Decreasing the thresholds for electroporation by sensitizing cells with local cationic anesthetics and substances that decrease the surface negative electric charge

Combination of irreversible electroporation with sustained release of a synthetic membranolytic polymer for enhanced cancer cell killing

Irreversible electroporation (IRE) is used clinically as a focal therapy to ablate solid tumors. A critical disadvantage of IRE as a monotherapy for cancer is the inability of ablating large tumors, because the electric field strength required is often too high to be safe. Previous reports indicate that cells exposed to certain cationic small molecules and surfactants are more vulnerable to IRE at lower electric field strengths. However, low-molecular-weight IRE sensitizers may suffer from suboptimal bioavailability due to poor stability and a lack of control over spatiotemporal accumulation in the tumor tissue. Here, we show that a synthetic membranolytic polymer, poly(6-aminohexyl methacrylate) (PAHM), synergizes with IRE to achieve enhanced cancer cell killing. The enhanced efficacy of the combination therapy is attributed to PAHM-mediated sensitization of cancer cells to IRE and to the direct cell killing by PAHM through membrane lysis. We further demonstrate sustained release of PAHM from embolic beads over 1 week in physiological medium. Taken together, combining IRE and a synthetic macromolecular sensitizer with intrinsic membranolytic activity and sustained bioavailability may present new therapeutic opportunities for a wide range of solid tumors.

The effects of electroporation buffer composition on cell viability and electro-transfection efficiency

Electroporation is an electro-physical, non-viral approach to perform DNA, RNA, and protein transfections of cells. Upon application of an electric field, the cell membrane is compromised, allowing the delivery of exogenous materials into cells. Cell viability and electro-transfection efficiency (eTE) are dependent on various experimental factors, including pulse waveform, vector concentration, cell type/density, and electroporation buffer properties. In this work, the effects of buffer composition on cell viability and eTE were systematically explored for plasmid DNA encoding green fluorescent protein following electroporation of 3T3 fibroblasts. A HEPES-based buffer was used in conjunction with various salts and sugars to modulate conductivity and osmolality, respectively. Pulse applications were chosen to maintain constant applied electrical energy (J) or total charge flux (C/m2). The energy of the pulse application primarily dictated cell viability, with Mg2+-based buffers expanding the reversible electroporation range. The enhancement of viability with Mg2+-based buffers led to the hypothesis that this enhancement is due to ATPase activation via re-establishing ionic homeostasis. We show preliminary evidence for this mechanism by demonstrating that the enhanced viability is eliminated by introducing lidocaine, an ATPase inhibitor. However, Mg2+ also hinders eTE compared to K+-based buffers. Collectively, the results demonstrate that the rational selection of pulsing conditions and buffer compositions are critical for the design of electroporation protocols to maximize viability and eTE.

Intra-arterial Injection of Lidocaine as a Cell Sensitizer during Irreversible Electroporation

PURPOSE

To investigate whether intra-arterial injection of lidocaine enhances irreversible electroporation (IRE) in a liver model.

MATERIALS AND METHODS

Conventional IRE (C-IRE) and lidocaine-enhanced IRE (L-IRE) were performed in 8 pig livers. Protocol 1 (tip exposure and electrode distance of 2.0 cm each) and protocol 2 (increased tip exposure and electrode distance 2.5 cm each) were used. Animals were sacrificed 3 hours after IRE. Study goals included electrical tissue properties (eg, current, conductivity) during IRE, geometry of IRE zones analyzed using computed tomography and magnetic resonance imaging (eg, volume and sphericity index), degree of acute liver damage, and irreversible cell death analyzed using microscopy (hematoxylin and eosin staining and terminal deoxynucleotidyl transferase deoxyuridine 5-triphosphate nick end labeling). Statistical comparisons were performed using the paired t test and Wilcoxon test.

RESULTS

All treatments were performed without adverse events. Electrical tissue properties were not significantly different between C-IRE and L-IRE. For protocol 1, the diameter of the largest sphere within the IRE zone was significantly larger for L-IRE than for C-IRE (25.0 ± 4.7 mm vs 18.4 ± 3.1 mm [P = .013]). For protocol 2, the volume of IRE zone was significantly larger for L-IRE compared with C-IRE (46.0 ± 5.4 cm³ vs 22.6 ± 6.4 cm³ [P = .018]), as well as the diameter of the largest sphere within the IRE zone (27.1 ± 2.2 mm vs 19.8 ± 2.3 mm [P = .020]). For protocol 1, a significantly higher degree of irreversible cell death was noted for L-IRE than for C-IRE (1.8 ± 1.0 vs 0.8 ± 1.0 [P = .046]).

CONCLUSIONS

Intra-arterial injection of lidocaine can enhance IRE in terms of larger IRE zones and an increase of irreversible cell death.

Avoiding the side effects of electric current pulse application to electroporated cells in disposable small volume cuvettes assures good cell survival

Background

The harmful side effects of electroporation to cells due to local changes in pH, the appearance of toxic electrode products, temperature increase, and the heterogeneity of the electric field acting on cells in the cuvettes used for electroporation were observed and discussed in several laboratories. If cells are subjected to weak electric fields for prolonged periods, for example in experiments on cell electrophoresis or galvanotaxis the same effects are seen. In these experiments investigators managed to reduce or eliminate the harmful side effects of electric current application.

Methods

For the experiments, disposable 20 μl cuvettes with two walls made of dialysis membranes were constructed and placed in a locally focused electric field at a considerable distance from the electrodes. Cuvettes were mounted into an apparatus for horizontal electrophoresis and the cells were subjected to direct current electric field (dcEF) pulses from a commercial pulse generator of exponentially declining pulses and from a custom-made generator of double and single rectangular pulses.

Results

More than 80% of the electroporated cells survived the dcEF pulses in both systems. Side effects related to electrodes were eliminated in both the flow through the dcEF and in the disposable cuvettes placed in the focused dcEFs. With a disposable cuvette system, we also confirmed the sensitization of cells to a dcEF using procaine by observing the loading of AT2 cells with calceine and using a square pulse generator, applying 50 ms single rectangular pulses.

Conclusions

We suggest that the same methods of avoiding the side effects of electric current pulse application as in cell electrophoresis and galvanotaxis should also be used for electroporation. This conclusion was confirmed in our electroporation experiments performed in conditions assuring survival of over 80% of the electroporated cells. If the amplitude, duration, and shape of the dcEF pulse are known, then electroporation does not depend on the type of pulse generator. This knowledge of the characteristics of the pulse assures reproducibility of electroporation experiments using different equipment.

9-AAA inhibits growth and induces apoptosis in human melanoma A375 and rat prostate adenocarcinoma AT-2 and Mat-LyLu cell lines but does not affect the growth and viability of normal fibroblasts

The present study found that, similarly to 5-fluorouracil, low concentrations (1-10 µM) of 9-aminoacridine (9-AAA) inhibited the growth of the two rat prostate cancer AT-2 and Mat-LyLu cell lines and the human melanoma A375 cell line. However, at the same concentrations, 9-AAA had no effect on the growth and apoptosis of normal human skin fibroblasts (HSFs). The differences between the cellular responses of the AT-2 and Mat-LyLu cell lines, which differ in malignancy, were found to be relatively small compared with the differences between normal HSFs and the cancer cell lines. Visible effects on the cell growth and survival of tumor cell lines were observed after 24-48 h of treatment with 9-AAA, and increased over time. The inhibition of cancer cell growth was found to be due to the gradually increasing number of cells dying by apoptosis, which was observed using two methods, direct counting and FlowSight analysis. Simultaneously, cell motile activity decreased to the same degree in cancer and normal cells within the first 8 h of incubation in the presence of 9-AAA. The results presented in the current study suggest that short-lasting tests for potential anticancer substances can be insufficient; which may result in cell type-dependent differences in the responses of cells to tested compounds that act with a delay being overlooked. The observed differences in responses between normal human fibroblasts and cancer cells to 9-AAA show the requirement for additional studies to be performed simultaneously on differently reacting cancer and normal cells, to determine the molecular mechanisms responsible for these differences.