Electrolyte imbalance causes suppression of NK and T cell effector function in malignant ascites

BACKGROUND

Malignant ascites commonly occurs in advanced or recurrent stages of epithelial ovarian cancer during peritoneal carcinomatosis and is correlated with poor prognosis. Due to its complex composition of cellular and acellular components malignant ascites creates a unique tumor microenvironment, which mediates immunosuppression and promotes progression of disease. However, the immunosuppressive mechanisms remain poorly understood.

METHODS

In the present study, we explored the antitumor activity of healthy donor NK and T cells directed against ovarian cancer cells in presence of malignant ascites derived from patients with advanced or recurrent peritoneal carcinomatosis. A wide range of methods was used to study the effect of ascites on NK and T cells (FACS, ELISA, EliSpot, qPCR, Live-cell and confocal microscopy, Western blot and electrolyte flux assays). The ascites components were assessed using quantitative analysis (nephelometry, potentiometry and clinical chemistry) and separation methods (dialysis, ultracentrifugal filtration and lipid depletion).

RESULTS

Ascites rapidly inhibited NK cell degranulation, tumor lysis, cytokine secretion and calcium signaling. Similarly, target independent NK and T cell activation was impaired in ascites environment. We identified imbalanced electrolytes in ascites as crucial factors causing extensive immunosuppression of NK and T cells. Specifically, high sodium, low chloride and low potassium content significantly suppressed NK-mediated cytotoxicity. Electrolyte imbalance led to changes in transcription and protein expression of electrolyte channels and impaired NK and T cell activation. Selected inhibitors of sodium electrolyte channels restored intracellular calcium flux, conjugation, degranulation and transcript expression of signaling molecules. The levels of ascites-mediated immunosuppression and sodium/chloride/potassium imbalance correlated with poor patient outcome and selected molecular alterations were confirmed in immune cells from ovarian cancer patients.

CONCLUSION

Our data suggest a novel electrolyte-based mechanism of immunosuppression in malignant ascites of patients with peritoneal carcinomatosis. We show for the first time that the immunosuppression of NK cytotoxicity in coculture assays is correlated to patient poor survival. Therapeutic application of sodium channel inhibitors may provide new means for restoring immune cell activity in ascites or similar electrolyte imbalanced environments.

Chemical and pharmacological characterization of the TRPML calcium channel blockers ML-SI1 and ML-SI3

The members of the TRPML subfamily of non-selective cation channels (TRPML1-3) are involved in the regulation of important lysosomal and endosomal functions, and mutations in TRPML1 are associated with the neurodegenerative lysosomal storage disorder mucolipidosis type IV. For in-depth investigation of functions and (patho)physiological roles of TRPMLs, membrane-permeable chemical tools are urgently needed. But hitherto only two TRPML inhibitors, ML-SI1 and ML-SI3, have been published, albeit without clear information about stereochemical details. In this investigation we developed total syntheses of both inhibitors. ML-SI1 was only obtained as a racemic mixture of inseparable diastereomers and showed activator-dependent inhibitory activity. The more promising tool is ML-SI3, hence ML-SI1 was not further investigated. For ML-SI3 we confirmed by stereoselective synthesis that the trans-isomer is significantly more active than the cis-isomer. Separation of the enantiomers of trans-ML-SI3 further revealed that the (-)-isomer is a potent inhibitor of TRPML1 and TRPML2 (IC₅₀ values 1.6 and 2.3 μM) and a weak inhibitor (IC₅₀ 12.5 μM) of TRPML3, whereas the (+)-enantiomer is an inhibitor on TRPML1 (IC₅₀ 5.9 μM), but an activator on TRPML 2 and 3. This renders the pure (-)-trans-ML-SI3 more suitable as a chemical tool for the investigation of TRPML1 and 2 than the racemate. The analysis of 12 analogues of ML-SI3 gave first insights into structure-activity relationships in this chemotype, and showed that a broad variety of modifications in both the N-arylpiperazine and the sulfonamide moiety is tolerated. An aromatic analogue of ML-SI3 showed an interesting alternative selectivity profile (strong inhibitor of TRPML1 and strong activator of TRPML2).

Effect of Crude Venom of Odonthobuthus doriae Scorpion in Cell Culture using Ion Channel Modulators

Scorpion venom toxicity is one of the major medical concerns from old years, due to its influence on human activities and health. From many years ago a lot of researches established to examine different aspects of venom toxicity and its effects on different organs. During these years researchers are doing more specific studies on the cytotoxicity of scorpion venom. In Iran, Odonthobuthus doriae, the yellow scorpion is one of the major threats based on its neuro toxicity and severe pathophysiologic effects and researchers tried to find the mechanism of these neuro toxic effects. The previous studies have shown that in isolated organs the yellow scorpion venom is affecting the ion channels. Also some studies showed that this venom has severe cytotoxic effects on the cell lines with many ion channels like nerve cell lines. In this study, the cytotoxic effect of the crude venom of O.doriae on the 1321N1 cell line (cancerous nerve cells) was studied. Primary cell cultured investigated in the presence of different ion channel blockers: Ouabain (1mmol as Na channel blocker), Nifedipin (100 µmol as Ca channel blocker), and TEA (40 mmol as K channel blocker) by MTT method. The result showed that the O.doriae crude venom has cytotoxic effect via Na channels.

Isolation of proflavine as a blocker of G protein-gated inward rectifier potassium channels by a cell growth-based screening system

The overexpression of Kir3.2, a subunit of the G protein-gated inwardly rectifying K(+) channel, is implicated in some of the neurological phenotypes of Down syndrome (DS). Chemical compounds that block Kir3.2 are expected to improve the symptoms of DS. The purpose of this study is to develop a cell-based screening system to identify Kir3.2 blockers and then investigate the mode of action of the blocker. Chemical screening was carried out using a K(+) transporter-deficient yeast strain that expressed a constitutively active Kir3.2 mutant. The mode of action of an effective blocker was electrophysiologically analyzed using Kir channels expressed in Xenopus oocytes. Proflavine was identified to inhibit the growth of Kir3.2-transformant cells and Kir3.2 activity in a concentration-dependent manner. The current inhibition was strong when membrane potentials (Vm) was above equilibrium potential of K(+) (EK). When Vm was below EK, the blockage apparently depended on the difference between Vm and [K(+)]. Furthermore, the inhibition became stronger by lowering extracellular [K(+)]. These results indicated that the yeast strain serves as a screening system to isolate Kir3.2 blockers and proflavine is a prototype of a pore blocker of Kir3.2.

Bisphenol A and 4-tert-Octylphenol Inhibit Cx46 Hemichannel Currents

Connexins (Cx) are membrane proteins and monomers for forming gap junction (GJ) channels. Cx46 and Cx50 are also known to function as conductive hemichannels. As part of an ongoing effort to find GJ-specific blocker(s), endocrine disruptors were used to examine their effect on Cx46 hemichannels expressed in Xenopus oocytes. Voltage-dependent gating of Cx46 hemichannels was characterized by slowly activating outward currents and relatively fast inward tail currents. Bisphenol A (BPA, 10 nM) reduced outward currents of Cx46 hemichannels up to ~18% of control, and its effect was reversible (n=5). 4-tert-Octylphenol (OP, 1 µM) reversibly reduced outward hemichannel currents up to ~28% (n=4). However, overall shapes of Cx46 hemichannel current traces (outward and inward currents) were not changed by these drugs. These results suggest that BPA and OP are likely to occupy the pore of Cx46 hemichannels and thus obstruct the ionic fluxes. This finding provides that BPA and OP are potential candidates for GJ channel blockers.

Pore-forming activity of pestivirus p7 in a minimal model system supports genus-specific viroporin function

Viroporins are small integral membrane proteins functional in viral assembly and egress by promoting permeabilization. Blocking of viroporin function therefore constitutes a target for antiviral development. Classical swine fever virus (CSFV) protein p7 has been recently regarded as a class II viroporin. Here, we sought to establish the determinants of the CSFV p7 permeabilizing activity in a minimal model system. Assessment of an overlapping peptide library mapped the porating domain to the C-terminal hydrophobic stretch (residues 39-67). Pore-opening dependence on pH or sensitivity to channel blockers observed for the full protein required the inclusion of a preceding polar sequence (residues 33-38). Effects of lipid composition and structural data further support that the resulting peptide (residues 33-67), may comprise a bona fide surrogate to assay p7 activity in model membranes. Our observations imply that CSFV p7 relies on genus-specific structures-mechanisms to perform its viroporin function.

Computational and experimental analysis of drug binding to the Influenza M2 channel

The Influenza Matrix 2 (M2) protein is the target of Amantadine and Rimantadine which block its H(+) channel activity. However, the potential of these aminoadamantyls to serve as anti-flu agents is marred by the rapid resistance that the virus develops against them. Herein, using a cell based assay that we developed, we identify two new aminoadamantyl derivatives that show increased activity against otherwise resistant M2 variants. In order to understand the distinguishing binding patterns of the different blockers, we computed the potential of mean force of the drug binding process. The results reveal that the new derivatives are less mobile and bind to a larger pocket in the channel. Finally, such analyses may prove useful in designing new, more effective M2 blockers as a means of curbing influenza. This article is part of a Special Issue entitled: Viral Membrane Proteins - Channels for Cellular Networking.