Histamine hyperpolarizes human glioblastoma cells by activating the intermediate-conductance Ca2+-activated K+ channel

Pathophysiological role of histamine signaling and its implications in glioblastoma

Glioblastoma (GBM), an extremely aggressive and prevalent malignant brain tumor, remains a challenge to treat. Despite a multimodality treatment approach, GBM recurrence remains inevitable, particularly with the emergence of temozolomide (TMZ) resistance and limited treatment options. Surprisingly, previous studies show that a history of allergies, atopy, or asthma is inversely associated with GBM risk. Further, the electronic medical record at the University Hospital of Lausanne showed that the GBM patients taking antihistamine during treatment had better survival. Histamine is an essential neurotransmitter in the brain and plays a significant role in regulating sleep, hormonal balance, and cognitive functions. Elevated levels of histamine and increased histamine receptor expression have been found in different tumors and their microenvironments, including GBM. High histamine 1 receptor (HRH1) expression has been shown to be inversely related to overall and progression-free survival in GBM patients, further emphasizing the role of histamine in disease progression. This review aims to provide insights into the challenges of GBM treatment, the role of histamine in GBM progression, and the rationale for considering antihistamines as targeted therapy. The review concludes by encouraging further investigation into antihistamine mechanisms and their impact on the tumor microenvironment.

Electrophysiological Impact of SARS-CoV-2 Envelope Protein in U251 Human Glioblastoma Cells: Possible Implications in Gliomagenesis?

SARS-CoV-2 is the causative agent of the COVID-19 pandemic, the acute respiratory disease which, so far, has led to over 7 million deaths. There are several symptoms associated with SARS-CoV-2 infections which include neurological and psychiatric disorders, at least in the case of pre-Omicron variants. SARS-CoV-2 infection can also promote the onset of glioblastoma in patients without prior malignancies. In this study, we focused on the Envelope protein codified by the virus genome, which acts as viroporin and that is reported to be central for virus propagation. In particular, we characterized the electrophysiological profile of E-protein transfected U251 and HEK293 cells through the patch-clamp technique and FURA-2 measurements. Specifically, we observed an increase in the voltage-dependent (Kv) and calcium-dependent (KCa) potassium currents in HEK293 and U251 cell lines, respectively. Interestingly, in both cellular models, we observed a depolarization of the mitochondrial membrane potential in accordance with an alteration of U251 cell growth. We, therefore, investigated the transcriptional effect of E protein on the signaling pathways and found several gene alterations associated with apoptosis, cytokines and WNT pathways. The electrophysiological and transcriptional changes observed after E protein expression could explain the impact of SARS-CoV-2 infection on gliomagenesis.

M2 muscarinic receptors negatively modulate cell migration in human glioblastoma cells

Glioblastoma (GB) is a very aggressive human brain tumor. The high growth potential and invasiveness make this tumor surgically and pharmacologically untreatable. Our previous work demonstrated that the activation of the M2 muscarinic acetylcholine receptors (M2 mAChRs) inhibited cell proliferation and survival in GB cell lines and in the cancer stem cells derived from human biopsies. The aim of the present study was to investigate the ability of M2 mAChR to modulate cell migration in two different GB cell lines: U87 and U251. By wound healing assay and single cell migration analysis performed by time-lapse microscopy, we demonstrated the ability of M2 mAChRs to negatively modulate cell migration in U251 but not in the U87 cell line. In order to explain the different effects observed in the two cell lines we have evaluated the possible involvement of the intermediate conductance calcium-activated potassium (IKCa) channel. IKCa channel is present in the GB cells, and it has been demonstrated to modulate cell migration. Using the perforated patch-clamp technique we have found that selective activation of M2 mAChR significantly reduced functional density of the IKCa current in U251 but not in U87 cells. To understand whether the M2 mAChR mediated reduction of ion channel density in the U251 cell line was relevant for the cell migration impairment, we tested the effects of TRAM-34, a selective inhibitor of the IKCa channel, in wound healing assay. We found that it was able to markedly reduce U251 cell migration and significantly decrease the number of invadopodia-like structure formations. These results suggest that only in U251 cells the reduced cell migration M2 mAChR-mediated might involve, at least in part, the IKCa channel.

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.

LY294002 Inhibits Intermediate Conductance Calcium-Activated Potassium (KCa3.1) Current in Human Glioblastoma Cells

Glioblastomas (GBs) are among the most common tumors with high malignancy and invasiveness of the central nervous system. Several alterations in protein kinase and ion channel activity are involved to maintain the malignancy. Among them, phosphatidylinositol 3-kinase (PI3K) activity and intermediate conductance calcium-activated potassium (KCa3.1) current are involved in several aspects of GB biology. By using the electrophysiological approach and noise analysis, we observed that KCa3.1 channel activity is LY294002-sensitive and Wortmannin-resistant in accordance with the involvement of PI3K class IIβ (PI3KC2β). This modulation was observed also during the endogenous activation of KCa3.1 current with histamine. The principal action of PI3KC2β regulation was the reduction of open probability in intracellular free calcium saturating concentration. An explanation based on the “three-gate” model of the KCa3.1 channel by PI3KC2β was proposed. Based on the roles of KCa3.1 and PI3KC2β in GB biology, a therapeutic implication was suggested to prevent chemo- and radioresistance mechanisms.

OPALS: A New Osimertinib Adjunctive Treatment of Lung Adenocarcinoma or Glioblastoma Using Five Repurposed Drugs

Background: Pharmacological targeting aberrant activation of epidermal growth factor receptor tyrosine kinase signaling is an established approach to treating lung adenocarcinoma. Osimertinib is a tyrosine kinase approved and effective in treating lung adenocarcinomas that have one of several common activating mutations in epidermal growth factor receptor. The emergence of resistance to osimertinib after a year or two is the rule. We developed a five-drug adjuvant regimen designed to increase osimertinib’s growth inhibition and thereby delay the development of resistance. Areas of Uncertainty: Although the assembled preclinical data is strong, preclinical data and the following clinical trial results can be discrepant. The safety of OPALS drugs when used individually is excellent. We have no data from humans on their tolerability when used as an ensemble. That there is no data from the individual drugs to suspect problematic interaction does not exclude the possibility. Data Sources: All relevant PubMed.org articles on the OPALS drugs and corresponding pathophysiology of lung adenocarcinoma and glioblastoma were reviewed. Therapeutic Opinion: The five drugs of OPALS are in wide use in general medicine for non-oncology indications. OPALS uses the anti-protozoal drug pyrimethamine, the antihistamine cyproheptadine, the antibiotic azithromycin, the antihistamine loratadine, and the potassium sparing diuretic spironolactone. We show how these inexpensive and generically available drugs intersect with and inhibit lung adenocarcinoma growth drive. We also review data showing that both OPALS adjuvant drugs and osimertinib have data showing they may be active in suppressing glioblastoma growth.

Stimulation of vascular smooth muscle cell proliferation by stiff matrix via the IKCa channel-dependent Ca2+ signaling

Vascular stiffening, an early and common characteristic of cardiovascular diseases (CVDs), stimulates vascular smooth muscle cell (VSMC) proliferation which reciprocally accelerates the progression of CVDs. However, the mechanisms by which extracellular matrix stiffness accompanying vascular stiffening regulates VSMC proliferation remain largely unknown. In the present study, we examined the role of the intermediate-conductance Ca²⁺ -activated K⁺  (IK_Ca ) channel in the matrix stiffness regulation of VSMC proliferation by growing A7r5 cells on soft and stiff polydimethylsiloxane substrates with stiffness close to these of arteries under physiological and pathological conditions, respectively. Stiff substrates stimulated cell proliferation and upregulated the expression of the IK_Ca channel. Stiff substrate-induced cell proliferation was suppressed by pharmacological inhibition using TRAM34, an IK_Ca channel blocker, or genetic depletion of the IK_Ca channel. In addition, stiff substrate-induced cell proliferation was also suppressed by reducing extracellular Ca²⁺ concentration using EGTA or intracellular Ca²⁺ concentration using BAPTA-AM. Moreover, stiff substrate induced activation of extracellular signal-regulated kinases (ERKs), which was inhibited by treatment with TRAM34 or BAPTA-AM. Stiff substrate-induced cell proliferation was suppressed by treatment with PD98059, an ERK inhibitor. Taken together, these results show that substrates with pathologically relevant stiffness upregulate the IK_Ca channel expression to enhance intracellular Ca²⁺ signaling and subsequent activation of the ERK signal pathway to drive cell proliferation. These findings provide a novel mechanism by which vascular stiffening regulates VSMC function.

Silver ions promote blebs growth in U251 glioblastoma cell by activating nonselective cationic currents

Glioblastoma (GBM) is the most common and aggressive human brain cancer with low prognosis and therefore the discovery of new anticancer agents is needful. Sulfydryl reagents, such as silver, have been shown to induce membrane vesiculation in several cellular models through a mechanism that has not been yet completely clarified. Using U251 glioblastoma cells, we observed that silver induced irreversible bleb formation of the plasma membrane. This morphological event was anticipated by an increase of intracellular Ca²⁺ associated to extracellular Ca²⁺ influx. Accordingly, using patch-clamp whole cell recording during silver ion application, inward current/s (IAg) at -90 mV were detected and cells were permeable to Ca²⁺ and monovalent ions such as Na⁺. IAg activation and the intracellular Ca²⁺ increase promoted by silver ions (Ag⁺) were prevented by co-application of 20 µM cysteine and 300 µM DIDS (4,4'-Diisothiocyanatostilbene-2,2'-disulfonic acid), suggesting a critical role of thiol groups in the biological effects of silver ions. IAg was partially inhibited by 1 mM Gd³⁺, an unspecific inhibitor of cationic currents. Cysteine, Gd³⁺ and extracellular free Ca²⁺ solution completely abolished blebbing formation promoted by Ag⁺. Furthermore, extracellular Na⁺ ion replacement with TEA or an increase of extracellular tonicity by sucrose (100 mM) reduced both size and growth of membrane blebbing. Our data suggest that Ag⁺ promotes the formation necrotic blebs as consequence of the increase of intracellular Ca²⁺ and intracellular hydrostatic pressure associated to the activation of cationic currents. Since silver-induced blebs were less evident in benign glial human Müller MIO-M1 cells, silver compounds could represent new adjuvant to anticancer agents to improve GBM therapies.

Ca2+-activated K+ channels modulate microglia affecting motor neuron survival in hSOD1G93A mice

Recent studies described a critical role for microglia in amyotrophic lateral sclerosis (ALS), where these CNS-resident immune cells participate in the establishment of an inflammatory microenvironment that contributes to motor neuron degeneration. Understanding the mechanisms leading to microglia activation in ALS could help to identify specific molecular pathways which could be targeted to reduce or delay motor neuron degeneration and muscle paralysis in patients. The intermediate-conductance calcium-activated potassium channel KCa3.1 has been reported to modulate the "pro-inflammatory" phenotype of microglia in different pathological conditions. We here investigated the effects of blocking KCa3.1 activity in the hSOD1G93AALS mouse model, which recapitulates many features of the human disease. We report that treatment of hSOD1G93A mice with a selective KCa3.1 inhibitor, 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34), attenuates the "pro-inflammatory" phenotype of microglia in the spinal cord, reduces motor neuron death, delays onset of muscle weakness, and increases survival. Specifically, inhibition of KCa3.1 channels slowed muscle denervation, decreased the expression of the fetal acetylcholine receptor γ subunit and reduced neuromuscular junction damage. Taken together, these results demonstrate a key role for KCa3.1 in driving a pro-inflammatory microglia phenotype in ALS.

Role of KCa3.1 Channels in Modulating Ca2+ Oscillations during Glioblastoma Cell Migration and Invasion

Cell migration and invasion in glioblastoma (GBM), the most lethal form of primary brain tumors, are critically dependent on Ca²⁺ signaling. Increases of [Ca²⁺]_i in GBM cells often result from Ca²⁺ release from the endoplasmic reticulum (ER), promoted by a variety of agents present in the tumor microenvironment and able to activate the phospholipase C/inositol 1,4,5-trisphosphate PLC/IP₃ pathway. The Ca²⁺ signaling is further strengthened by the Ca²⁺ influx from the extracellular space through Ca²⁺ release-activated Ca²⁺ (CRAC) currents sustained by Orai/STIM channels, meant to replenish the partially depleted ER. Notably, the elevated cytosolic [Ca²⁺]_i activates the intermediate conductance Ca²⁺-activated K (KCa3.1) channels highly expressed in the plasma membrane of GBM cells, and the resulting K⁺ efflux hyperpolarizes the cell membrane. This translates to an enhancement of Ca²⁺ entry through Orai/STIM channels as a result of the increased electromotive (driving) force on Ca²⁺ influx, ending with the establishment of a recurrent cycle reinforcing the Ca²⁺ signal. Ca²⁺ signaling in migrating GBM cells often emerges in the form of intracellular Ca²⁺ oscillations, instrumental to promote key processes in the migratory cycle. This has suggested that KCa3.1 channels may promote GBM cell migration by inducing or modulating the shape of Ca²⁺ oscillations. In accordance, we recently built a theoretical model of Ca²⁺ oscillations incorporating the KCa3.1 channel-dependent dynamics of the membrane potential, and found that the KCa3.1 channel activity could significantly affect the IP₃ driven Ca²⁺ oscillations. Here we review our new theoretical model of Ca²⁺ oscillations in GBM, upgraded in the light of better knowledge of the KCa3.1 channel kinetics and Ca²⁺ sensitivity, the dynamics of the Orai/STIM channel modulation, the migration and invasion mechanisms of GBM cells, and their regulation by Ca²⁺ signals.

Depression and glioblastoma, complicated concomitant diseases: a systemic review of published literature

Glioblastoma multiforme (GBM) is the most common primary brain cancer. Depression is a common co-morbidity of this condition. Despite this common interaction, relatively little research has been performed on the development of GBM-associated depression. We performed a literary search of the PubMed database for articles published relating to GBM and depression. A total of 85 articles were identified with 46 meeting inclusion criteria. Depression significantly impacts care, decreasing medication compliance, and patient survival. Diagnostically, because depression and GBM share intricate neuro-connectivity in a way that effect functionality, these diseases can be mistaken for alternative psychological or pathological disorders, complicating care. Therapeutically, anti-depressants have anti-tumor properties; yet, some have been shown to interfere with GBM treatment. One reason for this is that the pathophysiological development of depression and GBM share several pathways including altered regulation of the 5-HT receptor, norepinephrine, and 3':5'-cyclic monophosphate. Over time, depression can persist after GBM treatment, affecting patient quality of life. Together, depression and GBM are complicated concomitant diseases. Clinicians must be aware of their co-existence. Because of overlapping molecular pathways involved in both diseases, careful medication selection is imperative to avoid potential adverse interactions. Since GBMs are the most common primary brain cancer, physicians dealing with this disease should be prepared for the development of depression as a potential sequela of this condition, given the related pathophysiology and the known poor outcomes.

Structure, Gating and Basic Functions of the Ca2+-activated K Channel of Intermediate Conductance

BACKGROUND

The KCa3.1 channel is the intermediate-conductance member of the Ca2+- activated K channel superfamily. It is widely expressed in excitable and non-excitable cells, where it plays a major role in a number of cell functions. This paper aims at illustrating the main structural, biophysical and modulatory properties of the KCa3.1 channel, and providing an account of experimental data on its role in volume regulation and Ca2+ signals.

METHODS

Research and online content related to the structure, structure/function relationship, and physiological role of the KCa3.1 channel are reviewed.

RESULTS

Expressed in excitable and non-excitable cells, the KCa3.1 channel is voltage independent, its opening being exclusively gated by the binding of intracellular Ca2+ to calmodulin, a Ca2+- binding protein constitutively associated with the C-terminus of each KCa3.1 channel α subunit. The KCa3.1 channel activates upon high affinity Ca2+ binding, and in highly coordinated fashion giving steep Hill functions and relatively low EC50 values (100-350 nM). This high Ca2+ sensitivity is physiologically modulated by closely associated kinases and phosphatases. The KCa3.1 channel is normally activated by global Ca2+ signals as resulting from Ca2+ released from intracellular stores, or by the refilling influx through store operated Ca2+ channels, but cases of strict functional coupling with Ca2+-selective channels are also found. KCa3.1 channels are highly expressed in many types of cells, where they play major roles in cell migration and death. The control of these complex cellular processes is achieved by KCa3.1 channel regulation of the driving force for Ca2+ entry from the extracellular medium, and by mediating the K+ efflux required for cell volume control.

CONCLUSION

Much work remains to be done to fully understand the structure/function relationship of the KCa3.1 channels. Hopefully, this effort will provide the basis for a beneficial modulation of channel activity under pathological conditions.

Overexpression of Large-Conductance Calcium-Activated Potassium Channels in Human Glioblastoma Stem-Like Cells and Their Role in Cell Migration

Glioblastomas (GBMs) are brain tumors characterized by diffuse invasion of cancer cells into the healthy brain parenchyma, and establishment of secondary foci. GBM cells abundantly express large-conductance, calcium-activated potassium (BK) channels that are thought to promote cell invasion. Recent evidence suggests that the GBM high invasive potential mainly originates from a pool of stem-like cells, but the expression and function of BK channels in this cell subpopulation have not been studied. We investigated the expression of BK channels in GBM stem-like cells using electrophysiological and immunochemical techniques, and assessed their involvement in the migratory process of this important cell subpopulation. In U87-MG cells, BK channel expression and function were markedly upregulated by growth conditions that enriched the culture in GBM stem-like cells (U87-NS). Cytofluorimetric analysis further confirmed the appearance of a cell subpopulation that co-expressed high levels of BK channels and CD133, as well as other stem cell markers. A similar association was also found in cells derived from freshly resected GBM biopsies. Finally, transwell migration tests showed that U87-NS cells migration was much more sensitive to BK channel block than U87-MG cells. Our data show that BK channels are highly expressed in GBM stem-like cells, and participate to their high migratory activity. J. Cell. Physiol. 232: 2478-2488, 2017. © 2016 Wiley Periodicals, Inc.

Hypoxia Modulates the Swelling-Activated Cl Current in Human Glioblastoma Cells: Role in Volume Regulation and Cell Survival

The malignancy of glioblastoma multiforme (GBM), the most common human brain tumor, correlates with the presence of hypoxic areas, but the underlying mechanisms are unclear. GBM cells express abundant Cl channels whose activity supports cell volume and membrane potential changes, ultimately leading to cell proliferation, migration, and escaping death. In non-tumor tissues Cl channels are modulated by hypoxia, which prompted us to verify whether hypoxia would also modulate Cl channels in GBM cells. Our results show that in GBM cell lines, acute application of a hypoxic solution activates a Cl current displaying the biophysical and pharmacological features of the swelling-activated Cl current (ICl,swell ). We also found that acute hypoxia increased the cell volume by about 20%, and a 30% hypertonic solution partially inhibited the hypoxia-activated Cl current, suggesting that cell swelling and the activation of the Cl current are sequential events. Notably, the hypoxia-induced cell swelling was followed by a regulatory volume decrease (RVD) mediated mainly by ICl,swell . Since, a hypoxia-induced prolonged cell swelling is usually regarded as a death insult, we hypothesized that the hypoxia-activated Cl current could limit cell swelling and prevent necrotic death of GBM cells under hypoxic conditions. In accordance, we found that the ICl,swell inhibitor DCPIB hampered the RVD process, and more importantly it sensibly increased the hypoxia-induced necrotic death in these cells. Taken together, these results suggest that Cl channels are strongly involved in the survival of GBM cells in a hypoxic environment, and may thus represent a new therapeutic target for this malignant tumor. J. Cell. Physiol. 232: 91-100, 2017. © 2016 Wiley Periodicals, Inc.

Autophagy involvement in olanzapine-mediated cytotoxic effects in human glioma cells

The aim of this study was to investigate the effects of olanzapine on growth inhibition as well as autophagy in glioma cells in vitro and in vivo. The proliferation of both LN229 and T98 glioma cells, measured by MTT assay, was suppressed in a concentration-dependent and time-dependent manner. Moreover, apoptosis of both cells was significantly increased with the treatment of olanzapine as evidenced by increased Bcl-2 expression, Hoechst 33258 staining and annexinV-FITC/PI staining. Olanzapine treatment also enhanced activation of autophagy with increased expression of LC3-II, expression of protein p62, a substrate of autophagy, being decreased. The growth inhibition by olanzapine in both glioma cell lines could be blocked by co-treatment with 3-MA, an autophagy inhibitor. Furthermore, olanzapine effectively blocked the growth of subcutaneous xenografts of LN229 glioma cells in vivo. The increased level of protein LC3-II and decreased level of p62 followed by a decreased level of Bcl-2, suggesting that autophagy may contribute to apoptosis. In addition, reduced proliferation of glioma cells was shown by a decrease of Ki-67 staining and increased caspase-3 staining indicative of apoptosis in mouse xenografts. These results indicated that olanzapine inhibited the growth of glioma cells accompanied by induction of autophagy and apoptosis both in vitro and in vivo. Olanzapine-induced autophagy plays a tumor-suppressing role in glioma cells.

Ca2+-Activated IK K+ Channel Blockade Radiosensitizes Glioblastoma Cells

Ca(2+)-activated K(+) channels, such as BK and IK channels, have been proposed to fulfill pivotal functions in neoplastic transformation, malignant progression, and brain infiltration of glioblastoma cells. Here, the ionizing radiation (IR) effect of IK K(+) channel targeting was tested in human glioblastoma cells. IK channels were inhibited pharmacologically by TRAM-34 or genetically by knockdown, cells were irradiated with 6 MV photons and IK channel activity, Ca(2+) signaling, cell cycling, residual double-strand breaks, and clonogenic survival were determined. In addition, the radiosensitizing effect of TRAM-34 was analyzed in vivo in ectopic tumors. Moreover, The Cancer Genome Atlas (TCGA) was queried to expose the dependence of IK mRNA abundance on overall survival (OS) of patients with glioma. Results indicate that radiation increased the activity of IK channels, modified Ca(2+) signaling, and induced a G2-M cell-cycle arrest. TRAM-34 decreased the IR-induced accumulation in G2-M arrest and increased the number of γH2AX foci post-IR, suggesting that TRAM-34 mediated an increase of residual DNA double-strand breaks. Mechanistically, IK knockdown abolished the TRAM-34 effects indicating the IK specificity of TRAM-34. Finally, TRAM-34 radiosensitized ectopic glioblastoma in vivo and high IK mRNA abundance associated with shorter patient OS in low-grade glioma and glioblastoma.

IMPLICATIONS

Together, these data support a cell-cycle regulatory function for IK K(+) channels, and combined therapy using IK channel targeting and radiation is a new strategy for anti-glioblastoma therapy.

Reconciling the discrepancies on the involvement of large-conductance Ca(2+)-activated K channels in glioblastoma cell migration

Glioblastoma (GBM) is the most common and aggressive primary brain tumor, and is notable for spreading so effectively through the brain parenchyma to make complete surgical resection virtually impossible, and prospect of life dismal. Several ion channels have been involved in GBM migration and invasion, due to their critical role in supporting volume changes and Ca(2+) influx occuring during the process. The large-conductance, Ca(2+)-activated K (BK) channels, markedly overexpressed in biopsies of patients with GBMs and in GBM cell lines, have attracted much interest and have been suggested to play a central role in cell migration and invasion as candidate channels for providing the ion efflux and consequent water extrusion that allow cell shrinkage during migration. Available experimental data on the role of BK channel in migration and invasion are not consistent though. While BK channels block typically resulted in inhibition of cell migration or in no effect, their activation would either enhance or inhibit the process. This short review reexamines the relevant available data on the topic, and presents a unifying paradigm capable of reconciling present discrepancies. According to this paradigm, BK channels would not contribute to migration under conditions where the [Ca(2+)] i is too low for their activation. They will instead positively contribute to migration for intermediate [Ca(2+)] i , insufficient as such to activate BK channels, but capable of predisposing them to cyclic activation following oscillatory [Ca(2+)] i increases. Finally, steadily active BK channels because of prolonged high [Ca(2+)] i would inhibit migration as their steady activity would be unsuitable to match the cyclic cell volume changes needed for proper cell migration.

Identification of key signaling molecules involved in the activation of the swelling-activated chloride current in human glioblastoma cells

The swelling-activated chloride current (I Cl,Vol) is abundantly expressed in glioblastoma (GBM) cells, where it controls cell volume and invasive migration. The transduction pathway mediating I Cl,Vol activation in GBM cells is, however, poorly understood. By means of pharmacological and electrophysiological approaches, on GL-15 human GBM cells we found that I Cl,Vol activation by hypotonic swelling required the activity of a U73122-sensitive phospholipase C (PLC). I Cl,Vol activation could also be induced by the membrane-permeable diacylglycerol (DAG) analog OAG. In contrast, neither calcium (Ca(2+)) chelation by BAPTA-AM nor changes in PKC activity were able to affect I Cl,Vol activation by hypotonic swelling. We further found that R59022, an inhibitor of diacylglycerol kinase (DGK), reverted I Cl,Vol activation, suggesting the involvement of phosphatidic acid. In addition, I Cl,Vol activation required the activity of a EHT1864-sensitive Rac1 small GTPase and the resulting actin polymerization, as I Cl,Vol activation was prevented by cytochalasin B. We finally show that I Cl,Vol can be activated by the promigratory fetal calf serum in a PLC- and DGK-dependent manner. This observation is potentially relevant because blood serum can likely come in contact with glioblastoma cells in vivo as a result of the tumor-related partial breakdown of the blood-brain barrier. Given the relevance of I Cl,Vol in GBM cell volume regulation and invasiveness, the several key signaling molecules found in this study to be involved in the activation of the I Cl,Vol may represent potential therapeutic targets against this lethal cancer.

Does use of tetracyclic antidepressant-mirtazapine reduce cancer risk in depression patients?

PURPOSE

We conducted a nested case-control study to evaluate the association between risk of cancer and mirtazapine use in depression patients in Taiwan.

METHODS

We obtained data from the Taiwan National Health Insurance Research Database to conduct a population-based nested case-control study. The study cohort included 16 897 patients diagnosed with depression between January 1, 2000 and December 31, 2008. We identified 530 cancer patients as the study group and matched 4 non-cancer subjects with each cancer patient by incident density, age, and sex. Odds ratios and 95% confidence intervals were estimated using multivariate conditional logistic regression analysis.

RESULTS

Use of mirtazapine for depression did not have significant effect on overall cancer incidence (odds ratio: 1.03, 95% confidence interval: 0.72-1.48). Further analysis of annual mirtazapine dosages and the duration of mirtazapine use revealed no significant effect on cancer risk.

CONCLUSION

The findings of this population-based nested case-control study suggest that mirtazapine use may not provide a tumor suppression effect in humans such as that seen in the animal model. Future large-scale and in-depth investigations in this area are warranted.

Bumetanide hyperpolarizes madin-darby canine kidney cells and enhances cellular gentamicin uptake by elevating cytosolic Ca(2+) thus facilitating intermediate conductance Ca(2+)--activated potassium channels

Loop diuretics such as bumetanide and furosemide enhance aminoglycoside ototoxicity when co-administered to patients and animal models. The underlying mechanism(s) is poorly understood. We investigated the effect of these diuretics on cellular uptake of aminoglycosides, using Texas Red-tagged gentamicin (GTTR), and intracellular/whole-cell recordings of Madin-Darby canine kidney (MDCK) cells. We found that bumetanide and furosemide dose-dependently enhanced cytoplasmic GTTR fluorescence by ~60 %. This enhancement was suppressed by La(3+), a non-selective cation channel (NSCC) blocker, and by K(+) channel blockers Ba(2+) and clotrimazole, but not by tetraethylammonium (TEA), 4-aminopyridine (4-AP) or glipizide, nor by Cl(-) channel blockers diphenylamine-2-carboxylic acid (DPC), niflumic acid (NFA), and CFTRinh-172. Bumetanide and furosemide hyperpolarized MDCK cells by ~14 mV, increased whole-cell I/V slope conductance; the bumetanide-induced net current I/V showed a reversal potential (V r) ~-80 mV. Bumetanide-induced hyperpolarization and I/V change was suppressed by Ba(2+) or clotrimazole, and absent in elevated [Ca(2+)]i, but was not affected by apamin, 4-AP, TEA, glipizide, DPC, NFA, or CFTRinh-172. Bumetanide and furosemide stimulated a surge of Fluo-4-indicated cytosolic Ca(2+). Ba(2+) and clotrimazole alone depolarized cells by ~18 mV and reduced I/V slope with a net current V r near -85 mV, and reduced GTTR uptake by ~20 %. La(3+) alone hyperpolarized the cells by ~-14 mV, reduced the I/V slope with a net current V r near -10 mV, and inhibited GTTR uptake by ~50 %. In the presence of La(3+), bumetanide-caused negligible change in potential or I/V. We conclude that NSCCs constitute a major cell entry pathway for cationic aminoglycosides; bumetanide enhances aminoglycoside uptake by hyperpolarizing cells that increases the cation influx driving force; and bumetanide-induced hyperpolarization is caused by elevating intracellular Ca(2+) and thus facilitating activation of the intermediate conductance Ca(2+)-activated K(+) channels.

KCa3.1 channels are involved in the infiltrative behavior of glioblastoma in vivo

Glioblastoma multiforme (GBM) is a diffuse brain tumor characterized by high infiltration in the brain parenchyma rendering the tumor difficult to eradicate by neurosurgery. Efforts to identify molecular targets involved in the invasive behavior of GBM suggested ion channel inhibition as a promising therapeutic approach. To determine if the Ca(2+)-dependent K(+) channel KCa3.1 could represent a key element for GBM brain infiltration, human GL-15 cells were xenografted into the brain of SCID mice that were then treated with the specific KCa3.1 blocker TRAM-34 (1-((2-chlorophenyl) (diphenyl)methyl)-1H-pyrazole). After 5 weeks of treatment, immunofluorescence analyses of cerebral slices revealed reduced tumor infiltration and astrogliosis surrounding the tumor, compared with untreated mice. Significant reduction of tumor infiltration was also observed in the brain of mice transplanted with KCa3.1-silenced GL-15 cells, indicating a direct effect of TRAM-34 on GBM-expressed KCa3.1 channels. As KCa3.1 channels are also expressed on microglia, we investigated the effects of TRAM-34 on microglia activation in GL-15 transplanted mice and found a reduction of CD68 staining in treated mice. Similar results were observed in vitro where TRAM-34 reduced both phagocytosis and chemotactic activity of primary microglia exposed to GBM-conditioned medium. Taken together, these results indicate that KCa3.1 activity has an important role in GBM invasiveness in vivo and that its inhibition directly affects glioma cell migration and reduces astrocytosis and microglia activation in response to tumor-released factors. KCa3.1 channel inhibition therefore constitutes a potential novel therapeutic approach to reduce GBM spreading into the surrounding tissue.

Role of histidine/histamine in carnosine-induced neuroprotection during ischemic brain damage

Urgent need exists for new therapeutic options in ischemic stroke. We recently demonstrated that carnosine, an endogenous dipeptide consisting of alanine and histidine, is robustly neuroprotective in ischemic brain injury and has a wide clinically relevant therapeutic time window. The precise mechanistic pathways that mediate this neuroprotective effect are not known. Following in vivo administration, carnosine is hydrolyzed into histidine, a precursor of histamine. It has been hypothesized that carnosine may exert its neuroprotective activities through the histidine/histamine pathway. Herein, we investigated whether the neuroprotective effect of carnosine is mediated by the histidine/histamine pathway using in vitro primary astrocytes and cortical neurons, and an in vivo rat model of ischemic stroke. In primary astrocytes, carnosine significantly reduced ischemic cell death after oxygen-glucose deprivation, and this effect was abolished by histamine receptor type I antagonist. However, histidine or histamine did not exhibit a protective effect on ischemic astrocytic cell death. In primary neuronal cultures, carnosine was found to be neuroprotective but histamine receptor antagonists had no effect on the extent of neuroprotection. The in vivo effect of histidine and carnosine was compared using a rat model of ischemic stroke; only carnosine exhibited neuroprotection. Taken together, our data demonstrate that although the protective effects of carnosine may be partially mediated by activity at the histamine type 1 receptor on astrocytes, the histidine/histamine pathway does not appear to play a critical role in carnosine induced neuroprotection.

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.

The inhibition of KCa3.1 channels activity reduces cell motility in glioblastoma derived cancer stem cells

In the present study we evaluated the expression of the intermediate conductance calcium-activated potassium (KCa3.1) channel in human glioblastoma stem-like cells (CSCs) and investigated its role in cell motility. While the KCa3.1 channel is not expressed in neuronal- and glial-derived tissues of healthy individuals, both the KCa3.1 mRNA and protein are present in the glioblastoma tumor population, and are significantly enhanced in CSCs derived from both established cell line U87MG and a primary cell line, FCN9. Consistent with these data, voltage-independent and TRAM-34 sensitive potassium currents imputable to the KCa3.1 channel were recorded in the murine GL261 cell line and several primary human glioblastoma cells lines. Moreover, a significantly higher KCa3.1 current was recorded in U87MG-CD133 positive cells as compared to the U87MG-CD133 negative subpopulation. Further, we found that the tumor cell motility is strongly associated with KCa3.1 channel expression. Blockade of the KCa3.1 channel with the specific inhibitor TRAM-34 has in fact a greater impact on the motility of CSCs (reduction of 75%), which express a high level of KCa3.1 channel, than on the FCN9 parental population (reduction of 32%), where the KCa3.1 channel is expressed at lower level. Similar results were also observed with the CSCs derived from U87MG. Because invasion of surrounding tissues is one of the main causes of treatment failure in glioblastoma, these findings can be relevant for future development of novel cancer therapeutic drugs.

Expression and Role of the Intermediate-Conductance Calcium-Activated Potassium Channel KCa3.1 in Glioblastoma

Glioblastomas are characterized by altered expression of several ion channels that have important consequences in cell functions associated with their aggressiveness, such as cell survival, proliferation, and migration. Data on the altered expression and function of the intermediate-conductance calcium-activated K (KCa3.1) channels in glioblastoma cells have only recently become available. This paper aims to (i) illustrate the main structural, biophysical, pharmacological, and modulatory properties of the KCa3.1 channel, (ii) provide a detailed account of data on the expression of this channel in glioblastoma cells, as compared to normal brain tissue, and (iii) critically discuss its major functional roles. Available data suggest that KCa3.1 channels (i) are highly expressed in glioblastoma cells but only scantly in the normal brain parenchima, (ii) play an important role in the control of glioblastoma cell migration. Altogether, these data suggest KCa3.1 channels as potential candidates for a targeted therapy against this tumor.

Can the therapeutic effects of temozolomide be potentiated by stimulating AMP-activated protein kinase with olanzepine and metformin?

As current treatments for glioblastoma commonly fail to cure, the need for more effective therapeutic options is overwhelming. Here, we summarize experimental evidence in support of the suggestion that metformin and olanzepine have potential to enhance the cytotoxic effects of temozolomide, an alkylating chemotherapeutic agent commonly used to treat glioblastoma. Although the primary path leading to temozolomide-induced cell death is formation of O-6-methylguanine and apoptotic signalling triggered by O-6-methyl G:T mispairs, that apoptotic signalling goes through a step mediated by AMP-activated protein kinase (AMPK). Metformin or olanzapine have been shown independently to enhance AMPK activation. Metformin to treat diabetes and olanzapine to treat psychiatric disorders are well tolerated and have been used clinically for many years. Thus it should be feasible to increase AMPK activation and add to the pro-apoptotic effects of temozolomide, by adding metformin and olanzapine to the therapeutic regimen. Clinical assessment of the potential benefit of such combined therapy against glioblastoma is warranted.

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.

Serum-activated K and Cl currents underlay U87-MG glioblastoma cell migration

Glioblastoma cells in vivo are exposed to a variety of promigratory signals, including undefined serum components that infiltrate into high grade gliomas as result of blood-brain barrier breakdown. Glioblastoma cell migration has been further shown to depend heavily on ion channels activity. We have then investigated the modulatory effects of fetal calf serum (FCS) on ion channels, and their involvement in U87-MG cells migration. Using the perforated patch-clamp technique we have found that, in a subpopulation of cells (42%), FCS induced: (1) an oscillatory activity of TRAM-34 sensitive, intermediate-conductance calcium-activated K (IK(Ca) ) channels, mediated by calcium oscillations previously shown to be induced by FCS in this cell line; (2) a stable activation of a DIDS- and NPPB-sensitive Cl current displaying an outward rectifying instantaneous current-voltage relationship and a slow, voltage-dependent inactivation. By contrast, in another subpopulation of cells (32%) FCS induced a single, transient IK(Ca) current activation, always accompanied by a stable activation of the Cl current. The remaining cells did not respond to FCS. In order to understand whether the FCS-induced ion channel activities are instrumental to promoting cell migration, we tested the effects of TRAM-34 and DIDS on the FCS-induced U87-MG cell migration using transwell migration assays. We found that these inhibitors were able to markedly reduce U87-MG cell migration in the presence of FCS, and that their co-application resulted in an almost complete arrest of migration. It is concluded that the modulation of K and Cl ion fluxes is essential for the FCS-induced glioblastoma cell migration.

Histaminergic responses by hypothalamic neurons that regulate lordosis and their modulation by estradiol

How do fluctuations in the level of generalized arousal of the brain affect the performance of specific motivated behaviors, such as sexual behaviors that depend on sexual arousal? A great deal of previous work has provided us with two important starting points in answering this question: (i) that histamine (HA) serves generalized CNS arousal and (ii) that heightened electrical activity of neurons in the ventromedial nucleus of the hypothalamus (VMN) is necessary and sufficient for facilitating the primary female sex behavior in laboratory animals, lordosis behavior. Here we used patch clamp recording technology to analyze HA effects on VMN neuronal activity. The results show that HA acting through H1 receptors (H1R) depolarizes these neurons. Further, acute administration of estradiol, an estrogen necessary for lordosis behavior to occur, heightens this effect. Hyperpolarization, which tends to decrease excitability and enhance inhibition, was not affected by acute estradiol or mediated by H1R but was mediated by other HA receptor subtypes, H2 and H3. Sampling of mRNA from individual VMN neurons showed colocalization of expression of H1 receptor mRNA with estrogen receptor (ER)-alpha mRNA but also revealed ER colocalization with the other HA receptor subtypes and colocalization of different subtypes with each other. The latter finding provides the molecular basis for complex "push-pull" regulation of VMN neuronal excitability by HA. Thus, in the simplest causal route, HA, acting on VMN neurons through H1R provides a mechanism by which elevated states of generalized CNS arousal can foster a specific estrogen-dependent, aroused behavior, sexual behavior.

Histamine regulation of hyperplastic and neoplastic cell growth in cholangiocytes

Histamine has long been known to be involved in inflammatory events. The discovery of antihistamines dates back to the first half of the 20^th century when a Swiss-Italian pharmacologist, Daniel Bovet began his work. In 1957 he was awarded a Nobel Prize for his production of antihistamines for allergy relief. Since that time, histamine has been found to play a role in other events besides allergic reaction. Possibly unbelievable to Bovet and his peers, histamine has now been marked as playing a role in liver pathologies including hepatobiliary diseases.