BK channels in human glioma cells

Roles of TRPM channels in glioma

Gliomas are the most common type of primary brain tumor. Despite advances in treatment, it remains one of the most aggressive and deadly tumor of the central nervous system (CNS). Gliomas are characterized by high malignancy, heterogeneity, invasiveness, and high resistance to radiotherapy and chemotherapy. It is urgent to find potential new molecular targets for glioma. The TRPM channels consist of TRPM1-TPRM8 and play a role in many cellular functions, including proliferation, migration, invasion, angiogenesis, etc. More and more studies have shown that TRPM channels can be used as new therapeutic targets for glioma. In this review, we first introduce the structure, activation patterns, and physiological functions of TRPM channels. Additionally, the pathological mechanism of glioma mediated by TRPM2, 3, 7, and 8 and the related signaling pathways are described. Finally, we discuss the therapeutic potential of targeting TRPM for glioma.

Enhancing Human Cutaneous Wound Healing through Targeted Suppression of Large Conductance Ca2+-Activated K+ Channels

The modulation of K+ channels plays a crucial role in cell migration and proliferation, but the effect of K+ channels on human cutaneous wound healing (CWH) remains underexplored. This study aimed to determine the necessity of modulating K+ channel activity and expression for human CWH. The use of 25 mM KCl as a K+ channel blocker markedly improved wound healing in vitro (in keratinocytes and fibroblasts) and in vivo (in rat and porcine models). K+ channel blockers, such as quinine and tetraethylammonium, aided in vitro wound healing, while Ba2+ was the exception and did not show similar effects. Single-channel recordings revealed that the Ba2+-insensitive large conductance Ca2+-activated K+ (BKCa) channel was predominantly present in human keratinocytes. NS1619, an opener of the BKCa channel, hindered wound healing processes like proliferation, migration, and filopodia formation. Conversely, charybdotoxin and iberiotoxin, which are BKCa channel blockers, dramatically enhanced these processes. The downregulation of BKCa also improved CWH, whereas its overexpression impeded these healing processes. These findings underscore the facilitative effect of BKCa channel suppression on CWH, proposing BKCa channels as potential molecular targets for enhancing human cutaneous wound healing.

Pan-cancer ion transport signature reveals functional regulators of glioblastoma aggression

Ion channels, transporters, and other ion-flux controlling proteins, collectively comprising the "ion permeome", are common drug targets, however, their roles in cancer remain understudied. Our integrative pan-cancer transcriptome analysis shows that genes encoding the ion permeome are significantly more often highly expressed in specific subsets of cancer samples, compared to pan-transcriptome expectations. To enable target selection, we identified 410 survival-associated IP genes in 33 cancer types using a machine-learning approach. Notably, GJB2 and SCN9A show prominent expression in neoplastic cells and are associated with poor prognosis in glioblastoma, the most common and aggressive brain cancer. GJB2 or SCN9A knockdown in patient-derived glioblastoma cells induces transcriptome-wide changes involving neuron projection and proliferation pathways, impairs cell viability and tumor sphere formation in vitro, perturbs tunneling nanotube dynamics, and extends the survival of glioblastoma-bearing mice. Thus, aberrant activation of genes encoding ion transport proteins appears as a pan-cancer feature defining tumor heterogeneity, which can be exploited for mechanistic insights and therapy development.

Hypoxia, Ion Channels and Glioblastoma Malignancy

The malignancy of glioblastoma (GBM), the most aggressive type of human brain tumor, strongly correlates with the presence of hypoxic areas within the tumor mass. Oxygen levels have been shown to control several critical aspects of tumor aggressiveness, such as migration/invasion and cell death resistance, but the underlying mechanisms are still unclear. GBM cells express abundant K+ and Cl- channels, whose activity supports cell volume and membrane potential changes, critical for cell proliferation, migration and death. Volume-regulated anion channels (VRAC), which mediate the swelling-activated Cl- current, and the large-conductance Ca2+-activated K+ channels (BK) are both functionally upregulated in GBM cells, where they control different aspects underlying GBM malignancy/aggressiveness. The functional expression/activity of both VRAC and BK channels are under the control of the oxygen levels, and these regulations are involved in the hypoxia-induced GBM cell aggressiveness. The present review will provide a comprehensive overview of the literature supporting the role of these two channels in the hypoxia-mediated GBM malignancy, suggesting them as potential therapeutic targets in the treatment of GBM.

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.

BK Channel in the Physiology and in the Cancer of Pancreatic Duct: Impact and Reliability of BK Openers

BK (KCa 1.1, Slo-1) is a K⁺ channel characterized by an allosteric regulation of the gating mechanism by Ca²⁺ binding and voltage, and a high unitary conductance. The channel is expressed in many different tissues, where it is involved in the regulation or the fine-tuning of many physiological processes. Among other organs, BK is expressed in the pancreatic duct, a part of the gland important for the correct ionic composition of the pancreatic juice. Unfortunately, the pancreatic duct is also the site where one of the deadliest cancer types, the pancreatic duct adenocarcinoma (PDAC), develops. In the past years, it has been reported that continuous exposure of cancer cells to BK openers can have a significant impact on cell viability as well as on the ability to proliferate and migrate. Here, we first summarize the main BK channel properties and its roles in pancreatic duct physiology. Then we focus on the potential role of BK as a pharmacological target in PDAC. Moreover, we discuss how results obtained when employing BK activators on cancer cells can, in some cases, be misleading.

Glioblastoma Microenvironment and Cellular Interactions

Simple Summary

This paper summarizes the crosstalk between tumor/non-tumor cells and other elements of the glioblastoma (GB) microenvironment. In tumor pathology, glial cells result in the highest number of cancers, and GB is considered the most lethal tumor of the central nervous system (CNS). The tumor microenvironment (TME) is a complex peritumoral hallo composed of tumor cells and several non-tumor cells (e.g., nervous cells, stem cells, fibroblasts, vascular and immune cells), which might be a key factor for the ineffective treatment since the microenvironment modulates the biologic status of the tumor with the increase in its evasion capacity. A deeper understanding of cell–cell interactions in the TME and with the tumor cells could be the basis for a more efficient therapy.

Abstract

The central nervous system (CNS) represents a complex network of different cells, such as neurons, glial cells, and blood vessels. In tumor pathology, glial cells result in the highest number of cancers, and glioblastoma (GB) is considered the most lethal tumor in this region. The development of GB leads to the infiltration of healthy tissue through the interaction between all the elements of the brain network. This results in a GB microenvironment, a complex peritumoral hallo composed of tumor cells and several non-tumor cells (e.g., nervous cells, stem cells, fibroblasts, vascular and immune cells), which might be the principal factor for the ineffective treatment due to the fact that the microenvironment modulates the biologic status of the tumor with the increase in its evasion capacity. Crosstalk between glioma cells and the brain microenvironment finally inhibits the beneficial action of molecular pathways, favoring the development and invasion of the tumor and its increasing resistance to treatment. A deeper understanding of cell–cell interactions in the tumor microenvironment (TME) and with the tumor cells could be the basis for a more efficient therapy.

The VRAC blocker DCPIB directly gates the BK channels and increases intracellular Ca2+ in Melanoma and Pancreatic Duct Adenocarcinoma (PDAC) cell lines

BACKGROUND AND PURPOSE

The Volume Regulated Anion Channel (VRAC) is known to be involved in different aspects of cancer cell behavior and response to therapies. For this reason, we investigated the effect of DCPIB, a presumably specific blocker of VRAC, in two types of cancer: pancreatic duct adenocarcinoma (PDAC) and melanoma.

EXPERIMENTAL APPROACH

For this investigation, we used patch-clamp electrophysiology, supported by Ca²⁺ imaging, gene expression analysis, docking simulation and mutagenesis. We employed two PDAC lines (Panc-1 and MiaPaCa-2), as well as a primary (IGR39) and a metastatic (IGR37) melanoma line.

KEY RESULTS

Surprisingly, DCPIB induced a dramatic increase of whole-cell currents in Panc-1, MiaPaca2 and IGR39, but not in IGR37 cells. The currents were mostly mediated by the KCa1.1 channel, commonly known as BK. We verified DCPIB activation of BK also in HEK293 cells transfected with the α subunit of the channel. Further experiments showed that in IGR39, and to a smaller degree also in Panc-1 cells, DCPIB induces a rapid Ca²⁺ influx. This, in turn, indirectly potentiates BK and, in IGR39 cells, additionally activates other Ca²⁺ -dependent channels. However, the Ca²⁺ influx is not required for BK activation by DCPIB: indeed, we found that the activation of BK by DCPIB involves the extracellular part of the protein and identified two residues crucial for binding.

CONCLUSION AND IMPLICATIONS

DCPIB directly targets BK channels and, in addition, can acutely increase intracellular Ca²⁺ . Our findings elongate the list of DCPIB effects that have to be taken into consideration for future development of DCPIB-based modulators of ion channels and other membrane proteins.

TRP Channels in Brain Tumors

Malignant glioma including glioblastoma (GBM) is the most common group of primary brain tumors. Despite standard optimized treatment consisting of extensive resection followed by radiotherapy/concomitant and adjuvant therapy, GBM remains one of the most aggressive human cancers. GBM is a typical example of intra-heterogeneity modeled by different micro-environmental situations, one of the main causes of resistance to conventional treatments. The resistance to treatment is associated with angiogenesis, hypoxic and necrotic tumor areas while heterogeneity would accumulate during glioma cell invasion, supporting recurrence. These complex mechanisms require a focus on potential new molecular actors to consider new treatment options for gliomas. Among emerging and underexplored targets, transient receptor potential (TRP) channels belonging to a superfamily of non-selective cation channels which play critical roles in the responses to a number of external stimuli from the external environment were found to be related to cancer development, including glioma. Here, we discuss the potential as biological markers of diagnosis and prognosis of TRPC6, TRPM8, TRPV4, or TRPV1/V2 being associated with glioma patient overall survival. TRPs-inducing common or distinct mechanisms associated with their Ca²⁺-channel permeability and/or kinase function were detailed as involving miRNA or secondary effector signaling cascades in turn controlling proliferation, cell cycle, apoptotic pathways, DNA repair, resistance to treatment as well as migration/invasion. These recent observations of the key role played by TRPs such as TRPC6 in GBM growth and invasiveness, TRPV2 in proliferation and glioma-stem cell differentiation and TRPM2 as channel carriers of cytotoxic chemotherapy within glioma cells, should offer new directions for innovation in treatment strategies of high-grade glioma as GBM to overcome high resistance and recurrence.

Molecular Choreography and Structure of Ca2+ Release-Activated Ca2+ (CRAC) and KCa2+ Channels and Their Relevance in Disease with Special Focus on Cancer

Ca²⁺ ions play a variety of roles in the human body as well as within a single cell. Cellular Ca²⁺ signal transduction processes are governed by Ca²⁺ sensing and Ca²⁺ transporting proteins. In this review, we discuss the Ca²⁺ and the Ca²⁺-sensing ion channels with particular focus on the structure-function relationship of the Ca²⁺ release-activated Ca²⁺ (CRAC) ion channel, the Ca²⁺-activated K⁺ (K_Ca2+) ion channels, and their modulation via other cellular components. Moreover, we highlight their roles in healthy signaling processes as well as in disease with a special focus on cancer. As K_Ca2+ channels are activated via elevations of intracellular Ca²⁺ levels, we summarize the current knowledge on the action mechanisms of the interplay of CRAC and K_Ca2+ ion channels and their role in cancer cell development.

Differences in Gating Dynamics of BK Channels in Cellular and Mitochondrial Membranes from Human Glioblastoma Cells Unraveled by Short- and Long-Range Correlations Analysis

The large-conductance voltage- and Ca2+-activated K+ channels (BK) are encoded in humans by the Kcnma1 gene. Nevertheless, BK channel isoforms in different locations can exhibit functional heterogeneity mainly due to the alternative splicing during the Kcnma1 gene transcription. Here, we would like to examine the existence of dynamic diversity of BK channels from the inner mitochondrial and cellular membrane from human glioblastoma (U-87 MG). Not only the standard characteristics of the spontaneous switching between the functional states of the channel is discussed, but we put a special emphasis on the presence and strength of correlations within the signal describing the single-channel activity. The considered short- and long-range memory effects are here analyzed as they can be interpreted in terms of the complexity of the switching mechanism between stable conformational states of the channel. We calculate the dependencies of mean dwell-times of (conducting/non-conducting) states on the duration of the previous state, Hurst exponents by the rescaled range R/S method and detrended fluctuation analysis (DFA), and use the multifractal extension of the DFA (MFDFA) for the series describing single-channel activity. The obtained results unraveled statistically significant diversity in gating machinery between the mitochondrial and cellular BK channels.

Squaring the Circle: A New Study of Inward and Outward-Rectifying Potassium Currents in U251 GBM Cells

In the present study, the functional role of the inwardly rectifying K⁺ channel, Kir4.1, and large-conductance Ca²⁺-activated K⁺ (BK) channel during cell migration in U251 cell line was investigated. We focused on polarised cells which are positive for the active-Cdc42 migration marker. The perforated patch technique was used to avoid intracellular dialysis and to maintain physiological changes in intracellular calcium. Wound healing was employed to assay migration after 24 h. Polarised cells recorded displayed different hallmarks of undifferentiated glial cells: depolarised resting membrane potential and high membrane resistance. Cells recorded outside wounded area did not display either constitutive inward or outward rectification. After migration, U251 cells were characterised by a constitutively smaller Kir4.1 and larger BK currents with a linearly related amplitude. Menthol modulation increased both currents in a linearly dependent manner, indicating a common mechanism triggered by activation of transient receptor potential melastatin 8 (TRPM8), a Ca²⁺-permeable non-selective cation channel. We hypothesised that both migration and menthol modulation would share an increase of intracellular calcium triggering the increase in Kir4.1 and BK channels. Immunocytochemistry demonstrated the cytoplasmic expression of both Kir4.1 and BK channels and a mislocation in the nucleus under basal conditions. Before and after migration, polarised cells increased the expression of Kir4.1 and BK channels both in the cytoplasm and nucleus. TEM ultrastructural analysis displayed a different nuclear distribution of Kir4.1 and BK channels. In the present study, the physiological role of Kir4.1 and BK currents at membrane potential, their involvement in migration, and the functional role of nuclear channels were discussed.

Mechanosensitivity of the BK Channels in Human Glioblastoma Cells: Kinetics and Dynamical Complexity

BK channels are potassium selective and exhibit large single-channel conductance. They play an important physiological role in glioma cells: they are involved in cell growth and extensive migrating behavior. Due to the fact that these processes are accompanied by changes in membrane stress, here, we examine mechanosensitive properties of BK channels from human glioblastoma cells (gBK channels). Experiments were performed by the use of patch-clamp method on excised patches under membrane suction (0-40 mmHg) at membrane hyper- and depolarization. We have also checked whether channel's activity is affected by possible changes of membrane morphology after a series of long impulses of suction. Unconventionally, we also analyzed internal structure of the experimental signal to make inferences about conformational dynamics of the channel in stressed membranes. We examined the fractal long-range memory effect (by R/S Hurst analysis), the rate of changes in information by sample entropy, or correlation dimension, and characterize its complexity over a range of scales by the use of Multiscale Entropy method. The obtained results indicate that gBK channels are mechanosensitive at membrane depolarization and hyperpolarization. Prolonged suction of membrane also influences open-closed fluctuations-it decreases channel's activity at membrane hyperpolarization and, in contrary, increases channel's activity at high voltages. Both membrane strain and its "fatigue" reduce dynamical complexity of channel gating, which suggest decrease in the number of available open conformations of channel protein in stressed membranes.

Combating malignant astrocytes: Strategies mitigating tumor invasion

Malignant gliomas are glial-derived, primary brain tumors that carry poor prognosis. Existing therapeutics are largely ineffective and dramatically affect quality of life. The standard of care details a taxing combination of surgical resection, radiation of the resection cavity, and temozolomide (TMZ) chemotherapy, with treatment extending life by only an average of months (Maher et al., 2001; Stupp et al., 2005). Despite scientific and technological advancement, surgery remains the most important treatment modality. Therapeutic obstacles include xenobiotic protection conveyed by the blood-brain barrier (Zhang et al., 2015), invasiveness and therapeutic resistance of tumor cell populations (Bao et al., 2006), and distinctive attributes of secondary glioma occurrence (Ohgaki and Kleihues, 2013). While these brain malignancies can be classified by grade or grouped by molecular subclass, each tumor presents itself as its own complication. Based on all of these obstacles, new therapeutic approaches are urgently needed. These will likely emerge from numerous exciting studies of glioma biology that are ongoing and reviewed here. These show unexpected roles for ion channels, amino-acid transporters, and connexin gap junctions in supporting the invasive growth of gliomas. These studies have identified a number of proteins that may be targeted for therapy in the future.

Molecular structure and function of big calcium-activated potassium channels in skeletal muscle: pharmacological perspectives

The large-conductance Ca2+-activated K+ (BK) channel is broadly expressed in various mammalian cells and tissues such as neurons, skeletal muscles (sarco-BK), and smooth muscles. These channels are activated by changes in membrane electrical potential and by increases in the concentration of intracellular calcium ion (Ca2+). The BK channel is subjected to many mechanisms that add diversity to the BK channel α-subunit gene. These channels are indeed subject to alternative splicing, auxiliary subunits modulation, posttranslational modifications, and protein-protein interactions. BK channels can be modulated by diverse molecules that may induce either an increase or decrease in channel activity. The linkage of these channels to many intracellular metabolites and pathways, as well as their modulation by extracellular natural agents, have been found to be relevant in many physiological processes. BK channel diversity is obtained by means of alternative splicing and modulatory β- and γ-subunits. The association of the α-subunit with β- or with γ-subunits can change the BK channel phenotype, functional diversity, and pharmacological properties in different tissues. In the case of the skeletal muscle BK channel (sarco-BK channel), we established that the main mechanism regulating BK channel diversity is the alternative splicing of the KCNMA1/slo1 gene encoding for the α-subunit generating different splicing isoform in the muscle phenotypes. This finding helps to design molecules selectively targeting the skeletal muscle subtypes. The use of drugs selectively targeting the skeletal muscle BK channels is a promising strategy in the treatment of familial disorders affecting muscular skeletal apparatus including hyperkalemia and hypokalemia periodic paralysis.

Electrically Controlled "Sponge Effect" of PEDOT:PSS Governs Membrane Potential and Cellular Growth

PSS is a highly conductive material with good thermal and chemical stability and enhanced biocompatibility that make it suitable for bioengineering applications. The electrical control of the oxidation state of PEDOT:PSS films allows modulation of peculiar physical and chemical properties of the material, such as topography, wettability, and conductivity, and thus offers a possible route for controlling cellular behavior. Through the use of (i) the electrophysiological response of the plasma membrane as a biosensor of the ionic availability; (ii) relative abundance around the cells via X-ray spectroscopy; and (iii) atomic force microscopy to monitor PEDOT:PSS film thickness relative to its oxidation state, we demonstrate that redox processes confer to PEDOT:PSS the property to modify the ionic environment at the film-liquid interface through a "sponge-like" effect on ions. Finally, we show how this property offers the capability to electrically control central cellular properties such as viability, substrate adhesion, and growth, paving the way for novel bioelectronics and biotechnological applications.

Characterizing the biological and biochemical profile of six different scorpion venoms from the Buthidae and Scorpionidae family

The objective of this study was to characterize six different scorpion venoms using biological and biochemical methods, including a preliminary MS/MS and a post-translational modifications analysis. Despite the diversity of scorpion species of medical importance in Africa and Colombia, the venoms of these arachnids have been poorly studied in these two regions. We report the biochemical, electrophoretic, chromatographic profile, internal peptide sequences with a post-translational modification report, and a preliminary antitumor activity of five different scorpions of the Buthidae family, Androctonus amoreuxi, Babycurus jacksoni, Grosphus grandidieri, Hottentotta gentili and Tityus fuhrmanni, and one of the Scorpionidae family Pandinus imperator. No L-amino oxidase activity was detected in the evaluated venoms. Proteolytic activity using azocasein was detected only in G. grandidieri and P. imperator, indicating the possible presence of metalloproteinases in these two venoms. Proteolytic activity using NOBA was detected in all venoms indicating the possible presence of serine-proteinases. Phospholipase A₂ activity was detected in the venoms of P. imperator, G. grandidieri, H. gentili and A. amoreuxi, with P. imperator venom being the most active. All venoms analyzed contained defensin-like proteins, alpha toxins, metalloproteinases, neuropeptides, DBP affecting ion channels, DBP with antimicrobial activity, among others. Venoms from P. imperator, G. grandidieri and T. fuhrmanni showed a dose-dependent cytotoxic activity over MCF-7 cells. Only two isolated RP-HPLC fractions from P. imperator and T. fuhrmanni showed cytotoxic activity over MCF-7. No cytotoxic activity was found in the venoms from A. amoreuxi, B. jacksoni, and H. gentili.

Molecular Determinants of BK Channel Functional Diversity and Functioning

Large-conductance Ca2+- and voltage-activated K+ (BK) channels play many physiological roles ranging from the maintenance of smooth muscle tone to hearing and neurosecretion. BK channels are tetramers in which the pore-forming α subunit is coded by a single gene ( Slowpoke, KCNMA1). In this review, we first highlight the physiological importance of this ubiquitous channel, emphasizing the role that BK channels play in different channelopathies. We next discuss the modular nature of BK channel-forming protein, in which the different modules (the voltage sensor and the Ca2+ binding sites) communicate with the pore gates allosterically. In this regard, we review in detail the allosteric models proposed to explain channel activation and how the models are related to channel structure. Considering their extremely large conductance and unique selectivity to K+, we also offer an account of how these two apparently paradoxical characteristics can be understood consistently in unison, and what we have learned about the conduction system and the activation gates using ions, blockers, and toxins. Attention is paid here to the molecular nature of the voltage sensor and the Ca2+ binding sites that are located in a gating ring of known crystal structure and constituted by four COOH termini. Despite the fact that BK channels are coded by a single gene, diversity is obtained by means of alternative splicing and modulatory β and γ subunits. We finish this review by describing how the association of the α subunit with β or with γ subunits can change the BK channel phenotype and pharmacology.

Temozolomide induces the expression of the glioma Big Potassium (gBK) ion channel, while inhibiting fascin-1 expression: possible targets for glioma therapy

OBJECTIVE

Temozolomide (TMZ) improves Glioblastoma Multiforme (GBM) patient survival. The invasive behavior of the glioma cells is the cause of GBM relapse. The glioma BK ion channel (gBK) may provide glioma cells with a mechanism to invade surrounding tissue. gBK contains epitopes that cytolytic T lymphocytes (CTLs) can recognize and kill glioma cells. Fascin-1 is an actin crosslinking molecule that supports microvilli; these membrane protrusions provide a physical defense against CTLs. TMZ was investigated to determine its effect on gBK and fascin-1 expression.

RESEARCH DESIGN AND METHODS

Human glioma cells cultured in TMZ were analyzed for their altered mRNA and gBK protein levels by using quantitative real time PCR, immunostaining and cellular functional assays.

RESULTS

TMZ slowed glioma cell growth and inhibited their transmigratory properties due to loss of fascin-1. TMZ induced increased gBK and HLA expression and allowed these TMZ-treated cells to become better targets for gBK-specific CTLs.

CONCLUSIONS

Besides its traditional chemotherapeutic effect, TMZ can have four other targeted pathways: 1) slowed glioma cell growth; 2) inhibited glioma cell transmigration; 3) increased HLA-A2 and gBK tumor antigen production; 4) increased CTL-mediated cytolysis of the TMZ treated glioma cells due to the loss of their defensive membrane protrusions supported by fascin-1.

Ion channel blockers and glioblastoma risk and outcome: a nested case-control and retrospective cohort studies

PURPOSE

Mutations in ion channels are common among patients with glioblastoma multiforme (GBM) and promote cell migration and invasion. We sought to evaluate the association between the use of specific ion channel blockers such as digoxin, amiodarone, diltiazem and verapamil and GBM risk and survival.

METHODS

We conducted a nested case-control study in a large primary care database from the UK. Cases were defined as all individuals with incident diagnosis of GBM during follow-up. For each case, up to four controls were selected using incidence density sampling. The primary exposure of interest was active treatment with each of the four ion channel blockers. We used conditional logistic regression to estimate odds ratios and 95% confidence interval (CI) for the association between ion channel blocker use and GBM risk. We then performed a Cox regression analysis among those diagnosed with GBM in order to evaluate the association between use of ion channel blockers and overall survival. Both analyses were adjusted to common confounders.

RESULTS

The study included 1076 cases and 4253 matched controls. There was no statistically significant difference between cases and controls in cardiac and metabolic risk factors. There was no change in GBM risk in active users of ion channel blockers compared with non-users. Among patients with GBM, active users of amiodarone had worse survival compared with never users with an HR of 4.41 (95%CI 1.95-9.96). There was no statistically significant change in survival among diltiazem, verapamil or digoxin users.

CONCLUSION

Treatment with specific ion channel blockers was not associated with the risk of GBM but was associated with worse survival in patients with GBM. Copyright © 2016 John Wiley & Sons, Ltd.

Potential Roles of Amiloride-Sensitive Sodium Channels in Cancer Development

The ENaC/degenerin ion channel superfamily includes the amiloride-sensitive epithelial sodium channel (ENaC) and acid sensitive ionic channel (ASIC). ENaC is a multimeric ion channel formed by heteromultimeric membrane glycoproteins, which participate in a multitude of biological processes by mediating the transport of sodium (Na⁺) across epithelial tissues such as the kidney, lungs, bladder, and gut. Aberrant ENaC functions contribute to several human disease states including pseudohypoaldosteronism, Liddle syndrome, cystic fibrosis, and salt-sensitive hypertension. Increasing evidence suggests that ion channels not only regulate ion homeostasis and electric signaling in excitable cells but also play important roles in cancer cell behaviors such as proliferation, apoptosis, invasion, and migration. Indeed, ENaCs/ASICs had been reported to be associated with cancer characteristics. Given their cell surface localization and pharmacology, pharmacological strategies to target ENaC/ASIC family members may be promising cancer therapeutics.

Functional Role of Mitochondrial and Nuclear BK Channels

BK channels are important for the regulation of many cell functions. The significance of plasma membrane BK channels in the control of action potentials, resting membrane potential, and neurotransmitter release is well established; however, the composition and functions of mitochondrial and nuclear BK (nBK) channels are largely unknown. In this chapter, we summarize the recent findings on the subcellular localization, biophysical, and pharmacological properties of mitochondrial and nBK channels and discuss their molecular identity and physiological functions.

Generation of Kcnma1fl-tdTomato, a conditional deletion of the BK channel α subunit in mouse

BK large conductance calcium-activated K(+) channels (KC a1.1) are expressed widely across many tissues, contributing to systemic regulation of cardiovascular, neurological, and other specialized physiological functions. The pore-forming α subunit is encoded by the Kcnma1 gene, originally named mSlo1 in mouse and slowpoke in Drosophila. Global deletion in mouse (Kcnma1(-/-)) produces a plethora of defects in neuron and muscle excitability, as well as other phenotypes related to channel function in nonexcitable cells. While homozygous null mice are viable, the ubiquitous loss of BK function has complicated the interpretation of phenotypes involving the interaction of multiple cell types which independently express BK channels. Here, we report the generation of a targeted allele for conditional inactivation of Kcnma1 using the Cre-loxP system (Kcnma1(fl)-tdTomato). Cre-mediated recombination generates a null allele, and BK currents were not detectable in neurons and muscle cells from Nestin-Cre; Kcnma1(fl/fl) and SM22α-Cre; Kcnma1(fl/fl) mice, respectively. tdTomato expression was detected in Cre-expressing tissues, but not in Cre-negative controls. These data demonstrate the utility of Kcnma1(fl)-tdTomato for conditional deletion of the BK channel, facilitating the understanding of tissue-specific contributions to physiological function in vivo.

Blockage of potassium channel inhibits proliferation of glioma cells via increasing reactive oxygen species

The potassium (K⁺) channel plays an important role in the cell cycle and proliferation of tumor cells, while its role in brain glioma cells and the signaling pathways remains unclear. We used tetraethylammonium (TEA), a nonselective antagonist of big conductance K⁺ channels, to block K⁺ channels in glioma cells, and antioxidant N-acetyl-l-cysteine (NAC) to inhibit production of intracellular reactive oxygen species (ROS). TEA showed an antiproliferation effect on C6 and U87 glioma cells in a time-dependent manner, which was accompanied by an increased intracellular ROS level. Antioxidant NAC pretreatment reversed TEA-mediated antiproliferation and restored ROS level. TEA treatment also caused significant increases in mRNA and protein levels of tumor-suppressor proteins p53 and p21, and the upregulation was attenuated by pretreatment of NAC. Our results suggest that K⁺ channel activity significantly contributes to brain glioma cell proliferation via increasing ROS, and it might be an upstream factor triggering the activation of the p53/p21^Cip1-dependent signaling pathway, consequently leading to glioma cell cycle arrest.

The role of ion channels in malignant brain tumors

Malignant gliomas are the most common primary brain tumors and have poor clinical prognosis, despite multimodal therapeutic strategies. In recent years, ion channels have emerged as major players in tumor pathophysiology regarding all hallmarks of cancer. Since ion channels are easily accessible structures, they may prove to be effective targets for canner therapy, although their broad expression pattern and role in physiological processes should be taken into consideration. This review summarizes the current knowledge on the role of ion channels in the pathophysiology of malignant gliomas, especially glioblastoma, and evaluates their potential role in targeted antiglioma therapy.

Ion channel gene expression predicts survival in glioma patients

Ion channels are important regulators in cell proliferation, migration, and apoptosis. The malfunction and/or aberrant expression of ion channels may disrupt these important biological processes and influence cancer progression. In this study, we investigate the expression pattern of ion channel genes in glioma. We designate 18 ion channel genes that are differentially expressed in high-grade glioma as a prognostic molecular signature. This ion channel gene expression based signature predicts glioma outcome in three independent validation cohorts. Interestingly, 16 of these 18 genes were down-regulated in high-grade glioma. This signature is independent of traditional clinical, molecular, and histological factors. Resampling tests indicate that the prognostic power of the signature outperforms random gene sets selected from human genome in all the validation cohorts. More importantly, this signature performs better than the random gene signatures selected from glioma-associated genes in two out of three validation datasets. This study implicates ion channels in brain cancer, thus expanding on knowledge of their roles in other cancers. Individualized profiling of ion channel gene expression serves as a superior and independent prognostic tool for glioma patients.

Bradykinin enhances invasion of malignant glioma into the brain parenchyma by inducing cells to undergo amoeboid migration

The molecular and cellular mechanisms governing cell motility and directed migration in response to the neuropeptide bradykinin are largely unknown. Here, we demonstrate that human glioma cells whose migration is guided by bradykinin generate bleb-like protrusions. We found that activation of the B2 receptor leads to a rise in free Ca(2+) from internal stores that activates actomyosin contraction and subsequent cytoplasmic flow into protrusions forming membrane blebs. Furthermore Ca(2+) activates Ca(2+)-dependent K(+) and Cl(-) channels, which participate in bleb regulation. Treatment of gliomas with bradykinin in situ increased glioma growth by increasing the speed of cell migration at the periphery of the tumour mass. To test if bleb formation is related to bradykinin-promoted glioma invasion we blocked glioma migration with blebbistatin, a blocker of myosin kinase II, which is necessary for proper bleb retraction. Our findings suggest a pivotal role of bradykinin during glioma invasion by stimulating amoeboid migration of glioma cells.

A neurocentric perspective on glioma invasion

Malignant gliomas are devastating tumours that frequently kill patients within 1 year of diagnosis. The major obstacle to a cure is diffuse invasion, which enables tumours to escape complete surgical resection and chemo- and radiation therapy. Gliomas use the same tortuous extracellular routes of migration that are travelled by immature neurons and stem cells, frequently using blood vessels as guides. They repurpose ion channels to dynamically adjust their cell volume to accommodate to narrow spaces and breach the blood-brain barrier through disruption of astrocytic endfeet, which envelop blood vessels. The unique biology of glioma invasion provides hitherto unexplored brain-specific therapeutic targets for this devastating disease.

Mitochondrial but not plasmalemmal BK channels are hypoxia-sensitive in human glioma

Tumor cells are resistant to hypoxia but the underlying mechanism(s) of this tolerance remain poorly understood. In healthy brain cells, plasmalemmal Ca(2+)-activated K(+) channels ((plasma)BK) function as oxygen sensors and close under hypoxic conditions. Similarly, BK channels in the mitochondrial inner membrane ((mito)BK) are also hypoxia sensitive and regulate reactive oxygen species production and also permeability transition pore formation. Both channel populations are therefore well situated to mediate cellular responses to hypoxia. In tumors, BK channel expression increases with malignancy, suggesting these channels contribute to tumor growth; therefore, we hypothesized that the sensitivity of (plasma)BK and/or (mito)BK to hypoxia differs between glioma and healthy brain cells. To test this, we examined the electrophysiological properties of (plasma)BK and (mito)BK from a human glioma cell line during normoxia and hypoxia. We observed single channel activities in whole cells and isolated mitoplasts with slope conductance of 199 ± 8 and 278 ± 10 pA, respectively. These currents were Ca(2+)- and voltage-dependent, and were inhibited by the BK channel antagonist charybdotoxin (0.1 μM). (plasma)BK could only be activated at membrane potentials >+40 mV and had a low open probability (NPo) that was unchanged by hypoxia. Conversely, (mito)BK were active across a range of membrane potentials (-40 to +40 mV) and their NPo increased during hypoxia. Activating (plasma)BK, but not (mito)BK induced cell death and this effect was enhanced during hypoxia. We conclude that unlike in healthy brain cells, glioma (mito)BK channels, but not (plasma)BK channels are oxygen sensitive.

Application of ion-sensitive field effect transistors for ion channel screening

Cell-based screening assays are now widely used for identifying compounds that serve as ion channel modulators. However, instrumentation for the automated, real-time analysis of ion flux from clonal and primary cells is lacking. This study describes the initial development of an ion-sensitive field effect transistor (ISFET)-based screening assay for the acquisition of K(+) efflux data from cells cultured in multi-well plates. Silicon-based K(+)-sensitive ISFETs were tested for their electrical response to varying concentrations of KCl and were found to display a linear response relationship to KCl in the range of 10 µM-1 mM. The ISFETs, along with reference electrodes, were inserted into fast-flow chambers containing either human colonic T84 epithelial cells or U251-MG glioma cells. Application of the Ca(2+) ionophore A23187 (1 µM), to activate Ca(2+)-activated non-selective cation (NSC) channels (T84 cells) and large conductance Ca(2+)-activated K(+) (BK) channels (U251 cells), resulted in time-dependent increases in the extracellular K(+) concentration ([K(+)]o) as measured with the ISFETs. Treatment of the cells with blockers of either the NSC or BK channels, caused a strong inhibition of the A23187-induced increase in [K(+)]o. These results were consistent with ion current measurements obtained using the whole-cell arrangement of the patch clamp procedure. In addition, K(+) efflux data could be acquired in parallel from multiple cell chambers using the ISFET sensors. Given the non-invasive properties of the probes, the ISFET-based assay should be adaptable for screening ion channels in various cell types.

A BK (Slo1) channel journey from molecule to physiology

Calcium and voltage-activated potassium (BK) channels are key actors in cell physiology, both in neuronal and non-neuronal cells and tissues. Through negative feedback between intracellular Ca (2+) and membrane voltage, BK channels provide a damping mechanism for excitatory signals. Molecular modulation of these channels by alternative splicing, auxiliary subunits and post-translational modifications showed that these channels are subjected to many mechanisms that add diversity to the BK channel α subunit gene. This complexity of interactions modulates BK channel gating, modifying the energetic barrier of voltage sensor domain activation and channel opening. Regions for voltage as well as Ca (2+) sensitivity have been identified, and the crystal structure generated by the 2 RCK domains contained in the C-terminal of the channel has been described. The linkage of these channels to many intracellular metabolites and pathways, as well as their modulation by extracellular natural agents, has been found to be relevant in many physiological processes. This review includes the hallmarks of BK channel biophysics and its physiological impact on specific cells and tissues, highlighting its relationship with auxiliary subunit expression.

Ionizing radiation, ion transports, and radioresistance of cancer cells

The standard treatment of many tumor entities comprises fractionated radiation therapy which applies ionizing radiation to the tumor-bearing target volume. Ionizing radiation causes double-strand breaks in the DNA backbone that result in cell death if the number of DNA double-strand breaks exceeds the DNA repair capacity of the tumor cell. Ionizing radiation reportedly does not only act on the DNA in the nucleus but also on the plasma membrane. In particular, ionizing radiation-induced modifications of ion channels and transporters have been reported. Importantly, these altered transports seem to contribute to the survival of the irradiated tumor cells. The present review article summarizes our current knowledge on the underlying mechanisms and introduces strategies to radiosensitize tumor cells by targeting plasma membrane ion transports.

Targeted delivery of antibody-based therapeutic and imaging agents to CNS tumors: crossing the blood-brain barrier divide

INTRODUCTION

Brain tumors are inherently difficult to treat in large part due to the cellular blood-brain barriers (BBBs) that limit the delivery of therapeutics to the tumor tissue from the systemic circulation. Virtually no large molecules, including antibody-based proteins, can penetrate the BBB. With antibodies fast becoming attractive ligands for highly specific molecular targeting to tumor antigens, a variety of methods are being investigated to enhance the access of these agents to intracranial tumors for imaging or therapeutic applications.

AREAS COVERED

This review describes the characteristics of the BBB and the vasculature in brain tumors, described as the blood-brain tumor barrier (BBTB). Antibodies targeted to molecular markers of central nervous system (CNS) tumors will be highlighted, and current strategies for enhancing the delivery of antibodies across these cellular barriers into the brain parenchyma to the tumor will be discussed. Noninvasive imaging approaches to assess BBB/BBTB permeability and/or antibody targeting will be presented as a means of guiding the optimal delivery of targeted agents to brain tumors.

EXPERT OPINION

Preclinical and clinical studies highlight the potential of several approaches in increasing brain tumor delivery across the BBB divide. However, each carries its own risks and challenges. There is tremendous potential in using neuroimaging strategies to assist in understanding and defining the challenges to translating and optimizing molecularly targeted antibody delivery to CNS tumors to improve clinical outcomes.

Human glioma-initiating cells show a distinct immature phenotype resembling but not identical to NG2 glia

Glioma-initiating cells (GICs) represent a potential important therapeutic target because they are likely to account for the frequent recurrence of malignant gliomas; however, their identity remains unsolved. Here, we characterized the cellular lineage fingerprint of GICs through a combination of electrophysiology, lineage marker expression, and differentiation assays of 5 human patient-derived primary GIC lines. Most GICs coexpressed nestin, NG2 proteoglycan, platelet-derived growth factor receptor-α, and glial fibrillary acidic protein. Glioma-initiating cells could be partially differentiated into astrocytic but not oligodendroglial or neural lineages. We also demonstrate that GICs have a characteristic electrophysiologic profile distinct from that of well-characterized tumor bulk cells. Together, our results suggest that GICs represent a unique type of cells reminiscent of an immature phenotype that closely resembles but is not identical to NG2 glia with respect to marker expression and functional membrane properties.

Ophiobolin A induces paraptosis-like cell death in human glioblastoma cells by decreasing BKCa channel activity

Glioblastoma multiforme (GBM) is the most lethal and common malignant human brain tumor. The intrinsic resistance of highly invasive GBM cells to radiation- and chemotherapy-induced apoptosis accounts for the generally dismal treatment outcomes. This study investigated ophiobolin A (OP-A), a fungal metabolite from Bipolaris species, for its promising anticancer activity against human GBM cells exhibiting varying degrees of resistance to proapoptotic stimuli. We found that OP-A induced marked changes in the dynamic organization of the F-actin cytoskeleton, and inhibited the proliferation and migration of GBM cells, likely by inhibiting big conductance Ca(2+)-activated K(+) channel (BKCa) channel activity. Moreover, our results indicated that OP-A induced paraptosis-like cell death in GBM cells, which correlated with the vacuolization, possibly brought about by the swelling and fusion of mitochondria and/or the endoplasmic reticulum (ER). In addition, the OP-A-induced cell death did not involve the activation of caspases. We also showed that the expression of BKCa channels colocalized with these two organelles (mitochondria and ER) was affected in this programmed cell death pathway. Thus, this study reveals a novel mechanism of action associated with the anticancer effects of OP-A, which involves the induction of paraptosis through the disruption of internal potassium ion homeostasis. Our findings offer a promising therapeutic strategy to overcome the intrinsic resistance of GBM cells to proapoptotic stimuli.

Bradykinin-induced chemotaxis of human gliomas requires the activation of KCa3.1 and ClC-3

Previous reports demonstrate that cell migration in the nervous system is associated with stereotypic changes in intracellular calcium concentration ([Ca(2+)](i)), yet the target of these changes are essentially unknown. We examined chemotactic migration/invasion of human gliomas to study how [Ca(2+)](i) regulates cellular movement and to identify downstream targets. Gliomas are primary brain cancers that spread exclusively within the brain, frequently migrating along blood vessels to which they are chemotactically attracted by bradykinin. Using simultaneous fura-2 Ca(2+) imaging and amphotericin B perforated patch-clamp electrophysiology, we find that bradykinin raises [Ca(2+)](i) and induces a biphasic voltage response. This voltage response is mediated by the coordinated activation of Ca(2+)-dependent, TRAM-34-sensitive K(Ca)3.1 channels, and Ca(2+)-dependent, 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid (DIDS)-sensitive and gluconate-sensitive Cl(-) channels. A significant portion of these Cl(-) currents can be attributed to Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) activation of ClC-3, a voltage-gated Cl(-) channel/transporter, because pharmacological inhibition of CaMKII or shRNA-mediated knockdown of ClC-3 inhibited Ca(2+)-activated Cl(-) currents. Western blots show that K(Ca)3.1 and ClC-3 are expressed in tissue samples obtained from patients diagnosed with grade IV gliomas. Both K(Ca)3.1 and ClC-3 colocalize to the invading processes of glioma cells. Importantly, inhibition of either channel abrogates bradykinin-induced chemotaxis and reduces tumor expansion in mouse brain slices in situ. These channels should be further explored as future targets for anti-invasive drugs. Furthermore, these data elucidate a novel mechanism placing cation and anion channels downstream of ligand-mediated [Ca(2+)](i) increases, which likely play similar roles in other migratory cells in the nervous system.

A role for ion channels in glioma cell invasion

Many cells, including neuronal and glial progenitor cells, stem cells and microglial cells, have the capacity to move through the extracellular spaces of the developing and mature brain. This is particularly pronounced in astrocyte-derived tumors, gliomas, which diffusely infiltrate the normal brain. Although a significant body of literature exists regarding signals that are involved in the guidance of cells and their processes, little attention has been paid to cell-shape and cell-volume changes of migratory cells. However, extracellular spaces in the brain are very narrow and represent a major obstacle that requires cells to dynamically regulate their volume. Recent studies in glioma cells show that this involves the secretion of Cl(-) and K(+) with water. Pharmacological inhibition of Cl(-) channels impairs their ability to migrate and limits tumor progression in experimental tumor models. One Cl(-)-channel inhibitor, chlorotoxin, is currently in Phase II clinical trials to treat malignant glioma. This article reviews our current knowledge of cell-volume changes and the role of ion channels during the migration of glioma cells. It also discusses evidence that supports the importance of channel-mediated cell-volume changes in the migration of immature neurons and progenitor cells during development. New unpublished data is presented, which demonstrates that Cl(-) and K(+) channels involved in cell shrinkage localize to lipid-raft domains on the invadipodia of glioma cells and that their presence might be regulated by trafficking of these proteins in and out of lipid rafts.

Differential role of IK and BK potassium channels as mediators of intrinsic and extrinsic apoptotic cell death

An important event during apoptosis is regulated cell condensation known as apoptotic volume decrease (AVD). Ion channels have emerged as essential regulators of this process mediating the release of K(+) and Cl(-), which together with osmotically obliged water, results in the condensation of cell volume. Using a Grade IV human glioblastoma cell line, we examined the contribution of calcium-activated K(+) channels (K(Ca) channels) to AVD after the addition of either staurosporine (Stsp) or TNF-α-related apoptosis-inducing ligand (TRAIL) to activate the intrinsic or extrinsic pathway of apoptosis, respectively. We show that AVD can be inhibited in both pathways by high extracellular K(+) or the removal of calcium. However, BAPTA-AM was only able to inhibit Stsp-initiated AVD, whereas TRAIL-induced AVD was unaffected. Specific K(Ca) channel inhibitors revealed that Stsp-induced AVD was dependent on K(+) efflux through intermediate-conductance calcium-activated potassium (IK) channels, while TRAIL-induced AVD was mediated by large-conductance calcium-activated potassium (BK) channels. Fura-2 imaging demonstrated that Stsp induced a rapid and modest rise in calcium that was sustained over the course of AVD, while TRAIL produced no detectable rise in global intracellular calcium. Inhibition of IK channels with clotrimazole or 1-[(2-chlorophenyl) diphenylmethyl]-1H-pyrazole (TRAM-34) blocked downstream caspase-3 activation after Stsp addition, while paxilline, a specific BK channel inhibitor, had no effect. Treatment with ionomycin also induced an IK-dependent cell volume decrease. Together these results show that calcium is both necessary and sufficient to achieve volume decrease and that the two major pathways of apoptosis use unique calcium signaling to efflux K(+) through different K(Ca) channels.

Glioma big potassium channel expression in human cancers and possible T cell epitopes for their immunotherapy

Big potassium (BK) ion channels have several spliced variants. One spliced variant initially described within human glioma cells is the glioma BK (gBK) channel. This isoform consists of 34 aa inserted into the intracellular region of the basic BK ion channel. PCR primers specific for this inserted region confirmed that human glioma cell lines and freshly resected surgical tissues from glioblastoma multiforme patients strongly expressed gBK mRNA. Normal human brain tissue very weakly expressed this transcript. An Ab specific for this gBK isoform confirmed that human glioma cells displayed this protein in the cell membrane, mitochondria, Golgi, and endoplasmic reticulum. Within the gBK region, two putative epitopes (gBK1 and gBK2) are predicted to bind to the HLA-A*0201 molecule. HLA-A*0201-restricted human CTLs were generated in vitro using gBK peptide-pulsed dendritic cells. Both gBK1 and gBK2 peptide-specific CTLs killed HLA-A2⁺/gBK⁺ gliomas, but they failed to kill non-HLA-A2-expressing but gBK⁺ target cells in cytolytic assays. T2 cells loaded with exogenous gBK peptides, but not with the influenza M1 control peptide, were only killed by their respective CTLs. The gBK-specific CTLs also killed a variety of other HLA-A*0201⁺ cancer cells that possess gBK, as well as HLA-A2⁺ HEK cells transfected with the gBK gene. Of clinical relevance, we found that T cells derived from glioblastoma multiforme patients that were sensitized to the gBK peptide could also kill target cells expressing gBK. This study shows that peptides derived from cancer-associated ion channels maybe useful targets for T cell-mediated immunotherapy.

Microcoil-based MR phase imaging and manganese enhanced microscopy of glial tumor neurospheres with direct optical correlation

Susceptibility differences among tissues were recently used for highlighting complementary contrast in MRI different from the conventional T(1), T(2), or spin density contrasts. This method, based on the signal phase, previously showed improved image contrast of human or rodent neuroarchitecture in vivo, although direct MR phase imaging of cellular architecture was not available until recently. In this study, we present for the first time the ability of microcoil-based phase MRI to resolve the structure of human glioma neurospheres at significantly improved resolutions (10 × 10 μm(2)) with direct optical image correlation. The manganese chloride property to function as a T(1) contrast agent enabled a closer examination of cell physiology with MRI. Specifically the temporal changes of manganese chloride uptake, retention and release time within and from individual clusters were assessed. The optimal manganese chloride concentration for improved MR signal enhancement was determined while keeping the cellular viability unaffected. The presented results demonstrate the possibilities to reveal structural and functional observation of living glioblastoma human-derived cells. This was achieved through the combination of highly sensitive microcoils, high magnetic field, and methods designed to maximize contrast to noise ratio. The presented approach may provide a powerful multimodal tool that merges structural and functional information of submilimeter biological samples.

Ion channels in glioblastoma

Glioblastoma is the most common primary brain tumor with the most dismal prognosis. It is characterized by extensive invasion, migration, and angiogenesis. Median survival is only 15 months due to this behavior, rendering focal surgical resection ineffective and adequate radiotherapy impossible. At this moment, several ion channels have been implicated in glioblastoma proliferation, migration, and invasion. This paper summarizes studies on potassium, sodium, chloride, and calcium channels of glioblastoma. It provides an up-to-date overview of the literature that could ultimately lead to new therapeutic targets.

Quercetin-induced Growth Inhibition in Human Bladder Cancer Cells Is Associated with an Increase in Ca-activated K Channels

Quercetin (3,3',4',5,7-pentahydroxyflavone) is an attractive therapeutic flavonoid for cancer treatment because of its beneficial properties including apoptotic, antioxidant, and antiproliferative effects on cancer cells. However, the exact mechanism of action of quercetin on ion channel modulation is poorly understood in bladder cancer 253J cells. In this study, we demonstrated that large conductance Ca(2+)-activated K(+) (BK(Ca)) or MaxiK channels were functionally expressed in 253J cells, and quercetin increased BK(Ca) current in a concentration dependent and reversible manner using a whole cell patch configuration. The half maximal activation concentration (IC(50)) of quercetin was 45.5±7.2 µM. The quercetin-evoked BK(Ca) current was inhibited by tetraethylammonium (TEA; 5 mM) a non-specific BK(Ca) blocker and iberiotoxin (IBX; 100 nM) a BK(Ca)-specific blocker. Quercetin-induced membrane hyperpolarization was measured by fluorescence-activated cell sorting (FACS) with voltage sensitive dye, bis (1,3-dibutylbarbituric acid) trimethine oxonol (DiBAC(4)(3); 100 nM). Quercetin-evoked hyperpolarization was prevented by TEA. Quercetin produced an antiproliferative effect (30.3±13.5%) which was recovered to 53.3±10.5% and 72.9±3.7% by TEA and IBX, respectively. Taken together our results indicate that activation of BK(Ca) channels may be considered an important target related to the action of quercetin on human bladder cancer cells.

K(+) channels as therapeutic targets in oncology

Ion channels are involved in a variety of tumors. In particular, potassium channels are expressed abnormally in many cancer types, where their pharmacologic manipulation impairs tumor progression. Since this group of molecules has been successfully targeted for decades in other therapeutic areas, there is a significant body of knowledge on the pharmacology of potassium channels. Several groups of potassium channels with defined molecular identities have been proposed as candidates for therapeutic intervention. The strategies put forward range from classical small molecule blockade to gene therapy approaches, and include the use of potassium channels as targets for adjuvant therapy. We will discuss the reasons for these proposals and explore possible future developments.

Strategies for enhancing antibody delivery to the brain

Antibodies and antibody conjugates have emerged as important tools for cancer therapy. However, a major therapeutic challenge for the use of antibodies is their inability to cross the blood-brain barrier (BBB) to reach tumors localized in the central nervous system (CNS). Multiple methods have been developed to enhance antibody delivery to the CNS, including direct injection, mechanical or biochemical disruption of the BBB, conjugation to a 'molecular Trojan horse', cationization, encapsulation in nanoparticles and liposomes, and more recently, stem cell-mediated antibody delivery. In this review, we discuss each of these approaches, highlighting their successes and the obstacles that remain to be overcome.

Ion channels and transporters [corrected] in cancer. 2. Ion channels and the control of cancer cell migration

A hallmark of high-grade cancers is the ability of malignant cells to invade unaffected tissue and spread disease. This is particularly apparent in gliomas, the most common and lethal type of primary brain cancer affecting adults. Migrating cells encounter restricted spaces and appear able to adjust their shape to accommodate to narrow extracellular spaces. A growing body of work suggests that cell migration/invasion is facilitated by ion channels and transporters. The emerging concept is that K(+) and Cl(-) function as osmotically active ions, which cross the plasma membrane in concert with obligated water thereby adjusting a cell's shape and volume. In glioma cells Na(+)-K(+)-Cl(-) cotransporters (NKCC1) actively accumulate K(+) and Cl(-), establishing a gradient for KCl efflux. Ca(2+)-activated K(+) channels and voltage-gated Cl(-) channels are largely responsible for effluxing KCl promoting hydrodynamic volume changes. In other cancers, different K(+) or even Na(+) channels may function in concert with a variety of Cl(-) channels to support similar volume changes. Channels involved in migration are frequently regulated by Ca(2+) signaling, most likely coupling extracellular stimuli to cell migration. Importantly, the inhibition of ion channels and transporters appears to be clinically relevant for the treatment of cancer. Recent preclinical data indicates that inhibition of NKCC1 with an FDA-approved drug decreases neoplastic migration. Additionally, ongoing clinical trials demonstrate that an inhibitor of chloride channels may be a therapy for the treatment of gliomas. Data reviewed here strongly indicate that ion channels are a promising target for the development of novel therapeutics to combat cancer.

c-Jun is required for TGF-β-mediated cellular migration via nuclear Ca²⁺ signaling

Tumor progression involves the acquisition of invasiveness through a basement membrane. The c-jun proto-oncogene is overexpressed in human tumors and has been identified at the leading edge of human breast tumors. TGF-β plays a bifunctional role in tumorigenesis and cellular migration. Although c-Jun and the activator protein 1 (AP-1) complex have been implicated in human cancer, the molecular mechanisms governing cellular migration via c-Jun and the role of c-Jun in TGF-β signaling remains poorly understood. Here, we analyze TGF-β mediated cellular migration in mouse embryo fibroblasts using floxed c-jun transgenic mice. We compared the c-jun wild type with the c-jun knockout cells through the use of Cre recombinase. Herein, TGF-β stimulated cellular migration and intracellular calcium release requiring endogenous c-Jun. TGF-β mediated Ca(2+) release was independent of extracellular calcium and was suppressed by both U73122 and neomycin, pharmacological inhibitors of the breakdown of PIP(2) into IP(3). Unlike TGF-β-mediated Ca(2+) release, which was c-Jun dependent, ATP mediated Ca(2+) release was c-Jun independent. These studies identify a novel pathway by which TGF-β regulates cellular migration and Ca(2+) release via endogenous c-Jun.