Therapeutic potential of KCa3.1 blockers: recent advances and promising trends

Intermediate conductance calcium-activated potassium channel (KCa3.1) in cancer: Emerging roles and therapeutic potentials

The KCa3.1 channel (also known as the KCNN4, IK1, or SK4 channel) is an intermediate-conductance calcium-activated potassium channel that regulates the membrane potential and maintains calcium homeostasis. Recently, KCa3.1 channels have attracted increasing attention because of their diverse roles in various types of cancers. In cancer cells, KCa3.1 channels regulate key processes, including cell proliferation, cell cycle, migration, invasion, tumor microenvironments, and therapy resistance. In addition, abnormal KCa3.1 expression in cancers is utilized to distinguish between tumor and normal tissues, classify cancer stages, and predict patient survival outcomes. This review comprehensively examines the current understanding of the contribution of KCa3.1 channels to tumor formation, metastasis, and its mechanisms. We evaluated the potential of KCa3.1 as a biomarker for cancer diagnosis and prognosis. Finally, we discuss the advances and challenges of applying KCa3.1 modulators in cancer treatment and propose approaches to overcome these obstacles. In summary, this review highlights the importance of this ion channel as a potent therapeutic target and prognostic biomarker of cancer.

Chronic kidney disease leads to microglial potassium efflux and inflammasome activation in the brain

Cognitive impairment is common in extracerebral diseases such as chronic kidney disease (CKD). Kidney transplantation reverses cognitive impairment, indicating that cognitive impairment driven by CKD is therapeutically amendable. However, we lack mechanistic insights allowing development of targeted therapies. Using a combination of mouse models (including mice with neuron-specific IL-1R1 deficiency), single cell analyses (single-nuclei RNA-sequencing and single-cell thallium autometallography), human samples and in vitro experiments we demonstrate that microglia activation impairs neuronal potassium homeostasis and cognition in CKD. CKD disrupts the barrier of brain endothelial cells in vitro and the blood-brain barrier in vivo, establishing that the uremic state modifies vascular permeability in the brain. Exposure to uremic conditions impairs calcium homeostasis in microglia, enhances microglial potassium efflux via the calcium-dependent channel KCa3.1, and induces p38-MAPK associated IL-1β maturation in microglia. Restoring potassium homeostasis in microglia using a KCa3.1-specific inhibitor (TRAM34) improves CKD-triggered cognitive impairment. Likewise, inhibition of the IL-1β receptor 1 (IL-1R1) using anakinra or genetically abolishing neuronal IL-1R1 expression in neurons prevent CKD-mediated reduced neuronal potassium turnover and CKD-induced impaired cognition. Accordingly, in CKD mice, impaired cognition can be ameliorated by either preventing microglia activation or inhibiting IL-1R-signaling in neurons. Thus, our data suggest that potassium efflux from microglia triggers their activation, which promotes microglia IL-1β release and IL-1R1-mediated neuronal dysfunction in CKD. Hence, our study provides new mechanistic insight into cognitive impairment in association with CKD and identifies possible new therapeutic approaches.

Effects of Natural Products through Inhibiting Endoplasmic Reticulum Stress on Attenuation of Idiopathic Pulmonary Fibrosis

With ever-increasing intensive studies of idiopathic pulmonary fibrosis (IPF), significant progresses have been made. Endoplasmic reticulum stress (ERS)/unfolded protein reaction (UPR) is associated with the development and progression of IPF, and targeting ERS/UPR may be beneficial in the treatment of IPF. Natural product is a tremendous source of new drug discovery, and accumulating studies have reported that many natural products show potential therapeutic effects for IPF via modulating one or more branches of the ERS signaling pathway. Therefore, this review focuses on critical roles of ERS in IPF development, and summarizes herbal preparations and bioactive compounds which protect against IPF through regulating ERS.

Challenges in the Therapeutic Targeting of KCa Channels: From Basic Physiology to Clinical Applications

Calcium-activated potassium (KCa) channels are ubiquitously expressed throughout the body and are able to regulate membrane potential and intracellular calcium concentrations, thereby playing key roles in cellular physiology and signal transmission. Consequently, it is unsurprising that KCa channels have been implicated in various diseases, making them potential targets for pharmaceutical interventions. Over the past two decades, numerous studies have been conducted to develop KCa channel-targeting drugs, including those for disorders of the central and peripheral nervous, cardiovascular, and urinary systems and for cancer. In this review, we synthesize recent findings regarding the structure and activating mechanisms of KCa channels. We also discuss the role of KCa channel modulators in therapeutic medicine. Finally, we identify the major reasons behind the delay in bringing these modulators to the pharmaceutical market and propose new strategies to promote their application.

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.

Potassium channels as novel molecular targets in hepatocellular carcinoma (Review)

Hepatocellular carcinoma (HCC) poses a serious health burden worldwide. It is often not diagnosed until the patient is at an advanced stage of the disease, when treatment options are limited and the prognosis is poor. Therefore, novel treatment strategies are urgently required. Potassium (K+) channels have an important role in HCC, including regulating the proliferation, migration, invasion and drug resistance of HCC cells. The aim of the present review was therefore to survey the relevant publications that have investigated K+ channels not only as markers for the early diagnosis of HCC, but also as potential therapeutic targets for the treatment of HCC. Several of these channels have been indicated to be the sites of action for natural products previously known to inhibit HCC; however, more systematic studies are required to determine which K+ channels may be utilized for the clinical treatment of HCC, particularly in the advanced stages of the disease and in cases where patients are resistant to the existing drugs.

KCa2 and KCa3.1 Channels in the Airways: A New Therapeutic Target

K⁺ channels are involved in many critical functions in lung physiology. Recently, the family of Ca²⁺-activated K⁺ channels (K_Ca) has received more attention, and a massive amount of effort has been devoted to developing selective medications targeting these channels. Within the family of K_Ca channels, three small-conductance Ca²⁺-activated K⁺ (K_Ca2) channel subtypes, together with the intermediate-conductance K_Ca3.1 channel, are voltage-independent K⁺ channels, and they mediate Ca²⁺-induced membrane hyperpolarization. Many K_Ca2 channel members are involved in crucial roles in physiological and pathological systems throughout the body. In this article, different subtypes of K_Ca2 and K_Ca3.1 channels and their functions in respiratory diseases are discussed. Additionally, the pharmacology of the K_Ca2 and K_Ca3.1 channels and the link between these channels and respiratory ciliary regulations will be explained in more detail. In the future, specific modulators for small or intermediate Ca²⁺-activated K⁺ channels may offer a unique therapeutic opportunity to treat muco-obstructive lung diseases.

TRPM2 Channels: A Potential Therapeutic Target in Melanoma?

The transient receptor potential, the melastatin (TRPM) subfamily, which consists of eight known members, appears to have significant importance in melanoma progression, treatment, and prognosis. As several members were originally cloned from cancerous tissue, initial studies aimed towards identifying TRPM involvement in cancer progression and tumorigenesis. For relevance in skin cancer, previous research has shown roles for several TRPM members in skin cancer progression, growth, and patient prognosis. One unique member, TRPM2, appears to have notable therapeutic potential in the treatment of melanoma. Previous and recent studies have demonstrated increased TRPM2 expression levels in melanoma, as well as important roles for TRPM2 in melanoma growth, proliferation, and survival. TRPM2 is thus an emerging target in the treatment of melanoma, where TRPM2 antagonism may offer an additional treatment option for melanoma patients in the future.

5-Chloro-2-Guanidinobenzimidazole (ClGBI) Is a Non-Selective Inhibitor of the Human HV1 Channel

5-chloro-2-guanidinobenzimidazole (ClGBI), a small-molecule guanidine derivative, is a known effective inhibitor of the voltage-gated proton (H⁺) channel (H_V1, K_d ≈ 26 μM) and is widely used both in ion channel research and functional biological assays. However, a comprehensive study of its ion channel selectivity determined by electrophysiological methods has not been published yet. The lack of selectivity may lead to incorrect conclusions regarding the role of hHv1 in physiological or pathophysiological responses in vitro and in vivo. We have found that ClGBI inhibits the proliferation of lymphocytes, which absolutely requires the functioning of the K_V1.3 channel. We, therefore, tested ClGBI directly on hK_V1.3 using a whole-cell patch clamp and found an inhibitory effect similar in magnitude to that seen on hH_V1 (K_d ≈ 72 μM). We then further investigated ClGBI selectivity on the hK_V1.1, hK_V1.4-IR, hK_V1.5, hK_V10.1, hK_V11.1, hK_Ca3.1, hNa_V1.4, and hNa_V1.5 channels. Our results show that, besides H_V1 and K_V1.3, all other off-target channels were inhibited by ClGBI, with K_d values ranging from 12 to 894 μM. Based on our comprehensive data, ClGBI has to be considered a non-selective hH_V1 inhibitor; thus, experiments aiming at elucidating the significance of these channels in physiological responses have to be carefully evaluated.

Endothelial KCa channels: Novel targets to reduce atherosclerosis-driven vascular dysfunction

Elevated levels of cholesterol in the blood can induce endothelial dysfunction, a condition characterized by impaired nitric oxide production and decreased vasodilatory capacity. Endothelial dysfunction can promote vascular disease, such as atherosclerosis, where macrophages accumulate in the vascular intima and fatty plaques form that impair normal blood flow in conduit arteries. Current pharmacological strategies to treat atherosclerosis mostly focus on lipid lowering to prevent high levels of plasma cholesterol that induce endothelial dysfunction and atherosclerosis. While this approach is effective for most patients with atherosclerosis, for some, lipid lowering is not enough to reduce their cardiovascular risk factors associated with atherosclerosis (e.g., hypertension, cardiac dysfunction, stroke, etc.). For such patients, additional strategies targeted at reducing endothelial dysfunction may be beneficial. One novel strategy to restore endothelial function and mitigate atherosclerosis risk is to enhance the activity of Ca2+-activated K+ (KCa) channels in the endothelium with positive gating modulator drugs. Here, we review the mechanism of action of these small molecules and discuss their ability to improve endothelial function. We then explore how this strategy could mitigate endothelial dysfunction in the context of atherosclerosis by examining how KCa modulators can improve cardiovascular function in other settings, such as aging and type 2 diabetes. Finally, we consider questions that will need to be addressed to determine whether KCa channel activation could be used as a long-term add-on to lipid lowering to augment atherosclerosis treatment, particularly in patients where lipid-lowering is not adequate to improve their cardiovascular health.

Activated fibroblasts in cardiac and cancer fibrosis: An overview of analogies and new potential therapeutic options

Heart disease and cancer are two major causes of morbidity and mortality in the industrialized countries, and their increasingly recognized connections are shifting the focus from single disease studies to an interdisciplinary approach. Fibroblast-mediated intercellular crosstalk is critically involved in the evolution of both pathologies. In healthy myocardium and in non-cancerous conditions, resident fibroblasts are the main cell source for synthesis of the extracellular matrix (ECM) and important sentinels of tissue integrity. In the setting of myocardial disease or cancer, quiescent fibroblasts activate, respectively, into myofibroblasts (myoFbs) and cancer-associated fibroblasts (CAFs), characterized by increased production of contractile proteins, and by a highly proliferative and secretory phenotype. Although the initial activation of myoFbs/CAFs is an adaptive process to repair the damaged tissue, massive deposition of ECM proteins leads to maladaptive cardiac or cancer fibrosis, a recognized marker of adverse outcome. A better understanding of the key mechanisms orchestrating fibroblast hyperactivity may help developing innovative therapeutic options to restrain myocardial or tumor stiffness and improve patient prognosis. Albeit still unappreciated, the dynamic transition of myocardial and tumor fibroblasts into myoFbs and CAFs shares several common triggers and signaling pathways relevant to TGF-β dependent cascade, metabolic reprogramming, mechanotransduction, secretory properties, and epigenetic regulation, which might lay the foundation for future antifibrotic intervention. Therefore, the aim of this review is to highlight emerging analogies in the molecular signature underlying myoFbs and CAFs activation with the purpose of identifying novel prognostic/diagnostic biomarkers, and to elucidate the potential of drug repositioning strategies to mitigate cardiac/cancer fibrosis.

Functional Potassium Channels in Macrophages

Macrophages are the predominant component of innate immunity, which is an important protective barrier of our body. Macrophages are present in all organs and tissues of the body, their main functions include immune surveillance, bacterial killing, tissue remodeling and repair, and clearance of cell debris. In addition, macrophages can present antigens to T cells and facilitate inflammatory response by releasing cytokines. Macrophages are of high concern due to their crucial roles in multiple physiological processes. In recent years, new advances are emerging after great efforts have been made to explore the mechanisms of macrophage activation. Ion channel is a class of multimeric transmembrane protein that allows specific ions to go through cell membrane. The flow of ions through ion channel between inside and outside of cell membrane is required for maintaining cell morphology and intracellular signal transduction. Expressions of various ion channels in macrophages have been detected. The roles of ion channels in macrophage activation are gradually caught attention. K⁺ channels are the most studied channels in immune system. However, very few of published papers reviewed the studies of K⁺ channels on macrophages. Here, we will review the four types of K⁺ channels that are expressed in macrophages: voltage-gated K⁺ channel, calcium-activated K⁺ channel, inwardly rectifying K⁺ channel and two-pore domain K⁺ channel.

Characterization and Chemical Synthesis of Cm39 (α-KTx 4.8): A Scorpion Toxin That Inhibits Voltage-Gated K+ Channel KV1.2 and Small- and Intermediate-Conductance Ca2+-Activated K+ Channels KCa2.2 and KCa3.1

A novel peptide, Cm39, was identified in the venom of the scorpion Centruroides margaritatus. Its primary structure was determined. It consists of 37 amino acid residues with a MW of 3980.2 Da. The full chemical synthesis and proper folding of Cm39 was obtained. Based on amino acid sequence alignment with different K+ channel inhibitor scorpion toxin (KTx) families and phylogenetic analysis, Cm39 belongs to the α-KTx 4 family and was registered with the systematic number of α-KTx 4.8. Synthetic Cm39 inhibits the voltage-gated K+ channel hKV1.2 with high affinity (Kd = 65 nM). The conductance-voltage relationship of KV1.2 was not altered in the presence of Cm39, and the analysis of the toxin binding kinetics was consistent with a bimolecular interaction between the peptide and the channel; therefore, the pore blocking mechanism is proposed for the toxin-channel interaction. Cm39 also inhibits the Ca2+-activated KCa2.2 and KCa3.1 channels, with Kd = 502 nM, and Kd = 58 nM, respectively. However, the peptide does not inhibit hKV1.1, hKV1.3, hKV1.4, hKV1.5, hKV1.6, hKV11.1, mKCa1.1 K+ channels or the hNaV1.5 and hNaV1.4 Na+ channels at 1 μM concentrations. Understanding the unusual selectivity profile of Cm39 motivates further experiments to reveal novel interactions with the vestibule of toxin-sensitive channels.

Synergistic effects of agonists and two-pore-domain potassium channels on secretory responses of human pancreatic duct cells Capan-1

Mechanisms of synergistic agonist stimulation and modulation of the electrochemical driving force for anion secretion are still not fully explored in human pancreatic duct epithelial cells. The first objective of this study was therefore to test whether combined agonist stimulation augments anion transport responses in the Capan-1 monolayer model of human pancreatic duct epithelium. The second objective was to test the influence of H⁺,K⁺-ATPase inhibition on anion transport in Capan-1 monolayers. The third objective was to analyze the expression and function of K⁺ channels in Capan-1, which could support anion secretion and cooperate with H⁺,K⁺-ATPases in pH and potassium homeostasis. The human pancreatic adenocarcinoma cell line Capan-1 was cultured conventionally or as polarized monolayers that were analyzed by Ussing chamber electrophysiological recordings. Single-cell intracellular calcium was assayed with Fura-2. mRNA isolated from Capan-1 was analyzed by use of the nCounter assay or RT-PCR. Protein expression was assessed by immunofluorescence and western blot analyses. Combined stimulation with different physiological agonists enhanced anion transport responses compared to single agonist stimulation. The responsiveness of Capan-1 cells to histamine was also revealed in these experiments. The H⁺,K⁺-ATPase inhibitor omeprazole reduced carbachol- and riluzole-induced anion transport responses. Transcript analyses revealed abundant TASK-2, TWIK-1, TWIK-2, TASK-5, K_Ca3.1, and KCNQ1 mRNA expression. KCNE1 mRNA and TREK-1, TREK-2, TASK-2, and KCNQ1 protein expression were also shown. This study shows that the Capan-1 model recapitulates key physiological aspects of a bicarbonate-secreting epithelium and constitutes a valuable model for functional studies on human pancreatic duct epithelium.

Functional cooperation between IKCa and TRPC1 channels regulates serum-induced vascular smooth muscle cell proliferation via mediating Ca2+ influx and ERK1/2 activation

The increased proliferation of vascular smooth muscle cells (VSMCs) contributes to the pathogenesis of vascular diseases. The intermediate conductance calcium-activated potassium (IK_Ca ) channel plays a critical role in VSMC proliferation by raising the intracellular calcium concentration ([Ca²⁺ ]_i ), but the underlying mechanism is still not unclear. Here we investigated the cooperation between IK_Ca and transient receptor potential canonical 1 (TRPC1) channels in mediating extracellular Ca²⁺ entry, which in turn activates downstream Ca²⁺ signalling in the regulation of VSMC proliferation using serum-induced cell proliferation model. Serum-induced cell proliferation was accompanied with up-regulation of IK_Ca expression and an increase in [Ca²⁺ ]_i . Serum-induced cell proliferation and increase in [Ca²⁺ ]_i were suppressed by IK_Ca inhibition with TRAM-34 or IK_Ca knockdown. Serum-induced cell proliferation was strongly reduced by the removal of extracellular Ca²⁺ with EGTA or intracellular Ca²⁺ with BAPTA-AM and, additionally, by TRPC1 knockdown. Moreover, the increase in [Ca²⁺ ]_i induced by serum or by IK_Ca activation with 1-EBIO was attenuated by TRPC1 knockdown. Finally, serum induced ERK1/2 activation, which was attenuated by treatment with TRAM-34 or BAPTA-AM, as well as TRPC1 knockdown. Consistently, serum-induced cell proliferation was suppressed by ERK1/2 inhibition with PD98059. Taken together, these results suggest that the IK_Ca and TRPC1 channels cooperate in mediating Ca²⁺ influx that activates the ERK1/2 pathway to promote cell proliferation, thus providing new mechanistic insights into VSMC proliferation.

Ion channel regulation of gut immunity

Mounting evidence indicates that gastrointestinal (GI) homeostasis hinges on communications among many cellular networks including the intestinal epithelium, the immune system, and both intrinsic and extrinsic nerves innervating the gut. The GI tract, especially the colon, is the home base for gut microbiome which dynamically regulates immune function. The gut's immune system also provides an effective defense against harmful pathogens entering the GI tract while maintaining immune homeostasis to avoid exaggerated immune reaction to innocuous food and commensal antigens which are important causes of inflammatory disorders such as coeliac disease and inflammatory bowel diseases (IBD). Various ion channels have been detected in multiple cell types throughout the GI tract. By regulating membrane properties and intracellular biochemical signaling, ion channels play a critical role in synchronized signaling among diverse cellular components in the gut that orchestrates the GI immune response. This work focuses on the role of ion channels in immune cells, non-immune resident cells, and neuroimmune interactions in the gut at the steady state and pathological conditions. Understanding the cellular and molecular basis of ion channel signaling in these immune-related pathways and initial testing of pharmacological intervention will facilitate the development of ion channel-based therapeutic approaches for the treatment of intestinal inflammation.

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.

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.

Potassium Channels as a Target for Cancer Therapy: Current Perspectives

Potassium (K⁺) channels are highly regulated membrane proteins that control the potassium ion flux and respond to different cellular stimuli. These ion channels are grouped into three major families, Kv (voltage-gated K⁺ channel), Kir (inwardly rectifying K⁺ channel) and K2P (two-pore K⁺ channels), according to the structure, to mediate the K⁺ currents. In cancer, alterations in K⁺ channel function can promote the acquisition of the so-called hallmarks of cancer – cell proliferation, resistance to apoptosis, metabolic changes, angiogenesis, and migratory capabilities – emerging as targets for the development of new therapeutic drugs. In this review, we focus our attention on the different K⁺ channels associated with the most relevant and prevalent cancer types. We summarize our knowledge about the potassium channels structure and function, their cancer dysregulated expression and discuss the K⁺ channels modulator and the strategies for designing new drugs.

Retroviral glycoprotein-mediated immune suppression via the potassium channel KCa3.1 - A new strategy for amelioration of inflammatory bowel diseases

Peptides derived from retroviral envelope proteins have been shown to possess a wide range of immunosuppressive and anti-inflammatory activities. We have previously reported identification of such a peptide derived from the envelope protein coded by a human endogenous retrovirus (HERV). In this study, we identified that in vitro the peptide inhibits the K_Ca3.1 potassium channel, a potential target for therapy of immune diseases. We describe in vitro ENV59-GP3 effects with respect to potency of inhibition on K_Ca3.1 channels and calcium influx. Furthermore, we asses in vivo the effect of blocking K_Ca3.1 with ENV59-GP3 peptide or K_Ca3.1-blocker NS6180 on protection against DSS-induced acute colitis. ENV59-GP3 peptide treatment showed reduction of the disease score in the DSS-induced acute colitis mice model, which was comparable to effects of the K_Ca3.1 channel blocker NS6180. Analysis of cytokine production from DSS-mice model treated animals revealed equipotent inhibitory effects of the ENV59-GP3 and NS6180 compounds on the production of IL-6, TNF-α, IL-1β. These findings altogether suggest that ENV59-GP3 functions as a K_Ca3.1 channel inhibitor and underline the implications of using virus derived channel blockers for treatment of autoimmune diseases. Additionally, they open the possibilities whether K_Ca3.1 inhibition is efficacious in patients with inflammatory bowel diseases.

How the Potassium Channel Response of T Lymphocytes to the Tumor Microenvironment Shapes Antitumor Immunity

Competent antitumor immune cells are fundamental for tumor surveillance and combating active cancers. Once established, tumors generate a tumor microenvironment (TME) consisting of complex cellular and metabolic elements that serve to suppress the function of antitumor immune cells. T lymphocytes are key cellular elements of the TME. In this review, we explore the role of ion channels, particularly K+ channels, in mediating the suppressive effects of the TME on T cells. First, we will review the complex network of ion channels that mediate Ca2+ influx and control effector functions in T cells. Then, we will discuss how multiple features of the TME influence the antitumor capabilities of T cells via ion channels. We will focus on hypoxia, adenosine, and ionic imbalances in the TME, as well as overexpression of programmed cell death ligand 1 by cancer cells that either suppress K+ channels in T cells and/or benefit from regulating these channels’ activity, ultimately shaping the immune response. Finally, we will review some of the cancer treatment implications related to ion channels. A better understanding of the effects of the TME on ion channels in T lymphocytes could promote the development of more effective immunotherapies, especially for resistant solid malignancies.

Ca2+ Signalling and Hypoxia/Acidic Tumour Microenvironment Interplay in Tumour Progression

Solid tumours are characterised by an altered microenvironment (TME) from the physicochemical point of view, displaying a highly hypoxic and acidic interstitial fluid. Hypoxia results from uncontrolled proliferation, aberrant vascularization and altered cancer cell metabolism. Tumour cellular apparatus adapts to hypoxia by altering its metabolism and behaviour, increasing its migratory and metastatic abilities by the acquisition of a mesenchymal phenotype and selection of aggressive tumour cell clones. Extracellular acidosis is considered a cancer hallmark, acting as a driver of cancer aggressiveness by promoting tumour metastasis and chemoresistance via the selection of more aggressive cell phenotypes, although the underlying mechanism is still not clear. In this context, Ca2+ channels represent good target candidates due to their ability to integrate signals from the TME. Ca2+ channels are pH and hypoxia sensors and alterations in Ca2+ homeostasis in cancer progression and vascularization have been extensively reported. In the present review, we present an up-to-date and critical view on Ca2+ permeable ion channels, with a major focus on TRPs, SOCs and PIEZO channels, which are modulated by tumour hypoxia and acidosis, as well as the consequent role of the altered Ca2+ signals on cancer progression hallmarks. We believe that a deeper comprehension of the Ca2+ signalling and acidic pH/hypoxia interplay will break new ground for the discovery of alternative and attractive therapeutic targets.

Metabolic Reprogramming in Cancer Cells: Emerging Molecular Mechanisms and Novel Therapeutic Approaches

The constant changes in cancer cell bioenergetics are widely known as metabolic reprogramming. Reprogramming is a process mediated by multiple factors, including oncogenes, growth factors, hypoxia-induced factors, and the loss of suppressor gene function, which support malignant transformation and tumor development in addition to cell heterogeneity. Consequently, this hallmark promotes resistance to conventional anti-tumor therapies by adapting to the drastic changes in the nutrient microenvironment that these therapies entail. Therefore, it represents a revolutionary landscape during cancer progression that could be useful for developing new and improved therapeutic strategies targeting alterations in cancer cell metabolism, such as the deregulated mTOR and PI3K pathways. Understanding the complex interactions of the underlying mechanisms of metabolic reprogramming during cancer initiation and progression is an active study field. Recently, novel approaches are being used to effectively battle and eliminate malignant cells. These include biguanides, mTOR inhibitors, glutaminase inhibition, and ion channels as drug targets. This review aims to provide a general overview of metabolic reprogramming, summarise recent progress in this field, and emphasize its use as an effective therapeutic target against cancer.

Senicapoc treatment in COVID-19 patients with severe respiratory insufficiency-A randomized, open-label, phase II trial

BACKGROUND

The aim of the current study was to determine if treatment with senicapoc, improves the PaO₂ /FiO₂ ratio in patients with COVID-19 and severe respiratory insufficiency.

METHODS

Investigator-initiated, randomized, open-label, phase II trial in four intensive care units (ICU) in Denmark. We included patients aged ≥18 years and admitted to an ICU with severe respiratory insufficiency due to COVID-19. The intervention consisted of 50 mg enteral senicapoc administered as soon as possible after randomization and again after 24 h. Patients in the control group received standard care only. The primary outcome was the PaO₂ /FiO₂ ratio at 72 h.

RESULTS

Twenty patients were randomized to senicapoc and 26 patients to standard care. Important differences existed in patient characteristics at baseline, including more patients being on non-invasive/invasive ventilation in the control group (54% vs. 35%). The median senicapoc concentration at 72 h was 62.1 ng/ml (IQR 46.7-71.2). The primary outcome, PaO₂ /FiO₂ ratio at 72 h, was significantly lower in the senicapoc group (mean 19.5 kPa, SD 6.6) than in the control group (mean 24.4 kPa, SD 9.2) (mean difference -5.1 kPa [95% CI -10.2, -0.04] p = .05). The 28-day mortality in the senicapoc group was 2/20 (10%) compared with 6/26 (23%) in the control group (OR 0.36 95% CI 0.06-2.07, p = .26).

CONCLUSIONS

Treatment with senicapoc resulted in a significantly lower PaO₂ /FiO₂ ratio at 72 h with no differences for other outcomes.

Muscle Damage in Dystrophic mdx Mice Is Influenced by the Activity of Ca2+-Activated KCa3.1 Channels

Duchenne muscular dystrophy (DMD) is an X-linked disease, caused by a mutant dystrophin gene, leading to muscle membrane instability, followed by muscle inflammation, infiltration of pro-inflammatory macrophages and fibrosis. The calcium-activated potassium channel type 3.1 (K_Ca3.1) plays key roles in controlling both macrophage phenotype and fibroblast proliferation, two critical contributors to muscle damage. In this work, we demonstrate that pharmacological blockade of the channel in the mdx mouse model during the early degenerative phase favors the acquisition of an anti-inflammatory phenotype by tissue macrophages and reduces collagen deposition in muscles, with a concomitant reduction of muscle damage. As already observed with other treatments, no improvement in muscle performance was observed in vivo. In conclusion, this work supports the idea that K_Ca3.1 channels play a contributing role in controlling damage-causing cells in DMD. A more complete understanding of their function could lead to the identification of novel therapeutic approaches.

Evaluation of a novel combination of TRAM-34 and ascorbic acid for the treatment of corneal fibrosis in vivo

Corneal injury and aberrant wound healing commonly result in corneal fibrosis and subsequent vision loss. Intermediate-conductance calmodulin/calcium-activated K+ channels (KCa3.1) have been shown to promote fibrosis in non-ocular and ocular tissues via upregulation of transforming growth factor beta (TGFβ). TRAM-34 is a selective inhibitor of KCa3.1 and reduces fibrosis by downregulation of TGFβ-induced transdifferentiation of stromal fibroblasts to myofibroblasts. Ascorbic acid has been demonstrated to be effective in promoting corneal re-epithelialization and reduction of neovascularization via anti-VEGF and anti-MMP mechanisms. This study evaluates tolerability and efficacy of a novel combination of TRAM-34 (25μM) and ascorbic acid (10%) topical treatment for corneal fibrosis using an established in vivo rabbit model and conducting clinical eye examinations. Markers of corneal fibrosis were evaluated in all corneas at study endpoint via histopathology, immunofluorescence, and quantitative real-time PCR. The eyedrop treated eyes showed significantly improved clinical outcomes based on modified McDonald Shadduck scores, reduction of clinical haze on Fantes scores, and reduction of central corneal thickness (CCT). At cellular and molecular levels, eyedrop treatment also significantly reduced expression of alpha smooth muscle actin (α-SMA) mRNA and protein, collagen III mRNA, and fibronectin mRNA compared to non-treated eyes. Our study suggests that a tested new bimodal eyedrop is well tolerated and effectively reduces corneal fibrosis/haze in rabbits in vivo.

Reciprocal Relationship between Ca2+ Signaling and Ca2+-Gated Ion Channels as a Potential Target for Drug Discovery

Cellular Ca²⁺ signaling functions as one of the most common second messengers of various signal transduction pathways in cells and mediates a number of physiological roles in a cell-type dependent manner. Ca²⁺ signaling also regulates more general and fundamental cellular activities, including cell proliferation and apoptosis. Among ion channels, Ca²⁺-permeable channels in the plasma membrane as well as endo- and sarcoplasmic reticulum membranes play important roles in Ca²⁺ signaling by directly contributing to the influx of Ca²⁺ from extracellular spaces or its release from storage sites, respectively. Furthermore, Ca²⁺-gated ion channels in the plasma membrane often crosstalk reciprocally with Ca²⁺ signals and are central to the regulation of cellular functions. This review focuses on the physiological and pharmacological impact of i) Ca²⁺-gated ion channels as an apparatus for the conversion of cellular Ca²⁺ signals to intercellularly propagative electrical signals and ii) the opposite feedback regulation of Ca²⁺ signaling by Ca²⁺-gated ion channel activities in excitable and non-excitable cells.

Why do platelets express K+ channels?

Potassium ions have widespread roles in cellular homeostasis and activation as a consequence of their large outward concentration gradient across the surface membrane and ability to rapidly move through K+-selective ion channels. In platelets, the predominant K+ channels include the voltage-gated K+ channel Kv1.3, and the intermediate conductance Ca2+-activated K+ channel KCa3.1, also known as the Gardos channel. Inwardly rectifying potassium GIRK channels and KCa1.1 large conductance Ca2+-activated K+ channels have also been reported in the platelet, although they remain to be demonstrated using electrophysiological techniques. Whole-cell patch clamp and fluorescent indicator measurements in the platelet or their precursor cell reveal that Kv1.3 sets the resting membrane potential and KCa3.1 can further hyperpolarize the cell during activation, thereby controlling Ca2+ influx. Kv1.3-/- mice exhibit an increased platelet count, which may result from an increased splenic megakaryocyte development and longer platelet lifespan. This review discusses the evidence in the literature that Kv1.3, KCa3.1. GIRK and KCa1.1 channels contribute to a number of platelet functional responses, particularly collagen-evoked adhesion, procoagulant activity and GPCR function. Putative roles for other K+ channels and known accessory proteins which to date have only been detected in transcriptomic or proteomic studies, are also discussed.

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.

Comparison of K+ Channel Families

K⁺ channels enable potassium to flow across the membrane with great selectivity. There are four K⁺ channel families: voltage-gated K (K_v), calcium-activated (K_Ca), inwardly rectifying K (K_ir), and two-pore domain potassium (K_2P) channels. All four K⁺ channels are formed by subunits assembling into a classic tetrameric (4x1P = 4P for the K_v, K_Ca, and K_ir channels) or tetramer-like (2x2P = 4P for the K_2P channels) architecture. These subunits can either be the same (homomers) or different (heteromers), conferring great diversity to these channels. They share a highly conserved selectivity filter within the pore but show different gating mechanisms adapted for their function. K⁺ channels play essential roles in controlling neuronal excitability by shaping action potentials, influencing the resting membrane potential, and responding to diverse physicochemical stimuli, such as a voltage change (K_v), intracellular calcium oscillations (K_Ca), cellular mediators (K_ir), or temperature (K_2P).

Inhibition of KCa3.1 Channels Suppresses Atrial Fibrillation via the Attenuation of Macrophage Pro-inflammatory Polarization in a Canine Model With Prolonged Rapid Atrial Pacing

Aims: To investigate the role of KCa3. 1 inhibition in macrophage pro-inflammatory polarization and vulnerability to atrial fibrillation (AF) in a canine model with prolonged rapid atrial pacing.

Materials and Methods: Twenty beagle dogs (weighing 8–10 kg) were randomly assigned to a sham group (n = 6), pacing group (n = 7) and pacing+TRAM-34 group (n = 7). An experimental model of AF was established by rapid pacing. TRAM-34 was administered to the Pacing+TRAM-34 group by slow intravenous injection (10 mg/kg), 3 times each day. After 7 days of pacing, the electrophysiology was measured in vivo. The levels of interleukin-1β (IL-1β), monocyte chemotactic protein-1 (MCP-1), tumor necrosis factor-α (TNF-α), CD68, c-Fos, p38, and NF-κB p65 in both atriums were measured by Western blotting, and the levels of inducible nitric oxide synthase (iNOS) and arginase1 (Arg-1) were measured by real-time PCR. Macrophage and KCa3.1 in macrophage in the atrium were quantized following double labeled immunofluorescent.

Results: Greater inducibility of AF, an extended duration of AF and lower atrial effective refractory period (AERP) were observed in the pacing group compared with those in the sham group. Both CD68-labeled macrophage and the expression of KCa3.1 in macrophage were elevated in the pacing group and inhibited by TRAM-34, led to higher iNOS expression, lower Arg-1 expression, elevated levels of IL-1β, MCP-1, and TNF-α in the atria, which could be reversed by TRAM-34 treatment (all P < 0.01). KCa3.1 channels were possibly activated via the p38/AP-1/NF-κB signaling pathway.

Conclusions: Inhibition of KCa3.1 suppresses vulnerability to AF by attenuating macrophage pro-inflammatory polarization and inflammatory cytokine secretion in a canine model with prolonged rapid atrial pacing.

Microglial Displacement of GABAergic Synapses Is a Protective Event during Complex Febrile Seizures

Complex febrile seizures (FSs) lead to a high risk of intractable temporal lobe epilepsy during adulthood, yet the pathological process of complex FSs is largely unknown. Here, we demonstrate that activated microglia extensively associated with glutamatergic neuronal soma displace surrounding GABAergic presynapses in complex FSs. Patch-clamp electrophysiology establishes that the microglial displacement of GABAergic presynapses abrogates a complex-FS-induced increase in GABAergic neurotransmission and neuronal excitability, whereas GABA exerts an excitatory action in this immature stage. Pharmacological inhibition of microglial displacement of GABAergic presynapses or selective ablation of microglia in CD11b^DTR mice promotes the generation of complex FSs. Blocking or deleting the P2Y₁₂ receptor (P2Y₁₂R) reduces microglial displacement of GABAergic presynapses and shortens the latency of complex FSs. Together, microglial displacement of GABAergic presynapses, regulated by P2Y₁₂R, reduces neuronal excitability to mitigate the generation of complex FSs. Microglial displacement is a protective event during the pathological process of complex FSs.

Potassium Channels in Cancer

Neoplastic transformation is reportedly associated with alterations of the potassium transport across plasma and intracellular membranes. These alterations have been identified as crucial elements of the tumourigenic reprogramming of cells. Potassium channels may contribute to cancer initiation, malignant progression and therapy resistance of tumour cells. The book chapter focusses on (oncogenic) potassium channels frequently upregulated in different tumour entities, upstream and downstream signalling of these channels, their contribution to the maintenance of cancer stemness and the formation of an immunosuppressive tumour microenvironment. In addition, their role in adaptation to tumour hypoxia, metabolic reprogramming, as well as tumour spreading and metastasis is discussed. Finally, we discuss how (oncogenic) potassium channels may confer treatment resistance of tumours against radiation and chemotherapy and thus might be harnessed for new therapy strategies, for instance, by repurposing approved drugs known to target potassium channels.

Effect of the KCa3.1 blocker, senicapoc, on cerebral edema and cardiovascular function after cardiac arrest - A randomized experimental rat study

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Senicapoc was successfully administered intravenously.

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Senicapoc did not reduce cerebral edema 4 h after cardiac arrest.

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Senicapoc did not increase mean arterial pressure within 4 h from resuscitation.

Aim

Formation of cerebral edema and cardiovascular dysfunction may worsen brain injury following cardiac arrest. We hypothesized that administration of the intermediate calcium-activated potassium (KCa3.1) channel blocker, senicapoc, would reduce cerebral edema and augment mean arterial pressure in the early post-resuscitation period.

Method

Male Sprague-Dawley rats, aged 11–15 weeks, were utilized in the study. Rats were exposed to 8 min of asphyxial cardiac arrest. Shortly after resuscitation, rats were randomized to receive either vehicle or senicapoc (10 mg/kg) intravenously. The primary outcome was cerebral wet to dry weight ratio 4 h after resuscitation. Secondary outcomes included mean arterial pressure, cardiac output, norepinephrine dose, inflammatory cytokines and neuron specific enolase levels. Additionally, a sub-study was conducted to validate intravenous administration of senicapoc.

Results

The sub-study revealed that senicapoc-treated rats maintained a significantly higher mean arterial pressure during administration of SKA-31 (a KCa3.1 channel opener).

The plasma concentration of senicapoc was 1060 ± 303 ng/ml 4 h after administration. Senicapoc did not reduce cerebral edema or augment mean arterial pressure 4 h after resuscitation. Likewise, cardiac function and norepinephrine dose did not vary between groups. Inflammatory cytokines and neuron specific enolase levels increased in both groups after resuscitation with no difference between groups. Senicapoc enhanced the PaO₂/FiO₂ ratio significantly 4 h after resuscitation.

Conclusion

Senicapoc was successfully administered intravenously after resuscitation, but did not reduce cerebral edema or increase mean arterial pressure in the early post-resuscitation period.

Increased Levels of ER Stress and Apoptosis in a Sheep Model for Pulmonary Fibrosis Are Alleviated by In Vivo Blockade of the KCa3.1 Ion Channel

Idiopathic pulmonary fibrosis (IPF) is a fatal interstitial lung disease, characterized by progressive damage to the lung tissues. Apoptosis and endoplasmic reticulum stress (ER stress) in type II alveolar epithelial cells (AECs) and lung macrophages have been linked with the development of IPF. Therefore, apoptosis- and ER stress-targeted therapies have drawn attention as potential avenues for treatment of IPF. The calcium-activated potassium ion channel KCa3.1 has been proposed as a potential therapeutic target for fibrotic diseases including IPF. While KCa3.1 is expressed in AECs and macrophages, its influence on ER stress and apoptosis during the disease process is unclear. We utilized a novel sheep model of pulmonary fibrosis to demonstrate that apoptosis and ER stress occur in type II AECs and macrophages in sheep with bleomycin-induced lung fibrosis. Apoptosis in type II AEC and macrophages was identified using the TUNEL method of tagging fragmented nuclear DNA, while ER stress was characterized by increased expression of GRP-78 ER chaperone proteins. We demonstrated that apoptosis and ER stress in type II AECs and macrophages increased significantly 2 weeks after the final bleomycin infusion and remained high for up to 7 weeks post-bleomycin injury. Senicapoc treatment significantly reduced the rates of ER stress in type II AECs and macrophages that were resident in bleomycin-infused lung segments. There were also significant reductions in the rates of apoptosis of type II AECs and macrophages in the lung segments of senicapoc-treated sheep. In vivo blockade of the KCa3.1 ion channel alleviates the ER stress and apoptosis in type II AECs and macrophages, and this effect potentially contributes to the anti-fibrotic effects of senicapoc.

KCa3.1 Inhibition of Macrophages Suppresses Inflammatory Response Leading to Endothelial Damage in a Cell Model of Kawasaki Disease

Purpose

Macrophages-mediated inflammation is linked with endothelial damage of Kawasaki disease (KD). KCa3.1, a calcium-activated potassium channel, modulates inflammation of macrophages. However, little is known about the role of KCa3.1 in inflammation by macrophages involved in KD. Hence, this study is aimed to explore the potential role of KCa3.1 in regulating inflammatory response by macrophages and subsequent vascular injury in an in vitro model of KD.

Methods

RAW264.7 cells were stimulated with Lactobacillus casei cell wall extract (LCWE) with or without TRAM-34 or PDTC or AG490. Subsequently, mouse coronary artery endothelial cells (MCAECs) were incubated with RAW264.7 cells-conditioned medium to mimic local inflammatory lesions in KD. CCKi8 assay was used to evaluate cell viability. The mRNA levels of inflammatory mediators were detected by qRT-PCR. Expressions of KCa3.1, MCAECs injury-associated molecules, proteins involved in signal pathways of nuclear factor-κB (NF-κB), signal transducers and activators of transcription (STAT) 3 and p38 were evaluated by Western blot.

Results

Our study showed that LCWE increased KCa3.1 protein level in RAW264.7 macrophages and KCa3.1 inhibition by TRAM-34 notably suppressed the expression of pro-inflammatory molecules in LCWE-treated macrophages via blocking the activation of NF-κB and STAT3 pathways. Besides, the inflammation and damage of MCAECs were attenuated in the TRAM-34-treated group compared with the KD model group. This vascular protective role was dependent on the down-regulation of NF-κB and STAT3 signal pathways, which was confirmed by using inhibitors of NF-κB and STAT3.

Conclusion

This study demonstrates that KCa3.1 blockade of macrophages suppresses inflammatory reaction leading to mouse coronary artery endothelial cell injury in a cell model of KD by hampering the activation of NF-κB and STAT3 signaling pathway. These findings imply that KCa3.1 may be a potential therapeutic target for KD.

KCa3.1 Mediates Dysregulation of Mitochondrial Quality Control in Diabetic Kidney Disease

Mitochondrial dysfunction is implicated in the pathogenesis of diabetic kidney disease. Mitochondrial quality control is primarily mediated by mitochondrial turnover and repair through mitochondrial fission/fusion and mitophagy. We have previously shown that blockade of the calcium-activated potassium channel KCa3.1 ameliorates diabetic renal fibrosis. However, the mechanistic link between KCa3.1 and mitochondrial quality control in diabetic kidney disease is not yet known. Transforming growth factor β1 (TGF-β1) plays a central role in diabetic kidney disease. Recent studies indicate an emerging role of TGF-β1 in the regulation of mitochondrial function. However, the molecular mechanism mediating mitochondrial quality control in response to TGF-β1 remains limited. In this study, mitochondrial function was assessed in TGF-β1-exposed renal proximal tubular epithelial cells (HK2 cells) transfected with scrambled siRNA or KCa3.1 siRNA. In vivo, diabetes was induced in KCa3.1+/+ and KCa3.1−/− mice by low-dose streptozotocin (STZ) injection. Mitochondrial fission/fusion-related proteins and mitophagy markers, as well as BCL2 interacting protein 3 (BNIP3) (a mitophagy regulator) were examined in HK2 cells and diabetic mice kidneys. The in vitro results showed that TGF-β1 significantly inhibited mitochondrial ATP production rate and increased mitochondrial ROS (mtROS) production when compared to control, which was normalized by KCa3.1 gene silencing. Increased fission and suppressed fusion were found in both TGF-β1-treated HK2 cells and diabetic mice, which were reversed by KCa3.1 deficiency. Furthermore, our results showed that mitophagy was inhibited in both in vitro and in vivo models of diabetic kidney disease. KCa3.1 deficiency restored abnormal mitophagy by inhibiting BNIP3 expression in TGF-β1-induced HK2 cells as well as in the diabetic mice. Collectively, these results indicate that KCa3.1 mediates the dysregulation of mitochondrial quality control in diabetic kidney disease.

Sex-dependent alterations in the physiology of entorhinal cortex neurons in old heterozygous 3xTg-AD mice

While the higher prevalence of Alzheimer’s disease (AD) in women is clear, studies suggest that biological sex may also influence AD pathogenesis. However, mechanisms behind these differences are not clear. To investigate physiological differences between sexes at the cellular level in the brain, we investigated the intrinsic and synaptic properties of entorhinal cortex neurons in heterozygous 3xTg-AD mice of both sexes at the age of 20 months. This brain region was selected because of its early association with AD symptoms. First, we found physiological differences between male and female non-transgenic mice, providing indirect evidence of axonal alterations in old females. Second, we observed a transgene-dependent elevation of the firing activity, post-burst afterhyperpolarization (AHP), and spontaneous excitatory postsynaptic current (EPSC) activity, without any effect of sex. Third, the passive properties and the hyperpolarization-activated current (Ih) were altered by transgene expression only in female mice, whereas the paired-pulse ratio (PPR) of evoked EPSC was changed only in males. Fourth, both sex and transgene expression were associated with changes in action potential properties. Consistent with previous work, higher levels of Aβ neuropathology were detected in 3xTg-AD females, whereas tau deposition was similar. In summary, our results support the idea that aging and AD neuropathology differentially alter the physiology of entorhinal cortex neurons in males and females.

Strategies for cystic fibrosis transmembrane conductance regulator inhibition: from molecular mechanisms to treatment for secretory diarrhoeas

Cystic fibrosis transmembrane conductance regulator (CFTR) is an unusual ABC transporter. It acts as an anion‐selective channel that drives osmotic fluid transport across many epithelia. In the gut, CFTR is crucial for maintaining fluid and acid‐base homeostasis, and its activity is tightly controlled by multiple neuro‐endocrine factors. However, microbial toxins can disrupt this intricate control mechanism and trigger protracted activation of CFTR. This results in the massive faecal water loss, metabolic acidosis and dehydration that characterize secretory diarrhoeas, a major cause of malnutrition and death of children under 5 years of age. Compounds that inhibit CFTR could improve emergency treatment of diarrhoeal disease. Drawing on recent structural and functional insight, we discuss how existing CFTR inhibitors function at the molecular and cellular level. We compare their mechanisms of action to those of inhibitors of related ABC transporters, revealing some unexpected features of drug action on CFTR. Although challenges remain, especially relating to the practical effectiveness of currently available CFTR inhibitors, we discuss how recent technological advances might help develop therapies to better address this important global health need.

Hypoxia and metabolic inhibitors alter the intracellular ATP:ADP ratio and membrane potential in human coronary artery smooth muscle cells

ATP-sensitive potassium (KATP) channels couple cellular metabolism to excitability, making them ideal candidate sensors for hypoxic vasodilation. However, it is still unknown whether cellular nucleotide levels are affected sufficiently to activate vascular KATP channels during hypoxia. To address this fundamental issue, we measured changes in the intracellular ATP:ADP ratio using the biosensors Perceval/PercevalHR, and membrane potential using the fluorescent probe DiBAC4(3) in human coronary artery smooth muscle cells (HCASMCs). ATP:ADP ratio was significantly reduced by exposure to hypoxia. Application of metabolic inhibitors for oxidative phosphorylation also reduced ATP:ADP ratio. Hyperpolarization caused by inhibiting oxidative phosphorylation was blocked by either 10 µM glibenclamide or 60 mM K+. Hyperpolarization caused by hypoxia was abolished by 60 mM K+ but not by individual K+ channel inhibitors. Taken together, these results suggest hypoxia causes hyperpolarization in part by modulating K+ channels in SMCs.

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.

Voltage-Gated K+/Na+ Channels and Scorpion Venom Toxins in Cancer

Ion channels have recently been recognized as novel therapeutic targets in cancer research since they are overexpressed in different histological tissues, and their activity is linked to proliferation, tumor progression, angiogenesis, metastasis, and apoptosis. Voltage gated-potassium channels (VGKC) are involved in cell proliferation, cancer progression, cell cycle transition, and apoptosis. Moreover, voltage-dependent sodium channels (VGSC) contribute to decreases in extracellular pH, which, in turn, promotes cancer cell migration and invasion. Furthermore, VGSC and VGKC modulate voltage-sensitive Ca2+ channel activity by controlling the membrane potential and regulating Ca2+ influx, which functions as a second messenger in processes related to proliferation, invasion, migration, and metastasis. The subgroup of these types of channels that have shown a high oncogenic potential have become known as "oncochannels", and the evidence has highlighted them as key potential therapeutic targets. Scorpion venoms contain a high proportion of peptide toxins that act by modulating voltage-gated Na+/K+ channel activity. Increasing scientific data have pointed out that scorpion venoms and their toxins can affect the activity of oncochannels, thus showing their potential for anticancer therapy. In this review, we provide an update of the most relevant voltage-gated Na+\K+ ion channels as cellular targets and discuss the possibility of using scorpion venom and toxins for anticancer therapy.

New Insights on KCa3.1 Channel Modulation

The human intermediate conductance calcium-activated potassium channel, KCa3.1, is involved in several pathophysiological conditions playing a critical role in cell secretory machinery and calcium signalling. The recent cryo-EM analysis provides new insights for understanding the modulation by both endogenous and pharmacological agents. A typical feature of this channel is the low open probability in saturating calcium concentrations and its modulation by potassium channel openers (KCOs), such as benzo imidazolone 1-EBIO, without changing calcium-dependent activation. In this paper, we proposed a model of KCOs action in the modulation of channel activity. The KCa3.1 channel has a very rich pharmacological profile with several classes of molecules that selectively interact with different binding sites of the channel. Among them, benzo imidazolones can be openers (positive modulators such as 1-EBIO, DC-EBIO) or blockers (negative modulators such as NS1619). Through computation modelling techniques, we identified the 1,4-benzothiazin-3-one as a promising scaffold to develop new KCa3.1 channel modulators. Further studies are needed to explore the potential use of 1-4 benzothiazine- 3-one in KCa3.1 modulation and its pharmacological application.

Conditional KCa3.1-transgene induction in murine skin produces pruritic eczematous dermatitis with severe epidermal hyperplasia and hyperkeratosis

Ion channels have recently attracted attention as potential mediators of skin disease. Here, we explored the consequences of genetically encoded induction of the cell volume-regulating Ca2+-activated KCa3.1 channel (Kcnn4) for murine epidermal homeostasis. Doxycycline-treated mice harboring the KCa3.1+-transgene under the control of the reverse tetracycline-sensitive transactivator (rtTA) showed 800-fold channel overexpression above basal levels in the skin and solid KCa3.1-currents in keratinocytes. This overexpression resulted in epidermal spongiosis, progressive epidermal hyperplasia and hyperkeratosis, itch and ulcers. The condition was accompanied by production of the pro-proliferative and pro-inflammatory cytokines, IL-β1 (60-fold), IL-6 (33-fold), and TNFα (26-fold) in the skin. Treatment of mice with the KCa3.1-selective blocker, Senicapoc, significantly suppressed spongiosis and hyperplasia, as well as induction of IL-β1 (-88%) and IL-6 (-90%). In conclusion, KCa3.1-induction in the epidermis caused expression of pro-proliferative cytokines leading to spongiosis, hyperplasia and hyperkeratosis. This skin condition resembles pathological features of eczematous dermatitis and identifies KCa3.1 as a regulator of epidermal homeostasis and spongiosis, and as a potential therapeutic target.

Ca2+ signalling in fibroblasts and the therapeutic potential of KCa3.1 channel blockers in fibrotic diseases

The role of Ca²⁺ signalling in fibroblasts is of great interest in fibrosis-related diseases. Intracellular free Ca²⁺ ([Ca²⁺ ]_i ) is a ubiquitous secondary messenger, regulating a number of cellular functions such as secretion, metabolism, differentiation, proliferation and contraction. The intermediate conductance Ca²⁺ -activated K⁺ channel K_Ca 3.1 is pivotal in Ca²⁺ signalling and plays a central role in fibroblast processes including cell activation, migration and proliferation through the regulation of cell membrane potential. Evidence from a number of approaches demonstrates that K_Ca 3.1 plays an important role in the development of many fibrotic diseases, including idiopathic pulmonary, renal tubulointerstitial fibrosis and cardiovascular disease. The K_Ca 3.1 selective blocker senicapoc was well tolerated in clinical trials for sickle cell disease, raising the possibility of rapid translation to the clinic for people suffering from pathological fibrosis. This review after analysing all the data, concludes that targeting K_Ca 3.1 should be a high priority for human fibrotic disease.

KCa3.1 channel mediates inflammatory signaling of pancreatic β cells and progression of type 2 diabetes mellitus

Chronic islet inflammation is associated with development of type 2 diabetes mellitus (T2DM). Intermediate-conductance calcium-activated K⁺ (K_Ca3.1) channel plays an important role in inflammatory diseases. However, the role and regulation of K_Ca3.1 in pancreatic β cells in progression of T2DM remain unclarified. In the present study, we evaluated the effect of the specific K_Ca3.1 channel blocker 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34) on diabetic phenotype in the db/db model. In diabetic mice, blockade of K_Ca3.1 significantly improved glucose tolerance, enhanced secretion of postprandial insulin level, and reduced loss of β-cell mass through attenuating the expression and secretion of inflammatory mediators. Furthermore, in cultured pancreatic β cells, exposure to high levels of glucose or palmitic acid significantly increased expression and current density of the K_Ca3.1 channel as well as secretion of proinflammatory chemokines, and the effects were similarly reversed by preincubation with TRAM-34 or a NF-κB inhibitor pyrrolidinedithiocarbamate. Additionally, expression of K_Ca3.1 in pancreas islet cells was up-regulated by activation of NF-κB with IL-1β stimulation. In summary, up-regulated K_Ca3.1 due to activation of NF-κB pathway leads to pancreatic inflammation via expression and secretion of chemokines and cytokines by pancreatic β cells, thereby facilitating progression of T2DM.-Pang, Z.-D., Wang, Y., Wang, X.-J., She, G., Ma, X.-Z., Song, Z., Zhao, L.-M., Wang, H.-F., Lai, B.-C., Gou, W., Du, X.-J., Deng, X.-L. K_Ca3.1 channel mediates inflammatory signaling of pancreatic β cells and progression of type 2 diabetes mellitus.

Protein Kinase A-Mediated Suppression of the Slow Afterhyperpolarizing KCa3.1 Current in Temporal Lobe Epilepsy

Brain insults, such as trauma, stroke, anoxia, and status epilepticus (SE), cause multiple changes in synaptic function and intrinsic properties of surviving neurons that may lead to the development of epilepsy. Experimentally, a single SE episode, induced by the convulsant pilocarpine, initiates the development of an epileptic condition resembling human temporal lobe epilepsy (TLE). Principal hippocampal neurons from such epileptic animals display enhanced spike output in response to excitatory stimuli compared with neurons from nonepileptic animals. This enhanced firing is negatively related to the size of the slow afterhyperpolarization (sAHP), which is reduced in the epileptic neurons. The sAHP is an intrinsic neuronal negative feedback mechanism consisting normally of two partially overlapping components produced by disparate mechanisms. One component is generated by activation of Ca²⁺-gated K⁺ (K_Ca) channels, likely KCa3.1, consequent to spike Ca²⁺ influx (the K_Ca-sAHP component). The second component is generated by enhancement of the electrogenic Na⁺/K⁺ ATPase (NKA) by spike Na⁺ influx (NKA-sAHP component). Here we show that the K_Ca-sAHP component is markedly reduced in male rat epileptic neurons, whereas the NKA-sAHP component is not altered. The K_Ca-sAHP reduction is due to the downregulation of KCa3.1 channels, mediated by cAMP-dependent protein kinase A (PKA). This sustained effect can be acutely reversed by applying PKA inhibitors, leading also to normalization of the spike output of epileptic neurons. We propose that the novel "acquired channelopathy" described here, namely, PKA-mediated downregulation of KCa3.1 activity, provides an innovative target for developing new treatments for TLE, hopefully overcoming the pharmacoresistance to traditional drugs.SIGNIFICANCE STATEMENT Epilepsy, a common neurological disorder, often develops following a brain insult. Identifying key molecular and cellular mechanisms underlying acquired epilepsy is critical for developing effective antiepileptic therapies. In an experimental model of acquired epilepsy, we show that principal hippocampal neurons become intrinsically hyperexcitable. This alteration is due predominantly to the downregulation of a ubiquitous class of potassium ion channels, KCa3.1, whose main function is to dampen neuronal excitability. KCa3.1 downregulation is mediated by the cAMP-dependent protein kinase A (PKA) signaling pathway. Most importantly, it can be acutely reversed by PKA inhibitors, leading to recovery of KCa3.1 function and normalization of neuronal excitability. The discovery of this novel epileptogenic mechanism hopefully will facilitate the development of more efficient pharmacotherapy for acquired epilepsy.