Subsets of ATP-sensitive potassium channel (KATP) inhibitors increase gap junctional intercellular communication in metastatic cancer cell lines independent of SUR expression

Anti-invasive effects of minoxidil on human breast cancer cells: combination with ranolazine

A plethora of ion channels have been shown to be involved systemically in the pathophysiology of cancer and ion channel blockers can produce anti-metastatic effects. However, although ion channels are known to frequently function in concerted action, little is known about possible combined effects of ion channel modulators on metastatic cell behaviour. Here, we investigated functional consequences of pharmacologically modulating ATP-gated potassium (K_ATP) channel and voltage-gated sodium channel (VGSC) activities individually and in combination. Two triple-negative human breast cancer cell lines were used: MDA-MB-231 and MDA-MB-468, the latter mainly for comparison. Most experiments were carried out on hypoxic cells. Electrophysiological effects were studied by whole-cell patch clamp recording. Minoxidil (a K_ATP channel opener) and ranolazine (a blocker of the VGSC persistent current) had no effect on cell viability and proliferation, alone or in combination. In contrast, invasion was significantly reduced in a dose-dependent manner by clinical concentrations of minoxidil and ranolazine. Combining the two drugs produced significant additive effects at concentrations as low as 0.625 μM ranolazine and 2.5 μM minoxidil. Electrophysiologically, acute application of minoxidil shifted VGSC steady-state inactivation to more hyperpolarised potentials and slowed recovery from inactivation, consistent with inhibition of VGSC activation. We concluded (i) that clinically relevant doses of minoxidil and ranolazine individually could inhibit cellular invasiveness dose dependently and (ii) that their combination was additionally effective. Accordingly, ranolazine, minoxidil and their combination may be repurposed as novel anti-metastatic agents.

Ion-Switchable Quantum Dot Förster Resonance Energy Transfer Rates in Ratiometric Potassium Sensors

The tools for optically imaging cellular potassium concentrations in real-time are currently limited to a small set of molecular indicator dyes. Quantum dot-based nanosensors are more photostable and tunable than organic indicators, but previous designs have fallen short in size, sensitivity, and selectivity. Here, we introduce a small, sensitive, and selective nanosensor for potassium measurements. A dynamic quencher modulates the fluorescence emitted by two different quantum dot species to produce a ratiometric signal. We characterized the potassium-modulated sensor properties and investigated the photonic interactions within the sensors. The quencher's protonation changes in response to potassium, which modulates its Förster radiative energy transfer rate and the corresponding interaction radii with each quantum dot species. The nanosensors respond to changes in potassium concentrations typical of the cellular environment and thus provide a promising tool for imaging potassium fluxes during biological events.

Cyclooxygenase inhibitor induces the upregulation of connexin-43 expression in C6 glioma cells

The present study was performed to determine whether aspirin, a cyclooxygenase (COX) inhibitor, has an effect on the expression of connexin 43 (Cx43) in C6 glioma cells. Using an in vitro glioma invasion model, the expression of Cx43 protein in C6 cells was significantly increased following aspirin treatment at a dose of 8 mmol/l for 30, 60 and 120 min via western blot analysis. The peak value of the Cx43 expression was observed in C6 cells after 120 min of aspirin treatment, which was significantly reduced by prostaglandin E2 (PGE2). In addition, aspirin also significantly increased the gap junction intercellular communication (GJIC) activity and reduced glioma invasion, which was induced by PGE2. This led to the conclusion that the aspirin-induced glioma invasion decrease may be associated with the increased expression of Cx43 protein and formation of GJIC.

Ocular Hypotensive Effects of the ATP-Sensitive Potassium Channel Opener Cromakalim in Human and Murine Experimental Model Systems

Elevated intraocular pressure (IOP) is the most prevalent and only treatable risk factor for glaucoma, a leading cause of irreversible blindness worldwide. Unfortunately, all current therapeutics used to treat elevated IOP and glaucoma have significant and sometimes irreversible side effects necessitating the development of novel compounds. We evaluated the IOP lowering ability of the broad spectrum KATP channel opener cromakalim. Cultured human anterior segments when treated with 2 μM cromakalim showed a decrease in pressure (19.33 ± 2.78 mmHg at 0 hours to 13.22 ± 2.64 mmHg at 24 hours; p<0.001) when compared to vehicle treated controls (15.89 ± 5.33 mmHg at 0 h to 15.56 ± 4.88 mmHg at 24 hours; p = 0.89). In wild-type C57BL/6 mice, cromakalim reduced IOP by 18.75 ± 2.22% compared to vehicle treated contralateral eyes (17.01 ± 0.32 mmHg at 0 hours to 13.82 ± 0.37 mmHg at 24 hours; n = 10, p = 0.002). Cromakalim demonstrated an additive effect when used in conjunction with latanoprost free acid, a common ocular hypotensive drug prescribed to patients with elevated IOP. To examine KATP channel subunit specificity, Kir6.2(-/-) mice were treated with cromakalim, but unlike wild-type animals, no change in IOP was noted. Histologic analysis of treated and control eyes in cultured human anterior segments and in mice showed similar cell numbers and extracellular matrix integrity within the trabecular meshwork, with no disruptions in the inner and outer walls of Schlemm's canal. Together, these studies suggest that cromakalim is a potent ocular hypotensive agent that lowers IOP via activation of Kir6.2 containing KATP channels, its effect is additive when used in combination with the commonly used glaucoma drug latanoprost, and is not toxic to cells and tissues of the aqueous humor outflow pathway, making it a candidate for future therapeutic development.

Curcumin inhibits proliferation of gastric cancer cells by impairing ATP-sensitive potassium channel opening

BACKGROUND

This study was aimed to investigate whether ATP-sensitive potassium channel (KATP) is involved in curcumin's anti-proliferative effects against gastric cancer.

METHODS

In an in vitro study, gastric cancer cell line SGC-7901 was treated with curcumin at serial concentrations and co-administrated with the KATP opener, diazoxide. The effect of curcumin and diazoxide on proliferation were assessed by MTT assay. Mitochondrial membrane potential (MMP) was studied by flow cytometry detection of rhodamine 123 staining. Apoptosis was evaluated by flow cytometry detection of Annexin V propidium iodide double staining. In an in vivo study, SGC-7901 cells were planted into nude mice as xenografts. Animals were treated with curcumin co-administered with diazoxide. Tumor volume and tumor weight were observed.

RESULTS

Curcumin incubation significantly induced loss of MMP in SGC-7901 cells in a dose- dependent manner (P < 0.05); the cell apoptotic rate also dramatically increased after curcumin incubation in a dose-dependent manner (P < 0.05). After co-administration with diazoxide, however, we found that both the MMP-loss-inducing and the apoptosis-inducing effects of curcumin in SGC-7901 cells were significantly impaired (all P < 0.05). As a result, the proliferation of SGC-7901 cells was maintained by diazoxide treatment.

CONCLUSIONS

Impaired mitoKATP opening causes MMP loss, and is involved in curcumin-induced apoptosis in gastric cancer.

Glibenclamide inhibits cell growth by inducing G0/G1 arrest in the human breast cancer cell line MDA-MB-231

BACKGROUND

Glibenclamide (Gli) binds to the sulphonylurea receptor (SUR) that is a regulatory subunit of ATP-sensitive potassium channels (KATP channels). Binding of Gli to SUR produces the closure of KATP channels and the inhibition of their activity. This drug is widely used for treatment of type 2-diabetes and it has been signaled as antiproliferative in several tumor cell lines. In previous experiments we demonstrated the antitumoral effect of Gli in mammary tumors induced in rats. The aim of the present work was to investigate the effect of Gli on MDA-MB-231 breast cancer cell proliferation and to examine the possible pathways involved in this action.

RESULTS

The mRNA expression of the different subunits that compose the KATP channels was evaluated in MDA-MB-231 cells by reverse transcriptase-polymerase chain reaction. Results showed the expression of mRNA for both pore-forming isoforms Kir6.1 and Kir6.2 and for the regulatory isoform SUR2B in this cell line. Gli inhibited cell proliferation assessed by a clonogenic method in a dose dependent manner, with an increment in the population doubling time. The KATP channel opener minoxidil increased clonogenic proliferation, effect that was counteracted by Gli. When cell cycle analysis was performed by flow cytometry, Gli induced a significant cell-cycle arrest in G0/G1 phase, together with an up-regulation of p27 levels and a diminution in cyclin E expression, both evaluated by immunoblot. However, neither differentiation evaluated by neutral lipid accumulation nor apoptosis assessed by different methodologies were detected. The cytostatic, non toxic effect on cell proliferation was confirmed by removal of the drug.Combination treatment of Gli with tamoxifen or doxorubicin showed an increment in the antiproliferative effect only for doxorubicin.

CONCLUSIONS

Our data clearly demonstrated a cytostatic effect of Gli in MDA-MB-231 cells that may be mediated through KATP channels, associated to the inhibition of the G1-S phase progression. In addition, an interesting observation about the effect of the combination of Gli with doxorubicin leads to future research for a potential novel role for Gli as an adjuvant in breast cancer treatment.

Treatment with baicalin up-regulates the expression of connexion 26 and connexion 43 in human hepatocellular carcinoma cell line SMMC-7721

AIM: To investigate the effect of treatment with baicalin on the expression of connexion 26 (Cx26) and connexion 43 (Cx43) in human hepatocellular cell line SMMC-7721.

METHODS: SMMC-7721 cells were randomly divided into 4 groups: normal control group, low-dose (10 mg/L) baicalin group, medium-dose (20 mg/L) baicalin group, and high-dose (40 mg/L) baicalin group. Gap junction intercellular communication (GJIC) was measured by scrap loading/dye transfer assay (SL/DT). The expression of Cx26 and Cx43 mRNAs in SMMC-7721 cells was determined by RT-PCR. The expression of Cx26 protein was detected by Western blot, and that of Cx43 protein was detected by immunohistochemistry.

RESULTS: Compared to the normal control group, the expression of Cx26 mRNA and protein was significantly enhanced in SMMC-7721 cells treated with low, medium and high concentrations of baicalin (mRNA: 0.148 ± 0.111, 10.253 ± 0.222, 17.283 ± 0.024 vs 0.138 ± 0.111; all P < 0.05; protein: 0.516 ± 0.029, 0.759 ± 0.020, 1.019 ± 0.076 vs 0.367 ± 0.029; all P < 0.05). Compared to the normal control group, the expression of Cx43 mRNA showed no significant changes, but the expression of Cx43 protein was significantly enhanced in SMMC-7721 cells treated with different concentrations of baicalin.

CONCLUSION: Restoration or enhancement of GJIC induced by up-regulation of Cx26 and Cx43 is likely to be an important molecular mechanism by which baicalin inhibits tumor growth.