Electrical properties of normal and transformed mammalian cells

In Vitro Experimental and Numerical Studies on the Preferential Ablation of Chemo-Resistant Tumor Cells Induced by High-Voltage Nanosecond Pulsed Electric Fields

Chemoresistance causes tumor recurrence and metastasis, resulting in poor clinical outcomes and low survival, and has been considered an obstacle to tumor therapy. The development of novel therapeutic approaches that can effectively kill chemoresistant tumor cells (CRTCs) is therefore critical to overcoming these obstacles.

OBJECTIVE

Here, we introduce an emerging physical feature-based therapeutic approach based on nanosecond pulsed electric fields (nsPEFs). The goal of this study is to investigate the effect of nsPEFs on CRTCs.

METHODS

The cell viability, ablation effects on a 3D-cultured scaffold, and lethal thresholds of nsPEFs were evaluated according to fluorescence staining assays.

RESULTS

nsPEF treatment preferentially affected chemoresistant cells (A549/CDDP) with a higher cell viability inhibition ability/cell death rate, larger ablation area, and lower ablation threshold compared to their respective homologous tumor cells (A549). The experimental and theoretical studies suggested that nsPEFs displayed selective behavior toward intracellular structures. With this selective character, nsPEFs can induce higher electroporation effects (e.g., higher pore number, larger electroporation area, and faster fluorescence dissipation on the nuclear envelope) on CRTCs due to their larger nuclear size and cell membrane capacitance.

CONCLUSION

These findings demonstrated that nsPEFs induced preferential ablation of CRTCs over their respective homologous tumor cells.

SIGNIFICANCE

This study provides an experimental and theoretical basis for the study of killing CRTCs by electrical treatments and suggests potential applications in the optimization of novel anti-chemoresistance methods.

Application of bioimpedance spectroscopy to characterize chemoresistant tumor cell selectivity of nanosecond pulse stimulation

The discriminating effects of nanosecond pulsed electric fields (nsPEFs) between chemoresistant tumor cells (CRTCs) and their respective homologous chemosensitive tumor cells (CSTCs) were investigated based on bioimpedance spectroscopy (BIS). The electrical properties of individual untreated cells were determined by fitting the impedance spectra to an equivalent circuit model and then using aided simulations to calculate the nuclear envelope transmembrane potential (nTMP) and electroporation area on the nuclear envelope. Additionally, fluorescence staining assays of cell monolayers after nanopulse stimulation (80 pulses, 200 ns, 3 kV) were conducted to validate the simulation results. The staining results indicated that CRTCs showed a larger ablation area and lower lethal threshold compared to CSTCs after exposure to the same nsPEF energy, which was in accordance with the higher nTMP and larger electroporation area calculated for CRTCs. The increase in the lethal effects of nsPEFs on CRTCs compared to CSTCs mainly resulted from the superposition of the changes in the electrical properties and nuclear size. The work shows that BIS can distinguish CRTCs and CSTCs and the corresponding nsPEF effects, suggesting potential applications for the optimization of novel anti-chemoresistance methods, including nsPEF-treatments.

Transmembrane voltage potential of somatic cells controls oncogene-mediated tumorigenesis at long-range

The microenvironment is increasingly recognized as a crucial aspect of cancer. In contrast and complement to the field's focus on biochemical factors and extracellular matrix, we characterize a novel aspect of host:tumor interaction - endogenous bioelectric signals among non-excitable somatic cells. Extending prior work focused on the bioelectric state of cancer cells themselves, we show for the first time that the resting potentials of distant cells are critical for oncogene-dependent tumorigenesis. In the Xenopus laevis tadpole model, we used human oncogenes such as mutant KRAS to drive formation of tumor-like structures that exhibited overproliferation, increased nuclear size, hypoxia, acidity, and leukocyte attraction. Remarkably, misexpression of hyperpolarizing ion channels at distant sites within the tadpole significantly reduced the incidence of these tumors. The suppression of tumorigenesis could also be achieved by hyperpolarization using native CLIC1 chloride channels, suggesting a treatment modality not requiring gene therapy. Using a dominant negative approach, we implicate HDAC1 as the mechanism by which resting potential changes affect downstream cell behaviors. Based on published data on the voltage-mediated changes of butyrate flux through the SLC5A8 transporter, we present a model linking resting potentials of host cells to the ability of oncogenes to initiate tumorigenesis. Antibiotic data suggest that the relevant butyrate is generated by a native bacterial species, identifying a novel link between the microbiome and cancer that is mediated by alterations in bioelectric signaling.

Dose Dependent Effect of Iso-Octane on HaCaT: A Model Study

OBJECTIVE

Improved understanding of cytotoxicity under chemical assaults may be achieved by multimodal analysis of cellular morphology, viability, molecular expressions, and biophysical properties.

MATERIALS AND METHODS

In this study dose-dependent effects of an organic solvent (OS), iso-octane (IO), known to cause skin irritation, has been explored multimodally for understanding its effect on structural and functional profile of normal epithelial cell population in vitro.

RESULTS

Under IO exposures, after 5 h there was a sharp decrease in viability of HaCaT with increasing doses which may be due to disruption in cellular association noted via immunocytochemical study and was further supported by the decreased expression of E-cadherin at transcriptomic level. Dislocation of E-cadherin from membrane to the cytoplasm occurred with increasing doses. The dose-dependent changes in varied aspects of bioelectrical properties, having plausible correlation with cellular viability, association, and adherence were noteworthy at 5 h of IO exposure. Evaluation of biomechanical properties by micropipette aspiration showed a distinct change in cellular stiffness in terms of increase in suction force and post-suction alteration in cellular shape. The cells became stiffer and fragile with increasing IO doses.

CONCLUSION

Present study explicated dose-dependent cytotoxicity of IO on HaCaT and explored the usefulness of this approach to develop in vitro model system to evaluate epithelial toxicity with level-free markers.

Endogenous Voltage Potentials and the Microenvironment: Bioelectric Signals that Reveal, Induce and Normalize Cancer

Cancer may be a disease of geometry: a misregulation of the field of information that orchestrates individual cells' activities towards normal anatomy. Recent work identified molecular mechanisms underlying a novel system of developmental control: bioelectric gradients. Endogenous spatio-temporal differences in resting potential of non-neural cells provide instructive cues for cell regulation and complex patterning during embryogenesis and regeneration. It is now appreciated that these cues are an important layer of the dysregulation of cell: cell interactions that leads to cancer. Abnormal depolarization of resting potential (Vmem) is a convenient marker for neoplasia and activates a metastatic phenotype in genetically-normal cells in vivo. Moreover, oncogene expression depolarizes cells that form tumor-like structures, but is unable to form tumors if this depolarization is artificially prevented by misexpression of hyperpolarizing ion channels. Vmem triggers metastatic behaviors at considerable distance, mediated by transcriptional and epigenetic effects of electrically-modulated flows of serotonin and butyrate. While in vivo data on voltages in carcinogenesis comes mainly from the amphibian model, unbiased genetic screens and network profiling in rodents and human tissues reveal several ion channel proteins as bona fide oncogene and promising targets for cancer drug development. However, we propose that a focus on specific channel genes is just the tip of the iceberg. Bioelectric state is determined by post-translational gating of ion channels, not only from genetically-specified complements of ion translocators. A better model is a statistical dynamics view of spatial Vmem gradients. Cancer may not originate at the single cell level, since gap junctional coupling results in multi-cellular physiological networks with multiple stable attractors in bioelectrical state space. New medical applications await a detailed understanding of the mechanisms by which organ target morphology stored in real-time patterns of ion flows is perceived or mis-perceived by cells. Mastery of somatic voltage gradients will lead to cancer normalization or rebooting strategies, such as those that occur in regenerating and embryonic organs, resulting in transformative advances in basic biology and oncology.

Biomedical potentials of crown ethers: prospective antitumor agents

Crown ethers are of enormous interest and importance in chemistry, biochemistry, materials science, catalysis, separation, transport and encapsulated processes, as well as in the design and synthesis of various synthetic systems with specific properties, diverse capabilities, and programmable functions. Classical crown ethers are macrocyclic polyethers that contain 3-20 oxygen atoms separated from each other by two or more carbon atoms. They are exceptionally versatile in selectively binding a range of metal ions and a variety of organic neutral and ionic species. Crown ethers are currently being studied and used in a variety of applications beyond their traditional place in chemistry. This review presents additional applications and the ever-increasing biomedical potentials of these intriguing compounds, with particular emphasis on the prospects of their relevance as anticancer agents. We believe that further research in this direction should be encouraged, as crown compounds could either induce toxicities that are different from those of conventional antitumor drugs, or complement drugs in current use, thereby providing a valuable adjunct to therapy.

Modulation of potassium channel function confers a hyperproliferative invasive phenotype on embryonic stem cells

Ion transporters, and the resulting voltage gradients and electric fields, have been implicated in embryonic development and regeneration. These biophysical signals are key physiological aspects of the microenvironment that epigenetically regulate stem and tumor cell behavior. Here, we identify a previously unrecognized function for KCNQ1, a potassium channel known to be involved in human Romano-Ward and Jervell-Lange-Nielsen syndromes when mutated. Misexpression of its modulatory wild-type beta-subunit XKCNE1 in the Xenopus embryo resulted in a striking alteration of the behavior of one type of embryonic stem cell: the pigment cell lineage of the neural crest. Depolarization of embryonic cells by misexpression of KCNE1 non-cell-autonomously induced melanocytes to overproliferate, spread out, and become highly invasive of blood vessels, liver, gut, and neural tube, leading to a deeply hyperpigmented phenotype. This effect is mediated by the up-regulation of Sox10 and Slug genes, thus linking alterations in ion channel function to the control of migration, shape, and mitosis rates during embryonic morphogenesis. Taken together, these data identify a role for the KCNQ1 channel in regulating key cell behaviors and reveal the molecular identity of a biophysical switch, by means of which neoplastic-like properties can be conferred upon a specific embryonic stem cell subpopulation.

Antitumor Potential of Crown Ethers: Structure−Activity Relationships, Cell Cycle Disturbances, and Cell Death Studies of a Series of Ionophores

The present paper demonstrates the antiproliferative ability and structure-activity relationships (SAR) of 14 crown and aza-crown ether analogues on five tumor-cell types. The most active compounds were di-tert-butyldicyclohexano-18-crown-6 (3), which exhibited cytotoxicity in the submicromolar range, and di-tert-butyldibenzo-18-crown-6 (5) (IC50 values of approximately 2 microM). Also, 3 and 5 induced marked influence on the cell cycle phase distribution--strong G1 arrest, followed by the induction of apoptosis. A computational SAR modeling effort offers insight into possible mechanisms of crown ether biological activity, presumably involving penetration into cell membranes, and points out structural features of molecules important for this activity. The results reveal that crown ethers possess marked tumor-cell growth inhibitory activity, the extent of which depends on the characteristics of the hydrophilic macrocylic cavity and the surrounding hydrophobic ring. Our work supports the hypothesis that crown ether compounds inhibit tumor-cell growth by disrupting potassium ion homeostasis, which in turn leads to cell cycle perturbations and apoptosis.

Membrane permeability changes induce hyperpolarization in transformed lymphoid cells under high-density culture conditions

BACKGROUND

Membrane potential changes in cells from the human lymphoid B cell line, JY, evoked by increasing cell density in culture were investigated, as data published on other cell types are controversial. An attempt was also made to clear the underlying mechanism.

METHODS

Nonadherent JY cells were isolated from high-density plateau-phase cultures (type A cells), medium-density log-phase cultures (type B cells), and low-density lag-phase cultures (type C cells). They were analyzed for transmembrane potential, intracellular free concentration of potassium and sodium, membrane permeability for monovalent cations, cell cycle distribution by measuring DNA content, and glucose uptake.

RESULTS

C type cells proved to be relatively depolarized (-41 +/- 3 mV) and cells obtained from the highest density cultures hyperpolarized (-60 +/- 3 mV). Intracellular concentrations ([K](i) = 92-97 mM and [Na](i) = 34-35 mM) were almost identical for each type of cell. The sodium/potassium permeability constant ratio in the A and C type of cells was 0.047 and 0.094, respectively. High-density culture conditions resulted in a pronounced G(1)-phase arrest.

CONCLUSIONS

Differences in the membrane potential values induced by high-density culture conditions were maintained by changes in the membrane permeability for the monovalent cations.

A unifying model of the cell proliferation emphasizing plasma membrane fluxes

The regulation of cellular growth and proliferation is perhaps the most investigated and elusive problem in cell biology and seems to be possible to solve from almost any angle of study chosen. Among the non-systemic factors that have been discussed are genetic damage, genomic control, regulation by stimulatory and inhibitory peptide factors such as EGF, chalones, and fibronectin, protein kinase activation with tyrosine phosphorylation, adenylylcyclase and cAMP, cGMP, membrane perturbations and specifically in tumours the failure of the Pasteur effect in control of glycolysis, excessive membrane ATPase activity, and excessive hydrolytic and proteolytic activities at the cell surface. This article focuses on the central role of fluxes within the plasma membrane and re-examines the possibility that changes of flux of metabolites, ions, and reducing equivalents may be the common denominator regulating cellular proliferation.

Changes in cell surface charge and transmembrane potential accompanying neoplastic transformation of rat kidney cells

Free flow electrophoresis measurements have been used to determine the surface charge density of normal rat kidney (NRK) cells and a clone of NRK, designated as 6m2, that exhibit a transformed phenotype at 33 degrees C and a non-transformed phenotype at 39 degrees C. A clone of 6m2, designated 54-5A4, which is transformed at both 33 degrees C and 39 degrees C was also studied. A surface charge density of -1.42 microC/cm2 was obtained for the NRK and non-transformed 6m2 cells at 39 degrees C, whereas at 33 degrees C values of -1.85 and -1.78 microC/cm2 were determined for the transformed 6m2 and 54-5A4 cells, respectively. It was found that 72% of the increased charge that appeared on the transformed 6m2 cells compared with the non-transformed 6m2 cells was RNAase sensitive. The time-dependent decrease in surface charge that accompanied the shift of the 6m2 cells from their transformed to non-transformed state was found to mirror the increase in transmembrane potential previously reported using a fluorescent dye technique, and was also comparable to the reported temporal changes in their morphology and virally-coded protein content.

Membrane potentials and sodium channels: hypotheses for growth regulation and cancer formation based on changes in sodium channels and gap junctions

Based on several convergent lines of investigation, we make two hypotheses which are sufficient to explain many phenomena of growth regulation in both normal and cancer cells. 1. The first hypothesis is that there is a boundary or threshold of resting cell membrane potential that separates normal resting cells from normal proliferating cells and cancer cells. The basis for this in existing literature values of membrane potentials in resting and proliferating cells is established. A discussion of how these differences in potential can be explained focuses on changes in sodium permeability and internal sodium concentration. Of many sodium transfer mechanisms, the sodium channel is emphasized and how increased intracellular transfer may stimulate DNA synthesis. The effects of changing cell junctions, in particular gap junctions, on membrane potentials is also discussed, as well as the indications of altered junctions in tumor cells. The linking factor of the effects of growth factors on both cell junctions and sodium permeability leads to the second hypothesis. 2. Since growth initiation and inhibition involve sodium channels and gap junctions, several phenomena can be explained by postulating that they are one and the same entity. The basis for this hypothesis in existing descriptions of functional and structural similarities is outlined. The possible interchange of these elements in the cell cycle lead to several corollaries consequent to the conservation of their total number. The formation of gap junctions would consume sodium channels, decrease sodium permeability and stop DNA synthesis. Conversely, growth factors may competitively bind to channel-connexon elements, cleave gap junctions, liberate sodium channels to increase sodium permeability, and trigger DNA synthesis. Alterations in the structure of gap junction-channel elements in tumor cells would be sufficient to explain some carcinogenesis.

The influence of the membrane sodium pump activity on the ability of human peripheral blood lymphocytes to form early rosettes with SRBC

The influence of changes of the cation-transporting activity of the membrane Na,K ATP-ase of human peripheral blood lymphocytes on their ability to form 'early' and 'late' rosettes with SRBC was investigated. It was shown that inhibition of the Na,K ATP-ase-dependent cation transport through the lymphocyte membrane by means of incubation of the cells with various specific inhibitors of the enzyme (ouabain, vanadate) or depletion of the magnesium cations from the incubation medium caused the rise in the percentage of early rosettes, having no influence on the late E rosette percentage. The possible explanation of the observed phenomena is discussed with regard to (ion transport-dependent) electrical forces present at the surface of resting and activated lymphocytes.

Cell membranes after malignant transformation. Part I: Dynamic stability at low surface tension

A hydrodynamic cell model is introduced to analyze the dynamic stability of the cell membrane after malignant transformation. The cell membrane is considered as a two-dimensional charged interface between intra- and extra-cellular fluids. Employing a first order stability analysis, conditions are established under which growth of surface fluctuations can occur (leading to microvilli formation or cell division). The system is unstable if the total surface tension, i.e. the pure surface tension plus the free energy of formation of the double layers, is negative. Following that criterion, cell division is promoted in cancer cells; moreover, as cancer cells are more fluid than normal cells, they will divide more rapidly. The model also predicts that microvilli (protrusions of the cell membrane) will have a diameter of the order of the dominant wavelengths of perturbation (0.1 - 1 mu) which supports the view that such protrusions are consequences of amplified cell surface fluctuations.