Bursts of Bipolar Microsecond Pulses Inhibit Tumor Growth

Numerical assessments of geometry, proximity and multi-electrode effects on electroporation in mitochondria and the endoplasmic reticulum to nanosecond electric pulses

Most simulations of electric field driven bioeffects have considered spherical cellular geometries or probed symmetrical structures for simplicity. This work assesses cellular transmembrane potential build-up and electroporation in a Jurkat cell that includes the endoplasmic reticulum (ER) and mitochondria, both of which have complex shapes, in response to external nanosecond electric pulses. The simulations are based on a time-domain nodal analysis that incorporates membrane poration utilizing the Smoluchowski model with angular-dependent changes in membrane conductivity. Consistent with prior experimental reports, the simulations show that the ER requires the largest electric field for electroporation, while the inner mitochondrial membrane (IMM) is the easiest membrane to porate. Our results suggest that the experimentally observed increase in intracellular calcium could be due to a calcium induced calcium release (CICR) process that is initiated by outer cell membrane breakdown. Repeated pulsing and/or using multiple electrodes are shown to create a stronger poration. The role of mutual coupling, screening, and proximity effects in bringing about electric field modifications is also probed. Finally, while including greater geometric details might refine predictions, the qualitative trends are expected to remain.

Mitochondrial depolarization and ATP loss during high frequency nanosecond and microsecond electroporation

It is predicted that ultra-short electric field pulses (nanosecond) can selectively permeabilize intracellular structures (e.g., mitochondria) without significant effects on the outer cell plasma membrane. Such a phenomenon would have high applicability in cancer treatment and could be employed to modulate cell death type or immunogenic response. Therefore, in this study, we compare the effects of 100 µs x 8 pulses (ESOPE - European Standard Operating Procedures on Electrochemotherapy) and bursts of 100 ns pulses for modulation of the mitochondria membrane potential. We characterize the efficacies of various protocols to trigger permeabilization, depolarize mitochondria (evaluated 1 h  after treatment), the extent of ATP depletion and generation of reactive oxygen species (ROS). Finally, we employ the most prominent protocols in the context of Ca2+ electrochemotherapy in vitro. We provide experimental proof that 7.5-12.5 kV/cm x 100 ns pulses can be used to modulate mitochondrial potential, however, the permeabilization of the outer membrane is still a prerequisite for depolarization. Similar to 100 µs x 8 pulses, the higher the permeabilization rate, the higher the mitochondrial depolarization. Nevertheless, 100 ns pulses result in lesser ROS generation when compared to ESOPE, even when the energy input is several-fold higher than for the microsecond procedure. At the same time, it shows that even the short 100 ns pulses can be successfully used for Ca2+ electrochemotherapy, ensuring excellent cytotoxic efficacy.

The Effects of Bipolar Cancellation Phenomenon on Nano-Electrochemotherapy of Melanoma Tumors: In Vitro and In Vivo Pilot

The phenomenon known as bipolar cancellation is observed when biphasic nanosecond electric field pulses are used, which results in reduced electroporation efficiency when compared to unipolar pulses of the same parameters. Basically, the negative phase of the bipolar pulse diminishes the effect of the positive phase. Our study aimed to investigate how bipolar cancellation affects Ca2+ electrochemotherapy and cellular response under varying electric field intensities and pulse durations (3-7 kV/cm, 100, 300, and 500 ns bipolar 1 MHz repetition frequency pulse bursts, n = 100). As a reference, standard microsecond range parametric protocols were used (100 µs × 8 pulses). We have shown that the cancellation effect is extremely strong when the pulses are closely spaced (1 MHz frequency), which results in a lack of cell membrane permeabilization and consequent failure of electrochemotherapy in vitro. To validate the observations, we have performed a pilot in vivo study where we compared the efficacy of monophasic (5 kV/cm × ↑500 ns × 100) and biphasic sequences (5 kV/cm × ↑500 ns + ↓500 ns × 100) delivered at 1 MHz frequency in the context of Ca2+ electrochemotherapy (B16-F10 cell line, C57BL/6 mice, n = 24). Mice treated with bipolar pulses did not exhibit prolonged survival when compared to the untreated control (tumor-bearing mice); therefore, the bipolar cancellation phenomenon was also occurrent in vivo, significantly impairing electrochemotherapy. At the same time, the efficacy of monophasic nanosecond pulses was comparable to 1.4 kV/cm × 100 µs × 8 pulses sequence, resulting in tumor reduction following the treatment and prolonged survival of the animals.

The Enhancement of Tumor Ablation Effect by the Combination of High-Frequency and Low-Voltage Bipolar Electroporation Pulses

The H-FIRE (high-frequency irreversible electroporation) protocol employs high-frequency bipolar pulses (HFBPs) with a width of ∼1 µs for tumor ablation with slight muscle contraction. However, H-FIRE pulses need a higher electric field to generate a sufficient ablation effect, which may cause undesirable thermal damage.

OBJECTIVE

Recently, combining short high-voltage IRE monopolar pulses with long low-voltage IRE monopolar pulses was shown to enlarge the ablation region. This finding indicates that combining HFBPs with low-voltage bipolar pulses (LVBPs), which are called composited bipolar pulses (CBPs), may enhance the ablation effect.

METHODS

This study designed a pulse generator by modifying a full-bridge inverter. The cell suspension and 3D tumor mimic experiments (U251 cells) were performed to examine the enhancement of the ablation effect.

RESULTS

The generator outputs HFBPs with 0-±2.5 kV and LVBPs with 0-±0.3 kV in one period. The pulse parameters are adjustable by programming on a human-computer interface. The cell suspension experiments showed that CBPs could enhance cytotoxicity, as compared to HFBPs with no cell-killing effect. Even at lower electric energy, the cell viability by CBPs was significantly lower than that of the HFBPs protocol. The ablation experiments on the 3D tumor mimic showed that the CBPs could create a larger connected ablation area. In contrast, the HFBPs protocol with a similar dose generated a nonconnected ablation area.

CONCLUSION

Results indicate that the CBPs protocol can enhance the ablation effect of HFBPs protocol.

SIGNIFICANCE

This proposed generator that uses the CBPs principle may be a useful tool for tumor ablation.

Integrated Time Nanosecond Pulse Irreversible Electroporation (INSPIRE): Assessment of Dose, Temperature, and Voltage on Experimental and Clinical Treatment Outcomes

OBJECTIVE

This study sought to investigate a novel strategy using temperature-controlled delivery of nanosecond pulsed electric fields as an alternative to the 50-100 microsecond pulses used for irreversible electroporation.

METHODS

INSPIRE treatments were carried out at two temperatures in 3D tumor models using doses between 0.001 s and 0.1 s. The resulting treatment zones were quantified using viability staining and lethal electric field intensities were determined numerically. Computational modeling was then used to determine parameters necessary for INSPIRE treatments to achieve equivalent treatment zones to clinical electroporation treatments and evaluate the potential for these treatments to induce deleterious thermal damage.

RESULTS

Lethal thresholds between 1109 and 709 V/cm were found for nominal 0.01 s treatments with pulses between 350 ns and 2000 ns at physiological temperatures. Further increases in dose resulted in significant decreases in lethal thresholds. Given these experimental results, treatment zones comparable to clinical electroporation are possible by increasing the dose and voltage used with nanosecond duration pulses. Temperature-controlled simulations indicate minimal thermal cell death while achieving equivalent treatment volumes to clinical electroporation.

CONCLUSION

Nanosecond electrical pulses can achieve comparable outcomes to traditional electroporation provided sufficient electrical doses or voltages are applied. The use of temperature-controlled delivery may minimize thermal damage during treatment.

SIGNIFICANCE

Intense muscle stimulation and the need for cardiac gating have limited irreversible electroporation. Nanosecond pulses can alleviate these challenges, but traditionally have produced significantly smaller treatment zones. This study suggests that larger ablation volumes may be possible with the INSPIRE approach and that future in vivo studies are warranted.

Glioblastoma Therapy: Past, Present and Future

Glioblastoma (GB) stands out as the most prevalent and lethal form of brain cancer. Although great efforts have been made by clinicians and researchers, no significant improvement in survival has been achieved since the Stupp protocol became the standard of care (SOC) in 2005. Despite multimodality treatments, recurrence is almost universal with survival rates under 2 years after diagnosis. Here, we discuss the recent progress in our understanding of GB pathophysiology, in particular, the importance of glioma stem cells (GSCs), the tumor microenvironment conditions, and epigenetic mechanisms involved in GB growth, aggressiveness and recurrence. The discussion on therapeutic strategies first covers the SOC treatment and targeted therapies that have been shown to interfere with different signaling pathways (pRB/CDK4/RB1/P16ink4, TP53/MDM2/P14arf, PI3k/Akt-PTEN, RAS/RAF/MEK, PARP) involved in GB tumorigenesis, pathophysiology, and treatment resistance acquisition. Below, we analyze several immunotherapeutic approaches (i.e., checkpoint inhibitors, vaccines, CAR-modified NK or T cells, oncolytic virotherapy) that have been used in an attempt to enhance the immune response against GB, and thereby avoid recidivism or increase survival of GB patients. Finally, we present treatment attempts made using nanotherapies (nanometric structures having active anti-GB agents such as antibodies, chemotherapeutic/anti-angiogenic drugs or sensitizers, radionuclides, and molecules that target GB cellular receptors or open the blood-brain barrier) and non-ionizing energies (laser interstitial thermal therapy, high/low intensity focused ultrasounds, photodynamic/sonodynamic therapies and electroporation). The aim of this review is to discuss the advances and limitations of the current therapies and to present novel approaches that are under development or following clinical trials.

Calcium electroporation causes ATP depletion in cells and is effective both in microsecond and nanosecond pulse range as a modality of electrochemotherapy

Calcium electroporation is a modality of electrochemotherapy (ECT), which is based on intracellular electric field-mediated delivery of cytotoxic doses of calcium into the cells resulting in rapid cell death. In this work, we have developed a CHO-K1 luminescent cell line, which allowed the estimation of cell membrane permeabilization, ATP depletion and cytotoxicity evaluation without the use of additional markers and methodologies. We have shown the high efficiency of nanosecond pulses compressed into a MHz burst for application in calcium ECT treatments. The 5 kV/cm and 10 kV/cm nanosecond (100 and 600 ns) pulses were delivered in bursts of 10, 50 and 100 pulses (a total of 12 parametric protocols) and then compared to standard microsecond range sequences (100 µs × 8) of 0.4-1.4 kV/cm. The effects of calcium-free, 2 mM and 5 mM calcium electroporation treatments were characterized. It was shown that reversible electroporation is accompanied by ATP depletion associated with membrane damage, while during calcium ECT the ATP depletion is several-fold higher, which results in cell death. Finally, efficacy-wise equivalent pulse parameters from nanosecond and microsecond ranges were established, which can be used for calcium nano-ECT as a better alternative to ESOPE (European Standard Operating Procedures on Electrochemotherapy) protocols.

Investigation of integrated time nanosecond pulse irreversible electroporation against spontaneous equine melanoma

Introduction

Integrated time nanosecond pulse irreversible electroporation (INSPIRE) is a novel tumor ablation modality that employs high voltage, alternating polarity waveforms to induce cell death in a well-defined volume while sparing the underlying tissue. This study aimed to demonstrate the in vivo efficacy of INSPIRE against spontaneous melanoma in standing, awake horses.

Methods

A custom applicator and a pulse generation system were utilized in a pilot study to treat horses presenting with spontaneous melanoma. INSPIRE treatments were administered to 32 tumors across 6 horses and an additional 13 tumors were followed to act as untreated controls. Tumors were tracked over a 43-85 day period following a single INSPIRE treatment. Pulse widths of 500ns and 2000ns with voltages between 1000 V and 2000 V were investigated to determine the effect of these variables on treatment outcomes.

Results

Treatments administered at the lowest voltage (1000 V) reduced tumor volumes by 11 to 15%. Higher voltage (2000 V) treatments reduced tumor volumes by 84 to 88% and eliminated 33% and 80% of tumors when 500 ns and 2000 ns pulses were administered, respectively.

Discussion

Promising results were achieved without the use of chemotherapeutics, the use of general anesthesia, or the need for surgical resection in regions which are challenging to keep sterile. This novel therapeutic approach has the potential to expand the role of pulsed electric fields in veterinary patients, especially when general anesthesia is contraindicated, and warrants future studies to demonstrate the efficacy of INSPIRE as a solid tumor treatment.

Nanosecond pulsed electric fields increase antibiotic susceptibility in methicillin-resistant Staphylococcus aureus

IMPORTANCE

We have found that treatment with short electric pulses potentiates the effects of multiple antibiotics against methicillin-resistant Staphylococcus aureus. By reducing the dose of antibiotic necessary to be effective, co-treatment with electric pulses could amplify the effects of standard antibiotic dosing to treat S. aureus infections such as skin and soft-tissue infections (SSTIs). SSTIs are accessible to physical intervention and are good candidates for electric pulse co-treatment, which could be adopted as a step-in wound and abscess debridement.

Negative effects of cancellation during nanosecond range High-Frequency calcium based electrochemotherapy in vitro

Drug delivery using nanosecond pulsed electric fields is a new branch of electroporation-based treatments, which potentially can substitute European standard operating procedures for electrochemotherapy. In this work, for the first time, we characterize the effects of ultra-fast repetition frequency (1-2.5 MHz) nanosecond pulses (5-9 kV/cm, 200 and 400 ns) in the context of nano-electrochemotherapy with calcium. Additionally, we investigate the feasibility of bipolar symmetric (↑200 ns + ↓200 ns) and asymmetric (↑200 ns + ↓400 ns) nanosecond protocols for calcium delivery. The effects of bipolar cancellation and the influence of interphase delay (200 ns) are overviewed. Human lung cancer cell lines A549 and H69AR were used as a model. It was shown that unipolar pulses delivered at high frequency are effective for electrochemotherapy with a significant improvement in efficiency when the delay between separate pulses is reduced. Bipolar symmetric pulses trigger the cancellation phenomenon limiting applications for drug delivery and can be compensated by the asymmetry of the pulse (↑200 ns + ↓400 ns or ↑400 ns + ↓200 ns). The results of this study can be successfully used to derive a new generation of nsPEF protocols for successful electrochemotherapy treatments.

The Effects of Interphase and Interpulse Delays and Pulse Widths on Induced Muscle Contractions, Pain and Therapeutic Efficacy in Electroporation-Based Therapies

Electroporation is used in medicine for drug and gene delivery, and as a nonthermal ablation method in tumor treatment and cardiac ablation. Electroporation involves delivering high-voltage electric pulses to target tissue; however, this can cause effects beyond the intended target tissue like nerve stimulation, muscle contractions and pain, requiring use of sedatives or anesthetics. It was previously shown that adjusting pulse parameters may mitigate some of these effects, but not how these adjustments would affect electroporation's efficacy. We investigated the effect of varying pulse parameters such as interphase and interpulse delay while keeping the duration and number of pulses constant on nerve stimulation, muscle contraction and assessing pain and electroporation efficacy, conducting experiments on human volunteers, tissue samples and cell lines in vitro. Our results show that using specific pulse parameters, particularly short high-frequency biphasic pulses with short interphase and long interpulse delays, reduces muscle contractions and pain sensations in healthy individuals. Higher stimulation thresholds were also observed in experiments on isolated swine phrenic nerves and human esophagus tissues. However, changes in the interphase and interpulse delays did not affect the cell permeability and survival, suggesting that modifying the pulse parameters could minimize adverse effects while preserving therapeutic goals in electroporation.

Pulsed Electric Field Ablation of Esophageal Malignancies and Mitigating Damage to Smooth Muscle: An In Vitro Study

Cancer ablation therapies aim to be efficient while minimizing damage to healthy tissues. Nanosecond pulsed electric field (nsPEF) is a promising ablation modality because of its selectivity against certain cell types and reduced neuromuscular effects. We compared cell killing efficiency by PEF (100 pulses, 200 ns-10 µs duration, 10 Hz) in a panel of human esophageal cells (normal and pre-malignant epithelial and smooth muscle). Normal epithelial cells were less sensitive than the pre-malignant ones to unipolar PEF (15-20% higher LD50, p < 0.05). Smooth muscle cells (SMC) oriented randomly in the electric field were more sensitive, with 30-40% lower LD50 (p < 0.01). Trains of ten, 300-ns pulses at 10 kV/cm caused twofold weaker electroporative uptake of YO-PRO-1 dye in normal epithelial cells than in either pre-malignant cells or in SMC oriented perpendicularly to the field. Aligning SMC with the field reduced the dye uptake fourfold, along with a twofold reduction in Ca²⁺ transients. A 300-ns pulse induced a twofold smaller transmembrane potential in cells aligned with the field, making them less vulnerable to electroporation. We infer that damage to SMC from nsPEF ablation of esophageal malignancies can be minimized by applying the electric field parallel to the predominant SMC orientation.

Does the shape of the electric pulse matter in electroporation?

Electric pulses are widely used in biology, medicine, industry, and food processing. Numerous studies indicate that electroporation (EP) is a pulse-dependent process, and the electric pulse shape and duration strongly determine permeabilization efficacy. EP protocols are precisely planned in terms of the size and charge of the molecules, which will be delivered to the cell. In reversible and irreversible EP applications, rectangular or sine, polar or bipolar pulses are commonly used. The usage of pulses of the asymmetric shape is still limited to high voltage and low voltage (HV/LV) sequences in the context of gene delivery, while EP-based applications of ultra-short asymmetric pulses are just starting to emerge. This review emphasizes the importance and role of the pulse shape for membrane permeabilization by EP.

Substantially Improved Electrofusion Efficiency of Hybridoma Cells: Based on the Combination of Nanosecond and Microsecond Pulses

As the initial antibody technology, the preparation of hybridoma cells has been widely used in discovering antibody drugs and is still in use. Various antibody drugs obtained through this technology have been approved for treating human diseases. However, the key to producing hybridoma cells is efficient cell fusion. High-voltage microsecond pulsed electric fields (μsHVPEFs) are currently one of the most common methods used for cell electrofusion. Nevertheless, the membrane potential induced by the external microsecond pulse is proportional to the diameter of the cell, making it difficult to fuse cells of different sizes. Although nanosecond pulsed electric fields (nsPEFs) can achieve the fusion of cells of different sizes, due to the limitation of pore size, deoxyribonucleic acid (DNA) cannot efficiently pass through the cell pores produced by nsPEFs. This directly causes the significant loss of the target gene and reduces the proportion of positive cells after fusion. To achieve an electric field environment independent of cell size and enable efficient cell fusion, we propose a combination of nanosecond pulsed electric fields and low-voltage microsecond pulsed electric fields (ns/μsLVPEFs) to balance the advantages and disadvantages of the two techniques. The results of fluorescence experiments and hybridoma culture experiments showed that after lymphocytes and myeloma cells were stimulated by a pulse (ns/μsLVPEF, μsHVPEF, and control), compared with μsHVPEF, applying ns/μsLVPEF at the same energy could increase the cell fusion efficiency by 1.5–3.0 times. Thus far, we have combined nanosecond and microsecond pulses and provided a practical solution that can significantly increase cell fusion efficiency. This efficient cell fusion method may contribute to the further development of hybridoma technology in electrofusion.

Extended Focal Ablation of Localized Prostate Cancer With High-Frequency Irreversible Electroporation: A Nonrandomized Controlled Trial

IMPORTANCE

Focal therapy of prostate cancer must balance the oncologic outcome and functional outcome. High-frequency irreversible electroporation (H-FIRE) can destroy cancer cells while selectively preserving surrounding nerves and blood vessels, but no clinical trials have been conducted, to our knowledge.

OBJECTIVE

To evaluate the efficacy and safety of H-FIRE in the treatment of localized prostate cancer (PCa).

DESIGN, SETTING, AND PARTICIPANTS

This was a single-group, objective performance criteria, nonrandomized controlled trial. Recruitment began on May 2, 2018, and ended March 27, 2019. The follow-up duration was 6 months. This was a multicenter trial conducted at 4 tertiary teaching hospitals in China. Patients with low or intermediate risk of biochemical recurrence of localized and locally advanced PCa were eligible. Key inclusion criteria were serum prostate-specific antigen (PSA) level less than 20 ng/mL, clinical stage of T2c or less, and Gleason score of 7 or less. Data were analyzed from January 20 to February 20, 2021.

INTERVENTION

H-FIRE ablation of all lesions identified with biopsy.

MAIN OUTCOMES AND MEASURES

The primary end point was 6-month clinically significant PCa (csPCa), which was defined as any biopsy core with Gleason score of greater than or equal to 7, or Gleason score of 6 plus maximum cancer core length of greater than 3 mm or an increase from the original cancer burden. Secondary outcomes were calculated in patients who actually received H-FIRE treatment.

RESULTS

A total of 117 patients (median [IQR] age, 67 [62-73] years) were recruited from 4 centers, and 109 patients (27 [24.8%] low risk and 82 [75.2%] intermediate risk) actually received H-FIRE. Median (IQR) PSA level was 9.0 (6.0-12.7) ng/mL. Among the 100 patients who underwent biopsy at 6 months, the 6-month csPCa rate was 6.0% (95% CI, 2.2%-12.6%; P < .001; 1 in the treatment zone and 5 outside the treatment zone). Superiority criteria vs the historical control of 20% was achieved. PCa was detected in 14 patients, with a Gleason score of 7 in 2 patients and 6 in the remaining 12 patients. At 6 months, median (IQR) PSA level was 1.08 (0.4-3.2) ng/mL, median (IQR) International Prostate Symptom Score was 4.5 (2.0-9.5), and median (IQR) International Index of Erectile Function 5 score was 2.0 (0.5-12.5). Superiority vs the 20% historical control was also met in the subgroup analysis that only included the 57 patients with Gleason score of 7 at baseline (3.5% 6-month csPCa; 95% CI, 0.4%-12.1%).

CONCLUSIONS AND RELEVANCE

The rate of 6-month csPCa with H-FIRE ablation was lower than the historical control using other energy platforms.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT03838432.

Muscle contractions and pain sensation accompanying high-frequency electroporation pulses

To minimize neuromuscular electrical stimulation during electroporation-based treatments, the replacement of long monophasic pulses with bursts of biphasic high-frequency pulses in the range of microseconds was suggested in order to reduce muscle contraction and pain sensation due to pulse application. This treatment modality appeared under the term high-frequency electroporation (HF-EP), which can be potentially used for some clinical applications of electroporation such as electrochemotherapy, gene electrotransfer, and tissue ablation. In cardiac tissue ablation, which utilizes irreversible electroporation, the treatment is being established as Pulsed Field Ablation. While the reduction of muscle contractions was confirmed in multiple in vivo studies, the reduction of pain sensation in humans was not confirmed yet, nor was the relationship between muscle contraction and pain sensation investigated. This is the first study in humans examining pain sensation using biphasic high-frequency electroporation pulses. Twenty-five healthy individuals were subjected to electrical stimulation of the tibialis anterior muscle with biphasic high-frequency pulses in the range of few microseconds and both, symmetric and asymmetric interphase and interpulse delays. Our results confirm that biphasic high-frequency pulses with a pulse width of 1 or 2 µs reduce muscle contraction and pain sensation as opposed to currently used longer monophasic pulses. In addition, interphase and interpulse delays play a significant role in reducing the muscle contraction and/or pain sensation. The study shows that the range of the optimal pulse parameters may be increased depending on the prerequisites of the therapy. However, further evaluation of the biphasic pulse protocols presented herein is necessary to confirm the efficiency of the newly proposed HF-EP.

Effects of Ultra-Short Pulsed Electric Field Exposure on Glioblastoma Cells

Glioblastoma multiforme (GBM) is the most common brain cancer in adults. GBM starts from a small fraction of poorly differentiated and aggressive cancer stem cells (CSCs) responsible for aberrant proliferation and invasion. Due to extreme tumor heterogeneity, actual therapies provide poor positive outcomes, and cancers usually recur. Therefore, alternative approaches, possibly targeting CSCs, are necessary against GBM. Among emerging therapies, high intensity ultra-short pulsed electric fields (PEFs) are considered extremely promising and our previous results demonstrated the ability of a specific electric pulse protocol to selectively affect medulloblastoma CSCs preserving normal cells. Here, we tested the same exposure protocol to investigate the response of U87 GBM cells and U87-derived neurospheres. By analyzing different in vitro biological endpoints and taking advantage of transcriptomic and bioinformatics analyses, we found that, independent of CSC content, PEF exposure affected cell proliferation and differentially regulated hypoxia, inflammation and P53/cell cycle checkpoints. PEF exposure also significantly reduced the ability to form new neurospheres and inhibited the invasion potential. Importantly, exclusively in U87 neurospheres, PEF exposure changed the expression of stem-ness/differentiation genes. Our results confirm this physical stimulus as a promising treatment to destabilize GBM, opening up the possibility of developing effective PEF-mediated therapies.

Lab-on-chip microscope platform for electro-manipulation of a dense microtubules network

Pulsed electric field (PEF) technology is promising for the manipulation of biomolecular components and has potential applications in biomedicine and bionanotechnology. Microtubules, nanoscopic tubular structures self-assembled from protein tubulin, serve as important components in basic cellular processes as well as in engineered biomolecular nanosystems. Recent studies in cell-based models have demonstrated that PEF affects the cytoskeleton, including microtubules. However, the direct effects of PEF on microtubules are not clear. In this work, we developed a lab-on-a-chip platform integrated with a total internal reflection fluorescence microscope system to elucidate the PEF effects on a microtubules network mimicking the cell-like density of microtubules. The designed platform enables the delivery of short (microsecond-scale), high-field-strength (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\le$$\end{document}≤ 25 kV/cm) electric pulses far from the electrode/electrolyte interface. We showed that microsecond PEF is capable of overcoming the non-covalent microtubule bonding force to the substrate and translocating the microtubules. This microsecond PEF effect combined with macromolecular crowding led to aggregation of microtubules. Our results expand the toolbox of bioelectronics technologies and electromagnetic tools for the manipulation of biomolecular nanoscopic systems and contribute to the understanding of microsecond PEF effects on a microtubule cytoskeleton.

Electroporation and cell killing by milli- to nanosecond pulses and avoiding neuromuscular stimulation in cancer ablation

Ablation therapies aim at eradication of tumors with minimal impact on surrounding healthy tissues. Conventional pulsed electric field (PEF) treatments cause pain and muscle contractions far beyond the ablation area. The ongoing quest is to identify PEF parameters efficient at ablation but not at stimulation. We measured electroporation and cell killing thresholds for 150 ns–1 ms PEF, uni- and bipolar, delivered in 10- to 300-pulse trains at up to 1 MHz rates. Monolayers of murine colon carcinoma cells exposed to PEF were stained with YO-PRO-1 dye to detect electroporation. In 2–4 h, dead cells were labeled with propidium. Electroporation and cell death thresholds determined by matching the stained areas to the electric field intensity were compared to nerve excitation thresholds (Kim et al. in Int J Mol Sci 22(13):7051, 2021). The minimum fourfold ratio of cell killing and stimulation thresholds was achieved with bipolar nanosecond PEF (nsPEF), a sheer benefit over a 500-fold ratio for conventional 100-µs PEF. Increasing the bipolar nsPEF frequency up to 100 kHz within 10-pulse bursts increased ablation thresholds by < 20%. Restricting such bursts to the refractory period after nerve excitation will minimize the number of neuromuscular reactions while maintaining the ablation efficiency and avoiding heating.

Polymer Nanoparticles Enhance Irreversible Electroporation In Vitro

Expanding the volume of an irreversible electroporation treatment typically necessitates an increase in pulse voltage, number, duration, or repetition. This study investigates the addition of polyethylenimine nanoparticles (PEI-NP) to pulsed electric field treatments, determining their combined effect on ablation size and voltages. U118 cells in an in vitro 3D cell culture model were treated with one of three pulse parameters (with and without PEI-NPs) which are representative of irreversible electroporation (IRE), high frequency irreversible electroporation (H-FIRE), or nanosecond pulsed electric fields (nsPEF). The size of the ablations were compared and mapped onto an electric field model to describe the electric field required to induce cell death. Analysis was conducted to determine the role of PEI-NPs in altering media conductivity, the potential for PEI-NP degradation following pulsed electric field treatment, and PEI-NP uptake. Results show there was a statistically significant increase in ablation diameter for IRE and H-FIRE pulses with PEI-NPs. There was no increase in ablation size for nsPEF with PEI-NPs. This all occurs with no change in cell media conductivity, no observable degradation of PEI-NPs, and moderate particle uptake. These results demonstrate the synergy of a combined cationic polymer nanoparticle and pulsed electric field treatment for the ablation of cancer cells. These results set the foundation for polymer nanoparticles engineered specifically for irreversible electroporation.

Four Channel 6.5 kV, 65 A, 100 ns–100 µs Generator with Advanced Control of Pulse and Burst Protocols for Biomedical and Biotechnological Applications

Pulsed electric fields in the sub-microsecond range are being increasingly used in biomedical and biotechnology applications, where the demand for high-voltage and high-frequency pulse generators with enhanced performance and pulse flexibility is pushing the limits of pulse power solid state technology. In the scope of this article, a new pulsed generator, which includes four independent MOSFET based Marx modulators, operating individually or combined, controlled from a computer user interface, is described. The generator is capable of applying different pulse shapes, from unipolar to bipolar pulses into biological loads, in symmetric and asymmetric modes, with voltages up to 6.5 kV and currents up to 65 A, in pulse widths from 100 ns to 100 µs, including short-circuit protection, current and voltage monitoring. This new scientific tool can open new research possibility due to the flexibility it provides in pulse generation, particularly in adjusting pulse width, polarity, and amplitude from pulse-to-pulse. It also permits operating in burst mode up to 5 MHz in four independent channels, for example in the application of synchronized asymmetric bipolar pulses, which is shown together with other characteristics of the generator.

Characterization of dispersion and anisotropic-conductivity in tissue model during electroporation pulses

Electroporation occurs when biological cells are exposed to intensive, short-duration pulses, which can be used to ablate biological tumor tissues. Based on the traditional numerical models, the isotropic conductivity model with the non-dispersion effect (ICND), the anisotropic conductivity model with the dispersion effect (ACD) is developed in this study. The second-order Debye function is introduced to manifest the dielectric relaxation effect, and the two-dimensional Cartesian conductivity matrix is applied to describe the anisotropy of the tissue conductivity during the electroporation process. A monopolar pulse and a monopolar burst are applied to the breast tumor model through the two-needle electrodes configuration. The results show that taking the dispersion into account can increase the total electroporated area more than 2.31%. Considering the conductivity anisotropy, the total electroporated area increases, but the irreversible electroporation (IRE) area decreases by more than 3.99%. The ACD model can achieve a larger electroporated area but a relatively smaller IRE area than those of the ICND model, and comparably minor maximum thermal damage is evaluated in the ACD model. Our model analyzes the effects of the dielectric dispersion and anisotropic conductivity of tissue, which have strong guiding significance for making the treatment planning before clinical practice.

Electrotherapies for Glioblastoma

Non-thermal, intermediate frequency (100-500 kHz) electrotherapies present a unique therapeutic strategy to treat malignant neoplasms. Here, pulsed electric fields (PEFs) which induce reversible or irreversible electroporation (IRE) and tumour-treating fields (TTFs) are reviewed highlighting the foundations, advances, and considerations of each method when applied to glioblastoma (GBM). Several biological aspects of GBM that contribute to treatment complexity (heterogeneity, recurrence, resistance, and blood-brain barrier(BBB)) and electrophysiological traits which are suggested to promote glioma progression are described. Particularly, the biological responses at the cellular and molecular level to specific parameters of the electrical stimuli are discussed offering ways to compare these parameters despite the lack of a universally adopted physical description. Reviewing the literature, a disconnect is found between electrotherapy techniques and how they target the biological complexities of GBM that make treatment difficult in the first place. An attempt is made to bridge the interdisciplinary gap by mapping biological characteristics to different methods of electrotherapy, suggesting important future research topics and directions in both understanding and treating GBM. To the authors' knowledge, this is the first paper that attempts an in-tandem assessment of the biological effects of different aspects of intermediate frequency electrotherapy methods, thus offering possible strategies toward GBM treatment.

Reduction of muscle contraction and pain in electroporation-based treatments: An overview

BACKGROUND

In the first studies of electrochemotherapy (ECT), small cutaneous metastases were treated and only mild or moderate pain was observed; therefore, pain was not considered a significant issue. As the procedure began to be applied to larger cutaneous metastases, pain was reported more frequently. For that reason, reduction of both muscle contractions and pain have been investigated over the years.

AIM

To present an overview of different protocols described in literature that aim to reduce muscle contractions and pain caused by the electroporation (EP) effect in both ECT and irreversible EP treatments.

METHODS

Thirty-three studies published between January 1999 and November 2020 were included. Different protocol designs and electrode geometries that reduce patient pain and the number of muscle contractions and their intensity were analysed.

RESULTS

The analysis showed that both high frequency and bipolar/biphasic pulses can be used to reduce pain and muscle contractions in patients who undergo EP treatments. Moreover, adequate electrode design can decrease EP-related morbidity. Particularly, needle length, diameter and configuration of the distance between the needles can be optimised so that the muscle volume crossed by the current is reduced as much as possible. Bipolar/biphasic pulses with an inadequate pulse length seem to have a less evident effect on the membrane permeability compared with the standard pulse protocol. For that reason, the number of pulses and the voltage amplitude, as well as the pulse duration and frequency, must be chosen so that the dose of delivered energy guarantees EP efficacy.

CONCLUSION

Pain reduction in EP-based treatments can be achieved by appropriately defining the protocol parameters and electrode design. Most results can be achieved with high frequency and/or bipolar/biphasic pulses. However, the efficacy of these alternative protocols remains a crucial point to be assessed further.

High-Frequency and High-Voltage Asymmetric Bipolar Pulse Generator for Electroporation Based Technologies and Therapies

Currently, in high-frequency electroporation, much progress has been made but limited to research groups with custom-made laboratory prototype electroporators. According to the review of electroporators and economic evaluations, there is still an area of pulse parameters that needs to be investigated. The development of an asymmetric bipolar pulse generator with a maximum voltage of 4 kV and minimum duration time of a few hundred nanoseconds, would enable in vivo evaluation of biological effects of high-frequency electroporation pulses. Herein, from a series of most commonly used drivers and optical isolations in high-voltage pulse generators the one with optimal characteristics was used. In addition, the circuit topology of the developed device is described in detail. The developed device is able to generate 4 kV pulses, with theoretical 131 A maximal current and 200 ns minimal pulse duration, the maximal pulse repetition rate is 2 MHz and the burst maximal repetition rate is 1 MHz. The device was tested in vivo. The effectiveness of electrochemotherapy of high-frequency electroporation pulses is compared to “classical” electrochemotherapy pulses. In vivo electrochemotherapy with high-frequency electroporation pulses was at least as effective as with “classical” well-established electric pulses, resulting in 86% and 50% complete responses, respectively. In contrast to previous reports, however, muscle contractions were comparable between the two protocols.

Gene transfer by electroporation with high frequency bipolar pulses in vitro

High-frequency bipolar pulses (HF-BP) have been demonstrated to be efficient for membrane permeabilization and irreversible electroporation. Since membrane permeabilization has been achieved using HF-BP pulses we hypothesized that with these pulses we can also achieve successful gene electrotransfer (GET). Three variations of bursts of 2 µs bipolar pulses with 2 µs interphase delay were applied in HF-BP protocols. We compared transfection efficiency of monopolar micro and millisecond pulses and HF-BP protocols at various plasmid DNA (pDNA) concentrations on CHO - K1 cells. GET efficiency increased with increasing pDNA concentration. Overall GET obtained by HF-BP pulse protocols was comparable to overall GET obtained by longer monopolar pulse protocols. Our results, however, suggest that although we were able to achieve similar percent of transfected cells, the number of pDNA copies that were successfully transferred into cells seemed to be higher when longer monopolar pulses were used. Interestingly, we did not observe any direct correlation between fluorescence intensity of pDNA aggregates formed on cell membrane and transfection efficiency. The results of our study confirmed that we can achieve successful GET with bipolar microsecond i. e. HF-BP pulses, although at the expense of higher pDNA concentrations.

Continuum analysis to assess field enhancements for tailoring electroporation driven by monopolar or bipolar pulsing based on nonuniformly distributed nanoparticles

Recent reports indicate that nanoparticle (NP) clusters near cell membranes could enhance local electric fields, leading to heightened electroporation. This aspect is quantitatively analyzed through numerical simulations whereby time dependent transmembrane potentials are first obtained on the basis of a distributed circuit mode, and the results then used to calculate pore distributions from continuum Smoluchowski theory. For completeness, both monopolar and bipolar nanosecond-range pulse responses are presented and discussed. Our results show strong increases in TMP with the presence of multiple NP clusters and demonstrate that enhanced poration could be possible even over sites far away from the poles at the short pulsing regime. Furthermore, our results demonstrate that nonuniform distributions would work to enable poration at regions far away from the poles. The NP clusters could thus act as distributed electrodes. Our results were roughly in line with recent experimental observations.

Microsecond Pulsed Electric Fields: An Effective Way to Selectively Target and Radiosensitize Medulloblastoma Cancer Stem Cells

PURPOSE

Cancer stem cells constitute an endless reserve for the maintenance and progression of tumors, and they could be the reason for conventional therapy failure. New therapeutic strategies are necessary to specifically target them. In this context, microsecond pulsed electric fields have been selected to expose D283Med cells, a human medulloblastoma cell line resulted to be rich in cancer stem cells, and normal human astrocytes.

METHODS

We analyzed in vitro different endpoints at different times after microsecond pulsed electric field exposure, such as permeabilization, reactive oxygen species generation, cell viability/proliferation, cell cycle, and clonogenicity, as well as the expression of different genes involved in cell cycle, apoptosis, and senescence. Furthermore, the response of D283Med cells exposed to microsecond pulsed electric fields was validated in vivo in a heterotopic mouse xenograft model.

RESULTS

Our in vitro results showed that a specific pulse protocol (ie, 0.3 MV/m, 40 μs, 5 pulses) was able to induce irreversible membrane permeabilization and apoptosis exclusively in medulloblastoma cancer stem cells. In the surviving cells, reactive oxygen species generation was observed, together with a transitory G2/M cell-cycle arrest with a senescence-associated phenotype via the upregulation of GADD45A. In vivo results, after pulsed electric field exposure, demonstrated a significant tumor volume reduction with no eradication of tumor mass. In conjunction, we verified the efficacy of electric pulse pre-exposure followed by ionizing irradiation in vivo to enable complete inhibition of tumor growth.

CONCLUSIONS

Our data reveal novel therapeutic options for the targeting of medulloblastoma cancer stem cells, indicating nonionizing pulsed electric field pre-exposure as an effective means to overcome the radioresistance of cancer stem cells.

Analysis on reversible/irreversible electroporation region in lung adenocarcinoma cell model in vitro with electric pulses delivered by needle electrodes

Irreversible electroporation (IRE) is a minimally invasive tumor therapy using pulsed electric field with high intensity while the important tissues such as blood vessel, bile duct, and nerve are preserved. In addition to ablation area, reversible electroporation (RE) region is also generated using needle electrodes for pulse delivery. The goal of this work is to study the generation of RE region and ablation region on a 2D lung adenocarcinoma cell model in vitro. The tumor model is exposed to electric pulses with various number. The calcium AM and propidium iodide (PI) are examined to detect the ablation area and electroporation area, respectively. The results show that electroporation area firstly tends to plateau after approximately 50 pulses, while the ablation area continues to increase. The percentage of IRE area in total electroporation area increases with additional pulses, which means that RE region could be gradually turned into ablation area with increased pulse number. However, the percentage of IRE area only achieves to 54% for 200 pulses, which indicates that RE region still cannot be completely removed. RE and IRE thresholds appear to converge as the number of pulses increases. An equation between pulse number and the electric field threshold of ablation including the electric field threshold of RE is also provided for lung adenocarcinoma cell ablation. This work may have the value for the optimization of IRE protocols on tumor ablation.

Combination of Irreversible Electroporation and STING Agonist for Effective Cancer Immunotherapy

Recently, cancer immunotherapy has received attention as a viable solution for the treatment of refractory tumors. However, it still has clinical limitations in its treatment efficacy due to inter-patient tumor heterogeneity and immunosuppressive tumor microenvironment (TME). In this study, we demonstrated the triggering of anti-cancer immune responses by a combination of irreversible electroporation (IRE) and a stimulator of interferon genes (STING) agonist. Optimal electrical conditions inducing damage-associated molecular patterns (DAMPs) by immunogenic cell death (ICD) were determined through in vitro 2D and 3D cell experiments. In the in vivo syngeneic lung cancer model, the combination of IRE and STING agonists demonstrated significant tumor growth inhibition. We believe that the combination strategy of IRE and STING agonists has potential for effective cancer immunotherapy.

Incorporation of Reversible Electroporation Into Electrolysis Accelerates Apoptosis for Rat Liver Tissue

Tissue electrolysis is an alternative modality that uses a low intensity direct electric current passing through at least 2 electrodes within the tissue and resulting electrochemical products including chlorine and hydrogen. These products induce changes in pH around electrodes and cause dehydration resulting from electroosmotic pressure, leading to changes in microenvironment and thus metabolism of the tissues, yielding apoptosis. The procedure requires adequate time for electrochemical reactions to yield products sufficient to induce apoptosis of the tissues. Incorporation of electroporation into electrolysis can decrease the treatment time and enhance the efficiency of electrolytic ablation. Electroporation causes permeabilization in the cell membrane allowing the efflux of potassium ions and extension of the electrochemical area, facilitating the electrolysis process. However, little is known about the combined effects on apoptosis in liver ablation. In this study, we performed an immunohistochemical evaluation of apoptosis for the incorporation of electroporation into electrolysis in liver tissues. To do so, the study was performed with microelectrodes for fixed treatment time while the applied voltage varied to increase the applied total energy for electrolysis. The apoptotic rate for electrolytic ablation increased with enhanced applied energy. The apoptotic rate was 4.31 ± 1.73 times that of control in the synergistic combination compared to 1.49 ± 0.33 times that of the control in electrolytic ablation alone. Additionally, tissue structure was better preserved in synergistic combination ablation compared to electrolysis with an increment of 3.8 mA. Thus, synergistic ablation may accelerate apoptosis and be a promising modality for the treatment of liver tumors.

High-voltage 10 ns delayed paired or bipolar pulses for in vitro bioelectric experiments

Recent studies proved that classical bio-effects induced by nanosecond pulsed electric field (nsPEF) can be reduced by the delivery of a negative polarity pulse generated immediately after a positive polarity pulse. This phenomenon is known as "bipolar cancellation" and it was reported for a wide range of bipolar pulses with pulse duration from 2 ns to 900 ns. On the contrary, paired pulses, i.e., two identical pulses with the same polarity, increased traditional nsPEF outcomes. Herein, we propose a novel robust and flexible generator, based on the frozen-wave concept, able to produce a broad range of pulses with the duration of 10 ns and delay between 17 and 360 ns. Numerical simulations and experimental measurements were performed to fully characterize the proposed generator. YO-PRO^TM-1 uptake was investigated in the U87-MG human glioblastoma cell line as a marker of membrane permeabilization in response to 10 ns, 11.5MV/m nsPEF. Our results showed that bipolar cancellation occurred for delays of 0-30 ns and decreased as a function of the interphase interval. In addition, we observed that cellular response following the application of paired nsPEF was more than two-fold compared to the unipolar pulse response and was independent from the interphase interval.

Algorithmically Controlled Electroporation: A Technique for Closed Loop Temperature Regulated Pulsed Electric Field Cancer Ablation

OBJECTIVE

To evaluate the effect of a closed-loop temperature based feedback algorithm on ablative outcomes for pulsed electric field treatments.

METHODS

A 3D tumor model of glioblastoma was used to assess the impact of 2 μs duration bipolar waveforms on viability following exposure to open and closed-loop protocols. Closed-loop treatments evaluated transient temperature increases of 5, 10, 15, or 22 °C above baseline.

RESULTS

The temperature controlled ablation diameters were conditionally different than the open-loop treatments and closed-loop treatments generally produced smaller ablations. Closed-loop control enabled the investigation of treatments with steady state 42 °C hyperthermic conditions which were not feasible without active feedback. Baseline closed-loop treatments at 20 °C resulted in ablations measuring 9.9 ± 0.3 mm in diameter while 37 °C treatments were 20% larger (p < 0.0001) measuring 11.8 ± 0.3 mm indicating that this protocol induces a thermally mediated biological response.

CONCLUSION

A closed-loop control algorithm which modulated the delay between successive pulse waveforms to achieve stable target temperatures was demonstrated. Algorithmic control enabled the evaluation of specific treatment parameters at physiological temperatures not possible with open-loop systems due to excessive Joule heating.

SIGNIFICANCE

Irreversible electroporation is generally considered to be a non-thermal ablation modality and temperature monitoring is not part of the standard clinical practice. The results of this study indicate ablative outcomes due to exposure to pulses on the order of one microsecond may be thermally mediated and dependent on local tissue temperatures. The results of this study set the foundation for experiments in vivo utilizing temperature control algorithms.

Development of a Multi-Pulse Conductivity Model for Liver Tissue Treated With Pulsed Electric Fields

Pulsed electric field treatment modalities typically utilize multiple pulses to permeabilize biological tissue. This electroporation process induces conductivity changes in the tissue, which are indicative of the extent of electroporation. In this study, we characterized the electroporation-induced conductivity changes using all treatment pulses instead of solely the first pulse as in conventional conductivity models. Rabbit liver tissue was employed to study the tissue conductivity changes caused by multiple, 100 μs pulses delivered through flat plate electrodes. Voltage and current data were recorded during treatment and used to calculate the tissue conductivity during the entire pulsing process. Temperature data were also recorded to quantify the contribution of Joule heating to the conductivity according to the tissue temperature coefficient. By fitting all these data to a modified Heaviside function, where the two turning points (E₀, E₁) and the increase factor (A) are the main parameters, we calculated the conductivity as a function of the electric field (E), where the parameters of the Heaviside function (A and E₀) were functions of pulse number (N). With the resulting multi-factor conductivity model, a numerical electroporation simulation can predict the electrical current for multiple pulses more accurately than existing conductivity models. Moreover, the saturating behavior caused by electroporation can be explained by the saturation trends of the increase factor A in this model. The conductivity change induced by electroporation has a significant increase at about the first 30 pulses, then tends to saturate at 0.465 S/m. The proposed conductivity model can simulate the electroporation process more accurately than the conventional conductivity model. The electric field distribution computed using this model is essential for treatment planning in biomedical applications utilizing multiple pulsed electric fields, and the method proposed here, relating the pulse number to the conductivity through the variables in the Heaviside function, may be adapted to investigate the effect of other parameters, like pulse frequency and pulse width, on electroporation.

Temperature Dependence of High Frequency Irreversible Electroporation Evaluated in a 3D Tumor Model

Electroporation is a bioelectric phenomenon used to deliver target molecules into cells in vitro and irreversible electroporation (IRE) is an emerging cancer therapy used to treat inoperable tumors in situ. These phenomena are generally considered to be non-thermal in nature. In this study, a 3D tumor model was used to investigate the correlation between temperature and the effectiveness of standard clinical IRE and high frequency (H-FIRE) protocols. It was found for human glioblastoma cells that in the range of 2 to 37 °C the H-FIRE lethal electric field threshold value, which describes the minimum electric field to cause cell death, is highly dependent on temperature. Increasing the initial temperature from 2 to 37 °C resulted in a significant decrease in lethal electric field threshold from 1168 to 507 V/cm and a 139% increase in ablation size for H-FIRE burst treatments. Standard clinical protocol IRE treatments resulted in a decrease in lethal threshold from 485 to 453 V/cm and a 7% increase in ablation size over the same temperature range. Similar results were found for pancreatic cancer cells which indicate that tissue temperature may be a significant factor affecting H-FIRE ablation size and treatment planning in vivo while lower temperatures may be useful in maintaining cell viability for transfection applications.

Dynamics of Cell Death After Conventional IRE and H-FIRE Treatments

High-frequency irreversible electroporation (H-FIRE) has emerged as an alternative to conventional irreversible electroporation (IRE) to overcome the issues associated with neuromuscular electrical stimulation that appear in IRE treatments. In H-FIRE, the monopolar pulses typically used in IRE are replaced with bursts of short bipolar pulses. Currently, very little is known regarding how the use of a different waveform affects the cell death dynamics and mechanisms. In this study, human pancreatic adenocarcinoma cells were treated with a typical IRE protocol and various H-FIRE schemes with the same energized time. Cell viability, membrane integrity and Caspase 3/7 activity were assessed at different times after the treatment. In both treatments, we identified two different death dynamics (immediate and delayed) and we quantified the electric field ranges that lead to each of them. While in the typical IRE protocol, the electric field range leading to a delayed cell death is very narrow, this range is wider in H-FIRE and can be increased by reducing the pulse length. Membrane integrity in cells suffering a delayed cell death shows a similar time evolution in all treatments, however, Caspase 3/7 expression was only observed in cells treated with H-FIRE.

Cancellation effect is present in high-frequency reversible and irreversible electroporation

It was recently suggested that applying high-frequency short biphasic pulses (HF-IRE) reduces pain and muscle contractions in electrochemotherapy and irreversible ablation treatments; however, higher amplitudes with HF-IRE pulses are required to achieve a similar effect as with monophasic pulses. HF-IRE pulses are in the range of a microseconds, thus, the so-called cancellation effect could be responsible for the need to apply pulses of higher amplitudes. In cancellation effect, the effect of first pulse is reduced by the second pulse of opposite polarity. We evaluated cancellation effect with high-frequency biphasic pulses on CHO-K1 in different electroporation buffers. We applied eight bursts of 1-10 µs long pulses with inter-phase delays of 0.5 µs - 10 ms and evaluated membrane permeability and cell survival. In permeability experiments, cancellation effect was not observed in low-conductivity buffer. Cancellation effect was, however, observed in treatments with high-frequency biphasic pulses looking at survival in all of the tested electroporation buffers. In general, cancellation effect depended on inter-phase delay as well as on pulse duration, i.e. longer pulses and longer interphase delay cause less pronounced cancellation effect. Cancellation effect could be partially explained by the assisted discharge and not by the hyperpolarization by the chloride channels.

Temporal Characterization of Blood-Brain Barrier Disruption with High-Frequency Electroporation

Treatment of intracranial disorders suffers from the inability to accumulate therapeutic drug concentrations due to protection from the blood–brain barrier (BBB). Electroporation-based therapies have demonstrated the capability of permeating the BBB, but knowledge of the longevity of BBB disruption (BBBD) is limited. In this study, we quantify the temporal, high-frequency electroporation (HFE)-mediated BBBD in an in vivo healthy rat brain model. 40 male Fisher rats underwent HFE treatment; two blunt tipped monopolar electrodes were advanced into the brain and 200 bursts of HFE were delivered at a voltage-to-distance ratio of 600 V/cm. BBBD was verified with contrast enhanced T1W MRI (gadopentetate dimeglumine) and pathologically (Evans blue dye) at time points of 1, 24, 48, 72, and 96 h after HFE. Contrast enhanced T1W scans demonstrated BBBD for 1 to 72 h after HFE but intact BBB at 96 h. Histologically, tissue damage was restricted to electrode insertion tracks. BBBD was induced with minimal muscle contractions and minimal cell death attributed to HFE. Numerical modeling indicated that brief BBBD was induced with low magnitude electric fields, and BBBD duration increased with field strength. These data suggest the spatiotemporal characteristics of HFE-mediated BBBD may be modulated with the locally applied electric field.

High-Frequency Irreversible Electroporation Using 5,000-V Waveforms to Create Reproducible 2- and 4-cm Ablation Zones-A Laboratory Investigation Using Mechanically Perfused Liver

PURPOSE

To investigate if high-frequency irreversible electroporation (H-FIRE) treatments can be delivered at higher voltages and with greater energy delivery rates than currently implemented in clinical irreversible electroporation protocols.

MATERIALS AND METHODS

Treatments using 3,000 V and 5,000 V were administered to mechanically perfused ex vivo porcine liver via a single applicator and grounding pad (A+GP) as well as a 4-applicator array (4AA). Integrated energized times (IET) 0.01-0.08 seconds and energy delivery rates 25-300 μs/s were investigated. Organs were preserved at 4°C for 10-15 hours before sectioning and gross analysis using a metabolic stain to identify the size and shape of ablation zones.

RESULTS

A+GP ablations measured between 1.6 cm and 2.2 cm, which did not increase when IET was increased from 0.02 seconds to 0.08 seconds (P > .055; range, 1.9-2.1 cm). Changes in tissue color and texture consistent with thermal damage were observed for treatments with energy delivery rates 50-300 μs/s, but not for treatments delivered at 25 μs/s. Use of the 4AA with a 3-cm applicator spacing resulted in ablations measuring 4.4-4.9 cm with energy delivery times of 7-80 minutes.

CONCLUSIONS

H-FIRE treatments can rapidly and reproducibly create 2-cm ablations using an A+GP configuration. Treatments without thermal injury were produced at the expense of extended treatment times. More rapid treatments resulted in ablations with varying degrees of thermal injury within the H-FIRE ablation zone. Production of 4-cm ablations is possible using a 4AA.

A 2-D Cell Layer Study on Synergistic Combinations of High-Voltage and Low-Voltage Irreversible Electroporation Pulses

Irreversible electroporation (IRE) employs brief, high-electric field pulses to ablate tumors while preserving the extracellular matrix. Recently, we showed that combining short high-voltage (SHV) IRE pulses and long low-voltage (LLV) IRE pulses can enlarge the tissue ablation region, presumably through a synergistic effect.

OBJECTIVE

The goal of this study is to further investigate the effect of this combination on a 2-D cell layer tumor model.

METHODS

2-D layers of tumor cells are exposed to various SHV and LLV combinations, and the results of propidium iodide (PI) and fluorescein diacetate staining are examined to correlate treatment protocols with the ensuing irreversible and reversible electroporation areas.

RESULTS

The combination of SHV+LLV pulses produces a larger area of electroporation and ablation than LLV+SHV pulses, LLV pulses alone, and SHV pulses alone.

CONCLUSION

Judiciously combining SHV and LLV pulses can produce a synergistic effect that enlarges the electroporation-induced ablation area. A hypothetical explanation for this effect is that it involves a combination of pore expansion and electrolysis induced by LLV pulses in the area that had been reversibly permeabilized by the SHV pulses.

SIGNIFICANCE

This paper is valuable for the design of improved IRE protocols and provides a hypothesis for the mechanisms involved.

The use of high-frequency short bipolar pulses in cisplatin electrochemotherapy in vitro

Background

In electrochemotherapy (ECT), chemotherapeutics are first administered, followed by short 100 μs monopolar pulses. However, these pulses cause pain and muscle contractions. It is thus necessary to administer muscle relaxants, general anesthesia and synchronize pulses with the heart rhythm of the patient, which makes the treatment more complex. It was suggested in ablation with irreversible electroporation, that bursts of short high-frequency bipolar pulses could alleviate these problems. Therefore, we designed our study to verify if it is possible to use high-frequency bipolar pulses (HF-EP pulses) in electrochemotherapy.

Materials and methods

We performed in vitro experiments on mouse skin melanoma (B16-F1) cells by adding 1–330 μM cisplatin and delivering either (a) eight 100 μs long monopolar pulses, 0.4–1.2 kV/cm, 1 Hz (ECT pulses) or (b) eight bursts at 1 Hz, consisting of 50 bipolar pulses. One bipolar pulse consisted of a series of 1 μs long positive and 1 μs long negative pulse (0.5–5 kV/cm) with a 1 μs delay in-between.

Results

With both types of pulses, the combination of electric pulses and cisplatin was more efficient in killing cells than cisplatin or electric pulses only. However, we needed to apply a higher electric field in HF-EP (3 kV/cm) than in ECT (1.2 kV/cm) to obtain comparable cytotoxicity.

Conclusions

It is possible to use HF-EP in electrochemotherapy; however, at the expense of applying higher electric fields than in classical ECT. The results obtained, nevertheless, offer an evidence that HF-EP could be used in electrochemotherapy with potentially alleviated muscle contractions and pain.

High-frequency irreversible electroporation is an effective tumor ablation strategy that induces immunologic cell death and promotes systemic anti-tumor immunity

Background

Despite promising treatments for breast cancer, mortality rates remain high and treatments for metastatic disease are limited. High-frequency irreversible electroporation (H-FIRE) is a novel tumor ablation technique that utilizes high-frequency bipolar electric pulses to destabilize cancer cell membranes and induce cell death. However, there is currently a paucity of data pertaining to immune system activation following H-FIRE and other electroporation based tumor ablation techniques.

Methods

Here, we utilized the mouse 4T1 mammary tumor model to evaluate H-FIRE treatment parameters on cancer progression and immune system activation in vitro and in vivo.

Findings

H-FIRE effectively ablates the primary tumor and induces a pro-inflammatory shift in the tumor microenvironment. We further show that local treatment with H-FIRE significantly reduces 4T1 metastases. H-FIRE kills 4T1 cells through non-thermal mechanisms associated with necrosis and pyroptosis resulting in damage associated molecular pattern signaling in vitro and in vivo. Our data indicate that the level of tumor ablation correlates with increased activation of cellular immunity. Likewise, we show that the decrease in metastatic lesions is dependent on the intact immune system and H-FIRE generates 4T1 neoantigens that engage the adaptive immune system to significantly attenuate tumor progression.

Interpretation

Cell death and tumor ablation following H-FIRE treatment activates the local innate immune system, which shifts the tumor microenvironment from an anti-inflammatory state to a pro-inflammatory state. The non-thermal damage to the cancer cells and increased innate immune system stimulation improves antigen presentation, resulting in the engagement of the adaptive immune system and improved systemic anti-tumor immunity.

IGBT-Based Pulsed Electric Fields Generator for Disinfection: Design and In Vitro Studies on Pseudomonas aeruginosa

Irreversible electroporation of cell membrane with pulsed electric fields is an emerging physical method for disinfection that aims to reduce the doses and volumes of used antibiotics for wound healing. Here we report on the design of the IGBT-based pulsed electric field generator that enabled eradication of multidrug resistant Pseudomonas aeruginosa PAO1 on the gel. Using a concentric electric configuration we determined that the lower threshold of the electric field required to kill P. aeruginosa PAO1 was 89.28 ± 12.89 V mm^-1, when 200 square pulses of 300 µs duration are delivered at 3 Hz. These parameters disinfected 38.14 ± 0.79 mm² area around the single needle electrode. This study provides a step towards the design of equipment required for multidrug-resistant bacteria disinfection in patients with pulsed electric fields.

Scaling Relationship of In Vivo Muscle Contraction Strength of Rabbits Exposed to High-Frequency Nanosecond Pulse Bursts

We studied the influence of various parameters of high-frequency nanosecond pulse bursts on the strength of rabbit muscle contractions. Ten unipolar high-frequency pulse bursts with various field intensities E (1 kV/cm, 4 kV/cm, and 8 kV/cm), intraburst frequencies f (10 kHz, 100 kHz, and 1 MHz), and intraburst pulse numbers N (1, 10, and 100) were applied using a pair of plate electrodes to the surface skin of the rabbits' biceps femoris, and the acceleration signal of muscle contraction near the electrode was measured using a 3-axis acceleration sensor. A time- and frequency-domain analysis of the acceleration signals showed that the peak value of the signal increases with the increasing strength of the pulse burst and that the frequency spectra of the signals measured under various pulse bursts have characteristic frequencies (at approximately 2 Hz, 32 Hz, 45 Hz, and 55 Hz). Furthermore, we processed the data through multivariate nonlinear regression analysis and variance analysis and determined that the peak value of the signal scales with the logarithm to the base 10 of EN ^x, where x is a value that scales with the logarithm to the base 10 of intraburst frequency (f). These results indicate that for high-frequency nanosecond pulse treatment of solid tumors in or near muscles, when the field strength is relatively high, the intraburst frequency and the intraburst pulse number require appropriate selection to limit the strength of muscle contraction as much as possible.

Comparison of Bipolar and Unipolar Pulses in Cell Electrofusion: Simulation and Experimental Research

OBJECTIVE

Unipolar pulses have been used in cell electrofusion over the last decades. However, the problem of high mortality with unipolar pulses has not been solved effectively. The cell fusion rate is restricted by cell mortality. By using the advantages of bipolar pulses which cause less cell damage, this paper attempts to use bipolar pulses to increase the cell fusion rate.

METHODS

the transmembrane voltage and pore density of cells subjected to unipolar/bipolar pulses were simulated in COMSOL software. In an experiment, two 40 μs unipolar and two 20-20 μs bipolar pulses with electric fields of 2, 2.5, and 3 kV/cm were applied to SP2/0 murine myeloma cells. To determine the cell fusion rate and cell mortality, cells were stained with Hoechst 33342 and propidium iodide.

RESULTS

the simulation in this paper showed that a high transmembrane voltage and a high pores density were concentrated only at the contact area of cells when bipolar pulses were used. The results of the cell staining experiment verified the simulation analysis. When bipolar pulses were applied, the cell mortality was significantly reduced. In addition, the cell fusion rate with bipolar pulses was almost two times higher than that with unipolar pulses.

CONCLUSION

for cell electrofusion, compared with unipolar pulses, bipolar pulses can not only reduce the cell mortality remarkably but also improve the cell fusion rate obviously.

SIGNIFICANCE

this paper introduces a novel way to increase the fusion rate of cells.

Characterization of Nonlinearity and Dispersion in Tissue Impedance During High-Frequency Electroporation

OBJECTIVE

The use of high-voltage, high-frequency bipolar pulses (HFBPs) is an emerging electroporation-based therapy for the treatment of solid tumors. In this study, we quantify the extent of nonlinearity and dispersion during the HFBP treatment.

METHODS

We utilize flat-plate electrodes to capture the impedance of the porcine liver tissue during the delivery of a burst of HFBPs of widths 1 and 2  $\mu$s at different pulse amplitudes. Next, we fit the impedance data to a frequency-dependent parallel RC network to determine the conductivity and permittivity of the tissue as a function of frequency, for different applied electric fields. Finally, we present a simple model to approximate the field distribution in the tissue using the conductivity function at a frequency that could minimize the errors due to approximation with a nondispersive model.

RESULTS

The conductivity/permittivity of the tissue was plotted as a function of frequency for different electric fields. It was found that the extent of dispersion reduces with higher applied electric field magnitudes.

CONCLUSION

This is the first study to quantify dispersion and nonlinearity in the tissue during the HFBP treatment. The data have been used to predict the field distribution in a numerical model of the liver tissue utilizing two needle electrodes.

SIGNIFICANCE

The data and technique developed in this study to monitor the electrical properties of tissue during treatment can be used to generate treatment-planning models for future high-frequency electroporation therapies as well as provide insights regarding treatment effect.