Clofilium, a potassium channel blocker, induces apoptosis of human promyelocytic leukemia (HL-60) cells via Bcl-2-insensitive activation of caspase-3

Rhodamine hydrazide-linked naphthalimide derivative: Selective naked eye detection of Cu2+, S2- and understanding the therapeutic potential of the copper complex as an anti-cervical cancer agent

A naphthalimide-labeled rhodamine hydrazone derivative HL has been synthesized, characterized and examined in metal ion recognition. It shows selective colorimetric detection of Cu2+ over a number of other metal ions with a detection limit of 1.66 × 10-7 M in CH3CN/HEPES buffer (v/v = 2:1, pH = 6.8). The spirolactam ring of rhodamine and the imino-phenol motif of naphthalimide in HL are involved in complexation of Cu2+ as shown by single crystal X-ray. Single crystal of the copper-complex is prepared by utilizing NaSCN and it is characterized as CuL(SCN). The emergence of new absorption at 550 nm in UV-vis and the pink color of the solution reveal the selective interaction toward Cu2+. HL is characterized as a fluorescence resonance energy transfer (FRET) system that remains 'turned OFF' while spirolactam ring exists. In the presence of Cu2+, FRET is 'turned ON' via the opening of spirolactam ring to give emission at 580 nm which is less intense due to the quenching effect of Cu2+ ion. The complexation is reversible and the ensemble of Cu2+.HL selectively recognizes S2- over a series of different anions involving a color change from pink to colorless via the formation of spirolactam ring. The copper complex CuL(SCN) is further employed to understand its efficacy as a therapeutic agent. The complex is cytotoxic to high-risk HPV positive cervical cancer cell lines like SiHa and HeLa and is efficient in the generation and accumulation of reactive oxygen species (ROS). The complex also initiates nuclear blebbing and shows DNA degradation as understood by DNA laddering assay.

Drug Repositioning as a Therapeutic Strategy against Streptococcus pneumoniae: Cell Membrane as Potential Target

A collection of repurposing drugs (Prestwick Chemical Library) containing 1200 compounds was screened to investigate the drugs' antimicrobial effects against planktonic cultures of the respiratory pathogen Streptococcus pneumoniae. After four discrimination rounds, a set of seven compounds was finally selected, namely (i) clofilium tosylate; (ii) vanoxerine; (iii) mitoxantrone dihydrochloride; (iv) amiodarone hydrochloride; (v) tamoxifen citrate; (vi) terfenadine; and (vii) clomiphene citrate (Z, E). These molecules arrested pneumococcal growth in a liquid medium and induced a decrease in bacterial viability between 90.0% and 99.9% at 25 µM concentration, with minimal inhibitory concentrations (MICs) also in the micromolar range. Moreover, all compounds but mitoxantrone caused a remarkable increase in the permeability of the bacterial membrane and share a common, minimal chemical structure consisting of an aliphatic amine linked to a phenyl moiety via a short carbon/oxygen linker. These results open new possibilities to tackle pneumococcal disease through drug repositioning and provide clues for the design of novel membrane-targeted antimicrobials with a related chemical structure.

Novel thiazolidines of potential anti-proliferation properties against esophageal squamous cell carcinoma via ERK pathway

The discovery of a new class of extracellular-signal-regulated kinase (ERK) inhibitors has been achieved via developing novel 2-imino-5-arylidene-thiazolidine analogues. A novel synthetic method employing a solid support-mediated reaction was used to construct the targeted thiazolidines through a cascade reaction with good yields. The chemical and physical stability of the new thiazolidine library has successfully been achieved by blocking the labile C5-position to aerobic oxidation. A cell viability study was performed using esophageal squamous cell carcinoma cell lines (KYSE-30 and KYSE-150) and non-tumorous esophageal epithelial cell lines (HET-1A and NES-G4T) through utilization of an MTT assay, revealing that (Z)-5-((Z)-4-bromobenzylidene)-N-(4-methoxy-2-nitrophenyl)-4,4-dimethylthiazolidin-2-imine (6g) was the best compound among the synthesized library in terms of selectivity. DAPI staining experiments were performed to visualize the morphological changes and to investigate the apoptotic activity. Moreover, western blots were used to probe the mechanism/pathway behind the observed activity/selectivity of thiazolidine 6g which established selective inhibition of phosphorylation in the ERK pathway. Molecular modeling techniques have been utilized to confirm the observed activity. A molecular docking study revealed similar binding interactions between the synthesized thiazolidines and reported co-crystalized inhibitors with ERK proteins. Thus, the present study provides a starting point for the development of interesting bioactive 2-imino-5-arylidene-thiazolidines.

Alternative Targets for Modulators of Mitochondrial Potassium Channels

Mitochondrial potassium channels control potassium influx into the mitochondrial matrix and thus regulate mitochondrial membrane potential, volume, respiration, and synthesis of reactive oxygen species (ROS). It has been found that pharmacological activation of mitochondrial potassium channels during ischemia/reperfusion (I/R) injury activates cytoprotective mechanisms resulting in increased cell survival. In cancer cells, the inhibition of these channels leads to increased cell death. Therefore, mitochondrial potassium channels are intriguing targets for the development of new pharmacological strategies. In most cases, however, the substances that modulate the mitochondrial potassium channels have a few alternative targets in the cell. This may result in unexpected or unwanted effects induced by these compounds. In our review, we briefly present the various classes of mitochondrial potassium (mitoK) channels and describe the chemical compounds that modulate their activity. We also describe examples of the multidirectional activity of the activators and inhibitors of mitochondrial potassium channels.

4,4'-Diisothiocyanatostilbene-2,2'-disulfonate modulates voltage-gated K+ current and influences cell cycle arrest in androgen sensitive and insensitive human prostate cancer cell lines

The stilbene derivative, 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS), an anion channel blocker is used in the present study to evaluate its modulatory effect on voltage-gated K⁺ current (I_K) in human prostate cancer cell lines (LNCaP and PC-3). Voltage-gated K⁺ (K_V) channels in the plasma membrane are critically involved in the proliferation of tumor cells. Therefore, K_V channels are considered as a novel potential target for cancer treatment. The results of the present study show that the external perfusion of DIDS activates I_K in a concentration-dependent manner, although the known K⁺ channel blocker TEA failed to block the DIDS activated I_K in PC-3 cells. Whereas, in LNCaP cells, the higher concentration of DIDS blocked I_K, though this effect was not completely recovered after washout. The difference in function of DIDS might be due to the expression of different Kv channel isoforms in LNCaP and PC-3 cells. Further, the anticancer studies show that treatment of DIDS significantly induced G2/M phase cell cycle arrest and induced moderate and low level of cell death in LNCaP and PC-3 cells respectively. This finding reveals that DIDS modulates I_K and exerts cell cycle arrest and cell death in LNCaP and PC-3 cells.

Silencing of Kv1.5 Gene Inhibits Proliferation and Induces Apoptosis of Osteosarcoma Cells

Kv1.5 (also known as KCNA5) is a protein encoded by the KCNA5 gene, which belongs to the voltage-gated potassium channel, shaker-related subfamily. Recently, a number of studies have suggested that Kv1.5 is overexpressed in numerous cancers and plays crucial roles in cancer development. However, until now, the expression and functions of Kv1.5 in osteosarcoma are still unclear. To characterize the potential biological functions of Kv1.5 in osteosarcoma, herein, we examined the expression levels of Kv1.5 in osteosarcoma cells and tissues using quantitative real-time polymerase chain reaction (qRT-PCR), western blot, and immunohistochemistry assays. Four short hairpin RNAs (shRNAs) targeting Kv1.5 were designed and homologous recombination technology was used to construct pGeneSil-Kv1.5 vectors. In addition, the vectors were transfected into osteosarcoma MG63 cells and Kv1.5 mRNA level was measured by qRT-PCR and the Kv1.5 protein level was examined by western blot. We also examined the effects of Kv1.5 silencing on proliferation, cell cycle and apoptosis of the osteosarcoma cells using CCK-8, colony formation, flow cytometry and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays. Our results showed that Kv1.5 was aberrantly expressed in osteosarcoma and that the synthesized shRNA targeting Kv1.5 reduced Kv1.5 mRNA and protein expression effectively. Silencing Kv1.5 expression in the osteosarcoma cells significantly inhibited the proliferation of osteosarcoma cells, induced cell cycle arrest at G0/G1 phase, and induced cell apoptosis through up-regulation of p21, p27, Bax, Bcl-XL and caspase-3 and down-regulation of cyclins A, cyclins D1, cyclins E, Bcl-2 and Bik. In summary, our results indicate that Kv1.5 silencing could suppress osteosarcoma progression through multiple signaling pathways and suggest that Kv1.5 may be a novel target for osteosarcoma therapeutics.

Synthesis and biological evaluation of aminonaphthols incorporated indole derivatives

An efficient one pot condensation of naphthols (1), 2,5-disubstituted indole-3-carboxaldehydes (2), and secondary amines (3) has been achieved using dichloromethane as a solvent, stirring at room temperature. Some of the new [(disubstituted amino)(5-substituted 2-phenyl-1H-indol-3-yl)methyl]naphthalene-ols (4) derivatives were prepared in good yields. The significant features of this method are simple work-up procedure, inexpensive nontoxic solvent, shorter reaction times, and excellent product yields. The structures of newly synthesized compounds (4a–r) are confirmed by their elemental analysis, FTIR, ¹H and ¹³C NMR, and mass spectral data. These compounds were screened for their in vitro antioxidant, antimicrobial, antitubercular, and anticancer activities. Among the synthesized compounds (4a–r), the compound 4e exhibited highest activity for radical scavenging and ferric ions reducing antioxidant power activities; compounds 4b, 4h, and 4k showed good metal chelating activity. Compounds 4n and 4q showed excellent antimicrobial activities with MIC value 08 µg/mL against tested strains. Compounds 4h, 4k, 4n, and 4q exhibited promising antitubercular activity with MIC value 12.5 µg/mL. Compounds 4k and 4q exhibited 100% cell lysis at concentration 10 µg/mL against MDA-MB-231 (human adenocarcinoma mammary gland) cell lines.

The voltage-dependent K(+) channels Kv1.3 and Kv1.5 in human cancer

Voltage-dependent K⁺ channels (Kv) are involved in a number of physiological processes, including immunomodulation, cell volume regulation, apoptosis as well as differentiation. Some Kv channels participate in the proliferation and migration of normal and tumor cells, contributing to metastasis. Altered expression of Kv1.3 and Kv1.5 channels has been found in several types of tumors and cancer cells. In general, while the expression of Kv1.3 apparently exhibits no clear pattern, Kv1.5 is induced in many of the analyzed metastatic tissues. Interestingly, evidence indicates that Kv1.5 channel shows inversed correlation with malignancy in some gliomas and non-Hodgkin's lymphomas. However, Kv1.3 and Kv1.5 are similarly remodeled in some cancers. For instance, expression of Kv1.3 and Kv1.5 correlates with a certain grade of tumorigenicity in muscle sarcomas. Differential remodeling of Kv1.3 and Kv1.5 expression in human cancers may indicate their role in tumor growth and their importance as potential tumor markers. However, despite of this increasing body of information, which considers Kv1.3 and Kv1.5 as emerging tumoral markers, further research must be performed to reach any conclusion. In this review, we summarize what it has been lately documented about Kv1.3 and Kv1.5 channels in human cancer.

Thiamine deficiency in vitro accelerates A-type potassium current inactivation in cerebellar granule neurons

Thiamine deficiency during embryonic or early postnatal development causes deficits in cerebellum-dependent activities including motor control and procedural memory. Here, we give a detailed description of the changes to A-type current in cultured cerebellar granule neurons exposed to thiamine deficiency in vitro. A-type current in treated neurons was reduced to 51% of that in controls. The remaining A-type current in treated neurons exhibited normal activation kinetics and voltage dependence whereas inactivation was markedly faster. These effects were selective because the delayed-rectifier potassium current density and kinetics were unchanged in thiamine-deficient neurons. A computational model of the cerebellar granule neuron was used to test the impact of these alterations and predicts an increase in excitability that is especially pronounced for synaptic activation. Our results suggest that the loss of A-type potassium conductance leads to hyperactivity in cerebellar granule neurons and may contribute to cell death observed in the granule layer of cerebellum during thiamine-deficiency in vivo.

Chromene induces apoptosis via caspase-3 activation in human leukemia HL-60 cells

In this study, the potent anti-tumor effects of brown algae on human leukemia HL-60 cells were investigated. The Sargassum siliquastrum extract among the 14 species of brown algae exhibited profound growth inhibitory effect on HL-60 cells in the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, therefore, S. siliquastrum was selected for use in further experiments. The highest inhibitory activity of S. siliquastrum on HL-60 cells was detected in the chloroform fraction, and the active compound was identified as a kind of chromene, sargachromanol E (SE). SE treatment showed significant growth inhibitory effects on HL-60 cells in a dose-dependent manner by inducing apoptosis, as evidenced by the formation of apoptotic bodies, fragmented DNA ladder, and the accumulation of DNA in the sub-G(1) phase of cell cycle. SE induced apoptosis was accompanied by downregulation of Bcl-xL, upregulation of Bax, activation of caspase-3, and cleavage of poly (ADP-ribose) polymerase (PARP). Moreover, z-DEVD-fmk, a caspase-3 inhibitor, significantly inhibited cell cytotoxicity, apoptotic characteristics such as apoptotic bodies, sub-G(1) DNA content, and cleavage of PARP induced by SE. These results suggest that SE exerts its growth inhibitory effects on HL-60 cells through caspase-3-mediated induction of apoptosis. Therefore, SE offers promising chemotherapeuric potential to prevent cancers such as human leukemia.

The role of Eag and HERG channels in cell proliferation and apoptotic cell death in SK-OV-3 ovarian cancer cell line

BACKGROUND

The voltage gated potassium (K+) channels Eag and HERG have been implicated in the pathogenesis of various cancers, through association with cell cycle changes and programmed cell death. The role of these channels in the onset and progression of ovarian cancer is unknown. An understanding of mechanism by which Eag and HERG channels affect cell proliferation in ovarian cancer cells is required and therefore we investigated their role in cell proliferation and their effect on the cell cycle and apoptosis of ovarian cancer cells.

METHODS

The presence of Eag and HERG was determined in SK-OV-3 cells using immunofluorescence and western blotting. The effect of the Eag blockers (imipramine and clofilium) and HERG blockers (E-4031 and ergtoxin) on cell proliferation was assessed using the MTS assay with further investigation of their role in the cell cycle and apoptosis determined by flow cytometry.

RESULTS

Eag and HERG channels were present in the cytoplasm and nuclei of SK-OV-3 cells. There was significant inhibition of proliferation of SK-OV-3 cells by imipramine (P < 0.001) and ergtoxin (P < 0.05) at 72 hours of culture. Incubation of cells with ergtoxin led to the accumulation of cells in the S and G2/M phase, while cells accumulated in S phase after incubation with E-4031, with no effect on apoptosis. Imipramine did not affect the cell cycle but increased the proportion of SK-OV-3 cells undergoing early apoptosis.

CONCLUSION

Both Eag and HERG channels are expressed in SK-OV-3 ovarian cancer cells and have a role in cell proliferation. HERG channels affect the cell cycle while Eag channels are implicated in the inhibition of apoptosis of ovarian cancer cells. The family of Eag channels may represent a new therapeutic target for the treatment of ovarian cancer.

Effect of heat and pH denaturation on the structure and conformation of recombinant human hepatic stimulator substance

Hepatic stimulator substance (HSS) is a novel liver-specific growth-promoting factor. Although HSS has been successfully crystallized, several properties of this protein have yet to be determined. This study shows that recombinant human HSS (rhHSS) is a dimer with a molecular mass of 31 kDa, the protein is weakly acidic and has an isoelectric point (pI) of 4.50. RhHSS was able to protect hepatoma cells from H2O2-induced apoptosis and to stimulate cell growth. The recombinant protein was thermostable up to 80 degrees C and resistant to changes in pH, as determined by synchronous fluorescence and far-UV circular dichroism (CD). Within the range of pH 4.0-10.0, rhHSS assumed a folded conformation identical to the secondary structure of the original, native protein and a native-like far-UV CD spectrum. Denatured rhHSS could be partly reconstituted with respect to its structure, but not its activity. Thus, rhHSS is a structurally stable protein insensitive to thermal and acid-alkaline denaturation.

Hypertonicity induced apoptosis in HL-60 cells in the presence of intracellular potassium

Cell shrinkage is a hallmark of apoptosis. Potassium efflux, which is involved in cell shrinkage, has been previously described as an essential event of apoptosis. This study was designed to address the importance of potassium efflux in hypertonicity (450 mOsm and 600 mOsm) induced apoptosis. We initiated apoptosis in HL-60 cells in hypertonic medium consisting of either high concentrations of NaCl, mannitol or KCl. Apoptotic activity was evaluated based on the DNA content of the cells, annexin-V staining and calcium content. Apoptosis was initiated in hypertonic conditions consisting of high intracellular K(+). We demonstrate that apoptosis can occur in the presence of high intracellular potassium contrary to previous predictions.

The antitumor effect of LJ-529, a novel agonist to A3 adenosine receptor, in both estrogen receptor-positive and estrogen receptor-negative human breast cancers

Agonists to A3 adenosine receptor (A3AR) have been reported to inhibit cell growth and/or induce apoptosis in various tumors. We tested the effect of a novel A3AR agonist generically known as LJ-529 in breast cancer cells. Anchorage-dependent cell growth and in vivo tumor growth were attenuated by LJ-529, independently of its estrogen receptor (ER) alpha status. In addition, apoptosis was induced as evidenced by the activation of caspase-3 and c-poly(ADP)ribose polymerase. Furthermore, the Wnt signaling pathway was down-regulated and p27(kip) was induced by LJ-529. In ER-positive cells, the expression of ER was down-regulated by LJ-529, which might have additionally contributed to attenuated cell proliferation. In ER-negative, c-ErbB2-overexpressing SK-BR-3 cells, the expression of c-ErbB2 and its downstream extracellular signal-regulated kinase pathway were down-regulated by LJ-529. However, such effect of LJ-529 acted independently of its receptor because no A3AR was detected by reverse transcription-PCR in all four cell lines tested. In conclusion, our novel findings open the possibility of LJ-529 as an effective therapeutic agent against both ER-positive and ER-negative breast cancers, particularly against the more aggressive ER-negative, c-ErbB2-overexpressing types.

Effects of Antiarrhythmic Drugs on Apoptotic Pathways in H9c2 Cardiac Cells

Antiarrhythmic drugs may induce cellular apoptosis in the heart. By using representatives of 5 different categories of antiarrhythmic drugs, that is, pilsicainide, propranolol, nifekalant, verapamil, and amiodarone, we investigated whether these ion channel blockers or beta-antagonists affect cardiac apoptosis in cell cultures. Cultured H9c2 cells were treated with the drugs at varying concentrations. To determine the degree of apoptosis, the percentage of hypodiploid cells, mitochondrial transmembrane potential (DeltaPsi(m)), and activities of caspases were measured quantitatively. At 24 h after administration, only amiodarone induced apoptosis in the H9c2 cells. Amiodarone at a concentration of 14.8 microM or higher decreased DeltaPsi(m) and activated caspase-2 within 3 h of administration, and it caused the appearance of hypodiploid cells and activation of caspases-3 and -9 at 6 h or later. Thus, amiodarone, but none of the other antiarrhythmic drugs tested, possesses a pro-apoptotic effect, mainly via the mitochondrial pathway, suggesting that this effect is distinct from the blocking action of Na+, K+, and Ca2+ channels or the beta-adrenergic receptor. Furthermore, induction of apoptosis in a dose-dependent manner by amiodarone indicates the importance of monitoring the serum concentration in order to avoid its adverse effects.

HERG K+ channel expression-related chemosensitivity in cancer cells and its modulation by erythromycin

PURPOSE

Previous studies have found that the HERG K+ channel is highly expressed in some cancers. In the study reported here, we investigated HERG expression in various cancer cell lines, its correlation with chemosensitivity to vincristine, paclitaxel, and hydroxy-camptothecin, and its biochemical modulation.

METHODS

The MTT assay and clonogenic assay were used to detect the cytotoxicity of anticancer drugs in vitro. HERG expression was analyzed by Western blotting or immunocytochemistry. Gene transfection was used to examine the changes in HERG-related chemosensitivity. Cell cycle phase distribution was detected by flow cytometry and drug combinations were evaluated by the MTT assay.

RESULTS

HERG expression levels differed widely between various human cancer cell lines and HT-29 cells expressing high levels of HERG were more sensitive than A549 cells expressing low levels of HERG to vincristine, paclitaxel, and hydroxy-camptothecin. In terms of IC50, the chemosensitivities of herg-transfected A549 cells to vincristine, paclitaxel and hydroxy-camptothecin were significantly increased. However, for cisplatin and 5-fluorouracil, no significant difference between herg-transfected A549 cells and parent A549 cells was detected. Erythromycin, a HERG K+ channel blocker, suppressed the growth of various cancer cells and the potency was correlated with HERG expression levels. Combinations of erythromycin and vincristine, paclitaxel or hydroxy-camptothecin showed synergy in cytotoxicity to HT-29 cells. Erythromycin also enhanced the G2/M arrest induced by vincristine in HT-29 cells. There were synergistic effects between erythromycin and vincristine, paclitaxel, and hydroxy-camptothecin, and chemosensitivity was correlated with HERG expression level.

CONCLUSIONS

HERG expression levels and chemosensitivity were positively correlated for vincristine, paclitaxel, and hydroxy-camptothecin. Erythromycin was active as a modulator. These results suggest that HERG may serve as a molecular marker and modulating target for individualized cancer therapy.

Inhibitory Effects of Clofilium on Membrane Currents Associated with Ca2+ Channels, NMDA Receptor Channels and Na+, K+-ATPase in Cortical Neurons

The class III antiarrhythmic agent 4-chloro-N,N-diethyl-N-heptyl-benzene butanaminium (clofilium) is known as a K+ channel open-channel blocker and has either anti- or proapoptotic property due to undefined mechanisms. Based on the evidence that neuronal viability is largely, sometimes critically, affected by voltage- and ligand-gated Ca2+ channels and the Na+, K+-ATPase, we tested the hypothesis that clofilium might additionally act on Ca2+ permeable ion channels and the Na+, K+-ATPase. Membrane currents associated with activities of voltage-gated Ca2+ channels, N-methyl-D-aspartate (NMDA) receptor channels and Na+, K+-ATPase were recorded using whole-cell recordings in cultured murine cortical neurons. Clofilium (0.1-100 micromol/l) inhibited high voltage-activated Ca2+ currents in concentration- and use-dependent manners. Clofilium acted as a potent antagonist of NMDA receptor channels, preferably blocked the NMDA steady-state current at a low concentration (0.1 micromol/l). At concentrations of >100 micromol/l, clofilium blocked both peak and steady-state NMDA currents in a voltage-independent manner. Clofilium also inhibited the Na+, K+-ATPase current with an IC50 of 7.5 micromol/l. Our data suggest that the pharmacological action of clofilium is far more complex than recognized before; the multiple actions of clofilium on membrane conductance may explain its diverse effects on cellular events and cell viability.

Involvement of mitochondrial K+ release and cellular efflux in ischemic and apoptotic neuronal death

We measured and manipulated intracellular potassium (K+) fluxes in cultured hippocampal neurons in an effort to understand the involvement of K+ in neuronal death under conditions of ischemia and exposure to apoptotic stimuli. Measurements of the intracellular K+ concentration using the fluorescent probe 1,3-benzenedicarboxylic acid, 4,4'-[1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diylbis(5-methoxy-6,2-benzofurandiyl)]bis-, tetrakis [(acetyloxy) methyl] ester (PBFI) revealed that exposure of neurons to cyanide (chemical hypoxia), glutamate (excitotoxic insult) or staurosporine (apoptotic stimulus) results in efflux of K+ and cell death. Treatment of neurons with 5-hydroxydecanoate (5HD), an inhibitor of mitochondrial K+ channels, reduced K+ fluxes in neurons exposed to each insult and increased the resistance of the cells to death. K+ efflux was attenuated, levels of oxyradicals were decreased, mitochondrial membrane potential was stabilized and release of cytochrome c from mitochondria was attenuated in neurons treated with 5HD. K+ was rapidly released into the cytosol from mitochondria when neurons were exposed to the K+ channel opener, diazoxide, or to the mitochondrial uncoupler, carbonyl cyanide 4(trifluoromethoxy)phenylhydrazone (FCCP), demonstrating that the intramitochondrial K+ concentration is greater than the cytosolic K+ concentration. The release of K+ from mitochondria was followed by efflux through plasma membrane K+ channels. In vivo studies showed that 5HD reduces ischemic brain damage without affecting cerebral blood flow in a mouse model of focal ischemic stroke. These findings suggest that intracellular K+ fluxes play a key role in modulating neuronal oxyradical production and cell survival under ischemic conditions, and that agents that modify K+ fluxes may have therapeutic benefit in stroke and related neurodegenerative conditions.

Regulation and critical role of potassium homeostasis in apoptosis

Programmed cell death or apoptosis is broadly responsible for the normal homeostatic removal of cells and has been increasingly implicated in mediating pathological cell loss in many disease states. As the molecular mechanisms of apoptosis have been extensively investigated a critical role for ionic homeostasis in apoptosis has been recently endorsed. In contrast to the ionic mechanism of necrosis that involves Ca(2+) influx and intracellular Ca(2+) accumulation, compelling evidence now indicates that excessive K(+) efflux and intracellular K(+) depletion are key early steps in apoptosis. Physiological concentration of intracellular K(+) acts as a repressor of apoptotic effectors. A huge loss of cellular K(+), likely a common event in apoptosis of many cell types, may serve as a disaster signal allowing the execution of the suicide program by activating key events in the apoptotic cascade including caspase cleavage, cytochrome c release, and endonuclease activation. The pro-apoptotic disruption of K(+) homeostasis can be mediated by over-activated K(+) channels or ionotropic glutamate receptor channels, and most likely, accompanied by reduced K(+) uptake due to dysfunction of Na(+), K(+)-ATPase. Recent studies indicate that, in addition to the K(+) channels in the plasma membrane, mitochondrial K(+) channels and K(+) homeostasis also play important roles in apoptosis. Investigations on the K(+) regulation of apoptosis have provided a more comprehensive understanding of the apoptotic mechanism and may afford novel therapeutic strategies for apoptosis-related diseases.

Potassium channel blockers attenuate hypoxia- and ischemia-induced neuronal death in vitro and in vivo

BACKGROUND AND PURPOSE

In light of recent evidence suggesting that an upregulation of K+ efflux mediated by outward delayed rectifier (I(K)) channels promotes central neuronal apoptosis, we sought to test the possibility that blockers of I(K) channels might be neuroprotective against hypoxia/ischemia-induced neuronal death.

METHODS

Membrane currents were recorded with the use of patch clamp recordings in cultured murine cortical neurons. Protective effects of K+ channel blockers were examined in rats subjected to transient middle cerebral artery occlusion followed by 14-day reperfusion.

RESULTS

The K+ channel blocker tetraethylammonium (TEA) (5 mmol/L) selectively blocked I(K) without affecting N-methyl-D-aspartate receptor-mediated current or voltage-gated Ca2+ currents. Both TEA and a lipophilic K+ channel blocker, clofilium, attenuated neuronal apoptosis induced by hypoxia in vitro and infarct volume induced by ischemia in vivo.

CONCLUSIONS

These data are consistent with the idea that K+ channel-mediated K+ efflux may contribute to ischemia-triggered apoptosis and suggest that preventing excessive K+ efflux through K+ channels may constitute a therapeutic approach for the treatment of stroke.

Potassium channel antagonists influence porcine granulosa cell proliferation, differentiation, and apoptosis

This investigation determined the effects of K(+) channel antagonists on proliferation, differentiation, and apoptosis of porcine granulosa cells. The drugs screened for functional effects included the class III antiarrhythmic agents MK-499 and clofilium, the chromanol I(Ks) antagonist 293B, the benzodiazepine I(Ks) antagonists L-735,821 and L-768,673, and the peptidyl toxins charybdotoxin (CTX) and margatoxin (MTX). Granulosa cell proliferation and differentiation were assessed by serial measurements of cell number and progesterone accumulation in the culture media, respectively. Granulosa cell apoptosis was evaluated using flow cytometry. Additional information about drug effects was obtained by immunoblotting to detect expression of proliferating cell nuclear antigen, p27(kip1) and the caspase-3 substrate poly(ADP-ribose) polymerase. The ERG channel antagonist MK-499 had no functional effects on cultured granulosa cells. However, the broad spectrum K(+) channel antagonist clofilium decreased, in a concentration-dependent fashion, the number of viable granulosa cells cultured, and these effects were associated with induction of apoptosis. All three I(Ks) antagonists (293B, L-735,821, and L-768,673) increased basal, but not FSH-enhanced progesterone accumulation on Day 1 after treatment without affecting the number of viable cells in culture, an effect that was blocked by pimozide. In contrast, CTX and MTX increased the number of viable cells in FSH-stimulated cultures on Day 3 after treatment without affecting progesterone output per cell. These data demonstrate that selective antagonism of granulosa cell K(+) channels with distinct molecular correlates, electrophysiological properties, and expression patterns can influence differential granulosa cell proliferation, steroidogenic capability, and apoptosis. Thus, K(+) channels may represent pharmacological targets for affecting Granulosa cell function and oocyte maturation, in vivo or in vitro.

Ethyl acetate extract of the stem bark of Cudrania tricuspidata induces apoptosis in human leukemia HL-60 cells

Apoptosis is now widely accepted as playing a role in tumorigenesis. An effective compound which can kill tumors via apoptotic pathway appears to be a relevant strategy to suppress various human tumors. The ethyl acetate extract from the stem bark of Cudrania tricuspidata (EACT) showed dose- and time-dependent cytotoxic effects on human leukemia HL-60 cells. DNA fragmentation and morphological changes, accompanied by condensed and fragmented nuclei, were observed in the cells cultured for 6 hr with EACT. These results suggest that the cytotoxicity of the crude extract from Cudrania tricuspidata against HL-60 cells is due to apoptosis.

Ion homeostasis and apoptosis

Alterations in the transmembrane gradients of several physiological ions may influence programmed cell death. In particular, recent data suggest that increases in intracellular calcium may either promote or inhibit apoptosis, depending on the level, timing and location, whereas loss of intracellular potassium promotes apoptosis.

Prodrugs of butyric acid. Novel derivatives possessing increased aqueous solubility and potential for treating cancer and blood diseases

The synthesis and biological activities of acidic, basic and neutral types of butyric acid (BA) prodrugs possessing increased aqueous solubility are described. The compounds are butyroyloxyalkyl derivatives of carboxylic acids, which possess functionalities suitable for aqueous solubilization. The anticancer activity of the prodrugs in vitro was evaluated by examining their effect on the growth of human colon, breast and pancreatic carcinoma cell lines, and their solubility in aqueous media was determined. The most promising compounds, with respect to activity and solubility, were found to be the butyroyloxymethyl esters of glutaric 2a and nicotinic acids 4a and phosphoric acid as its diethyl ester 10a, which displayed IC(50) values of 100 microM or lower. These prodrugs are expected to release formaldehyde upon metabolic hydrolysis. The corresponding butyroyloxyethyl esters (2b, 4b and 10b) that release acetaldehyde upon metabolism were significantly less potent. A similar correlation was observed for growth inhibition of the human prostate carcinoma cell lines PC-3 and LnCap and for induction of differentiation and apoptosis in the human myeloid leukemia cell line HL-60. The higher biological activity of the formaldehyde-releasing prodrugs 2a and 10a was further confirmed when induction of hemoglobin (Hb) synthesis in the human erythroleukemic cell line K562 was measured. Moreover, a therapeutic index (IC(50)/ED(50)) of ca. 5 was observed. The acute i.p. toxicity LD(50) in mice for 2a, 2b, 10a and 10b was similar and in the range of 400-600 mg kg(-1). The results obtained support the potential use of the butyric acid prodrugs for the treatment of neoplastic diseases and beta-globin disorders.