e. g. Piezo and TRP channels), or indirectly, by maintaining the electrochemical gradient necessary for Ca²⁺ influx (e. g. K_2P, K_Ca channels). This review aims to discuss the diverse roles of mechanosenstive ion channels in cancer progression, especially those involved in Ca²⁺-signaling, by pinpointing their functional relevance in tumor pathophysiology.

KCa3.1 Transgene Induction in Murine Intestinal Epithelium Causes Duodenal Chyme Accumulation and Impairs Duodenal Contractility

The epithelial intermediate-conductance calcium/calmodulin-regulated KCa3.1 channel is considered to be a regulator of intestine function by controlling chloride secretion and water/salt balance. Yet, little is known about the functional importance of KCa3.1 in the intestinal epithelium in vivo. Our objective was to determine the impact of epithelial-specific inducible overexpression of a KCa3.1 transgene (KCa3.1+) and of inducible suppression (KCa3.1−) on intestinal homeostasis and function in mice. KCa3.1 overexpression in the duodenal epithelium of doxycycline (DOX)-treated KCa3.1+ mice was 40-fold above the control levels. Overexpression caused an inflated duodenum and doubling of the chyme content. Histology showed conserved architecture of crypts, villi, and smooth muscle. Unaltered proliferating cell nuclear antigen (PCNA) immune reactivity and reduced amounts of terminal deoxynucleotide transferase mediated X-dUTP nick end labeling (TUNEL)-positive apoptotic cells in villi indicated lower epithelial turnover. Myography showed a reduction in the frequency of spontaneous propulsive muscle contractions with no change in amplitude. The amount of stool in the colon was increased and the frequency of colonic contractions was reduced in KCa3.1+ animals. Senicapoc treatment prevented the phenotype. Suppression of KCa3.1 in DOX-treated KCa3.1− mice caused no overt intestinal phenotype. In conclusion, inducible KCa3.1 overexpression alters intestinal functions by increasing the chyme content and reducing spontaneous contractions and epithelial apoptosis. Induction of epithelial KCa3.1 can play a mechanistic role in the process of adaptation of the intestine.

Designing Ruthenium Anticancer Drugs: What Have We Learnt from the Key Drug Candidates?

After nearly 20 years of research on the use of ruthenium in the fight against cancer, only two Ru(III) coordination complexes have advanced to clinical trials. During this time, the field has produced excellent candidate drugs with outstanding in vivo and in vitro activity; however, we have yet to find a ruthenium complex that would be a viable alternative to platinum drugs currently used in the clinic. We aimed to explore what we have learned from the most prominent complexes in the area, and to challenge new concepts in chemical design. Particularly relevant are studies involving NKP1339, NAMI-A, RM175, and RAPTA-C, which have paved the way for current research. We explored the development of the ruthenium anticancer field considering that the mechanism of action of complexes no longer focuses solely on DNA interactions, but explores a diverse range of cellular targets involving multiple chemical strategies.

The potassium channel KCa3.1 promotes cell proliferation by activating SKP2 and metastasis through the EMT pathway in hepatocellular carcinoma

The intermediate conductance calcium-activated potassium channel (KCa3.1) plays an important role in maintaining intracellular calcium homeostasis and is involved in the tumorigenesis of many human cancers. However, it is unknown whether KCa3.1 plays a role in the genesis of hepatocellular carcinoma (HCC), one of the most common malignant tumors worldwide with a very poor prognosis. In our study, we found that the expression of KCa3.1 was significantly elevated in poorly differentiated HCC tissues compared to adjacent noncancerous tissues. In vitro and in vivo experiments showed that KCa3.1 could promote cell proliferation, migration, and invasion of HCC. Mechanistically, KCa3.1 promoted cell cycle progression and migration and invasion of HCC cells by activating S-phase protein kinase 2 (SKP2) to trigger the degradation of p21 and p27 and targeting Reelin (RELN) to induce epithelial-mesenchymal transition (EMT), respectively. Taken together, our results demonstrate that KCa3.1 plays an important role in the genesis and progression of HCC, implying that it might be a promising therapeutic target in HCC.